MODELING SORPTION OF TRACE-METALS ON NATURAL SEDIMENTS BY SURFACE COMPLEXATION MODEL

The potential possibility of the surface complexation models to descri be the sorption of trace metals on natural sediments has been suggeste d since the late 1980s, which should be of natural importance to predi ct the bioavailability of trace metals in aquatic sediments. This poss ibility was tested based on 11 geographically and hydrologically diver se natural aquatic sediment samples. The sorption of Cu(II), Zn(II), P b(II), and Cd(II) on these sediments was studied by both sorption isot herm 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 comp lexation constants (K-s) of trace metals on the sediments and the corr esponding first-hydrolysis constants (K-(1)) was observed, which coul d 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 carbo n and Oxides (%) include reactive iron oxide, amorphous iron oxide, cr yptocrystalline manganese oxide, and aluminum oxide. The results stron gly suggest that the sorption of trace metals on natural sediments cou ld be described reasonably by the surface complexation model and predi cted potentially from the relationships between K-s and K-(1) and the sediment composition.