Diffusion dialysis and extraction integr

This paper presents multistage hydrometallurgical separation of Co(II) from wastewater, achieved in an integrated system containing diffusion dialysis (DD) to decrease the acidity of the industrial effluent – pregnant leach solution (PLS), followed by precipitation of Ag(II), Fe(III) and Cr(III) hydroxides, selective extraction of Co(II) with bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272), stripping of Co(II) from the loaded organic phase to form an electrolyte. DD results indicate that minimum metal ion content in the dialysate and high concentration of H+ (3.5–3.0 min) can be achieved by conducting the process at a low flow rate, but for a longer time. The retentate of DD was effectively purified by precipitation of Cu(II), Ag(II) hydroxides, and some admixtures of Cu(II) and Fe(III) to ensure that these metals will not disturb the liquid-liquid extraction of Co(II) at pH 5.2. High distribution ratio values for Co(II) extraction mean that ions of this metal can be selectively separated from the remaining important ions such as the excessively nickel Ni(II). The use of sulfuric acid and H2SO4 solution and the dialysate as stripping phases indicates that the dialysate more efficiently stripped most of the metal ions from the extract, thus forming Co(II) electrolyte for further electrodeposition of the metal. Finally, Co(II) electrowinning from a model stripping solution was investigated and the preliminary results showed that good quality metallic cobalt can be deposited.