Negatively charged organic-inorganic hybrid silica nanofiltration membranes for lithium extraction

Effective extraction of lithium from high Mg2+/Li+ ratio brine lakes is of great challenge. In this work, organic-inorganic hybrid silica nanofiltration (NF) membraneswere 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 degrees C (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 > MgCl2, revealing that Donnan exclusion effect dominated the salt rejection mechanism. In addition, the triple-coated membrane calcined at 400 degrees C (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. (C) 2019 The Chemical Industry and Engineering Society of China, and Chemical Industry Press Co., Ltd. All rights reserved.