氧化还原条件对土壤砷(Ⅴ)稳定化作用的影响

Effect of Redox Conditions on the Stabilization Process of Arsenate in Soils

探讨了不同氧化还原条件下土壤外源砷（Ⅴ）的稳定化作用。研究结果表明不同氧化还原条件下外源水溶性砷（Ⅴ）进入土壤体系后,各种形态砷随培养时间增加的变化规律总体上表现较为一致。培养180天之后,水溶态和交换态砷在微孔扩散等作用下随培养时间分别下降至2.4%~4.7%和2.8%~3.2%。碳酸盐态砷主要受控于p H以及相应的表面沉淀作用。有机态砷存在再分配现象,最高值达48.8%~50.1%,有机态砷下降的同时,伴随氧化物态和残渣态砷的上升。越趋向氧化环境会使得土壤外源砷（Ⅴ）的稳定化程度越高,反之,越趋向还原环境土壤外源砷（Ⅴ）的稳定化程度越低。各种氧化还原条件下,土壤外源砷（Ⅴ）的稳定化过程均具有明显的阶段性特征,缺氧和过渡条件下表现为3阶段特征,而好氧条件下表现为4阶段特征。

Effect of redox conditions on the stabilization process of arsenate in soils has been investigated. The results show that the changes of arsenic fractions with increasing contact time are basically consistent after exoge- nous arsenate entering into soils under different redox conditions. After 180 days, with increasing contact time, water soluble and exchangeable arsenic were down to 2.4% - 4.7% and 2.8% - 3.2% , respectively, due to the diffusion of arsenic into micropores. Arsenic bound to carbonate is mainly controlled by the pH and the process of surface precipitation. The redistribution phenomenon of arsenic bound to organic matter occurs, and the highest values were up to 48.8 % - 50. 1% , respectively. During the later period of incubation, arsenic bound to organic matter decreases with increasing contact time, while arsenic bound to Fe-Mn oxides and the re- sidual fraction of arsenic increase with increasing contact time. The stabilization process of arsenate in soils will be strengthened when the redox condition is from anoxic condition to oxic condition. In contrast, the stabiliza- tion process of arsenate in soils will be inhibited when the redox condition is from oxic condition to anoxic condi- tion. The stabilization process of arsenate in soils is obviously characterized by phases under different redox con- ditions. There are three phases for the stabilization process of arsenate in soils under the anoxie and transition conditions, while four phases occur under the oxic condition.