Peparation And Adsorption Properties Of Lithium Ion Sieve Membrane

The spinel manganese oxides （derived from spinel-type lithium manganese oxide） arepromising adsorbents for extracting lithium from salt lake brine and sea water and have goodpreferential adsorption for lithium ions. The liquidity and permeability of spinel manganeseoxides ion sieve powders are poor, which is disadvantageous for industrial operation andhinders their commercial application. So many researchers pay close attention to preparingcomposite adsorbents. In recent years, the membrane-type lithium ionic sieve also has beenprepared by a phase-inversion method using polyvinyl chloride （PVC） as membrane-formingmaterial. Compared with lithium ionic sieve power，membrane has its unique advantage ofbeing wound, which is beneficial to its industrial application.A series of lithium ion sieve membranes of PVC were prepared by adding Li_1.6Mn_1.6O₄to the solution of PVC. The preparation conditions were investigated by changing the PVCconcentration、different solvents、the precursor content by means of SEM and adsorptionexperiments. Adsorption experiments showed that when the content of Li_1.6Mn_1.6O₄wasmaintained at10wt.%, the adsorption capacity of Li⁺decreased with an increase of the PVCconcentration. Select10wt.%and12wt.%PVC concentration, the suitable content ofLi_1.6Mn_1.6O₄was uniformly15wt.%, the adsorption capacity were respectively1012mg/m2and983mg/m2. As shown in SEM images, the membrane pore size became smaller andmembrane surface became dense with the increase of PVC concentration and the decrease ofthe content of Li_1.6Mn_1.6O₄. Using solvents of DMF，NMP and DMAc to investigate theinfluence of different solvents on membrane structure and adsorption capacity, compared withDMF and DMAc solvents, when using NMP solvent, there were cracks on the membranesurface, the penetrability of membrane pore structure was weaker, the precursors falled off seriously. When using DMF and DMAc, there was no the above phenomenon and theadsorption capacity of the membranes resembled each other. Adsorption experiments showedthat the membrane thickness had great influence on the membrane adsorption capacity when itwas less than0.089mm; SEM images showed that the section structure of membrane withfinger-like pores structure disappeared and something similar sponge formed when themembrane thickness was more than0.309mm. The cycle adsorption showed that themembrane-type adsorbent of PVC had good stability. The study found that Langmuiradsorption isotherm was more suitable to simulate the membrane-type adsorbents adsorptionprocess for lithium. The membrane-type adsorbent had good preferential adsorption of lithiumions, although the concentration of Li⁺ion was lower than other metal ions （Na⁺, K⁺, Mg2⁺,and Ca2⁺） in artificial sea water with rich lithium.A series of lithium ion sieve membranes with different amounts of spinel-typemanganese oxide were prepared by adding Li_1.6Mn_1.6O₄to the solution of PVDF via thephase-inversion process. The preparation conditions were investigated changing the PVDFconcentration and the precursor content by means of SEM and adsorption experiments.Adsorption experiments showed that when the content of Li_1.6Mn_1.6O₄was maintained at5wt.%, the adsorption capacity of Li⁺increased with an increase of the PVDF concentration.When the PVDF concentration was20wt.%, the casting membrane liquid was too sticky. Sothe PVDF concentration of20wt%was not suitable for preparing the membrane-typeadsorbent. Select16wt.%PVDF concentration and18wt.%PVDF concentration, thesuitable content of Li_1.6Mn_1.6O₄were respectively15wt.%and9wt.%, the adsorptioncapacity were respectively698mg/m2and869mg/m2. As shown in SEM images, there werecracks on the16%PVDF membrane surface and the section structure mutated with finger-likepores structure disappearing and something similar sponge forming. After four times cycleadsorption, the membrane adsorption capacity decreased slightly which indicated that themembrane-type adsorbent had good stability. Using PES as membrane-forming materials, the suitable content of Li_1.6Mn_1.6O₄was8wt.%when the PES concentration was16wt.%and the adsorption capacity was600mg/m2.Using18wt.%PS concentration, the precursors falled off seriously when the content ofLi_1.6Mn_1.6O₄was5wt.%.