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Home , Fayalite, Forsterite, Olivine, Tephroite

Article Geological Mapping and Characterization of Possible Primary Input Materials for the Sequestration of in Europe

Dario Kremer 1,*, Simon Etzold 2,*, Judith Boldt 3, Peter Blaum 4, Klaus M. Hahn 1, Hermann Wotruba 1 and Rainer Telle 2

1 AMR Unit of Mineral Processing, RWTH Aachen University, Lochnerstrasse 4-20, 52064 Aachen, Germany 2 Department of Ceramics and Refractory Materials, GHI - Institute of Mineral Engineering, RWTH Aachen University, Mauerstrasse 5, 52064 Aachen, Germany 3 HeidelbergCement AG-Global Geology, Oberklamweg 2-4, 69181 Leimen, Germany 4 HeidelbergCement AG-Global R&D, Oberklamweg 2-4, 69181 Leimen, Germany * Correspondence: [email protected] (D.K.); [email protected] (S.E.); Tel.: +49-241-80-96681(D.K.); +49-241-80-98343 (S.E.)  Received: 19 June 2019; Accepted: 10 August 2019; Published: 13 August 2019 

Abstract: This work investigates the possible mineral input materials for the process of mineral sequestration through the carbonation of or under high pressure and high temperatures in an autoclave. The choice of input materials that are covered by this study represents more than 50% of the global production. Reaction products are amorphous silica and or , respectively. Potential sources of magnesium containing materials in Europe have been investigated in regards to their availability and capability for the process and their harmlessness concerning asbestos content. Therefore, characterization by X-ray fluorescence (XRF), X-ray diffraction (XRD), and QEMSCAN® was performed to gather information before the selection of specific material for the mineral sequestration. The objective of the following carbonation is the storage of a maximum amount of CO2 and the utilization of products as pozzolanic material or as fillers for the cement industry, which substantially contributes to anthropogenic CO2 emissions. The characterization of the potential mineral resources for mineral sequestration in Europe with a focus on the content led to a selection of specific input materials for the carbonation tests. The mineralogical analysis of an Italian sample before and after the carbonation process states the reasons for the performed evaluation. The given data serves as an example of the input material suitability of all the collected mineral samples. Additionally, the possible conversion of natural asbestos occurring in minerals as a side effect of the carbonation process is taken into consideration.

Keywords: olivine; mineral sequestration; geological mapping; mineral deposits; characterization

1. Introduction The increasing greenhouse gas (GHG) emissions into our atmosphere lead to a serious threat to our future. Especially, the concentration of CO2, volume-based the most important GHG, is significantly and continuously rising. There are different approaches to reduce CO2 emissions or to store it by carbon capture and storage (CCS). Another approach is carbon capture and utilization (CCU), the separation of CO2 out of exhaust gas flows, and the subsequent use in chemical processes. One possible approach of CCU is the mineral sequestration of CO2. Suitable minerals are mainly calcium or magnesium silicates, which form insoluble carbonates (mainly calcite and magnesite) and silica in an exothermic reaction. This reaction continuously takes place as a natural process of in geological timeframes.

Minerals 2019, 9, 485; doi:10.3390/min9080485 www.mdpi.com/journal/minerals Minerals 2019, 9, 485 2 of 12

It can be accelerated with high temperature and high pressure in an autoclave [1]. The produced carbonates are stable and will only degas at temperatures above 400 ◦C[2]. CO2 sequestration by these minerals can be an opportunity for CO2 intensive industries, like the cement industry. Due to the mineral composition of , ~500 kg CO2 are emitted for each ton of cement clinker produced [3]. The goal is the utilization of the emitted CO2 from cement clinker production processes through CCU and the substitution of primary materials in cement or concrete with the produced carbonate and silica. Possible applications can be, e.g., adding value to concrete mixes as filler material, or partly replacing the pozzolanic supplementary cementitious materials in cement. To implement the mentioned process, the selection of suitable input material is necessary for ensuring an optimal process flow. Part of this paper is the mapping of possible minerals as input materials in Europe and the characterization of these materials to evaluate the possible use for CCU. The CO2MIN project target is to find and characterize the possible feedstock material for mineral sequestration of CO2, find the optimum conditions for maximum carbonation degree of magnesium silicates and to separate the products of the carbonation reaction to evaluate the possible applications in the cement industry. A theoretical model is created for the evaluation of the process. Besides, a social-economic analysis and a Life Cycle Assessment (LCA) are performed to define the success of the process regarding the carbon footprint and the economic feasibility. After the performance of a sufficient amount of large-scale experiments, their data will allow for global projections of the process capability. The aim of this paper is to provide an overview of the potential of possible feedstock for mineral sequestration of carbon dioxide. Therefore, samples from different European countries have been taken into consideration, mainly from deposits that produce the majority of the European . Firstly seven producers of peridotites have delivered a 10 kg sample to have a cross-section of peridotites in Europe. After pretreatment of the possible input material and its characterization, a preselection of samples has been made for the carbonation tests. These tests were carried out in an autoclave with high pressure, high temperature and the addition of additives.

2. Materials and Methods Olivine is no single, clearly defined mineral, but a group of minerals. They are minerals in the series of -forsterite with their end-members calcio-olivine and , whereas forsterite is a magnesium silicate and fayalite is an silicate. The most common olivine of this solution 2+ series has a magnesium-iron ratio of 1.6:0.4, with a formula of Mg1.6Fe 0.4(SiO4). It is of intermediate composition and it has an olive-green color, from which the name is derived [4]. Olivine has two main occurrences:

1. , which is an ultramafic rock that contains a minimum of 90% olivine with additional minerals, like ortho- and clinopyroxenes, as well as serpentine group minerals, magnesite, , ilmenite, rutile, and . Additionally, in small volumes, , garnet, and can be found in . 2. , a metamorph rock that was built through serpentinization, i.e., through transformation and alteration of ultramafic rocks, which originally contained large amounts of olivine. are mainly composed of serpentine minerals, like , clinochrysotile, orthochrysotile, lizardite, antigorite, and others [5].

There are many small deposits of olivine bearing rocks, but only a limited number of deposits represent manufacturing units due to economic factors. Olivine bearing rocks are normally found within the following geological settings: Ultramafic intrusions (e.g., Norway, Germany); • Ophiolite complexes (e.g., Greece, Italy, Turkey); • Alpine peridotites (ophiolite or subcontinental ) emplaced along thrust faults (e.g., Italy, • Spain); Minerals 2019, 9, 485 3 of 12

Rift zones/ of mid-ocean ridges (e.g., Iceland); • Minerals 2019, 9, x FOR PEER REVIEW 3 of 12 Volcanic (e.g., German Eifel and Kaiserstuhl, Iceland). • • Volcanic xenoliths (e.g., German Eifel and Kaiserstuhl, Iceland). The big deposits normally occur in settings of ultramafic intrusions and ophiolite complexes [6,7]. For possibleThe big deposits usage of normally olivine occur bearing in settings rocks for of sequestration,ultramafic intrusions samples and from ophiolite different complexes European countries,[6,7]. namely Norway, Spain, Italy, Turkey, and Greece, and one sample from Japan, have been collectedFor and possible investigated usage of regarding olivine bearing their rocks MgO for content sequestration, and phase samples composition. from different Besides, European German countries, namely Norway, Spain, Italy, Turkey, and Greece, and one sample from Japan, have been has been tested due to local proximity. The investigated deposits are marked in Figure1. As a collected and investigated regarding their MgO content and phase composition. Besides, German first investigationBasalt has been step, tested each due producerto local proximity. has delivered The investigated one compounded deposits are sample marked of in 10 Figure kg. The 1. As material a has beenfirst investigation crushed by step, jaw crusher,each producer milled has by delivered rollermill, one compounded sampled, and sample sieved of 10 to kg. produce The material a fraction belowhas 63 beenµm crushed for analysis by jaw and crusher, three milled different by roller fractions mill, forsampled, carbonation and sieved tests, to asproduce it can a befraction seen with Stopicbelow et al. 63 [1 µm]. for analysis and three different fractions for carbonation tests, as it can be seen with Stopic et al. [1].

FigureFigure 1. Origin1. Origin of of samples samples testedtested for the the us usee in in the the carbonation carbonation process process [8]. [8].

TheThe main main deposits, deposits, which which are are part part of of thethe investigationinvestigation for for CO2MIN CO2MIN project, project, will willbe presented be presented belowbelow and and its locations its locations are are marked marked on on the the mapmap in Fi Figuregure 11 with with the the name name of the of theproducing producing company. company. The globalThe global production production numbers numbers of of peridotites peridotites cancan be found in in Figure Figure 2.2 . Norway, Spain, Greece, Italy, and Turkey are major olivine producing countries in Europe, with Norway, Spain, Greece, Italy, and Turkey are major olivine producing countries in Europe, with a a total amount of between 4200 to 5400 ktpa, which represents more than 50% of the global olivine total amount of between 4200 to 5400 ktpa, which represents more than 50% of the global olivine production of 7800 to 9000 ktpa (Figure 2). The production numbers differ due to published data productionfrom O’Driscoll of 7800 to [6] 9000 from ktpa 2004 (Figure and the2). Thecurrent production numbers numbersfrom the diproducersffer due of to publishedthe investigated data from O’Driscollsamples. [6 ]The from annual 2004 production and the current of the numbersseven peridotite from theproducers producers in Eu ofrope the plus investigated the Horoman samples. The annualMine in production Japan, which of thewere seven examined peridotite in the producers CO2MIN inproject Europe account plus thefor Horoman4595 ktpa, Minewhich in is Japan, whichbetween were examined 51% and 58% in the of the CO2MIN global peridotite project account production. for 4595 ktpa, which is between 51% and 58% of the globalNorway peridotite is the production. most important producer of olivine in the world, with a production between Norway2525 and is3500 the ktpa most (Figure important 2). The producer material of is olivinedirectly in mined the world, as a target with material/product. a production between Many 2525 and 3500deposits ktpa are (Figure already2). explored, The material but not is directlyor only periodically mined as a mined target due material to the/ product.supply from Many Aheim deposits Gusdal Mine (mainly mined from Sibelco, but also from Steinsvik) is sufficient for the market. For are already explored, but not or only periodically mined due to the supply from Aheim Gusdal Mine this reason, only the Aheim Gusdal Mine will be presented in this paper. It is a large olivine deposit (mainly mined from Sibelco, but also from Steinsvik) is sufficient for the market. For this reason, only situated in the Almklovdalen peridotite massif, a large Alpine-type ultramafic body emplaced the Aheim Gusdal Mine will be presented in this paper. It is a large olivine deposit situated in the

Minerals 2019, 9, 485 4 of 12

Almklovdalen peridotite massif, a large Alpine-type ultramafic body emplaced within the granitoid gneisses of the Western Gneiss Region. The massif contains serpentinized ultramafics with a core of dunite.Minerals This 2019 dunitic, 9, x FOR core PEER has REVIEW a large-scale dunite zone with a thickness of up to 300 m with4 ofchlorite 12 bearing dunites, as well as 1 to 20 m thick zones of eclogite and chlorite- dunites [9]. For this paperwithin a sample the granitoid from Sibelco gneisses and fromof the SteinsvikWestern Gn haseiss been Region. investigated The massif but contains the Steinsvik serpentinized material has beenultramafics selected for with further a core examinations. of dunite. This dunitic core has a large-scale dunite zone with a thickness of up to 300 m with chlorite bearing dunites, as well as 1 to 20 m thick zones of eclogite and Different companies mine the deposit, but the biggest mine, the Gusdal olivine pit, produces chlorite-amphibole dunites [9]. For this paper a sample from Sibelco and from Steinsvik has been about 2 ktpa. With this production rate, the proved reserve will last for 150 years with a potential investigated but the Steinsvik material has been selected for further examinations. propertyDifferent life of more companies than 400 mine years, the deposit, which but makes the itbiggest the largest mine, the commercial Gusdal olivine olivine pit, depositproduces in the world.about Other 2 ktpa. mines With that this are production currently rate, producing the proved are locatedreserve will in Steinsvik last for 150 and years Bjørkedal with a potential [9]. Olivineproperty bearinglife of more rocks than in Greece400 years, are which mainly makes mined it the in thelargest north, commercial in Western olivine Macedonia, deposit in Northern the Euboeaworld. (Grecian Other Magnesitemines that S.A.),are currently the central producing mainland, are located and in in Chalkidiki Steinsvik and (Thermolith Bjørkedal S.A.).[9]. Most Greek deposits areOlivine of industrial bearing rocks interest in Greece mainly are because mainly of mined its chromite in the north, and PGE in Western (platin-group Macedonia, elements) contentNorthern utilizing Euboea peridotites (Grecian as Magnesite by-products. S.A.), the central mainland, and in Chalkidiki (Thermolith VourinosS.A.). Most ophiolite Greek deposits complex, are a fragmentof industrial of oceanicinterest ,mainly because is located of its chromite in Macedonia and PGE between (platin-group elements) content utilizing peridotites as by-products. Kozani and Grevena. The deposit/complex contains four distinct peridotite varieties from Vourinos ophiolite complex, a fragment of oceanic lithosphere, is located in Macedonia to fine and coarse-grained dunite [10]. between Kozani and Grevena. The deposit/complex contains four distinct peridotite varieties from Inharzburgite central Greece, to fine and harzburgite coarse-grained deposits dunite can [10]. be found in the Megaplatanos ultrabasic body, which is part ofIn the central western Greece, Neotethyan harzburgite ophiolitic deposits belt, can situated be found along in the the Megaplatanos western margin ultrabasic of the Pelagonianbody, zonewhich of Greece, is part belonging of the western to the Neotethyan Sub-Pelagonian ophiolitic zone. belt, situated The primary along the minerals western of margin this harzburgite of the depositsPelagonian are olivine zone (forsterite of Greece,/fayalite), belonging with to 65–80the Sub-Pelagonian vol. %, orthopyroxene zone. The (15–30primary vol. minerals %), clinopyroxene of this (3–5 vol.harzburgite %), and deposits Cr-spinel are (olivine<5 vol. (forsterite/fayalite), %). The dominant with secondary 65–80 vol. phase %, orthopyroxene is serpentine (15-30 with vol. a range %), of 5 up toclinopyroxene 70 vol. % [11 (3–5]. vol. %), and Cr-spinel (<5 vol. %). The dominant secondary phase is serpentine with a range of 5 up to 70 vol. % [11].

FigureFigure 2. World 2. World production production of of peridotite peridotite (Current (Current numbers for for the the prod productionuction from from the producers the producers of of the investigatedthe investigated samples samples (Figure (Figure1); 1); *: *: Data Data from from O’DriscollO’Driscoll [6]). [6]).

SpainSpain is one is one of theof the main main producers producers of of olivineolivine be bearingaring dunite. dunite. In Innorthwes northwesterntern Spain Spain (La Coruna (La Coruna District),District), the proventhe proven reserves reserves are are estimated estimated at at 600600 Mt (stated (stated by by Pasek Pasek Minerales). Minerales). Ultramafic Ultramafic massifs massifs are located in Sierra de la Capelada and Cabo Ortegal in the Herbaria massif. Ultrabasic peridotites are located in Sierra de la Capelada and Cabo Ortegal in the Herbaria massif. Ultrabasic peridotites occur in Sierra de Ronda near Málaga [12]. This Ronda peridotite massif is formed of different occurgroups in Sierra of de Ronda rocks, near namely Málaga , [12]. This olivine-rich Ronda peridotite lherzolites, massif , is formed and of dunites different [13]. groups In of

Minerals 2019, 9, 485 5 of 12 mafic rocks, namely lherzolites, olivine-rich lherzolites, harzburgites, and dunites [13]. In comparison to the Herbaria massif, the industrial production of dunite is not of importance at Ronda. The ultramafic rocks of the Herbaria massif can be described as a heterogeneous enriched , where the ultramafic section represents a wedge of lithospheric mantle above a subduction zone, whereas the initial subduction was interoceanic. The dunite has primary mineralization of olivine, orthopyroxenes, and clinopyroxenes and secondary mineralization of Ca- classified as hornblendes and serpentines, which derived from different geological processes, like hydrothermal alterations that are promoted by seawater contact [14]. In Italy, olivine/dunite is mined by Nuova Cives S.R.L. from a deposit in the north near Turin in the municipalities of Castellamonte, Vidracco and Baldissero Canavese. This deposit’s expected reserves contain about 100 Mt of dunites, with grades of 95% to 97% of olivine [5]. The mafic-ultramafic Ivrea-Verbano Zone in Northwest Italy bears several peridotite massifs, namely Finero, Balmuccia, and Baldissero. Additionally, there are two open-pit mines currently producing: “Bric Carleva” with ~300 Mt resources and “Finero” with ~250 Mt reserves (stated by Nuova Cives SRL). Dunite rocks and harzburgites are the main sources of olivine in Turkey. There are many Mesozoic ophiolite and peridotite complexes along the suture zones. The important chromite, magnesite, and olivine deposits in Turkey contain peridotite host rocks that consist of harzburgite, verlite, , or dunite. Often alteration/serpentinization has taken place within some parts of the peridotite. [15] There are many deposits with a significant amount of olivine bearing rocks, but only a few deposits are mined to date, due to economic and location aspects. There are no deposits for peridotites in Germany, but some deposits with lower olivine contents mainly in the areas of former volcanic activity as the Eifel, the Rhoen and the Northern Hessian Depression. The olivine occurs as and in corresponding gangue rocks, dolerites, in olivine bearing basalts, olivine , “olivine-bombs”, and as xenoliths. The “olivine bombs” in the Eifel can contain nearly pure olivine, whereas the olivine basalts and normally contain up to 10% or a minimum of 10% of olivine, respectively [16]. One sample from Japan has also been analyzed as Japan is the second-largest producer of peridotites for comparison of European olivine sources with worldwide deposits. The sample comes from the Horoman Mine in the Hidaka Province in Hokkaido. Chemical and mineralogical characterization steps are conducted to establish a basis for a proper assessment of the suitability of primary raw materials from various deposits. To provide the background behind the evaluation of the collected mineral samples as proper input materials for the carbonation in an autoclave, the mineralogical composition of an Italian olivine sample before and after the process serves as an example and it is presented in more detail. Nevertheless, the full extent of process-related parameters as well as further information on both the autoclave reactor and executed experiments are mentioned in prior publications focusing on the process performance [1,17].

3. Results—Characterization Olivine bearing samples from Norway, Greece, Italy, Turkey, Japan and basalt samples from Germany have been analyzed by XRF and qualitative and semi-quantitative XRD. As in the reaction for the sequestration of carbon dioxide (Figure3), magnesium silicate reacts with carbon dioxide to magnesite and silica, the magnesium oxide content of the samples has been used as an indicator for their carbonation potential. Minerals 2019, 9, 485 6 of 12 Minerals 2019, 9, x FOR PEER REVIEW 6 of 12

FigureFigure 3. 3. FormulaFormula for for the theexothermic exothermic reaction reaction of olivin ofe olivine(forsterite) (forsterite) with carbon with dioxide carbon (mineral dioxide (mineralsequestration). sequestration). 3.1. Analysis of the Chemical Composition 3.1. Analysis of the Chemical Composition BeforeBefore the the analysis analysis ofof the olivine olivine bearing bearing samples samples of ofdifferent different origin origin and andbasalt basalt samples samples by byX-ray X-ray fluorescence fluorescence (XRF) (XRF) technique technique using a usingPW2404 a device PW2404 (Malvern device PANalytical (Malvern B.V., PANalytical Eindhoven, B.V., Eindhoven,Netherlands), The the Netherlands), given mineralthe samples given mineralwere fused samples to glass were disks fused by a toClaisse glass LeNeo disks instrument by a Claisse LeNeo(Malvern instrument PANalytical (Malvern B.V., PANalyticalEindhoven, Netherlands). B.V., Eindhoven, The respective Netherlands). deviations The respective of the determined deviations ofvalues the determined are not further values mentioned are not further to enhance mentioned the readability to enhance since the the readability measuring since inaccuracy the measuring of the inaccuracyresulting ofvalues the resulting resides valuesbelow resides 0.3% belowfor main 0.3% components for main components and 1.0% andfor 1.0%trace for elements. trace elements. As Aspreparation preparation method method grinding grinding by by roller roller mill mill and and wet wet sieving sieving to toa fraction a fraction below below 63 63µmµ mhave have been been usedused to to produce produce a a narrow narrow and and precise precise particleparticle range.range. AsAs a firsta first indicator indicator to to decide decide whetherwhether thethe examinedexamined minerals minerals exhibit exhibit promising promising carbonation carbonation potential,potential, the the chemical chemical composition composition (Table (Table1 )1) may may be be compared: compared: SiO22, ,Fe Fe2O2O3, 3and, and MgO MgO are are the the main main componentscomponents for for all all olivine olivine samples samples analyzed.analyzed. Furthe Furthermore,rmore, the the share share of of thes thesee major major constituents constituents is is fairlyfairly even even with with detected detected amounts amounts between between 46–50 46–5 wt.0 wt. % for% for silica, silica, 7–10 7–10 wt. wt. % for% for ferric ferric oxide oxide and and 35–43 35–43 wt. % for magnesia. Both the CaO and Al2O3 content of all olivine samples fall below 1 wt. %, wt. % for magnesia. Both the CaO and Al2O3 content of all olivine samples fall below 1 wt. %, except except for the Italian mineral, which exhibits a value of 2 wt. %. Further components as TiO2, K2O, for the Italian mineral, which exhibits a value of 2 wt. %. Further components as TiO2, K2O, Na2O, Na2O, and NiO do not significantly exceed detected amounts of 1 wt. %. and NiO do not significantly exceed detected amounts of 1 wt. %. The German Basalt sample exhibits a comparable composition regarding SiO2 and Fe2O3. Since The German Basalt sample exhibits a comparable composition regarding SiO and Fe O . Since the the CaO content of about 10 wt. % does not compensate for the comparatively2 low MgO2 3amount, CaO content of about 10 wt. % does not compensate for the comparatively low MgO amount, both both components considered to function as educts for the carbonation process [18] are components considered to function as educts for the carbonation process [18] are underrepresented in underrepresented in this comparison. this comparison. Table 1. Chemical composition of the examined mineral samples. Table 1. Chemical composition of the examined mineral samples. Component Olivine Basalt (wt. %) Italy Norway GreeceOlivine Turkey Japan Basalt Germany Component (wt. %) SiO2 47.5 Italy48.6 Norway46.2 Greece Turkey47.4 Japan50.5 Germany 49.7 Al2O3 2.6 0.5 0.4 0.4 0.8 13.0 Fe2O3 SiO2 10.5 47.57.8 48.6 8.4 46.2 47.49.6 50.58.1 49.7 10.5 Al O 2.6 0.5 0.4 0.4 0.8 13.0 TiO2 2 30.1 0.0 0.0 0.0 0.0 1.5 CaO Fe2O3 2.1 10.50.2 7.80.5 8.4 9.60.4 8.10.8 10.5 9.8 MgO TiO2 35.3 0.141.1 0.043.6 0.040.3 0.0 0.038.0 1.5 9.0 CaO 2.1 0.2 0.5 0.4 0.8 9.8 K2O 0.2 0.1 0.1 0.0 0.0 1.4 MgO 35.3 41.1 43.6 40.3 38.0 9.0 Na2O 0.1 0.0 0.0 0.1 0.1 4.4 K O 0.2 0.1 0.1 0.0 0.0 1.4 NiO 2 1.0 1.2 0.2 1.2 1.0 0.0 Na2O 0.1 0.0 0.0 0.1 0.1 4.4 NiO 1.0 1.2 0.2 1.2 1.0 0.0 3.2. Examination of the Present Mineral Phases

3.2. ExaminationX-ray diffraction of the Present (XRD) Mineral method Phases has been applied using a Bruker D8 Advance device in Bragg–Brentano geometry equipped with LynxEye detector (Bruker AXS, Karlsruhe, Germany), X-ray diffraction (XRD) method has been applied using a Bruker D8 Advance device in Bragg–Brentano geometry equipped with LynxEye detector (Bruker AXS, Karlsruhe, Germany),

Minerals 2019, 9, 485 7 of 12

CuKα tube, and filter, in order to investigate the mineralogical composition. The chosen XRD parameters include a measurement range from 5–90◦ 2θ in 0.02◦ steps at 2 s per step. MineralsTo enable 2019, 9, ax comparisonFOR PEER REVIEW of the present mineral phases, as indicated by the components detected7 of 12 via the XRF technique. As this study focusses on natural resources, which are subject to fluctuations, CuKα tube, and nickel filter, in order to investigate the mineralogical composition. The chosen XRD the performance of a semi-quantitative analysis of the mineral phase composition is considered to be parameters include a measurement range from 5–90° 2θ in 0.02° steps at 2 s per step. sufficient for the aimed process suitability evaluation. To enable a comparison of the present mineral phases, as indicated by the components detected viaWithin the XRF the technique. given accuracy As this range,study focusses Table2 provides on natural information resources, regardingwhich are subject the main to mineralfluctuations, phase fractions,the performance as detected of a in semi-quantitative the olivine samples, analysis which of the includes mineral forsterite, phase composition , lizardite, is considered and, to in be case of thesufficient Italian for olivine the aimed sample, process . suitability evaluation. UnlikeWithin the the analysis given accuracy of the chemical range, Table composition, 2 provides the information examination regarding of the present the main mineralogical mineral phasesphase reveals fractions, significant as detected diff erences,in the olivine which samples, were primarily which includes caused forsterite, by the presence enstatite, of lizardite, larger enstatite and, fractions.in case of The the largest Italian shares olivine of sample, forsterite tremolite. are found in olivine samples from Norway, Turkey, and Japan (75–80%Unlike each); the the analysis Greek of and the chemical Italian olivine composition, samples the exhibitexamination 65–70% of the and present 55–60% mineralogical of forsterite, respectively.phases reveals Therefore, significant all ofdifferences, the examined which olivine were samplesprimarily constitute caused by promising the presence potential of larger in the carbonationenstatite fractions. process. ForThe purposes largest shares of comparison, of forsterite the mineralogicalare found in compositionolivine samples of the from German Norway, basalt sampleTurkey, is takenand Japan into (75–80% account additionally,each); the Greek but and the Italian comparatively olivine samples low magnesia exhibit 65–70% amount and given 55–60% in the XRFof resultsforsterite, also respectively. reflects in a ratherTherefore, small all forsterite of the examined fraction of olivine 10–15%. samples constitute promising potential in the carbonation process. For purposes of comparison, the mineralogical composition of theTable German 2. Mineralogicalbasalt sample compositionis taken into byaccount semi-quantitative additionally, examination but the comparatively of the present low mineralmagnesia amountphase given fractions. in the XRF results also reflects in a rather small forsterite fraction of 10–15%.

Olivine Basalt TableMineral 2. Mineralogical Phase Fraction composition (%) by semi-quantitative examination of the present mineral phase fractions. Italy Norway Greece Turkey Japan Germany

Forsterite 55–60 75–80Olivine 65–70 75–80 75–80 10–15Basalt Mineral Phase Fraction (%) EnstatiteItaly 15–20 Norway 10–15 Greece 25–30 10–15Turkey 20–25Japan Germany - Lizardite 5 5 5 5 - - Forsterite 55–60≤ 75–80≤ 65–70≤ ≤75–80 75–80 10–15 Tremolite 10–15 - - - - - Enstatite 15–20 10–15 25–30 10–15 20–25 - Lizardite ≤5 ≤5 ≤5 ≤5 - - In a complementaryTremolite step of the present10–15 study,- first carbonation- experiments- have - been conducted,- autoclaving a previously milled and sieved olivine bearing sample material from Italy within a fraction In a complementary step of the present study, first carbonation experiments have been of 20–63 µm. For these tests, a rocking batch autoclave was operated at 175 C and 100 bars in an conducted, autoclaving a previously milled and sieved olivine bearing sample◦ material from Italy aqueous solution (S/L ratio of 0.2 g/ml) and a CO -rich gas phase from 0.5 to 12 h [1]. Figure4 compares within a fraction of 20–63 µm. For these tests, a2 rocking batch autoclave was operated at 175 °C and the X-ray powder diffractograms of the initial olivine sample (l.) and the product (r.). Apparently, 100 bars in an aqueous solution (S/L ratio of 0.2 g/ml) and a CO2-rich gas phase from 0.5 to 12 h [1]. theFigure main 4 mineralogical compares the phaseX-ray powder changes diffractograms from forsterite of to the magnesite, initial olivine whereas sample the (l.) further and the components product undergo(r.). Apparently, only minor the modification main mineralogical due to phase the autoclave changes from process. forsterite The presenceto magnesite, of magnesite whereas the after processingfurther components indicates the undergo successful only carbonationminor modification of the input due to material. the autoclave process. The presence of

Figure 4. X-ray diffraction (XRD) analysis of Italian olivine sample; initial state (left) and carbonation product (right)[1]. Figure 4. X-ray diffraction (XRD) analysis of Italian olivine sample; initial state (left) and carbonation product (right) [1]. Minerals 2019, 9, 485 8 of 12

To highlight the contained mineral phase fractions, a semi-quantitative analysis of the X-ray powder diffractograms, as illustrated in Figure4, is performed by pattern fitting via “ Diffrac.Suite Topas” software (version 5.0, Bruker AXS, Karlsruhe, Germany): As presented in Table3, the fractions of enstatite and lizardite are found to be rather unaffected by the carbonation process, but the amount of forsterite that is present in the semi-quantitative examination has decreased in the order of approximately 20% after the reaction with carbon dioxide, which facilitates the formation of magnesite. The formed fraction of magnesite, about 30%, is also based on the conversion of tremolite, which shows a decrease of approximately 10%.

Table 3. Semi-quantitative examination of the present mineral phase fractions in Italian olivine before and after carbonation.

Olivine (Italy) Mineral Phase Fraction (%) Input Material Carbonation Product Forsterite 55–60 35–40 Enstatite 15–20 15–20 Lizardite 5 5 ≤ ≤ Tremolite 10–15 5 ≤ Magnesite 25–30

Tremolite bears certain risks to health due to its possible occurrence as respirable fibers. Tremolite is characterized by repeating double chains of silica tetrahedral, which is causative for its fibrous habit [19]. The fibrous form of the amphibole tremolite is considered to be of aggravated risk due to its raised bio-persistence compared to chrysotile, which exhibits enhanced bio-solubility in direct comparison. [20,21] While considering these facts, a potential decomposition of natural asbestos could be a significant side effect of the carbonation process. As stated by Ryu et al., the direct aqueous carbonation of tremolite fibers, forming reaction products as calcite, and the triggered morphological modification to a rhombohedral habitus may reduce or even eliminate the hazardous character of tremolite [22]. Still, the investigation by Scanning Electron Microscopy (LEO Type 440i, Leo Electron Microscopy, Cambridge, UK) reveals acicular material (Figure5), which makes the careful handling of these materials indispensable. It is also indicated that the given carbonation parameters are not capable of enabling a complete reaction process from tremolite to magnesite. Nevertheless, fibrous tremolite has not been observed in the Italian olivine samples, which does not exclude this material from subsequent processing and analysis steps. The results of the quantitative modal determination via QEMSCAN® are shown in Figure6, enabling a phase assignment to olivine, orthopyroxene, and clinopyroxene (Table4), which leads to a classification of the investigated samples via QAPF (, Alkali , Plagioclase, Feldspathoid diagram).

Table 4. Quantitative analysis by QEMSCAN® of four different samples of olivine bearing rocks from Europe.

Vol. % in Sample Mineral Phase Fraction Thermolith Grecian Magnesite Steinsvik Nuova Cives Olivine 67.36 52.21 79.80 59.08 Orthopyroxene 25.93 18.86 11.98 18.98 Clinopyroxene 2.23 3.38 0.89 8.76 Others 4.48 25.55 7.33 13.18 Minerals 2019, 9, x FOR PEER REVIEW 8 of 12

To highlight the contained mineral phase fractions, a semi-quantitative analysis of the X-ray powder diffractograms, as illustrated in Figure 4, is performed by pattern fitting via “Diffrac.Suite Topas” software (version 5.0, Bruker AXS, Karlsruhe, Germany): As presented in Table 3, the fractions of enstatite and lizardite are found to be rather unaffected by the carbonation process, but the amount of forsterite that is present in the semi-quantitative examination has decreased in the order of approximately 20% after the reaction with carbon dioxide, which facilitates the formation of magnesite. The formed fraction of magnesite, about 30%, is also based on the conversion of tremolite, which shows a decrease of approximately 10%.

Table 3. Semi-quantitative examination of the present mineral phase fractions in Italian olivine before and after carbonation.

Mineral Phase Fraction Olivine (Italy) (%) Input Material Carbonation Product Forsterite 55–60 35–40 Enstatite 15–20 15–20 Lizardite ≤5 ≤5 Tremolite 10–15 ≤5 Magnesite 25–30

Tremolite bears certain risks to health due to its possible occurrence as respirable fibers. Tremolite is characterized by repeating double chains of silica tetrahedral, which is causative for its fibrous habit [19]. The fibrous form of the amphibole tremolite is considered to be of aggravated risk due to its raised bio-persistence compared to chrysotile, which exhibits enhanced bio-solubility in direct comparison. [20,21] While considering these facts, a potential decomposition of natural asbestos could be a significant side effect of the carbonation process. As stated by Ryu et al., the direct aqueous carbonation of tremolite fibers, forming reaction products as calcite, and the triggered morphological modification to a rhombohedral habitus may reduce or even eliminate the hazardous character of tremolite. [22] Still, the investigation by Scanning Electron Microscopy (LEO Type 440i, Leo Electron Microscopy, Cambridge, UK) reveals acicular material (Figure 5), which makes the careful handling of these materials indispensable. It is also indicated that the given carbonation parameters are not capable of enabling a complete reaction process from tremolite to magnesite. Nevertheless, fibrous Minerals 2019 9 tremolite, , 485has not been observed in the Italian olivine samples, which does not exclude this material9 of 12 from subsequent processing and analysis steps.

Minerals 2019, 9, x FOR PEER REVIEW 9 of 12

Figure 5. Acicular tremolite as found within the microstructure investigation of an olivine sample after carbonation.

The results of the quantitative modal determination via QEMSCAN® are shown in Figure 6, Figure enabling 5. Acicular a phase tremoliteassignment as to found olivine, within orthopyroxene, the microstructure and clinopyroxene investigation (Table of 4), an which olivine leads sample to a classification of the investigated samples via QAPF (Quartz, Alkali Feldspar, Plagioclase, after carbonation. Feldspathoid diagram).

® Figure 6.FigureQuantitative 6. Quantitative Modal Modal determination determination by by QEMSCANQEMSCAN® (A() AThermolith) Thermolith (B) Grecian (B) Grecian Magnesite Magnesite (C) Steinsvik(C) Steinsvik (D) Nuova (D) Nuova Cives. Cives.

Table 4. Quantitative analysis by QEMSCAN® of four different samples of olivine bearing rocks from Europe.

Vol. % in Sample Mineral Phase Fraction Thermolith Grecian Magnesite Steinsvik Nuova Cives Olivine 67.36 52.21 79.80 59.08 Orthopyroxene 25.93 18.86 11.98 18.98 Clinopyroxene 2.23 3.38 0.89 8.76 Others 4.48 25.55 7.33 13.18

Minerals 2019, 9, 485 10 of 12 Minerals 2019, 9, x FOR PEER REVIEW 10 of 12

Mineralogically, the olivine bearing materials tested for the CO2MIN project are neither pure olivine nor dunites, but peridotites, more preciselyprecisely harzburgites oror lherzoliteslherzolites (Figure(Figure7 7).).

Figure 7. Classification of ultramafic rocks (QAPF) based on the proportion of olivine, orthopyroxene, Figureand clinopyroxene 7. Classification [23]. of ultramafic rocks (QAPF) based on the proportion of olivine, orthopyroxene, and clinopyroxene [23]. 4. Discussion 4. Discussion As shown by the example of olivine samples within the present study, many parts of Europe, and alsoAs shown Asia, possess by the example mineral resourcesof olivine that samples are capable withinof the significant present study, carbon many dioxide parts sequestration. of Europe, Vicariouslyand also Asia, for possess regions mineral not exhibiting resources such that olivineare capable deposits, of significant a basalt carbon sample dioxide from Germanysequestration. was Vicariouslyalso taken into for consideration,regions not exhibiting which merely such olivine contained deposits, minor a basalt fractions sample of magnesia-rich from Germany phases was also that weretaken foundinto consideration, to have larger which relevance merely within contained the evaluationminor fractions of the ofminerals’ magnesia-rich carbonation phases that potential. were foundNevertheless, to have countries, larger suchrelevance as Germany, within exhibitthe eval secondaryuation of resources the minerals’ as steel slags,carbonation fly ashes, potential. and filter Nevertheless,ashes bearing countries, potential forsuch CO as2 Germany,sequestration exhibit due secondary to their high resources CaO content. as steel Kelemenslags, fly etashes, al. have and filterpointed ashes out bearing that mantle potential peridotite for CO is2 capablesequestration of consuming due to their more high than CaO one content. billion tons Kelemen of CO et2 per al. haveyear, inpointed Oman out alone, that forming mantle reactionperidotite products is capable as MgCO of consuming3 and CaCO more3 by than an industrial one billion acceleration tons of CO of2 pernatural year, peridotite in Oman weathering alone, forming [18]. reaction products as MgCO3 and CaCO3 by an industrial accelerationWhich ofof thenatural magnesia-rich peridotite phasesweathering constituting [18]. the main parts of the examined olivine samples, forsteriteWhich or of enstatite, the magnesia-rich exhibits the phases better performanceconstituting th withine main the parts carbonation of the examined process olivine and whether samples, the forsteritemere presence or enstatite, of further exhibits mineral the phases better aff perfectsormance the overall within carbonation the carbonation potential, process has to be and investigated whether thein future mere studies.presence Although of further the mineral complete phases carbonation affects ofthe a syntheticoverall carbonation magnesia material potential, to magnesitehas to be investigatedin a previous in step future of the studies. study Although proves the the capability complete of carbonation the process, of the a esyntheticffects hindering magnesia or material slowing todown magnesite the carbonation in a previous reaction step of magnesiaof the study containing proves phases the capability as Enstatite of havethe process, to be understood the effects in hinderingdetail. [1] However,or slowing at thisdown stage the ofcarbonation the project, reaction the first resultsof magnesia that were containing gathered phases by Stopic as Enstatite et al. are havepointing to be to understood forsterite as in the detail. more [1] reactive However, mineral at th phaseis stage within of the the project, carbonation the first process, results that as shown were gathered by Stopic et al. are pointing to forsterite as the more reactive mineral phase within the carbonation process, as shown by the processing and examination of e.g., Norwegian and Italian

Minerals 2019, 9, 485 11 of 12 by the processing and examination of e.g., Norwegian and Italian olivine samples [1,17]. The next steps are the comparison of the products after carbonation of selected input material, separation of the carbonation products, and also the investigation of residual materials, like slags, fly ash, and red mud as the possible input materials for the sequestration process.

Author Contributions: D.K. performed the geological mapping and was responsible for the preparation of the olivine materials (grinding, sieving) and co-wrote the paper; S.E. supervised and evaluated the XRF- and XRD-analyses and co-wrote the paper with R.T.; J.B. investigated the geology of olivine deposits; P.B. co-wrote the paper, K.M.H. procured the samples for lab tests and characterization and co-wrote the paper; H.W. co-wrote the paper. Funding: The authors are grateful for the financial support within the CO2MIN project which was funded by BMBF (Federal Ministry of Education and Research), project number: 033RCO14B. Acknowledgments: For the continuous support and cooperation, we would like to thank our project partners Srecko Stopic and Christian Dertmann, IME, Andreas Bremen, AVT and Hesam Ostovari, LTT, RWTH Aachen, Till Strunge, IASS Potsdam and Pol Knops, Green Minerals. Conflicts of Interest: The authors declare no conflict of interest.

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