Modeling sorption of trace metals on natural sediments by surface complexation model

The potential possibility of the surface complexation models to describe the sorption of trace metals on natural sediments has been suggested since the late 1980s, which should be of natural importance to predict the bioavailability of trace metals in aquatic sediments. This possibility was tested based on 11 geographically and hydrologically diverse natural aquatic sediment samples. The sorption of Cu(II), Zn(II), Pb(II), and Cd(II) on these sediments was studied by both sorption isotherm and pH-edge sorption experiments. The experimental sorption data were fit well by the surface complexation model(the double-layer model). The linear free energy relationship (LFER) between the surface complexation constants (K-s) of trace metals on the sediments and the corresponding first-hydrolysis constants (K-*(1)) was observed, which could be expressed as log K-s = a log K-*(1) + b. The slope of the linear regression, a, was dependent on the sediment composition: a = 0.19TOC - 0.09Oxides + 1.31 (n = 11), where TOC (%) is the total organic carbon and Oxides (%) include reactive iron oxide, amorphous iron oxide, cryptocrystalline manganese oxide, and aluminum oxide. The results strongly suggest that the sorption of trace metals on natural sediments could be described reasonably by the surface complexation model and predicted potentially from the relationships between K-s and K-*(1) and the sediment composition.