Method for selective recovery of cadmium from cadmium-bearing waste

A method for the selective recovery of cadmium, nickel and cobalt from a nickel-cadmium battery waste which comprises:

• a. leaching the waste with an ammoniacal carbonate solution wherein the sum of ammonia and ammonium ions ranges from 1 to 10 molar and the sum of hydrogen carbonate ions and carbonate ions ranges from 0.2 to 5 molar, thus forming an aqueous ammoniacal carbonate solution containing cadmium, nickel and cobalt(II) ammine complexes and a leaching residue, wherein any iron in the waste remains in the undissolved leaching residue;
• b. adding air to the aqueous ammoniacal carbonate solution from step (a) to thereby oxidize the cobalt (II) ammine complex to cobalt (III) ammine complex;
• c. contacting the resulting aqueous ammoniacal carbonate solution with an organic solution substantially insoluble in water which contains a hydroxyoxime with which nickel forms a nickel compound readily soluble in the organic solution, but which does not affect cadmium and cobalt (III) in the aqueous ammoniacal carbonate solution to thereby remove nickel therefrom;
• d. precipitating the cadmium in the form of a carbonate by removing ammonia from the aqueous ammoniacal carbonate solution and removing said cadmium in the form of a carbonate;
• e. withdrawing a portion of the aqueous ammonicacal carbonate solution resulting from step (d) after the precipitation of cadmium as a carbonate and precipitating the cobalt from the thus withdrawn solution by the removal of ammonia therefrom;
• f. returning the ammonia resulting from step (e) to the aqueous ammoniacal carbonate solution which has been freed from cadmium in step (d) and replacing the loss of carbonate ions due to any precipitations by the addition of carbon dioxide in gaseous form, whereafter the resulting aqueous ammoniacal carbonate solution is reused in the leaching of step (a);
• g. stripping the nickel compound readily soluble in the organic solution generated in step (c) by washing the organic solution with an aqueous solution of sulphuric acid containing 10 - 800 g/l of free sulphruic acid, whereby the nickel is stripped into the aqueous solution in the form of nickel sulphate, and thereafter reusing the organic solution stripped of nickel in step (c).