Effect of Aging on Stabilization of Cd2+ Through Biochar Use in Alkaline Soil of Bayan Obo Mining Area

Abstract

Although biochar has been widely used in the remediation of heavy metal pollution in acidic and neutral soils, less attention has been paid to whether biochar will alter its structural properties and the ability to retain heavy metals after different degrees of aging in alkaline soils. In this study, two artificial accelerated aging methods (freeze-thaw cycle and dry-wet cycle) and a short-term natural aging method were used to simulate the aging process of biochar prepared from corn stalk. We investigated the changes in the soil pH and bioavailability, total content, and transformation of Cd2+ before and after aging treatments. Biochar was separated from the soil for characterization to explore the effect of aging on the passivation of Cd2+ by biochar in the alkaline soil of the mining area. The results showed that adding biochar to alkaline soil in the Bayan Obo mining area had no significant liming effect, and pH decreased after the freeze-thaw and dry-wet accelerated aging treatments. Compared with that in the control, the CaCl2-extractable contents of Cd2+ decreased by 19.32%-30.67%, and the total contents of Cd2+ decreased by 5.02%-7.18%. Aging did not significantly change the transformation of Cd2+ but reduced the distribution of acid-soluble and reducible fractions, indicating that biochar could immobilize Cd2+ for a long time after aging, which was related to the increase in oxygen-containing functional groups and the pore structure of biochar. These results are important for evaluating its long-term application prospects in the mining environment.