Study on lithium separation from salt lake brines by nanofiltration (NF) and low pressure reverse osmosis (LPRO)

The aim of the present work is to study the separation of lithium from salt lake brines by NF and LPRO. NF90 membrane compared to the XLE a LPRO membrane appeared more efficient for Li⁺ extraction due to its higher hydraulic permeability to pure water and 0.1 M NaCl solution, its lower critical pressure (Pc = 0), its higher selectivity between monovalent ions (40%) obtained at low operating transmembrane pressure (below 15 bar) and its lower average roughness (105 ± 10 nm) decreasing the propensity to be fouled. NF90 exhibited 100% rejection of magnesium in the first step separation from brine diluted ten times as 15% for Li⁺, with a final separation of 85% between Mg^{2 +}/Li⁺. The permeability to the diluted brine is 0.7 L.h^{- 1}.m^{- 2}.bar^{- 1} usable to size full scale experiments, but the fouling mechanism has to be discovered in the future work. In a second step we have not succeeded to separate totally Li⁺ and Na⁺ in the permeate obtained before (15% of separation only between Li⁺ and Na⁺). To solve this problem, we did dialysis. We obtained a total separation between Li⁺ and Na⁺ with a diffusion flux (4.42 10^{- 7} mol.s^{- 1}.m^{- 2} at 20 °C) for NaCl 0.1 M 5 times higher for NF90 vs XLE.