Remediation of lime-free roasting chromite ore processing residue (COPR) by water leaching and pyrolysis process

Abstract

ABSTRACTLime-free roasting process, instead of high lime roasting process and less lime roasting process, has become the dominant method producing chromate salt all over the world. Remediation process and utilization treatment of chromite ore processing residue (COPR) is an environmental issue which is not solved completely. Based on the characteristics of industrial lime-free COPR, a two-step treatment procedure including water leaching and biomass pyrolysis was proposed in this study. The results indicated that the main components of the COPR were (Fe, Mg) (Cr, Fe)2O4 and MgCr2O4, and the contents of Cr2O3 and Cr (VI) in untreated COPR were 12.2% and 1130 mg/kg, respectively. After water leaching, the Cr (VI) content reduced to 312 mg/kg. The removal rate was 72.3%. Pyrolysis parameters, including heating temperature, sawdust ratio, heating time, were systematically studied and the optimal experimental values were 500°C, 20%, and 25 min. The content of Cr (VI) in the final treated COPR was 3.7 mg/kg, which could be further utilized as resource material.