Electrochlorination of sea nodules to recover copper, nickel and cobalt

Abstract

The idea of using sodium chloride, readily available from sea water, for the processing of sea nodules led to a proposal to explore the possibilities of its electro-chlorination. Electrochlorination of complex oxidic ores such as sea nodules is difficult. Anodic polarization studies revealed that the process could be made feasible with the addition of sodium sulphide to the ore body. Electrochlorination in a diaphragm cell was initially carried out with ammonium chloride electrolyte to confirm the beneficial effect of sodium sulphide addition, as well as to achieve a satisfactory level of metal recovery. It was found that electrochlorination of sea nodules for 4 h at cell voltage of 7.5 V recorded 95% Cu, 81% Ni and 82% Co with 40% sodium sulphide addition, in comparison to the 40% Cu, 31% Ni and 14% Co without addition of sodium sulphide. The metal recoveries of the order of 88% Cu, 85% Ni and 88% Co were obtained by using sodium chloride electrolyte under optimised conditions. The investigation also revealed the possible reaction mechanisms as well as the dissolution behaviour of various metals during the electrochlorination of sea nodules with sodium sulphide addition.