The concurrent presence of heavy metal ions such as chromium and arsenic at acid mine drainage locations significantly complicates the treatment of wastewater. This research developed a synergistic redox strategy for Cr(VI) and As(III) using iodide( \({\mathrm{I}}^{-}\) ) as an activator under UV light irradiation to enhance the removal of these metal ions from acidic solutions. Experimental findings indicate that \({\mathrm{I}}^{-}\) notably boosts the redox process for both Cr(VI) and As(III) when present together in the solution. During UV irradiation, \({\mathrm{I}}^{-}\) converts into iodine radicals (I•) and triiodide ions ( \({\mathrm{I}}_{3}^{-}\) ), facilitating the oxidation of As(III) to As(V). Furthermore, the simultaneous presence of Cr(VI) significantly enhances the formation of I• and \({\mathrm{I}}_{3}^{-}\) while also contributing to the reduction of Cr(VI) to Cr(III). \({\mathrm{I}}_{3}^{-}\) was identified as the main oxidant in the conversion of As(III) to As(V), with hydroxyl radicals (•OH) playing a minimal role in the reaction. The study introduces a “clock reaction” mechanism, based on the cycling of \({\mathrm{I}}^{-}\) and \({\mathrm{I}}_{3}^{-}\) , to explain the redox interactions in the Cr(VI)/KI/As(III) system.
