Solvent extraction: a potential tool for the separation of metals from leach liquor of electronic scraps

Abstract

Worldwide, the advent of modernization brought increase in demand of electronic products which generated huge amount of e-wastes. These materials contain precious, valuable and hazardous metals. To conserve the natural resources and protect the environment, the recovery of metals from these wastes is necessary. Present work is a part of a process which consists of pre-treatment, leaching and solvent extraction. In this paper, solvent extraction process has been discussed for the selective extraction and separation of metals from synthetic and actual leach liquor of PCBs as it is a proven technology for separation of various non-ferrous metals from industrial effluents and leach solutions containing low metallic values. The studies were carried out to recover and separate the valuable and hazardous metals viz. Cu, Zn, Cd, Ni, etc. from the synthetic solution similar to leach liquor of PCBs using cationic extractants 2-hydroxy-5-nonylacetophenoneoxime (LIX 84) and dialkyl monothiophosphinic acid (Cyanex 302) or di-(2-ethylhexyl) phosphoric acid (D2EHPA) diluted in kerosene. The copper was selectively extracted by LIX 84 from aqueous solution containing 2.0 g/L Cu at pH 2.0 and O/A ratio 1:1 leaving zinc, cadmium and nickel in aqueous raffinate. Copper was stripped from loaded LIX 84, by 10% sulfuric acid to get pure copper sulfate solution to produce metal or salt. Subsequently, metals viz. zinc, cadmium and nickel were separated with the application of Cyanex 302 or D2EHPA diluted in kerosene by controlling the acidity of the solution during process. Bench scale results obtained for effective extraction and separation of metals were validated in continuous mode in mixer settler unit at flow rate 2.5 L/h of organic and aqueous. The developed process could be employed on commercial scale for extraction and separation of metals from the sulfate solution after validating the data on large scale.