LIX®-loaded polymer inclusion membrane for copper(II) transport: 2. Optimization of the efficiency factors (permeability, selectivity, and stability) for LIX® 84-I

Polymer inclusion membrane transport of copper(II) in chloride and sulfate medium is studied using CTA (support), tris(2-n-butoxyethyl)phosphate (plasticizer), LIX® 84-I (carrier), and ethanol (additive). An optimization in the aqueous phases (pH, type of anions and buffer concentration) and membrane compositions (extractant and plasticizer concentrations) was performed and the efficiency factors (permeability, selectivity, and stability) of the system evaluated. It was observed that besides the improvement in metal ion flux and reduction in metal accumulation in the membrane by the incorporation of the additive in the casting solution, an increase in membrane stability is also attained. A transport model for the system in sulfate medium is proposed. Values for the aqueous and organic resistances (Δa = 104.7 and Δo = 108.0 s m−1, respectively), true organic diffusion coefficient and membrane diffusion coefficient of the Cu(II)–carrier complex in the membrane phase (Db,o = 10−13 and Do = 10−12.2 m2 s−1, respectively) were calculated assuming that a carrier–diffusion mechanism is mainly responsible for ion transport, as suggested for the transport profiles, and the value of the conditional extraction constant (log K′ext=−5.6)(log K′ext=−5.6) determined in an independent form by solid–liquid extraction experiments. A highly selective separation of Cu(II) from Zn(II) and Fe(III) was achieved as well.