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.