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

ABSTRACT

Lime-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.

KEYWORDS:

• Calcium-free roasting process
• COPR
• hexavalent chromium
• pyrolysis
• remediation

Acknowledgments

The authors thank the following projects for financial support: Research Starting Project of Chongqing University of Technology, Key and Common Technologies of Key Industry of Chongqing China (cstc2017zdcy-zdyfX0003) and Excellent Achievement Transformation Project of Chongqing (KJZH17128).