Impact of SPEEK on PEEK membranes: Demixing, Morphology and Performance Enhancement in Lithium Membrane Extraction

Tao Huang, Jianfeng Song, Hailong He, Yue-Biao Zhang, Xue-Mei Li, and Tao He*
 J. Membr. Sci. 2020615, 118448
Acid resistance membrane plays a key role in membrane extraction of lithium ions for ensuring performance stability, yet many are not suitable because of their high ion diffusion resistance. We report here our endeavor in further reducing the ion diffusion resistance of a novel poly (ether ether ketone, PEEK) membrane for lithium extraction from salt-lake brine. We blended PEEK with sulfonated PEEK (SPEEK) and their miscibility was researched by evaluating the mixing free energy and glass transition temperature in the whole mixing range. Using methanesulphonic acid (MSA) and sulfuric acid (SA) as the solvent and water as precipitation media, thermodynamic and kinetic behaviors in phase separation were analyzed. Cloud point of a quasi-ternary PEEK/SPEEK-MSA/SA-H2O indicated a low water tolerance; the nominal diffusion coefficient showed maximal value at 50/50% mixing ratio, indicating the quickest demixing. PEEK/SPEEK 50/50 showed the highest water permeability and lithium diffusion, extraction and stripping fluxes. Nearly five times lithium extraction flux and about two times stripping flux as compared to the PEEK membrane were obtained. Disruption of crystalline formation in PEEK by amorphous SPEEK contributed to the open morphology and reduced resistance. The results widen the scopes of membrane materials for membrane extraction of lithium and other ions.