Selective recovery of lithium ion from its mixed solution with potassium and sodium by electrobaromembrane method

Recovery of valuable (such as Li+) ions from natural and technogenic brines is an important issue. Pressure-driven and electrically-driven membrane processes that employ only one driving force are effective in separating monovalent and multivalent ions. However, these processes are not quite suitable for separating different monovalent ions. In this study, two oppositely directed fields, electric and pressure fields, were applied simultaneously across a track-etched membrane. The separation of Li+ from a mixed solution simulating a natural brine from Siberia was studied at fixed current density 117 A/m2 and pressure difference 0.2 bar. The Li+ flux and the Na+ and K+ fluxes occurred in opposite directions. The all fluxes were stable during the 40 h continuous experiment and were close to 0.08 mol/(m2 × h) (Na+), 0.24 mol/(m2 × h) (K+) and –0.07 mol/(m2 × h) (Li+). Initially, the both solutions circulating next to the track-etched membrane were identical and contained 0.07 M LiCl, 0.075 M KCl and 0.055 M NaCl. With increasing time, one of the circulating solutions was enriched in Li+ and the other one enriched in Na+ and K+. A mathematical model based on the TMS theory was developed and applied to describe ion concentration profiles and fluxes in the membrane and boundary solution.