MnSO4-modified woodchip biochar “dual fixation” mechanism: Functional group-electron synergistic stabilization of heavy metals and carbon structure

To solve the problem of soil carbon loss due to mineralization of soil organic carbon caused by heavy metal pollution. In this study, MnSO 4 -modified biochar prepared by impregnation pyrolysis successfully reduced the mobility of copper (Cu) and lead (Pb) in the soil, inhibited the mineralization of soil organic carbon , and thus reduced CO 2 emissions. The loading of MnSO 4 and MnS particles promoted the carbon sequestration of biochar from 44 % to 53 %, synchronizing the stabilized carbon content of the material with the soil organic carbon content. Combined with experimental and DFT calculations, the loading of MnSO 4 and MnS increased the active sites on the surface of the biochar with a significant increase in the energy gap. The -COOH and S 2- groups were combined with Cu and Pb, and the residual contents of Cu and Pb were increased from 9 % and 8–33 % and 23 %, respectively. Furthermore, the mineralization rate of soil organic carbon decreased from 0.5 mg‧g −1 ‧d −1 and 0.48 mg‧g −1 ‧d −1 to 0.38 mg‧g −1 ‧d −1 and 0.35 mg‧g −1 ‧d −1 , respectively. The binding of MSC with Cu and Pb reduced carbon activity near the reaction site, prevented the oxidative degradation of the carbon skeleton by forming a stable residue state complex with Cu and Pb, and achieved the synergistic effect of heavy metal stabilization and carbon sequestration simultaneously. The MnSO 4 -modified biochar of the present study provides new insights into the synergistic stabilization of heavy metals and carbon sequestration. • MnSO 4 modification increased the carbon sequestration of biochar to 53 %. • MnSO 4 modified biochar achieves dual effects of carbon sequestration and heavy metal immobilization. • The complexes formed by the moiety with heavy metal ions protect the stability of the carbon near the reaction site.