Selective reductive leaching of oxidised cobalt containing residue

•Ni, Co and Mn are selectively leached from an oxidised hydroxide residue.•The reaction is fast and the observed behaviour is in line with thermodynamic predictions.•A process for primary processing of Ni and Co is proposed.

Nickel was selectively leached from an industrial nickel-cobalt Mixed Hydroxide Precipitate (MHP) under mildly acidic, strongly oxidizing conditions. The resulting cobalt rich residues contained 14-21 wt.% Ni, 3-7 wt.% Co and 3-9 wt.% Mn. The selective extraction of nickel and cobalt from these residues was studied using weak acid and weak acid-reductive leaching. Without the reducing agent, nickel preferentially leached. The controlled addition of a reducing agent increased the extent of nickel leaching and solubilised a portion of the cobalt while manganese remained stable in the solid phase. The extent of copper, iron and aluminium leaching was controlled by pH adjustment.