Long-Term Leaching Characteristics of Chromite Ore Processing Residue Using Synthetic Groundwater

Long-term leaching characteristics of chromium ore processing residue (COPR) (≈ 250 pore volumes of flow, PVF) was investigated using laboratory flow-through column testing with synthetic groundwater (GW). Two saturated flow-through column experiments simulated the long-term migration of total [Cr(T)] and hexavalent chromium [Cr(VI)] from two types of COPR [unweathered, gray-black (GB) and weathered, hard-brown (HB)] via advective groundwater flow. The release of Cr(T) and Cr(VI) from GB and HB COPR showed peak concentration before 5.5 PVFs, and decreased significantly thereafter. The long-term concentration of Cr(T) and Cr(VI) from GB COPR after 150 PVFs were found to be 21 ± 4 mg/L and 20 ± 5 mg/L, respectively, while, concentration of Cr(T) and Cr(VI) from HB COPR after 150 PVFs were found to be 25 ± 4 mg/L and 23 ± 3 mg/L, respectively. The GB COPR released 21.3% w/w Cr(T), and the HB released more Cr(T) (32.4% w/w) within the testing period. However, a significant amount (> 65%) of chromium remained in the COPR and will continue releasing for an even longer period. Amorphous compounds may be an important sink related to release of chromium, which can explain the higher release of Cr from HB COPR.