Preparation Of Lithium Ion Sieve Nanofibrous Adsorbents And Property Research Of Extracting Lithium From Seawater

In this paper, the precursors were prepared by four methods (hydrothermal method, high-temperature solid-phase method, sol-gel method and co-precipitation method), then the lithium adsorption capacities of their corresponding ion sieves were analysed and compared to screen out the optimum ion sieve. However, Lithium ion sieves as powder-type adsorbents had poor liquidity and permeability, so that they had difficulties in implementating industrial application. As known to all, nanofibers had small diameters, so the particles on the nanofibers could expose more active sites; meanwhile, nanofibers can be used in industry conveniently owing to their good flexibilities. Polyacrylonitrile (PAN) was chosed as electrospinning polymer material for its good chemical stability, easy film-forming and cheap price. For the first time, the ion sieves were loaded on the nanofibers, and then the effects of various experimental parameters on the morphologies and lithium adsorption capacities of nanofibrous adsorbents were discussed.Firstly, the precursors of ion sieves were prepared through hydrothermal method, and the various conditions involved in the preparation process were investigated. Ultimately, the appropriate reaction conditions were confirmed as follows:1.20g MnOOH,1.74g LiOH·H2O (the mole ratio of Li and Mn is3.0) and22mL deionized water were transferred into a30mL Teflon-lined stainless steel vessel, and autoclaved at100℃for24h; then the precipitates were roasted at400℃for4h (the heating rate is10℃/min). The products were Li1.6Mn1.6O4, whose corresponding ion sieves had a lithium adsorption capacity of34mg/g or so. In addition, the precursors were prepared by high-temperature solid-phase method, sol-gel method and co-precipitation method, but their corresponding ion sieves had worse lithium adsorption capacities. Compared with the previous study, the ion sieves prepared in the work were more conducive to achieve their industrial application because the lithium adsorption rate improved, and the energy and raw material consumption reduced.Secondly, PAN, Li1.6Mn1.6O4and DMF were mixed into uniform polymer suspension to prepare nanofibers by electrospinning. With the reduction of PAN content in the polymer solution, the lithium adsorption capacity of nanofibrous adsorbents increased, but when the PAN concentration was too low, the viscosity of polymer solution would be too small to collect nanofibers. Replacing parts of PAN in the polymer solution by adding a water-solube polymer-PVP, then washing it away in the pickling process of nanofibrous membranes, so that the lithium adsorption capacity of nanofibrous adsorbents would be improved. But the actual lithium adsorption capacity decreased because the dissolution of PVP led to more ion sieves loss. The lithium adsorption capacity was improved by increasing the content of precursors; however, with the increase of precursors’concentration, their efficiencies declined. For example, when the concentration was10wt%and20wt%, the content of ion sieves on the nanofibers and lithium adsorption capacity increased by only15%and5.2mg/g in theory, respectively. What’s worse, the increment of actual lithium adsorption capacity was only1.5mg/g. Finally, a simple and economic polymer solution formula was obtained, PAN7wt%, Li1.6Mn1.6O410wt%and DMF83wt%, whose lithium adsorption capacity and lithium recovery capacity were13.61mg/g and12.45mg/g, respectively.Finally, through the investigation of the effects of electrospinning process parameters on the nanofibers’ morphologies, it’s found that the increase of receiving distance and the decrease of injection velocity and nozzle diameter led to the reduction of the nanofibrous diameters; while with the increase of the operating voltage, the diameter of nanofibers increased first and then decreased.