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| Effect of Mg-Al-CO3 LDH on adsorption and migration of cadmium in soil in the presence of conventional cations |
| Received:February 28, 2019 |
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| KeyWord:soil;Layered Double Hydroxide;cadmium;adsorption;migration |
| Author Name | Affiliation | E-mail | | WANG Yu-huan | College of Environmental Science and Engineering, Qingdao University, Qingdao 266071, China | | | LIN Qing | College of Environmental Science and Engineering, Qingdao University, Qingdao 266071, China | | | XU Shao-hui | College of Environmental Science and Engineering, Qingdao University, Qingdao 266071, China | shhxu@qdu.edu.cn |
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| Abstract: |
| Although Na+, K+, Ca2+ and Mg2+ are the main cations in soil water, coexisting with heavy metal pollutants in soil, Layered Double Hydroxide (LDH)is a common mineral component in soil. How Na+, K+, Ca2+ and Mg2+ affect the behavioral processes of heavy metal pollutants in a soil under coexistence conditions is a scientific issue that needs further exploration. By using batch static adsorption experiments, adsorption kinetics experiments and soil column migration experiments, the adsorption and transport process of cadmium in soil was examined when different cation species were used for LDH. The pseudo-second-order kinetic model, the Elovich model and the intra-particle diffusion model were used to examine differences in our experimental data; all samples were analyzed using infrared spectroscopy and Xray diffraction analysis to explore adsorption mechanisms. Results show that:The presence of Mg-Al-CO3 LDH increased soil pH, and Mg-Al-CO3 LDH contained a large amount of CO32-; the adsorption capacity of soil for heavy metal cadmium was also enhanced. When cation species differ, the adsorption capacity of soil for heavy metal cadmium also differs, and the higher the cationic valence is, the smaller is the amount of adsorption. The pseudo-second-order kinetic model fitted the data well, having R2 levels ≥ 0.999. The Elovich model fitted L soil adsorption kinetics better than natural soil, and results from the intra-particle diffusion model indicated that the rate of soil adsorption to Cd2+ was controlled by the combination of liquid membrane diffusion, interparticle diffusion and chemical reaction. Different cation types had different effects on the adsorption of Cd2+ by soils, and the migration of Cd2+ increased with the valence of background cations; Mg-AlCO3 LDH could inhibit the migration of Cd2+. Infrared spectroscopy and X-ray diffraction analysis results indicate that the adsorption mechanism of Cd2+ by Mg-Al-CO3 LDH is predominantly Cd2+ reacting with CO32- to form CdCO3 precipitate. Results from this study show that the adsorption mechanism of Mg-Al-CO3 LDH on different cations differs, thereby affecting adsorption and migration of cadmium in soil. |
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