Extraction of Hexavalent Chromium from Chromium Ore Processing Residue Using Salted Aqueous Solutions

Extraction of hexavalent chromium (Cr(VI)) from chromite ore processing residue (COPR) with salted aqueous solutions containing ammonium, sodium, sulfate and chloride was investigated. Batch experiments scheduled with Experimental Design Methodology were performed. The results showed that aqueous solutions of ammonium sulfate were superior to others for the Cr(VI) extraction. Under the condition of room temperature, 24 h of liquid-solid contact with reciprocal vibration, liquid-solid ratio 10 mL/g and COPR size in 0.1-1.0mm, 1 M aqueous solutions of ammonium sulfate extracted twice more Cr(VI) than the USEPA Method 3060a procedure did. Mathematical analysis based on the experimental data demonstrated that 0.2M aqueous solutions of ammonium sulfate, liquid-solid ratio 5 mL/g and COPR size in 0.1-0.5mm are adequate to extract Cr(VI) from COPR. This research indicates that assessment of the Cr(VI) content in COPR with the USEPA Method 3060a procedure is inadequate, and extraction of Cr(VI) with the solution of ammonium sulfate may be as one of the choices to detoxify COPR.