A study of membrane distillation and crystallization for lithium recovery from high-concentrated aqueous solutions

Membrane distillation is emerging as an interesting solution to address the difficulties and limits of conventional pressure driven membrane processes to treat highly concentrated solutions. Mineral depletion, new environmental regulations and emerging opportunities emphasize the treatment of waste streams with extraordinary high concentrations. In this current study, comparative analysis of membrane crystallization in direct-contact, osmotic and vacuum configurations have been carried out with the aim to recover lithium chloride from aqueous solutions. To precipitate LiCl from single salt solutions, a concentration above 14 M is required. The osmotic pressure associated with this concentrated solution is very high and its treatment is challenging for direct-contact membrane distillation and osmotic membrane distillation. The phenomena of osmotic pressure has been avoided by using vacuum membrane distillation. Only the application of vacuum membrane distillation, among the studied configurations, ensures the achievement of supersaturation required for crystallization. Moreover, studies on crystal morphology has been performed. Crystals can be recovered in cubic or orthorhombic polymorphic structures depending on the operative conditions. In general, this study provides an interesting comparative analysis of various membrane distillation configurations to treat highly concentrated solutions, which can contribute to the future integrated membrane desalination systems for simultaneously water, energy and minerals production.