Field assessment of arsenic immobilization in soil amended with iron rich acid mine drainage sludge

Arsenic (As) immobilization in soil using acid mine drainage sludge (AMDS) is described following batch, column, and field experiments. The AMDS is a by-product from electrochemical treatment of acid mine drainage and mainly contains Fe-oxide. Batch experiments were carried out to determine optimum mixing ratio of AMDS for As immobilization. Continuous flow column experiments were carried out to identify the optimal excavation method and field experiments were used to assess As immobilization efficiency and feasibility. In the batch experiments, the optimum mixing ratio was determined to be 3.0 wt%. Column experiments indicated that the surface soil amendment was adequate for As immobilization. In the field experiments, the average As concentration in pore water was observed to be 4.9 μg L−1 at the immobilization layer, and 11.6 μg L−1 at the contaminated layer in the AMDS amended plot. In addition, rice grain contained 0.06 mg kg−1 of As. The XANES analysis confirmed that As(V) was the main species in the soil and rice grain. These results indicated that soil amendment with AMDS could induce As immobilization in soil, and prevent As transfer from soil to pore water and crops.