title: Iron(VI) and iron(V) oxidation of copper(I) cyanide.
abstract: Copper(Il) cyanide (Cu(CN)4(3-)) in the gold mine industry presentsthe biggest concern in cyanide management because it is much more stable than free cyanide. Cu(CN)4(3-) is highlytoxic to aquatic life; therefore, environmentally friendly techniques are required for the removal of Cu(CN)4(3-) from gold mine effluent. The oxidation of Cu(CN)4(3-) by iron-(VI) (FeVIO4(2-), Fe(VI)) and iron(V) (FeVO4(3-), Fe(V)) was studied using stopped-flow and premix pulse radiolysis techniques. The stoichiometry with Fe(VI) was determined to be 5HFeO(4-) + Cu(CN)4(3-) + 8H2O - > 5Fe(OH)3 + Cu2+ + 4CNO- +3/202 + 6OH-. The rate law for the oxidation of Cu(CN)4(3-) by Fe(VI) was found to be first-order with each reactant. The rates decreased with increasing pH and were mostly related to a decrease in concentration of reactive protonated Fe(VI) species, HFeO4-. A mechanism is proposed that agrees with the observed reaction stoichiometry and rate law. The rate constant for the oxidation of Cu(CN)4(3-) by Fe(V) was determined at pH 12.0 as 1.35 +/- 0.02 x 10(7) M(-1) s(-1), which is approximately 3 orders of magnitude larger than Fe(VI). Results indicate that Fe(VI) is highly efficient for removal of cyanides in gold mill effluent.
authors.affiliation: Chemistry Department, Florida Institute of Technology, 150 West University Boulevard, Melbourne, Florida 32901, USA. vsharma@fit.edu
authors.forename: Virender K
authors.initials: VK
authors.lastname: Sharma
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Burnett
authors.forename: Ria A
authors.initials: RA
authors.lastname: Yngard
authors.forename: Diane E
authors.initials: DE
authors.lastname: Cabelli
mesh_terms: D003300:Copper / Q000302:isolation & purification*; D003486:Cyanides / Q000302:isolation & purification*; D006046:Gold; D007501:Iron / Q000737:chemistry*; D008906:Mining; D010084:Oxidation-Reduction; D014874:Water Pollutants, Chemical / Q000302:isolation & purification*; D018508:Water Purification / Q000379:methods*
chemical_list: D003486:Cyanides; D014874:Water Pollutants, Chemical; D006046:Gold; D003300:Copper; D007501:Iron; C057807:copper(II) cyanide