Abstract:

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 exogenous 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 residual 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 stabilization process of arsenate in soils will be inhibited when the redox condition is from oxic condition to anoxic condition. The stabilization process of arsenate in soils is obviously characterized by phases under different redox conditions. There are three phases for the stabilization process of arsenate in soils under the anoxic and transition conditions, while four phases occur under the oxic condition.

Key words: redox condition, soil, arsenate, stabilization, exogenous