Study on the kinetics and mechanisms of Cr(VI) removal by nZVI modified with four modifiers

Abstract

To improve the nanoscale zero-valent iron (nZVI) utilization efficiency in environmental remediation and explore the performance enhancement mechanisms, the treatment of chromium pollution by pyrogallic acid modified nZVI (pyGA-nZVI), sodium dihydrogen phosphate modified nZVI (MSP-nZVI), ethylenediamine modified nZVI (EDA-nZVI) and sodium persulfate modified nZVI (PS-nZVI) were investigated in this study. The characterization of modified nZVIs demonstrated the successful bonding of modifiers onto nZVIs. Among the four modified materials, pyGA-nZVI exhibited the highest Cr(VI) removal performance (complete removal within 4 min), followed by MSP-nZVI (81.7 % within 30 min), EDA-nZVI (77.1 % within 30 min) and PS-nZVI (55.1 % within 30 min). The H2 production was all suppressed due to the presence of modifiers, boosting the electronic selectivity in the reaction with Cr(VI). Fe0 was the main contributor to the reduction of Cr(VI) by nZVI, EDA-nZVI and PS-nZVI, whereas Fe(II) played a major role in Cr(VI) reduction by pyGA-nZVI and MSP-nZVI. The decrease of element P and S contents indicated the direct involvement of MSP and PS in Cr(VI) removal, while the same content of N on nZVI before and after reaction implied an indirect participation of EDA in Cr(VI) removal.