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Abstract: Sorption of selenium(IV) and silicic acid onto magnetite (Fe3O4) was investigated in binary systems, with concentrations of silicic acid under the solubility limit of amorphous silica. Using the double diffuse layer model (DDLM), surface complexation constants of selenium(IV) and H4SiO4 onto magnetite were extracted using Fiteql 4.0. Then, prediction curves of the sorption of selenium(IV) in the presence of silicic acid onto magnetite were obtained, using the calculated surface complexation constants. Finally, laboratory experiments were performed and showed a competition between selenium(IV) and silicic acid for the surface sites of magnetite. Experimental results matched the model predictions, confirming its ability to model qualitatively and quantitatively the ternary system. [Copyright &y& Elsevier]

Sorption of H4SiO4 (including experiments as a function of time, Kd measurement with different m/v ratios and sorption edges) onto different iron (hydro)oxides as goethite (α-FeOOH), hematite (α-Fe2O3), and magnetite (Fe3O4) has been studied with concentration of silicates under solubility limit. A surface complexation model has been used to account for sorption edge of silicates onto these iron oxide surfaces. It reveals that two types of surface complex namely ≡ FeH3SiO4 and ≡ FeH4SiO− 4, are needed to describe properly the experimental observations. [Copyright &y& Elsevier]