Treatment of Polymetallic Sea Nodules by Ammoniacal Reduction Leaching

Abstract

The polymetallic sea nodules from the Indian Ocean can be leached in ammoniacal solutions in the presence of cuprous ions as the reductant. The advantage of ammonia leaching lies in the fact that metals such as copper, nickel and cobalt can be solubilized while rejecting manganese and iron in the residue. Bench scale work at the scale of 20 g nodules was undertaken at N.M.L. The recoveries of copper, nickel and cobalt were in the order of 81%, 96% and 80% respectively at an ammonia concentration of 142.5 g71 and carbon dioxide of 41.67 g/l. The cuprous ions were introduced either as cuprous chloride or copper powder. To maintain the concentration of cuprous ions, purified carbon monoxide was introduced into the leaching reactor. The paper describes in detail various parameters viz concentration of ammonia, sodium chloride additive, solid to liquid ratio, time of leaching etc which affect the leaching of the desired metals.