title: Immobilization of chromate in hyperalkaline waste streams by green rusts and zero-valent iron.
abstract: Zero-valent iron (ZVI) and green rusts can be used as reductants to convert chromium from soluble, highly toxic Cr(VI) to insoluble Cr(III). This study compared the reduction rates of Cr(VI) by ZVI and two carbonate green rust phases in alkaline/hyperalkaline solutions. Batch experiments were carried out with synthetic chromate solutions at pH 7.7-12.3 and a chromite ore processing residue (COPR) leachate (pH approximately 12.2). Green rust removes chromate from high pH solutions (pH 10-12.5) very rapidly (<400 s). Chromate reduction rates for both green rust phases were consistently higher than for ZVI throughout the pH range studied; the surface area normalized rate constants were two orders of magnitude higher in the COPR leachate solution at pH 12.2. The performances of both green rusts were unaffected by changes in pH. In contrast, ZVI exhibited a marked decline in reduction rate with increasing pH to become almost ineffective above pH12.
authors.affiliation: School of Earth and Environment, Earth Surface Science Institute, University of Leeds, Leeds LS2 9JT UK. c.m.rogers@leeds.ac.uk
authors.forename: Christine M
authors.initials: CM
authors.lastname: Rogers
authors.affiliation: School of Earth and Environment, Earth Surface Science Institute, University of Leeds, Leeds LS2 9JT UK.
authors.forename: Ian T
authors.initials: IT
authors.lastname: Burke
authors.affiliation: School of Earth and Environment, Earth Surface Science Institute, University of Leeds, Leeds LS2 9JT UK.
authors.forename: Imad A M
authors.initials: IA
authors.lastname: Ahmed
authors.affiliation: School of Earth and Environment, Earth Surface Science Institute, University of Leeds, Leeds LS2 9JT UK.
authors.forename: Samuel
authors.initials: S
authors.lastname: Shaw
mesh_terms: D000327:Adsorption; D000468:Alkalies / Q000737:chemistry; D002840:Chromates / Q000737:chemistry / Q000302:isolation & purification*; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry*; D058085:Iron Compounds / Q000737:chemistry*; D008903:Minerals / Q000737:chemistry*; D010087:Oxides / Q000737:chemistry*; D045483:Rivers / Q000737:chemistry*; D014462:Ultrafiltration / Q000379:methods; D062065:Wastewater / Q000032:analysis*; D014874:Water Pollutants, Chemical / Q000737:chemistry / Q000302:isolation & purification*; D018508:Water Purification / Q000379:methods*
chemical_list: D000468:Alkalies; D002840:Chromates; D007501:Iron; D058085:Iron Compounds; D008903:Minerals; D010087:Oxides; D062065:Wastewater; D014874:Water Pollutants, Chemical; C517972:fougerite