常规阳离子存在时Mg-Al-CO<sub>3</sub> LDH对土壤中Cd吸附迁移的影响

王玉环; 林青; 徐绍辉

文章摘要

王玉环,林青,徐绍辉.常规阳离子存在时Mg-Al-CO₃ LDH对土壤中Cd吸附迁移的影响[J].农业环境科学学报,2019,38(9):2129-2137.

常规阳离子存在时Mg-Al-CO₃ LDH对土壤中Cd吸附迁移的影响

Effect of Mg-Al-CO₃ LDH on adsorption and migration of cadmium in soil in the presence of conventional cations

投稿时间：2019-02-28

DOI：10.11654/jaes.2019-0212

中文关键词: 土壤层状双氢氧化物 Cd 吸附迁移

英文关键词: soil Layered Double Hydroxide cadmium adsorption migration

基金项目:国家自然科学基金项目（41571214，41807010）

作者	单位	E-mail
王玉环	青岛大学环境科学与工程学院, 山东青岛 266071
林青	青岛大学环境科学与工程学院, 山东青岛 266071
徐绍辉	青岛大学环境科学与工程学院, 山东青岛 266071	shhxu@qdu.edu.cn

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中文摘要:

层状双氢氧化物（Layered double hydroxide，LDH）是土壤中常见的矿物组分，而Na⁺、K⁺、Ca²⁺和Mg²⁺更是土壤溶液中的主要阳离子，它们共存条件下对重金属污染物在土壤中的行为过程影响如何是一个需要探讨的科学问题。通过批量静态吸附实验、动力学实验和室内土柱迁移实验，研究不同阳离子与Mg-Al-CO₃ LDH共存时对重金属Cd在土壤中吸附迁移的影响。运用伪二级动力学模型、Elovich模型及内扩散模型对吸附动力学数据进行拟合，并对Mg-Al-CO₃ LDH吸附Cd前后的样品进行红外光谱分析及X射线衍射分析，以探究其吸附机理。结果表明：Mg-Al-CO₃ LDH的存在使土壤pH升高，且Mg-Al-CO₃ LDH含有大量CO₃^2-，使得土壤对Cd的吸附能力增强；阳离子类型不同时，无论土壤中是否含有LDH，其对Cd的吸附量均表现为阳离子价态越高，吸附量越小。伪二级动力学模型拟合效果非常好，R²均接近于1，说明土壤对Cd的吸附能力与吸附位点有关；内扩散模型拟合结果揭示土壤对Cd²⁺吸附的速率受液膜扩散、颗粒间扩散、化学反应等综合作用的控制。不同阳离子类型对Cd在土壤中吸附迁移的影响不同，Cd迁移能力表现为随背景阳离子价态升高迁移能力增强；Mg-Al-CO₃ LDH的存在抑制了Cd的迁移。红外光谱及X射线衍射分析表明，Mg-Al-CO₃ LDH对Cd²⁺的吸附机理主要为Cd²⁺与Mg-Al-CO₃ LDH上的CO₃^2-反应生成CdCO₃沉淀。Mg-Al-CO₃ LDH对不同阳离子的吸附机制不同，影响着重金属Cd在土壤中的吸附迁移过程。

英文摘要:

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 CO₃^2-; 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 CO₃^2- 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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