Remediation of arsenic-spiked soil by biochar-loaded nanoscale zero-valent iron: Performance, mechanism, and microbial response

Given the increasingly serious problem of arsenic-contaminated soil, biochar-loaded nanoscale zero-valent iron (nZVI@BC) was prepared in this study for remediation of arsenic-contaminated soil. Characterization analysis showed that nZVI was evenly dispersed on the biochar, the characteristic functional groups of biochar, including -CH, -OH, C--O, C-O-C, -OH, etc., were enriched and strengthened, and a relatively stable Fe-OH was formed. The effects of various factors (different materials, nZVI loading ratio, and remediation time) on arsenic frac-tionation, pH, and CEC in soil were comprehensively investigated. The results demonstrated that arsenic sta-bilization was positively correlated with the dosage, nZVI loading ratio, and remediation time. 5% nZVI@BC (3:1) exhibited the best immobilization performance, significantly promoted the transformation from labile arsenic to iron-aluminum oxide binding state and residue state, and improved the available iron, pH, and CEC of the soil. The remediation mechanism was revealed, involving electrostatic attraction, surface adsorption, redox, complexation and co-precipitation. In addition, the bacterial community abundance, diversity, and species composition displayed discrepancies with various treatments, especially with 5% nZVI@BC (3:1). Sixty-six biomarker species were screened, mainly belonging to Actinobacteria and Gemmatimonadetes with biochar treatment as well as Firmicutes, Acidobacteria, and Chloroflexi with nZVI@BC treatment. This study will provide the essential theoretical basis and extensive application value for nZVI@BC remediation of arsenic-contaminated soil.