Recovery of Cu, Ni, Co and Mn from sea nodules by direct reduction smelting

Abstract

Polymetallic nodule contains various metals like copper, nickel, cobalt, manganese, iron, lead, zinc, aluminum, etc. Of these, copper, nickel and cobalt are of much importance and in great demand world over. In fact, due to their extensive technological use these three metals are fast depleting from the earth surface. Hence a world-wide research is progressing on sea nodules as an alternative future source of these metals. India is entirely dependent on imports to meet its requirements of cobalt and nickel both of which are most strategic in nature. In this respect, India has made remarkable progress in recovering these metals from sea nodules. The recovery process so far developed in India is based on either purely hydrometallurgical or pyro-hydrometallurgical routes. The processes generate very dilute leach solution, the downstream processing of which is very difficult. Generation of concentrated leach solution from sea nodule would make the process simpler and economical which may not be possible by direct leaching process. Therefore, it has been planned to explore direct smelting of sea nodules to recover copper, nickel and cobalt along with part of iron in the form of alloy followed by individual metal recovery through matte formation and dissolution. Initial studies on direct reduction smelting of Indian sea nodule were conducted using coke as reductant in lab scale experiments. Various parameters like smelting temperature, reductant concentration, holding time etc. have been optimized to obtain an alloy of suitable composition. At a smelting temperature of 1400 oC, recovery of 90-92% Cu, 92-95% Ni and 80-85% Co is obtained in the form of alloy in a recrystallized alumina crucible which can be further treated to recover these metals in pure form. The iron content in the alloy varies significantly with coke concentration. The slag generated after smelting can be directly treated for production of standard grade Fe-Si-Mn without blending.