The sulphide leach liquor obtained from ocean nodules contains number of impurities like iron, copper and zinc in addition to valuable metals like nickel and cobalt. Both precipitation and solvent extraction techniques are used for removing these impurities for further processing for making pure nickel and cobalt. Extensive studies have been carried out in our laboratory to develop a solvent extraction route using 50% saponified 0.5M di-(2-ethyl hexyl) phosphoric acid and 5% isodecanol in kerosene for the purpose. This paper highlights the influence of two important parameters viz. aqueous to organic ratio A/O and equilibrium pH on separation factor, β of combined nickel and cobalt with respect to impurities. The separation factor in turn influences the recovery and purity of combined nickel and cobalt which remain in the raffinate.
The sulphide leach liquor used in this work has been provided by Regional Research Laboratory, Bhubaneswar. The processing of ocean nodules is done by ammonia-SO2 leaching route in which metals like nickel, cobalt, copper and zinc enter in to solution as their amine complexes leaving iron and manganese in the residue. Major portion of copper is then recovered by solvent extraction using LIX 84. This solution contains nickel and cobalt along with impurities like copper and zinc which must be removed before cobalt/nickel separation is attempted. A variety of methods (Fujimori et aI, 1980, Nath Sarma, 1987) have been used in industry for removal of impurities. Iron is generally removed by precipitation as ferric hydroxide, copper by precipitation as copper sulphide or by cementation with iron or cobalt line is removed by precipitation as sulphide or by SX if its concentration is significant. Selective precipitation does not yield high purity products and there is always some loss of valuable metals by way of co-precipitation.