Abstract:Through batch equilibrium experiment, the isothermal adsorption characteristics of divalent lead (Pb2+) on complex colloid of humic acid and goethite including the influences of pH, ion strengths (IS), temperature and the co-ion Cd2+ were all investigated. The results showed that under same conditions of IS and temperature, the maximum adsorption amount (Smax) and adsorption equilibrium constant (k) both increased with pH increasing, indicating that the increase of pH enhanced adsorption process. Meanwhile, the isotherm process was best fitted by Langmuir equation.While Pb2+ equilibrium concentration was 124.7mg/L, the increasing degree of adsorption was greatest, up to 35mg/g. In addition, for complex colloid, Elovich equation was best for fitting Pb2+ adsorption kinetic process, involving equilibrium adsorption rate increasing with pH increasing. At constant pH and IS, increasing temperature, Smax, k and absolute value of free energy change (ΔGo) all increasing, suggesting increasing temperature was liable to promote adsorption reaction. Furthermore, the adsorption of complex colloid for Pb2+ also increased with increasing IS while temperature and pH were same. However, while Cd2+ coexisted, the whole complex colloid showed a slight decreasing trend for Pb2+ adsorption. but the competitive effect of Cd2+ for Pb2+ adsorption was not significantly observed.