UNIVERSITA` degli STUDI di ROMA TOR VERGATA

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1 Carbonation of minerals and industrial residues for CO 2 storage: perspectives of application in energy generation systems 1 R. Baciocchi, 1 G. Costa, 2 M. Mazzotti, 3 A. Polettini, 3 R.Pomi, 2 V. Prigiobbe (1) University of Rome Tor Vergata, Italy (2) ETH, Swiss Federal Institute of Technology, Zurich, Switzerland (3) Sapienza, University of Rome, Italy

2 Outline Fundamentals of mineral carbonation Source of alkaline materials Process routes Mineral carbonation - Dissolution - Precipitation Carbonation of steel slags Conclusions and Challenges

3 Mineral carbonation MO + CO 2 MCO 3 + heat M = Calcium, Magnesium, Iron Issues stability of carbonates availability of alkalinity sources reactivity of alkaline materials

4 Mineral carbonation

5 Sources of metal oxide - Minerals Mg silicates are found in Ophiolite belt complexes US Klamath mountains: 3000 Gt A comprehenisve evaluation of available minerals still missing Olivine: Serpentine: Mg 2 SiO 4 + 2CO 2 2MgCO 3 + SiO2 Mg 3 Si 2 O 5 (OH) 4 + 3CO 2 3MgCO 3 + 2SiO 2 + 2H 2 O Wollastonite: CaSiO 3 + CO 2 CaCO 3 + SiO 2

6 Sources of metal oxide - Residues Steel Industry (60-80 MtCO 2 /y) Energy sector Steel slag AOD process slag Steel converter slag Lignite fly ash APC fly ash MSWI ash PF ash 100s MtCO 2 /y Cement industry Waste cement Cement Kiln Dust

7 Mineral carbonation

8 Mineral carbonation Process routes Gas-solid Single-step Multi-step without chemicals Aqueous Single-step salts with chemicals bicarb. acid / base swing Multi-step (ph swing) P/T swing chelant

9 Mineral carbonation: aqueous route Olivine Dissolution enhancers: -Strong acids, but precipitation difficult - weak acids / ligands, but precipitation possible -CO 2 promising compromise Mg 2 SiO 4 CO 2 MgCO 3 SiO Mg 2(am) 2 SiO CO 2 2 MgCO 3 + SiO 2(am)

10 Mineral carbonation: Experimental set-up Operating conditions Temperature: C CO 2 pressure: bar Particles size: µm ph 2-8 adjusted using P CO2, HCl, and LiOH Addition of NaCl and NaNO 3 Addition of Na 2 C 2 O 4 and Vessel: 300 ml Volume solution: 170 ml Flow rate: 2-10 ml min -1 Mass of olivine: mg Off-line analyses: Si and Fe measurements XRD SEM Na 3 C 3 H 5 O(CO 2 ) 3

11 Dissolution experiments - Olivine Activation energy: 25 C - Pokrovsky und Schott (2000) E A = 52.9 kj/mol Hänchen et al., Geochim. Cosmochim. Acta 70(2006)

12 Dissolution: effect effect of P CO2 and ligands at 120 C H2 C 2 O 4 HC 2 O - 4 C 2 O 2-4 pk 1 = 1.78, pk 2 = 4.95 Prigiobbe et al., CES. (2009), in preparation

13 Precipitation experiments MgCO 3 Magnesite MgCO 3 Barringtonite MgCO 3 2H 2 O Nesquehonite MgCO 3 3H 2 O Lansfordite MgCO 3 5H 2 O Artinite MgCO 3 Mg(OH) 2 3H 2 O Hydromagnesite (MgCO 3 ) 4 Mg(OH) 2 4H 2 O Dypingite (MgCO 3 ) 4 Mg(OH) 2 5H 2 O Initial conditions: Na 2 CO 3 + MgCl 2 solution Hydromagnesite Magnesite Hänchen et al., CES, 62 (2007)

14 Precipitation experiments - Olivine Hydromagnesite / Magnesite precipitation Supersaturation ratio no precipitation --- Hydromagnesite Magnesite Magnesite immediate precipitation T=120 C P(CO 2 )=100 bar Hänchen et al., CES, 62 (20

15 Carbonation of residues Costa et al., Env. Monit. Ass. 135 (2007)

16 Carbonation of residues Industrial residues are often associated with CO 2 point source emissions They also tend to be more unstable than geologically derived materials They require a lower degree of pre-treatment and less energy intensive conditions Carbonation may also be seen as a stabilisation process The leaching behaviour of alkaline residues may be improved by stabilisation OPC: ordinary Portland Cement PFA: pulvurized fly ash (coal fired power station) GGBS: Ground granulated Blast Furnace Slags MSWI-b: Muncipal Solid Waste Incineration (Bottom ash) MSWI-f: Muncipal Solid Waste Incineration (Fly ash) Costa et al., Env. Monit. Ass. 135 (2007)

17 Carbonation of stainless steel slags SSS investigated: mixture of the slag produced by the EAF and AOD units of a stainless steel manufacturing plant Particle size distribution wt.)100 finer particles (% wt.) ,01 0, grain size d (mm) (%) 50 A B D C d< <d< <d< <d<2000 grain size (µm) Sandy granular material with a high % of fines Class A was milled to < 425 µm Baciocchi et al. Envergy Procedia 1(2009)

18 Characterization of steel slags Elemental composition: Main constituents (% w/w) A

19 Experimental: carbonation experiments Set up 150 ml stainless steel reactor Thermostatic bath for temperature control 100% CO 2 flow humidified in the reactor with a salt solution 3 g of humidified SSS size fractions treated in each experiment Varied operational conditions Slag humidity (L/S): 0, 0.1, 0.15, 0.2, 0.4, 0.5, 0.6 l/kg Temperature: 30, 40, 50 C PCO 2 : 1, 3, 10 bar Experiment duration: 10, 20, 30, 1, 2, 4, 8, 24 h Evaluation of the CO 2 storage capacity of the residues Calcimetry analysis Effects of carbonation on material properties XRD analysis Leaching tests: EN and CEN

20 Results: carbonation tests Effect of L/S Effect of grain size CO2uptake (%) CO2uptake (%) unmilled milled L/S (l/kg) Class D, t = 2 h, T = 30 ⁰C and P = 3 bar maximum particle size (µm) t = 2 h, T = 50 ⁰C P = 3 bar and L/S = 0.4 l/kg Baciocchi et al. Envergy Procedia 1(2009)

21 Results: carbonation kinetics AOD residues only CO2 (%) P=1 bar P=3 bar P=10 bar t (ore) Increased CO 2 uptake due to the high reactivity of dicalcium silicate (C 2 S).

22 Results: effect on mineralogy MgO MgCr 2 O 4 Ca 12 Al 114 Fe 0.14 O 32 Ca 2 SiO 4 carbonated CaCO 3 CaMg(CO 3 ) θ( ) untreated Disappearance of MgOand MgCr 2 O 4 Significant reduction of Ca 12 Al 114 Fe 0.14 O 3 Decrease of Ca 2 SiO 4 Increase of CaCO 3 classd, carbonatedfor2 h at 50 ⁰C, P = 3 bar and L/S = 0.4 l/kg Baciocchi et al. Envergy Procedia 1(2009)

23 Results: effects on metal leaching Landfill leaching compliance test (EN ) 2) in mg/l A B untreated carbonated untreated carbonated untreated carbonated untreated carbonated ph Ca Cr Fe Mg Si Critical parametersfor untreated SSS inert landfill disposal and reuse: ph > 12 and Cr > 0.05 mg/l ph decrease for all fractions, more pronounced for class D Cr no significant effect (some reduction for B and C) C Significant Ca decrease and Si release in the eluate D Baciocchi et al. Envergy Procedia 1(2009)

24 Conclusions Pro - CO 2 stored in a safe and definitive manner - CO 2 storage potential basically unlimited - It can be done with existing technologies - Ca-silicates/Residues carbonation at relatively mild conditions - Industrial residues are a start-up option Cons - Energy penalty and associated costs still too high - Mg-silicates carbonation needs energy intensive pre-treatment - Many process issues still unresolved and needing optimization - Lack of demonstration units (pilot-scale)