title: Ferrate(VI) oxidation of weak-acid dissociable cyanides.
abstract: Cyanide is commonly found in electroplating, mining, coal gasification, and petroleum refining effluents, which require treatment before being discharged. Cyanide in effluents exists either as free cyanide or as a metal complex. The kinetics of the oxidation of weak-acid dissociable cyanides by an environmentally friendly oxidant, ferrate(VI) (Fe(VI)O4(2-), Fe(VI)), were studied as a function of pH (9.1-10.5) and temperature (15-45 degrees C) using a stopped-flow technique. The weak-acid dissociable cyanides were Cd(CN)4(2-) and Ni(CN)4(2-), and the rate-laws for the oxidation may be -d[Fe(VI)]/dt = k[Fe(VI)][M(CN)4(2-)]n where n = 0.5 and 1 for Cd(CN)4(2-) and Ni(CN)4(2-), respectively. The rates decreased with increasing pH and were mostly related to a decrease in concentration of the reactive protonated Fe(VI) species, HFeO4(-). The stoichiometries with Fe(VI) were determined to be: 4HFeO4(-) + M(CN)4(2-) + 6H2O --> 4Fe(OH)3 + M(2+) + 4NCO(-) + O2 + 4OH(-). Mechanisms are proposed that agree with the observed reaction rate-laws and stoichiometries of the oxidation of weak-acid dissociable cyanides by Fe(VI). Results indicate that Fe(VI) is effective in removing cyanide in coke oven plant effluent, where organics are also present.
authors.affiliation: Chemistry Department, Florida Institute of Technology, 150 West University Boulevard, Melbourne, Florida 32901, USA.
authors.forename: Ria A
authors.initials: RA
authors.lastname: Yngard
authors.forename: Virender K
authors.initials: VK
authors.lastname: Sharma
authors.forename: Jan
authors.initials: J
authors.lastname: Filip
authors.forename: Radek
authors.initials: R
authors.lastname: Zboril
mesh_terms: D003077:Coke; D003486:Cyanides / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007220:Industrial Waste; D007501:Iron / Q000737:chemistry*; D007700:Kinetics; D010084:Oxidation-Reduction; D013696:Temperature; D014865:Waste Disposal, Fluid / Q000379:methods; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D018508:Water Purification / Q000379:methods
chemical_list: D003077:Coke; D003486:Cyanides; D007220:Industrial Waste; D014874:Water Pollutants, Chemical; C017311:ferrate ion; D007501:Iron