Remediation of chromite ore processing residue using ferrous sulfate and calcium polysulfide

Mahmoud Wazne, Deok Hyun Moon, Santhi Chandra Jagupilla, Sarath Chandra Jagupilla, Christos Christodoulatos, Dimitris Dermatas, Maria Chrysochoou

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29 Scopus citations

Abstract

Batch tests were conducted to assess the potential use of ferrous sulfate and calcium polysulfide for the remediation of chromite ore processing residue (COPR). The remediation process entails addition of ferrous sulfate or calcium polysulfide to chemically reduce hexavalent chromium [Cr(VI)] to trivalent chromium [Cr(III)] in slurry form and pH adjustment to precipitate Cr(IIl) as chromium hydroxide. The present study investigates the effects of COPR particle size, treatment pH, and chemical dosage on the performance of the treatment. Smaller particle size resulted in increases in alkaline digestion and Toxicity Characteristic Leaching Procedure (TCLP) Cr(VT) concentrations for the untreated samples. The chemical reduction of Cr(VI) with ferrous iron and sulfides was non-stoichiometric. Four times the stoichiometric amount of ferrous iron or two times the stoichiometric amount of polysulfide were needed to meet both the New Jersey Department of Environmental Protection (NJDEP) regulatory limit of 240 mg/kg for Cr(VI) and EPA TCLP regulatory limit of 5mg/L for chromium [Cr]. pH adjustment was necessary to prevent the formation of ettringite, a swell causing mineral, upon the introduction of sulfate to the COPR material via ferrous sulfate or calcium polysulfide. The slow hydration of some COPR minerals caused the pH of the treated COPR to creep upward during the curing period. However, when sufficient acid was added, the pH value was controlled at less than 9.27 for a curing period of 1.5 years, which prevented the formation of ettringite.

Original languageEnglish
Pages (from-to)105-110
Number of pages6
JournalGeosciences Journal
Volume11
Issue number2
DOIs
StatePublished - 30 Jun 2007

Keywords

  • COPR
  • Chromite
  • Ettringite
  • Ferrous
  • Polysulfide

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