Properties of aged mixed nickel–cobalt hydroxide intermediates produced from acid leach solutions and subsequent metal recovery

Synthetic mixed nickel–cobalt hydroxide precipitates (MHP) were produced containing varying levels of Ni, Co, Mn, Mg, Al, Fe, Cr, Cu, Zn and Si to understand and characterize the ageing processes and subsequent nickel and cobalt leach recovery. Precipitates were monitored over a 12 week period using X-ray diffraction (XRD), scanning electron microscopy (SEM) and leach tests in ammonia–ammonium carbonate solution. Manganese and cobalt incorporation into MHP was beneficial for subsequent nickel recovery; most likely preventing or slowing nickel–magnesium hydroxide formation. High magnesium MHP generally lowered subsequent nickel recovery due to its stability and slow leaching kinetics. n 94–100% Ni and 84–100% Co were leached from nearly all high magnesium MHP precipitates after soaking in the leach solution for 72 h, except for the precipitate containing about 5% Al which only recovered 87% Ni and 61% Co. An XRD of this precipitate showed that it was much more amorphous than any other MHP whilst the XRD of the leach residues revealed a magnesium–aluminium hydrotalcite structure. Both nickel–magnesium hydroxide and hydrotalcite-like structures appear to inhibit nickel and cobalt recovery because of their slow leaching characteristics.