Quality Management of Chromium Containing Steel Slags from Melt Phase to Cooling

2005:029 CIV MASTER’S THESIS

JOUNI YLIPEKKALA

MASTER OF SCIENCE PROGRAMME

Luleå University of Technology Department of Chemical Engineering and Geosciences Division of Process Metallurgy

2005:029 CIV • ISSN: 1402 - 1617 • ISRN: LTU - EX - - 05/29 - - SE

Foreword

This master’s thesis concludes my studies for a master’s of science in Process metallurgy and mineral technology at Luleå University of technology. This thesis has been carried out at MiMer in co-operation with Outokumpu Stainless Oy, Tornio Finland. The investigation was made during the period of January to August 2004 at Outokumpu Stainless Oy in Tornio and some of the analyses (XRD) were made at Luleå University of technology.

I will thank my supervisor Dr. Margareta Lidström-Larsson at MiMeR/ Division of process metallurgy at university of technology in Luleå and my instructor M.Sc. Juha Roininen at Outokumpu Stainless Oy. Special thanks go to personell at Tornio Research Centre and steel melting shop who have helped me with my work, with analyses and practical tests. I would also like to thank M.Sc. Fredrik Engström at MiMeR for all his help with the analyses I have made in Luleå.

I will also thank my family, Marja-Riitta and Anna, at home in Haparanda who have support me during my studies.

Haparanda December 2004

Jouni Ylipekkala

Abstract

Outokumpu Stainless Oy Tornio works produces in close future around 1.7 million tonnes steel slabs annually. As all in the metallurgical processes the production of stainless steel producing by-products as slags. The different kinds of processes produce about 300 000 tonnes slags annually, almost the whole amount of this has been deposited after the metal separation up to recent days. The project to utilize the steel slag started during 2001 with the aim to increase the amount of recycled by-products and to develop new slag-products.

By-products are produced from the different process part as Electric Arc Furnaces (EAF1, EAF2), Argon Oxygen Decarburization converters (AOD1, AOD2), ladle stations and Chromium Converter (CRC). The chemical composition of slags from a process has a slight variation, but between the different processes the variations in analyses are greater. The chemical composition of the slags is dependent to the characters of the slag, as volume stability by basicity of the material. The aim of this work was to investigate the quality control of chromium containing steel slags during cooling into solid phase. The product should be an aggregate with sufficient hardness and low leaching behaviors.

The investigation started when the slag was poured into a slag pot at melting shop, any addition of stabilizers or other chemical components has not been done. The aim was to investigate the dependence of different cooling methods to spinel forming. The physical properties of the product of the tests were tested by Nordic ball mill test ( prEN 1097-9). The chemical analyses were: total analyses (XRF), and leaching test (Shaking test prEN 12457-3). A powder X-ray diffraction meter analyses (XRD) was used to estimate the mineralogy of the samples. The solid aggregate samples were studied with Scanning Electron Microscope (SEM). Simulations with respective chemical analysis of the slags were done by the data program FactSage. The slags, included in this work, were mainly EAF2 and CRC slags because of less variation in chemical analysis of these slags. These slags contain chromium, a minor part of chromium is not bound in spinels, which is a reason for leaching. During the first tests, which were carried out by water-cooling, no significant decreasing of leaching of chromium was observed. When pouring out the slag as a thin bed the leaching of chromium was lower compared to the massive bed of the same slag part. Lower leaching of chromium from the massive material from the thin bed can be caused by the smaller active surface of material. Reference test with semi- quenched slag were made and they showed low leaching values compared with the slags from normally pouring practices. Semi-quenched slag is porous and cannot be analyzed in SEM and was hence milled as powder and analyzed in XRD. The mineralogy of semi- quenched slag is varying in some degree from the mineralogy of normally poured slag. The semi-quenched slag, pumice, is partly amorphous which can be the reason for lower leaching values of chromium. Granulation tests have been made earlier with all of the three types of slag, but all of these showed higher leaching values than those of pumice. During granulation material may come in contact with air and become oxidized and chromium oxides leach more than other compounds of chromium.

The lowest leaching values of slag can be attained by semi-quenching of material but the product is not an aggregate and cannot be used in all of the civil engineering applications. Aggregates can be produced by cooling on the slabs, but the slag bed should be maximum 10 cm thick, so that the gases can flow out before solidification of material.

Sammanfattning

Outokumpu Stainless Oy Torneå verket kommer under de närmste åren att producera ca 1,7 miljoner ton rostfria stålämnen årligen. Liksom i alla metallurgiska processer innebär tillverkning av rostfritt stål även produktion av biprodukter, slagg. De olika delprocesserna, inom ståltillverkningen, producerar ca 300 000 ton slagg som deponerats som blandslagg efter metallseparering. För att minska mängden deponerad slagg startades under 2001 projektet för produktifiering av stålslagger. Målet var att öka mängden återanvänd stålslagg genom att utveckla nya slaggprodukter.

Biprodukter framställs i delprocesser som ljusbågsugn (LB1, LB2), AOD-konverter (AOD1 och AOD2), kromkonverter (CRK) och från skänkstationer. Variationen i den kemiska sammansättningen inom respektive delprocess är liten, men skiljer sig mellan de olika processerna. Den kemiska sammansättningen påverkar biprodukternas volymstabilitet, halten lakbara ämnen mm. Målet med detta arbete är att finna metoder att kontrollera kvalitén på kromhaltiga stålslagger med hjälp av olika avsvalningsmetoder. Den eftersökta produkten skall vara ett tillräckligt stabilt aggregat med låga lakningsvärden på krom och andra tungmetaller.

Undersökningen började då slaggen hade tippats i en slaggryta vid stålverket, inga kemiska tillsatser i den smälta slaggen användes. Avsvalningshastighetens påverkan på spinellbildning undersöktes. Erhållen produkt testades fysikaliskt med nordiska kulkvarnstestet (prEN 1097-9). Kemiska analyser som gjordes var: totalanalys (XRF) och lakningtest ( SKAKTEST prEN 12457-3). Mineralogin hos pulverformiga biprodukter undersöktes med röntgen diffraktometer (XRD) och de aggregatformiga proven med svepelektron mikroskop (SEM). Med datorprogram FactSage gjordes några simuleringar med respektive sammansätting av olika testslagger. De undersökta slaggerna kom i huvudsak från LB2 och CRK, eftersom processtabiliteten är bra och fluktuationen i de kemiska analyserna är liten. Dessa slagger innehåller krom och en del av kromet finns inte i spinellstrukturer vilket innebär att kromet delvis är i lättlakad form. Under de första testerna, vilka utfördes med vattenkylning av slaggbädd kunde inte någon signifikant minskning i lakningen observeras. När slaggen tippades till en tunn bädd var material tätt och hårt och lakningen mindre än från en tjockare bädd av samma slaggparti. Den lägre lakningen kan vara resultatet av den mindre specifika ytan hos det täta materialet. Vid referenstester med snabbkylning med vatten (semi-quenched), som ger en produkt liknande pimpsten sk. lättstensmaterial, erhålles låga lakningsvärden. Denna produkt undersöktes med XRD eftersom den inte går att undersöka med SEM pga. materialets porositet. Mineralogin hos lättsten varierar något mot den på marken normalt tippad slaggen. Lättstenmaterial är partiellt ett amorft material. Granulationstester för slagger har gjorts tidigare, men resultaten av dessa visar på högre lakningsvärden av krom jämfört med semi-quenched material. Orsaken till detta kan vara oxidering under själva granulationen då de kylda slaggdropparna flyger genom luften till en vattendamm. Kromoxider är mer lättlakade än andra kromföreningar.

Lägsta lakningsvärden på krom hos produkter fås med semi-quenching, men då är materialet inte aggregatformigt utan liknar granulerad slagg och pimpsten. Semi- quenched slagg har goda isolerings- och dräneringsegenskaper. Aggregatformigt material med lägsta möjliga lakning av krom erhålls med kylning från en riktning, t.ex. med hjälp av slabsbotten och relativt tunn bädd av tippad material, så att gaserna hinner strömma ut utan att göra materialet poröst.

Yhteenveto

Outokumpu Stainless Oy Tornion tehtaitten vuosittainen tuotanto nousee lähivuosina 1,7 miljoonaan tonniin teräsaihioita. Ruostumattoman teräkseen valmistusprosessiin kuten muihin metallurgisiin prosesseihin kuuluu vääjäämättä myös sivutuotteiden kuten kuonan valmistaminen. Eri osaprosesseista muodostuu vuosittain sivutuotteita noin 300 000 tonnia, josta suurin osa on loppusijoitettu sekakuonana metallinerotusprosessin jälkeen vielä näihin päiviin asti. Terässulattokuonien tuotteistamisprojekti aloitettiin vuonna 2001 tavoitteena lisätä hyötykäytettävän sivutuotemäärän osuutta ja kehittää uusia tuotteita.

Sivutuotteita muodostuu osaprosesseista kuten, valokaariuuneista (VKU1, VKU2), AOD- konverttereista (AOD1, AOD2), senkka-asemilta sekä kromikonvertterilta (CRK). Kuonien kemiallisen koostumuksen vaihtelu kussakin prosessissa on pientä, mutta eri prosessien välillä kemiallinen koostumus on erilainen. Kemiallinen koostumus vaikuttaa lähinnä emäksisyyden osalta sivutuotteen koossa pysymiseen tai mahdolliseen pulverisoitumiseen. Tämän työn tarkoituksena on kromipitoisten teräskuonien laadun hallitseminen eri jäähdytysmenetelmiä käyttäen. Tavoiteltu tuote tulisi olla aggregaatti joka olisi riittävän luja sekä kemiallisilta ominaisuuksiltaan sellainen että kromin ja muiden raskasmetallien liukoisuus olisi alhainen.

Tutkittavana materiaalina oli sula kuona joka oli kaadettu prosessista kuonapataan, mitään lisäaineita ei käytetty sulassa. Tavoitteena oli tutkia kuonassa olevan kromin sitoutumista spinelleihin eri jäähdytysmenetelmillä. Saatua sivutuotetta tutkittiin myös fysikaalisesti, pohjoismaisen kuulamyllytestin (prEN 1097-9) avulla. Kemialliset analyysit olivat : kokonaisanalyysi (XRF) ja liukoisuustesti (ravistelutesti prEN 12457-3). Sivutuotteiden mineralogiaa jauhetuista näytteistä selvitettiin röntgendiffraktiometrin (XRD) ja kappalemuotoisesta näytteestä pyyhkäisyelektronimikroskoopin (SEM) avulla. Lisäksi suoritettiin simulointeja FactSage ohjelmalla eri yhdisteiden aktiivisuuden tutkimiseksi. Tutkitut sivutuotteet tulivat pääosin VKU2 ja CRK:lta joiden prosessitasapaino on hyvä eikä kemiallisen analyysin vaihtelu ole merkittävää. Kyseiset tuotteet sisältävät kromia ja osa siitä ei ole spinelleissä joten kromin liukenemista tapahtuu. Käytettäessä vesijäähdytystä kuonapatjan yläpinnan jäähdyttämiseksi ei merkittävää liukoisuuden pienenemistä havaittu . Kaadettaessa sula kuona aihion päälle ohueksi kerrokseksi tuli patjasta tiivis ja liukoisuus oli vähäisempää verrattuna samaan erään joka oli kaadettu paksummaksi patjaksi. Liukoisuuden pienenemiseen vaikuttanee eniten aktiivisen ominaispinta-alan pieneneminen tiiviissä materiaalissa. Vertailukokeita tehtäessä pikajäähdyttämällä kuonaa ns. kevytkiveksi saatiin alhaisia liukoisuusarvoja kromin osalta. Kevytkiviaineksen mineralogiaa tutkittiin XRD:lllä koska sitä ei huokoisuuden vuoksi voi tutkia SEM:llä. Kevytkiviaines, joka on osittain amorfista, sisältää joitakin eri mineraaleja normaaliin maassa jäähdytettyihin kuoniin verrattuna. Kuonatyypeille on myös tehty granulointitestejä, jossa sula kuona jäähtyy nopeasti sulasta kiinteään muotoon. Granuloidun kuonan liukoisuusarvot ovat korkeammat kuin kevytkiven, joten on syytä epäillä hapettumisen tapahtuvan granuloinnin yhteydessä minkä vuoksi kromiyhdisteet ovat suurimmalta osalta oksideja jotka liukenevat.

Matalimmat liukoisuusarvot saadaan vesi-pikajäähdytyksen avulla mutta tuote ei ole silloin aggregaattimuotoista, vaan muistuttaa granuloitua kuonaa tai hohkakiveä. Haluttaessa aggregaattia, jossa kromin liukoisuus olisi vähäistä, olisi kuona kaadettava jäähdyttävän metallialustan päälle suhteellisen ohueksi kerrokseksi jotta jäähtyminen tapahtuisi yhdestä suunnasta ja kaasut ehtisivät virrata ylös materiaalista ennen yläpinnan muuttumista kiinteään muotoon.

Table of Contents ______

1. INTRODUCTION ...... 7 1.1. Introduction...... 7 1.2. Aim of this work ...... 7 1.3. Limitations ...... 8 2. STEEL MAKING AND BY-PRODUCTS FROM STEEL PLANTS ...... 9 2.1. Stainless steel production at the Tornio works ...... 9 2.2. By-products from steel making...... 10 3 THEORY ...... 12 3.1. General slag properties ...... 12 3.1.1. Slag ...... 12 3.1.2. Thermodynamics of the stainless steel slags ...... 12 3.1.3. Activity of chromium compounds in slags ...... 14 3.1.4. Chromium in steel slags...... 15 3.1.5. Density of slag ...... 15 3.1.6. Viscosity ...... 15 3.1.7. Basicity ...... 15 3.1.8. Solubility of water...... 16 3.1.9. Spinels...... 16 4. LITERATURE STUDY...... 18 4.1. Investigations of slag and their properties in Europe...... 18 4.1.1. Reduction of EAF slag by carbon blowing or remelting in carbon crucible...... 19 4.1.2. Modification of the basicity of the liquid slag at KTN...... 20 4.1.3.Treatment of solid slags...... 20 4.2. Utilization of steel slags...... 21 4.2.1. Utilization ...... 21 4.2.2. Production and utilization of slag in Europe...... 22 4.2.3. The Weathering process...... 24 4.3. Analyses of slags and test methods for technical properties...... 25 4.3.1. Test methods, technical properties...... 25 4.3.2. Test methods, environmental properties...... 26 4.3.3. Technical properties of slags compared with natural materials...... 27 4.4. Environmental considerations...... 29 4.4.1. Finnish guidance for the use of secondary products in earth and road construction...... 29 4.5. Mineralogical investigations of steel slags ...... 30 4.5.1. Investigations at Acerinox and KTN ...... 30 4.5.2. Mineralogical investigation in Tornio ...... 31 5. METHODS and MATERIALS...... 32 5.1. Test materials...... 32 5.2. Physical properties...... 32 5.2.1. Nordic ball mill test prEN 1097-9 ...... 32 5.2.2. Crushing properties...... 35 5.3. Chemical and mineralogical properties ...... 35 5.3.1. XRF...... 35 5.3.2. The standard shaking-test prEN 124 57-3 ...... 35 5.3.3. XRD ...... 35 5.3.4. SEM analyses...... 36

Table of Contents ______

5.3.5. Simulation with FactSage ...... 36 6. EXPERIMENTAL and VISUAL OBSERVATIONS from the tests ...... 38 6.1. Test 0 and 1, FeCr slag by normal pouring...... 39 6.2. Test 2, FeCr slag with water-cooling...... 40 6.3. Test 3, with water- and metal-cooling ...... 40 6.4. Test 4, EAF slag cooled in the slag pot ...... 41 6.5. Test 5, EAF slag cooled with scrap ...... 41 6.6. Test 6, EAF slag cooled with scrap ...... 41 6.7. Test 7, CRC slag cooled with scrap...... 42 6.8. Test 8, CRC slag cooled with the scrap ...... 42 6.9. Test 9, AOD slag poured on the slabs...... 43 6.10. Test 10, EAF slag poured on the slabs...... 44 6.11. Test 11, EAF slag poured on the slabs...... 44 6.12. Test 12, CRC slag poured on the slabs ...... 45 6.13. Test 13, CRC slag poured on the ground...... 45 6.14. Test 14, semi-quenched slags ...... 45 7. RESULTS ...... 46 7.1. Earlier tests and investigations...... 47 7.2. Nordic ball mill test prEN 1097-9 ...... 48 7.3. Chemical composition from XRF analyses ...... 50 7.4. Shaking test...... 51 7.5. SEM analysis ...... 55 7.5.1. Tests with EAF slag...... 56 7.5.2. Test 7 with CRC slag, scrap-cooled...... 60 7.5.3. Test 10 with EAF slag poured out on the slabs as a thin layer...... 61 7.6. XRD analysis ...... 64 7.7. Simulation with FactSage ...... 67 8. DISCUSSION...... 69 9. CONCLUSIONS...... 75 REFERENCES ...... 76 APPENDIX...... 79

Introduction ______

1. INTRODUCTION

1.1. Introduction

Steel slags have been utilized around the world for a long period of time. The economical loss in form of metals in the slag is a marked disadvantage with depositing these slags. A high chromium recovery from the slag is necessary for overall process economy. High leaching of chromium from the slag materials is not environmental friendly and should be stopped in the process by treatments. Spinels in the slag are binding the chromium hard and hence the leaching of chromium is low or negligible. The control of leaching behaviours in slags has become more essential due to the stringent requirements for several aggregates for road construction.

1.2. Aim of this work

The aim of this thesis is to study chemical and physical properties of chromium containing steel slags. These properties can be made to vary by different cooling rate and chemical accessory substances, stabilizers. The goal was to establish a cooling method that produce slag materials with low leaching behaviours and sufficient hardness to be used as a rock material in road constructions and civil engineering applications. A proper cooling method can be able to relive the utilization of slag materials. Steel slags are utilized in road constructions, since its physical properties are quite similar to natural stone materials. Mineralogical and chemical properties of every test samples were studied to examine the variations in compositions of slags. Differences in element concentration can affect leaching behavior. In this study the effect of different cooling methods as to leaching of chromium was investigated. The leaching behaviors of heavy metals e.g. chromium and molybdenum are often limiting factors for the use of slag products, as construction materials. The results from other investigations of slag utilization and leaching behaviours were compared with results of this work. The different methods of handling and characterizing slags in several countries were also investigated. The cooling methods tested, were, cooling by water-spray, by scrap in a slag pot and by pouring into a basin with the foundation of slabs. The dependence of thickness of the slag bed was investigated for stone material class and leaching behaviours.

Introduction ______

1.3. Limitations

EAF- and AOD slags from line 1 were not included in this investigation because of the larger fluctuations in the chemicals analysis of these slags compared with slags from line 2. Ladle slags, which mainly have the similar analysis as AOD slag, has not been investigated. At moment the praxis in Tornio is to add sodium tetraborax into liquid AOD2 slag, which results into a stable stone material with low leaching behaviors. Stabilized AOD slag is included in this investigation as a reference material, with low chromium content and for some Nordic ball mill tests. Addition of chemical compounds into the slag pot, for example adding spinel formers into CRC or EAF slag, at the melting shop has not occurred. The investigation started when the slag pot was coming out of the melting shop and was continued during the whole cooling period.

Steel making and by-products from steel plants ______

2. STEEL MAKING AND BY-PRODUCTS FROM STEEL PLANTS

2.1. Stainless steel production at the Tornio works

In the close future the production capacity of the steel plant at the Tornio works is 1.7 million tonnes cast slabs annually. The steel melting shop consist of two lines, the charge weight of line No 1 is 95 tonnes and of line No 2 150 tonnes. The specialty of line 1 is a chromium converter for treating liquid Ferrochrome from the Ferrochrome melting shop (Outokumpu Chrome Oy). The stainless steel production is mostly scrap based and begins at the raw material yard. The raw materials are melted in an electric arc furnace (EAF). After melting, the liquid steel is charged in an Argon Oxygen Decarburisation- converter (AOD) to reach the final quality of the steel (Figure 1). The AOD No 1. is charged with liquid ferrochromium from the chromium converter(CRC) and molten steel from the Electric Arc Furnace No 1. During the AOD process first oxygen and the mixture of oxygen and an inert gas, as argon or nitrogen, are injected in the melt. Carbon content in the melt is reduced to specified limits and the desulphurisation process is reducing the sulphur content. Between the AOD batch process and continuous casting is a ladle station one for each line for adjusting the steel quality to final limits. Special alloy elements may also be added at this stage and the melt is homogenized by argon injection. The required temperature for the continuous casting machine is adjusted at the ladle stations.

After ladle treatments, the melts are transferred to the continuous casting units. The melt is solidified and torch cut into 800-1620 mm wide slabs. Most of the slabs are transferred hot from continuous casting units to the hot rolling mill. Prior to hot rolling, possible surface defects are removed by grinding. Two of the four grinding machines are able to grind hot slabs. The hot rolling mill is able to roll the slabs to a black hot band with a thickness of a few millimeters. The 14-metre long slab is first rolled to 22 mm thickness in the roughing mill. The finishing is made in a Steckel-type finishing mill with a maximum rolling speed of 600 m per minute. Leader strips are welded to the beginning and the end of each coil, increasing the amount of usable products in subsequent process stages. The black hot strips are first softened or annealed in the annealing furnace. The cold rolling is carried out in reversible Senzimir mills. The final product, stainless steel, is cut in specific dimension in sheets or coils, [1].

Steel making and by-products from steel plants ______

Fig. 1. Flow sheet of the melting shop line 1 and 2, Outokumpu Stainless Oy

2.2. By-products from steel making

Slags are produced from EAF´s , AOD´s and (Ferro)chromium converter( CRC) and even from ladle stations. Slag from AOD 2 is stabilized at the moment by the addition of sodium tetraborax, Na2B4O7, during the slag tipping into the slag pot at the melt shop, but the other slags are poured out without any chemical additions. There are different types of technologies to make products of these slags, semi-quenching by strong water-jet results in a porous, pumice like product, also called “kevytkivi” and normally poured slag, which has to be crushed to smaller aggregates to be used in road constructions. Slags from ladle stations have no applications as products but ideas of their recycling in melt shop exist.

When the steel production increases to 1.7 million tons, the production of the by-product of different slag species will be about 366 000 tonnes. A project “ Utilizing slag from melting shop to products” started at 2001, the aim for this project is to find new slag products mainly for road construction. Until the year of 2003 all slags from the melting shop were processed in the Bergslagen process to separate the metals from crushed and milled mixed slags (AOD´s, CRC, EAF´s and ladle slags). The total amount of mixed slag was pumped in a waste pond as slurry. The slag is final deposited in the pond. In the future feasible products are for road construction, cement factory and for the manufacture of bricks and concrete blocks.

Steel making and by-products from steel plants ______

Oxidation of chrome, iron and molybdenum is undesirable. Reducing alloys to decrease the oxidization of these metals can be done in EAF. In EAF coke is charged during melting to reduce the scorification of metals. Limestone is used as a slagbuilder in EAF 1 and burned lime in EAF 2, [1, 11].

Theory ______

3 THEORY

3.1. General slag properties

3.1.1. Slag

Slags contain most of the non-metallic compounds of the input materials charged into the metallurgical process, or metals, which have been oxidized during the process. Parts of the metallurgical slag also contain metallic droplets, which still are in the slag because of the viscosity of the slag. Two different theories exist about the composition of slag, one is the molecule theory and the second the ionic theory. In pursuance of the molecule theory the components do not appear as a pure material, but as chemical compounds. According to the ionic theory the slag components are positive or negative ions and could be divided into three blocks, alkaline, acid and amphoteric ions. Alkaline ionic compounds can deliver an oxygen-ion. Acid ionic complex can consume an oxygen ion and amphoteric ions can behave as an acid in alkaline slags and as a base in acid slags. Steel slags have some alkaline compound such as CaO, FeO, MgO and MnO. The most common of the acids are SiO2 and P2O5. In steel slags the common amphoteric compounds are Al2O3 and TiO2. The molecule theory has a more classical chemistry approach of stoichiometri and described the build-up of the slag as a compound of different components, which are in equilibrium with each other. In pursuance of ionic theory the SiO4 tetrahedron is the main-component, with four oxygen atoms around each silica-atom. These tetrahedrons form a regular lattice arrangement, which are broken in melt phase. This phenomenon is called depolymerisation of the silica network. Molten silica network is dissymmetrical compared to crystalline silica. Addition of an oxide of a divalent metaloxide such as CaO results in a breakdown of the lattice of molten silica. A SiO4 tetrahedron is a strong entity, which cannot breakdown into atoms in the slag, [2, 3].

3.1.2. Thermodynamics of the stainless steel slags

Chromium has four electrons in orbital 3d and two electron in orbital 4s, thus exists in a variety of oxidation states. The behaviour of oxides in metallurgical processes is very complex due to the co-existence of multivalent chromium ions, the high melting points of slags containing chromium oxides, the characteristic of chromium oxides volatization and the sophisticated structures of chromite materials, [4]. Three different chromium ions 2+ 3+ 6+ exist in different environment; blue Cr , green Cr and yellow to red Cr . Cr2O3 is moderately stable with respect to its constituent’s elements. Quantitive data on the thermodynamics of chromium oxide in silica melts are practically very few, and the phase equilibrium data in systems containing chromium are available mostly at high oxygen pressures under poorly defined reducing conditions. All of the slags contain Cr3+,

Theory ______

but normally none of them contain Cr2+ or Cr6+ in significant amount, [6]. The constitution of each slag should be ascertained from the total chromium content and the amount of the redox-species, Cr2+ or Cr6+. Cr2+ is a very powerful reductant, which means that divalent chromium in the slag will easily be oxidised when the slag is dissolved into a solution. This will cause certain difficulties or errors in the chemical analysis of chromium. When iron and chromium exist in the slag at the same time two redox- systems occur together. Therefore Cr2+ will be oxidised to Cr3+ and the corresponding amount of Fe3+ is reduced to Fe2+, [6]. Iron-Chromium equilibrium reaction; x(FeO) + Cr = xFe + CrOx ( 1.1)

Slags containing chromium oxide have been investigated at temperatures between 1400 and 1650ºC under different oxygen partial pressures, ranging from a very strong reducing atmosphere to ambient air. The results showed that the chromium exists in the silicate slags as divalent, trivalent, pentavalent or hexavalent, depending on temperature, slag composition and partial pressure of oxygen. The chromium phase relations in slags are very complex caused by the multivalences of chromium. It has been observed that the existing form of chromium in air was hexavalent if the system was CaO-CrOx. In lime rich systems chromium is oxidised to hexavalent in air. When the molar ratio CaO/Cr2O3 is higher than 3, the chromium oxidation state becomes higher in air between temperatures of 800 and 1000ºC. Trivalent chromium was found to be incorporated into the lattice of CaO at low chromium content, but pentavalent chromium was favoured when chromium oxide concentration was higher. Earlier investigations have showed that the ratio of Cr2+/Cr3+ increases with increasing temperature and decreasing oxygen partial pressure, as well as decreasing the slag basicity from 1.5 to 1.3, [6]. The chromium oxidation state has been observed to be a function of FeO content of the slags and Si content in the metal. Activity of chromium oxides is dependent on the partial pessure of oxygen.

2CrO + ½ O = Cr O when ∆G o = −38654 ± 2500 cal (1.2.) 2 2 3 1700o C a Cr2O3 ½ 4 and 2 = pO 2 ⋅1.9 ⋅10 (1.3.) a CrO

Xiao has studied the equilibrium of chromium containing slags in metallic chromium crucible at 1500, 1550 and 1600ºC temperatures [6]. The system CaO-SiO2-CrOx was analysed by wet chemical method. The effects of addition of MgO and Al2O3, slag basicity and temperature were investigated. The results showed that increasing temperature increased the fraction of divalent chromium, but increasing of the basicity decreased the fraction of divalent chromium.

Theory ______

Partially substituting CaO for MgO did not result in any significant change in the oxidation state of chromium. Increasing of the Al2O3 content from 0 to 10 mol-% resulted in a lower divalent chromium fraction at the slag basicity of 1.0 mole ratio. A further increasing in the Al2O3 content didn’t cause any obvious change in the oxidation state of chromium, [5, 6].

Fig. 2. The phase-system CaO-Cr2O3-Al2O3 versus temperature (Ford and Rees. 1958), [6]

In Figure 2. the formation of the intermediate phase 10CaO* 8Al2O3* 2CrO3* Cr2O3 at the temperature about 1400ºC, can be seen. This indicates that the chromium exists with 6+ an oxidation state of Cr while CaO * Al2O3 content is more than 15 wt.-%. The intermediate phase exist with a solid solution (ss) CaO * Al2O3, when the CaO* Al2O3 content is higher than 75%.

3.1.3. Activity of chromium compounds in slags

Although the activity measurements in chromium containing slags have been an interesting topic for over 20 years, the existing activity data in the literature are still very restricted especially for the slag system under stainless steel production circumstances. Studies of solubility of MgCr2O4 in CaO-MgO-Al2O3-SiO2 slags at 1600ºC have shown that when %CaO/%SiO2 ratio is constant the chromium solubility decreases with increasing Al2O3 content in the melt. The activity of CrO decreases weakly with increased temperature, but increasing basicity is increasing the activity. The activity of chromium is strongly decreased by building spinels between Cr and Magnesia or Iron. [6, 10].

Theory ______

3.1.4. Chromium in steel slags

Chromium exists universally in slags as Cr2O3 or bounded in mineral structure by substituting several equivalent cations. Chromium exists in slags as tri- or divalent cation. The hexavalent cation can be produced by oxidation with atmospheric oxygen and contact with free lime, [6, 12].

3.1.5. Density of slag

With increasing temperature the density of material is often linearly decreasing, because of the oscillating motion of atoms are longer and the distance between atoms are increasing. The temperature has quite a small effect on the density. Adding some material, which changes the composition of slag, can vary the density. The density of EAF-slag is about 2.6 – 3.0 Mg/m3 at 1500ºC, [2].

3.1.6. Viscosity

The viscosity is describing the friction forces between particles in a liquid, which could stop the particles moving. Most of the steel slags are Newton’s liquids. The viscosity is a function of temperature, chemical composition and pressure and is decreasing with increasing temperature. Increasing the concentration of SiO2 and Al2O3 increases the viscosity, because of more of the aluminate- silicate chains. Addition of metal oxides brakes down the silica network and thereby decreases the viscosity. Chrome oxides, occurring in slag, CrO and Cr2O3, have different functions. CrO decreases the viscosity and Cr2O3 increases. When viscosity is low metal droplets can easily fall down through the melt; at high viscosity more of the droplets stay in the slag and therefore cause higher metal losses, [2].

3.1.7. Basicity

The basicity of calcium aluminate slag can be calculated by several formulas but is often calculated by formula: % CaO B4 = (3.1.) (%SiO 2 ⋅ %Al2O3 )

The availability of chromium in slags is correlated to the basicity. The leachability decreases with a rise of basicity above 1. The lowest leaching values were obtained at

Theory ______

basicity around 2 and leachability of chromium increases again at higher basicity. The formula (3.1.) was developed for systems where all of the components are totally dissoluted in the slag. In practice all steel slags contain CaO and MgO, not dissoluted in the molten slag. The content of chromium in the steel slags is strongly correlated with the bacisity of the slag, at higher basicity than 2.0 chromium mainly exist as CaCr2O4. In alkaline circumstances and with presence of atmospheric oxygen CaCr2O4 can easily be oxidized to CaCrO4, a compound that is easily leaching chromium and building hexavalent chromium from divalent or trivalent chromium. With basicity higher than 1.0 (B4) chromium content is low and increasing with low basicity. The desirable basicity of AOD slag in Tornio is about 2.2 and 1.5 for EAF slag, when basicity index calculated by formula (3.2.), [2, 12]:

(CaO + MgO) B = (3.2.) (SiO 2 + Al2O3 )

3.1.8. Solubility of water

To be soluble in slag a gaseous element must be in ionic phase. This solubility reaction is strongly depending on the basicity of the system. Solubility of H2O is increasing strongly when the mole fraction of CaO/ SiO2 is higher than 1.0 and is approximately 500 ppm at mole fraction 1.3. At the mole fraction 1.0 the water solubility is lowest, about 375 ppm, [2].

3.1.9. Spinels

The spinel group comprises a large number of binary oxide minerals, such as spinel (MgAl2O4), chromite (FeCr2O4) and hercynite (FeAl2O4). 2- The spinel structure AB2O4 consist of a face centered cubic (fcc) array of oxide ions (O ) in which the A cations occupy one-eighth of the tetrahedral holes and the B cations occupy the octahedral holes. Face centered cubic is also called cubic close packed. Examples of compounds that have spinel structures include some of d-block oxides, such as Fe3O4 and Mn3O4, where A and B are the same element. Lattice enthalpy calculations based on a simple ionic model indicate that for A2+ and B3+ the normal spinel structure is more stable than the invers spinel structure B[AB]O4. The occupation factor, λ, of a spinel describes the degree of occupation of B atoms in the tetrahedral sites. For a normal spinel is λ = 0 and is often depending on the temperature. When B is Cr3+ the probable A2+ atoms, which correspond to a normal spinel are Mg2+, 2+ 2+ 2+ 2+ 2+ 2+ Mn , Fe , Co , Ni , Cu and Zn . Cr2O3 (Eskolaite) is known to exhibit nonstoichiometric spinel modifications whereby the normally six-coordinate cations

Theory ______

occupy both octahedral and tetrahedral sites. This structural change is decreasing the overall packing efficiency of the structure, [2, 3]. In a face centered cubic structure atoms are packed at maximal possible density, of 74% packing density.

The activity of Cr2O3 in a spinel phase, FeO* Cr2O3 or MgO* Cr2O3, is reduced and formation Cr6+ is suppressed. When the analysis of a slag is known factor sp. can be calculated by formula (3.3.), [9, 20]:

Factor sp. = 0,2 ⋅ MgO +1,0 ⋅ Al2O3 ⋅ (n ⋅ Fe tot ) − 0,5⋅ Cr2O3 (in wt.- %) (3.3.)

Factor sp, which is an empiric formula, shows the amount of possible spinelphases in a system based on the stoichiometri of the elements (MgO, Al2O3, Fen and Cr2O3) in slags. The formula has been formulated by FehS in Germany, [9]. The coefficient for Fe has been changed between 1 and 4 and in the latest version of formula Fe has the coefficient n. When factor sp is higher than 5 leaching of chromium is low because of the spinel formations in the slag (Figure 3.).

The rapidly cooled slag has an amorphous structure, which has no sharply defined melting point, transition from solid to liquid state occurs gradually. One can say that an amorphous solid is a liquid with extremely high viscosity at room temperature. The slowly cooled slag is crystalline solid; atoms are homogenously distributed into the structure. The atoms mobility is limited to small vibrations about fixed equilibrium sites, [4, 20].

Literature study ______

4. LITERATURE STUDY

4.1. Investigations of slag and their properties in Europe

Steel is infinitely recyclable and also its by-products, as slag, should be recycled, not deposited to establish a good environmental awareness. In stainless steel production the raw material cost dominate the total production cost for the primary product. Since chrome is one of the major constituents of stainless steel, it represents a large portion of the raw material cost. The most significant disadvantage with classification the slag as waste and the deposition of slag is the enormous economical losses of metals and alloys in the slagheaps, which have been deposited. A high chromium recovery is essential for overall process economy. Investigations of properties and different behaviours of slag have been done in Europe especially research on decreasing of scorification of chrome. These tests were done at Forschungsgemeinschaft Eisenhüttenschlacken e. V. (FEhS) in Germany, at Krupp Thyssen Nirosta (KTN) in Germany, at Centro Sviluppo Materiali S.p.a. (CSM) in Italy and at ACERINOX (ACN) in Spain. The results of these investigations were accounted in a report EUR 19382. The final aim in EAF practice was to avoid and/or decrease the scorification of chromium with addition of mixtures of slag forming materials. In AOD process operationally tests have been made to optimise the process in order to blowing and Ar/O2-ratio. Additions of different slag forming materials to avoid the chrome scorification have been tested in both the EAF- and AOD process, with the aim of binding chromium into stable mineral phases in the slag.

One method has been the addition of carbon dioxide, resulting in a lower partial pressure of the oxygen and oxidation potential. The injection of reduction materials, as Al, and Si, into furnace has been investigated. The materials have been added in the liquid slag for the desirable result with stable minerals phases with low content of chromium in leachate. In AOD practice at KTN the decreasing of chromiumoxides in the slag was made with the optimisation of the blowing by top-lance and Ar/O2- ratio. At FEhS liquid and solid slag has been treated with different methods: - Reducing of EAF- and AOD –slag - Mixing of solid slag with FeSO4 . - Addition of spinel forming compounds in liquid slag.

Addition of iron sulphate to solid slag prohibited the leaching of chromium reducing the chrome in leachate. The hexavalent chromium cannot be stable with divalent iron (formula 4.1.).

3Fe2+ + Cr6+ Æ 3Fe3+ + Cr3+ (4.1.)

Literature study ______

There are several treatments of liquid EAF-slag that can be used in remelted or primary molten slag: - Remelting of high alloy steelmaking slag under different atmospheres and crucibles (carbon) and addition of coal to reduce the chrome in the slag. - Modification of the liquid slag with sand or lime - Addition of pure oxides into the slag. - Addition of bauxite or Al2O3- MgO and FeOn-containing residues.

The results of the operational tests with EAF-slags have shown that an increased content of MgO and Al2O3 can decrease leaching of chromium. Injection of reducing agents such as FeSi into the steel bath has shown to be successful. Laboratory tests at FehS concerning the binding of chromium into stable mineral phases have been confirmed by operational tests at KTN’s EAF. The addition of bauxite has given good results when bauxite is added into transfer ladle when steel and slag are tapped into it at the same time. Laboratory and operational tests have shown a correlation between MgO-, Al2O3- and FeOn content and leaching behaviours. Laboratory investigations have shown that the influence of these compounds to leaching of chromium is different. The Factor sp (Figure 3, formula 3.3) for EAF slag has been formulated; when the factor is lower than 5 the chromium leaching is high but with the value higher than 25 is the leaching very low. (Below detection limit 0.01 mg/l)

The test at KTN had been planned with the knowledge of factor sp. In practice bauxite was added into the transfer-ladle slag. By SEM analyses they have demonstrated that the chrome is bound in spinel phases if the spinels are of type Me’O*Me2’’O3, where Me’ is 2+ 2+ 3+ 3+ 3+ 3+ Mg , Fe and Me’’ Fe , Al or Cr . Chromium (Cr ) is placed on the lattice places formerly used by Fe3+ or Al3+. The investigations by FehS have showed that there is a strong relationship between the MgO-, Al2O3-, FeOn- and Cr2O3-content in the slag and the leaching behaviours of chromium, [9].

4.1.1. Reduction of EAF slag by carbon blowing or remelting in carbon crucible.

The reduction of slag with coal can be achieved by injection coal into the liquid slag with the chemical reaction:

2Cr2O3 + 3C Æ 4Cr + 3CO2 (4.2) The remaining chrome in the slag was found in small metal droplets, whose number and size increased with the blowing time. Spherical pores in the reduced slag were observed after the solidification that indicated the not complete reaction and CO-gas formation. CO-formation took place during the solidification and formed pores in the EAF-slag, [9].

Literature study ______

Fig. 3. Correlation between factor-sp and leaching of chromium [9] Observe the coefficient for Fetotal, which is 4.0 in this formula but is in the latest investigations n. Each point or square is a specific slag sample.

4.1.2. Modification of the basicity of the liquid slag at KTN

The tests were carried out by adding lime or sand at 1650ºC with 10 min holding time. Modifying of the basicity of EAF-slag by adding lime or sand had no effects on the leaching of chromium of the slag. Lower basicity is of advantage when the desirable result is a foamy slag, but the basicity of the slag has no dependence on the leaching behaviours of chromium from slag. KTN had in tests been able to vary the cooling rate in the slag pit to determine its influence on the stability and leaching behaviour of the slag, [9].

4.1.3.Treatment of solid slags

Solid slag can be treated by mixing with FeSO4. It was possible to decrease the leaching of chromium with addition of iron(II)sulfate, as chromium (Cr6+) always reduces into Cr3+ in the presence of Fe2+. Leaching of chromium increases as soon as the iron (Fe2+) is oxidized into Fe3+. Addition of iron-sulfate results also in leaching of sulfate from the slag, which can be defined as an undesirable effect. The result of long-term investigations

Literature study ______

has shown that, when all of the Fe2+ have been oxidized to Fe3+ the Cr-leaching has increased to the same level as the untreated slag. The final result is that the iron sulphate addition will reduce the chromium leaching only for a period a time. Another method of treatment with solid slag is the mixing of solid slag with cement or ground granulated blast furnace slag. The aim with this mix is to form a compound, which is like concrete with low active surface of chromium leaching. The leaching process includes both surface reaction and diffusion and will be started by surface reaction. A diffusion process follows and this process is very dependent of temperature. The surface can be minimized by briquetting or by mixing e.g. cement or other hydraulically binding agents.

A good environmental compatibility over long-term conditions can be obtained only with the modification of liquid slag. Additions of bauxite to the liquid EAF-slag do not influence their mechanical and technical properties. They are suitable for utilization in road constructions, [9].

4.2. Utilization of steel slags

4.2.1. Utilization

Slag is a multifunctional material, which is used across many fields of application. Utilization of slag products helps to conserve finite, maiden field, natural resources and also minimizes the emissions to atmosphere. Slag produced by right methods can be considered as an environmentally friendly raw material, [13, 16].

Slags from different melting plants and processes have different chemical and physical properties and will influence on the utilization possibilities of slags. In production of stainless steel EAF- and converter slags are produced as co-products. One of the most important properties is the volume stability of slag used as aggregates in road construction. Fine milled quenched slag powder can be utilised in cement industries. Slags can be used in different fields of applications. The use of steel slags for road construction is well experienced and has a long tradition in Europe. Many roads, ways and airfields in the neighbourhood of steel plants have been built on slag aggregates. The Canadian company succeeded in recovering the remaining stainless steel from the slag, using the Swedish patented technology. The principle of this technology is mainly the wet grinding followed of magnetic separation of the metals. Steel slag has even been used as a fertilizer, as recycled materials in melt shop and as aggregates in road construction. In Germany during the 1960´s the use of steel slag for the production of fertilizer amounted to more than 3 million tonnes per year. Today only some blast furnace (BF)-, basic oxygen steelmaking (BOS)- and secondary steel making slags are used in the production of lime fertilizer.

Literature study ______

Table 1. Chemical composition of several stainless steel slag (CANADA)[14], in Italy, Germany and Spain [9] and Outokumpu Stainless Oy Average chemical analyses

EAF CaO SiO2 Al2O3 MgO Cr2O3 Fe2O3 B4 Factor sp EAF´s in Canada 33.4 30.8 6.0 5.9 7.8 3.2 1.07 6.5 Outokumpu Stainless 43.3 26.9 7.0 5.6 2.2 0.9 1.44 7.6 Acerinox 42.8 31.3 7.8 10.2 3.4 0.5 1.36 8.6 CSM 46.0 33.0 4.0 3.1 7.0 1.5 1.33 2.6 KTM (1998) 39.3 28.5 6.5 11.2 3.0 0.6 1.44 7.8

An application for iron and steel slags is the use as a fertilizer. These fertilizers have shown good effects on the growing of plants. Test fields, which have been under investigations for nearly 100 years indicate no harmful effects on the soil and plants. These types of utilization of slags make it valuable and sustainable products. Slags from different melting plants have varying contents of metals and calcium that is an important component for a fertilizer (Table 1), [14].

4.2.2. Production and utilization of slag in Europe

Use of Steel slag in Europe 2000 (Euroslag)

final deposid cement production road construction hydraulic engineering fertilizer internal recycling interim storage

Fig. 4. Use of steel slag in Europe /Euroslag 2000

Literature study ______

In the year 2000 in Europe was around 25 millions tonnes blast furnace slag was produced, about 29% of this as a slow cooled crystalline, 69% as granulated and 2% pelletised slag. In Germany it is expected that in 2007 nearly 98% of the blast furnace slag will be granulated due to environmental reasons, [22]. Figure 4 shows that the largest amount of steel slag was used in road construction followed by final deposit and internal utilisation in the steel plant. Granulation of blast furnace slag generates a slag with latent hydraulic properties. Approximately 56 % of produced blast furnace slag in Europe is used in cement production and 39.5 % in road construction. In Europe were 16.8 million tonnes steel slag produced in 2000 and 59 % of this amount was basic oxygen furnace (BOF) slag and 28 % EAF-slag. As a road construction material 39 % of 16.8 million tonnes was used and 24 % was finally deposed. Some countries have a utilization rate higher than 95% for the steel slags.

Air-cooled blast furnace and steel slag has a long and qualified application field in road constructions in Europe. Slags as a raw material are processed in plants by crushing and screening simultaneous with natural stone material. The speciality of steel slag is its high density, which can be a considerable factor for transportations and for the necessary amount of bitumen in bituminous bound layers. The high density can even open new possibilities for the use of slag, as high-density concrete for special applications. One potential object for this building-material could be the foundation of the wind power plants at sea. There are two current trials of four pre-cast dollos, large blocks used for sea defense essentially to replace natural aggregates used for armourstone. These blocks have been exposed in severe wetting and drying environments for about eighteen months. A visual monitoring has not showed any cracking or spalling of these blocks.

The first standard for blast furnace cement was established in 1917. In Germany more than 60% of the blast furnace slag was granulated in 1999. In 1936 a part of motor highway in Saxonia was built with a Portland-slag cement, it has constantly been used for 55 years, every winter salted and has endured about 6000 freeze-thaw cycles. The capillary porosity of concrete with blast furnace cement is lower than that of concrete with Portland cement, chemical resistance is in general also higher. One of the most important properties for concrete is durability. Blast furnace cement improves its durability in a field of applications. Low energy, sustainable, materials incorporating blast furnace and basic oxygen steel slag for highway construction and maintenance are used in the UK. In Germany steel slag products utilization was 5.61 Mt by the latest statistics (2000). 12.6% of this amount has been recycled in metallurgical processes, 6 % have been used as fertilizer and 11.4% had to be deposited. BOS-slag is particularly well suited to the new generation of “quiet” asphalt thin surfacing because of its high abrasion resistance and aggregate shape that contributes to surface structure, a key requirement for high speed skidding resistance

Literature study ______

In Denmark EAF slag has been used as aggregate in high performance asphalt surface course. The surface of EAF slag has a structure, which is very resistant to stripping of binding agent by moisture and mechanical wear off the surface by traffic with studded tyres. This results in environmental benefits; the amount of deposited slag is lower and the asphalt pavements withstand for a longer time wearing. Slag aggregates have been exported from Denmark to a number of different countries. EAF slags are high quality building materials and cannot be classified as a waste material. The content of free lime and the basicity of the slag are two important properties for slag being used as a pavement. The basicity of the slag is one of the most important chemical properties, when the basicity is more than 1.55 the amount of free lime causes a volume expansion and further decomposition of the slag. Slag can be deposited as a waste as in part of Russia, Ukraine and the USA. In Japan, Korea and many of the EU-countries is slag used as a component in cement production. Slag is even equal with cement in several countries as in China and India, countries with scarce capital and raw material. Some countries, with high population density and countries with high environmental awareness as Taiwan, Belgium and Holland, favour development and utilization of slag products, [16].

Several” environmentally friendly” materials have been reviewed; cold mix steel slag asphalt wearing course, slag bound materials as alternative sub-base, road base and base course layer and hot mix steel slag wearing courses for use on heavily trafficked roads. Low energy slag bound materials (SBM). European standard for slag bound mixtures is EN 227 402.

The utilization and recycling of steel slag is not as well developed as for blast furnace slag. The recycling grade of steel slag varies from country to country mostly because of chemical composition and local environmental regulations. Problems with the use of steel slag aggregates concerns the large amount of CaO (free lime and even MgO), which especially EAF-slag is containing (Figure 5). Compositions of certain slags and natural stone minerals are rather equal, [16].

4.2.3. The Weathering process

Generally the slag aggregates must be aged before utilization in civil engineering applications. The weathering is one of the most common methods for ageing. The traditional weathering occurs during storage outdoors for several months, which has often yielded fairly good results, example lower volume expansion. One condition for that is that the slag is not crushed to smaller size, causing new crush surfaces. New surface always leach more elements, weakly bound in the mineral structure, by the diffusion theory. A series of weathering trials have been carried out at several works locations. The size of the heaps has varied widely. Samples were then taken when the heaps were constructed and subsequently at time intervals of up to 2 years. The results have clearly

Literature study ______

demonstrated that hydration of free CaO occurred progressively within the weathering heaps. It has been shown that it would be preferable to weather slag in its final size, that should not exceed 2 cm. The undersized material needs to be screened out from the product. Crushing the product material after weathering make new surfaces that have higher leaching compared to aged surfaces. This particle size, 2 cm, is too small for using as a construction material in certain of the road layers.

One method developed in Germany is injection of sand and oxygen into the molten slag. Free lime can be stabilized with injection of sand and oxygen: [20]

O2 + 2FeO Æ Fe2O3 + energy

2 CaOfree + SiO2 Æ 2CaO * SiO2

2 CaOfree + Fe2O3 Æ 2CaO * Fe2O3

4.3. Analyses of slags and test methods for technical properties

There are many test methods to investigate chemical and physical properties of slags and other constructions materials. In the following paragraphs these methods are described.

4.3.1. Test methods, technical properties

The most important properties for road construction and civil engineering materials are the resistance to weathering, the shape and the grain size distribution. Several other properties, which may be investigated are: Bulk density, shape, impact value crushing value, 10%-fines, polishing, water absorption resistance to freeze-thaw and binder adhesion, [20]. Several standardized methods for analysis of properties have been used: Technical Terms of delivery for Armourstones by definition for special test for steel slag armourstones. At least 20 pieces of natural size are to be placed in water at the temperature of 25 degrees for 20 days. If less than 5% of the slag pieces have got cracks or are disintegrated the material is sufficient to be used as a road construction aggregate.

Water absorption test, prEN 1097-6, where the sample is saturated in water for 24 hours. After this time the weight is measured. The wet surface of the sample is dried with a swab and the sample mass will be weighed again. Then the sample will be place warm, until the mass of the sample is constant. The difference between the wet mass and the final mass gives the water absorption of the material.

Literature study ______

Heat conductive test (Sond method) and the freezing test by Hermansson are certain tests, which are used on road construction materials. Dynamic triaxis test has been used often with investigation of aggregates used in road construction, [8, 10, 18].

The volume stability test, used for example in the Netherlands, slag pieces are placed in boiling water for 8 hours and after that time a limited quantity of disintegration cracks and loss of mass is allowed.

One of the test methods for volume stability is the steam test. The volume stability is correlating with the MgO- and the free lime content in the slag. The steam test, that at the present time is a European aggregate standard test method for steel slags (prEN 1744- 1) has in Germany been used from 1980 as a test for quality control of slags. In the steam test are pieces of slag placed over a heating element and water, in steam flow. The grain size distribution of the sample is from 0 to 22mm. The steam test evaluates the volume increase of sample in percent.

The resistance against abrasion of steel slags and natural rock materials, as basalt and diabase, has been tested by test in a rotary drum, Nordic ball mill test, prEN 1097-9. The results have confirmed that steel slags have better resistance to abrasion than several natural rock materials.

4.3.2. Test methods, environmental properties

Environmental properties are content of harmful elements, their availability and leaching in naturally circumstances. The active surface area has a correlation to the leachability, therefore the measuring of pore volume and surface area are important.

Leaching behaviors are detected by two-step batch leaching test prEN 12457-3 by L/S 2 and 8 or column test NEN 7343 or NT ENVIR 002, [8, 17].

Dutch availability test (NEN 7341) is carried out in two steps at L/S 100. The amount of test material used is 8± 0.01g with d95 = 125µm. During the test is pH constant of 7.0 for 3 hours in the first step and at pH 4.0 for 4 hours in the second step. Between the two steps the liquid is filtered and the residue is added in the second step. The sample and leachant are well mixed during the whole test period, [8].

To simulate the natural behaviours a Lysimeter test has been developed. In the lysimeter test the leachant is continuously circulated in the material and the amount of test material is rather high, about 15 m3, which has been packed as a bed to decrease the flow rate of the leachant, [7, 8].

Literature study ______

Determination of the total grain surface area, make it possible to estimate the leaching behaviours. The determination can be carried out in a gas absorption apparatuses, in which the in sample absorpd gas volume can be measured and specific area can be calculated as m2/g of sample material, [12].

Pore volume can be measured with Quatachrome Autoscan, which forces mercury in the pores in the material and the mercury volume can be measured after the measuring.

The tank-leaching test seems to be more practically orientated than the shaking test, but the shaking tests are widely used with investigation of the leaching behavior of rock materials. In Netherlands the diffusions analysis prEN 7345 is used by investigation of bounded materials, which is even made by Finnish technical research center, [17].

The mineralogy of slags has been investigated by Scanning electron microscope SEM and by X-ray diffractmeter XRD. Total analyses of chemical components have been done by X-ray fluorescence (XRF)

Determination of the total amount of harmful metal is made by the prEN 13657 or prEN 13656 methods. A sample is taken from the fines from the crush, of grain size less than 4mm. Like all samples it’s divided into the right amount, 2kg. The metals must be defined before tests and this process occurs by standard prEN 12506 and prEN 13370.

4.3.3. Technical properties of slags compared with natural materials

Table 2. Technical properties of processed steel slag aggregates [25] Characteristics Aggregates Property Dimension BOF-slag EAF-slag Granite Flint gravel Bulk density (g/cm3) 3.3 3.5 2.5 2.6 Shape (%) < 10 < 10 < 10 < 10 Impact value (% by weight) 22 18 12 21 Crushing value (% by weight) 15 13 17 21 10%-fines (KN) 320 350 260 250 Polishing (PSV) 58 61 48 45 Water absorption (% by weight) 1.0 0.7 < 0.5 < 0.5 Resistance to freeze-thaw (% by weight) < 0.5 < 0.5 < 0.5 < 1 Binder adhesion (%) > 90 >90 > 90 > 85

Literature study ______

The mineralogy of slags and natural stones is quite similar, but there are differences in slag compositions between different steel plants and processes. The mineralogy of natural bedrock also differs in different regions on Earth. Some elements such as chromium exist essentially at a low amount but is in several regions a general component in bedrock. In the Table 2 several properties are compared between natural materials and slags. The density of slag is always higher than natural stones, but the water absorption is higher by slags because of the pores in the slags. One of the most important factors for leaching behavior is the porosity of material; material with high porosity has a large active surface for leaching.

Fällman has investigated the dependence of micro- and macropores in leaching of chromium from steels slags. Discrimination between solubility controlled leaching and diffusion controlled leaching release from micro as well macropores, [8]. The leaching estimations of heavy metals from a material should be measured and calculated as a degree of the total amount of respective element, not only as a objective leaching values. For example, the degree in ppm estimates the leaching properties better than the objective leaching values in dimension (kg/l), [19].

Fig. 5. Comparison of the composition of iron and steelmaking slags with natural stones, shown in the system

CaO-SiO2-MgO-Al2O3-Fe2O3-Cr2O3. [25]

Literature study ______

Figure 5 shows certain species of slags and natural minerals in three-phase systems, which make it possible to see the similarity between certain slags and minerals. EAF-slag from stainless steel making often have insufficient properties, such as high chromium leaching, to be used as construction material for qualified applications. To meet demands on a good construction material the liquid slag will be treated in order to stabilize the slag and bind remaining chromium in the slag into stable mineral phases. It seems possible to favour the formation of spinel phases during solidification. To compare the slag with and without treatment, slag samples have been investigated of their mineralogical composition, chemical composition, their mechanical properties and their environmental behaviours. Another important information on the environmental behaviour of slag is the melting history, in the furnace, temperature of melt, partial pressure of oxygen during melting and the kind of materials used as slag formers.

4.4. Environmental considerations

4.4.1. Finnish guidance for the use of secondary products in earth and road construction.

Every year are about 70 million tonnes of natural stone aggregate used in Finland for earth and road construction. Utilisation of by-products from industry requires that they be proven to be environmentally friendly. The methods for investigations have been continuously developed and for that reason the older data cannot be compared with the data on new investigations. The environmental demands were tightened after 1980. Suggested Finnish leaching values for the mineral materials used in earth construction

Cr granular material unpaved 2.0 mg/kg Granular material paved 5.1 mg/kg Monolithic (bounded) material 550 mg/m2

In Sweden there are no current restrictions for using slag products and respective county administrative board and in some cases municipality has supplied the permission to the utilization of slag in certain projects, [10, 15].

Literature study ______

4.5. Mineralogical investigations of steel slags

4.5.1. Investigations at Acerinox and KTN

Acerinox: The mineralogy of slags is greatly varying between different melt shops and processes; investigations of mineralogy have been done at several plants. Mineralogical determination by XRD of slags from ACERINOX have shown following mineral phases in AOD-slag : Lime CaO, Calcite CaCO2, Chromite FeCr2O4, Merwinite, Ca3Mg(SiO4)2, Akermanite Ca3MgSiO7, and Donathite (Fe,Mg)(Cr,Fe)2O4. EAF- slag without treatment: MgCr2O4, Modified slag with bauxite addition: (Mg,Fe)(Fe,Al,Cr)2O4

KTN:

Bredigite Ca1,7Mg0,3SiO4, Larnite CaSiO4, Akermanite Ca2MgSi2O7, Merwinite Ca3Mg(SiO4)2 , spinel (Mg,Fe)O*(Fe,Al)2O3 spinel (Mg,Fe)O*(Fe,Al,Cr)2O3 ,CAO, MgO, [9] The main mineral phases in the EAF-slags from austenic steel making are Merwinite and Akermanite (MgO rich)

Table 3. Mineralogical composition of three different EAF slags (FEhS)

Element Electric Arc Furnace slag 1 2 3

Ca C2S, C3S, Ca-Mg-Si, Ca(OH)2, C2S, Mellite, Monticellite, C2S, Mellite, Ti-Ca-Oxide Calcite Fluorite (Perowskite type) Si Silicate Silicate Silicate Al Mg-Cr-Al-ferrite Mg-Cr-Al-ferrite, Mellite Mg-Cr-Al-Ferrite, Mellite Mg Periclase, Silicate Silicate, Periclase Silicate, Periclase Mn (Mn)FeO (Mn)FeO (MN)FeO

Fe Wustite, α-Fe Wustite, α-Fe, FeO*Fe2O3 Wustite, α-Fe, FeO*Fe2O3 Cr and Ni Ferrites Ferrites Ferrites

The wide-ranging minerals in EAF-slag are; Dicalcium silicate, Tricalcium phosphate, Wüstite, Lime, Merwinite, Spinel. Caused of the relative low basicity in average EAF slag tricalcium silicate is less presented in these slags compared with BOF-slags, [9].

Literature study ______

4.5.2. Mineralogical investigation in Tornio

In the investigations in Tornio at Outokumpu Stainless in 2003 were some EAF slags evaluated on mineralogical characteristics and the results showed the following main mineral phases: Merwinite, Bredigite, Perovskite, Gehletite. Spinels were obtained in low amount; in slag cooled in a slag pot spinels as Chromite and Magnetite and in quenched slag as Spinel and Chromite and Magnesiochromite. The amounts of spinelphases were mainly low. Chrome could even be observed in Ilmenite substituting iron ions. In FeCr slag could also residual Chromite be observed, but the sizes of these were often up to 300-500 µm when spinels usually are smaller than 100 µm, [12]. XRD analysis of EAF slag showed that the proper identification of all the major and minor phases was difficult because of the innumerable peak overlapping of major phases. A typical X-ray pattern included phases like; Melilite (Akermanite + Gehletite) Merwinite, Monticellite(Ca,Mg,SiO4) Chromite, Magnetite, (Fe,Mg)(Al,Cr,Fe,Ti)2O4, Calcite. The slag was usually crystallized but amorphous grains were detected, the metallic phases consisted mostly of Chromite and Magnetite. Chromites were well shaped crystals of varying sizes that can be up to 5 µm, usually embedded in larger non- metallic crystals. Magnetite occurred as spherical inclusion that could be embedded in both metallic and non-metallic phases. Mineral phases in CRC slag have been investigated 1998 and the results have been compared with the results of this investigation, [26, 31].

Methods and Materials ______

5. METHODS and MATERIALS

5.1. Test materials

The slag materials included in this investigation came from the steel melt shop from the scrap based stainless steel production, mainly EAF and CRC slag and also from AOD, but in a less significant scale. Samples were taken from the slag from EAF 2, because it is operating stable, with no high fluctuations in the chemical analyses. As reference material, with well-known mineralogy, chemical analyses and leachability, was slag from Ferrochrome melting shop used in the three first tests. The Ferrochrome melting shop produces liquid FeCr, which is fed into the Chromium converter (CRC) and after blowing into the AOD 1.

The slag-samples were taken after the cooling in the slag yard. Some of the test materials were cooled in the slag pot, but most of the tests were carried out by pouring out slag with varying cooling methods as a water spray and/or cooling with metal. The samples were crushed, dried and milled if possible, and divided into required samples for respective analysis. Slag cooled with large amount water after pouring out on the ground, semi-quenched slag, were tested and analyzed. Some earlier results of granulated slag (AOD and CRC), were also compared with the leaching results from actually tests.

5.2. Physical properties

The samples from the tests with steel slags were analysed for physical properties after preparing by crushing and screening. All of the slags in aggregate form were tested by ball mill.

5.2.1. Nordic ball mill test prEN 1097-9

The physical properties were investigated by the Nordic ball-mill test (abrasion test), prEN 1097-9. The sample mass was calculated by formula (M in figure 6), when grain density was known. The grain densities were measured in Oulun Ammattikorkeakoulu (OAMK) in Oulu and at Outokumpu Chrome at Kemi mine. All slag materials in this investigation, except semi-quenched slag called “pumice” were tested by the Nordic ball mill test to determine the resistance to abrasion. The semi-quenched materials, pumice, are porous and light materials with insufficient resistance for abrasion. Natural stones were included in this physical test, to compare the stone material class between slag and natural material. Figure 6, shows the flow scheme of test material during the ball mill test. Abrasiveness is the physical properties, which enables the material to abrade particles from materials with which it is in contact or abrade itself during the process. The Nordic ball mill test simulates the abrasion of studded tyres.

Methods and Materials ______

The samples were prepared from massive slag, by crushing with a laboratory jawcrusher and screening it to particle size between 11.3 and 16 mm. To minimize the dependence of used crusher type the aggregates were screened with a flakiness sieve. A flakiness sieve is a sieve with long apertures, which do not stop long and thin particles to pass the sieve. Undersize in this screening was the material with elongated form, too thin and narrow pieces, which should not be included in the sample. The sample mass fed into the ball mill was around 1000g depending on the material density. The ball mill was filled with 7000 g balls of 15 mm diameter, aggregates sample and 2000 grams of water. The mill rotated with the rotation rate of 90 rotations per minute during 5400 cycles. After the test the balls and sample were separated, washed and dried. The aggregates were screened with a 2 mm sieve and the mass was measured. The undersize of 2 mm in percent is the ball mill value, the smaller the better. In stone aggregate class 1 the value must be smaller or equal to 7 (Table 4).

Table 4. Stone material classes

Stone material class Value (K) from ball mill test

I K ≤ 7 II 7< K ≤10 III 10

Methods and Materials ______

SLAG SAMPLE

Second crushing Crushing Jaw crush

C +16 mm Sieving (16mm)

-16 mm F - 11.3 mm Sieving (11.3 mm)

P 11.3 /16 mm

Sieving (14 mm) Flakiness sieve

A 14/16mm B 11.3/14 mm

Washing /Drying Washing/Drying

1000 ⋅ρs ρ = solid density M = ± 5 S ρs 2.66

M = (0.35*A) +(0.65*B) = M1

M1 -2mm Ball Mill EN 1097-9 90 rpm 5400 r

M2 + 2mm

Washing/Drying

100⋅(M1 − M 2 ) K = Stone Material Class =K M1

Fig. 6. Flow scheme. Sample material in Nordic ball-mill test

Methods and Materials ______

5.2.2. Crushing properties

During sample crushing the masses of the fractions were noted for evaluating of the hardness of respective materials. Crushing of very hard material with a jawcrush produces more fines than crushing of a soft material. For best available crushing result both primary and secondary/ final crushing should be used, which in industrial scale is normal. These characteristics are presented in the diagram in Appendix 1.

5.3. Chemical and mineralogical properties

Chemical and mineralogical properties were tested by XRF, XRD, SEM and leaching test. The cooled slag was taken from the slag yard and crushed, milled and screened into the right grain size for respective analysis.

5.3.1. XRF

Chemical compositions were analysed on samples prepared by crushing and milling into a smaller than 74 microns grain size, divided into an amount of 40 grams. 250.0 milligrams of the sample was blended with fluxes (lithium tetraborate, strontium nitrate and sodium chlorite) and melted in a platinum crucible in 10 minutes at a temperature of 1300ºC. The melt was poured out into a mould and the solid button was analyzed in the X-ray fluorescence apparatus.

5.3.2. The standard shaking-test prEN 124 57-3

This test is a two-step batch test with L/S 2, 8 and cumulative 10, which is used in characterization of waste- leaching – compliance test for leaching of granular waste materials and sludge’s. The presentable samples for shaking tests were crushed aggregate with d95 = 4mm and the mass of 175 grams. d95 means that 95 percent of the particles passed the sieve with 4 mm apertures. This batch test was used to study leaching properties of the samples. The leaching tests were always done as soon as possible after the slagpouring test and in practice 3-4 days after the test.

5.3.3. XRD

X-rays are electromagnetic radiation of wavelength about 1 Å (10-10 m), which is about the same size as a normal atom. They occur in that portion of the electromagnetic spectrum between gamma rays and the ultraviolet. XRD, X-ray diffraction has been in used in two main areas, for the fingerprint characterization of crystalline materials and the determination of their structure. Each crystalline solid has its unique characteristic X-

Methods and Materials ______ray powder pattern, which may be used as a "fingerprint" for identification of respectively compound. X-ray diffraction is one of the most important characterization tools used in solid-state chemistry and materials science. We can determine the size and the shape of the unit cell for any compound most easily using the diffraction of X-rays. In this investigation XRD was used to determine the mineralogical structure and differences between that in several slags. The sample for XRD was crushed and milled into very fine powder. The XRD analyses were done at Luleå University of technology with the Siemens Diffrac Plus X-ray diffractometer with 40 kV, 40 mA, steptime 1.00000 s and stepsize 0.02000 start 10.0000 and 2 theta 10.0000.

5.3.4. SEM analyses

Scanning electron microscope (SEM) analyses were performed at Outokumpu Stainless in Tornio and the test materials were crushed pieces of slag with the cross-section area of around 1-2 cm2. Each sample was molded into an epoxy mass and thereafter the sample surface were polished very fine without any scratch. The results of SEM were further analysed with INCA-program of Oxford. INCA makes it possible to investigate the distribution of the mineral phases in samples. The user can describe the limits for the classes and determine the mineral phases in respective sample. In all of the 9 samples were 10 areas determined and in respective area were 100 points analysed. Total 1000 points were analysed in each sample. One overview picture was taken from an area of every sample before working with the INCA-program. The area for the figure was chosen as an area with less porosity and as good presentability as possible. From the figure about 15 points were manually analysed, which gave an average distribution of the phases in the sample and helped to determine the limits for the classes. The sample surfaces were covered with both gold and carbon and therefore the analyses points with more than 10 % gold or carbon have been excluded. The amount of unclassified points should be below 10 % and the amount of multiclassified points as low as possible. The multiclassified points are points, which are included in more than one class and often occurred when the minerals for example Akermanite and Merwinite contain almost the same composition of elements. The pictures are included in chapter results as Figure 17 to 29.

5.3.5. Simulation with FactSage

FactSageTM is a integrated thermodynamic database system for inorganic applications. It made it possible to simulate various types of multicomponent phase systems. FactSage uses standard databases for oxides, metals and general alloys. Fact SageTM is used in a diverse range of applications and provides a flexible solution platform for complex thermochemical problems. Equilib permits the calculation of the chemical equilibrium state of a system that is defined with regard to temperature, pressure and total amounts or equilibrium activities of any phase constituent in the system. Other conditions for equilibrium can also be set, for example that a certain phase is formed when temperature

Methods and Materials ______changes or that the enthalpy change is zero when a reaction proceeds. The data program, which was used in the investigation, was Fact-Sage. FactSage is a program that is based on thermodynamic databases of certain slag compounds and elements. FactSage makes it possible to simulate the reactions with different temperatures, pressures and respective amounts of component in each case. The chemical composition can be varied to correspond the slag, which should be evaluated. In this investigation are activities of spinel and several chromium compounds simulated with FactSage.

Experimental and Visual observations ______

6. EXPERIMENTAL and VISUAL OBSERVATIONS from the tests

All the tests in this work were full-scale test, where the initially mass of slag usually was between 10 and 15 tonnes. The three first experiments were carried out at Ferrochrome plant with Ferrochrome slag and the aim with them were to investigate the function of the actual test-equipment, such as possibilities to vary tip height and the water-cooling parameters. The mineralogy and leaching behaviors of the FeCr-slag are well known from earlier, having small variations due to the varying type of ore from Kemi mine, but the influence of the cooling rate had not been investigated. After the test, the test materials were visually estimated to plan the following test. Sometimes the same methods were used but sometimes the parameters were changed depending on how the previous test had succeeded, [27, 28].

When the experiment started in January the outdoor temperature was – 25 ºC, which has been considered when deciding the cooling rate. During the following tests the temperature of slabs in the bottom of the basin (Figure 8) was always higher than 0ºC to minimize the risk for explosion with water below the liquid slag on a dry bottom. The nozzle used in the tests divided the water at an angle of 90º and into small droplets, which should have maximum effect to cool down the surface. The height of the water spray was about 2 meters and was not varied during the tests. The goal was to spray an amount of water, which should directly be vaporized so that water could not flow into the melt and affect an explosion. With too high water flow water is collected and boiled on the slag surface. Heat transfer at surface, by boiling water-cooling, is less effective than vaporizing of water at the surface. The heat transfer from the solid material depends strongly on the temperature of the surface. At high temperature, strongly overheating the body, the surface is covered with vapor. This vapor layer is continuous and separates the liquid from the overheated body. The layer is drastically decreasing the heat transfer between body and liquid. The forenamed phenomenon occurs in water-spray cooling of the slag when slag temperature is just below the liquidus temperature of the slag and also higher than the boiling temperature of water.

The minimum pouring height was around 1 meter, a lower height was not possible because of the geometry of the ladle. A higher height than 1.5 meters that was used in the tests would not have had any influence on the results. A lower height than 1 meter would probably have influenced the test results.

Experimental and Visual observations ______

Fig. 7. Pouring of the slag into a slag pot in test 4

From test 4 to test 13 all test were carried out in slag yard with EAF and CRC slags. The slag pot truck was pouring out the slag in a test slag pot (see Figure 7) or on the ground. Water-cooling over a slag pot was tested in test 4 and cooling with a metal bottom or cooling scrap in the slag pot was carried out in the remaining tests. The slag amount in tests with cooling scrap in the slag pot was smaller, around a half part, which means 5-6 tonnes.

6.1. Test 0 and 1, FeCr slag by normal pouring

A reference test (Test 0) with normal pouring practice of ferrochromium slag on the ground was carried out and the sample was taken from the cooled slag. The sample was taken after solidification and crushed and milled to XRF analyses and leaching test. Crushed aggregates of the test were tested in Nordic ball mill test for abrasion and in SEM to determine the normal mineralogy of this type of slag. Test 1 with the same slag, as in test 0, was poured into a pouring basin with slab bottom and walls of crushed FeCr-slag, (Figure 8). When the surface was solidified, after a few minutes, one part of the slag bed was cooled by water-spray and the cold bottom (- 25ºC) cooled the undersize of the whole bed. The thickness of the bed was around 25 cm and the material was porous in the middle region. Samples for XRF, leaching test and for Nordic ball mill test were taken from the cooled slag.

Experimental and Visual observations ______

Water-spray

Heat flux Liquid Slag Crushed slag

Slabs

Fig. 8. The slag-pouring basin (tests 0-3), and the heat fluxes from melt slag into the slabs and air

6.2. Test 2, FeCr slag with water-cooling

Test 2 was equal to test 1 but the water spray was in action for around 3 minutes and the whole surface area was water-cooled. The powerful generation of vapour between the crane-line and the moving of the nozzle stopped further water-cooling and the test was modified. Samples were taken and analyzed analogous with earlier tests.

6.3. Test 3, with water- and metal-cooling

In the same way as test 1 and 2 was test 3 carried out, but the water-cooling time was longer, totally about 25 minutes. The water-cooling was done in cycles: of only a few minutes’ water spray when the vapour generation was lower the water-cooling started again etc. Samples from these tests were analysed with ball mill, XRD, XRF and SEM.

Experimental and Visual observations ______

6.4. Test 4, EAF slag cooled in the slag pot

Test 4 with EAF slag, was carried out in two parallel steps, one half of the slag amount was poured into a slag pot, which was cooling down in air and the other half was cooled with water-spray over the half-full slag pot. The cooling was done in steps, the first water-cooling started 20 minutes after the pouring into the slag pot and cooling water was on for 5 seconds. Then the water was off for 25 seconds, thereafter 5 second water- cooling etc., the total time of this test was 7 minutes and with 14 cooling steps. The generating of vapour was powerful and continued for more than one hour after the finished water spraying. The slag pot was tipped after 1.5 hours. The slag surface was like a granulated slag and ran out during tipping of the slag pot and the remaining slag fell down as a big clump, which had liquid slag in the middle region. The solid slag under the porous surface layer had long and thin pores in vertical direction. The region nearest the bottom of the slag pot was most solid but included small round gas-pores. The air-cooled slag pot was cooled for 18 hours and was tipped as full-solidified slag. The material was similar to the material in the bottom region of the water-cooled slag in the same test. Samples were taken from the solid region in the lower region in the slag pot. The porous surface slag was investigated by XRD and by shaking test to investigate the leaching behaviours.

6.5. Test 5, EAF slag cooled with scrap

Test 5, EAF-slag cooled with iron scrap in the slag pot. A warm slag pot was half filled with scrap (CRC-cooling scrap) and EAF-slag was poured into this slag pot from another slag pot by the slag pot truck. The goal was to achieve a hasty cooling of the total amount of slag, with cooling in all directions from liquid slag into the scrap. The slag was poured out into the slag pot and flowed into relative small cavities between the rail pieces. In small cavities the slag is always near a metal surface and the cooling occurs rapidly. The slag pot was tipped after one and a half hour. The slag was almost completely solidified, only the middle region was aglow like the pieces of iron rails (Figure 9). The slag cooled down in air several hours before samples for analyses were taken. Slag from this test included more metal in form of small droplets than slag from other tests.

6.6. Test 6, EAF slag cooled with scrap

Test 6, similar as test 5. The EAF slag was cooling down for two hours after the pouring and tipped on the ground as a massive clump that was divided into pieces by an excavator with a hydraulic hammer. In the middle region the slag was still aglow and

Experimental and Visual observations ______

almost molten. In this case the scrap amount was larger than in test 5 and the slag did not cover the scrap. In the solid slag material elongated pores were observed. The pore directions were towards the inner metal surfaces in the rail pieces, similar as in test 8, see Figure 10.

6.7. Test 7, CRC slag cooled with scrap

Test 7, equal with test 6, but the poured slag was from chromium converter, CRC. The tipping was done after two hours with the slag still glowing and red. Glowing pieces of the slag was taken out and cooled down, in water, of a temperature of about 20 ºC. The purpose was to investigate the influence of cooling rate from molten slag to room temperature versus molten to hot solidified slag and their leaching behaviours.

Fig. 9. Aglow slag and cooling scrap after tipping in test 6

6.8. Test 8, CRC slag cooled with the scrap

Test 8 was similar to test 7, slag poured from CRC, tipped 2 hours after the pouring. The slag was glowing and red but less porous than in test 7 with the same kind of slag. The elongated pores, with direction from the metal surface into the last melt, also occurred in this slag.

Experimental and Visual observations ______

In Figure 10 one can clearly see the direction of pores and cooling gradient, when the slag piece had been taken from the rail surface (right part of figure).

Fig. 10. Solid CRC-slag with pores in direction to gradient on decreasing temperature. Test 8 CRC-slag cooled in the slag pot with cooling scrap (pieces of railway rails).Gas transport from the cooled surface into last melt between pieces of rails.

6.9. Test 9, AOD slag poured on the slabs

Test 9 with AOD slag with boron addition, poured out on slabs at the slag yard. The poured layer was thin and rapidly cooled. The structure of the material was solid with negliable amount of pores. Between the upper and bottom layer was a thin, a few millimeters thick, crystalline and porous layer separating the layers from each other. In the slag bed, which was not on the slabs two layers with a porous layer between them, also could be observed. This slag material was not tested chemically, only the ball mill test was done. The stabilised AOD slag has low leaching values, a usually not detected amount of chromium in leachate.

Experimental and Visual observations ______

6.10. Test 10, EAF slag poured on the slabs

EAF slag was poured out on slabs and between them on a bottom of crushed slag. The slag bed on slabs was thin, less than 10 cm and therefore rapidly cooled. The massive bed was up to 20 cm and the cooling rate was lower. Samples were taken both from the massive and the thin layer. Chemical analyses were as usual.

Liquid slag

Solid slag

Fig. 11. Solid EAF slag with gas pores and cooling shrinkage pores. Rapid cooling from bottom of the slabs and upper surface with air. Gases in the slag not permeable to the surface, were bunched in the layer up from molten slag in the middle part of the bed.

6.11. Test 11, EAF slag poured on the slabs

Test 11 was part of test 10, the poured slag layer was on the crushed slag and the thickness was larger than test 10. This gave in the middle region small round pores and in the top layer long thin pores making the material porous (Figure 11).

Experimental and Visual observations ______

6.12. Test 12, CRC slag poured on the slabs

Test 12 with CRC slag was similar to test 10 on the slab-bottom. Slag was poured out on slabs and between them on the bottom of crushed slag. The slag bed on the slabs was thin, less than 10 cm and therefore rapidly cooled. The massive bed was up to 20 cm and the cooling rate was lower. Samples were taken both from the massive and the thin layer. Chemical analyses were done with shaking test and also the ball mill test was made to investigate the stone class.

6.13. Test 13, CRC slag poured on the ground

Test 13, CRC slag poured on crushed slag as a layer of 20 cm, resulted in a material more porous than the material from test 12. Samples for chemical analyses, shaking test and Nordic ball mill test were taken after cooling as usual.

6.14. Test 14, semi-quenched slags

Tests with semi-quenched slags, which are water-jet cooled slags, resulted in material similar to pumice. Several tests were made with normal practice at slag yard by water- cooling. The materials of this was foaming slag which cannot be used as coarse aggregate but it is mentioned in this investigations since that leaching are low in spite of the high specific surface. Some granulations of EAF and CRC slag have been done earlier and these results have been compared with the results of tests in this work.

Results ______

7. RESULTS

Results from the analyzing methods used are presented in this part. A three-phase system SiO2 –CaO-Al2O3 (Figure 12) with the investigated slags is presented first to show the small differences between the chemical compositions of these slags, see Fig 12. The chemical analysis of the slags used in the investigation is presented in Table 8. Earlier test, with cooled slag in the slag pot, which gave important facts before the start of this work are also shown as a comparison material.

EAF AOD CRC

Fig. 12. Phase diagram with the average analysis of AOD,EAF and CRC slags in the system of SiO2 –CaO- Al2O3, [2]

Results ______

Table 5. Average chemical analyses (wt.-%) of steel slags from Outokumpu Stainless

Cr2O3 Al2O3 MgO CaO SiO2 MnO TiO2 CaO/SiO2 B4 Sp

CRC 1.3 3.4 16.7 36.0 35.0 0.3 1.8 1.08 1.41 6.3 AOD 2 0.4 0.2 7.5 57.0 29.0 0.3 1.4 1.97 2.12 2.9 EAF 2 2.2 0.9 5.6 43.3 26.9 1.3 7.5 1.59 1.43 7.6

7.1. Earlier tests and investigations

The dependence of cooling behaviours has been estimated earlier when the slag had been cooled down in a slag pot during several days. The highest leaching value were measured from aggregates from the middle, slowly cooled part, of the slag pot, see Table 6. Because of the density difference between slag and metal metaldroplets were falling down and the highest concentration of metals in the slag could be found in the bottom region (3 in Fig 13.) of the cooled mass. When leaching of chromium was calculated in percent of the total chromium content the results showed no correlation between the high leaching values and regions in the slag pot.

Fig. 13. Slag pot with the different cooling regions (1,2,3)

Results ______

Table 6. Chemical total analysis and result from shaking test LS 10 prEN 12457-3 and leached amount in percent of the total amount Cr2O3

Slag Aggregate Analyses (%Cr2O3) Shaking test (mg/kg) % Leached of total size (mm) from different regions analyze 1 2 3 1 2 3 1 2 3

CRC 11/18 3 3 3 5.65 3.58 2.31 0.019 0.012 0.008 CRC 11.3/16 1.8 3.8 4.2 1.3 1.46 0.58 0.007 0.004 0.014 CRC 0/4 2 3 5.3 1.5 2.48 1.62 0.008 0.008 0.003 CRC 11.3/16 1.8 3.8 4.2 1.3 1.46 0.58 0.007 0.004 0.001 CRC 0/4 2 3 5.3 1.5 2.48 1.63 0.008 0.008 0.003 EAF - * * 2.2 1.63 2.68 3.29 * * 0.015 EAF - * * 1.9 1.27 26.01 2.53 * * 0.013 AODb - 1.1 0.8 6.3 1.73 3.1 0.12 0.016 0.038 0.000 AODb - 0.6 0.6 0.6 0.45 5.3 0.26 0.008 0.088 0.004 * No total analyses. Aggregate size means the initial particle size before crushing, all of the shaking test were carried out with material with particle size less than 4 mm, d95. The highest value of respective case is written with bold numbers.

7.2. Nordic ball mill test prEN 1097-9

The ball mill test results are showed in Table 7 as stone class for each material, the smallest value is equal with a good stone material with high resistance for abrasion. The best ball mill value is as low as possible. Table 7 shows that natural stone (I) aggregate which is used as bearing layer in road constructions has a value worse than most of the slag aggregates. The ball mill test with natural stone (II), which is used as railway construction aggregate, has a better value, 8.3, which is in class II, equal to the best slag materials. Two of the FeCr slag aggregates have a ball mill value less than 7 which is equal to the stone material of class I. Some of the best slag aggregates have a value around 8, as natural stone of the class II.

Railway aggregate is generally classed as a good stone material because of its specific utilizations area. The two slags from thin bed got a value almost the same as railway aggregate. The porous slags from test 4 air-cooled EAF slag and 7 scrap cooled CRC slag have the highest ball mill value equal to the class IV and V, and these slags were the most porous materials after the solidification. The content of metal droplets and the porosity of materials have a great dependence into the solid density of materials. The highest ball mill value, 33.5, was calculated with the test of natural stone warmed below liquid slag. The stone material was after the warming like crystalline, weak, aggregate. The solid density of certain materials was measured in Oulu OAMK and in Kemi mine. The solid density for remaining materials was calculated with the average proportion between the known solid and bulk density. The solid density of steel slags is generally 2.7 – 2.9 kg/dm3, but the porosity of material and the amount of metal droplets in slag have a dependence on density.

Results ______

Table 7. Results of Nordic ball mill test prEN 1097-9

Nordic ball mill test prEN 1097-9

Sample Ball mill value Density (Mg/m3) Class of mineral aggregate

Natural stone I 22.4 2.8 V (Crushed aggregate) Natural stone I (warmed) 33.5 2.8 VI

Natural stone II (granite) 8.3 2.9 II

FeCr-slag Test 0 9.2 3.2 II

FeCr-slag Test 1 water cooled 6.2 3.1 I

FeCr-slag Test 2 water cooled 8.3 3.1 II (surf+bottom) FeCr-slag Test 3 water cooled 6.2 3.1 I on the slabs EAF-slag Test 4 water cooled 17.4 2.8 IV in the slag pot EAF-slag Test 4 air cooled in 19.4 2.8 IV the slag pot EAF-slag Test 5 scrap cooled 13.8 3.3 III

EAF-slag Test 6 scrap cooled 13.4 2.8 III

CRC-slag Test 7 scrap cooled 22.7 2.7 V

CRC-slag Test 8,scrap cooled 13.3 2.8 III

AOD-boron addition 10.8 3.1 III

EAF-slag Test 10 thin bed 9.4 2.9 II

EAF-slag Test 11 massive bed 11.2 2.8 III

CRC-slag Test 12 thin bed 8.2 3.0 II

CRC-slag Test 13 massive bed 10.7 2.9 III

Results ______

7.3. Chemical composition from XRF analyses

In Table 8 the chemical composition of the samples from test 0 to test 13 are shown.

Table 8. Chemical composition total analysis presented as oxide of respective element.

Sample slag Cr2O3 Fe2O SiO2 MgO Al2O3 CaO MnO TiO2 B4 factor type 3 sp (%) (%) (%) (%) (%) (%) (%) (%)

Test 0 FeCr 13.2 6.7 28.5 21.3 26.1 2.4 0.3 0.6 0.43 28.4 Test 1 air FeCr 14.2 7.0 27.1 20.8 25.8 2.4 0.3 0.6 0.42 27.8 Test 1 water FeCr 13.5 6.6 28.0 21.3 26.2 1.7 0.3 0.6 0.43 28.3 Test 3 FeCr 14.2 6.4 28.3 22.6 26.1 1.3 0.2 0.5 0.44 28.0 Test 4 air EAF 7.3 0.9 32.2 1.7 6.1 40.4 3.4 5.8 1.10 3.4 Test 4 water EAF 6.9 0.8 32.3 1.6 6.2 40.5 3.3 5.8 1.09 3.6 Test 5 EAF 14.1 2.1 27.4 3.9 6.4 35.7 4.6 3.2 1.17 1.6 Test 6 EAF 4.6 0.7 29.1 3.4 6.5 44.6 2.5 5.8 1.35 5.4 Test 7 slow CRC 1.2 0.4 34.0 17.6 4.0 39.2 0.2 1.5 1.49 7.2 Test 7 scrap CRC 1.1 0.4 35.1 17.0 2.7 40.9 0.2 1.6 1.53 5.8

Test 7 scrap+w CRC 1.1 0.4 34.6 17.5 2.7 39.5 0.2 1.8 1.53 5.9 Test 8- 0 CRC 1.1 0.4 35.0 16.9 3.7 39.8 0.2 1.7 1.47 6.8 Test 8 scrap CRC 1.4 0.5 33.0 14.9 2.4 43.5 0.2 1.7 1.65 5.0 Test10 EAF 2.6 0.4 30.54.6 6.7 45.3 1.3 6.5 1.33 6.6 Test11 EAF 2.3 0.4 30.84.1 6.7 45.8 1.4 6.5 1.34 6.6 Test12 CRC 3.6 0.4 32.812.2 4.4 41.4 0.9 2.7 1.45 5.3 Test 13 CRC 4.3 0.7 33.6 14.4 3.6 39.4 0.9 1.8 1.44 4.8

The chromium content in sample 5 is high, 14.1 %. The reason for this is not detected; but the sample included metal droplets, which can be milled to fines, and cause incorrectness in analysis. The FeCr slag has been shown in this table because of its high Factor sp, about 28, when factor sp for EAF slag is around 5-7. EAF slag samples 4 air and 4 water, actually the same slag, showed low contents of magnesia, around 1.7 %, when the normally content is between 3 to 4 %. CRC slag sample 7 held a low amount of chromium, only 1.1 percent calculated as Cr2O3.

Results ______

7.4. Shaking test

Table 9. Results from shaking test in mg/kg and in ppm compared with factor sp and total analysis of chromium in respective sample.

Sample Slag Analyze Factor sp Leaching Leached of type Cr2O3 (mg/kg) total (%) Cr Cr6+ (ppm)

Test 0 * FeCr 13.2 28.4 0.33 0.3 2.5

Test 1 air FeCr 14.2 27.8 0.76 0.59 5.3 Test 1 water FeCr 13.5 28.3 0.83 0.63 6.1 Test 3 water FeCr 14.2 28.0 0.52 0.4 3.7

Test 4 air EAF 7.3 3.4 2.17 2.74 29.7

Test 4 water EAF 6.9 3.6 3.04 3.4 44.1 Test 5 EAF 14.1** 1.6 2.17 2.65 15.4 Test 6 EAF 4.6 5.4 5.6 5.2 121.7

Test 7 slow CRC 1.2 7.2 1.02 0.2 85.0

Test 7 scrap CRC 1.1 5.8 1.13 0.88 102.7 Test 7 scrap+w CRC 1.1 5.9 0.81 0.77 73.6 Test 8- 0 * CRC 1.1 6.8 1.93 0.72 175.4

Test 8 scrap CRC 1.4 5.0 0.75 0.33 53.6 Test 10 * EAF 2.6 6.6 2.06 1.82 79.2 Test 11 EAF 2.3 6.6 1.63 1.4 70.8 Test 12 * CRC 3.6 5.3 1.91 1.69 53.1

Test 13 CRC 4.3 4.8 1.07 0.8 24.9 Semi-quenched CRC 1.1 5.7 0.34 0.34 30.9 Semi-quenched CRC 2.0 6.2 0.47 0.33 23.5 Semi-quenched CRC 5.6 6.4 0.53 0.66 9.5 Semi-quenched EAF 3.0 7.1 0.59 0.43 19.7 Semi-quenched EAF 3.2 10.4 0.18 0.10 5.6

Semi-quenched EAF 1.9 7.8 0.44 0.32 23.2 Semi-quenched EAF 16.6*** 1.6 1.55 1.36 9.3 Semi-quenched EAF 16.1*** 1.9 1.37 1.17 8.5

Semi-quenched EAF 14.3*** 0.9 2.38 2.27 16.6

*** Semi-quenched EAF 12.1 2.6 0.54 0.4 4.5 Granulated(fine) AOD 0.6 2.4 1.31 - 218.3

Granul.(coarse) AOD 0.6 2.4 1.22 - 203.3 Granul. (fine) CRC 1.4 4.7 1.69 - 120.7

Granul. (coarse) CRC 1.4 4.8 1.34 - 95.7

* poured out on the ground, slow cooling ** very high chromium content in the XRF analysis and low factor sp. *** Semi-quenched slags with high content of chromium

Results ______

In Table 9. results from two step shaking test prEN 12457-3 from test 0 to test 13, 10 semi-quenched and 4 granulated slags are shown. Results of the leaching tests from test 0 to 13 showed that slags poured on the ground as a more massive bed have the highest leaching values calculated in parts per million (ppm). The three tests with ferrochromium slag should be left out of this comparison since their factor sp value is mainly higher and the leaching of chromium therefore low. Tests 0 to 3 showed no difference in the leaching behaviours in the face of the varied pouring and cooling methods. The ferrochromium slag generally includes spinels, which bind the chromium hard and stop leaching of chromium. Leaching values of the semi-quenched slags can be verified low, despite the fact that the specific surface of this type of slags is large, up to 12m2/g for particle size less than 0.063mm, of the CRC slag and 3 m2/g, with particle size less than 0.063 mm, of the EAF slag. The four last semi-quenched samples with high chromium content were included as references, to show the rather low leaching values in ppm in spite of high total content of chromium in the slag. Good correlation between high factor sp and low leaching values can be observed in each case, (Fig 14- 16). The last four samples in Table 9. are granulated AOD and CRC slags, which showed highest leaching values in ppm compared to all of the samples. The cooling time is shortest in the granulation, less than two minutes, but the granulated material is in contact with atmospheric oxygen and oxidation can occur. Oxidation of chromium is the possible reason for the higher leaching rate.

AOD slag (boron stabilized)

1 Leached Cr (mg/kg) 0 02468101214

Factor sp

Normal cooled Semi-quenched Cooled in the slag pot

Fig. 14. Diagram correlation between factor sp. and leached amount of chromium (mg/kg) in boron stabilized AOD slag.

Results ______

In Figure 14. the correlation for different way cooled AOD slag samples versus factor sp. The few semi-quenched samples shows no leaching, not detected, but two of the in the slag pot cooled samples shows high values (triangles in red circles). These two samples are both from the middle, slowly cooled, region of the slag pot. In Figure 14 the y-axis value are shown in mg/kg when dimension in y-axis in the Figure 3. is mg/l. The form of the curvature is not dependent of the different dimension of the axis. It can be observed, in Table 9, that leaching of Cr6+ is uniformly about 95 percent of the total leaching of chromium. In some of the tests the value for Cr6+ is higher than the value for Cr, which can be considered as an error in the analyses or the content of Cr may be too low to be able to measure exactly.

EAF slag

5 4

3 2

(mg/kg) Cr leached 1

02468101214

factor sp Semi-quenched Normal cooled

Fig. 15. Correlation between factor sp. and leached amount of chromium (mg/kg) in EAF slag.

In Fig.15 one can clearly see the differences in leaching behaviours between pumice and on the ground (normally) cooled slag. All of the rapid cooled slags show lower leaching values than normally cooled slags. Leached amount of chromium is increasing when the factor sp decreases below 4, a phenomena which is equal with test in FEhS (Fig. 3).

Results ______

CRC slag

5 4 3

2 1 Leached (mg/kg) Cr 0 02468101214

Factor sp

"Normal cooled" Semi-quenched

Fig. 16. Correlation between factor sp. and leached amount of chromium (mg/kg) in CRC slag.

Figure 16 shows the increased leached values when factor sp is below 5 and the three semi-quenched slag shows lowest values. In all of the Figures 14-16 the similar correlation between factor sp and leaching values are observed, the leaching is lower, when the factor sp is higher than 6.

Results ______

7.5. SEM analysis

Test 0, 1, 2 and 3, with FeCr slag, contained chrome bound in spinel structure and the leaching of chromium was low since the factor sp is mainly high, over 20. The different cooling methods resulted in varying material properties; porosity was higher in the slags poured out normally on the slag yard and in the water-cooled slag especially in the upper-layer of the slag bed.

Mineralogy tests by SEM seem to show that the results from earlier investigations of FrCr slag do not correspond exactly to samples in this work caused of the different type of ore at Kemi mine. In Figure 17. all features of test 0 and 3 are showed in three-phase diagram Al2O3-MgO-Cr2O3. One can see three groups of points in the area of different spinels in solid solution. Comparing these two samples with different cooling methods no significant difference in mineralogy can bee seen. The flocked points exist almost equal in both of the figures.

Fig. 17. Test 0 (left) Test 3 (right), All features and three phase system Al2O3-MgO-SiO2, all of the points is red when great amount points in the same scatter the color is darker.

Results ______

Fig. 18. Three phase system Al2O3-MgO-SiO2, the same system as in Figure 17. with samples 0 and 3.

The samples from test 0 and 3 contained mainly phases Mullite and Cordierite- Forsterite, Chromium exists in spinels and as residual chromite from ore. In the phase diagram with INCA (Fig. 17) can bee seen that several minerals exist in the samples and the groups of points are centering in certain places in the phase diagram.

7.5.1. Tests with EAF slag.

Fig. 19. Test 4 water cooled EAF slag (T4W) in the slag pot, all features and measuring points for Melilite

Results ______

Samples T4 and T4W were from the same slag tipping which was divided into two tests. The cooling method varied between these but the mineralogy is mainly equal and normal for EAF slag, Larnite (C2S), Melilite ( Akermanite + Monticellite).

Fig 20. Test 4 (T4) all features versus points for Melilite in sample 4 The scatter for Melilite occurs when the class limit for Melilite has been programmed in the data program INCA and only one class (Melilite) has been plotted. The class limit for all of the used classes are described in Appendix 4.

Fig. 21. Three-phase system SiO2 – CaO - MgO with the region of Melilite (circle)

Results ______

In three-phase diagram SiO2- CaO-MgO, in Fig 21 shows the area for Melilite. Melilite is a common slag mineral, which contain Akermanite and Monticellite (Ca2MgSi2O7 + CaMgSiO4). Samples from test 5 and 6 with EAF slag, scrap cooled in the slag pot and tipped after 2 hours, measuring points for sample 5 are shown in Figure 22.

Fig. 22. Test 5 all features and features (left) for Magnesiochromite (right) in sample 5

In Figure 22. it can be observed that a big amount of the points are in the area of calcium silicates, dicalcium silicate is usual in EAF slag (see Fig. 20). Sample 5 was containing Magnesiochromite, which is shown in the right part of Fig. 22. Figures 21- 22 and 24 also show how the certain three-phase diagrams can be used in the estimation of minerals in the sample. The scatters got different form and placing in different systems.

Results ______

Fig. 23 Sample 5 field 7, overview of area with metal droplets with diameter around 300µm.

In Figure 23 the uniform structure of sample 5 is shown. Small pores exist generally in the whole area and the same phases are divided over the total area. Small grains of mineral phases can be observed. Metal droplets exist in this area of the sample. The determined mineral classes by INCA are presented in Appendix.4

Fig. 24 . Overview figure of sample 6 Scrap cooled EAF slag, which shows pores in the slag and the geometrical forms of phases. Spinels are often phases with straight sides (1). Chemical composition of these spinels are Cr Mg Al and O

Results ______

Figure 24 shows a field in sample 6, EAF slag, and the composition of the marked phase (1) was: Cr 48 %, Mg 7 %, Al 3% and O 37% , (Mg,Al)Cr2O4 , this phase contained also F and a negliable amount of Ca. Overview figures with chemical analyses of phases of all samples are shown in Appendix 3.

Fig. 25. Test 6 EAF slag, all features in two different three-phase systems.

It can be observed that also sample 6 includes Magnesiochromite and dicalcium silicate. The points have a certain centering which shows the main minerals in the sample.

7.5.2. Test 7 with CRC slag, scrap-cooled

Cooled with scrap in the slag pot, similar as tests 5 and 6.

Fig. 26. Test 7 CRC slag, features for Akermanite and for all features.

Results ______

Fig. 27. Features for Akermanite (red) and Monticellite (green) in the sample 7.

Test 7 CRC slag showed two main phases, Monticellite and Akermanite. The measuring points were more centered than in the EAF samples. Phases with high chromium content were not detected in the CRC slag. CRC slag is also including compounds with CaTiSiMgCr like EAF slag. These compounds contains low amount of Cr but Ti content can be higher, [11][31].

7.5.3. Test 10 with EAF slag poured out on the slabs as a thin layer.

Fig. 28. Sample 10, EAF slag poured on the slabs.

Figure 28, the right side, shows most points in the area of dicalcium silicates and Melilite.

Results ______

Fig. 29. Sample 10 features for Perovskite, Magnesiochromite, Melilite and Titanite.

Two centering, one for Melilite and one for Perovskite, can bee observed in Fig. 29.

Table 10. shows the summary of the mineralogical estimation of the samples. Significant mineralogical variation in respective slag type cannot be observed between the different samples. Chromium and Manganese containing Calcium silicates are one of the most general groups of minerals in the EAF slags. Melilite and Bredigete occur also in all of the EAF samples. Presence of metal means the droplets in the sample, which is varying greatly between the samples.

Results ______

Table 10 . Results from investigation of minerals by SEM

TESTS

Mineral T0 T2 T3 T4 T4W T5 T6 T7 T10 FeCr FeCr FeCr EAF EAF EAF EAF CRC EAF

Al-rich spinel ++ ++ ++

Metal - + + + + ++ + -

Protoenstatite + +++

Classy phase 1 +++ ++ +++

Resid. chromite ++ +

Chromite ++ +

Mullite/Cordierite ++ +++ +++

Spinel - - -

Spinel 2 +++ +++ +++

Forsterite +

Magnesiochromite + ++ +++ ++ -

Calciumsilicate(Cr, +++ +++ ++ +++ +++ Mn) Perovskite ++ + + ++

Melilite + + +++ ++ ++

Titanite - - + + -

Bredigite ++ ++ - ++ ++ Larnite + - +++ ++ +

Merwinite - - - +++

Akermanite +++

Monticellite +++

- mineral exist in negligible amount + mineral exist in low amount ++ element exist in relative high amount +++ mineral exist in high amount

Results ______

7.6. XRD analysis

The X-ray diffaction analyses were carried out in April and May 2004. 10 different samples were crushed and milled to XRD-sample. Some reference samples of slag from normal processing from both EAF and CRC were included in the investigations. So called “pumice”, which were possible by using powder samples for the tests.

Test 4 EAF slag

1 1 1 1 1

Fig. 30. Pattern for Chromite in sample 4, EAF slag (air cooled in the slag pot)

Figure 30 shows the pattern for sample 4, EAF slag, peaks for Chromite, FeCr2O4, are marked (1). All the patterns are in Appendix 5. X-axis shows 2-theta and Y-axis Lin (Counts)

Results ______

EAF slag, test 5

5 4

2 4 3 4 1 1

2 2 3 4 5

Fig. 31. Sample 5 EAF slag

Figure 31. shows the XRD patterns for sample 5, which demonstrates Magnesiochromite, MgCr2O4 (1), Bredigete, Ca14Mg2(SiO4)8 (2), Donathite, (Fe,Mg)(Cr,Fe)2O4 (3), Chromium oxide, CrO (4) and Chromite, FeCr2O4 (5). Spinels are common in this sample, cooled with scrap, which had low leaching values calculated in percent of total amount of chromium in the sample. The semi-quenched samples were included in the investigation because of their low leaching of chromium compared with normally poured EAF and CRC slag. Most of the mineral phases include Calcium, Magnesium, Silicate and Oxygen, even compounds with Titanium are common especially in EAF slags.

Results ______

Table 11. XRD analyses: the most common minerals in the samples

Mineral Sample 0 3 4S 4W 4A 5 6 7 CRC CRC-sq EAF EAF-sq

Ca2MgSi2O7 x x x

CaMgSiO4 x x x

Ca2Al(Al,Si)2SiO7 x x x x

Ca3Mg(SiO4)2 x x x x

Ca5MgSi3O12 x x x x x

Ca14Mg2(SiO4)8 x x x x x

Ca3Ti8Al12O37 x x x x x x

MgCr2O4 x x x x

CaTiO3 x x x x x x x x

CaxTizO x x x x

MgAlCrO4 x x

Fe(Al,Cr)2O4 x

(Fe,Mg)(Cr,Fe)2O4 x x x x x x x x x

Ca4Ti3O10 x x x x x x x Samples 0 and 3 FeCr slag, Sample 4S surface region EAF slag, 4W water-cooled EAF slag, 4A Air cooled EAF slag, 5 and 6 Scrap cooled EAF slags. 7 Crap cooled CRC slag, CRC means CRC slag poured on the ground, CRC-sq CRC pumice. EAF EAF slag poured on the ground and EAF-sq is EAF pumice.

Ca2MgSi2O7 Akermanite, CaMgSiO4 Monticellite, Ca2Al(Al,Si)2SiO7 Gehletite, Ca3Mg(SiO4)2 Merwinite syn, Ca5MgSi3O12 Calcium Magnesium Silicate, Ca14Mg2(SiO4)8 Bredigete, MgCr2O4 Magnesiochromite syn, CaTiO3 Perovskite, Fe(Al,Cr)2O4 Chromite, (Fe,Mg)(Cr,Fe)2O4 Donathite

X-ray fluorescence analyses showed similar results as the determination by SEM. Spinels occurs in these slags, but the relative high detection limit with XRD, around 5%, left out some phases with low concentration in the samples. The overlap of patterns of different compounds may have caused misinterpretation especially when the chemical composition Ca-Mg-Si-O was common. The patterns for each sample are presented in Appendix 5.

Results ______

7.7. Simulation with FactSage

CRC slag Test 6 Fe-, Al-spinels

FeAl2O4(spinel)

Fig. 32. Simulation with FactSage with the amount of Al and Cr corresponding to sample 6.

Figure 32. shows the good correlation between amount of spinel and temperature, in the case of Fe-Al-O compounds (spinels). In earlier investigations the activity of spinels has demonstrated decreasing when spinels were formed between chromium and magnesia compared with chromium and iron, [10].

Results ______

Cr2O3 + SiO2 + CaO + MgO

CaOMgOSiO2

MgOCa3O3Si2O4

(MgO)(Cr2O3) mass

Mg2SiO4

0 0 200 400 600 800 1000 1200 1400 1600 T(C)

Fig. 33. Simulation of sample 6 with Cr2O3, SiO2, CaO and MgO amount versus temperature.

(MgO)(Cr2O3) is equal with MgCr2O4 Magnesiochromite and CaOMgOSiO2 with CaMgSiO4 Monticellite. MgOCa3O3Si2O4 can write as Ca3Mg(SiO4)2 Merwinite (synthetic). Figure 33 shows that amount of Magnesiochromite is constant during the whole temperature interval but Monticellite start to build when the temperature decreases below 1100º C.

Discussion ______

8. DISCUSSION

The water-cooling gives as a result an impermeable top-layer, which stops the gas transport and bunches the gases into material below the cover. The material becomes more porous and the active surface for leaching increases. The liquid slag contains several gases from chemical reactions and from the air, which get into the slag bed during the pouring of the slag into the slag pot and also on the slag yard. Gaspores are transported upwards in the melt because the densities of gases are lower than the density of the melt. When the upper layer has been solidified is it impassable for gases. Gaspores are bunched underneath the solid layer, when the solidification process continues downward. The solubility of gases is higher in the liquid slag than in the solid phase. Higher gas concentration results in a higher porosity (specific surface) and higher leaching values of heavy metals. The active surface is significantly dependent on the viscosity and gas concentration of the liquid slag when the cooling starts, some of the cooled solid slag had cavities of both cooling shrinkages and gaspores, which increase the specific surface of the material greatly. The leachability of elements has a correlation with active surface of the material and the massive substances always have the lowest leaching value. This phenomenon can be seen in results from test 10, 11, 12 and 13, when samples 10 and 12 were taken from the slowly cooled slag. Samples 11 and 13 were taken from the rapidly cooled, on the slabs poured, slag. In Table 9. the difference can be seen, both sample 10 and 12 have higher leaching values compared to samples 11 and 13. Slag in Test 8 was cooled with two methods, with scrap and poured on the ground. Leaching values from the slowly cooled part from sample 8 had higher leaching. Pieces of the in Test 7 the scrap-cooled slag were further cooled with water so that the final temperature of the sample was about 20 ºC. This pieces showed the lowest leaching values in Test 7. The porosity of forenamed samples was not measured, but the results from Nordic ball mill test showed better value for the massive, rapid cooled, samples (Table 7. tests 10 – 13). The mechanical properties of slags, produced by optimal method, are in the same class as the natural stone species.

Chemical compositions of slags were varying (Table 8.) because of the different species of melted scrap and produced steel quality. The chemical composition of the slag is not possible to predict before the test, which can give unexpected results as in the test 5 with high chromium content. The desired circumstance for the tests, which was not fulfilled, was the exactly same chemical composition of the samples from the same process. The differences in chemical composition, however, made it possible to investigate the correlation of Factor sp. and leaching.

The rapid cooling from one-direction forces the gasflux out of the material and the result is a dense solid material with a smaller surface for leaching. Earlier analyses at TRC have shown a correlation between cooling rate and leaching behaviours (Fig 13.

Discussion ______

and Table 6.). The segregation of metals as chromium, nickel and molybdenum cannot be ignored from the observed results. It seams that the metals often segregates into the last melt, in the bottom part of the slag.

Leaching of chromium correlated with factor sp in all of the made tests. When factor sp is higher than 25 the leaching of chromium is low. Low factor sp., below 5, increases leaching values drastically. The reference tests are plotted in the same diagram (Fig. 34.) where the correlation can be seen.

Leaching (Cr) vs factor sp

5 4

2 1 Leached (mg/kg) Cr 0 0 5 10 15 20 25 30 Factor sp

Fig 34. Leaching vs Factor sp. from all of the samples.

Fig. 34 illustrates all the analyses from this investigation and used reference samples. It shows the leachability of chromium compared with Factor sp. The four points with high Factor sp in Fig. 34. are the samples of FeCr slag, which all are showing stable low leaching values. The trend for increasing leaching with decreasing Factor sp can be observed in the interval 2 to 8. The granulated slags correlated well with the Factor sp in this figure but calculated in percent the granulated slag shows the highest leaching value in spite of the highest cooling rate of these samples. Tests 0 to 3 show no difference in the leaching behaviours despite the varied pouring and cooling methods. The ferrochromium slag uniformly includes spinels, which bind the chromium hard and stop the leaching of chromium. Leaching values of the semi-quenched slags can be verified low because the specific surface of this type of slags are high, up to 12 m2/g of CRC slag and 3 m2/g of EAF slag when milled into grain size smaller than 0.063 mm.

Discussion ______

The effect of cooling rate can be estimated in Fig 35. The slag has often a composition, which corresponds to the composition in the circle in Fig 35. When the cooling occurs slowly the spinels are decomposed to Periclase ss and spinels ss, but with rapid cooling (arrow downwards) the spinels are still in the same form in the lower temperature. This phenomenon should be equal with the spinels where Cr has substituted Al (Magnesiochromite).

Periclase ss + spinel ss

Fig. 35. Equilibrium diagram of system Al2O3- MgO versus temperature.

When granulating slags the cooling rate is the highest possible of used industrial cooling methods, but the shaking test showed high leaching values for these slags. The effects of used cooling methods to leaching of chromium is limited but the slowly cooled material is often porous and the specific surface is larger which according to the diffusion theory enables the highest leaching of elements from the surfaces.

Mineralogical variations between the different way cooled slags were small, but the difficulties in the determination of minerals can bee a reason to the similar results. The mineral phases often contain several small grains of different minerals, which the visual determination of SEM figures shows.

Discussion ______

The semi-quenched slag and the upper layer of the water-cooled slag have similar XRD patterns as amorphous materials; the tops were blunter and not so high as the tops of hard crystalline materials. These materials have uniformly low leaching values, but cannot be used as aggregates in road construction or civil engineering.

CRC slag

2 1 2 2 1 2 2 3 1 2 3

Fig. 36. XRD pattern for CRC pumice, Perovskite syn (1), Monticellite (2), Gehletite (3)

Fig 36. shows patterns for Perovskite, Monticellite and Gehletite of CRC pumice sample. Intensity of this pattern was low and there are more than one peak in each top, which is typical for a amorphous material.

Discussion ______

Fig. 37. Test 10 EAF slag, examples of all features in different three- phase systems.

In Fig. 37 the possibilities to evaluate mineralogy of samples with help of certain existing three-phase system are shown. The actual three-phase system diagram must exist for the evaluating of minerals in certain region of diagrams. All of the SEM samples were evaluated with help of several systems and all of the figures cannot be shown in this work. Final evaluating of respective mineral was made when only a few or the respective class was plotted into the three-phase system (see Fig. 26. Akermanite and Monticellite in sample 7). The mineralogical investigation was strongly dependent of the limits for the classes and differences between two persons who make these investigations are possibly.

Discussion ______

Leaching results of the tests show that slags poured on the ground as a more massive bed have the highest leaching properties seemed in parts per million. The three tests with ferrochromium slag should be left out of this comparing since their factor sp value is mainly higher and the leaching of chromium therefore low.

Test 5, with high chromium content and low factor sp has one of the lowest leaching values of chromium in ppm of the total analyses of the slags. The mineral structure was equal with sample 6 with similar behaviours.

The difficulties with sample taking are well known when the total amount of a test material was up to 15 tonnes and the sample weight when the preparation begins is around 20-30 kg. The final sample mass for chemical analyses is only 250 milligrams and in shaking test 175 grams. It can be discussed if the samples were representative, when they were taken from the slag yard with crushed slag at the bottom. This fact can cause that pieces of older slag was mix with the new sample.

The rapid cooling alone is not sufficient to decrease the leaching rate, but the different composition and phases of the slag can result in a mineral structure, which decreases the leaching of chromium.

The cooling with water from upside blocks in the gases into the liquid slag, which results in a porous layer in the material. When specified aggregate should be as massive as possible the best cooling method is the cooling from bottom by metal with high thermodynamic capacity.

Conclusions ______

9. CONCLUSIONS

Results from Nordic ball mill test showed that the best aggregates came from the tests with thin slag layer cooled on the slabs. The best stone class for slag was class II, which is the same as natural stone (granite). The porosity decreased the stone class and main part of the test had a stone class III or IV.

Results from XRF analyses showed differences between EAF slags, which has dependence into the Factor sp. and leaching behaviours. EAF slags have in general a Factor sp. around 5-7. Shaking test with crushed slags showed correlation between Factor sp. and leaching values. The best way to estimate leaching was to calculate the leaching of chromium in percent or ppm of the total content of chromium in the respective sample.

Simulation with FactSage showed that the amount of spinels increases with increasing temperature, which supports the holding time of the slag pot at the melting shop before the slag pouring on the slag yard. Metal droplets have time to sink into the bottom of slag pot during the holding time. The disadvantage with the holding time is the increasing viscosity, which results in more gases (pores) in the solidified materials.

Mineralogical estimations with XRD and SEM showed similar results. Minerals with small grains in the main mineral made the estimation difficult.

• The cooling rate has a limited effect on the leaching of chromium, by smaller active surface in the rapid cooled massive material. • Slags containing gases, as carbon monoxide from EAF, should bee poured out as quick as possible to hold the viscosity low and so that the gas passage out of the melt is easy. High temperature favours spinel formation, which decreases leaching of chromium from the solid materials. • The cooling with water- spray give no sufficient stone quality, the material is often porous, but not equal to pumice • The granulated slags have higher leaching in spite of highest cooling rate. The reason for this may be contact with atmospheric oxygen and oxidizing of chromium into an easily leached form of chromium oxides. • The semi-quenched slag, pumice, has the lowest leaching values because of its amorphous structure and seems to be the best product despite the goal in beginning of this investigation. The bearing, insulation and drainaging properties of pumice are sufficient in road constructions and civil engineering. • By adding spinel formers and the best cooling method the best optimal product with low leaching values will be possible to reach.

References ______

REFERENCES

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6. Xiao Yanping, Holappa Lauri, Thermodynamic properties of chromium bearing slags and minerals, Helsinki University of Technology, Espoo 1996, Report TKK- V-B118, ISBN 951-22-3170-0

7. Fällman Ann-Marie, Kartläggning av stålverksslaggens utlakningsegenskaper, Stockholm Jernkontoret 1996, JK 2311/93

8. Fällman Ann-Marie, Characterisation of residues release of contiminants from slags and ashes, Linköping universitet 1997, ISBN 91-7871-940-2

9. Decreasing the scorification of chrome, Report EUR 19382 EN ISBN 92-828-9527-0 Luxembourg 2000

10. Nilsson Niklas, Inverkan av MgO på Ljusbågsugnsslaggens lakningsegenskaper, Examensarbete, Luleå tekniska universitet, Institutionen för kemi och metallurgi 2002:327 CIV ISSN:1402-1617* ISRN:LTU-EX- - 02/327- - SE

11. Leinonen M, Dahl O, Härkki J, Teräsulaton kuonien tuotteistaminen, Esiselvitys kuonien tuotteistamis- ja muista hyötykäyttömahdollisuuksista, Tilannekatsaus 04/2003, Oulun yliopisto

12. Hookana Hanna, Liukoisuustestien prEN 14405, SFS 12457-3, EN 1744-3 validointi ja vertailututkimus. Erikoistyö,Jyväskylä,2003 Jyväskylän yliopisto, Kemian laitos, epäorgaanisen ja analyyttisen kemian osasto

References ______

13. 1996 Steel making conference proceedings, Publications of the Iron and Steel society, vol 79 Pittsburg PA 1996 The properties of steel slag aggregates and their dependence on melt shop practice

14. A Kortbaoui, A.Tagnit-Hanou,PC.Aitcin, The use of stainless steel slags in concrete, Proc Cements division meeting, Cincinnati 18-22 April 1993 Cerami, Trans No 37p 77-90

15. Definition of environmental criteria for the industrial by-products used in earth construction, J.Sorvari,J.Tenhunen, Finnish Environmental Institute,VTT2004

16. Iron and steel slags - properties and utilisation, Reports from 1974- 2000 FehS, ISSN 0948-4787, Duisburg Germany 2000

17. Forsman, J. Korjus. H, Viatek ltd, Kiveskäs, L. Määttänen, A. The quality control and the geotechnical properties of reclaimed concrete in earth construction, Lohja Envirotec Ltd, Technical research center of Finland, VTT symposium 204, ISBN 951-38-5701-8, Espoo 2000

18. Engström F. Stabilisering av krom i ljusbågsugnsslagg, MiMeR 2004, Division of process metallurgy Luleå university of technology

19. Personell discussion with Tossavainen M., Maj 2004

20. Kuehn M, Mubach D., Treatment of liquid EAF-slag from stainless steel making to produce environmental friendly construction material, FehS, Sannfil 2004 Luleå

21. Pillay K, von Blottnitz H, Petersen J, Ageing of chromium(III)-bearing slag and its relation to the atmospheric oxidation of solid chromium(III)-oxide in the presence of calcium oxide, CHEMOSPHERE 52 (2003) 1771-1779

22. Mäkikyrö Marko, Converting raw materials into the products-road base materials stabilized with slag-based binders, Depardement of Process and Environmental engineering, University of Oulu, Finland

23. Sorvari J, Tenhunen J, Definition of environmental criteria for the industrial by- products used in earth construction, Finnish Environmental Institute, VTT 2004

24. Korkiala-Tanttu L, Ratmayer H, ALT-MAT-project, Finnish national report, VTT communities and infrastructure Espoo, VTT 2004

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25. Motz H, Kuehn M, Iron and steel slags as sustainable constuction resources and fertilizer, FehS, Duisburg Germany 2004./Scanmet Luleå 2004

26. Lopez F. A, Lopez-Delgano A, Balcazar N, Physico-chemical and Mineralogical properties of EAF and AOD slags, , EOSC’97 2nd European Oxygen Steelmakin Congress, Taranto 13-15-oct. 1997, ISBN 88-85298-28-1, pp 417-426

27. Lintumaa T, Automaattisen faasiosuuslaskentamenetelmän kehittäminen uudelle SEM´ille. Ferrokromikuonat, Outokumpu Polarit 1993, Raportti 5397-42/93, 34 pages

28. Karekivi P, Kromihäviöt kuonaan Ferrokromin valmistuksessa, Masters thesis, Oulun yliopisto prosessi ja ympäristötekniikan osasto 2002,

29. Hiltunen A & R, Treatment of slags- and part of sustainable steelmaking, SKJ- companies Ltd Raahe, Finland /Luleå 2004

30. Kilau H.W, Shak I. D, Chromium-bearing waste slag: Evaluation of leachibility when exposed to simulated acid precipitation

31. Alamäki P, CRK-kuonan faasimääritykset, Raportti 5397-4698/98, Avesta Polarit, Tornio 7p.

32. FactSage Thermochemical Software and Databases Bale C.W., Chartrand P., Degeterov S.A., Ben Mahfound R., Melancon J., Pelton A.D., Eriksson G., Hack K., Petersen S.

Standards

PrEN 1097-9 Standard for Nordic ball mill test, Abrasion test

PrEN 12457-3 standard for two-step shaking test for sludge’s and granular waste materials

Appendix

APPENDIX

1. List of symbols and abbreviations 2. Crushing properties of slags 3. Overview figures from SEM analyses 4. Minerals classes used in SEM estimations 5. XRD patterns for samples

Appendix 1

Acronyms:/ Symbols and abbreviations

AOD = Argon Oxygen Decarburization

BFS = Blast furnace slag

BOF = Basic oxygen furnace

BOS = Bacic oxygen steelmaking

CRC = (Ferro)Chromium converter

C2S = Dicalcium silicate

C3S = Tricalcium silcate

EAF = Electric arc furnace

FeCr = Ferrochrome

MPE = Maximum Permissible Emission

OAMK = Oulun seudun Ammattikorkeakoulu

OSTo = Outokumpu Stainless Oy Tornio

VTT = Technical Research Centre of Finland

TEKES = National Technology Agency of Finland

TRC= Tornio Research Centre (Outokumpu Stainless Oy)

SMART = Simple Multi-attribute Rating Technique

XRD = X-ray diffraction

XRF = X-ray fluorescence

SEM = Scanning electron microscope

Ss = Solid solution dw = demolition waste fs = foundry sand

Appendix 1

d95 = grain size with a pass rate of 95%, mm wt.-% = weight percent fines = particle size less than 0.063 mm

11.3/16 mm = Grain size between 11.3 mm and 16 mm

undersize = The part of aggregates passing the smaller of the limiting sieves used in the particle size contribution. oversize = The part of the aggregate retained on the larger of the limiting sieves used in the aggregate size distribution.

Appendix 2

Crushing properties

Contribution of the product to Nordic ball mill test,11.3/16mm, of the total amount of crushed aggregates in percent

Contribution of grain size after the crushing T0 60 T Nat T1W 50 T13 T1A 40

T12 30 T2S+B

T11 10 T2S

0 undersize product 11,3/16 T10 T3 oversize

T9 T4W

T8 T4A

T7 T5 T6

T0 Test 0 FeCr slag T1W Test 1 FeCr slag water-cooled T1A Test 1 FeCr slag air-cooled T2 S+B Test 2 FeCr slag water-cooled surface and bottom region T2S Test 2 FeCr slag surface T3W Test 3 FeCr slag water-cooled T4W Test 4 EAF slag water-cooled T4A Test4 EAF slag air-cooled T5 Test 5 EAF slag scrap-cooled T6 Test 6 EAF slag scrap-cooled T7 Test 7 CRC slag scrap cooled T8 Test 8 CRC slag scrap cooled T9 Test 9 AOD slag T10 Test 10 EAF slag thin layer on the slabs T11 Test 11 EAF slag massive layer T12 Test 12 CRC slag thin layer T13 Test 13 CRC slag massive layer Natural Reference test with natural stone material

Appendix 3

Test 0 FeCr slag, poured on the ground

14 11

6 8 4 13 9 3 2 5 7

10 12

Spectrum O F Na Mg Al Si K Ca 1 Ti Cr Fe Ni 1 50,7 0,8 0,4 4,2 11,6 24,8 1,0 4,3 0,5 0,6 1,0 0,1 2 50,5 1,1 0,5 4,4 11,1 25,7 0,9 3,8 0,5 0,9 0,6 3 44,2 0,9 14,3 24,9 0,1 0,1 13,9 1,4 4 43,2 0,2 14,3 24,4 0,1 0,1 0,2 16,2 1,1 0,3 5 36,2 0,5 11,4 10,5 0,1 0,2 29,6 11,3 0,2 6 36,0 0,8 11,4 9,2 0,1 0,4 34,7 7,5 7 47,4 0,1 0,1 15,9 34,7 0,2 0,1 0,4 1,1 0,1 8 51,0 0,2 0,4 3,8 11,7 25,8 0,9 4,4 0,5 0,6 0,7 9 49,3 0,7 19,4 5,4 22,0 0,1 0,6 1,9 0,7 10 1,6 0,1 0,1 0,1 0,7 96,7 0,7 11 1,0 0,1 0,1 0,1 1,1 96,8 0,6 12 49,2 0,7 18,9 5,8 22,1 0,2 0,5 1,8 0,7 0,1 13 46,5 0,8 31,9 18,3 0,1 1,2 1,0 0,2 14 46,7 0,9 31,7 18,4 0,1 1,0 1,2 0,2

Appendix 3

Test 2 FeCr slag, water-cooled on the slabs

3 1 2

7 5 6 8

4 9

Spectrum O F Mg Al Si Ca Ti Cr Mn Fe Ni 1 49,2 0,5 11,1 8,9 23,4 3,0 0,5 1,9 0,5 0,7 2 48,6 0,6 14,6 8,1 22,5 1,6 0,5 2,2 0,2 1,0 3 43,6 0,5 14,4 26,8 0,2 13,0 0,2 1,4 0,1 4 43,6 0,6 14,7 25,5 0,1 0,1 0,2 13,9 0,1 1,0 0,2 5 46,4 0,4 15,9 35,4 0,1 0,1 0,5 0,1 1,1 6 42,4 13,6 20,0 0,3 0,1 0,2 22,6 0,1 1,0 7 30,8 1,1 10,5 10,9 0,1 0,2 21,9 24,6 8 1,7 0,1 3,7 0,1 89,2 5,5 9 0,2 1,3 0,1 0,1 0,1 9,9 87,1 1,2 10 1,5 0,2 0,1 0,1 1,1 96,6 0,6

Appendix 3

Test 3 FeCr slag, water cooled on the slabs

12 5 9 17 14 15 16 13 4 18 1 6 1 3 1 21 11 8

2 7 10 19

Spectrum O F Na Mg Al Si K Ca Ti Cr Fe Ni 1 47,3 31,5 0,2 19,2 0,1 1,3 0,7 2 46,4 0,3 31,3 0,1 19,0 0,1 0,1 1,4 1,0 0,4 3 47,4 31,5 0,1 18,8 0,2 1,5 0,6 4 46,9 0,2 31,9 19,4 1,2 0,5 0,1 5 45,3 0,2 14,4 25,4 0,1 0,1 13,1 1,2 0,2 6 44,1 - 14,6 25,5 0,1 0,1 0,1 0,1 14,3 1,1 7 45,1 0,2 0,1 14,6 25,9 0,1 0,1 13,2 0,9 8 48,9 0,5 19,0 5,1 23,6 0,1 0,3 2,2 0,4 0,1 9 49,4 0,3 18,8 5,5 23,0 0,1 0,4 2,2 0,6 10 49,2 0,3 18,9 4,7 23,7 0,1 0,6 2,1 0,2 0,2 11 50,8 0,4 4,4 11,0 26,9 0,8 3,7 0,5 1,3 0,5 12 50,2 0,7 0,4 4,2 11,2 26,7 0,7 3,7 0,4 1,4 0,3 0,1 13 50,5 0,7 0,4 4,6 11,1 26,3 0,6 4,3 0,4 1,2 0,1 14 38,9 0,9 0,1 12,6 11,7 0,1 0,2 32,7 2,9 0,1

15 37,7 0,5 0,1 16,5 6,7 0,1 0,2 31,5 6,9

16 1,9 2,0 0,1 0,8 0,4 0,1 4,0 91,2

17 38,9 0,3 12,2 9,7 0,1 0,2 35,8 2,3 0,5

18 0,3 2,4 0,1 0,1 0,2 0,1 0,2 1,3 95,4 19 0,5 1,7 0,2 0,1 0,1 1,3 95,5 0,7 20 2,3 0,1 0,2 1,1 96,9 21 1,7 0,1 0,1 1,8 96,3 0,3

Appendix 3

Test 4 EAF slag cooled in the slag pot

5 9 1 4 10

2 11 12

6 13 3 7 14

Spectrum O F Mg Al Si Ca Ti Cr Mn Fe Ni 1 44,3 0,9 4,2 16,9 26,8 2,6 1,7 2,5 0,1 2 43,5 0,7 0,9 4,1 16,9 27,3 2,3 1,9 2,3 3 41,4 0,3 2,6 15,0 38,1 0,3 1,0 1,3 4 40,2 0,8 2,6 15,5 38,3 0,4 1,0 1,1 5 40,0 0,8 2,6 15,1 38,2 0,4 1,2 1,4 0,2 6 35,2 1,5 7,2 3,2 0,1 0,4 0,8 42,0 9,1 0,6 7 34,9 1,4 7,1 3,2 0,1 0,4 0,9 42,0 9,3 0,6 0,2 8 35,7 0,7 7,2 3,4 0,0 0,6 1,0 41,7 9,6 0,1 9 41,7 5,7 15,5 34,2 0,4 1,1 1,3 10 38,6 1,4 2,0 0,4 7,3 31,1 15,7 2,9 0,6 0,1 11 41,8 0,1 6,0 15,5 34,3 0,4 0,8 1,1 12 38,8 0,4 2,0 0,5 7,0 30,7 16,6 3,0 0,7 0,1 0,2 13 0,6 1,0 0,2 0,9 0,1 55,3 0,5 40,9 0,4 14 1,0 0,2 0,5 0,1 54,1 0,0 43,9 0,2

Appendix 3

Test 4 EAF slag, water-cooled in the slag pot

9 7 6

1 8 14 4 3 11 12

10 13

Spectrum O F Na Mg Al Si Ca Ti Cr Mn Fe Ni 1 40,1 1,1 2,6 15,0 38,3 0,5 1,0 1,1 0,2 2 41,0 0,3 2,5 15,2 38,5 0,3 1,1 0,9 0,1 0,1 3 41,5 0,1 2,6 15,1 38,2 0,1 1,1 1,1 0,1 4 43,5 0,6 1,0 3,9 16,6 27,3 2,8 1,8 2,2 0,2 5 44,3 0,2 0,9 4,4 17,0 26,9 2,4 1,4 2,3 0,4 6 35,7 0,6 6,9 3,4 0,5 0,9 42,6 8,4 0,8 7 36,2 0,6 7,1 3,5 0,8 1,2 41,1 8,9 0,5 8 35,6 1,0 7,1 3,3 0,6 0,7 42,3 8,7 0,7 9 40,0 0,3 0,1 2,1 0,4 8,1 30,8 14,5 2,5 0,8 0,1 0,1 10 39,7 0,7 2,2 0,4 7,7 30,8 15,0 2,5 0,7 0,2 11 42,3 0,1 0,1 5,8 15,5 33,6 0,4 0,9 1,2 0,1 12 42,0 0,1 6,0 15,4 33,6 0,5 1,1 1,2 0,3 13 0,4 1,7 0,2 0,3 0,2 45,4 0,5 50,1 1,3 14 0,1 2,2 0,2 0,6 0,3 45,8 0,5 49,7 0,5

Appendix 3

Test 5 EAF slag, scrap-cooled in the slag pot

1 2 6 5 14 12 15 9 8 3

10 11

7 4 13

1 Spectrum O F Na Mg Al Si K Ca Ti Cr Fe Ni Sn 1 44,9 0,3 0,3 4,4 5,4 17,3 0,3 25,6 0,1 0,5 1,0 2 44,2 0,5 0,1 3,6 7,7 16,0 0,2 25,9 0,3 0,5 0,3 0,8 3 43,9 0,8 0,2 4,4 6,0 17,0 0,3 25,9 0,2 0,4 0,3 0,7 4 38,1 2,8 6,7 2,1 0,5 0,3 47,9 1,1 0,5 5 35,1 3,6 6,7 2,6 0,1 0,6 0,3 50,3 0,9 0,2 6 36,8 2,3 6,6 3,0 0,1 0,5 0,5 49,7 1,0 7 41,9 0,5 0,1 19,0 0,1 36,8 0,6 0,3 1,1 8 41,9 0,6 0,2 18,7 0,2 36,4 0,1 0,5 0,1 1,3 9 42,5 0,4 0,2 18,9 0,1 36,6 0,1 0,2 0,1 1,2 10 1,5 0,2 0,1 0,1 0,2 0,1 29,1 62,1 6,9 11 1,7 0,1 0,1 0,9 0,1 32,1 64,2 0,8 0,3 12 41,5 0,8 0,2 0,7 3,2 0,1 26,8 23,9 3,1 0,6 13 39,9 1,1 0,2 1,0 3,9 0,2 25,9 22,7 3,7 0,1 1,5 14 45,5 2,2 0,2 3,9 17,6 0,4 22,3 3,0 4,0 0,1 1,0 15 43,9 2,2 0,7 4,6 17,7 0,4 23,0 3,0 3,3 0,3 1,0

Appendix 3

Test 6 EAF slag, scrap-cooled in the slag pot

7 2 13 11 6 8 1 14 12

15 9 10 95 3

Spectrum O F Na Mg Al Si K Ca Ti Cr Fe Ni 1 37,2 2,2 7,3 4,0 0,1 0,1 0,6 1,1 46,3 1,0 2 37,2 1,6 0,2 7,7 3,1 0,1 0,7 0,4 48,0 1,1 3 37,0 2,5 7,0 2,7 0,5 0,3 48,7 1,2 4 37,9 2,6 0,1 7,4 3,8 0,1 0,9 0,6 45,1 1,2 0,1 5 1,3 0,9 0,1 0,1 0,3 0,2 20,2 63,8 13,1 6 1,2 0,3 0,1 0,5 31,3 59,1 7,4 7 1,6 0,9 0,2 0,1 0,6 0,1 31,6 59,0 6,0 8 46,5 1,0 0,1 1,1 4,0 17,5 0,2 26,4 1,4 1,6 9 44,3 1,3 0,6 5,5 17,8 0,2 25,4 2,7 1,8 0,1 0,1 10 45,9 1,5 0,1 0,6 5,6 17,4 0,2 24,2 2,6 1,7 0,2 11 42,6 0,5 0,1 2,5 0,1 16,2 0,3 35,6 0,4 1,4 0,2 0,1 12 42,1 1,1 2,8 0,1 16,1 0,1 36,5 0,3 1,0 0,1 13 41,7 1,3 0,1 2,7 0,1 16,2 0,1 36,2 0,2 1,2 0,1 14 44,9 0,5 0,1 1,8 2,7 14,1 0,2 26,6 6,6 2,6

Appendix 3

Test 7 CRC slag, scrap-cooled in the slag pot

5 12

10 2 13 1

9 4 3 6 14 8 11

Spectrum O F Mg Al Si Ca Ti Cr Mn Fe Ni 1 41,0 0,4 56,3 0,1 0,1 0,2 0,1 1,2 0,2 0,3 0,1 2 40,3 0,7 55,1 0,3 0,1 0,2 0,2 2,7 0,3 0,2 0,1 3 40,2 0,2 57,3 0,1 0,3 1,3 0,2 0,2 0,1 4 41,8 0,2 7,4 16,1 34,4 0,2 0,1 0,1 5 41,6 7,6 16,0 34,6 0,1 0,3 6 38,3 2,0 1,4 0,9 3,6 29,6 23,0 1,3 0,1 7 38,7 1,8 2,8 0,9 6,8 30,4 18,1 0,9 0,0 8 36,5 3,1 0,9 0,8 2,9 29,6 24,8 1,3 0,2 9 43,9 0,2 4,8 7,5 15,2 27,7 0,4 0,1 0,1 10 43,8 0,6 4,9 7,4 15,3 27,7 0,1 0,1 11 42,5 1,0 4,8 7,4 15,5 27,6 0,4 0,1 0,2 0,1 0,2 12 43,5 0,3 15,5 16,8 23,3 0,1 0,5 0,1 13 43,2 0,5 15,8 0,1 16,6 23,1 0,1 0,6 14 0,3 0,9 0,2 0,1 0,1 1,0 0,2 16,0 0,2 81,3

Appendix 3

Test 10 EAF slag, cooled on the slabs

5 4 19

23 21 22 9 10 17 18 2 8 20 11 6 1 14 7 3 13 12 15 16

Spectrum O F Mg Al Si Ca Ti Cr Fe Ni 1 38,9 0,5 11,5 6,2 0,1 0,5 1,5 40,5 0,5 2 40,7 0,9 2,9 0,5 8,3 30,2 14,1 2,5 0,1 3 39,9 1,0 11,7 6,8 0,1 0,9 1,3 37,9 0,2 0,4 4 40,5 0,3 2,9 0,6 8,3 30,2 14,3 2,6 0,3 5 40,2 0,9 2,9 0,6 8,0 29,9 14,4 2,8 0,1 6 40,7 2,9 0,6 8,2 30,5 14,6 2,4 0,1 0,2 7 42,5 6,6 16,5 33,4 0,2 0,5 0,2 0,3 8 41,7 6,7 16,9 33,9 0,3 0,5 0,4 9 42,2 0,4 6,6 16,6 33,5 0,3 0,6 10 40,7 0,9 6,6 16,8 34,1 0,3 0,4 0,2 0,1 11 41,5 0,7 3,1 16,3 38,0 0,4 0,4 0,1 12 41,2 0,3 3,2 16,2 38,1 0,2 0,7 0,3 13 41,1 0,6 0,1 16,1 42,1 0,1 0,3 14 41,1 0,3 0,2 16,1 42,0 0,4 0,1 15 42,1 0,1 3,1 16,1 37,8 0,3 0,7 0,2 16 41,5 0,1 16,2 42,0 0,1 0,5 17 44,7 0,2 0,9 8,1 16,1 26,0 2,1 1,4 0,4 18 45,3 1,4 0,7 8,4 16,1 25,4 1,6 1,3 19 43,9 1,7 0,8 8,0 16,4 25,6 1,9 1,5 0,1 20 1,2 0,1 0,1 1,2 40,6 58,7 21 1,6 0,2 1,3 0,1 39,6 59,2 22 41,1 0,9 2,9 16,5 38,1 0,4 0,5 23 41,0 0,6 4,6 2,0 16,5 33,3 0,8 1,0 0,2

Appendix 4

SEM analyses of sample 0 (test 0, FeCr slag poured on the ground)

Class Rank Features % total Feature area (sq. % total area features µm) Al-rich spinel 1 35 3.9 1.64E+02 4.11E-04 Metal 1 8 0.9 3.75E+01 9.39E-05 Forsterite 1 159 17.6 7.46E+02 1.87E-03 Class7 1 19 2.1 8.91E+01 2.23E-04 Classy phase 1 195 21.6 9.14E+02 2.29E-03 Chromite 1 35 3.9 1.64E+02 4.11E-04 Residual chromite 1 61 6.8 2.86E+02 7.16E-04 Mullite/ 1 125 13.8 5.86E+02 1.47E-03 Cordierite Spinel 1 7 0.8 3.28E+01 8.22E-05 Spinel 2 2 204 22.6 9.57E+02 2.39E-03

SEM analyses of sample 2 (Test 2 water-cooled FeCr slag on the slabs)

Class Rank Features % total Feature area (sq. % total area features µm) Al-rich spinel 1 81 8.4 3.80E+02 9.51E-04 Metal 1 10 1.0 4.69E+01 1.17E-04 Protoenstatite 1 73 7.6 3.42E+02 8.57E-04 Class7 1 46 4.8 2.16E+02 5.40E-04 Classy phase 1 16 1.7 7.50E+01 1.88E-04 Residual Chromite 1 72 7.5 3.38E+02 8.45E-04 Cordierite/ 1 471 49.0 2.21E+03 5.53E-03 Mullite Spinel 1 2 0.2 9.38E+00 2.35E-05 Spinel 2 2 175 18.2 8.21E+02 2.05E-03

SEM analyses of sample 3 (test 3 water-cooled FeCr slag on the slabs)

Class Rank Features % total Feature area (sq. % total area features µm) Al-rich spinel 1 74 7.9 3.47E+02 8.69E-04 Metal 1 8 0.9 3.75E+01 9.39E-05 Protoenstatite 1 210 22.4 9.85E+02 2.46E-03 Class7 1 23 2.5 1.08E+02 2.70E-04 Classy phase 1 181 19.3 8.49E+02 2.12E-03 Chromite 1 25 2.7 1.17E+02 2.93E-04 Residual Chromite 1 37 3.9 1.73E+02 4.34E-04 Cordierite/ 1 149 15.9 6.99E+02 1.75E-03 Mullite Spinel 1 2 0.2 9.38E+00 2.35E-05 Spinel 2 2 205 21.9 9.61E+02 2.41E-03

Appendix 4

SEM analyses of sample 4 (test 4 air cooled EAF slag in a slag pot)

Class Rank Features % total Feature area (sq. % total area features µm) Metal 1 8 0.9 3.75E+01 9.39E-05 Magnesiochromite 1 42 4.7 1.97E+02 4.93E-04 Cr and Mn containing 1 638 71.7 2.99E+03 7.49E-03 calciumsilicate Perovskite 1 59 6.6 2.77E+02 6.93E-04 Melilite 1 8 0.9 3.75E+01 9.39E-05 Merwinite 1 4 0.4 1.88E+01 4.70E-05 Titanite 1 4 0.4 1.88E+01 4.70E-05 Bredigete 2 108 12.1 5.06E+02 1.27E-03 Larnite 3 7 0.8 3.28E+01 8.22E-05

SEM analyses of sample 4W (test4 water-cooled EAF slag in a slag pot)

Class Rank Features % total Feature area (sq. % total area features µm) Metal 1 9 1.1 4.22E+01 1.06E-04 Magnesiochromite 1 47 5.7 2.20E+02 5.52E-04 Cr and Mn containing 1 572 69.8 2.68E+03 6.71E-03 calciumsilicate Perovskite 1 25 3.0 1.17E+02 2.93E-04 Melilite 1 10 1.2 4.69E+01 1.17E-04 Merwinite 1 2 0.2 9.38E+00 2.35E-05 Titanite 1 4 0.5 1.88E+01 4.70E-05 Bredigete 2 115 14.0 5.39E+02 1.35E-03 Larnite 3 1 0.1 4.69E+00 1.17E-05

SEM analyses of sample 5 (test 5 EAF slag scrap cooled in a slag pot)

Class Rank Features % total Feature area (sq. % total area features µm) Metal 1 32 3.7 1.50E+02 3.76E-04 Magnesiochromite 1 141 16.1 6.61E+02 1.65E-03 Cr and Mn containing 1 83 9.5 3.89E+02 9.74E-04 calciumsilicate Perovskite 1 21 2.4 9.85E+01 2.46E-04 Melilite 1 268 30.6 1.26E+03 3.15E-03 Merwinite 1 2 0.2 9.38E+00 2.35E-05 Titanite 1 5 0.6 2.34E+01 5.87E-05 Bredigete 2 52 5.9 2.44E+02 6.10E-04 Larnite 3 207 23.7 9.71E+02 2.43E-03

Appendix 4

SEM analyses of sample 6 (test 6 EAF slag scrap cooled in the slag pot)

Class Rank Features % total Feature area (sq. % total area features µm) Metal 1 46 5.3 2.16E+02 5.40E-04 Magnesiochromite 1 131 15.1 6.14E+02 1.54E-03 Cr and Mn containing 1 542 62.5 2.54E+03 6.36E-03 calciumsilicate Melilite 1 33 3.8 1.55E+02 3.87E-04 Bredigete 2 20 2.3 9.38E+01 2.35E-04 Larnite 3 15 1.7 7.03E+01 1.76E-04

SEM analyses of sample 7 (test 7 CRC slag cooled with scrap)

Class Rank Features % total features Feature area (sq. % total area µm) Akermanite 1 396 47.5 1.86E+03 4.65E-03 Titanite 1 20 2.4 9.38E+01 2.35E-04 Monticellite 1 308 36.9 1.44E+03 3.62E-03 Class6 1 28 3.4 1.31E+02 3.29E-04

SEM analyses of sample 10 (test 10 EAF slag, thin bed)

Class Rank Features % total Feature area (sq. % total area features µm) metal 1 1 0.1 4.69E+00 1.17E-05 Magnesiochromite 1 1 0.1 4.69E+00 1.17E-05 Cr and Mn containing 1 305 36.0 1.43E+03 3.58E-03 calciumsilicate Perovskite 1 56 6.6 2.63E+02 6.57E-04 Melilite 1 81 9.6 3.80E+02 9.51E-04

Merwinite 1 217 25.6 1.02E+03 2.55E-03 Titanite 1 9 1.1 4.22E+01 1.06E-04 Bredigete 2 62 7.3 2.91E+02 7.28E-04 Larnite 3 31 3.7 1.45E+02 3.64E-04

Appendix 4

Classification samples 0-3 FeCr slag

Class Rank Criteria Measure1 Min Max Al-rich spinel 1 10 <= Cr <= 22 w/Threshold Cr 10.00 22.00 Al-rich spinel 1 15 <= Mg <= 20.1 w/Threshold Mg 15.00 20.10 Al-rich spinel 1 20 <= Al <= 31 w/Threshold Al 20.00 31.00 Al-rich spinel 1 0.01 <= Fe <= 6 w/Threshold Fe 0.01 6.00 Metal 1 35 <= Fe <= 100 w/Threshold Fe 35.00 100.00 Metal 1 1 <= Cr <= 75 w/Threshold Cr 1.00 75.00 Protoenstatite 1 17 <= Mg <= 32 w/Threshold Mg 17.00 32.00 Protoenstatite 1 0.8 <= Cr <= 5 w/Threshold Cr 0.80 5.00 Protoenstatite 1 0.3 <= Al <= 9.7 w/Threshold Al 0.30 9.70 Protoenstatite 1 19 <= Si <= 29 w/Threshold Si 19.00 29.00 Class7 1 6 <= Al <= 20 w/Threshold Al 6.00 20.00 Class7 1 4 <= Si <= 22.99 w/Threshold Si 4.00 22.99 Class7 1 5 <= Mg <= 16 w/Threshold Mg 5.00 16.00 Class7 1 1.5 <= Cr <= 12 w/Threshold Cr 1.50 12.00 Classy phase 1 0.5 <= Mg <= 5 w/Threshold Mg 0.50 5.00 Classy phase 1 21 <= Si <= 33 w/Threshold Si 21.00 33.00 Classy phase 1 2 <= Al <= 14 w/Threshold Al 2.00 14.00 Classy phase 1 0.3 <= Ca <= 5.8 w/Threshold Ca 0.30 5.80 Chromite 1 30 <= Mg <= 35 w/Threshold Mg 30.00 35.00 Chromite 1 18 <= Si <= 22 w/Threshold Si 18.00 22.00 Chromite 1 0.5 <= Cr <= 2.4 w/Threshold Cr 0.50 2.40 Residual 1 6 <= Mg <= 15.8 w/Threshold Mg 6.00 15.80 chromite Residual 1 6 <= Al <= 15 w/Threshold Al 6.00 15.00 chromite Residual 1 0.5 <= Fe <= 55 w/Threshold Fe 0.50 55.00 chromite Residual 1 25 <= Cr <= 42.5 w/Threshold Cr 25.00 42.50 chromite Cordierite/ 1 5 <= Mg <= 20 w/Threshold Mg 5.00 20.00 Mullite Cordierite/ 1 23 <= Si <= 35 w/Threshold Si 23.00 35.00 Mullite

Cordierite/ 1 0 <= Cr <= 5 w/Threshold Cr 0.00 5.00 Mullite Cordierite/ 1 0.1 <= Ca <= 7 w/Threshold Ca 0.10 7.00 Mullite Cordierite/ 1 5.9 <= Al <= 14 w/Threshold Al 5.90 14.00 Mullite Spinel 1 16 <= Mg <= 18 w/Threshold Mg 16.00 18.00 Spinel 1 36 <= Al <= 39 w/Threshold Al 36.00 39.00 Spinel 2 2 1 <= Cr <= 40 w/Threshold Cr 1.00 40.00 Spinel 2 2 14 <= Al <= 38 w/Threshold Al 14.00 38.00 Spinel 2 2 11 <= Mg <= 21 w/Threshold Mg 11.00 21.00

Appendix 4

Classification of minerals in samples 4, 4W, 5, 6, 10, EAF slag

Class Rank Criteria Measure1 Min Max Metal 1 10 <= Fe <= 90 w/Threshold Fe 10.00 90.00 Metal 1 0 <= Cr <= 55 w/Threshold Cr 0.00 55.00 Magnesiochromite 1 25 <= Cr <= 62 w/Threshold Cr 25.00 62.00 Magnesiochromite 1 2 <= Mg <= 9 w/Threshold Mg 2.00 9.00 Magnesiochromite 1 0.2 <= Mn <= 20 w/Threshold Mn 0.20 20.00 Magnesiochromite 1 0.1 <= Al <= 10 w/Threshold Al 0.10 10.00 Cr and Mn containing 1 10 <= Ca <= 38.59 w/Threshold Ca 10.00 38.59 calciumsilicate Cr and Mn containing 1 0.3 <= Cr <= 6 w/Threshold Cr 0.30 6.00 calciumsilicate Cr and Mn containing 1 0 <= Mn <= 3.4 w/Threshold Mn 0.00 3.40 calciumsilicate Cr and Mn containing 1 10 <= Si <= 25 w/Threshold Si 10.00 25.00 calciumsilicate Perovskite 1 15 <= Ti <= 35 w/Threshold Ti 15.00 35.00 Perovskite 1 21 <= Ca <= 37 w/Threshold Ca 21.00 37.00 Melilite 1 0.2 <= Mg <= 7 w/Threshold Mg 0.20 7.00 Melilite 1 4 <= Al <= 12 w/Threshold Al 4.00 12.00 Melilite 1 17 <= Ca <= 33 w/Threshold Ca 17.00 33.00 Melilite 1 10 <= Si <= 25 w/Threshold Si 10.00 25.00 Monticellite 1 12 <= Mg <= 18 w/Threshold Mg 12.00 18.00 Monticellite 1 14 <= Si <= 19 w/Threshold Si 14.00 19.00 Monticellite 1 22 <= Ca <= 29 w/Threshold Ca 22.00 29.00 Merwinite 1 4 <= Mg <= 10 w/Threshold Mg 4.00 10.00 Merwinite 1 14 <= Si <= 20 w/Threshold Si 14.00 20.00 Merwinite 1 32 <= Ca <= 39 w/Threshold Ca 32.00 39.00 Titanite 1 10 <= Ti <= 30 w/Threshold Ti 10.00 30.00 Titanite 1 11 <= Si <= 18 w/Threshold Si 11.00 18.00 Bredigete 2 35 <= Ca <= 50 w/Threshold Ca 35.00 50.00 Bredigete 2 13 <= Si <= 20 w/Threshold Si 13.00 20.00 Bredigete 2 0 <= Mg <= 6 w/Threshold Mg 0.00 6.00 Larnite 3 12 <= Si <= 25 w/Threshold Si 12.00 25.00 Larnite 3 30 <= Ca <= 50 w/Threshold Ca 30.00 50.00

Appendix 4

Classification of minerals, sample 7 CRC slag

Class Rank Criteria Measure1 Min Max Akermanite 1 2 <= Mg <= 10 w/Threshold Mg 2.00 10.00 Akermanite 1 11 <= Si <= 25 w/Threshold Si 11.00 25.00 Akermanite 1 28 <= Ca <= 43 w/Threshold Ca 28.00 43.00 Titanite 1 0.1 <= Mg <= 5 w/Threshold Mg 0.10 5.00 Titanite 1 3 <= Ti <= 35 w/Threshold Ti 3.00 35.00 Titanite 1 27 <= Ca <= 33 w/Threshold Ca 27.00 33.00 Titanite 1 2 <= Si <= 18 w/Threshold Si 2.00 18.00 Melilite 1 1 <= Mg <= 7 w/Threshold Mg 1.00 7.00 Melilite 1 7 <= Al <= 12 w/Threshold Al 7.00 12.00 Melilite 1 13 <= Si <= 19 w/Threshold Si 13.00 19.00 Melilite 1 18 <= Ca <= 26 w/Threshold Ca 18.00 26.00 Metal 1 10 <= Fe <= 80 w/Threshold Fe 10.00 80.00 Metal 1 10 <= Cr <= 100 w/Threshold Cr 10.00 100.00 Monticellite 1 13 <= Mg <= 17 w/Threshold Mg 13.00 17.00 Monticellite 1 17 <= Si <= 22 w/Threshold Si 17.00 22.00 Monticellite 1 20 <= Ca <= 29 w/Threshold Ca 20.00 29.00 Class6 1 4 <= Mg <= 10 w/Threshold Mg 4.00 10.00 Class6 1 1 <= Al <= 9 w/Threshold Al 1.00 9.00 Class6 1 14 <= Si <= 19 w/Threshold Si 14.00 19.00 Class6 1 20 <= Ca <= 28 w/Threshold Ca 20.00 28.00 Merwinite 1 4 <= Mg <= 10 w/Threshold Mg 4.00 10.00 Merwinite 1 14 <= Si <= 20 w/Threshold Si 14.00 20.00 Merwinite 1 32 <= Ca <= 39 w/Threshold Ca 32.00 39.00

Appendix 5

XRD patterns for certain samples

Test 0 FeCr- slag

350 1

300

250

200 1

1 150 Lin (Counts) 3 1

1 100 3 3 50

0 10.0000 20.0000 30.0000 40.0000 50.0000 60.0000 70.0000 80.0000 90.0000 2Theta

Minerals in sample 0; Spinel , MgAl2O4(1), Fe(Al,Cr)2O4 (3)

Test 3 FeCr-slag

450

400

350 1

300

250

1 200 1 Lin (Counts) 1

150 1 1

100

1 50

0 10.0000 20.0000 30.0000 40.0000 50.0000 60.0000 70.0000 80.0000 90.00 2Theta

Minerals in sample 3, FeCr slag; Spinel MgAl2O4(1)

Appendix 5

EAF slag

300

250 6

200

7 150 Lin (Counts)

100 7 6 6 4

50 7 4 5 5

0 10.0000 20.0000 30.0000 40.0000 50.0000 60.0000 70.0000 80.0000 90.000 2Theta

Minerals in EAF slag; Merwinite Ca3Mg(SiO4)2(4), Magnesiochromite MgCr2O4(5), Gehletite Ca2Al2SiO7(6), Akermanite Ca2MgSi2O7(7)

Test 4 Water-cooled EAF- slag (surface)

100

80 11

70 8

50 8 8 8 Lin (Counts) 40 8 11 9 10 30 5

20 9

0 10.0000 20.0000 30.0000 40.0000 50.0000 60.0000 70.0000 80.0000 90.000 2Theta

Minerals in sample 4WS, EAF slag water cooled in a slag pot , surface region; Magnesiochromite MgCr2O4(5), Chromite syn FeCr2O4(8), Perovskite CaTiO3(9), Donathite (FeMg)(Fe,Cr)2O4(10), Calcium magnesiaoxide Ca5MgSi3O11(11)

Appendix 5

Test 4 air-cooled EAF slag

250 12

12 200

11 150

5 Lin (Counts) 100

9 9 5 10 50 11 5 12 11 12 10 12 12 5 12 11

0 10.0000 20.0000 30.0000 40.0000 50.0000 60.0000 70.0000 80.0000 90.000 2Theta

Minerals in sample 4A, EAF slag air cooled I a slag pot; Bredigete(12), Magnesiochromite MgCr2O4(5), Donathite (Fe,Mg)(Fe,Cr)2O4 (10), Perovskite CaTiO3(9), Calciummagnesiasilicate CaMgSiO4(11)

Test 4 water-cooled EAF-slag

250

200

150

9 5 Lin (Counts) 100

12 10 12 10 5 12 50 9 5 5

0 10.0000 20.0000 30.0000 40.0000 50.0000 60.0000 70.0000 80.0000 90.000 2Theta

Minerals in sample 4W, EAF slag water cooled in a slag pot; Magnesiochromite MgCr2O4(5), Perovskite CaTiO3(9), Donathite (Fe,Mg)(Fe,Cr)2O4 (10), Bredigete Ca14Mg2(SiO4)8(12)

Appendix 5

Test 5 scrap-cooled EAF-slag

250

200

150 5

10 12 Lin (Counts) 100 10

5 10 10

50 6 12

0 10.0000 20.0000 30.0000 40.0000 50.0000 60.0000 70.0000 80.0000 90.000 2Theta

Minerals in sample 5 scrap cooled EAF slag; Magnesiochromite MgCr2O4(5), Gehletite Ca2Al2SiO7(6), Chromite syn FeCr2O4(8), Donathite (Fe,Mg)(Fe,Cr)2O4 (10), Bredigete Ca14Mg2(SiO4)8(12)

Test 6 Scrap-cooled EAF-slag

300

7 250

200

150 13 Lin (Counts)

100 7

7 7 8 8 50 7 13 13 9 13 7 8 9 7 77 7 9

0 10.0000 20.0000 30.0000 40.0000 50.0000 60.0000 70.0000 80.0000 90.000 2Theta

Minerals in sample 6 , scrap cooled EAF slag; ; Akermanite Ca2MgSi2O7(7), Chromite syn FeCr2O4(8), Calcium aluminium oxide, Ca3Al2O6(13)

Appendix 5

Semi-quenched EAF-slag

250

12 7 200

150 6

Lin (Counts) 100 9 12

6 50 6 6 9 12 10 12 9

0 10.0000 20.0000 30.0000 40.0000 50.0000 60.0000 70.0000 80.0000 90.000 2-theta

Minerals in semi-quenched EAF slag; Gehletite Ca2Al2SiO7(6), Akermanite Ca2MgSi2O7(7), Perovskite CaTiO3(9), Donathite (Fe,Mg)(Fe,Cr)2O4 (10), Bredigete Ca14Mg2(SiO4)8(12)

Test 7 Scrap-cooled CRC-slag

400 15

350

300 4

250 15

200 17 15 Lin (Counts) 15 16 150 15 15 4 15 4 100 15 4 17

17 50 4 15

0 10.0000 20.0000 30.0000 40.0000 50.0000 60.0000 70.0000 80.0000 90.000 2Theta

Minerals in sample 7 , scrap cooled CRC slag; MerwiniteCa3Mg(SiO4)2 (4), Monticellite(15), Calcium titanite, Ca2Ti5O12(16), Calcium Titanite Ca2Ti2O6(17)

Appendix 5

CRC slag

300 15

250

200 15

15 4 15 15 150 Lin (Counts)

100 15 15 9 9 50

0 10.0000 20.0000 30.0000 40.0000 50.0000 60.0000 70.0000 80.0000 90.000 2Theta

Minerals in CRC slag, normal poured on the ground; Merwinite Ca3Mg(SiO4)2 (4), Perovskite CaTiO3(9), Monticellite(15),

Semi-quenched CRC slag

300

250

200 4 9 15

150 15 Lin (Counts)

100 15 15 15 15 9 15 4 15 15 15 50 9 9 6 15

0 10.0000 20.0000 30.0000 40.0000 50.0000 60.0000 70.0000 80.0000 90.000 2Theta

Minerals in semi-quenched CRC slag; Merwinite Ca3Mg(SiO4)2 (4), Gehletite Ca2Al2SiO7(6), Perovskite CaTiO3(9), Monticellite(15)