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

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doi: 10.1016/S0016-7037(02)00977-8
Authors:Geelhoed, Jeanine S.; Meeussen, Johannes C. L.; Hillier, Stephen; Lumsdon, David G.; Thomas, Rhodri P.; Farmer, John G.; Paterson, Edward
Author Affiliations:Primary:
Macaulay Institute, Aberdeen, United Kingdom
University of Edinburgh, United Kingdom
Volume Title:Geochimica et Cosmochimica Acta
Source:Geochimica et Cosmochimica Acta, 66(22), p.3927-3942. Publisher: Pergamon, Oxford, International. ISSN: 0016-7037
Publication Date:2002
Note:In English. 56 refs.; illus., incl. 7 tables
Summary:Chromite ore processing residue (COPR) contains very high levels of chromium as Cr(III) and Cr(VI) and has a pH of ∼11.5 to 12. Millions of tonnes of COPR have in the past been deposited in urban areas. We have studied the factors that control leaching of Cr(VI), Ca, Al, Si, and Mg from COPR by means of batch experiments, mineralogical characterization of COPR via X-ray powder diffraction and scanning electron microscopy, and chemical equilibrium modeling. Batch experiments at a range of pH values and two liquid:solid ratios showed that mineral solubility control exists for aqueous concentrations of Cr(VI) above pH 10. Calculations indicate that the solid phases that control the solubility of Cr(VI) at pH values above 11 are Cr(VI)-substituted hydrogarnet (Ca3Al2(H4O4, CrO4)3) and Cr(VI)-hydrocalumite (Ca4Al2(OH)12CrO4·6 H2O), a layered double-hydroxide clay with chromate anions held in the interlayers. In the pH range 9.5 to 11, the description of the Cr(VI) concentration in solution was strongly improved by the incorporation in the model of Cr(VI)-ettringite (Ca6Al2(OH)12(CrO4)3·26 H2O), which precipitates as a secondary phase when hydrocalumite dissolves. The proposed model for leaching of COPR at high pH includes Cr(VI)-bearing hydrogarnet, Cr(VI)-hydrocalumite, Cr(VI)-ettringite, brucite, calcite, Ca2Al2(OH)10·3 H2O, CaH2SiO4, and gehlenite hydrate (Ca2Al2(OH)6SiO8H8·H2O). The model accurately predicts the concentrations of Cr(VI), Ca, Al, Si, and Mg in solution in the pH range 10 to 12 as well as the pH-buffering behavior. Below pH 8, a decrease in the Cr(VI) concentration in solution is observed, which may be attributed to sorption of chromate onto freshly precipitated Al and Fe hydroxide surfaces. Sulfate and carbonate show the same type of behavior as chromate. The chemistry of COPR shows similarities with cement and high-pH municipal waste incinerator bottom ash. Abstract Copyright (2002) Elsevier, B.V.
Subjects:Beneficiation; Case studies; Chromite ores; Chromium; Concentration; Controls; Experimental studies; Geochemistry; Identification; Leaching; Major elements; Metal ores; Metals; PH; Pollution; Powder method; Quantitative analysis; SEM data; Soils; Spectra; Spoils; Toxic materials; Waste disposal; X-ray diffraction data; X-ray fluorescence spectra; X-ray spectra; XANES spectra; Europe; Glasgow Scotland; Great Britain; Scotland; United Kingdom; Western Europe; Strathclyde region Scotland
Coordinates:N555300 N555300 W0041500 W0041500
Record ID:2003007084
Copyright Information:GeoRef, Copyright 2018 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
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