Comparison between stagnant sandwich and supported liquid membranes in copper(II) removal from aqueous solutions: flux, stability and model elaboration

Abstract

The performance of a supported liquid membrane (SLM) and a stagnant thin liquid film named as sandwich LM (SSwLM), in terms of flux and stability has been investigated. Both configurations were tested to transport the Cu 2+ ion across the LM from an aqueous solution by using D2EHPA as carrier and n-decane as the organic solvent. The operating conditions of the LM separation were optimised by means of liquid–liquid extraction tests, giving particular attention to copper hydroxide formation and precipitation phenomena. Experimental data showed that carrier concentration had a strong influence on avoiding hydroxide formation by shifting the equilibrium curve of the Cu 2+-D2EHPA complex at lower pH by increasing the carrier concentration from 0.3 to 30% (v/v). The transport and stability tests showed an higher copper flux for the SSwLM versus the SLM (83.26 mmol m −2 h −1 versus 52.4 mmol m −2 h −1) and a higher lifetime too (100 h versus 15 h). The developed chemical–physical model evidenced a lower overall resistance for copper ion transport through the SSwLM compared to the SLM because the transport in the stagnant sandwiched organic liquid bulk is not influenced by the presence of pores and their tortuosity.