Enhanced remediation of cadmium-polluted soil and water using facilely prepared MnO2-coated rice husk biomass

•Coating of MnO2 on biomass improves its surface activity and remediation rate.•MnO2 with a high surface activity plays a key role in immobilizing cadmium.•MnO2 greatly facilitates the conversion of exchangeable Cd to Fe/Mn oxide bound Cd.•Complexation is dominant mechanism for Cd immobilization on MnO2 modified bioamss.•Specific adsorption or electrostatic effect is the possible Cd remediation mechenism.