1. Se(IV)/Se(VI) sorption on illite du Puy Breynaert, E.; Bruggeman, C.; Vancluysen, C.; Dom, D.; Maes, A. Katholieke Universiteit Leuven, Center for Surface Chemistry and Catalysis, Kasteelpark Arenberg 23, B-3001 Leuven, Belgium Illite du Puy Se(VI) [SeO 4 2- ] sorption on illite du Puy Se(IV) sorption on illite du Puy Conclusions Adsorption on short-term can be described based on 2 SPNE surface complexation model with ligand exchange Se(IV) adsorbs onto illite clay forming surface complexes, most likely with aluminol sites at clay platelet edges Acknowledgements: ONDRAF/NIRAS – TRANCOM II – FUNMIG Purification procedure grinding (ball mill) of the clay < 200 µm transformation to homo-ionic Na-form oxidation of organic matter (Kunze and Dixon, 1986) removal of free iron oxide (Kunze and Dixon, 1986) removal of carbonate (Van Reeuwijk, 1986) washing Size fractionation: < 2 µm, 2-50 µm, 50-200 µm Characterisation CEC 108 µEq/g 22 Na-CEC at neutral pH (7.05  0.07) 0.01 N NaCl, ~ 8 g/L, overnight specific surface BET surface area (N 2 ) :132.8  0.6 m²/g Micropore area (< 2 nm): 11.9 m²/g No significant sorption of selenate between pH 3 and 10 Solubility Solubility data agrees with data from Bradbury and Baeyens (2005). Ca concentration after purification may determine number of available sites Ca concentrations too low for CaSeO 3 precipitation Se(IV) sorption model BASIS: 2 SPNE model ( Bradbury and Baeyens, 1997 ). illite du Puy surface description with 2 amphoteric surface hydroxyl sites ╟S wa,I OH + H + ⇌ ╟S wa,I OH 2 + log k = 5.5 ╟S wa,I OH ⇌ ╟S wa,I O - + H + log k = -6.2 ╟S wb,I OH + H + ⇌ ╟S wb,I OH 2 + log k = 9.0 ╟S wb,I OH ⇌ ╟S wb,I O - + H + log k = -10.5 ╟S wa, I 4.5 x 10 -2 mol/kg ╟S wb, I 4.5 x 10-2 mol/kg Selenite speciation (Olin et al., 2005; Seby et al., 2001) SeO 3 -2 + H + ⇌ HSeO 3 - log k = 8.36 HSeO 3 - + H + ⇌ H 2 SeO 3 log k = 2.64 Selenite sorption model additions/changes - Small change in pK a value ╟S wb,I OH site ╟S wb,I OH + H + ⇌ ╟S wb,I OH 2 + log k = 8.2 - Addition of 2 extra minor surface sites to model the concentration dependent sorption behaviour ╟S wa,II 2 x 10 -6 mol/kg ╟S wb,II 4 x 10 -7 mol/kg ╟S wa,II OH + H + ⇌ ╟S wa,II OH 2 + log k = 4.5 ╟S wa,II OH ⇌ ╟S wa,II O - + H + log k = -6.2 ╟S wb,II OH + H + ⇌ ╟S wb,I OH 2 + log k = 9.5 ╟S wb,II OH ⇌ ╟S wb,II O - + H + log k = -10.5 - 2 types of reactions with charged and uncharged Se(IV) ╟S wa,I OH 2 + + HSeO 3 - ⇌ ╟S wa,I OH 2 HSeO 3 log k = 2.7 ╟S wa,II OH 2 + + HSeO 3 - ⇌ ╟S wa,II OH 2 HSeO 3 log k = 7.7 ╟S wb,I OH 2 + + HSeO 3 - ⇌ ╟S wb,I OH 2 HSeO 3 log k = 2.45 ╟S wb,II OH 2 + + HSeO 3 - ⇌ ╟S wb,II OH 2 HSeO 3 log k = 7.65 ╟S wa,I OH 2 + + H 2 SeO 3 ⇌ ╟S wa,I OH 2 H 2 SeO 3 + log k = 3.7 ╟S wa,II OH 2 + + H 2 SeO 3 ⇌ ╟S wa,II OH 2 H 2 SeO 3 + log k = 8.0 ╟S wb,I OH 2 + + H 2 SeO 3 ⇌ ╟S wb,I OH 2 H 2 SeO 3 + log k = 3.7 ╟S wb,II OH 2 + + H 2 SeO 3 ⇌ ╟S wb,II OH 2 H 2 SeO 3 + log k = 8.0 Se(IV) sorption on illite du Puy Short term (24u) adsorption edge (0.01M NaCl) Short term (24u) adsorption isotherm at pH 4 adsorption ~ f(pH, [Se]) classical anion sorption edge on oxidic surface adsorption (pH 4) ~ f([Se], I) (almost) linear isotherm independent of ionic strength