Extraction of zinc-cobalt from sulphate solution of cobalt cake by D2EHPA in the processing of indian ocean nodules

During the processing of Indian ocean nodules, cobalt cake containing zinc in equal proportion is produced. In order to get pure cobalt and zinc from the sulphate leach solution of cake, a solvent extraction process has been considered using an organic extractant, di-(2-ethylhexyl)
phosphoric acid (D2EHPA). Separation of cobalt and zinc has been carried out by mixing aqueous and organic phases in a rectangular vessel and separating the phases after equilibration in a glass funnel. The analysis of the metal from the aqueous phase was made by atomic absorption spectrometer to compute the metal transfer. The extraction and separation studies carried out under the different operating conditions indicated favourable zinc extraction at the lower pH (- 2) with partially saponified D2EHPA. The small amount of cobalt co-extracted with zinc was scrubbed with dilute sulphuric acid. With completely saponified D2EHPA, a high degree of cobalt extraction (99.8%) was
achieved at aqueous feed pH of 5.0. The flow sheet developed could be used for the selective extraction and separation of zinc and cobalt from the leach liquor of cobalt cake.