RI 8754 Compatibility of Nickel Electrolyte Containing Sodium Sulfate With a Solvent Extraction System

A Bureau of Mines method for recovering nickel, cobalt, and copper from low-grade domestic laterites is described, which includes the unit operations of solvent extraction and electrowinning. Previous Bureau work indicated that addition of Na2S04 (sodium sulfate) to the nickel electrolyte improved current efficiency in nickel electrowinning. The present study determines the compatibility of Na2S04 with nickel strip-ping in the solvent extraction operation of the Bureau method. The effect of adding 100 g/l Na2S04 on nickel stripping, phase disengagement, and pH was determined in comparative laboratory-scale tests. In continuous-circuit testing, Na2S04 reduced stripping efficiency to the extent that five, instead of four, strip stages were required for complete stripping of nickel from the loaded solvent. In tests made in a phase-disengagement cell that had a variable settler area, the addition of Na2S04 did not significantly affect phase separation characteristics. The pH of the nickel electrolyte in the temperature range of 20° to 65° C was also unaffected by the addition of Na2S04. An economic evaluation showed that the energy saved by adding Na2S04 to the electrolyte would more than offset the cost of adding another stripping stage.