Preparation Of Three-dimensionally Ordered Macroporous HAlMnO₄ Lithium Ion-sieve And Its Adsorption Properties

Lithium is an important metal of promoting the world forward. In the past half century, several methods like solvent extraction, precipitation, and ion exchange, etc. have been extensively investigated for lithium recovery from seawater and salt lake brine. Among them, the adsorption method is considered to be the most promising scheme because certain inorganic sieve materials exhibit an extremely high selectivity for Li+ and environmentally friendly effect. Multiple kinds of lithium manganese oxide especially including spinel phase have been studied and characterized. However, the blockage of binder and the diffusion resistance in solid phase suppress the adsorption capacities of adsorbents, and the variable valence of manganese is liable to dissolution in the Li+ extraction/insertion process. In order to overcome the shortcomings, chemical doping and three-dimensinally ordered macropores can be applied to improve the lithium ion-sieve. Chemical doping improved the stability of materials, and three-dimensinally ordered macropores enhanced the diffusion ability of Li+ and the ion-exchange capacity. This work includes four parts: preparation of colloidal crystal template; synthesis of three-dimensinally ordered macropore LiAlMnO4; acid treatment of precursor and adsorption properties of lithium ion-sieve.PMMA, PS and SiO2 monodisperse microsphere was prepared by the method of emulsion polymerization, emulsifier-free emulsion polymerization and sol-gel, respectively, and assembled to colloidal crystal template by centrifugal sedimentation or natural sedimentation. The influences of preparative conditions to the diameter of microspher and assembly methods to the quality of template had been investigated.The Al-incorporated three-dimensionally ordered macroporous lithium manganese oxide LiAlMnO4 is synthesized by the polymethyl methacrylate colloidal crystal template filled with the LiNO3, Al(NO3)3·9H2O and Mn(Ac)2·4H2O mixed solution. The microcosmic morphology and macroporous size were observed using a fieldemission scanning electron microscope (SEM), the sample surface being sprayed with gold for ¹00 s as pretreatment. Powder X-ray diffractometry (XRD) was used for the characterization of crystal phase and the estimation of the crystalline size. The BET surface area was measured by using a surface area analyzer, samples being degassed at 100℃overnight before sorption measurements. The influences of preparative conditions to the morphology and crystal structure of three dimensinally ordered macoporous lithium manganese oxide had been studied.The corresponding HAlMnO4 as a lithium ion-sieve is obtained after extracting of Li+. The experiments show that the macroporous diameter and porous wall thickness are 240 nm and 52 nm or so, respectively, and the X-ray diffraction patterns of samples belong to the pure spinel phase. The Li+ extraction rate of LiAlMnO4 reaches above 97% in the 0.1 M HCl solution, while the solution losses of aluminum and manganese only have 0.45% and 0.23%, respectively, owing to the substitution of aluminium for tervalence manganese, the influence of the Jahn-Teller effect on the solid structure is suppressed effectively.The Li⁺ maximum uptake capacity is equal to 45.5 mg/g, reaching 96.3% of the theoretical value of HAlMnO4. Meanwhile, the uptake speed of Li+ is obviously speeded up, and there is the quite high selectivity of Li+ in the solution containing K+, Na+, Mg2+ and Ca²⁺. Therefore, this material presents excellent properties and is promising in the lithium extraction from extremely dilute solution.