Adsorption studies of lead on lateritic minerals from aqueous media

Minerals produced by lateritic weathering have been exploited to evaluate their potential for the decontamination of lead ions from aqueous solutions and for understanding decontamination mechanism in nature. Various physico-chemical parameters such as selection of appropriate electrolyte, equilibration time, amount of adsorbent, concentration of adsorbate, effect of diverse ions and temperature were studied in order to simulate the best conditions in which the particular material could be used as an adsorbent. Maximum adsorption was observed at 0.005 mol L− 1 acid solutions (HNO3, HCl, and HClO4) using 0.2 g of adsorbent for 4.82 × 10− 5 mol L− 1 lead concentration in five minutes equilibration time. Studies show that the adsorption of lead decreases with the increase in the concentrations of all the acids. The adsorption data follows the Freundlich isotherm over the range of 2.41 × 10− 6–9.65 × 10− 4 mol L− 1 lead concentration. The characteristic Freundlich constants, i.e., 1/n=0.42±0.02 and K=0.57±0.01 mmol g− 1 have been computed for the sorption system. The sorption mean free energy from the Dubinin–Radushkevich isotherm is 13.96 ± 0.74 kJ mol− 1 indicating an ion-exchange mechanism of chemisorption. The uptake of lead increases with the rise in temperature (278–323K). Thermodynamic quantities, i.e., ΔG, ΔS, and ΔH also have been calculated for the system. The sorption process was found to be endothermic.