Recently, low-energy forward osmosis (FO) technology has been employed in the lithium concentration stage during the extraction of lithium from brine sources. The interlayer FO membrane is renowned for its exceptional structural characteristics; however, challenges remain in selecting suitable interlayer materials and exploring their control mechanisms on amine monomers. As interlayer materials, traditional 3D nanomaterials are prone to detachment, while traditional 2D materials without micropores can increase the transmission resistance of water molecules. This study introduces a novel FO membrane utilizing Zr-BTB nanosheets with 5.4 Å micropores as the interlayer material. Based on detection and simulation calculations, it was found that the increase in steric hindrance and interaction forces jointly slowed the diffusion of amine monomers in the presence of the Zr-BTB interlayer. This results in a thinner separation layer, facilitating water transport. The interlayer also plays crucial roles in preventing defective pore formation in the separation layer and assisting in intercepting salt ions. The Zr-BTB interlayer membrane exhibited a water flux of 29.14 L m −2 h −1 and a reverse salt flux of 0.16 g m −2 h −1 , which are superior to those of many FO membranes reported in the field. The prepared membrane also has excellent performance in lithium concentration applications, and its separation mechanism was explored by MD simulations.
Nan Sun,Shucheng Mo,Pengjia Dou,Chenjun Dong,Tao He
Forward osmosis (FO) has been proposed as an ecologically friendly and low carbon footprint technology for concentrating enriched lithium brine from the salt lake using freely available MgCl 2 onsite as the draw. In this process, Li + concentration is raised from a few hundred mg/L to 20-30 g/L (Li + ) before precipitation of Li 2 CO 3 . To allow FO technology a wide margin in competing with other concentration technologies, it is highly desirable to develop a simple, low cost method to fabricate FO membrane . Besides, due to both feed and draw solutions being of high salinity, FO membranes should also have a defect-free polyamide (PA) separation layer and a low structural parameter ( S ) substrate. This paper presents a simple guideline called approaching ratio (α) to adjust the substrate pore morphology based on a ternary polysulfone (PSf)/N,N-dimethylacetamide (DMAc)/diethylene glycol (DEG) solution. The α ranging between 0 and 100 % is a metric measuring how close the solution is to the cloud point. The increase of α endows instant phase separation, resulting in the substrate with increased surface porosity and sponge-like structure. Pore connectivity is improved following an increase of α below a threshold value of 50 %. Water permeability dramatically increases from α = 0 % to α = 50 % and declines at above 50 % for forming the closed cellular pores at α = 80 %. The FO water flux shows a similar trend which was found to be closely related to the substrate pore interconnectivity. The FO membrane was applied in the lithium concentration process using saturated MgCl 2 as the draw, the experimental results fit well with the FO model. The results demonstrate a simple, low-cost generic method to prepare FO membranes for applications with very high salinity feed and draw.
Nan Sun,Pengjia Dou,Wentao Zhai,Hailong He,Long D. Nghiem,Vahid Vatanpour,Yuebiao Zhang,Changkun Liu,Tao He
To extract lithium from salt lake brine involves a process of separation and concentration. After separating lithium from brine, the lithium ion concentration is generally a few hundred mg/L which is far below the required 20-30 g/L (as Li + ) before precipitation as lithium carbonate. The concentration step of a lithium enriched brine is crucial but highly energy-intensive. Spontaneous forward osmosis (FO) technology offers the possibility for concentrating lithium ions with low energy. Because the concentrating process involves both feed and draw solution with very high salinity, it is highly desirable to have a high performance FO membrane with a low structural parameter as well as a high rejection to ions. In this work, thin polyethylene separator supported FO (PE-FO) membranes were prepared and post-treated stepwise with benzyl alcohol (BA) and hydraulic compaction. The effect of the post-treatment on the FO performance was systematically analyzed. Excellent FO performance was achieved: the water flux and reverse salt flux selectivity were 66.3 LMH and 5.25 L/g, respectively, when the active layer is oriented towards the 0.5 M NaCl draw solution with deionized water as the feed. To the best of our knowledge, this FO flux is the highest ever reported in the open literature under similar test conditions. Applied in concentrating lithium enriched brine, the membrane showed superior water flux using saturated MgCl 2 as draw solution. A new FO model was established to simulate the water flux during the concentration process with good agreement with the experimental results. The promising results using PE-FO membrane for lithium enrichment opens a new frontier for the potential application of FO membranes.
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