Water/acid/reductive biomass leaching of Cr(VI) in chromium ore processing residue (CORP) for safe discharge of effluent and to recover Cr (III) and gypsum

The hydrolyzed biomass, a green and renewable resource, was used as a reducing agent to achieve the harmless treatment of chromium ore processing residue (COPR). This paper proposes a detoxification process of two-stage sulfuric acid leaching accompanied by biomass reduction of hexavalent chromium and a one-step combined leaching and reduction process. The orthogonal tests and single factor tests allowed to propose the most suitable operating conditions of different stages such as biomass hydrolysis, two-stage acid leaching, reduction of the acid leachate and combined leaching and reduction. The Cr(VI) content in both the leach residue and reduction so-lution reached the discharge criterion. The FTIR and XPS measurements showed that the reducing sugars pro-duced by the hydrolysis of biomass reacted with the leached Cr(VI) to generate chromium sulfate adsorbed on the surface of COPR. In addition, XRD, SEM-EDS showed that the gypsum was generated after COPR detoxification, which can be used for resource utilization, providing a new idea and reference for the harmless treatment of COPR producing Cr(III) and gypsum.

Automated summary

This study proposed a method of using hydrolyzed biomass as a reducing agent to achieve the harmless treatment of chromium ore processing residue. By a two-stage sulfuric acid leaching and biomass reduction of hexavalent chromium, as well as a one-step combined leaching and reduction process, the detoxification of the residue was successfully achieved. The suitable operating conditions for different stages were determined through orthogonal tests and single factor tests, including biomass hydrolysis, acid leaching, reduction, and combined leaching and reduction. The content of Cr(VI) in both the leach residue and reduction solution met the discharge criteria. FTIR and XPS measurements showed that the reducing sugars produced by the hydrolysis of biomass reacted with the leached Cr(VI) to generate chromium sulfate adsorbed on the surface of the residue. XRD and SEM-EDS results indicated that gypsum was generated after the detoxification, which can be utilized as a resource.