Geochemical constraints in slag valorisation: The case of oxyanions and nanoparticles

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1 Geochemical constraints in slag valorisation: The case of oxyanions and nanoparticles Geert Cornelis, Tom Van Gerven, Carlo Vandecasteele, Jason. K. Kirby, Mike J. McLaughlin

2 Oxyanions + 2+ O O Sb 5+, As 5+ Sb(OH) 6-, AsO 4 3-2

3 Oxyanions 3

4 Oxyanions Arsenic As v O 3-4, As III O 3-3 Chromium Cr VI O 2-4, Cr III (OH) 0 3 Molybdenum Mo VI O 2-4 Selenium Se VI O 2-4, Se IV O 2-3 Antimony Sb V (OH) 6-, Sb III (OH) 0 3 Vanadium V V O 3-4, V IV O(OH) 20, V III (OH) 0 3 Tungsten W VI O 2-4 4

5 Oxyanions Have oxidation states that are oxyanionic Redox sensitive Enriched in many industrial wastes Legislation is recent for all except As and Cr MSWI residues Fossil Fuel Combustion residues Metallurgical slags Element Lithosphere Soils Bottom ash Fly ash APC * residues Coal bottom ash Coal fly ash FGD ** ash Blast furnace slag Steel slag Non-ferrous slags As < Cr Mo < Sb NA NA NA NA NA < Se NA NA 2 6 V W NA NA NA NA NA < Cornelis et al. 2008a 5

6 Solubility control Ca[Sb(OH) 6 ] 2 + Precipitation Adsorption Solid solution 6

7 Solubility control Log (Me) solid phase Density of Surface sites E B (Me) crystalline C A (Me) amorphous D A. Precipitation of an amorphous compound B. Precipitation of a crystalline compound C. Ageing D. Adsorption E. Solid solution Log (Me) aq Langmuir,

8 Adsorption Alkaline waste porewaters S C Fe 3+ Ca 2+ S C C S S C Adsorption Si Al 3+ Al 3+ 8

9 Precipiation Cornelis et al. 2008a 9

10 conc (mol/l) Knowledge gaps No knowledge of the redox speciation Errors in thermodynamic database Insufficient knowledge of possible interactions b Se VI Se IV ph For example: Se leaching from residue from physico-chemical treatment of wastewaters from Se production (Umicore) Cornelis et al. 2008b, J. Hazard. Mat. 159, Most critical elements: Se, Mo, Sb, V, (W) 10

11 Antimony 11

12 log(conc) (mol/l) Antimony in OPC paste Ca 2+ + Sb(OH) 6- = Ca[Sb(OH) 6 ] 2 logk sp = Experimental Sb leaching as a function of ph in a 1000 mg kg -1 spiked OPC paste -4-6 Model ph Ca 2+ + Sb(OH) 6- = CaSb(OH) + 6 logk ass = 2.15 Cornelis et al., Appl. Geochem. 26, Sb(OH) 6- interaction with CSH Monosulphate Portlandite Ettringite Log (Me) solid phase Density of Surface sites E B (Me) crystalline C A (Me) amorphous D Log (Me) aq 12

13 log Sb (sorbed) (mol/l) log Sb (sorbed) (mol/l) log Sb(sorbed) (mol/l) log Sb (sorbed) (mol/l) Antimony in OPC paste Adsorption isotherms Roméite y = 0,991x - 0,327 R² = 0,988 Ca[Sb(OH)6]2(a) Portlandite log Sb (aq) (mol/l) Roméite CaAlSb y = 1,027x + 0,675 R² = 0, log Sb (aq) (mol/l) -3-4 Roméite Roméite CaAlSb CSH Surface Adsorption Log (Me) solid phase Density of Surface sites E B (Me) crystalline Log (Me) aq C A (Me) amorphous D y = 0,974x - 0,414 R² = 0,98 Ettringite log Sb (aq) (mol/l) Monosulphate log Sb (aq) (mol/l) Solid solution formation 13

14 log Sb (sorbed) (mol/l) log Sb (sorbed) (mol/l) log Sb(sorbed) (mol/l) log Sb (sorbed) (mol/l) Antimony in OPC paste Sb K-edge EXAFS Afm phases: Stacked Ca 4 Al 2 (OH) 12+ layers Ca Roméite y = 0,991x - 0,327 R² = 0,988 Ca[Sb(OH)6]2(a) Portlandite log Sb (aq) (mol/l) Al Ca Roméite Ca CaAlSb y = 0,974x - 0,414 R² = 0,98 Ettringite log Sb (aq) (mol/l) Roméite y = 1,027x + 0,675 R² = 0,995 CSH log Sb (aq) (mol/l) Si Roméite Si Si CaAlSb AFm solid solution Monosulphate log Sb (aq) (mol/l) Ca 4 Al 2 [Sb(OH) 6 ] 2 (OH) 12.3H 2 O logk sp = 65.4 Ca 4 Al 2 (SO 4 )(OH) 12.26H 2 O 14

15 Romeite - structure Calcium antimonate = Romeite Low ph and [Ca] Vacancy High ph and [Ca] Cornelis et al., Appl geochem 26: CaO 8 SbO 6 XRD + Rietveld analysis EXAFS analysis 15

16 Antimony in OPC paste ph dependent leaching Ca[Sb(OH) 6 ] 2 = Ca Sb(OH) - 6 logk sp = Ca 1.13 Sb 2 O 6 (OH) xh 2 O H + = 1.13 Ca Sb(OH) 6- + xh 2 O logk sp =

17 Antimony in OPC paste Carbonation dependent leaching Carbonation: [Ca] decreases ph decreases Composition of rometie changes Sb becomes more soluble 17

18 log(sb) (mol/l) Antimony in bottom ash HPLC-ICP-MS -3 ph-dependent leaching -4-5 Sb(V) Sb(III) ph Carbonation -dependent leaching 18

19 Importance of precipitation Element Oxidation state Mechanism As V Calcium arsenate precipitation III Calcium arsenite precipitation Cr VI solid solution formation with AFt phases III Ca 2 Cr 2 O 5 precipitation Mo VI CaMoO 4 precipitation, solid solution formation with AFm-phases Se VI solid solution formation with AFt phases IV CaSeO 3 precipitation Adsorption to CSH Sb V Calcium antimonate precipitation III Sb 2 O 3 precipitation, adsorption to oxides, spinels V V Pb 2 (VO 4 ) 3 or Ca 3 (VO 4 ) 2 precipitation III W VI CaWO 4 precipitation III V(OH) 3 precipitation or contained in spinels Contained in spinels Solubility control by Calcium metalates Spinels for +III states Reduced states generally have lower solubilities 19

20 What can be done? ph and Ca-concentration needs to be high Ageing Slow cooling may e.g. Improve Cr III, V III, Sb III uptake in spinels Reduction to less soluble species In some cases accelerated carbonation combined with neoformation of iron oxides Log (Me) solid phase Density of Surface sites E B (Me) crystalline Log (Me) aq C A (Me) amorphous D 20

21 Nanoparticles Nanoparticles: having at least one dimension less than 100 nm 21

22 Absorbance Nanoparticles Heat of fusion (ΔH m ) and melting point of Sn nanoparticles (Auffan et al., 2009 Nature Nanotechnol. 4, ) nm 66 nm 183 nm ZnO 0.5 Gold nanoparticles of different size Wavelength nm UV absorption by ZnO nanoparticles of different size 22

23 Nanoparticles today 23

24 Nanoparticles today Carbon allotropes Metal and metal oxides 24

25 Environmental applications High strength cements using Carbon nanotubes, SiO 2, Cr 2 O 3, TiO 2 nanoparticles Fe 0 nanoparticles reducing solubility of CrO 4 2-, AsO 4 3-, organohalogens,... Films of SiO 2 and TiO 2 nanoparticles on slags Interest in: Geochemistry of nanoparticles Environmental fate and effect of nanoparticles 25

26 Aggregation Repulsion Repulsive electrostatic and steric forces Vs. Attractive Van der Waals Attraction 26

27 Aggregation Decrease in aggregation rate Increase in aggregation rate ph IEP High surface charge Ion adsorption Low surface charge Sedimentation Surface coating High ionic strength 27

28 Fate in solid matrices Dissolution 2. Sorption/aggregation 3. Plant bioaccumulation 4. Invertebrate accumulation and toxicity 5. Microbial toxicity 5 M n Direct particle uptake/toxicity 7. Particle migration 28

29 log(w -1 ) Fate in solid matrices homocoagulation AgNP + Fe 2 O 3 b heterocoagulation Fe 2 O AgNP NaClO 4 concentration (mm) Cornelis et al., Environ. Sci. Technol. 45,

30 Fate in solid matrices Dissolved Ag + Sandy soil: Retention time ~ K d Clayey soil: 30

31 Fate in solid matrices Colloid mediated Nanoparticle transport

32 Nanoparticles in slags/wastes? High ph High negative nanoparticle charge stability Most NP have coatings stability Ionic strength high mm whereas critical coagulation concentrations are generally < 100 mm Aggregation 32

33 Acknowledgments An Van Damme, Evelien Martens, Ozlem Cizer, Koen Van Balen, Michele Van Roelen, Herman Cooreman, Herman Mönch, Sebastiaan Marien, Erik Smolders, Fiend Degryse, Andreas Scheinost, Barbara Etschmann, Victoria Coleman, Catherine Fiebiger, Margaret Yam, Claire Wright, Casey Doolette, Madeleine Thomas, Shannon McCall, Conference organisers and sponsors THANK YOU 33