Evaluating the adsorption of Shanghai silty clay to Cd(II), Pb(II), As(V), and Cr(VI): kinetic, equilibrium, and thermodynamic studies

The adsorption properties of Shanghai silty clay (SSC) towards heavy metal ions Cd(II), Pb(II), As(V), and Cr(VI) were investigated by batch experiments. effects solid-solution ratio, pH, temperature, reaction time, concentration on sorption analyzed. In order to better understand the mechanisms, X-ray diffraction (XRD), scanning electron microscopy (SEM), fluorescence (XRF) used analyze soil specimen before after sorption. Three kinetic models three isotherm characteristics. Thermodynamic parameters including changes in Gibbs free energy (ΔG0), enthalpy (ΔH0), entropy (ΔS0) also calculated. Sorption capacity SSC was compared with other minerals reported literatures. results show that selectivity sequence is Pb(II) > Cd(II) As(V) Cr(VI), equilibrium capacities 26.46, 8.90, 2.80, 1.85 mg g−1, respectively. Adsorption largely effective surface rather than crystals. turns be flat slippery adsorption. Langmuir model shows best fit for data, while Freundlich more suitable Cr(VI). optimum ratios are 15, 6, 40, 40 g L−1, pHs 9.0, 6.0, 7.0, 2.0, pseudo-second-order found dominant mechanism these four SSC. For both particle diffusion film rate-limiting factors, whereas intraparticle rate-controlling factor. thermodynamic analysis reveals spontaneous endothermic system disorder increases, exothermic decreases. Compared most minerals, natural exhibits comparable thus can potentially as a landfill liner material retard migration metals.