Insights into remediation of cadmium and lead contaminated-soil by Fe-Mn modified biochar

Heavy metal contamination, particularly by lead and cadmium, poses a significant environmental challenge. Indiscriminate disposal of crop residues exacerbates environmental concerns. In this study, broad bean straw was utilized to produce biochar (BC), and further modifications were made using FeCl3-6H2O and KMnO4 to obtain Iron-Manganese Modified Biochar (FMBC) for remediating cadmium and lead-contaminated soil. Results show that both BC and FMBC increased soil pH, available phosphorus, and potassium compared to the control groups. Adding 5% BC led to a notable reduction of 60.98% in available cadmium and 51.63% in available lead. Simultaneously, FMBC decreased active cadmium and lead by 57.51% to 73.73% and 52.25% to 69.87%, respectively. Furthermore, FMBC decreased the content of cadmium and lead in the unstable state while increasing content in the residual state, demonstrating its ability to reduce accumulation in plant tissues. FMBC adsorption mechanisms primarily involve surface complexation and co-precipitation, where oxygen-containing functional groups form stable complexes with free cadmium and lead ions. In conclusion, FMBC proved to be an effective, environmentally friendly soil remediation agent with strong adsorption capabilities and a prolonged shelf-life. This provides a promising solution to alleviate the pollution of heavy metals such as cadmium and lead in soil.