LEACHING OF ROAST-REDUCED POLYMETALLIC SEA NODULES TO OPTIMIZE THE RECOVERIES OF COPPER, NICKEL AND COBALT

The reduction-roasting ammoniacal-leaching technology, widely used for the processing of nickel laterites, has been applied for the extraction of copper, nickel and cobalt from polymetallic sea nodules of the Indian Ocean. Results are presented of the various leaching experiments conducted under different conditions to optimise the recoveries of copper, nickel and cobalt. Leaching of the ground roasted product was carried out in ammoniacal ammonium carbonate solution. The effect of preconditioning of the reduced nodules in strong ammoniacal solution prior to leaching was studied. The leaching behaviour of the metals after grinding the roasted product in air, water, leachant and preconditioning solution was carefully examined. Air grinding of the roasted product, preconditioning and leaching was found to give the best recoveries of copper, nickel and cobalt. Cobalt was recovered to a maximum of about 60% in 2 h, but dropped to 40% at the end of 4 h of leaching. Based on these observations, a two-stage leaching scheme (each stage of 2 h duration) was devised to optimise the recoveries of all the three metals, which has yielded copper, nickel and cobalt recoveries of 91%, 94% and 62%, respectively.