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How are nickel, cobalt, and copper extracted from ores using ammine complexes?

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Structural diagram of the vitamin B12 coenzyme molecule, highlighting its organometallic core with five nitrogen-cobalt bonds and one cobalt-carbon bond at the center, surrounded by complex organic groups. — coordination compound Coordination compounds contain a central metal atom surrounded by nonmetal atoms or groups of atoms, called ligands. For example, vitamin B₁₂ is made up of a central metallic cobalt ion bound to multiple nitrogen-containing ligands.

In hydrometallurgical processes, nickel, cobalt, and copper can be extracted from their ores by using aqueous ammonia to form ammine complexes.

The extraction relies on the ability of ammonia to dissolve these metals into solution as stable, soluble coordination compounds. Once in solution, the metals are separated through selective precipitation procedures that exploit the differences in the stabilities and solubilities of their respective ammine complexes.1

For example, in the ammonia pressure leaching of nickel, the metal is recovered from the resulting solution through reduction with hydrogen under pressure. This method is advantageous as it allows for the recovery of sulfur as ammonium sulfate, which can be utilized as a fertilizer. By utilizing these coordination chemistry principles, industries can effectively isolate and purify these transition metals from complex ore mixtures.231