Mitigating cadmium contamination in soil using Biochar, sulfur-modified Biochar, and other organic amendments

Biochar is a novel approach to remediating heavy metal-contaminated soil. Using various organic amendments like phyllosilicate-minerals (PSM), compost, biochar (BC) and sulfur-modified biochar (SMB), demonstrates superior adsorption capacity and stability compared to unmodified biochar (BC). The adsorption mechanisms of SMB are identified for its potential to increase soil-pH and reduce available cadmium (Cd). The study reveals the potential of BC and SMB in immobilizing Cd in contaminated soil. SMB demonstrated the highest adsorption capacity for Cd, followed by BC, PSM, and compost, with capacities ranging from 7.47 to 17.67 mg g^-1. Both BC and SMB exhibit high adsorption capacities (12.82 and 17.67 mg g^-1, respectively) and low desorption percentages (4.46-6.23%) at ion strengths of 0.01 to 0.1 mol-L^-1 and pH levels ranging from 5 to 7. SMB showed a higher adsorption capacity (17.67 mg g^-1) and lower desorption percentage (4.46-6.23%) compared to BC. The adsorption mechanism involves surface-precipitation, ion exchange, and the formation of Cd(OH)₂ and CdCO₃ precipitates, as well as interactions between Cd and organic sulfur, leading to more stable-Cd and CdHS⁺ compounds. Adding 1% SMB increased soil pH and significantly reduced available Cd, demonstrating its potential for pollutant remediation. The study underscores the promise of SMB in providing a sustainable solution for Cd-contaminated soil remediation.