Discussion on the Risk of Falsely Meeting the Standard of Arsenic Contaminated Soil Treated by Ferric Sulfate

Stabilization of ferric sulfate is an important technology for remediation of arsenic-contaminated soil,but residual agents formed by excessive addition and uneven mixing would conduct secondary remediation in the process of soil leaching test, resulting in the risk of falsely meeting the standard. In this paper, the changes of soil arsenic leaching concentration at different time points and the differences with the theoretical calculated concentration were compared under the conditions of mixing uniformity of 100%, 67% and 33%, respectively, through two groups of experiments with the dosage ratio of 3. 3% and 6. 7%. It found out that the risk of falsely meeting the standard did exist. The risk increased with the increasing dosage and mixing unevenness. At the same time, because ferric sulfate itself has good stability, the risk would not completely disappear with the extension of time. In addition, this paper explored the soil of effectiveness of eliminating the residual ferric sulfate using potassium dihydrogen phosphate and sodium pyrophosphate. The results showed that the potassium dihydrogen phosphate is a kind of effective chemicals residue Fe³⁺ competitive agent, which helped to reduce the false target risk, but there was a risk of activating soil arsenic, and it was necessary to strictly control the dosage to prevent soil arsenic from being greatly activated. Sodium pyrophosphate had no obvious effect on the elimination of residual ferric sulfate,and had a risk of activation of soil arsenic, so it was not recommended to be used as residual agent.