Novel LIS-doped mixed matrix membrane absorbent with high structural stability for sustainable lithium recovery from geothermal water

LIS-doped thin-film nanocomposite membrane adsorbent with low shielding effect for effective lithium recovery from geothermal water

“…31 Lagergren pseudo-first-order (eqn (4)) and pseudo-second-order (eqn (5)) kinetic reaction models were used to simulate the Li + adsorption process, 3 where k 1 and k 2 were the pseudo-first-order and pseudo-second-order rate constants, respectively. The adsorption properties of the TFN membrane adsorbent were evaluated with the Langmuir (eqn (6)) 15 and Freundlich (eqn (7)) 15 models, from which the Langmuir maximum adsorption capacity ( q m ), adsorption energy constant ( K L ), Freundlich adsorption capacity ( K F ) and adsorption intensity ( n ) were derived by OriginPro software.ln( q e − q t ) = ln q e − k 1 × t …”

“…3(a)). 15 Meanwhile, the supernatant was transparent without Tyndall phenomena, indicating no leakage of HTO and the structural integrity of the TFN membrane. However, excessive addition of HTO with an L a of 32.2 g m À2 would destroy the membrane structure, causing the leakage of the extra HTO.…”

“…To reduce the shielding effect of the polymer matrix on LIS adsorption sites and improve interfacial compatibility, in our previous study, dopamine-modified LIS was doped into a PSF matrix by the breath figure approach to prepare mixed matrix membrane adsorbents of LIS (MMMs-LIS) with low thickness, high exposure area of H 2 TiO 3 (HTO) and high structural stability. 15 The well-designed MMM adsorbent reached a comparable Li + adsorption capacity of 25.01 mg g À1 and a shorter equilibrium adsorption time of 45 minutes during the dynamic adsorption process in natural geothermal water. Although the MMMs showed high adsorption performance, structural stability and cyclic operation, the low loading amount of HTO per unit membrane area (18.5 g m À2 ) still limited its practical application.…”

“…This was consistent with the core material of powdery LIS. 15 Temperature also plays a great role in controlling the ion diffusion rate in solution, thus affecting the adsorption process. As can be seen in Fig.…”

“…These limitations have triggered research into combining powdery LIS with membrane technology to make mixed matrix membrane (MMM) adsorbents in the form of spheres, 13 foam, 14 sheets 15 and fibers, 16,17 where LIS as a dispersed phase fills the continuous phase of a polymer, such as polysulfone (PSF), polyacrylonitrile (PAN), or polyvinyl chloride (PVC), by non-solventinduced phase inversion, electrospinning and freeze-drying methods, respectively. Despite improvements in the fluidity and cyclability of MMMs, some challenges urgently need solving: (1) the severe decrease in Li + adsorption capacity and rate due to the shielded active adsorption sites of LIS by the polymer matrix; (2) the poor interfacial compatibility between inorganic LIS and organic polymer matrix caused by the lack of chemical bonds, which affects the structural stability and operational durability of MMMs.…”