Arsenic release in contaminated soil amended with unmodified and modified biochars derived from sawdust and rice husk

Purpose Biochar, due to its heterogeneity, may not be equally effective for cationic and anionic metals/metalloid immobilization in soil. Biochar modification could facilitate the immobilization of specific metals/metalloids in soil. Materials and methods This study explored the potential of unmodified and modified (with KMnO4) biochars derived from sawdust and rice husk at two different temperatures (300 and 700 degrees C) on the mobility of arsenic (As) in contaminated soil. Soil column leaching experiments were performed with two application rates (2% and 5%; w/w) of different biochars, and the pore waters at different time intervals were analyzed for As and other cations and anion concentrations. Results and discussion In general, all the biochars increased As mobility in soil. The biochars produced at 300 degrees C significantly and highly increased As concentrations (up to 341%) in pore waters, as compared with the unamended soil. However, the modified biochars showed As immobilization in soil as compared with their unmodified counterparts. The mechanisms of biochar interaction with As in soil were investigated by developing correlations of As with various chemical constituents. It was inferred that As mobilization was increased due to competition between As and PO43-. Contrarily, immobilization of As in soil by modified biochars was related to sorption onto Fe- and Mn-oxides. Conclusions Pristine biochar may not be an efficient remediation measure for As-contaminated soil. There could be a risk of As leaching into groundwater from soils amended with biochar. However, it is recommended that modification of biochar may assist the immobilization of As in soil.