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

Wang, Xu, Li, Yueming, Mao, Na, Zhou, Yanqiu, Guo, Ping
Water, air, and soil pollution 2017 v.228 no.5 pp. 193
adsorption, cadmium, freeze-thaw cycles, iron oxides, lead, organic matter, pH, soil properties
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.