Treatment of Cr(VI)-containing wastewater with FeC2O4<middle dot>2H2O prepared from chromite ore processing residue

Chromite ore processing residue (COPR) is a solid waste produced in the process of producing chromium salts from chromite. It contains highly toxic and carcinogenic Cr(VI), which has high solubility and mobility. Excessive accumulation of Cr(VI) in the environmental can lead to environmental pollution and pose serious threats to human health. Despite its hazardous components, COPR also contains metal elements such as Fe, which can be potentially recycled as valuable resources. In this study, the COPR was first leached with hydrochloric acid, and the leachate is then reacted with oxalic acid to prepare FeC2O4<middle dot>2H2O. Subsequently, this compound was employed for the treatment of chromium-containing wastewater. The findings reveal a remarkable 98.17% conversion rate of Fe during the preparation of FeC2O4<middle dot>2H2O from the leachate. In the treatment of chromium-containing wastewater using FeC2O4<middle dot>2H2O, Cr(VI) was adsorbed and subsequently reacted with Fe(II) to generate Cr(III), leading to the co-precipitation of Fe(III) and Cr(III). The removal efficiency of Cr(VI) reached 99.66%, with an initial concentration of 40 mg/L in chromium-containing wastewater at pH 3.0, and a treatment time of 55 min. The residual content was found to be lower than the Chinese national emission standard (0.5 mg/L). This study introduces a novel approach to COPR utilization, enhancing the value of chromium waste while addressing Cr(VI) pollution. It demonstrates an effective strategy for treating waste with waste, contributing to both resource recovery and environmental remediation.