Long-term treatment issues with chromite ore processing residue (COPR): Cr6+ reduction and heave

Deok Hyun Moon, Mahmoud Wazne, Dimitris Dermatas, Christos Christodoulatos, Adriana M. Sanchez, Dennis G. Grubb, Maria Chrysochoou, Min Gyu Kim

Research output: Contribution to journalArticlepeer-review

70 Scopus citations

Abstract

A pugmill treatability study was conducted to remediate chromite ore processing residue (COPR) using ferrous sulfate heptahydrate (FeSO4·7H2O) as a reductant. Two different types of COPR, with respect to particle size and mineralogy, were tested in this study. Two different stoichiometric ratios of FeSO4·7H2O to Cr6+ (5× and 8×) were applied to reduce Cr6+ to Cr3+. The effectiveness of FeSO4·7H2O treatment was assessed using the toxicity characteristic leaching procedure (TCLP) tests and X-ray absorption near edge structure (XANES) analyses. TCLP results obtained from the pugmill treatability study showed that TCLP Cr concentrations were less than the TCLP regulatory limit of 5 mg/L upon 8× FeSO4·7H2O treatment for up to 420 days but may fail to meet this regulatory limit in the long-term. XANES results obtained from samples cured for 300 days showed that all of the treated samples failed the New Jersey Department of Environmental Protection (NJDEP) clean up level for Cr6+ of 240 mg/kg. However, the Cr6+ concentration from the sample with the smaller particle size approached 240 mg/kg (338 mg/kg), suggesting that particle size reduction prior to the addition of reductant may improve the effectiveness of the treatment. COPR heaving was investigated with unconfined swell tests upon 5× and 8× FeSO4·7H2O treatment. The formation of ettringite, an expansive material, was investigated following the swell tests using X-ray powder diffraction (XRPD). Significant heaving (>50 vol%) was observed at curing times of 138 days for the 5× treatment and the ettringite formation was identified by XRPD analyses.

Original languageEnglish
Pages (from-to)629-635
Number of pages7
JournalJournal of Hazardous Materials
Volume143
Issue number3
DOIs
StatePublished - 17 May 2007

Keywords

  • Chromite ore processing residue (COPR)
  • Chromium (Cr)
  • Ettringite
  • Ferrous sulfate heptahydrate (FeSO·7HO)
  • Heaving
  • X-ray absorption near edge structure (XANES)
  • X-ray powder diffraction (XRPD)

Fingerprint

Dive into the research topics of 'Long-term treatment issues with chromite ore processing residue (COPR): Cr6+ reduction and heave'. Together they form a unique fingerprint.

Cite this