Cr(VI) reduction and immobilization by magnetite under alkaline pH conditions: the role of passivation.
This study investigated Cr(VI) reduction and immobilization by magnetite under alkaline pH conditions similar to those present at the Hanford site. Compared to acidic and neutral pH, chromium(VI) reduction by magnetite at high pH conditions is limited (<20% of potential reduction capacity), and the extent of reduction does not vary significantly with increasing NaOH concentration. This is due to the formation of maghemite, goethite, and/or Fe1-xCrxOOH, which may form a passivation layer on the magnetite surface, stopping further chromate reduction. Maghemite is formed in lower NaOH concentrations. The extent of goethite formation increases with NaOH concentration. Goethite may be formed through two mechanisms: (i) dissolution of magnetite leads to the precipitation of goethite and/or (ii) dissolution of newly formed maghemite intermediate, followed by precipitation of goethite. Extended X-ray absorption fine structure spectroscopy shows that Cr has a similar structural environment at alkaline pH as at acidic and circumneutral conditions.
He
Y Thomas
YT
Environmental Science Graduate Program, The Ohio State University, Columbus, Ohio 43210, USA. he.51@osu.edu
Traina
Samuel J
SJ
D002857:Chromium / Q000737:chemistry*; D052203:Ferrosoferric Oxide / Q000138:chemical synthesis / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D058085:Iron Compounds / Q000138:chemical synthesis; D046529:Microscopy, Electron, Transmission; D008903:Minerals; D010084:Oxidation-Reduction; D012972:Sodium Hydroxide / Q000737:chemistry; D013057:Spectrum Analysis; D014961:X-Ray Diffraction
D058085:Iron Compounds; D008903:Minerals; D002857:Chromium; C094886:goethite; C074702:chromium hexavalent ion; D012972:Sodium Hydroxide; D052203:Ferrosoferric Oxide