Characterization of chromium-bearing mineral species in the chromite ore processing residue and leaching characteristics

In order to investigate the leachability of chromium from chromite ore processing residue (COPR) during the detoxification process, the leaching behavior of total chromium, hexavalent chromium and other main metal elements in the COPR samples under different pH were evaluated. The chemical compositions and mineral phases of COPR were analyzed by X-ray fluorescence spectrometry (XRF), X-ray power diffraction (XRPD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The results indicated that Cr⁶⁺ exist as the major fraction in both leachates of the sulfuric acid/nitric acid extraction and the toxicity characteristic leaching procedure (TCLP) extraction. Strong alkaline properties of COPR and its large alkaline buffer capacity were the two main factors affected the detoxification process using reduction method. Therefore, the chosen of an optimum pH is the key process to enhance the leachability of hexavalent chromium from COPR. High leachability of hexavalent chromium from COPR can be achieved under pH8.0, with a relatively low operational cost.