西南地区典型农田土壤中Cd^(2+)、Pb^(2+)的吸附特性研究

Adsorption Characteristics of Cd^(2+) and Pb^(2+) in Typical Agricultural Soils in the Southwest of China

为了解西南地区土壤对污染毒性较强的Cd和Pb元素的吸附过程及作用机制,针对性地为预防和治理土壤污染提供理论依据,采用批试验的方法研究了典型黄棕壤和紫色土对Cd^(2+)、Pb^(2+)的吸附动力学、等温吸附过程以及土壤有机质、溶液pH对吸附过程的影响。结果表明:土壤吸附Cd^(2+)、Pb^(2+)均能在12 h内达到平衡,土壤对Pb^(2+)平衡吸附量远大于Cd^(2+),准二级动力学模型最适合表征其动力学过程(R^2≥0.99)。吸附等温线可用Langmuir方程和Freundlich方程拟合,土壤对Pb^(2+)的吸附能力和缓冲能力较Cd^(2+)更大,吸附是自发进行的物理化学作用并存的过程。黄棕壤对Pb^(2+)的吸附为放热反应,紫色土对Pb^(2+)以及两种土壤对Cd^(2+)的吸附为吸热反应。去除有机质的土壤对重金属的吸附量降低,Cd^(2+)在黄棕壤和紫色土中的试验最大吸附量分别减少了37.89%、29.62%;Pb^(2+)则分别减少了12.87%、20.71%。土壤对金属离子的吸附量随溶液初始pH的增加而增加。

In order to understand the adsorption process and mechanism of Cd and Pb with strong toxicity on soil in the southwest region of China, and provide a theoretical basis for the prevention and control of soil pollution, we investigated the adsorption kinetics and thermodynamics of Cd^2＋and Pb^2＋in Yellow Brown Soil and Purple Soil and analyzed the effect of soil organic matter and solution pH on the adsorption process by batch experiment. Results showed that the adsorption of soil to Cd^2＋and Pb^2＋was balanced in 12 h, the equilibrium adsorption of soil to Pb^2＋was much greater than that to Cd^2＋, and the pseudo-second-order kinetic model with R^2 more than 0.99 fitted the adsorption kinetics well. The adsorption isotherms were described by Langmuir equation and Freundlich equation, and the adsorption capacity and buffering capacity of Pb^2＋were higher than those of Cd^2＋in the tested soils, the isothermal adsorption process was spontaneous with physical and chemical effects. Adsorption process of Pb^2＋in Yellow Brown Soil was exothermic, but that of Cd^2＋in Purple Soil and that of Pb^2＋in the two soils were endothermic. Soil removal of organic matter reduced the adsorption of heavy metals. The maximum adsorption amount of Cd^2＋decreased by 37.89%and 29.62%, respectively, and that of Pb^2＋decreased by 12.87% and 20.71%, respectively, in Yellow Brown Soil and Purple Soil. Adsorption amount of metal ions increased with the pH value of initial solution.