title: On the removal of hexavalent chromium from a Class F fly ash.
abstract: Coarse and fine samples of a Class F fly ash obtained from commercial combustion of Illinois bituminous coal have been exposed to two long-term leaching tests designed to simulate conditions in waste impoundments. ICP-AES analysis indicated that the coarse and fine fly ash samples contained 135 and 171mg/kg Cr, respectively. Measurements by XAFS spectroscopy showed that the ash samples originally contained 5 and 8% of the chromium, respectively, in the hexavalent oxidation state, Cr(VI). After exposure to water for more than four months, the percentage of chromium as Cr(VI) in the fly-ash decreased significantly for the coarse and fine fly-ash in both tests. Combining the XAFS data with ICP-AES data on the concentration of chromium in the leachates indicated that, after the nineteen-week-long, more aggressive, kinetic test on the coarse fly ash, approximately 60% of the Cr(VI) had been leached, 20% had been reduced to Cr(III) and retained in the ash, and 20% remained as Cr(VI) in the ash. In contrast, during the six-month-long baseline test, very little Cr was actually leached from either the coarse or the fine fly-ash (<0.1mg/kg); rather, about 66% and 20%, respectively, of the original Cr(VI) in the coarse and fine fly-ash was retained in the ash in that form, while the remainder, 34% and 80%, respectively, was reduced and retained in the ash as Cr(III). The results are interpreted as indicating that Cr(VI) present in Class F fly-ash can be reduced to Cr(III) when in contact with water and that such chemical reduction can compete with physical removal of Cr(VI) from the ash by aqueous leaching.
authors.affiliation: Department of Chemical and Materials Engineering, University of Kentucky, Lexington, KY 40506, USA.
authors.forename: F E
authors.initials: FE
authors.lastname: Huggins
authors.affiliation: Mining Engineering Department, University of Kentucky, Lexington, KY 40506, USA. Electronic address: m.rezaee98@gmail.com.
authors.forename: M
authors.initials: M
authors.lastname: Rezaee
authors.affiliation: Mining Engineering Department, University of Kentucky, Lexington, KY 40506, USA.
authors.forename: R Q
authors.initials: RQ
authors.lastname: Honaker
authors.affiliation: Center for Applied Energy Research, University of Kentucky, Lexington, KY 40506, USA.
authors.forename: J C
authors.initials: JC
authors.lastname: Hower
mesh_terms: D002857:Chromium / Q000737:chemistry* / Q000302:isolation & purification*; D060729:Coal Ash / Q000737:chemistry*; D004785:Environmental Pollutants / Q000032:analysis* / Q000302:isolation & purification*; D012037:Refuse Disposal; D013054:Spectrophotometry, Atomic; D018505:Waste Management / Q000379:methods*; D014867:Water / Q000737:chemistry*; D056928:X-Ray Absorption Spectroscopy
chemical_list: D060729:Coal Ash; D004785:Environmental Pollutants; D014867:Water; D002857:Chromium; C074702:chromium hexavalent ion
keywords: Aqueous leaching; Chemical reduction; Chromium; Cr(VI); Fly ash