Processing mixed nickel‑cobalt hydroxide precipitate by sulfuric acid leaching followed by selective oxidative precipitation of cobalt and manganese

Abstract

In this study, an alternative method for processing mixed nickel‑cobalt hydroxide precipitate to separate the nickel from cobalt and manganese is proposed and evaluated. The proposed method comprises a leaching step using sulfuric acid to dissolve the nickel and cobalt from mixed hydroxide precipitates, and subsequently, an oxidative precipitation step to separate the dissolved nickel from cobalt and manganese using ozone as the oxidant. The results of the leaching experiments showed that 97% and 96% of the nickel and cobalt can be dissolved in the leaching step while leaving 92% of the manganese in the residue using 1.0 mol/L sulfuric acid solution at 25 °C, a slurry density of 100 g/L and leaching duration of 2.5 h. The results of the oxidative precipitation experiments showed that complete precipitation of the dissolved cobalt and manganese can be achieved using ozone as oxidant with nickel co-precipitation of about 8.8% at 25 °C, equilibrium pH of 5.0, oxidant gas flow rate of 1 L/min and precipitation duration of 2 h. The ability of ozone to affect cobalt and manganese oxidation into their higher valence enables their precipitation as cobalt oxyhydroxide and manganese dioxide, respectively, and their separation from nickel was demonstrated in this study.