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 alpha-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 of ternary surface complexes predominates in the case of alpha-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 = 0 M) : GRAPHICS with log K-=SOHgCl(int) = 7.0 +/- 0.1 for alpha-SiO2, log K-=SOHgCl(int) = 9.8+/- 0.4 for HFO.