Study of the nano zero-valent iron stabilized by carboxymethyl cellulose loaded on biochar for remediation of Cr(VI)-contaminated groundwater

Hexavalent chromium (Cr(VI)) contamination in groundwater poses a significant threat to human and environmental health. In this study, nanoscale zero-valent iron stabilized by carboxymethyl cellulose loaded on biochar (CMC-nZVI@BC) was used as an in-situ reaction zone material to remove Cr(VI) from groundwater. The experimental results demonstrated that CMC-nZVI@BC effectively removed 99.9 % of Cr(VI) within 180 min, which was 22.4 % and 10.7 % higher than that of nZVI@BC and CMC-nZVI, respectively. Physisorption and chemisorption were responsible for Cr(VI) removal. Electrochemical analysis showed that the number of transferred electrons in Cr(VI) removal by CMC-nZVI@BC was approximately 47 times greater than that of BC, which indicated that BC mainly acted as an electron shuttle to facilitate the electron transfer between nZVI and Cr(VI). The maximum breakthrough C/C0 values of CMC-nZVI@BC in coarse and medium sand were 0.86 and 0.72, respectively, demonstrating its good mobility. The in-situ reaction zone based on CMC-nZVI@BC was suitable for media with particle size greater than 0.25 mm. The reaction zone continuously removed Cr(VI) from the groundwater, and the effective remediation periods in the coarse sand and medium sand were 4 and 6 days, respectively. This study confirms the great potential of CMC-nZVI@BC for contaminated groundwater remediation.