Mechanochemical\nSynthesis of Manganese-Modified Microscale\nZerovalent Iron for Efficient Cr(VI) Removal: Performance and Mechanism

Metal\ndoping for improving the reactivity of zerovalent iron (ZVI)\nhas been well studied, while Mn(II)-modified microscale ZVI (Mn-mZVI)\nhas not yet been explored. Herein, ball-milled Mn-mZVI was fabricated\nand used for Cr(VI) removal. Characterization analysis showed that\nthe structure, composition, and charge of mZVI changed after the Mn(II)\nmodification. The comparative test showed that Mn-mZVI could remove\n100% of Cr(VI) within 10 min, whereas mZVI removed negligible Cr(VI)\nwithin 60 min. The zeta-potential and electrochemical evidence verified\nthat the enhanced electrostatic attraction and electron-transfer ability\ncontributed to the superior Cr(VI) removal performance of Mn-mZVI.\nMoreover, the solution pH increase caused the decline of Cr(VI) removal,\nand the presence of NO<sub>3</sub><sup>–</sup> inhibited Cr(VI)\nremoval, whereas other coexisting ions showed little influence on\nthe Cr(VI) removal performance of Mn-mZVI. Chemical and material characterization\nanalyses revealed that Cr(VI) reduction by Mn-mZVI was the combined\naction of Fe(0) and generated Fe(II). In addition, the reusability\nof Mn-mZVI was not ideal due to the surface passivation and loss of\nMn(II), but the reactivity could be reactivated by ball-milling the\nreacted Mn-mZVI again with Mn(II). Overall, this work provides a new\nmentality for mZVI modification and is important to develop promising\nmZVI-based materials for Cr(VI) pollution control.