Transport of cobalt(II) through a hollow fiber supported liquid membrane containing di-(2-ethylhexyl) phosphoric acid (D2EHPA) as the carrier

Abstract

This work presents experimental, modeling and simulation studies for Co2+ ion extraction using hollow fiber supported liquid membrane (HFSLM) operated in a recycling mode. Extractant di-(2-ethylhexyl) phosphoric acid (D2EHPA) diluted with kerosene has been used as the membrane phase. The Co2+ ion concentration in the aqueous feed phase was varied in the range of 1–3mM. Also, D2EHPA concentration was varied in the range of 10–30% (v/v). A mass transfer model has been developed considering the complexation and de-complexation reactions to be fast and at equilibrium. Equations for extractant mass balance and counter-ion (H+) transport have also been incorporated in the model. Extraction equilibrium constant (Kex) for cobalt–D2EHPA system has been estimated from equilibration experiments and found to be 3.48×10−6. It was observed that the model results are in good agreement with the experimental data when diffusivity of metal-complex (Dm) through the membrane phase is 1.5×10−10m2/s. Feed phase pH and strip phase acidity had negligible effect on the extraction profiles of Co2+ ions. An increase in D2EHPA concentration increased extraction rates of Co2+ ions. The membrane phase diffusion step was found to be the controlling resistance to mass transfer.