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

摘要

BACKGROUND: Pb(II) is common in both waste-waters and gas emissions. In developing countries, public health problems havebeen 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 onpurified kaolin equilibrates within 35 min. The enthalpy changes of Pb(II) adsorption on purified kaolin were 63.683, 20.488 and21.371 kJ mol~(-1)with entropy changes 262.250, 112.210 and 105.120 J mol~(-1) K~(-for solutions containing 50, 100 200 mgL~(-1)Pb(II) respectively, indicating an endothermic and spontaneous adsorption process. The desorption of Pb(II) from kaolinwas difficult with more than 85% Pb(II) removal. Based on X-ray diffraction (XRD) analysis, the Pb(II) adsorption on natural andpurified 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 optimumconditions for adsorption were: ionic strength = 0.01 mol L~(-1); pH>7.2; dosage=10 g L-1; temperature= 25°C; duration>16h (Ci = 80 mg L-1); and the optimum conditions for desorption were ionic strength = 0.1 mol L-1 and pH < 5.0.