Adsorption and desorption behaviour of Pb(II) on a natural kaolin: equilibrium, kinetic and thermodynamic studies

BACKGROUND: Pb(II) is common in both waste-waters and gas emissions. In developing countries, public health problems have been reported concerning Pb(II) pollution, so that stringent measures are required to deal with it. MAJOR RESULTS: The adsorption and desorption behaviour of Pb(II) has been investigated on a natural Chinese kaolin. Several factors, including initial concentration, pH, equilibration time, dosage and temperature correlated positively with Pb(II) adsorption. The Pb(II) adsorption capacity of natural kaolin was 165.117 mg g(-1). A kinetic study shows that Pb(II) adsorption on purified kaolin equilibrates within 35 min. The enthalpy changes of Pb(II) adsorption on purified kaolin were 63.683, 20.488 and 21.371 kJ mol(-1) with entropy changes 262.250, 112.210 and 105.120 J mol(-1) K-1 for solutions containing 50, 100 and 200 mg L-1 Pb(II) respectively, indicating an endothermic and spontaneous adsorption process. The desorption of Pb(II) from kaolin was difficult with more than 85% Pb(II) removal. Based on X-ray diffraction (XRD) analysis, the Pb(II) adsorption on natural and purified kaolin was attributed mainly to the magnesite component and complexation with the mineral surface. CONCLUSIONS: Natural kaolin exhibits a satisfactory performance for adsorption of Pb(II) from aqueous solution. The optimum conditions for adsorption were: ionic strength = 0.01 mol L-1; pH >= 7.2; dosage = 10 g L-1; temperature = 25 degrees C; duration >= 16 h (C-i = 80 mg L-1); and the optimum conditions for desorption were ionic strength = 0.1 mol L-1 and pH <= 5.0. (c) 2009 Society of Chemical Industry