Enhanced remediation of cadmium-contaminated farmland by smooth vetch (Vicia villosa var.) coupled with phosphorus/sulfur co-doped biochar: Synergetic performance and mechanism

Herein, phosphorus/sulfur co-doped biochar (P/S-BC) coupled with smooth vetch (SV) as an innovative remediation strategy was proposed for the remediation of Cd-contaminated farmland. P/S-BC showed a high adsorption performance for Cd(II) and strong tolerance for the change of environmental pH, and the maximum uptake amount reached 204.26 mg/g. Furthermore, the bioavailability of Cd was significantly reduced by 37.27% with addition of 1.0% P/S-BC into soil for 20 days. Noticeably, when crushed fresh SV and 1.0% P/S-BC were applied to soil, the bioavailability of Cd in soil descended by 58.01%, meanwhile, the contents of soil organic matter (SOM) and available phosphorus (AP) in soil increased sharply, thereby improving the soil fertility. This double improvement was owing to that the application of P/S-BC could release more P through the action of organic acids produced by the decomposition of SV, which further bound with Cd to form stable compounds. The synergistic passivation mechanisms of SV + P/S-BC on Cd were surface chelation, precipitation, pore filling, and electrostatic interaction. Overall, this study proposed a promising strategy for achieving simultaneous remediation of heavy metals and supplement of nutrient to soil using heteroatom doped biochar coupled with green fertilizer.