Separation of Cadmium, Cobalt, and Nickel by Solvent Extraction using the Nickel Salts of the Extractants

Abstract

A new solvent‐extraction process for the separation of cadmium, cobalt, and nickel in sulphate solutions coming from the hydrometallurgical processing of spent Ni‐Cd batteries is proposed. The main innovation is to use nickel salts of the extractants, thus avoiding external pH control in the extraction operation. The extractants are first loaded with nickel in conditioning steps, using a neutralizer for pH control, and afterwards contacted with the aqueous processing solutions for extraction of interested metals with no further need of neutralization. This process is an alternative to the usual approach, which uses the sodium or ammonium salts of the extractants, avoiding introducing these cations in the process stream. Using this approach, the extraction of cadmium with nickel salt of 1 M DEHPA was performed at resulting pH values of 3.8–4.3 producing an organic phase loaded with 35 g/L Cd. Cobalt extraction with the nickel salt of Cyanex 272 was further achieved at resulting pH of 5.1–5.7 obtaining a organic loaded with 6.5 g/L Co.

Keywords:

• Solvent extraction
• recycling
• cadmium
• cobalt
• nickel
• DEHPA
• Cyanex 272

ACKNOWLEDGMENTS

Part of the work presented was financed by Fundação para a Ciência e Tecnologia – Programa Praxis XXI, Project 3/3.1/CEG/2574/95, which is greatly acknowledged by the authors.