tense experimental work concerning toxic metal adsorption
The adsorption of toxic heavy metal cations, i.e., Cu(II), on hydrous-oxide-type well-characterized particulates (6, 7) Cd(II), and Pb(II), on red muds has been modeled with the aid and corresponding modeling of sorption (8, 9, 10) have been of a modified Langmuir approach assuming single-site adsorption carried out. Although these models were effective, they could and of a double-site binding model incorporating the effect of pH. not explain heavy metal adsorption onto heterogeneous sor-For equilibrium concentrations of metal solutions between 0.03 bents composed of various hydrated oxides since these would and 5.8 mmol.dm 03 and equilibrium pH between 4.4 and 5.6, admore usefully serve as model sorbents exhibiting metal adsorption equilibrium constants corresponding to single-and dousorption and desorption onto and from soil layers through ble-site binding were found by linear and nonlinear least-squares which contaminated groundwater would flow (4). Thus mobiapproximation, respectively, and the double-site model was shown to conform better to experimental data. The contributions of the lization of toxic heavy metals across a contaminated zone by monomeric and dimeric hydroxo-complexes of Cu(II) to total copfixation and migration would be better predicted. per adsorption at a fixed pH were also investigated. The Langmuir Bentonite clay, amorphous iron oxide, hydrous mangaparameters of adsorption were found with the aid of the linearized nese(IV) oxide, and humic acid were chosen as possible Langmuir isotherm. This work aims to clarify heavy metal adsorpconstituents of composite sorbents simulating various types tion behavior on composite sorbents consisting of hydrated oxides. of soil, and the distribution coefficients of heavy metals ᭧ 1998 Academic Press between geochemical solid and aqueous phases were deter-