Cost-effective strategy of treating chromite ore processing residue (COPR); production of chromate, subsequent detoxification and in-situ stabilization

Abstract

It is a great importance of finding the cost-effective strategy of treating chromite ore processing residue (COPR). Cr(Ⅵ), presented in aqueous media, could easily be reduced, adsorption and removed from water body through a proper treatment, but Cr(Ⅵ), incorporated in COPR, could not, due to its characteristic inherent to COPR. In general, the reduction and adsorption of Cr(Ⅵ) could take place at a low pH, the COPR, however, has a high acid neutralizing capacity, so that a great deal of the inorganic acid would be required to maintain its pH at low value. In this work, a series of treatment trials, comprised of the production of chromate from COPR by leaching process, the subsequent detoxification and in-situ stabilisation of post-leached COPR (plCOPR) were conducted. After column extracting process using the seawater, Cr(Ⅵ)-containing leachate of 600~800 mg/L is led to the ion exchange columns, charged with the anion exchange resin, to adsorb the Cr(Ⅵ) until the effluent contains Cr(Ⅵ) of 5 mg/L. The Cr(Ⅵ) loaded ion exchange column was eluted by NaOH solution and the maximum concentration of Cr(Ⅵ) in the elution was 43.1 g/L. Afterward, plCOPR was mixed with sodium sulfide and iron sulfide+lime as a reductant and a stabiliser, respectively, and the mixture was discharged directly from the mixer and piled on a certain area. After 360 d of curing, Cr(VI) concentration in the leachate from the toxicity characteristic leaching procedure (TCLP) was arrived at 1.2 mg/L, below the regulatory limit disposal standard (HJ/T 301-2007, 3 mg/L).