Mitigation of arsenic release by calcium peroxide (CaO2) and rice straw biochar in paddy soil

Biochar has a great potential in the stabilization of soil heavy metals; however, the application can actually enhance the mobility of Arsenic (As) in soil. Here, a biochar-coupled calcium peroxide system was proposed to control the increase in As mobility caused by biochar amendment in paddy soil environment. The capability of rice straw biochar pyrolyzed at 500 degrees C (RB) and CaO2 to control As mobility was evaluated by incubation for 91 days. CaO2 encapsulation was performed for pH control of CaO2, and As mobility was evaluated using a mixture of RB + CaO2 powder (CaO2-p), and RB + CaO2 bead (CaO2-b), respectively. The control soil solely and RB alone were included for comparison. The combination of RB with CaO2 exhibited remarkable performance in con-trolling As mobility in soil, and As mobility decreased by 40.2% (RB + CaO2-p) and 58.9% (RB + CaO2-b) compared to RB alone. The result was due to high dissolved oxygen (6 mg L-1 in RB + CaO2-p and RB + CaO2-b) and calcium concentrations (296.3 mg L-1 in RB + CaO2-b); oxygen (O2) and Ca2+ derived from CaO2 is able to prevent the reductive dissolution and chelate-promoted dissolution of As bound to iron (Fe) oxide by biochar. This study revealed that the simultaneous application of CaO2 and biochar could be a promising way to mitigate the environmental risk of As.