Mechanism for Mn oxide‐modified biochar to remediate Cd‐contaminated alkaline soil and decrease Cd uptake of wheat plants

Abstract Biochar has been widely applied to remediate heavy metal‐contaminated soils, but its performance is generally far from satisfactory. Manganese (Mn) oxide‐modified biochar (MBC) has shown superior performance in heavy metal removal from wastewater. However, its potential to remediate heavy metal‐contaminated soils and the corresponding immobilization mechanism at soil aggregate scale remain unclear. In this work, MBC was prepared and used for the remediation of Cd‐contaminated weakly alkaline arable soils via a wheat pot experiment. The impacts of MBC on soil Cd fraction, Cd distribution in soil aggregates and Cd accumulation in wheat plants were investigated. The results indicated that MBC could improve Cd immobilization in silt‐sized micro‐aggregates (<53 μm) by increasing the content of free MnO 2 and enhance the transformation of soil acid‐soluble Cd to reducible Cd (Fe/Mn oxide‐bound Cd), resulting in significant decreases in the bioavailability of soil Cd and Cd accumulation in wheat plants. The maximum decrease ratio of the DTPA‐Cd content reached 44.7%, and Cd content in wheat grains, straw, and roots declined by 66.4%, 38.4% and 62.9%, respectively. These findings provide a new strategy to remediate Cd‐contaminated weakly alkaline arable soils, as well as improve the understanding of the application of Mn oxides‐related amendments to remediate heavy metal‐contaminated soils.