In this study, we provide a single model capable of describing the behavior of mercury(II) at two different solid/water interfaces. Mercury(II) sorption on amorphous ferric oxide (HFO) and α-SiO2 can be simulated using the surface complexation approach. In both cases, experiments are best reproduced when ternary surface complexes between the surface (≡S-OH0), Hg2+, OH- or Cl- are included in the model. Sorption or ternary surface complexes predominates in the case of α-SiO2. In addition, in the case of HFO, additional precipitation reactions of a nonideal Hg(OH)2-Fe(OH)3 solid solution are needed at high sorbate to sorbent ratios. The modeling leads to a new set of surface complexation constants for the interaction between Hg2+ and these oxide surfaces which are described by the following equilibria (298.15 K, I = 0M):
≡S–OH0 + Hg2+ ↔ ≡S–OHg+ + H+
with log KintSOHg+ = 6.9 ± 0.2 for HFO;
≡S–OH0 + Hg2+ + H2O ↔ ≡S–OHgOH0 + 2 H+
with log KintSOHgOH = -3.2 ± 0.1 for α-SiO2, log KintSOHgOH = -0.9 ± 0.2 for HFO; and
≡S–OH0 + Hg2+ + Cl− ↔ ≡S–OHgCl0 + H+
with log KintSOHgCl = 7.0 ± 0.1 for α-SiO2, log KintSOHgCl = 9.8 ± 0.4 for HFO.
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