Study on leaching characteristics of Cr(VI) from chromite ore processing residue

Chromite ore processing residue (COPR) is a type of hazardous wastes listed in the "National Catalog of Hazardous Wastes of China", while a large amount of COPR is treated in wasteful ways, such as simple in-situ storage or burial, which poses serious threat to ecological system and human health. The leaching characteristics of Cr(VI) from COPR under various environmental conditions were investigated by batch experiment and column experiment. The X-ray diffraction (XRD) analysis revealed major minerals in COPR including brownmillerite, hydrogarnet, periclase, larnite, and chromite. The leaching ratio of Cr(VI) increased with decreasing solid-liquid ratio, which was hardly changed at the solid-liquid ratio of higher than 1:200. The amount of leaching Cr(VI) increased with the decrease of pH, while there was little difference in Cr(VI) leaching at the pH value of lower than 3. The dissolution of Cr(VI) in water is an endothermic process, resulting in increasing leaching Cr(VI) at higher temperatures. The leaching of Cr(VI) reached equilibrium in 8 hours in the batch experiments. The results of column experiment show that Cr(VI) should be rapidly washed away from a waste site during a precipitation, which causes severe hazard to the surrounding environment.