title: Oxidation of Ni(II)-cyano and Co(III)-cyano complexes by Ferrate(VI): effect of pH.
abstract: Free cyanide (CN(-)) and metal-cyanide complexes (tetracyanonickelate(II)), Ni(CN)4(2-) and hexacyanocobaltate(III)), Co(CN)6(3-) are common constituents of effluents of mining, coal gasification, and petroleum refining. This article presents the degradation of Ni(CN)4(2-) and Co(CN)6(3-) by ferrate(VI) (Fe(VI)O4(2-), Fe(VI)) in alkaline media. The effect of pH (9.0-11.0) and reactant molar ratios on the degradation of the cyanide complexes was investigated. The removal of Ni(CN)4(2-) ion in 200 min was found to be > 90% at pH 9.0; forming cyanate (NCO(-)) ions as the stoichiometric products ([Fe(VI)]:[Total CN(-)] = [Fe(VI)]:[NCO(-)] ≈ 1.0). The degradation efficiency decreased with an increase in pH from 9.0 to 11.0. Comparatively, the Co(CN)6(3-) ion could be degraded only up to 10% in 200 min at pH 9.0 and the final oxidized products were nitrite and nitrate ions. The oxidation efficiency of removing Co(CN)6(3-) did not vary significantly with pH. Fe(VI) consumptions as a result of the oxidation of free cyanide and metal-cyanides and their products are compared and discussed.
authors: a Department of Environmental Engineering, Faculty of Engineering , Chulalongkorn University , Thailand.
authors: Khemarath
authors: K
authors: Osathaphan
authors: Wasinee
authors: W
authors: Kittisarn
authors: Prapaporn
authors: P
authors: Chatchaitanawat
authors: Ria A
authors: RA
authors: Yngard
authors: Hyunook
authors: H
authors: Kim
authors: Virender K
authors: VK
authors: Sharma
mesh_terms: D003035:Cobalt / Q000737:chemistry*; D003486:Cyanides / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry*; D008906:Mining; D009532:Nickel / Q000737:chemistry*; D010084:Oxidation-Reduction
chemical_list: D003486:Cyanides; C017311:ferrate ion; D003035:Cobalt; C047503:tetracyanonickelate; D009532:Nickel; D007501:Iron
keywords: Complexed cyanide; cyanate; cyanide; ferrate; nitrate; nitrite; removal