Detoxification of Chromite Ore Processing Residue by Combination Process of Heap Leaching and Reduction

With Na2CO3 solution as leaching reagent and FeSO4 as reductant,a new combination process of heap leaching and reduction was investigated to detoxify chromite ore processing residue(COPR).The results show that the pH value of leaching solution varies from 10 to 12,and the factual concentration of Cr(VI) in leaching solution after reduction exceeds the theoretic value slightly in the whole process.In the first leaching stage,most of Cr(VI) in brownmillerite or hydrogarnet in COPR may be released,the concentration of Na2CO3 in solution reduces from 9.3 g/L to 7.98 g/L,and the leaching rate of Cr(VI) is 62.67%.For the later cycles,the concentration of Na2CO3 maintains about 8 g/L,the leaching rate of Cr(VI) increases slowly.After the twelfth cycle,the leaching rate of Cr(VI) is up to 85%,and the remaining Cr(VI) in final detoxificated COPR may be present in hydrotalcite.Particle size of COPR has a big influence on detoxification effect,and the Cr(VI) and total Cr concentration in leachate of toxicity characteristic leaching procedure(TCLP) of the final detoxificated COPR is 1.98 mg/L and 2.45 mg/L,respectively,meeting the landfill standard for common industrial solid waste when the particle size of COPR is less than 0.15 mm.