Hydrophilic nanoporous ion-exchange membranes as a stabilizing barrier for liquid-liquid membrane extraction of lithium ions

Stability of supported liquid membrane (SLM) has been a key issue in the application of high efficiency liquid membranes. In this paper, a nanoporous ion exchange membrane, prepared by blending polyethersulfone (PES) with sulfonated poly (phenyl ether ketone, SPPESK), was utilized as the stabilizing barrier for the extraction of lithium ion based on liquid-liquid membrane extraction. The membrane was prepared via immersion precipitation and the ratio between PES and SPPESK was varied in order to obtain a membrane with the best performance. It was found that at a PES/SPPESK ratio of 6/4 and a polymer concentration of 30 wt%, the membrane showed a Li+ flux of 1.67×10−8 mol cm−2 s−1 at a Li+ feed concentration of 0.13 mol/L. The membrane demonstrated nearly unchanged stress but a slight decline in elongation after 50 days in contact with the organic extractant, indicating the potential solvent resistance. Using tributylphosphate (TBP) as the extractant and kerosene as the diluent, lithium extraction and stripping were demonstrated in both single-staged and sandwiched membrane extraction contactor systems. The preliminary results on using SPPESK/PES barrier membrane for stabilizing the liquid membrane will lead to a new scientific and technology development in lithium mining from brine and seawater in the near future.