Electro-membrane extraction of lithium with D2EHPA/TBP compound extractant

Abstract A polymer inclusion membrane (PDT-PIM) composed of bis(2-ethylhexyl) phosphate (D2EHPA) and tributylphosphate (TBP) compound carrier is developed in this study. The PIM membrane carrier composition, thickness, voltage, two-phase solution environment and other factors for Li+ electro-membrane extraction (EME) behaviour are investigated using applied electric field assessment. Results showed that the PDT-PIM system composed of alkaline feed phase and acidic stripping phases can achieve preferential mass transfer to Li+ in the coexisting solution of Na+ and K+ ions. The D2EHPA functional group is responsible for the main mass transfer of ions. Synergistic extraction effect of TBP appears when D2EHPA/TBP (w/w) ratio is 1/2 and reaches maximum at a ratio close to 1/1. The total optimised carrier accounts for 70.6% of the mass percentage of PIM. The applied electric field can effectively increase the mass transfer rate but will reduce the selectivity of Li+ relative to Na+ and K+. Mass transfer coefficient (P) of 70.6% of PDT-PIM to Li+ can reach 12.9 μm s−‍1 and the initial flux of Li+ is 249 mg m−2 s−1 under a voltage of 20 V. Separation factor of Li+ relative to Na+ and K+ (SLi/Na and SLi/K) are 6.41 and 5.64 on 10 V as well as 2.56 and 2.51 on 20 V, respectively. Enrichment factor of Li+ of up to 9.02 shows acceptable stability after 120 h of continuous mass transfer of 1 L of 20 mg L−1 Li+ solution.