Solvent extraction recovery of nickel from spent electroless nickel plating baths by a mixer-settler extractor

The treatment of spent electroless nickel plating baths has attracted much attention from the standpoints of environmental protection and nickel recycling. In order to design a nickel recovery process from the spent baths, the continuous extraction and stripping of nickel in the spent baths were carried out using a mixer-settler extractor. 2-Hydroxy-5-nonylacetophenone oxime (LIX84I) and 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (PC88A) were used as the extractant and the accelerator, respectively. The effects of the accelerator, flow rates and total stage number were investigated. It was found that the extraction efficiency was significantly increased by adding the accelerator. The extraction and stripping efficiencies were affected by the flow rates of the organic and aqueous phases, and its mechanism was qualitatively discussed on the basis of the stoichiometric relation of the extraction and the hydrodynamic properties of the mixer. A high nickel extraction efficiency (99.9%) was achieved using a countercurrent three-stage extraction process, while the most concentrated nickel sulfate solution (0.49 kmol/m3) was obtained with the stripping efficiency of 98.4% in a countercurrent two-stage stripping. This continuous extraction–stripping technique is expected to be effective for recycling nickel from the spent baths.