Radiolytic formation of non-toxic Cr(III) from toxic Cr(VI) in formate containing aqueous solutions: A system for water treatment

Highlights: ► Cr(VI) is radiolytically reduced to Cr(III) in presence formate. ► Reduction is pH, dose rate dependent. A mechanism is proposed. ► Cr(VI) recovers when all the formate is consumed. ► Irradiation of wastewater can remove Cr(VI). - Abstract: Toxic hexavalent chromium Cr(VI) in the form of potassium dichromate was radiolytically reduced to non-toxic trivalent chromium Cr(III) in N2O-saturated aqueous solutions containing formate. This reduction by the electron donor (CO2H·/CO2·−) produced by continuous radiolysis of water, was a linear function of the absorbed dose. This reaction was pH and dose rate dependent. pH was an important parameter in the reduction, as it affects both chemical speciation of Cr(VI) and formate. Possible mechanisms related to dose rate dependence of removal of Cr(VI) are presented. At pH 3 a decrease in the radiation induced reduction of Cr(VI) was observed with increasing hydrogen peroxide concentration. A mechanism to account for this variation is proposed. These findings suggest that irradiation of Cr(VI) solutions in presence of formate can be effective, economical and simple means for treatment of waste water contaminated with hexavalent Cr(VI).