Abstract: Effective extraction of lithium from high Mg²⁺/Li⁺ ratio brine lakes is of great challenge. In this work, organic- inorganic hybrid silica nanofiltration (NF) membranes were prepared by dip-coating a 1,2-bis(triethoxysilyl)ethane (BTESE)-derived separation layer on tubular TiO₂ support, for efficient separation of LiCl and MgCl₂ salt solutions. We found that the membrane calcinated at 400 ℃ (M1-400) could exhibit a narrow pore size distribution (0.63-1.66 nm) owing to the dehydroxylation and the thermal degradation of the organic bridge groups. All as-prepared membranes exhibited higher rejections to LiCl than to MgCl₂, which was attributed to the negative charge of the membrane surfaces. The rejection for LiCl and MgCl₂ followed the order: LiCl N MgCl₂, revealing that Donnan exclusion effect dominated the salt rejection mechanism. In addition, the triplecoated membrane calcined at 400 ℃ (M3-400) exhibited a permeability of about 9.5 L·m^-2·h^-1·bar^-1 for LiCl or MgCl₂ solutions, with rejections of 74.7% and 20.3% to LiCl and MgCl₂, respectively, under the transmembrane pressure at 6 bar. Compared with the previously reported performance of NF membranes for Mg²⁺/Li⁺ separation, the overall performance of M3-400 is highly competitive. Therefore, this work may provide new insight into designing robust silica-based ceramic NF membranes with negative charge for efficient lithium extraction from salt lakes.

Key words: Nanofiltration, Membrane, BTESE, Water lithium resource, Lithium recovery

摘要： Effective extraction of lithium from high Mg²⁺/Li⁺ ratio brine lakes is of great challenge. In this work, organic- inorganic hybrid silica nanofiltration (NF) membranes were prepared by dip-coating a 1,2-bis(triethoxysilyl)ethane (BTESE)-derived separation layer on tubular TiO₂ support, for efficient separation of LiCl and MgCl₂ salt solutions. We found that the membrane calcinated at 400 ℃ (M1-400) could exhibit a narrow pore size distribution (0.63-1.66 nm) owing to the dehydroxylation and the thermal degradation of the organic bridge groups. All as-prepared membranes exhibited higher rejections to LiCl than to MgCl₂, which was attributed to the negative charge of the membrane surfaces. The rejection for LiCl and MgCl₂ followed the order: LiCl N MgCl₂, revealing that Donnan exclusion effect dominated the salt rejection mechanism. In addition, the triplecoated membrane calcined at 400 ℃ (M3-400) exhibited a permeability of about 9.5 L·m^-2·h^-1·bar^-1 for LiCl or MgCl₂ solutions, with rejections of 74.7% and 20.3% to LiCl and MgCl₂, respectively, under the transmembrane pressure at 6 bar. Compared with the previously reported performance of NF membranes for Mg²⁺/Li⁺ separation, the overall performance of M3-400 is highly competitive. Therefore, this work may provide new insight into designing robust silica-based ceramic NF membranes with negative charge for efficient lithium extraction from salt lakes.

关键词: Nanofiltration, Membrane, BTESE, Water lithium resource, Lithium recovery