Influence of Polymer Inclusion Membrane Composition on Cd(II) Transport in Seawater and Desalination Brines.

The transport of metal ions from highly saline matrices remains challenging due to the elevated ionic strength and complex chemical speciation that characterize seawater and desalination brines. In this work, the influence of membrane composition on Cd(II) transport through polymer inclusion membranes (PIMs) was evaluated using cellulose triacetate (CTA), poly(vinyl chloride) (PVC), and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) membranes containing Aliquat 336. Membranes were tested using model NaCl solutions, seawater, and desalination brine, and the effects of membrane mass, polymer matrix, carrier/plasticizer composition, and receiving phase were investigated. Reducing the CTA membrane mass by 50% did not significantly affect transport efficiency, indicating that membrane composition had a greater influence on Cd(II) transport than membrane mass under the conditions evaluated. Among the evaluated formulations, the optimum PVDF-HFP membrane contained 60 wt.% PVDF-HFP, 30 wt.% Aliquat 336, and 10 wt.% butyl stearate (BTS), achieving a transport efficiency of 95.5% and an initial flux of 2.7 × 10-6 mol m-2 s-1 in desalination brine. The use of 0.5 M HNO3 as the receiving phase markedly improved Cd(II) transport in both synthetic saline solutions and real seawater and desalination brine compared with ultrapure water. These results highlight the importance of polymer-plasticizer interactions in controlling Cd(II) transport and demonstrate the potential of PVDF-HFP/Aliquat 336/BTS membranes for metal recovery from complex saline media.