Study of the Remediation Effect and Mechanism of Biochar-Loaded nZVI on Heavy Metal Contaminated Soil

Soil heavy metal pollution has become an important environmental problem in the world. Therefore, it is particularly important to find effective remediation methods for heavy metal contaminated soil. Biochar (BC) is a kind of soil heavy metal passivator with a wide range of applications. It also has a good effect on the control of soil heavy metal pollution. However, BC does not have sufficient fixation capacity for para-anionic contaminants. Nano-zero-valent iron (nZVI) has a strong reducing ability, which can make up for this defect of BC. Therefore, to improve the passivation effect of heavy metals, nanomaterial modification is proposed to optimize biochar performance. Nanoparticles are used as carriers to impregnate biochar (BC). Biochar-supported nano-ferric zero-valent materials are prepared to repair soil contaminated by heavy metals. Results show that the physicochemical properties of modified biochar are significantly optimized. At 5%, the modified biochar (1:3) treatment group had the best remediation effect on Cd-contaminated soil, which significantly promoted soil catalase activity. The modified biochar (3:1) treatment group had the best remediation effect on As-contaminated soil, and significantly increased soil pH, Cation Exchange Capacity (CEC), and available Fe content. Modified biochar (1:3) with 3% added content was used to repair actual composite heavy metal contaminated soil, and the relative percentage content of Cu, Zn, As, Cd, and Pb residue state increased by 10.28%, 7.81%, 7.44%, 9.26%, and 12.75%, respectively. The effects of nZVI@BC on the remediation effect and soil enzymes of Cd- and As-contaminated soil under different factors such as mass ratio of carbon and iron and dosage were studied. The remediation mechanism of Cd- and As-contaminated soil was clarified, and a good solidification and stabilization effect was obtained. This provides a theoretical basis for nZVI@BC remediation of soil contaminated by Cd and As. It has good application value in the treatment and remediation of complex heavy metal contaminated soil.