土壤矿物质吸附砷的研究进展

砷是一种有毒的重金属元素,由于自然和人为的原因,世界上的许多国家存在砷污染问题,因此有关砷污染的研究与控制日益受到人们的关注。本文介绍了土壤砷污染的产生原因及污染状况,重点集中在探讨土壤中的各种矿物质对砷吸附行为的作用机理。这些矿物质包括铁铝氧化物和氢氧化物、锰氧化物、黏土矿物和碳酸盐类。关于砷在各类矿物质上的吸附机理,普遍接受的观点认为:砷氧阴离子与矿物质的表面发生了配位体交换过程并通过共价键的作用,形成了表面配位体。表面配位体以内层双齿双核鳌合形式为主,受矿物质的种类、pH值和氧化还原电位等因素的影响,外层吸附和其他鳌合状态可能存在。砷在土壤矿物质上的吸附效果强烈依赖于体系的pH值,这与吸附的理论模型和数学计算结果相一致。矿物质的种类、组成、结晶状态和表面积等影响了砷的吸附过程和吸附效果。土壤中存在的各种阴阳离子通过与砷阴离子竞争吸附位而影响砷在矿物质上的吸附。

A Review of Arsenic Adsorption onto Mineral Constitutions in the Soil

Arsenic is a toxic heavy metal.As the result of natural process and anthropogenic activities,many countries are suffering from the arsenic pollution.Because of the high toxicity of arsenic compounds,there is more widespread concern about the arsenic control and disposal.The origin and current status of the arsenic pollution are reviewed here.This paper focuses on the mechanism of arsenic adsorption onto the mineral constituents such as iron oxides,aluminum oxides,clay mineral,manganese oxides,carbonate etc.By ligand exchange and chemical bonding,As oxyanions can form surface complex on the mineral surfaces.Inner-sphere bidentate binuclear bonding is the main mechanism,companying out-sphere adsorption.Arsenic adsorption is affected by pH,minerals,crystallization and surface area etc.,which is in good agreement with the model and calculations.Also,many ions(cations or anions) existed in the soil have a effect on As adsorption by competing for the surface sites.