title: Mechanisms and efficiency of the simultaneous removal of metals and cyanides by using ferrate(VI): crucial roles of nanocrystalline iron(III) oxyhydroxides and metal carbonates.
abstract: The reaction of potassium ferrate(VI), K(2)FeO(4), with weak-acid dissociable cyanides--namely, K(2)[Zn(CN)(4)], K(2)[Cd(CN)(4)], K(2)[Ni(CN)(4)], and K(3)[Cu(CN)(4)]--results in the formation of iron(III) oxyhydroxide nanoparticles that differ in size, crystal structure, and surface area. During cyanide oxidation and the simultaneous reduction of iron(VI), zinc(II), copper(II), and cadmium(II), metallic ions are almost completely removed from solution due to their coprecipitation with the iron(III) oxyhydroxides including 2-line ferrihydrite, 7-line ferrihydrite, and/or goethite. Based on the results of XRD, Mössbauer and IR spectroscopies, as well as TEM, X-ray photoelectron emission spectroscopy, and Brunauer-Emmett-Teller measurements, we suggest three scavenging mechanisms for the removal of metals including their incorporation into the ferrihydrite crystal structure, the formation of a separate phase, and their adsorption onto the precipitate surface. Zn and Cu are preferentially and almost completely incorporated into the crystal structure of the iron(III) oxyhydroxides; the formation of the Cd-bearing, X-ray amorphous phase, together with Cd carbonate is the principal mechanism of Cd removal. Interestingly, Ni remains predominantly in solution due to the key role of nickel(II) carbonate, which exhibits a solubility product constant several orders of magnitude higher than the carbonates of the other metals. Traces of Ni, identified in the iron(III) precipitate, are exclusively adsorbed onto the large surface area of nanoparticles. We discuss the relationship between the crystal structure of iron(III) oxyhydroxides and the mechanism of metal removal, as well as the linear relationship observed between the rate constant and the surface area of precipitates.
authors.affiliation: Regional Centre of Advanced Technologies and Materials, Palacký University in Olomouc, 17. listopadu 12, 771 46 Olomouc, Czech Republic.
authors.forename: Jan
authors.initials: J
authors.lastname: Filip
authors.forename: Ria A
authors.initials: RA
authors.lastname: Yngard
authors.forename: Karolina
authors.initials: K
authors.lastname: Siskova
authors.forename: Zdenek
authors.initials: Z
authors.lastname: Marusak
authors.forename: Vojtech
authors.initials: V
authors.lastname: Ettler
authors.forename: Petr
authors.initials: P
authors.lastname: Sajdl
authors.forename: Virender K
authors.initials: VK
authors.lastname: Sharma
authors.forename: Radek
authors.initials: R
authors.lastname: Zboril
mesh_terms: D002104:Cadmium / Q000737:chemistry; D002254:Carbonates / Q000737:chemistry*; D003486:Cyanides / Q000737:chemistry*; D005290:Ferric Compounds / Q000737:chemistry*; D058085:Iron Compounds / Q000737:chemistry*; D008670:Metals / Q000737:chemistry*; D053758:Nanoparticles / Q000737:chemistry*; D009532:Nickel / Q000737:chemistry; D017680:Potassium Compounds / Q000737:chemistry*; D015032:Zinc / Q000737:chemistry
chemical_list: D002254:Carbonates; D003486:Cyanides; D005290:Ferric Compounds; D058085:Iron Compounds; D008670:Metals; D017680:Potassium Compounds; D002104:Cadmium; C021024:ferric hydroxide; C044384:potassium ferrate; D009532:Nickel; D015032:Zinc