Mechanochemical Synthesis of Manganese-Modified Microscale Zerovalent Iron for Efficient Cr(VI) Removal: Performance and Mechanism

Metal doping for improving the reactivity of zerovalent iron (ZVI) has been well studied, while Mn(II)-modified microscale ZVI (Mn-mZVI) has not yet been explored. Herein, ball-milled Mn-mZVI was fabricated and used for Cr(VI) removal. Characterization analysis showed that the structure, composition, and charge of mZVI changed after the Mn(II) modification. The comparative test showed that Mn-mZVI could remove 100% of Cr(VI) within 10 min, whereas mZVI removed negligible Cr(VI) within 60 min. The zeta-potential and electrochemical evidence verified that the enhanced electrostatic attraction and electron-transfer ability contributed to the superior Cr(VI) removal performance of Mn-mZVI. Moreover, the solution pH increase caused the decline of Cr(VI) removal, and the presence of NO3– inhibited Cr(VI) removal, whereas other coexisting ions showed little influence on the Cr(VI) removal performance of Mn-mZVI. Chemical and material characterization analyses revealed that Cr(VI) reduction by Mn-mZVI was the combined action of Fe(0) and generated Fe(II). In addition, the reusability of Mn-mZVI was not ideal due to the surface passivation and loss of Mn(II), but the reactivity could be reactivated by ball-milling the reacted Mn-mZVI again with Mn(II). Overall, this work provides a new mentality for mZVI modification and is important to develop promising mZVI-based materials for Cr(VI) pollution control.