Adsorption and Desorption Characteristics of Cadmium in Three Purplish Paddy Soils

[Objective] The research aimed to study the characteristics of cadmium adsorption and desorption in purplish paddy soil,providing scientific evidence for clarifying environmental fate of cadimium in purplish paddy soil.[Method]The batch method was used to study the characteristics of cadmium adsorption and desorption in three purplish paddy soils including an acidic purplish paddy soil(APPS),a neutral purplish paddy soil(NPPS) and a calcareous purplish paddy soil(CPPS).Langmuir equation and Freundlich equation were used to describe the adsorption data and the relationship between adsorption ability and basic properties of the tested soils were examined.[Result]The adsorption of cadmium in three paddy soils increasd with the increase of initial concentrations of cadmium in solution,with the highest adsorption ability being observed in CPPS.The amount of cadmium adsorbed by NPPS was slightly higher than that of APPS.The adsorption data of the soils could be well described with Langmuir equation and Freundlich equation.The desorption of cadmium from those soils increaseed with the increase of cadmium adsorbed by soils.Among them,the desorption rate of cadmium by CPPS was the lowest and the percentages of cadmium desorbed from APPS and NPPS were higher than 50%.There was close relationship between adsorption ability and basic properties of the tested soils and soil pH played an important role.No obvious relationship was found between the ability of cadmium adsorption and the content of amorphous iron and manganese oxide or clay.[Conclusion]CPPS had the strongest ability to fix cadmium,thus had greater buffer capacity to the exogenous input cadmium.And there was high environmental risk as exogenous cadmium was input into APPS and NPPS.Soil pH played an important role in controlling the behavior of cadmium adsorption and desorption in soils.