Redox processes during cobalt extraction to the systems with bis(2,4,4-trimethylpentyl)dithiophosphinic acid

The paper presents data on cobalt extraction from sulfate solutions with bis(2,4,4-trimethylpentyl) dithiophosphinic acid (HR, trade mark Cyanex 301) diluted with nonane and toluene. It was concluded that cobalt extraction with bis(2,4,4-trimethylpentyl)dithiophosphinic acid is characterized by a fast reaction resulting in the formation of the tetrahedral СоR 2 complex in the organic phase followed by Co(II) oxidation with air oxygen and the formation of the octahedral СоR 3 complex. The cobalt oxidation reaction is first order with regard to both the metal and bis(2,4,4-trimethylpentyl)dithiophosphinic acid concentrations. Oxidation of cobalt(II) dithiophosphinate to cobalt(III) dithiophosphinate by the disulfide of dithiophosphinic acid (RR) has been studied. The cobalt oxidation reaction is second order with regard to the metal concentration and first order with regard to the disulfide concentration. The redox process was shown to be reversible. Cobalt extraction in the presence of various electron donor additives (L) has been studied. Trioctyl amine (TOA), octylamin (OA), n-octanol, tributylphosphate (TBP) were used as additives. On degree of suppression of oxidation of cobalt in systems with Cyanex 301 + additives it is possible to arrange in following seriesr ТОА> ТБФ>> n-oktanol ≈ НR without additives. A decrease in cobalt extraction is observed in the series: HR+ octylamin > HR ≈ HR+ n-octanol>> HR +TOA.