Synthesis Of Lithium Ion Sieve Composites And Research Of The Properties

As the lightest metal element in nature,lithium and its compounds are widely used in all aspects of modern society and they are regarded as important strategic resources.Nowadays,with the popularization and application of new energy sources,especially lithium-ion batteries,the demand for lithium resources in various countries is increasing sharply day by day.However,the global lithium ore is decreasing and it is no longer able to meet the needs.The lithium resources in salt lake brines and seawater could solve the contradiction well,so extracting lithium from salt lake brines and seawater is of great significance.In contrast,lithium reserves in salt lake brines accounts for 61.8%of total lithium resources,and its extracting cost is low,and it is more environmentally friendly comparing with extracting lithium from lithium ores.Salt lake brines will gradually replace lithium ores to be the main source of lithium resources in the future.At present,there are many lithium extraction methods.In contrast,the ion sieve adsorption method has many advantages,and it's a relatively promising method for lithium extraction from salt lake brines.Due to the relatively high adsorption capacity,simple recycling and environmental friendliness,manganese oxide type lithium ion sieves are brought into sharp focus by researchers.However,how to further improve the adsorption capacity of manganese-based lithium ion sieve and prolong the service life are the key to realize the industrial application of manganese-based lithium ion sieve.In view of this,this thesis focuses on the synthesis,membrane formation and application of lithium extraction in high-dispersion,high-adsorption capacity lithium-rich manganese-based lithium ion sieves.The highly dispersed sphere-like Mn₂O₃ manganese source was prepared by calcination of MnCO₃ which was synthesized by modified carbonization method.The spherical MnCO₃ was successfully prepared by the carbonization method by using CO₂as the carbon source and ethylene glycol as the solvent.According to the experimental conditions,it is suitable to react at 60°C for 4 h to obtain spherical MnCO₃ with good dispersibility.The preparation of MnCO₃ hasn't added any surfactant,which is in line with the principle of green chemistry,and our work was a bit innovative compared with other work reported in the literature.The highly dispersed mesoporous spherical Mn₂O₃was prepared by calcination of MnCO₃ microspheres at 550°C.The specific surface area was about 36.71 m²/g,and the pore size was concentrated at 23.4 nm.The formation mechanism of Mn₂O₃ was analyzed simply,and owing to the existences of many mesopores and good dispersibility,the Mn₂O₃ performed excellent adsorption effects on Congo red dyes.In the subsequent experiments,Li_1.6Mn_1.6O₄ was prepared by using spherical Mn₂O₃ as manganese source.Highly dispersed spherical precursor was synthesized by facile two-step solid phase method and the corresponding lithium ion sieve MnO₂·0.5H₂O was obtained after acid treantment,the Li⁺adsorption performance of MnO₂·0.5H₂O was studied.The above-mentioned synthesized spherical Mn₂O₃ and commercial LiOH·H₂O were ground and mixed well,and the porous spinel type spherical Li_1.6Mn_1.6O₄ precursor was successfully synthesized by solid phase synthesis.As a comparison,changed the solvent and prepared cubic Mn₂O₃ and corresponding cubic Li_1.6Mn_1.6O₄ was synthesized further.After the precursors were treated by acid,porous cubic lithium ion sieves were obtained.By comparison,the prepared spherical lithium ion sieves have higher specific surface area and more mesopores,and thus has a high Li⁺adsorption capacity up to 42.46 mg/g,and the adsorption process of Li⁺in the spherical lithium ion sieve could be explained by the Freundlich isotherm model and the pseudo-first-order kinetic model.In addition,the porous spherical lithium ion sieve has good reusability and high Li⁺selectivity,thus,the prepared spherical porous lithium ion sieves have great prospects of application for extracting Li⁺in aqueous environment including brines and seawater.The PVDF-Li_1.6Mn_1.6O₄ precursor membranes were prepared by phase inversion method and the Li⁺adsorption performance of the corresponding ion sieve membranes were studied.The synthesized Li_1.6Mn_1.6O₄ powders were added into the PVDF casting solution,and the PVDF-Li_1.6Mn_1.6O₄ porous hybrid membranes were prepared successfully,and the corresponding lithium ion sieve membranes PVDF-MnO₂·0.5H₂O with lithium extraction performance were obtained after acid treatment of precursor membranes.The adsorption experiments show that the lithium ion sieve membranes had a certain adsorption capacity for Li⁺in Li⁺-containing solution,the acid elution of Li⁺and the adsorption rate were relatively fast.The loading of Li_1.6Mn_1.6O₄ in the casting solution affected the adsorption performance,it is found that when the content of Li_1.6Mn_1.6O₄ is 11.9%,the adsorption capacity of corresponding PVDF-MnO₂·0.5H₂O lithium ion sieve membrane is up to 404 mg/m²,and the cycle experiment and selectivity test show that the obtained lithium ion sieve membranes had better recycle performance and higher Li⁺selectivity.The Mn loss is suppressed to some extent after film formation comparing with Li_1.6Mn_1.6O₄ powders,which is initially solved the problems of fine particle size and poor fluidity of the adsorbent material and lay a good foundation for further research and application of powder industrialization.