The Adsorption Behavior of Pb2+ and Cd2+ in the Treated Black Soils with Different Freeze-Thaw Frequencies

摘要

Batch experiments were conducted to study the effect of freeze-thaw frequency on the adsorption behavior of Pb2+ and Cd2+ and its related mechanisms. The results indicated that the adsorption capacities of Pb2+ and Cd2+ to the freeze-thaw treated soil were lower than those to the unfrozen soil, and with increasing freeze-thaw frequency, the adsorption capacities of them decreased. These were attributed to the fact that freeze-thaw cycles reduced pH value, CEC, organic matter content, and free iron oxide content of soil, and these soil properties presented negative correlations with freeze-thaw frequency. Freeze-thaw cycles reduced specific adsorption capacities of Pb2+ and Cd2+ and enhanced nonspecific adsorption ratios of Pb2+ and Cd2+ compared with the unfrozen soil. The higher freeze-thaw frequency, the higher nonspecific adsorption ratio was. However, the relationship between specific adsorption capacities of Pb2+ and Cd2+ and freeze-thaw frequency was opposite. Furthermore, the adsorption processes to the unfrozen and freeze-thaw treated soils were spontaneous, for Pb2+, its adsorption to soil was endothermal process, for Cd2+, on the contrary.