Effect of organic matter and calcium carbonate on behaviors of cadmium adsorption-desorption on/from purple paddy soils

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• 作者：XiuLan Zhao ; Tao Jiang ; Bin Du
• 关键词：Cadmium ; Purple paddy soil ; Adsorption&ndash ; desorption ; Thermodynamic ; Organic matter ; Calcium carbonate
• 刊名：Chemosphere
• 出版年：March, 2014
• 年：2014
• 卷：99
• 期：Complete
• 页码：41-48
• 全文大小：581 K

文摘

Batch experiments and sequential extraction analysis were employed to investigate the effects of soil organic matter and CaCO₃ on the adsorption and desorption of cadmium (Cd²⁺) onto and from two purple paddy soils, an acidic purple paddy soil (APPS) and a calcareous purple paddy soil (CPPS). The Cd²⁺ adsorption isotherms on both soils could be well-described by the Langmuir and Freundlich equations. CPPS had a higher capacity and a stronger affinity for Cd²⁺ adsorption compared with APPS. The adsorption process of Cd²⁺ on APPS was dominated by electrostatic attractions, whereas the adsorption mechanism varied depending on the Cd²⁺ concentrations in equilibrium solutions on CPPS. At low equilibrium concentrations, the adsorption process was primarily specific adsorption, but nonspecific adsorption dominated at high equilibrium concentrations. Removal of organic matter decreased the amount of Cd²⁺ adsorption on both of the soils, slightly affected the Cd²⁺ desorption rate and exchangeable Cd (EXC-Cd) in APPS and increased the desorption rate and EXC-Cd in CPPS, suggesting that the effect of organic matter on Cd²⁺ adsorption-desorption depends on the soils. CPPS and APPS containing CaCO₃ exhibited higher adsorption amounts but lower desorption rates and lower proportions of EXC-Cd than those of their corresponding soils without CaCO₃, demonstrating that CaCO₃ played an important role in Cd²⁺ specific adsorption on soil. The changes in the thermodynamic parameters, including free energy (螖G⁰), enthalpy (螖H⁰) and entropy (螖S⁰), as evaluated by the Van鈥檛 Hoff equations, indicated that the adsorption was a spontaneous and endothermic process with the primary interaction forces of dipole interactions and hydrogen bonds on APPS, whereas both physical and chemical interactions dominated the adsorption on CPPS.