Effective removal of Cr(VI) from water by ball milling sulfur-modified micron zero-valent iron：Influencing factors and removal mechanism

Abstract

To address the issues of ZVI's susceptibility to oxidation and aggregation, ball milling and Na₂S·9H₂O modification were employed on ZVI to enhance its efficiency in removing Cr(VI) from effluent. The characterization results expressed that S-mZVI_bm had mesoporous and macroporous structures, enabling successful capture of Cr(VI). Moreover, S-mZVI_bm had the highest adsorption capacity for Cr(VI) (350.04 mg/g) at pH = 2.00 and reached kinetic equilibrium within 420 min. Furthermore, the adsorption of Cr(VI) by S-mZVI_bm conformed to the Avrami-fractional-order model, demonstrated that the adsorption process indicated a complex multi-adsorption process. Meanwhile, the adsorption also fit to Langmuir and Sips models, suggesting monolayer-level adsorption with heterogeneous sites located on S-mZVI_bm. The S-mZVI_bm could enhance Cr(VI) adsorption through various synergistic mechanisms, such as electrostatic interaction, chemical precipitation, surface complexation, and reduction. Overall, this research presented an innovative perspective for the modification of ZVI, and S-mZVI_bm could be widely applied in the practical remediation of wastewater containing Cr(VI).