A novel mechanism for in-situ mechanochemical reduction and immobilization of Cr(VI)

While mechanochemical reactions have garnered attention for their broad applicability and readily attainable operational conditions, their utilization in wastewater purification, particularly for the treatment of chromium-containing effluents, remains limited. In this study, we present a novel mechanism for ball milling-mediated reduction and immobilization of hexavalent chromium, achieving removal efficiencies of up to 93.7% over a pH range of 2.0 to 10.0. This mechanism advocates for the concurrent effect of mechanical force to facilitate the reduction of Cr(VI) to its stable surface form (Cr(III)), and the precipitation of BaCrO 4 , thereby immobilizing the chromium species. Density functional theory calculations demonstrate that oxygen vacancies can efficiently adsorb Cr(VI), thereby imparting electrons to it, consequently facilitating reduction processes. This study provides novel insights into metal ion-contaminated wastewater treatment and the role of naturally generated mechanical forces on the redox processes of chromium species.