Sustainable Lithium Recovery from Hypersaline Salt-Lakes by Selective Electrodialysis: Transport and Thermodynamics

Advanced electrochemical membrane technologies for near-complete resource recovery and zero-discharge of urine: Performance optimization and evaluation

The depletion of nutrient sources in fertilizers demands a paradigm shift in the treatment of nutrient-rich wastewater, such as urine, to enable efficient resource recovery and high-value conversion. This study presented an integrated bipolar membrane electrodialysis (BMED) and hollow fiber membrane (HFM) system for near-complete resource recovery and zero-discharge from urine treatment. Computational simulations and experimental validations demonstrated that a higher voltage (20 V) significantly enhanced energy utilization, while an optimal flow rate of 0.4 L/min effectively mitigated the negative effects of concentration polarization and electro-osmosis on system performance. Within 40 min, the process separated 90.13% of the salts in urine, with an energy consumption of only 8.45 kWh/kgbase. Utilizing a multi-chamber structure for selective separation, the system achieved recovery efficiencies of 89% for nitrogen, 96% for phosphorus, and 95% for potassium from fresh urine, converting them into high-value products such as 85 mM acid, 69.5 mM base, and liquid fertilizer. According to techno-economic analysis, the cost of treating urine using this system at the lab-scale was $6.29/kg of products (including acid, base, and (NH4)2SO4), which was significantly lower than the $20.44/kg cost for the precipitation method to produce struvite. Excluding fixed costs, a net profit of $18.24/m3 was achieved through the recovery of valuable products from urine using this system. The pilot-scale assessment showed that the net benefit amounts to $19.90/m3 of urine, demonstrating significant economic feasibility. This study presents an effective approach for the near-complete resource recovery and zero-discharge treatment of urine, offering a practical solution for sustainable nutrient recycling and wastewater management.

Bound Water Enhances the Ion Selectivity of Highly Charged Polymer Membranes

Electrochemical technologies for water treatment, resource recovery, energy generation, and energy storage rely on charged polymer membranes to selectively transport ions. With the rise of applications involving hypersaline brines, such as management of desalination brine or the recovery of ions from brines, there is an urgent need for membranes that can sustain high conductivity and selectivity under such challenging conditions. Current membranes are constrained by an inherent trade-off between conductivity and selectivity, alongside concerns regarding their high costs. Moreover, a gap in the fundamental understanding of ion transport within charged membranes at high salinities prevents the development of membranes that could meet these stringent requirements efficiently. Here, we present the synthesis of scalable, highly charged membranes that demonstrate high conductivity and selectivity while contacting 1 and 5 molal NaCl solutions. A detailed analysis of the membrane transport properties reveals that the high proportion of bound water in the membranes, enabled by the high charge content and hydrophilic structure of the polymers, enhances both the ion partitioning and diffusion selectivities of the membranes. These structure/property relationships derived from this study offer valuable guidance for designing next-generation membranes that simultaneously achieve exceptional conductivity and selectivity in high-salinity conditions.

Solar-enhanced lithium extraction with self-sustaining water recycling from salt-lake brines

Lithium is an emerging strategic resource for modern energy transformation toward electrification and decarbonization. However, current mainstream direct lithium extraction technology via adsorption suffers from sluggish kinetics and intensive water usage, especially in arid/semiarid and cold salt-lake regions (natural land brines). Herein, an efficient proof-of-concept integrated solar microevaporator system is developed to realize synergetic solar-enhanced lithium recovery and water footprint management from hypersaline salt-lake brines. The 98% solar energy harvesting efficiency of the solar microevaporator system, elevating its local temperature, greatly promotes the endothermic Li+ extraction process and solar steam generation. Benefiting from the photothermal effect, enhanced water flux, and enriched local Li+ supply in nanoconfined space, a double-enhanced Li+ recovery capacity was delivered (increase from 12.4 to 28.7 mg g-1) under one sun, and adsorption kinetics rate (saturated within 6 h) also reached twice of that at 280 K (salt-lake temperature). Additionally, the self-assembly rotation feature endows the microevaporator system with distinct self-cleaning desalination ability, achieving near 100% water recovery from hypersaline brines for further self-sufficient Li+ elution. Outdoor comprehensive solar-powered experiment verified the feasibility of basically stable lithium recovery ability (>8 mg g-1) directly from natural hypersaline salt-lake brines with self-sustaining water recycling for Li+ elution (440 m3 water recovery per ton Li2CO3). This work offers an integrated solution for sustainable lithium recovery with near zero water/carbon consumption toward carbon neutrality.

Membrane Design Principles for Ion-Selective Electrodialysis: An Analysis for Li/Mg Separation

Selective electrodialysis (ED) is a promising membrane-based process to separate Li+ from Mg2+, which is the most critical step for Li extraction from brine lakes. This study theoretically compares the ED-based Li/Mg separation performance of different monovalent selective cation exchange membranes (CEMs) and nanofiltration (NF) membranes at the coupon scale using a unified mass transport model, i.e., a solution-friction model. We demonstrated that monovalent selective CEMs with a dense surface thin film like a polyamide film are more effective in enhancing the Li/Mg separation performance than those with a loose but highly charged thin film. Polyamide film-coated CEMs when used in ED have a performance similar to that of polyamide-based NF membranes when used in NF. NF membranes, when expected to replace monovalent selective CEMs in ED for Li/Mg separation, will require a thin support layer with low tortuosity and high porosity to reduce the internal concentration polarization. The coupon-scale performance analysis and comparison provide new insights into the design of composite membranes used for ED-based selective ion-ion separation.