Remediation mechanism of Cu, Zn, As, Cd, and Pb contaminated soil by biochar-supported nanoscale zero-valent iron and its impact on soil enzyme activity

Recently, heavy metal contaminated soil has been widespread concerned. Herein, rice straw-derived biochar-supported nanoscale zero-valent iron (nZVI@BC) composite was prepared and characterized, and its remediation performance in Cu, Zn, As, Cd, and Pb contaminated soil were evaluated. nZVI@BC demonstrated better immobilization effect on multiple heavy metals than biochar, and the residual component of Cu, Zn, As, Cd, and Pb increased by 10.27%, 7.18%, 7.44%, 9.26%, and 12.75%, respectively. After nZVI@BC treatment, the soil pH, the available iron, cation exchange capacity, total organic carbon, and dissolved organic carbon increased. Be-sides, soil enzyme (catalase, urease, and fluorescein diacetate hydrolase) activities significantly increased, especially, the catalase activity was doubled. Furthermore, the immobilization mechanism was explored, including surface adsorption, electrostatic attraction, ion exchange, coprecipitation, oxidation-reduction, and complexation. Additionally, the adsorption sites of Pb and Cu were more competitive, and As synergistically promoted the adsorption of Pb, forming a ternary surface complex PbFeAsO4OH. Therefore, it well demonstrates that nZVI@BC may be a potential technology for remediation of multiple heavy metals contaminated soil.

Automated summary

This study investigates the performance of rice straw-derived biochar-supported nanoscale zero-valent iron composite in the remediation of heavy metal-contaminated soil. The results demonstrate that this composite has a better immobilization effect on heavy metals, and it can increase soil parameters such as pH, available iron, cation exchange capacity, and soil enzyme activities. The study also reveals the mechanism of immobilization, including surface adsorption, electrostatic attraction, and ion exchange.