五种土壤胶体对重金属镉的吸附特征研究

Study on the adsorption characteristics of cadmium by five soil colloids

摘要:

土壤胶体作为土壤中最细微、最活跃的部分，在土壤对重金属的累积方面起主要作用. 研究不同土壤胶体对镉的吸附-解吸行为、化学形态转化等的影响，有利于摸清不同土壤类型中镉的迁移性和生物危害性, 对开展区域农田镉污染修复有重要意义. 本文选取蒙皂石、高岭土、针铁矿、氢氧化铝、腐殖酸五种土壤中常见的胶体，探究不同土壤胶体对镉的吸附特征. 结果表明：（1）五种胶体对镉的吸附均属于单分子层吸附，蒙皂石能快速吸附大量的镉，但吸附的镉不稳定，解吸率最高；腐殖酸和针铁矿吸附的镉解吸率较低. 吸附-解吸实验结果显示，五种土壤胶体对镉的保留吸附量为：腐殖酸（41.38 mg/g） > 针铁矿（24.95 mg/g） > 高岭土（19.43 mg/g） > 蒙皂石（15.06 mg/g） > 氢氧化铝（10.84 mg/g）. （2）镉的形态分析结果显示，蒙皂石和高岭土吸附的镉大多以可交换态存在，针铁矿和腐殖酸吸附的镉形态较稳定，除针铁矿外，残渣态含量均较低，形态分析结果与吸附-解吸实验结果一致. （3）pH对于五种胶体吸附镉的影响程度大小为：腐殖酸 > 针铁矿 > 高岭土 > 蒙皂石 > 氢氧化铝.

Abstract:

Soil colloids, as the most subtle and active part of the soil, play a major role in the accumulation of heavy metals in the soil. Study on the effect of different soil colloids on the adsorption-desorption behavior and the transformation of chemical forms of cadmium will help to understand the environmental chemical behavior of cadmium, which has a great significance to the remediation of cadmium pollution in regional farmland. In this study, smectite, kaolin, goethite, aluminum hydroxide and humic acid which colloids are commonly found in soil were collected to explore the adsorption characteristics of cadmium on different soil colloid. The following conclusions were obtained: (1) The adsorption of the five colloids to cadmium belongs to monomolecular adsorption. Smectite can quickly absorb a large amount of cadmium, but the adsorption of cadmium is unstable and the desorption rate is the highest. The cadmium desorption rates of humic acid and goethite are lower. Adsorption-desorption experiment results show the retained adsorption capacity: humic acid (41.38 mg/g) > goethite (24.95 mg/g) > kaolin (19.43 mg/g) > smectite (15.06 mg/g) > aluminum hydroxide (10.84 mg/g). (2) The species analysis results show that the cadmium adsorbed by smectite and kaolin mostly exists in exchangeable state, and the cadmium adsorbed by goethite and humic acid is relatively stable. Except for goethite, the residual state content is relatively low. The species analysis results are consistent with the results of adsorption-desorption experiment. (3) The degree of influence of pH on cadmium adsorption by five colloid is: humic acid > goethite > kaolin > smectite > aluminum hydroxide.