Karla Pérez, Juan Cárdenas, Constanza Bustamante, Humberto Estay
The management of spent lithium brines is becoming increasingly critical as the industry shifts toward direct lithium extraction (DLE) technologies, which generate highly saline residual brines containing water that can be recovered and reused within the process. Thus, this study proposes and evaluates an integrated osmotically assisted reverse osmosis-membrane crystallization (OARO-MCr) system as an energy-efficient alternative for brine concentration and water recovery. A phenomenological model was developed and coupled with multi-objective optimization to identify optimal operating conditions for the OARO stage while preventing premature crystallization. The optimized configuration was integrated with a previously optimized air gap membrane distillation-crystallization (AGMD) system and evaluated at industrial scale. Results show that OARO operates effectively as a low-energy pre-concentration step under sub-saturation conditions, while MCr enables further water recovery and salts crystallization. Compared with membrane distillation (MD) at similar early-stage water recovery, OARO achieves approximately 4.7 times higher water flux and 3.8 times lower specific electrical energy consumption (SEEC), highlighting its superior performance as a subsaturated pre-concentration technology. The integrated system achieves 50% water recovery, with a SEEC of 56 kWh/m³, Opex of 3.48 US$/m³, and Capex of 548 kUS$/(m3/h). Compared to conventional membrane distillation-crystallization configurations, the proposed configuration reduces Capex by 25%, SEEC by up to 6.5 times, and Opex by up to 2.2 times due to the replacement of the MD stage with OARO, and the higher thermal efficiency of AGMD. These findings demonstrate that OARO-MCr is an economically competitive strategy for treating high-salinity spent brines and recovering water within DLE technologies.