Cadmium stability in biochar-remediated soil response to simulated acid rain

To study the Cd stability immobilized by biochar-remediated soil under acid rain, the Cd-contaminated soil in an acid rain region of southern China was selected and remediated using biochar. The characteristics of soil Cd leaching and availability and the organic matter content in the leaching solution were studied under acid rain with different acidities. The results showed that the pH values increased by 0.48-1.45 units of the leaching solutions from the biochar-remediated soils compared with soils without biochar, while the Cd contents decreased by 3.56%-78.37%. The biochar addition induced decreases in the content of dissolved organic matter (DOM) in the soil leaching solutions, but increases in the leaching loss of DOM with acid rain acidities increasing and over time. The DOM three-dimensional fluorescence spectrum results implied that the highest load of the macromolecular humus component was in the first collected leaching solution, while that of the small molecule humus component was in the final collected leaching solution. The acid rain generally induced the soil available Cd contents in the 0-5, 5-10. 10-15 and 15-20 cm soil layers to decrease by 17.44%. 17.55%. 12.67% and 13.49%. The available Cd content decreases were attributed to the significant decreases in the content of exchangeable Cd and the increases in the contents of carbonate-, iron-manganese oxide- and organic bonded Cd. The results indicate that biochar performs well in the immobilization of Cd in soil when it serves as a remediator even in acid rain regions.