溶液化学环境对Cr(Ⅵ)和As(V)在农田土壤中吸附和垂向迁移的影响

Effects of Chemical Environment in Solution on the Adsorption and Vertical Transport of Cr(Ⅵ) and As(Ⅴ) in Farmland Soil

选择工业固体废物附近的农田土壤，研究共存金属离子、无机盐、有机质、pH值及温度对土壤吸附Cr（Ⅵ）和As（Ⅴ）的影响。结果表明，在众多影响因素中，pH值和KH2PO4是对Cr（Ⅵ）和As（Ⅴ）吸附影响最明显的两个因素，pH值的升高（2．0～8．0）和KH2PO4（0．01～1．0mol·L^-1）的存在不利于Cr（Ⅵ）和As（Ⅴ）的吸附。利用土柱淋溶实验考察pH值和KH2PO。对Cr（Ⅵ）和As（Ⅴ）在土壤中迁移、转化的影响发现，较高的pH值（7．0）和KH2PO4（0．1mol·L^-1）的存在有利于Cr（Ⅵ）和As（Ⅴ）的迁移。低pH（4．0）下的淋溶增加了土壤中交换态Cr和As的相对和绝对含量，提高了重金属的生物可利用性。高pH（7．0）及KH2PO4存在时的淋溶减小了交换态Cr和As的含量，降低了重金属的生物可利用性。淋溶实验后，土壤中分别平均有95％的Cr（Ⅵ）和11％As（Ⅴ）发生了还原反应生成了Cr（Ⅲ）和As（Ⅲ），从而在一定程度上降低了Cr（Ⅵ）和As（Ⅴ）的迁移性。

The effects of coexistent metallic ion, inorganic salt, organic matter, pH value and temperature on the adsorption of Cr （Ⅵ） and As （Ⅴ） by soil were investigated. Among these factors, pH value and KH2PO4 affected Cr（Ⅵ） and As（ Ⅴ ） adsorption more obviously. Increase of pH value （2.0-8.0） and the existence of KH2PO4 （0.01-1.0 mol·L^-1） had reduced the adsorption of Cr （Ⅵ） and As （Ⅴ） by soil. Soil column leaching tests were used to study the effects of pH value and KH2PO4 on the vertical transport of Cr（Ⅵ） and As（Ⅴ） in soil. High pH value （7.0） and the existence of KH2PO4 （0.1 mol·L^-1） were advantageous to the vertical transport of Cr （Ⅵ） and As （Ⅴ） in soil. Under lower pH （4.0）, the relative and absolute concentrations of exchangeable Cr and As in soil were increased after soil column leaching tests, therefore, the bioavailability of Cr and As in soil were increased. Under higher pH （7.0） or the existence of KH2PO4 （0.1 mol·L^-1）, the relative and absolute concentrations of exchangeable Cr and As in soil were reduced after soil column leaching tests. Averagely, 95% of Cr and 11% of As were deoxidized to Cr （Ⅲ） and As （Ⅲ）, which reduced the transport of Cr（Ⅵ） and As（Ⅴ） in soil.