Characteristics of Cd and Pb adsorption-desorption in paddy soils developed from various parent materials and its impacting factors

This study examined the characteristics of Cd and Pb adsorption-desorption in paddy soils(red and purple soils)and their relationships with soil physical and chemical properties. Results of this study could be beneficial for the understanding of Cd and Pb migration in soils and impacts of paddy soil types on Cd and Pb adsorption and desorption.The results showed that the adsorption data of Cd2+could be simulated with both Langmuir and Freimdlich models(r 0.95).In contrast, the adsorption data of Pb2+could be simulated using the Freimdlich equation(r 0.99). The adsorption capacities of two tested soil types both increased with the increasing concentrations of Cd2+, Pb2+. The desorption capacity was also on the increase in accordance to increased adsorption capacity. The maximum adsorption capacity of Cd2+-red soil, Cd2+-purple soil, Pb2+-red soil and Pb2+-purple soil were 2871.34 mg/kg, 4353.69 mg/kg, 10914.65 mg/kg and14249.07 mg/kg, respectively. As a result, the maximum desorption rate reached 3.12%, 2.43%, 1.02% and 0.33%respectively. While the adsorption capacity of Cd2+and Pb2+in the purple soil was greater than that of the red soil, the desorption rate was smaller. Furthermore, under the same heavy metal concentration, the adsorption of Pb2+in red soil and purple soil was higher than that of Cd2+. Soil clay, organic matter and CEC content were the major factors to control the differences of adsorption and desorption capacity between red and purple soils.