Control of arsenic release from paddy soils using alginate encapsulated calcium peroxide

The mobilization of As in paddy soils is affected by iron redox cycles. In this regard, calcium peroxide (CaO2) can be used as an alternative to maintaining oxidizing conditions by liberating oxygen under flooding environments. Nevertheless, the problem of increase in pH by CaO2 dissolution remains unresolved. In this study, the encapsulation of CaO2 using alginate is proposed. Encapsulated CaO2 (CaO2-b) using 1% sodium alginate was applied to As-contaminated soil to evaluate the ability of pH control and As mobility during flooding conditions. The pH increased rapidly from 6.8 to 9.0 in unencapsulated CaO2 (CaO2-p) within 1 day, while CaO2-b increased slowly to 8.6 over 91 days. CaO2 created an oxidizing condition in the soil by providing oxygen, thus effectively prevented the reductive dissolution of iron. The mobility of As decreased by 50% (CaO2-p) and 83% (CaO2-b) compared with that of the control soil. Furthermore, the As in pore water was three times lower than CaO2-p because CaO2-b released 1.8 times more Ca2+ to form Ca-As complexes than CaO2-p. Consequently, the encapsulated CaO2 reduced the negative effects of CaO2 treatment on increasing pH of the soil and furnished a better environmental condition for inhibiting As mobility.