Preparation Of Spinel Lithium Ion-sieves And Their Li~+/H~+Exchange Properties

Ion exchange technique is considered as the best promising way of beneficiate Li⁺fromsalt lake brine or seawater, and spinel LiMn₂O₄or its doping compound is commonlyconsidered as a kind of ideal lithium ion sieve precursor material and has been researched byscientist for many years in different countries.The first part of this essay is the foreword, mainly includes the introduction of the theproject background、review of the literatures and the summary of work of the whole essay.The second part is about the preparing of the LiMn₂O₄microspheres with holes and thestudying of its ion exchange properties. We prepared500mL MnSO₄solution with the moleconcentration of0.03000mol/L and then added100mL absolute ethyl alcohol, and thenadded500mL0.3000mol/L NH₄HCO₃solution slowly at the condition of magnetic stirring,and then let stand for2–3h, discarded supernatant and then filtered it, then dried the filterresidue, we got MnCO₃microsphere. Then we heated the MnCO₃microsphere sample at350oC for4h, waited until the sample turns as cold as the environment and then dipped it into0.1mol/L hydrochloric acid, waited until no bubble appears. Then filtered it and dried thefilter residue, the dried filter residue was the sample of MnO₂microspheres. Then we dippedthe MnO₂microsphere into LiOH solution and evaporated water at temperature80oC, heatedthe mixture at700oC for10h for preparing LiMn₂O₄microspheres with holes. The rate of thelosts of Li⁺and the dissolution of Mn in （NH₄）₂S₂O₈solution with different temperatures wasstudied, and the result showed that90oC was the best temperature for increasing theextraction rate of Li⁺and reducing the dissolution of Mn. H-Mn-O samples was got after theLiMn₂O₄sample was dipped in0.5mol/L of （NH₄）₂S₂O₈solution with t=90oC for1h, andthe measurement result of XRD and SEM of the sample H-Mn-O showed that its crystallinephase and appearance nearly remain the same with LiMn₂O₄. We studied how the dippingtime、the basicity of solution and the temperature influenced the adsorption properties ofH-Mn-O, and the result showed that H-Mn-O could reach the balance of the Li⁺adsorption（3.04mmol/g） after dipping in pH=10LiCl solution for12h. The measurement of theadsorptive selectivity showed that H-Mn-O has high adsorptive selectivity to Li⁺.The third part is about the preparing of the rodlike LiMn₂O₄and the studying of its ionexchange properties. β-MnO₂was prepared with hydrothermal way, which MnSO₄·H₂O wasused as the source of Mn, NaClO₃was used as the oxidant, and PVP was used as the additive.Then the micro/nano tube of MnO₂was dipped in LiOH solution with stiring. Then the waterwas evaporated at80oC, and the solid reagents was heated on700oC for10hours （heatingrate2oC/min）, the sample of rodlike LiMn₂O₄had been prepared. Then the Li⁺of theLiMn₂O₄was extracted in order to prepare the rodlike H-Mn-O, then the Li⁺adsorptionproperties of the acid-modification-sample H-Mn-O was studied, whose results showed thatthe adsorption ability also linked to time、temperatures and pH values of the solution. TheH-Mn-O sample had the Li⁺adsorption capacity of2.31mmol/g at pH=10、t=24h. Therodlike H-Mn-O had50.6of the separation factor of Li⁺/Mg2⁺.The fourth part is about the preparing of the micro/nano tube Li1⁺xMn₂O₄⁺yfor the presoma of lithium ion-sieve. The β-MnO₂prepared by hydrothermal synthesis way wasdipped into LiOH solution （controlling n（Li）/n（Mg）=0.65:1）, then the mixture was evaporatedat80oC to eliminate H₂O and put into temperature-controlled furnace. Then we increased thetemperature to650oC with speed2oC/min and kept the temperature at650oC for5h, thelithium ion-sieve presoma had been prepared. The SEM diagram showed that the samplecould keep the micro/nano tube form after heating, but the XRD pattern showed that the theimpurity turned more.Then we prepared LiAlMnO₄with rheological phase way and studied its ion exchange properties. Theresult showed that rheological phase preparation could reduce the heating temperature and the time （heatingat600oC for five hours）, and the prepared sample wass LiAlMnO₄with high spinel crystallinephase. The sample could keep the spinel crystalline phase after extracting Li⁺. The lithium ionsieve HAMO got from LiAlMnO₄after extracting Li⁺had the largest Li⁺adsorptive capacityof over30mg/g.