title: Ettringite-induced heave in chromite ore processing residue (COPR) upon ferrous sulfate treatment.
abstract: A pilot-scale treatment study was implemented at a deposition site of chromite ore processing residue (COPR) in New Jersey. Ferrous sulfate heptahydrate (FeSO4 x 7H2O) was employed to reduce hexavalent chromium in two dosages with three types of soil mixing equipment. XANES analyses of treated samples cured for 240 days indicated that all treatment combinations failed to meet the Cr(VI) regulatory limit of 240 mg/kg. More importantly, the discrepancy between XANES and alkaline digestion results renders the latter unreliable for regulatory purposes when applied to ferrous-treated COPR. Regardless of Cr-(VI), the introduction of reductant containing sulfate, mechanical mixing, water, acidity, and the resulting temperature increase in treated COPR promoted dissolution of brownmillerite (Ca2FeAlO5), releasing alumina and alkalinity. The pH increase caused initially precipitated gypsum (CaSO4 x 2H2O) to progressively convert to ettringite (Ca6Al2(SO4)3 x 32H2O) and its associated volume expansion under both in situ and ex situ conditions, with a maximum of 0.8 m vertical swell within 40 days of curing. While Cr-(VI) treatment remains a challenge, the intentional exhaustion of the heave potential of COPR by transforming all Al sources to ettringite emerges as a possible solution to delayed ettringite formation, which would hamper site redevelopment.
authors.affiliation: W.M. Keck Geoenvironmental Laboratory, Center for Environmental Systems, Stevens Institute of Technology, Hoboken, New Jersey 07030, USA.
authors.forename: Dimitris
authors.initials: D
authors.lastname: Dermatas
authors.forename: Maria
authors.initials: M
authors.lastname: Chrysochoou
authors.forename: Deok Hyun
authors.initials: DH
authors.lastname: Moon
authors.forename: Dennis G
authors.initials: DG
authors.lastname: Grubb
authors.forename: Mahmoud
authors.initials: M
authors.lastname: Wazne
authors.forename: Christos
authors.initials: C
authors.lastname: Christodoulatos
mesh_terms: D017608:Chromium Compounds / Q000737:chemistry*; D005296:Ferrous Compounds / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007220:Industrial Waste / Q000517:prevention & control; D008903:Minerals / Q000737:chemistry*; D010084:Oxidation-Reduction; D013052:Spectrometry, X-Ray Emission
chemical_list: D017608:Chromium Compounds; D005296:Ferrous Compounds; D007220:Industrial Waste; D008903:Minerals; C501337:ettringite; C020748:ferrous sulfate