Quick viewing(Text Mode)

Recycling of Steel Bo Bjo¨Rkman, Caisa Samuelsson Mimer E Minerals and Metallurgical Research Laboratory, Lulea˚ University of Technology, Lulea˚, Sweden

Recycling of Steel Bo Bjo¨Rkman, Caisa Samuelsson Mimer E Minerals and Metallurgical Research Laboratory, Lulea˚ University of Technology, Lulea˚, Sweden

CHAPTER 6

Recycling of Steel Bo Bjo¨rkman, Caisa Samuelsson MiMeR e Minerals and Metallurgical Research Laboratory, Lulea˚ University of , Lulea˚, Sweden

6.1 INTRODUCTION the EAF process. Almost all of the steel produc- tion based solely on is produced in the of steel is a very old business, and EAF process. Assuming then 100% of scrap use it should be pointed out that in most developed in an EAF and about 15% of the steel produced parts of the world we have a very - in -based originating from scrap developed system of scrap collectors, scrap- used as coolant gives about 40% of steel produc- processing companies and steel plants utilizing tion in the world based on scrap. Some references the scrap. For the scrap-treating companies indicate a lower value, thus indicating that in and the steel plants, steel scrap is a very valu- developing countries ore is more often used as able resource. From the scrap that is collected, coolant in BOF steelmaking than scrap. The share losses occur to residues in the scrap processing of steel produced from scrap in Western Europe and in material streams that are recycled in in 2012 was about 50e55%, calculated based on other cycles, e.g. units present in the same assumptions (Eurofer, 2013). This scrap sorted as scrap for making. figure is in good agreement with statistics on Steel scrap in steelmaking is usually recycled the scrap consumption in Western Europe, indi- to either an (EAF), in what cating about 55% of steel production is based on usually is labeled scrap-based steelmaking, scrap. or to the basic furnace (BOF), in In addition to much lower emissions to the ore-based steelmaking, where there exists a environment in general, steel production in an considerable need for cooling to avoid too high EAF process based on scrap contributes much temperatures as a result of exothermic reactions. less to the emission of CO2 and has a much It should be pointed out that in the steel pro- lower total energy consumption. The focus in duced in ore-based steelmaking, about 10e20% recent years has been on research toward is from scrap used for cooling in the BOF. The decreased emissions of greenhouse gases from world production of steel was 1547 Mt in 2012 steelmaking in among others the European (World Steel Association, 2013), a record high ULCOS project (ULCOS, 2013), and in this production. Of these 29.3% was produced in context a comprehensive evaluation of CO2

Handbook of Recycling Copyright Ó 2014 Bo Bjo¨rkman and Caisa Samuelsson. http://dx.doi.org/10.1016/B978-0-12-396459-5.00006-4 65 Published by Elsevier Inc. All rights reserved. 66 6. RECYCLING OF STEEL emissions and energy consumption in bench- final products that have a quite long life time, mark BOF steelmaking and EAF steelmaking a considerable amount of the steel produced as well as for different alternative processing has to come from ore-based steel production, routes has been presented. The benchmark despite the high recycling rate of collected scrap, emissions of CO2 from the BOF route and the cf. Table 6.1. EAF route are about 1770 and 380 kg CO2 per Figure 6.2 illustrates the use of steel split into ton liquid steel, respectively, and the benchmark different product groups. The by far largest use total energy consumption is about 4900 and of steel is in construction, an application which 1100 kWh, respectively, per ton of liquid steel (e.g. Birat et al., 2004). TABLE 6.1 Steel Industry Recycling Rates Figure 6.1 illustrates the increase in world steel production by region in recent years, Application Estimate Target Area for 2007 (%) for 2050 (%) showing a drastic increase in steel consumption, mainly driven by economic development in Construction 85 90 China. China’s steel production has increased Automotive 85 95 from 182 Mt in 2002 to 716 Mt in 2012. About Machinery 90 95 46% of today’s world production of crude steel is produced in China. It is important when Appliances 50 75 considering the share of steel produced from Containers 69 75 scrap that as long as the world consumption of Total 83 90 steel increases in the way illustrated in Figure 6.1, and as a majority of the steel is in From World Steel Association (2013).

FIGURE 6.1 Crude steel produc- tion by country and region, 1980e2012 (Swedish Steel Producers Association, 2013).

II. RECYCLING e APPLICATION & TECHNOLOGY 6.1 INTRODUCTION 67

FIGURE 6.2 The distribution of steel use in emerging and advanced countries across sectors. From World Steel Association. has a very long time in use, cf. Table 6.2, but that showed the fastest-growing steel consump- most of the steel applications have a quite long tion so far in this twenty-first century, consump- time in use. tion are expected to peak between 2015 and 2020 Steel stocks in use have reached saturation in (Pauliuk et al., 2012). As a saturation of steel several developed countries and are not stocks in use occurs, the fraction of steel produc- increasing anymore, even declining in some tion based on scrap can and will increase. In countries, whereas some developed countries 2050, the share of steel produced from scrap and most of the rest of the world still have has been estimated as about 80% (Pauliuk increasing stocks of steel in use. The saturation et al., 2012). Other estimates give a figure of level for steel stock in use is at 13 2 t/capita 50% of the world steel production based on (Pauliuk et al., 2013). In China, the country scrap in 2050 (Swedish Steel Producers Associa- tion, 2012). Steel is an and is produced into a large TABLE 6.2 Steel Product Lifespan (Brooks variety of different alloys depending on the and Pan, 2004) application intended for the steel, usually Product Years divided into what is labeled low-alloyed steel and high-alloyed steel. Depending on the alloy, e Buildings 20 60 steel contain alloying elements like , Major industrial 40 , , , , Heavy industrial 30 etc., in varying amounts, for high-alloyed steels machinery is from 1% and upward. The alloys are often added as ferroalloys, by which is meant an alloy Rails 25 comprising iron and the alloying element. Fer- Consumer durables 7e15 roalloy production almost always consumes 5e15 more resources than iron production, and green- house gas emissions are, for example, 2e20 Steel cans <1 times higher for the ferroalloys than for iron.

II. RECYCLING e APPLICATION & TECHNOLOGY 68 6. RECYCLING OF STEEL

One type of high-alloyed steel is , obsolete scrap is the scrap coming from spent based on the noncorrosive properties that chro- consumer products or other origins, as collected mium and nickel introduces to the steel. The by the scrap dealers. The scrap is generally simplest stainless steel grade is composed of sorted into different scrap categories depending 18 and 8 wt% of chromium and nickel, respec- on composition and size of the scrap as illus- tively, but the chromium content is in some trated in Table 6.3. grades much higher and stainless steel is also As mentioned earlier, steel has a high recov- usually alloyed with Mo, W, Mn etc. ery of collected scrap. However, as also is obvious from the sorting specifications given in Table 6.3, the steel scrap is very seldom sorted 6.2 SCRAP PROCESSING AND into different alloys, thus the recovery of alloy- MATERIAL STREAMS FROM ing elements into the same type of steel is SCRAP PROCESSING much lower. 6.2.1 Scrap Classification Scrap used can be of several different ori- 6.2.2 Scrap Processing gins, as illustrated in Figure 6.3.Homescrap Larger scrap from, e.g. , white wares and is the scrap that emanates from recycling WEEE, is usually treated in a shredder, cf. within the plant, e.g. reverts from the furnace Figure 6.4, where the scrap is fragmented into surrounding, from ladles, from separation of smaller pieces with the aim of obtaining contained in , melts that has to be different materials in separate pieces to facilitate recycled due to some specifications that are sorting. A typical process scheme for the not fulfilled as well as pieces cut off during upgrading and sorting of different materials heat treatment, and finishing of the from the shredder is given in Figure 6.5. products. This type of scrap is usually well The steel scrap is loaded into the shredder and sorted into different qualities and with low fragmented into about hand-sized pieces. Very content of impurity elements, raising the pos- small and light particles, mainly with organic sibility of recycling the scrap back to the pro- content, is pneumatically conveyed and duction of the same steel quality. collected as a dust. The material then passes a Manufacturing scrap is the scrap coming number of separation steps, at a minimum con- from the manufacturing of the consumer goods; sisting of magnetic separation, sieving and air it can be very well sorted and of high purity and separation, whereby the majority of the steel is definitely has the potential to be so. Old scrap or collected in the magnetic fraction, nonferrous metals are collected in the nonmagnetic fraction and very small and light particles are separated from the scrap fractions. These process steps can then be complemented with a number of different separation steps to improve the sorting: separation, weak magnetic separation, eddy-current separation, hand sorting, auto- matic sorting based on color or physical proper- ties, etc. FIGURE 6.3 Scrap recycling. Labels indicates 1/home Typically the material coming from the scrap, 2/manufacturing scrap and 3/old or obsolete scrap. shredder is not completely separated. Pieces

II. RECYCLING e APPLICATION & TECHNOLOGY 6.2 SCRAP PROCESSING AND MATERIAL STREAMS FROM SCRAP PROCESSING 69

TABLE 6.3 European Steel Scrap Specifications (Eurofer, 2013)

Impurity Content

Category Specification Density Cu Sn Cr, Ni, Mo P Old scrap E3 0.6 0.250 0.010 0.250 P E1 0.5 0.40 0.020 0.30 New scrap E2 0.6 0.30 Low residuals E8 0.4 0.30 Uncoated E6 1 0.30

Shredded E40 0.9 0.250 0.020 Steel E5H P Tunings E5M 0.40 0.030 1 P High residual EHRB 0.5 0.450 0.030 0.350 P Scrap EHRM 0.6 0.40 0.030 1.0 Fragmented, from incineration E46 0.8 0.50 0.070

with steel together with copper, aluminum or other metals are quite common (e.g. van Schaik, 2004; Reuter et al., 2005, van Schaik et al. 2002), and depending on the sorting process a piece with, e.g. steel together with copper, might either end up in the steel or copper material after sort- ing due to inappropriate liberation in the shred- ding or due to inappropriate particle size for the separation process used. Copper content in steel scrap is one thing that limits the possible steel qualities that can be produced, an issue that will be further discussed in Section 6.5. For the moment we can simply just note that the require- ments on impurity content in the final steel is very much dependent on the steel quality pro- duced, from above 0.3% Cu to below 0.1% Cu for different steel grades. Therefore, the tradition has been that steel qualities with very low limits on copper content, which usually also have a higher , are produced in ore-based steel- making, the ore usually having low copper con- tent. Copper content in steel scrap from a shredder plant has been about 0.25% to 0.3% FIGURE 6.4 Schematic illustration of a shredder. and rising. An interesting observation is that

II. RECYCLING e APPLICATION & TECHNOLOGY 70 6. RECYCLING OF STEEL

Magnetic material conveyor Cyclone separator Ferrous Dust Magnetic metals Nonmagnetic Dust collector separation drums material conveyor

Pneumatic fine particle separator Nonferrous metal separator Preshredder power house Shredder power Ferrous house metals

Feeding roller

Nonferrous metals Dust conveyor pit Feeding apron conveyor

Shredder Washing water tank

Preshredder

FIGURE 6.5 Typical process scheme for sorting of material from a shredder into different material categories. From www. morita119.com. shredded steel scrap in Sweden has decreasing Eco-Cycle program in Sweden (Gurell et al., copper content nowadays, about 0.22% Cu, 2012). The technique has proven to be feasible because the copper has become very valuable, to rapidly determine different type of steel al- therefore giving an incentive for handpicking loys and works well as an aid at the scrap of larger copper pieces present in the steel scrap. yard to determine the exact use of different Equipment for sorting of scrap based on scrap deliveries to optimize the use of alloying properties such as color and magnetic proper- elements and not risk contamination by un- ties is already on the market and is to some wanted impurities. The technique is still too extent also used by the scrap-treating com- slow for use as an online sorting aid at a panies. An alternative is sorting based on the in a shredder plant. chemical composition as determined, e.g. through spectroscopic techniques. Scrap sort- ing of aluminum using laser induced break- 6.3 THE PROCESSES USED down spectroscopy (LIBS) has already proven FOR STEEL SCRAP to work very well (Gesing et al., 2003; Aydin et al., 2004). The use of the same technique Figure 6.6 illustrates the process scheme for for sorting of steel scrap has been tested production of steel from both ore and scrap. recently in a research project within the Steel Scrap-based steelmaking is almost 100% based

II. RECYCLING e APPLICATION & TECHNOLOGY 6.3 THE PROCESSES USED FOR SMELTING STEEL SCRAP 71

FIGURE 6.6 Schematic process scheme of steelmaking based on or scrap (Swedish Steel Producers Association, 2011). on smelting the scrap in an EAF, cf. Figure 6.7, fuel in burners, etc. has led to a substantial where electricity is used as energy source for decrease in energy consumption and also has the smelting. Development of the process with added some flexibility in the use of energy slag foaming through injection of a source. Depending on the actual processing source and oxygen, oxygen lancing, preheating technology, electricity consumption for smelt- of the scrap, bottom tapping, cocombustion of ing steel scrap in a modern EAF is in the range

Electrodes

Arc Furnace

Tapping over mouth

Induction Slag stirring port

FIGURE 6.7 Principals of an (EAF) for smelting steel scrap.

II. RECYCLING e APPLICATION & TECHNOLOGY 72 6. RECYCLING OF STEEL of 400e450 kWh/t steel. Slag formers are added blow, until the blow is stopped at about 0.05% to take up some of the impurities coming with C left in the steel. Oxidation of Mn and Fe is of the steel. The steel is then refined in ladle course only partial. Hot metal from the processes, casted, rolled and finished. furnace usually has a temperature of about A recent trend is that also within scrap-based 1300e1400 C when it arrives at the converter. steelmaking in an EAF, more and more virgin As a consequence of the heat evolution from iron units are used, in the form of direct the exothermic reactions, large quantities of reduced iron (DRI) or hot briquetted iron coolant have to be added to ensure that the tem- (HBI), which will be discussed further in Sec- perature is not raised above approximately tions 6.7 and 6.8. The furnace can either be oper- 1700 C. Coolant is either ore or scrap. If scrap ated on AC current with three electrodes, which is used as coolant the amount added is usually is the dominating alternative and also the in the range 15e20% of the amount of steel pro- version illustrated in Figure 6.7, or operated duced. Since the volumes of steel produced in on DC current with one electrode. the BFeBOF route are large, the amounts of The EAF is a very efficient smelting unit but scrap consumed within what is usually labeled not a very good reactor type for carrying out ore-based steelmaking are quite large. refining reactions or for adding large amounts Stainless steel is produced in a process flow of nonmetallic material. Scrap smelting in an similar to the process route illustrated in EAF is thus dependent on subsequent refining Figure 6.6 for producing scrap-based ordinary to give a high-quality steel. steel except for one important difference. Most Ore-based steelmaking, cf. Figure 6.6, is usu- stainless steel produced in the Western world ally based on a sintered ore and charged to is based on scrap melted in an EAF, but because a blast furnace (BF), where the iron oxides in the the amount of stainless steel scrap not is enough, ore are reduced to metal. As the material in the also ordinary steel scrap has to be used. The lack blast furnace is always in contact with carbon in of alloying elements such as chromium and coke, the hot metal tapped from the blast nickel in the latter makes it necessary to alloy furnace will be almost saturated with carbon, with ferrochromium and ferronickel or pure typically about 4.5 wt% carbon in hot metal. nickel. Carbon is then introduced with the fer- Some tenths of a percent of will also be roalloys and a refining step using oxygen to dissolved in the tapped hot metal. convert carbon into CO(g) has to be introduced, After tapping from the blast furnace, the hot often carried out in an Argon Oxygen Decarbu- metal is usually refined at least from , rization (AOD)-converter. Stainless steel can be sometimes also from . The refined either ferritic or austenitic, a difference that can hot metal is decarburized with pure oxygen in be of large importance for recycling, as dis- the converter, usually a BOF. Reactions taking cussed further in Section 6.4. place are: ½ þ ¼ ð Þ (6.1) 6.4 TRENDS IN QUALITY Si Fe O2 SiO2 slag ½ þ 1=2 ¼ ð Þ (6.2) OF THE SCRAP AVAILABLE C Fe O2 CO g ½ þ 1=2 ¼ ð Þ (6.3) FOR STEEL PRODUCTION Mn Fe O2 MnO slag þ 1=2 ¼ ð Þ (6.4) Fe O2 FeO slag Steel is produced in a large number of All these reactions are exothermic, generating different alloy compositions containing a lot of heat. Silicon content in the metal will different amount of alloying elements like Cr, very rapidly decrease to almost zero, whereas Mn, Nb, B, V, etc. In the final product the steel carbon content decreases during the whole may be provided with a coating of ,

II. RECYCLING e APPLICATION & TECHNOLOGY 6.4 TRENDS IN QUALITY OF THE SCRAP AVAILABLE FOR STEEL PRODUCTION 73 pigments etc. The share of coated steel pro- From 1992 to 2001, the generation of steel duced is globally increasing, resulting in an packaging increased by 22% in the EU, and an increasing amount of recirculated scrap with increasing part is recycled (Baeyens et al., different types of coatings. The scrap used in 2010). In 2007, the amount of steel used for pack- steel making tends therefore to be a more com- aging in EU was slightly less than 5 Mt. The steel plex material. In conventional scrap used for packaging is mainly of two types: steel processes (steel converters or EAF’s), some of coated with a very thin layer of or steel coated the impurities evaporate and leave the process with chromium and chromium oxide. Both types with the off-gas and with particulate matter can also be combined with a polymer film. and are collected in the gas cleaning. Others When stainless steel is recycled through a either are oxidized and report to the slag or shredder plant, the ferritic part of the stainless are dissolved in the steel, or both. steel will be collected with the ordinary carbon The average North American today con- steel scrap because ferritic stainless steel is mag- tains not only more of metals other than steel netic. Whereas the recovery rate of austenitic (Al, Mg, Cu) and more of other materials but stainless steel can be expected to be high, also more of speciality alloyed steels, as shown much of the ferritic stainless steel will be recov- by the difference in composition when data for ered as scrap. Oda et al. carried out 1975 and 2007 are compared, cf. Figure 6.8 an analysis of the substance flow of chromium (Bevans et al., 2013). As can be seen, the share in steel in Japan and predicted that the mean of steel present as mild, low-alloyed steel has chromium content in EAF carbon steel will drastically decreased. Projections from the auto- gradually increase and reach 0.24% in 2030 motive industry indicate that the advanced (Oda et al., 2010). high-strength steels will account for up to 65% Zinc present as a coating on steel will during of the ’s body and structure by 2020 (Bev- melting at reducing conditions evaporate and is ans et al., 2013). Some of these steels can contain collected in the gas cleaning and is not any prob- as much as up to 24 wt% Mn and 6 wt% Al. To lem for steel quality. Provided that the zinc con- be able to also recover the alloying elements tent in the dust collected is high enough, the with high efficiency will then be of utmost dust is a raw material for extraction of zinc in, importance. e.g. Waelz-kilns and fuming . In the

FIGURE 6.8 Material composition (wt%) of an average North American vehicle from 1975 to 2007. Adapted from Bevans et al. (2013).

II. RECYCLING e APPLICATION & TECHNOLOGY 74 6. RECYCLING OF STEEL ore-based steel industry, on the other hand, the used and controlled and which ones that usu- share of scrap used is lower, and the zinc con- ally are referred to as tramp elements. tent is not at a level where extraction of zinc is Sources for tramp elements can be many, ore, economically feasible. In this case, the zinc con- scrap, reductants used, fluxing agents or coming tent becomes an obstacle for internal recycling with alloying additions. Usually the ore used of dust and sludge to the blast furnace, which has much less impurity content than the scrap cannot tolerate high zinc loads. used, although depending of the ore, some im- purities may come with the ore, like Cr, As and Cd. The behavior of several impurity and 6.5 HINDRANCES FOR tramp elements during oxidation in, e.g. the RECYCLINGdTRAMP ELEMENTS BOF process, is illustrated in Table 6.4 (Vallomy, 1985). 6.5.1 Definition of Tramp Elements As Figure 6.9 shows, some of these elements are added intentionally as alloying elements in Tramp elements are those elements that are certain steel grades, like Mo, Cr, Ni and Cu, present in steel, but usually not intentionally but are detrimental for the quality of the steel added, and are difficult to refine from the steel, in other steel grades or are lost to the slag in and therefore will be kept in the steel cycle once the processing of another type of steel grade. entered, coming back over and over again when Low-alloyed steel is often produced by melting steel is recycled. Some of these have detrimental the scrap in quite oxidizing conditions, resulting effects on the steel properties, others being in a substantial loss of chromium to the slag alloying elements for some steel grades, but even when chromium-containing low-alloyed not for all. As iron is a quite un-noble metal, steel is produced. Stainless steel can either be not as e.g. aluminum, but still, the iron will react ferritic or austenitic stainless steel or both, and with a refining agent before the tramp element as ferritic stainless steel is magnetic it will report reacts, thereby making refining from these ele- to the ordinary carbon steel fraction during sep- ments difficult. For the elements defined as aration after shredding. In the upgrading from a tramp elements no commercially feasible shredder plant, steel scrap is not sorted to any refining processes exist today. Figure 6.9 illus- larger extent than into an ordinary steel fraction trates common elements in steel, how they are and a stainless steel fraction. Also, in the

I A II A III A IV A V A VI A VII A VIII H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn Fr Ra Ac

Tramp element Alloying element Gas dissolved in steel Dissolved in steel, can be controlled Alloying element that also is a tramp element, depending on steel grade

FIGURE 6.9 Common elements in steel, how they are used and which ones that are referred to as tramp elements.

II. RECYCLING e APPLICATION & TECHNOLOGY 6.5 HINDRANCES FOR RECYCLINGdTRAMP ELEMENTS 75

TABLE 6.4 Distribution of Some Common Alloying, Impurity and Tramp Elements to Different Phases During of Steel

To Bath To Slag To Gases

Sb Cr B Al B Zn Pb

As Pb Cd Be Cr

Bi P Ca Cd

Co Se Hf P

Cu S Mg Se

Mo Te Si S

Ni V Ti Te

Ta Zn Zr V

Sn

W

Totally Mostly Partially

manufacturing industry, it is very seldom that of Sn has the same effect at a content higher the scrap is sorted into various types of alloys than 0.05 wt% and a combination of Cu þ Sn en- and depending on the content of alloying ele- hances the effect. The presence of these elements ments. This means that in addition to containing is also responsible for an increased probability tramp elements that have detrimental influence for transverse cracking during continuous cast- on the steel quality, alloying elements valuable ing (Mintz, 1999). The mechanism of crack for- in the production of some steel grades might mation due to copper is due to a preferential get lost. oxidation of iron at the surface and liquid cop- per precipitating at the steel surface when the copper content in remaining exceeds 6.5.2 Influence on Steel Quality by the solubility limit. The liquid copper is wetting Tramp Elements the iron and thus easily penetrates into the austenite grains, giving rise to the cracks (Kaji- Copper is known to induce surface cracks tani et al., 1996). By increasing the Sn content, during hot rolling if reheating is carried out in the domain of liquid is widened, which oxidizing atmosphere (Vallomy, 1985), at con- is why Sn increases the probability of crack for- tents above 0.15% (Marique, 1996). Presence mation (Yamamoto et al., 2006). Marique (1996)

II. RECYCLING e APPLICATION & TECHNOLOGY 76 6. RECYCLING OF STEEL showed that the rejection rate due to crack for- the rate for accumulation of tramp elements mation during rod rolling was drastically was not very well developed and hence steel increased at copper content above 0.15%. The producers looked on increasing levels of e.g. crack depth was shown to increase with copper in the steel scrap with fear. In this cen- increasing reheating temperature above tury steel production has increased rapidly 1000 C and increasing copper content (Kajitani and hence a larger potion of steel is produced et al., 1996). Decreased silicon content in the from ores. Scrap sorting has become more effi- steel also increases the upper temperature limit cient, and the increased for metals like for crack initiation (Kajitani et al., 1996). Calvo copper has even made hand-picking of larger et al. (2007) have shown that the width and copper pieces from the steel scrap on the depth of the cracks depend on both the reheat- conveyor belt in the shredder plant economi- ing cycle and the as-received condition, i.e. the cally feasible. Thus, e.g. copper content in the condition from the caster. shredded scrap has not continued to increase Several tramp elements have a negative effect but instead decreased on average. Nevertheless, on cold forming and cold drawing, e.g. Sn, Cu, scrap-based steel producers sometimes need to As and Cr. The upper limit for copper and tin dilute the steel scrap with virgin iron units for deep drawing grades is 0.1 and 0.02%, from HBI or DRI, if they are producing steel respectively (Vallomy, 1985). deterio- grades with very low tolerance for tramp ele- rated when testing was performed in oxidising ments. If and when the world once again comes atmosphere (Mintz et al., 1995) and it was pro- into a situation with small or no increase in the posed that observed precipitation of Cu2S was consumption of steel and the share of scrap- responsible and that an equal amount of nickel based steelmaking is increasing, the question could prevent this from happening. In inert at- of how to handle the tramp elements will once mosphere the influence of Cu on hot ductility again be of fundamental importance for sustain- is confusing, with no clear conclusions. Another able recycling of steel. phenomenon reported is that increased nickel content has been shown to reduce the scale removability from rolled steel (Asai et al., 1997). 6.6 PURIFICATION OF SCRAP These are only a few examples, and excellent reviews of the existing knowledge on influence 6.6.1 Dezincing of Galvanized Scrap of tramp elements on steel properties can be found in the literature (e.g. Vallomy, 1985; Two main principles are used, leaching and Marique, 1996; Herman and Leroy, 1996; Mintz thermal treatment. Leaching in both acid solu- and Crowther, 2010). tions (HCl, H2SO4) and in basic (NaOH) is discussed in the literature (Sen and Roy, 1975; Niedringshaus et al., 1992; Koros, 6.5.3 Importance of Tramp Elements 1992; Rome, 1992; Ijomah and Ijomah, 2003). When removing zinc at high pH, Zn is trans- for a Sustainable Recycling of Steel þ ferred to Zn and recovered either in the form There was much focus on tramp elements in of sodium zincates (Na2ZnO2 or NaHZnO2) steel, especially during 1980s and 1990s, but precipitated from a saturated solution or zinc not as much later on. This period was character- recovered by electrolysis. In acid leaching, zinc ized by stagnant level of world steel production is recovered via a saline solution of Zn(NO3)2, and a rapidly increasing share of steel produced ZnSO4, or ZnCl2. Leaching at high pH is a selec- from scrap. Scrap sorting and knowledge about tive process which not affect the iron, but is a

II. RECYCLING e APPLICATION & TECHNOLOGY 6.6 PURIFICATION OF SCRAP 77 time-consuming process, while acid leaching is violent gas explosions and (3) if heat can less selective but much faster. Since leaching is be used, this will result in an overall saving of a surface reaction, the surface area available be- the energy need. However, the presence of halo- comes important and the leaching proceeds gens and organic matter together with the scrap much faster for shredded scrap than for bun- may result in the formation of dioxins and fu- dles. A leaching process with a treatment time rans and therefore preheating temperature is ac- of 6 h at high pH with high, >90%, recovery of cording to regulations in e.g. Sweden limited to the zinc through electrolysis was described by 300 C in conventional scrap preheating equip- Niedringshaus et al. (1992). Formation of cya- ment. Possibilities to increase the scrap preheat- nide was indicated as one possible problem. ing temperature to temperatures where a One commercialized process, the Meretec pro- simultaneous evaporation of e.g. zinc can be ob- cess, is based on this concept. The concept is tained would have many benefits for the steel said to be competitive and fully functional. industry. This concept has been studied by Lars- Several studies describe thermal treatment of son et al. (2012) in a project in the Swedish scrap. The possibility of evaporating Zn, Ni, Cr research program “The Steel Eco-cycle” (Steel and Sn from coated materials using chlorine is Eco-cycle, 2013) and is also part of an ongoing one alternative (Dapper et al., 1978). Because European research project financed within ZnCl2 is more stable than FeCl2 and the ZnCl2 RFCS (Research Fund and Steel). is much more volatile, a selective evaporation The idea is to separately combust energy- of Zn can be obtained as long as there is metallic containing waste as auto shredder residue Zn present. Rinsing of noniron oxides and (ASR) with oxygen. The hot gas is used for pre- metals using HCl from the combustion of PVC heating scrap. Off-gases from this preheating has been described by Fray (1999). Tee and are partially recirculated and mixed with gases Fray have shown that to selectively evaporate from the combustion to control the temperature compounds in the coatings oxychlorination of the hot gases entering the scrap preheating, with controlled ratio of O2:Cl2 in the gas mixture but also giving enough gas volumes to ensure is necessary (Tee and Fray, 1999a,b; Tee and rapid enough preheating. Preheating of the Fray, 2005). Zn boils at a temperature of scrap is controlled at <900 C in a separate shaft 906 C, and it has been shown that vaporization reactor. Exhaust gases are cleaned and chlorides of zinc in CO/CO2 and N2 gas mixtures is very are captured. rapid and almost complete at temperatures Results from the small-scale tests showed higher than 850 C(Ozturk and Fruehan, 1996). that chlorine-rich gases, e.g. exhaust gases, Another alternative for removing highly vol- from ASR combustion can be a suitable gas for atile compounds present in coatings on steel is cleaning and preheating scrap (Larsson et al., vacuum treatment. A method to clean scrap by 2012). Pilot tests have shown that it is possible heating and vacuum treatment was suggested to achieve a uniform scrap preheating at by Okada et al. (1995). High removal efficiency 650 C, where the zinc removal efficiency is was obtained already at 700 C as compared to high. Preheating to 650 C generates a metal preheating with CO/CO2 gas mixtures. Almost loss of less than 1%. The process concept, 97% zinc recovery was achieved. including oxyfuel combustion, dedicated gas Steel scrap is often preheated before charging scrubbing and exhaust gas recirculation, has to the EAF. This has several purposes: (1) to been proved. The low gas volumes and low decrease the meltdown time in the EAF, (2) to amount of gas vented to the surrounding will remove water and especially in cold climates allow for treatment of the gas and the removal to remove ice, which otherwise can result in of harmful elements in a cost-efficient manner.

II. RECYCLING e APPLICATION & TECHNOLOGY 78 6. RECYCLING OF STEEL

A number of different methods to remove zinc proposed methods include selective evapora- from surface coatings of steel have been pro- tion or by oxidizing (Savov et al., 2000). posed during the years but very few have yet reached a commercial stage. For new methods to be commercially introduced, they have to be 6.6.3 Others cost-competitive with the traditional way of dealing with zinc in steel scrap, namely the pro- It is technically and sometimes also econom- cessing of zinc rich dust from the EAF in Waelz ically quite possible to refine steel from metals kilns, the dominant process route, or, e.g. in a or impurities present as a surface coating using zinc fuming furnace. The low zinc content in leaching or evaporation techniques because the dust from ore-based steelmaking makes it these methods are acting on the surface. For im- very expensive to send the dust for zinc recovery. purities or tramp elements present in the steel The strategy for many ore-based steel producers alloy, it is a different question. Although some- has therefore been to purchase only comparably times detrimental for the properties of the steel, clean scrap as coolant. Market shortness of clean the content in the steel is low, a few hundredths scrap in the future would perhaps make the ore- up to a few tenths of weight percentage, and based steel industry interested in scrap rinsed thus they have a low thermodynamic activity. from zinc, if the prices can be comparable with Furthermore, iron is sometimes the least noble the cost for use of ores as coolant. metal. Both factors make it difficult to find a suitable reagent. In addition, steel has a compa- rably low value per tonne and the volumes of 6.6.2 Detinning of Steel Scrap steel scrap are huge in comparison with other metals, necessitating a refining concept to be Electrolytic detinning of tinplate scrap has very cost effective. been in commercial use for a long time. Scrap Many different processes for refining steel pressed into bundles serve as immersed from copper have nevertheless been proposed, in a caustic soda bath at about 85 C. Tin is including dissolution in a solvent like Al, Pb, deposited on a steel cathode as a sponge mate- sodium sulfideeiron sulfide, soda-iron sulfide rial, which is scraped off (Savov and Janke, or aluminum sulfideeiron sulfide, reacting 1998). The tin content in the steel is below with a chlorinating agent or vacuum treatment 0.02 wt% after this processing. The process re- of the steel. The thermodynamics of the removal quires rather large volumes to be economical of tramp elements from steel scrap was evalu- and is claimed to be suitable only for prompt ated by Tsukihashi (2003). The conclusion was scrap. Because the process is a surface process, that calciumemetal halide fluxes have an excel- it will be applicable only where tin is present lent refining ability. No figures were given on as a surface coating. A proposed alternative the amount of different tramp elements that method for detinning tinplate scrap has been possibly could be removed. None of these to react the surface with a sulfur-containing suggestions have, however, reached a commer- gas at moderate temperature to form a tin sul- cial stage. Several aspects of tramp element fide layer. The tin content in the steel could be control in steel have been studied by a group decreased to levels of about 0.1 wt% from above of steel producers and research institutes in 0.3% originally. At higher temperatures the the European Union (Boom and Steffen, 2001). diffusion of tin from the surface layer and into To give one example, the high distribution of the steel becomes fast and limits the possibilities some impurity elements to a phase in con- for detinning based on surface reactions. Other tact with a carbon-containing iron phase could

II. RECYCLING e APPLICATION & TECHNOLOGY 6.8 MEASURES TO SECURE SUSTAINABLE RECYCLING OF STEEL 79 be utilized (Yamaguchi and Takeda, 2003a,b). A TABLE 6.5 Typical Content of the Impurity Elements miscibility gap exists between an iron phase Cu, Sn, Ni, Cr, Mo (Given as the Sum of with 95.4%Fee4.5%Ce0.1%Pb and 99.9% These Elements in wt%) in Different Type e of Raw Materials for Production of Steel Pb 0.1%Fe. Copper, tin, zinc, gold, silver and and the Requirements for Production of palladium are primarily distributed to the lead Different Steel Grades phase. An equal amount of iron and lead makes 70% of the copper and tin contained in the iron Total Impurity Content to report to the lead phase. The temperature for in wt% (Sum of Raw Material Cu D Sn D Ni D Cr D Mo) the study was 1453 K. The quite high amount of lead needed to dissolve a considerable amount 0.02 of copper and tin makes such a process depen- 0.06 dent on the value of recoverable noniron ele- ments, not only for the purpose of cleaning the No. 1 factory bundles 0.13 steel scrap. Bushelling 0.13 No. 1 heavy melting 0.20 6.7 TO LIVE WITH IMPURITIES Shredded auto scrap 0.51 No. 2 heavy melting 0.73 In a world with an increased share of steel STEEL GRADE produced from scrap, the issue of the impurity content in the scrap will be of high importance. Tin plate for draw and iron 0.12 cans The question is illustrated in Table 6.5 showing the typical content of impurity elements (given Extra deep drawing quality 0.14 as the sum of content in wt% of the elements sheet Cu, Sn, Ni, Cr, Mo) in different types of raw Drawing quality and 0.16 materials, as well as the limits for the content enameling steels of these impurity elements for the production Commercial quality sheet 0.22 of different type of steels. Fine wire grades 0.25 Although these data are somewhat old and the separation processes at the shredder plants Special bar quality 0.35 and the sorting of scrap have improved, they Merchant bar quality 0.50 illustrate that it is difficult to produce all steel Adapted from Vallomy (1985). grades based on 100% of scrap, if the scrap is not well sorted before it enters a shredder plant. That is also the reality for scrap-based steel producers in the business sectors for high- 6.8 MEASURES TO SECURE quality sheet products, speciality and ma- SUSTAINABLE chinery as well as scrap-based production of RECYCLING OF STEEL iron powder. They are all dependent on having access to a very well sorted scrap, usually home Steel is, based on volume, the most recycled or manufacturing scrap, and to a much lesser metal, and there exists a well-functioning busi- extent on obsolete scrap. If well-sorted scrap ness structure for the recycling of steel. Losses not is available to affordable prices, ore-based are inevitable in the processing and handling iron units suitable for charging to an EAF is their of any metal. Losses occur to byproduct only alternative today. streams and waste in the processing (slag,

II. RECYCLING e APPLICATION & TECHNOLOGY 80 6. RECYCLING OF STEEL dust, sludge) and into other material cycles, Although design for recycling has been on the material fractions aimed for energy recovery table within the research communities dealing or into waste that is landfilled. These losses with sustainability and recycling for long time, can and will be decreased as technology de- the impression is that the issue has not yet really velops and as awareness of the issue grows reached the designers and construction engi- among all the stakeholders involved in the pro- neers. Issues on appearance, functionality and duction of products, from designers to manu- manufacturing are still considered more facturers. The amount of collected steel that is important. lost from the recycling cycle is nevertheless Improved sorting at the shredder plant. Tech- probably small in comparison with the total niques for sorting of scrap where physical prop- production. Not at least if metal prices increase erties or composition is utilized have been in comparison with the living standard, what is developed and new techniques will surely worth recycling will be recycled. If and when emerge. Hitherto, more advanced sorting tech- the increase in world consumption of steel de- niques have not been implemented at larger creases, there will be greater possibilities of scale, possibly because the steel producers are producing a large amount of the steel from not willing to pay for the extra cost through an recycled scrap. increased scrap price and also because the The largest question for the steel and scrap need has not been there, as “pure” ore-based processing industry in order to obtain long- iron units are cheaper. Rem et al. (2012) has term sustainable steel recycling is perhaps the shown by the introduction of a shape-sensitive question of scrap quality and avoiding quality magnetic separator that it is possible to pre- losses when recycling steel. As the share of steel sort scrap into two products. One product is a produced from ore has increased in the last bulky, thin-walled steel fraction of high purity, decade, accumulation of tramp elements has the other a volumetrically small flow of heavy not been an issue of high importance recently, parts containing the contaminants. The latter is but it is an issue that will have to be tackled in very well suited for cost-effective hand sorting the future. or sensor sorting. Several actions can be taken to minimize the A better knowledge of the composition of the detrimental effects of tramp elements: scrap will increase possibilities to utilize the scrap for production of the same type of alloy, • Design for recycling thereby not only securing the recycling of iron • Improve sorting at the shredder plant units but also securing a better utilization of • Improve processing at the steel plant the alloying elements and decreasing the losses • Live with impurities based on development of the same. of new alloys Improved processing at the steel plant.Directcast- • Dilute scrap with ore-based iron units ing of thin strips or in-line strip production (ISP) • Improve the understanding of steel flow in is a technique that will give higher tolerances for the society impurity elements such as copper due to a faster Design for recycling. By proper choice of mate- cooling and making a reheating procedure un- rials placed together in different parts of a con- necessary (Arvedi, 2010; Spitzer et al., 2003). struction and by the choice of fittings between However, as long as not all steel would be different materials, it is possible to ensure a produced in these new thin-strip pro- good separation of crucial parts, by manual cesses, steels produced with higher content of dismantling or in the following shredding and e.g. copper would have to be kept in a separate processing of the scrap (Reuter et al., 2005). recycling loop.

II. RECYCLING e APPLICATION & TECHNOLOGY REFERENCES 81

Tolive with impurities through development of new technological development. Many Material alloys that can accept a higher content of impurity Flow Analysis (MFA) and Substance Flow Anal- and tramp elements. Although introducing detri- ysis (SFA) studies of the steel flow have been mental properties in many steel grades with the carried out, but very few on steel grade level. present processing of steel, some of the tramp el- Some exceptions exist (e.g. Oda et al., 2010) ements are also used as alloying elements for where the recycling of different types of stain- some steel grades to improve resistance less steel was analyzed. and enhance the mechanical properties. It is possible to improve the properties of steel by precipitating nanoscale copper sulfides (e.g. Liu et al., 2006, 2007; Yamamoto et al., References 2006) through a rapid solidification and/or con- Arvedi, G., 2010. Achievements of ISP steelmaking tech- trolling the balance between Cu, S and Mn con- nology. Ironmaking and Steelmaking 37, 251e256. tent or by adding phosphorus, which promotes Asai, T., Soshiroda, T., Miyahara, M., 1997. Influence of Ni precipitation of copper sulfide from ferrite impurity in steel on the removability of primary scale in instead of from austenite and suppresses precip- hydraulic descaling. ISIJ International 37, 272e277. ¨ itation of MnS at higher temperature. Precipita- Aydin, U., Makowe, J., Noll, R., 2004. Fast identification of light metal alloys by laser-induced breakdown spec- tion of copper sulfide is preferable compared to troscopy for material recycling: development of a MnS. From a steel recycling point of view, it demonstrator for automatic sorting of scrap. must, however, be noted that the copper content VDI-Berichte, 401e412, 471. in the alloys studied is low, below 0.1 wt%. In Baeyens, J., Brems, A., Dewil, R., 2010. Recovery and recy- extra-low-carbon titanium added interstitial cling of post-consumer waste materials. Part 2. Target (glass beverage bottles, , scrap metal and free steel sheet, Cu is the useful alloying element steel cans, end-of-life tyres, batteries and household for increasing . Addition of Cu or hazardous waste). International Journal of Sustainable Cu þ Ni at a level of 0.5 and 0.4 wt%, respec- Engineering 3, 232e245. tively, has been shown to increase the volume Bevans, K., et al., 2013. Importance of advanced high- fraction of retained austenite and to improve strength steels and electronic units on the recycling of automobiles: a review. Iron and Steel Technology 10, elongation and the strength ductility balance 266e277. (Kim et al., 2002, 2003). Birat, J.-P., Hanrot, F., Danloy, G., 2004. CO2 mitigation As pointed out regarding ISP technology, if in the steel industry: a benchmark study the new alloys developed contain substantial based on process calculations. In: Scanmet II, 2nd In- amounts of tramp elements and as long as ternational Conference on Process Development in Iron and Steelmaking, June 2004, Lulea˚, Sweden, pp. 73e80. many steel grades require a very low content Boom, R., Steffen, R., 2001. Recycling of scrap for high of tramp elements, it has to be possible to keep quality steel products. Steel Research 72, 91e96. these steels in a separate recycling loop by Brooks, G., Pan, Y., 2004. Developments in steel recycling well-functioning collection and sorting. technology. In: Green Processing 2004, 2nd International Dilution of scrap with ore-based iron units. The Conference on the Sustainable Processing of Minerals. Australasian Institute of and , last choice will, as it already is, be to dilute pp. 65e72. Publication Series No 2. impure scrap with ore-based iron units pro- Calvo, J., Cabrera, J.M., Rezaeian, A., Yue, S., 2007. Evalu- duced in the form of DRI or HBI. ation of the hot ductility of a C-Mn steel produced from Finally, an improved understanding of steel scrap recycling. ISIJ International 47, 1518e1526. flows in the society, on a steel grade level, would Dapper, G., Sloferdijk, W., Verbach, C.A., 1978. Removal of surface layers from plated materials: upgrading of scrap. give us a to model the possible accumula- Conservation Recycling 2, 117e121. tion of tramp and impurity elements depending Eurofer, The European Steel Assiociation, 2013. European on reasonable scenarios for future economic and Steel Scrap Specification. www.eurofer.eu/docs/.

II. RECYCLING e APPLICATION & TECHNOLOGY 82 6. RECYCLING OF STEEL

Fray, D.J., 1999. Use of poly(vinyl chloride) as chlorinating . International Materials Reviews 55, agent in recycling of metals. Plastics, Rubber and Com- 168e196. posites 28, 327e329. Mintz, B., 1999. Influence of composition on the hot ductility Gesing, A., et al., 2003. Assuring continued recyclability of of steels and to the problem of transverse cracking. ISIJ automotive aluminium alloys: chemical composition International 39, 833e855. based sorting of wrought and cast Al shred. In: Das, S.K. Mintz, B., Abushosha, R., Crowther, D.N., 1995. The influ- (Ed.), Aluminium 2003. TMS, pp. 3e14. ence of small additions of Cu and Ni on the hot ductility Gurell, J., Bengtson, A., Falkenstro¨m, M., Hansson, B.A.M., of steels. and Technology 11, 474e481. 2012. Laser induced breakdown spectroscopy for fast Niedringshaus, J.C., Rodabaugh, R.D., Leeker, J.W., elemental analysis and sorting of metallic scrap pieces Steribick, A.E., 1992. A technical evaluation of dezinci- using certified reference materials. Spectrochimica Acta fication of galvanized steel scrap. In: 1992 Steelmaking B: Atomic Spectroscopy 74e75, 46e50. Conference Proceedings, p. 725. Herman, J.C., Leroy, V., 1996. Influence of residual elements Oda, T., Daigo, I., Matsuno, Y., Adachi, Y., 2010. Substance on steel processing and mechanical properties. Iron and flow and stock of chromium associated with cyclic use of Steelmaker 23, 35e43. steel in Japan. ISIJ International 50, 314e323. Ijomah, M.N.C., Ijomah, A.I., 2003. Chemical recycling of Okada, Y., Raheachi, Y., Fujio, S., 1995. Development of galvanized steel scrap. Indian Journal of Chemical method for removal of zinc from automobile body Technology 10. . In: Galvatech ’95 Conference Proceedings, Kajitani, T., Wakoh, M., Tokumitsu, N., Ogibayashi, S., pp. 549e554. Mizoguchi, S., 1996. Influence of temperature and strain Ozturk, B., Fruehan, R.J., 1996. Vaporization of zinc from on surface crack to residual copper in carbon steel. In: steel scrap. ISIJ International 36, 239e242. 79th Steelmaking Conf., Pittsburgh, pp. 621e626. Pauliuk, S., Wang, T., Mu¨ ller, D.B., 2013. Steel all over the Kim, S.-J., Lee, C.G., Lee, T.-H., Oh, C.-S., 2003. Effect of Cu, world: estimating in-use stocks of iron for 200 countries. Cr and Ni on mechanical properties of 0.15 wt.% C Resources, Conservation and Recycling 71, 22e30. TRIP-aided cold rolled steels. Scripta Materialia 48, Pauliuk, S., Wang, T., Mu¨ller, D.B., 2012. Moving toward the 539e544. circular economy: the role of stocks in the Chinese steel Kim, S.-J., Lee, C.G., Lee, T.-H., Oh, C.-S., 2002. Effects of cycle. Environmental Science and Technology 46, copper addition on mechanical properties of 0.15C- 148e154. 1.5Mn-1.5Si TRIP-aided multiphase cold-rolled steel Rem, P.C., van den Broeck, F., Bakker, M.C.M., 2012. Puri- sheets. ISIJ International 42, 1452e1456. fication of post-consumer steel scrap. Ironmaking and Koros, P.J., 1992. Recycling of galvanized steel scrap e is- Steelmaking 39, 504e507. sues and . In: 1992 Steel Making Conference Reuter, M., et al., 2005. The Metrics of Material and Proceedings, p. 687. Metal Ecology; Harmonizing the Resource, Technology Larsson, M., Hahlin, P., A˚ ngstro¨m, S., 2012. The future of and Environmental Cycles. Elsevier, Amsterdam, scrap preheating and surface cleaning. In: Scanmet IV e Netherlands. 4th International Conference on Process Development in Rome, C.L., 1992. A contribution to the recycling of coated Iron and Steelmaking, 10e13 June 2012, Lulea˚, Sweden, steels e the results of a consultation of experts. In: 1992 pp. 83e92. Steelmaking Conference Proceedings, p. 687. Liu, Z., Kobayashi, Y., Kuwabara, M., Nagai, K., 2007. Savov, L., Janke, D., 1998. Recycling of scrap in steelmaking in Interaction between phosphorus micro-segregation and view of the tramp element problem. Metall 52, 374e383. sulfide precipitation in rapidly solidified steel-utilization Savov, L., Tu, S., Ja, R., Janke, D., 2000. Methods of of impurity elements in scrap steel. Materials Trans- increasing the rate of tin evaporation from iron based actions 48, 3079e3087. melts. ISIJ International 40, 654e663. Liu, Z., Kobayashi, Y., Yang, J., Nagai, K., Kuwabara, M., Sen, P.K., Roy, S., 1975. Recovery of zinc from galvanized 2006. Effect of nano-scale copper sulfide precipitation on steel scrap. Transactions of the Indian Institute of Metals mechanical properties and of rapidly 28 (5). solidified steel with tramp copper element. Materials Schaik, A., van, Reuter, M.A., Boin, U., Dalmijn, W.L., 2002. Transactions 47, 2312e2320. Dynamic modelling and optimisation of the resource Marique, C., 1996. Scrap recycling and production of high cycle of passenger vehicles. Minerals Engineering 15, quality steel grades in Europe. In: 79th Steelmaking 1001e1016. Conf., Pittsburgh, pp. 613e619. van Schaik, A., 2004. Theory of Recycling Systems e Mintz, B., Crowther, D.N., 2010. Hot ductility of steels and Applied to Car Recycling (thesis). Delft Univ. Techn., its relationship to the problem of transverse cracking in ISBN: 90-9018839.

II. RECYCLING e APPLICATION & TECHNOLOGY REFERENCES 83

Spitzer, K.-H., Ru¨ppel, F., Viscorova´, R., Scholz, R., Kroos, J., Symposium: Metallurgical and Materials Processing: Flaxa, V., 2003. Direct strip casting (DSC) e an option for Principles and Techologies; Materials Processing Fun- the production of new steel grades. Steel Research In- damentals and New Technologies, vol. 1, pp. 927e936. ternational 74, 724e731. ULCOS, 2013. www.ulcos.org. Steel Eco-cycle, 2013. www.stalkretsloppet.se. Vallomy, J.A., 1985. Adverse effects of tramp elements on Swedish Steel Producers Association, 2011. http://www. steel processing and product. Industrial Heating 52, jernkontoret.se/. 34e35, 37. Swedish Steel Producers Association, 2012. http://www. World Steel Association. World Steel in Figures 2013. www. jernkontoret.se/. worldsteel.org. Swedish Steel Producers Association, 2013. http://www. Yamaguchi, K., Takeda, Y., 2003a. Impurity removal from jernkontoret.se/. carbon saturated liquid iron using lead solvent. Mate- Tee, J.K.S., Fray, D.J., 1999a. Recycling of galvanised steel rials Transactions 44, 2452e2455. scrap using chlorination. In: EDP Congress 1999. The Yamaguchi, K., Takeda, Y., 2003b. Impurity removal from Minerals, Metals & Materials Society, pp. 883e891. carbon saturated liquid iron using lead solvent. In: Tee, J.K.S., Fray, D.J., August 1999b. Removing impurities Yazawa International Symposium: Metallurgical and from steel scrap using air and chlorine mixtures. JOM, Materials Processing: Principles and Techologies; Mate- 24e27. rials Processing Fundamentals and New Technologies, Tee, J.K.S., Fray, D.J., 2005. Recycling of galvanised steel vol. 1, pp. 485e492. scrap using chlorination. Ironmaking and Steelmaking Yamamoto, K.-I., Shibata, H., Mizoguchi, S., 2006. Precipi- 32, 509e514. tation behavior of copper, tin and manganese sulfide at Tsukihashi, F., 2003. Thermodynamics of removal of tramp high temperature in Fe-10%Cu-0.5%Sn alloys. ISIJ elements from steel scrap. In: Yazawa International International 46, 82e88.

II. RECYCLING e APPLICATION & TECHNOLOGY

Top View