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.

Application of Potassium Ferrate(vi) for Oxidation of Selected Pollutants in Aquatic Environment – Short Review

“…Therefore, the use of potassium ferrate(VI) has allowed decomposition of copper-cyanide complexes, while the oxidation of nickel-cyanide complexes may require a long reaction time. Literature data [8,[10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] indicate that it is also possible to decompose other inorganic compounds, which are summarized in Table 1.…”

Rapid and efficient removal of Ni(II) in water using constant-current electrolysis

“…Removal of Ni is a challenging task and numerous treatment methods have been suggested, which include biological methods, ion exchange on either resin or zeolite, adsorption on red mud or activated carbon, microfiltration, chemical precipitation, and electrochemical techniques [8,[12][13][14][15][16][17] treatment methods seem promising as it is a relatively cleaner process involving the application of electrons and electrodes. The different methods comprise electrocoagulation, electrodialysis, electrodeionization, and electrodeposition [18][19][20][21][22][23].…”