Direct electrowinning of valuable metals from sea nodules using aqueous chloride bath

Direct electrowinning of copper, nickel and cobalt from the Indian ocean nodules has been attempted in a diaphragm cell. Experiments have been conducted to examine the effect of sodium sulphide addition to ground nodules on the dissolution behaviour of various metals in 3M ammonium chloride electrolyte. It is observed that in the absence of sodium sulphide, metal recoveries are very poor. On addition of 40% sodium sulphide, dissolution of metals has been found to be enhanced considerably. A mechanism of such electrodissolution process has been proposed. Finally electrochlorination of the nodules mixed with Na2S has been carried out using 3M sodium chloride electrolyte solution buffered with 7.5 vol% formic acid. Cathode deposition of the order of 53% Cu, 58% Ni and 36% Co has been achieved during 8 hours of operation. The cathode deposits have been characterised by XRD and SEM investigations.