Recovering water from lithium-rich brines by a fractionation process based on membrane distillation-crystallization

In recent years, lithium production has been increasing as a result of the growing market demand. Salt-lake brines are one of the main sources of raw lithium, which can be concentrated and purified by natural evaporation. This time-consuming production causes a loss of around 85–95 % of the water contained in the extracted brine. In this context, new technologies could replace the current process with the aim to improve the water management by recognizing the evaporated water as a critical resource. This study proposes a novel fractionation method, based on a membrane distillation-crystallization process, for concentrating and purifying the lithium brine while recovering fresh water. Synthetic brines containing the major components present in Li-rich brines were assessed at different temperatures, reaching a water flux higher than 3.0 kg/m²h at 50 °C. The process was continuously protracted achieving the fractionation of Na and K salts by controlling the supersaturation of the brine and crystallization. Subsequently, the observed water flux for Mg brine was 0.22 kg/m²h as a result of the water activity decline at high brine concentration (>7.0 mol/kgH₂O). Moreover, thermodynamic speciation simulation supported the potentialities of this process, showing the capacity to recover around 95 % of the water contained in real brines from salt-lakes after three stages of separation. Overall, a conceptual flow-sheet of a new membrane-based fractional crystallization method was proposed for: i) the intensification of the brine concentration; ii) the recovery of water (up to 95 %); iii) the brine purification from in presence of major ions (i.e. Li, Na, K and Mg).