A study of a solvent extraction method for the treatment of spent electrolyte solutions generated in nickel-cadmium (Ni-Cd) battery manufacturing

Spent electrolyte generated in the Ni-Cd rechargeable battery manufacturing process containing about 400 g l(-1) KOH, 50 g l(-1) K2CO3 and 20 mg l(-1) Cd, has a high reuse value if the cadmium is removed. We performed a syste matic investigation to apply the solvent extraction technique to remove cad mium from the spent electrolyte. Potential extractants for cadmium were car efully selected and the performances of the solvents containing these extra ctants were studied. Amongst the ten extractants that were tested, three ac idic chelating extractants, viz., Cyanex 301 (Cytec Canada Inc., a dithioph osphinic acid), Cyanex 302 (Cytec Canada Inc., a monothiophosphinic acid) a nd Kelex 100 (Witco, 7-alkyl-8-hydroxyquinolines) showed favourable extract ion characteristics for cadmium from the highly concentrated alkaline mediu m. Kelex 100 also showed excellent back-extraction (stripping) characterist ics for the cadmium extracted; cadmium could be quantitatively stripped fro m the Kelex 100 solutions with a 0.1 M HCl or 0.1 M H2SO4 solution. A proce ss employing Kelex 100 as the extractant was developed. The feasibility of this process was demonstrated with automated mixer-settler solvent extracti on units using real spent electrolyte generated in a Ni-Cd battery manufact uring plant.