Co-Ni alloy coatings electrodeposited using real leachates generated from positive electrodes of Ni Cd batteries

Abstract

The feasibility to recover a Co Ni alloy is evaluated in the present study by electrodeposition using real liquors from the leaching of Ni Cd batteries (positive electrodes) in H 2 SO 4 , with saccharin as additive. Ni content in the alloy rises with increasing the applied current density for all baths, while current efficiencies higher than 70% are achieved with the use of the sulfate-chloride electrolyte containing saccharin. The additive could strongly interact with chloride to suppress the occurrence of parasitic reactions (H + and H 2 O reductions), while the formation of chlorocomplexes particularly of Ni(II) accelerate their reduction on the electrode surface. This mixed electrolyte also enables to obtain more pure Co Ni alloys at −600 A m −2 , as detected in the analysis of O composition (5.12 at.%/1.36 wt%). The impurities favorably affected the contributions of both parasitic reactions. Saccharin predominantly blocks H 2 O reduction at high overpotential, but not H + discharge at low overpotential. The particle size and shape of the alloys strongly rely on current density imposed and bath composition. All deposits contain Cd, although its content is considerably less favored as the current density is increased to −600 A m −2 . XRD confirms the microstructure of the formed alloys, mainly comprised of the following planes: Ni(111) and Co(111), CoOOH(003) and Cd(OH) 2 (001). • Ni content in the alloy rises in all baths as current density is increased. • Sulfate-chloride electrolyte with saccharin presents the highest current efficiency. • Metal chlorocomplexes reduce faster than sulfate species on electrode surface. • Cd content is considerably decreased at high current density for real baths. • Alloy texture strongly depends on current density and bath composition.