Mass Transfer and Immobilized Organic Phase Instability Studies for Cobalt(II)–Nickel(II) Separation by PEHFSD

Abstract

Pseudo-emulsion-based hollow-fiber strip dispersion (PEHFSD) technique was examined as an alternative to solvent extraction for simultaneous separation and concentration of cobalt(II)–nickel(II) mixture using Cyanex-272 as the extractant. Experiments were carried out by continuous recirculation of the feed and pseudo-emulsion phases through a hollow-fiber module. The separation factor increased rapidly after 60 min of operation. The maximum value after 120 min of operation was ∼128 (pH = 6.5) for the operating conditions studied. The mass transfer resistance from the extraction reaction appeared to be dominant. The results of mathematical modeling of the mass transfer process indicated that higher separation factor and extraction rate can be achieved using PEHFSD in comparison to solvent extraction. Mixing of the stripping and the feed solution was observed at high dispersed phase volume fraction in the pseudo-emulsion and low flow rate of this phase. The maximum value of backtransport flux from the stripping phase due to mixing was estimated to be approximately two orders lower than the initial extraction rates.