Identification and geochemical modeling of processes controlling leaching of Cr(VI) and other major elements from chromite ore processing residue

Geelhoed, Jeanine S.; Meeussen, J.C.L.; Hillier, S. J.; Lumsdon, David G.; Thomas, R.P.; Farmer, John G.; Paterson, E.

doi:10.1016/s0016-7037(02)00977-8

Cited by 153 publications

(144 citation statements)

References 39 publications

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“…5. The mineral assemblage of untreated COPR in this study was consistent with COPR mineralogy reported previously [35,36]. Cr(VI)-bearing minerals identified in the untreated COPR included hydrocalumite and katoite hydrogarnet, which are demonstrated hosts for Cr(VI) in COPR samples through anionic substitution [35,37].…”

Section: X-ray Powder Diffraction (Xrpd) Analysissupporting

confidence: 88%

Reduction and immobilization of chromate in chromite ore processing residue with nanoscale zero-valent iron

et al. 2012

Journal of Hazardous Materials

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Keywords:Chromite ore processing residue (COPR) Nanoscale zero-valent iron (nZVI) X-ray absorption near edge structure (XANES) spectroscopy Chromate leachability Speciation a b s t r a c t Chromite ore processing residue (COPR) poses a great environmental and health risk with persistent Cr(VI) leaching. To reduce Cr(VI) and subsequently immobilize in the solid matrix, COPR was incubated with nanoscale zero-valent iron (nZVI) and the Cr(VI) speciation and leachability were studied. Multiple complementary analysis methods including leaching tests, X-ray powder diffraction, X-ray absorption near edge structure (XANES) spectroscopy, and X-ray photoelectron spectroscopy (XPS) were employed to investigate the immobilization mechanism. Geochemical PHREEQC model calculation agreed well with our acid neutralizing capacity experimental results and confirmed that when pH was lowered from 11.7 to 7.0, leachate Cr(VI) concentrations were in the range 358-445 mg L −1 which contributed over 90% of dissolved Cr from COPR. Results of alkaline digestion, XANES, and XPS demonstrated that incubation COPR with nZVI under water content higher than 27% could result in a nearly complete Cr(VI) reduction in solids and less than 0.1 mg L −1 Cr(VI) in the TCLP leachate. The results indicated that remediation approaches using nZVI to reduce Cr(VI) in COPR should be successful with sufficient water content to facilitate electron transfer from nZVI to COPR.

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Section: X-ray Powder Diffraction (Xrpd) Analysissupporting

confidence: 88%

Reduction and immobilization of chromate in chromite ore processing residue with nanoscale zero-valent iron

et al. 2012

Journal of Hazardous Materials

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“…The presence of Mg-rich phases is important for Cr(VI) release, given the fact that they are stable over a wider range of pH than Ca-Al-rich hydrogarnet and CACs. Geelhoed et al (23), Chrysochoou (19), and Tinjum et al (6) showed hydrotalcite and brucite peaks surviving down to pH 7 upon acid addition to COPR. Given that the majority of Cr(VI) (∼50%) was associated with this fraction, it is concluded that to facilitate quick release of Cr(VI) from GB COPR, the addition of substantial amounts of acid and particle size reduction would likely be required.…”

Section: Discussion and Environmental Significancementioning

confidence: 99%

Microstructural Analyses of Cr(VI) Speciation in Chromite Ore Processing Residue (COPR)

Chrysochoou

Fakra

Marcus

et al. 2009

Environ. Sci. Technol.

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The speciation and distribution of Cr(VI) in the solid phase was investigated for two types of chromite ore processing residue (COPR) found at two deposition sites in the United States: gray-black (GB) granular and hard brown (HB) cemented COPR. COPR chemistry and mineralogy were investigated using micro-X-ray absorption spectroscopy and micro-X-ray diffraction, complemented by laboratory analyses. GB COPR contained 30% of its total Cr(VI) (6000 mg/kg) as large crystals (>20 µm diameter) of a previously unreported Na-rich analog of calcium aluminum chromate hydrates. These Cr(VI)-rich phases are thought to be vulnerable to reductive and pH treatments. More than 50% of the Cr(VI) was located within nodules, not easily accessible to dissolved reductants, and bound to Fe-rich hydrogarnet, hydrotalcite, and possibly brucite. These phases are stable over a large pH range, thus harder to dissolve. Brownmillerite was also likely associated with physical entrapment of Cr(VI) in the interior of nodules. HB COPR contained no Cr(VI)-rich phases; all Cr(VI) was diffuse within the nodules and absent from the cementing matrix, with hydrogarnet and hydrotalcite being the main Cr(VI) binding phases. Treatment of HB COPR is challenging in terms of dissolving the acidity-resistant, inaccessible Cr(VI) compounds; the same applies to ∼50% of Cr(VI) in GB COPR.

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“…Typical mineral phases include Calcite, Ettringite, Hydrogarnet and Brownmillerite 7 Although the exact mineralogy depends on the initial processing mixture and whether constituents such as Brownmillerite have undergone hydration reactions post processing. 7 Water in contact with high-lime COPR has a characteristically high pH of 11.5-12, 6 and can contain up to 1.6 mmol.L -1 Cr(VI) as chromate 8 . Until recently COPR has been used as a fill material for roads and other construction projects, 4,6,9 or was dumped in unlined tips [10][11][12][13] .…”

Section: Introductionmentioning

confidence: 99%

“…7 Water in contact with high-lime COPR has a characteristically high pH of 11.5-12, 6 and can contain up to 1.6 mmol.L -1 Cr(VI) as chromate 8 . Until recently COPR has been used as a fill material for roads and other construction projects, 4,6,9 or was dumped in unlined tips [10][11][12][13] . As a result there are numerous sites around the world where water from COPR is contaminating the surrounding area with Cr(VI), which is a major concern as Cr(VI) is carcinogenic, mutagenic and toxic.…”

Section: Introductionmentioning

confidence: 99%

Chromate Reduction in Highly Alkaline Groundwater by Zerovalent Iron: Implications for Its Use in a Permeable Reactive Barrier

Fuller

Stewart

Burke

2013

Ind. Eng. Chem. Res.

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It is not currently known if the widely used reaction of zero valent iron (ZVI) and Cr(VI) can be used in a permeable reactive barrier (PRB) to immobilise Cr leaching from hyper alkaline chromite ore processing residue (COPR). This study compares Cr(VI) removal from COPR leachate and chromate solution by ZVI at high pH. Cr(VI) removal occurs more rapidly from the chromate solution than from COPR leachate. The reaction is first order with respect to both [Cr(VI)] and the iron surface area, but iron surface reactivity is lost to the reaction.Buffering pH downwards produces little change in the removal rate or the specific capacity of iron until acidic conditions are reached. SEM and XPS analysis confirm that reaction products accumulate on the iron surface in both liquors, but that other surface precipitates also form in COPR leachate. Leachate from highly alkaline COPR contains Ca, Si and Al that precipitate on the iron surface and significantly reduce the specific capacity of iron to reduce Cr(VI). This study suggests that although Cr (VI) reduction by ZVI will occur at hyper alkaline pH, other solutes present in COPR leachate will limit the design life of a PRB. 4

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Identification and geochemical modeling of processes controlling leaching of Cr(VI) and other major elements from chromite ore processing residue

Cited by 153 publications

References 39 publications

Reduction and immobilization of chromate in chromite ore processing residue with nanoscale zero-valent iron

Reduction and immobilization of chromate in chromite ore processing residue with nanoscale zero-valent iron

Microstructural Analyses of Cr(VI) Speciation in Chromite Ore Processing Residue (COPR)

Chromate Reduction in Highly Alkaline Groundwater by Zerovalent Iron: Implications for Its Use in a Permeable Reactive Barrier

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