Recovery of valuable metals from sea nodules through reduction-roasting ammonia leaching process

Polymetallic Sea Nodules are considered to be futuristic sources of several valuable metals like Cu, Ni, Co, Mn. etc. Since last two decades or more, NML is involved in developing a process flow-sheet for extracting these valuable metals from Sea Nodules through pyro-hydrometallurgical routes. The process developed at NML comprised of reduction roasting of Sea Nodules with Low Diesel (LD) oil followed by ammoniacal leaching, SX and EW for recovering Cu, Ni and Co; and electro-thermal smelting of leaching residue for recovering Mn as standard grade Fe-Si-Mn. This process was demonstrated on pilot scale (100 kg/day) with satisfactory metal recoveries (Cu and Ni >90%, Co 75% and Mn 70%). Recently, NML also explored a similar process route for recovering the metals from Sea Nodules with use of coal as the reductant instead of LD oil, in view of better process economy. The present paper describes the evolution of this alternate sea nodule processing route at various scales, starting from 50g to 10 Kg/batch scale. Detail results on optimization of roasting and leaching parameters at bench scale are discussed, while some important results from large scale trials are presented.