Solvent stable nanoporous poly (ethylene-co-vinyl alcohol) barrier membranes for liquid-liquid extraction of lithium from a salt lake brine

Loss of organic extraction in membrane extraction process could be avoided by using an ion permeable, solvent stable barrier membrane. Development of solvent stable materials has been a key issue for liquid-liquid membrane extraction. A new type of solvent resistant membrane, prepared from block copolymer poly (ethylene-co-vinyl alcohol) (EVAL) via immersion precipitation, is introduced as the barrier in membrane extraction of lithium from a real salt lake brine. The influence of EVAL concentration on the casting solution viscosity and the membrane properties was investigated. The membranes were characterized by scanning electron microscopy (SEM), water uptake, pure water flux, mechanical strength, and Li+ diffusion flux. Membrane phase separation was conducted at a temperature below the crystallization temperature of the polymer to ensure suitable membrane structure. The membrane prepared from 30 wt% EVAL content showed a Li+ flux of 2.7×10−8 mol cm−2 s−1 at a Li+ feed concentration of 0.1 mol/L in a diffusion test. Using a tributylphosphate (TBP)/kerosene extractant, the lithium flux in a membrane extraction showed a linear relationship with the feed lithium concentration. In addition, long term stability tests showed a stable lithium extraction flux for about 1037 h. These results indicate that EVAL material is a promising stabilizing barrier membrane in liquid-liquid extraction of lithium.