Sorption of lead on variable charged soils as affected by temperature and time in three Provinces of China

Effect of temperature and time on Lead (Pb) adsorption and affinity of the adsorbed Pb was evaluated in three acidic soils from China. The distribution coefficient increased slightly with increasing temperature up to 35 0C and then decreased at 450C.The increase of temperature was not favorable to sorption. The heat of reaction (△H) was positive (endothermic) at lower temperatures, while it was negative (exothermic) at higher temperatures. It was observed that there was an increase in the percent adsorption of Pb2+ within the first 8 min of the reaction and a decrease within 20 min of the reaction. The equilibrium was reached after 40min with 95.8 %, 87.4 % and 83.8 % for the Yellow brown soil (YBS), Latosol soil (LS) and Lateritic red soil (LRS) respectively. The analysis of images obtained by scanning electron microscope (SEM) with adsorbed Pb showed coverage of the surface with white layer (molecular cloud).