Abstract: Desorption kinetics of Cu(II) and Pb(II) in two paddy soils and effects of citric and tartaric acids on desorption of Cu(II) and Pb(II) were investigated with a batch method.Results show that although much more Pb(II) than(Cu(II)) was adsorbed by the soils,more Cu(II) than Pb(II) was desorbed in either single metal system or bi-metal system.The findings suggest that the greater the adsorption affinity of a soil for a heavy metal,the more difficult the desorption of the heavy metal from the soil.The Elovich equation (Q_t =a+blnt) can be used to fit the kinetics data with fairly satisfactory results,which indicates that the desorption rate of Cu(II) and Pb(II) decreased sharply with the time going on.Constant b in the Elovich equation can be used to compare desorption rates in different systems.The desorption rate of Cu(II) was greater than that of Pb(II).The presence of citric and tartaric acids increased desorption of heavy metals in both quantity and rate,especially Cu(II). The effect of citric acid was greater than that of tartaric acid.

Key words: Cu(II), Pb(II), desorption kinetics, organic acid, paddy soil