Preparation,Properties And Applications Of Li-Rich Lithium Manganese Oxides And Their Lithium Ion-Sieves

Lithium is an important energy metal.The development and application of lithium resources have been considerably concerned worldwide.The development of the lithium resources in the liquid salt lake is a spot orientation of the industry due to its abundant deposit.Ion-sieve adsorption method is commonly regarded as one of the most promising way to extract and separate lithium from salt lake brine and underground brine.Manganese oxide ion-sieve,which was obtained by acid leaching from spinel type lithium,has the best performance to adsorb inorganic lithium species.Lithium ion-sieve shows the high selectivity to lithium in solution and can be used in lithium extraction from brine,sweater and waste lithium batteries.The spinel-type manganese oxides have been discussed extensively as the best inorganic lithium ion adsorbents.However,high Mn solubility loss,poor stability and the difficulty of granulating have been recently recognized as the most important issues to be addressed before the commercialization of lithium ion-sieve.It still needs lots of research.In this work,the technology and theory of the preparation of Li-rich spinel-type lithium manganese oxide ion sieves were investigated,which have low Mn dissolubility and high adsorption capacity,and the extraction of lithium by the ion sieve from low lithium solution system.Firstly,the Spinel-type LiMn₂O₄ precursors were prepared from MnCO₃ and LiOH·H₂O as initial substrate by adoption of high temperature solid-phase reaction.Effect of reaction time on the precursors'structure was discussed.The effect of hydrochloric acid concentration&leaching duration on Li⁺dissolution was also concerned.During the acid treatment,the Li and Mn extraction ratios of the sample prepared at 600?were 96.22%and 11.15%.MnO₂ ion-sieve and LiMn₂O₄ precursor were found to maintain the spinel structure and share the same morphology.The maximum adsorption capacity of MnO₂ ion-sieve was 30mg/g in pure lithium solution of pH=12.10,with the adsorption equilibrium time of 24 hours..Secondly,spinel-type Li₄Mn₅O₁₂2 precursors were synthesized from?-MnOOH and LiOH·H₂O by low temperature solid-phase reaction.Furthermore,MnO₂ ion-sieves with Li⁺selective adsorption property were prepared by the acid treatment process to extract Li⁺from the spinel Li₄Mn₅O₁₂2 precursor.The effects of solid-phase reaction process on the structure,chemical composition and ion-exchange property of the ion-sieve material were characterized with XRD,SEM,FT-IR and Li⁺selective adsorption measurements.The results showed that Li/Mn ration,reaction temperature and reaction time had considerable effects on the precursor.The precursor synthesized at 400?for 32 h was a pure Li₄Mn₅O₁₂.Li and Mn extraction ratios of Li₄Mn₅O₁₂were 96.84%and 2.86%.Final MnO₂ ion-sieve and Li₄Mn₅O₁₂2 precursor have a low-dimensional rod-like morphology and share the same structure of spinel.The adsorption capacity of the final MnO₂ ion-sieve increased with the increase of pH in LiCl-LiOH solution and the maximum adsorption capacity was 38.2mg/g with the adsorption equilibrium time of 20 hours.Spinel-type Li₂O·nMnO₂?n=1.75,2.0,2.25,2.5,3.0?precursors were synthesized by EDTA-citrate complexing method under atmosphere,using LiNO₃ and Mn?NO₃?₂·4H₂O as starting materials.MnO₂ ion-sieves with Li⁺selective adsorption property were prepared by the acid treatment process to extract Li⁺from the spinel Li₂O·nMnO₂?n=1.75,2.0,2.25,2.5,3.0?precursors.As-prepared samples were characterized by thermo-gravimetry,XRD,SEM,XPS,FT-IR and Li⁺selective adsorption measurements,respectively.The results showed that only Li_1.33Mn_1.67O₄ and Li_1.45Mn_1.64O₄ could be obtained when n value was 2.5 and 2.25,respectively.The precursor synthesized at 400?for 24h was a pure phase of Li_1.45Mn_1.64O₄.Li and Mn extraction ratios of Li_1.45Mn_1.64O₄ were 96.35%and 0.86%after the acid treatment.Final MnO₂ ion-sieve and Li_1.45Mn_1.64O₄ precursor were about 200 nm spherical pellets and had the same structure of spinel.The adsorption capacity of the final MnO₂ion-sieve increased with the increase of pH in LiCl-LiOH solution and the maximum adsorption capacity was 43.2mg/g with the adsorption equilibrium time of 10 hours.Adsorption properties of the ion-sieve SMO prepared by EDTA-citrate complexing method have been investigated in detail.The effects of adsorption time,initial lithium concentration,adsorption temperature and liquid-solid ratio on the lithium ion adsorbing have been studied from technological aspects.The Langmuir equation and Freundlich equation have been used to describe the isothermal adsorption curves.The isosteric enthalpy and free energy of adsorption of Li+onto ion-sieve SMO were estimated.Negative?G indicated that the process of adsorption of Li⁺onto ion sieve SMO was spontaneous.Positive?H and?S values showed that this process was endothermic and entropy driven process.The lithium adsorption process of ion sieve SMO was fitted with the quasi-second dynamics equation.The activation energy is 15.70kJ/mol.Intraparticle diffusion has controlled the adsorption process,but the boundary layer diffusion in the initial stage also has a remarkable influence on adsorption kinetic.The selectivity of lithium ion-sieve SMO has been studied by ion-exchange equilibrium curve and partition coefficient.Lithium ion-sieve SMO showed selectivity for Li⁺and the selection sequence was Li⁺>Mg²⁺>Ca²⁺>K⁺>Na⁺.The direct industrial application of the powder ion sieve is difficult because of the separation difficulty of liquid and solid,the serious adhesion loss,the poor fluidity and permeability in the fixed bed and the great bed resistance.The suitable molding method was explored and the molding conditions were optimized.EC was chosen as a binder and the optimal conditions were shown as follow:8%binder dosage,65?drying temperature,10%pore forming agent KCl addition relative to the binder as well as1mm extrusion diameter.The obtained granular adsorbent was solidified for 1 hour at120?.The specific area of the granular lithium ion-sieve decreased and pore volume increased compared with the power lithium ion-sieve'result.The adsorption capacity of the granular lithium ion-sieve was only 70%of that of the power lithium ion-sieve in LiCl-LiOH solution under pH of 12.The adsorption capacity was 17.52 mg/g to the second brine and showed a good cyclical stability.Finally,the process of extracting lithium from salt lake brine in the fixed-bed column was explored and the product lithium carbonate was obtained.The effects of flow velocity of the capacity of the granular lithium ion-sieve were investigated.The results showed that the faster the flow rate,the earlier the penetration point appeared,which resulted in the reduction of the adsorption capacity and of utilization ratio of granular ion-sieve.The Li⁺can be completely desorbed with 0.5mol/L hydrochloric acid at the flow rate of 5 mL/min and a highly pure LiCl solution was obtained.The adsorption capacity of granular ion-sieve was 12.54 mg/g and Mn extraction ratio was0.521%after five adsorption-desorption cycle,which showed a good cyclical stability.Lithium ion-sieve adsorption method is very promising for extracting lithium from natural brine.The total yield of lithium was 90%from natural brine to the product lithium carbonate.The obtained Li₂CO₃ products have higher purity and better quality than the national industrial first class product standard.The research achievements in this work will be a theoretical and technical foundation for application of the adsorption technology into the extraction and purification of lithium from low-contented lithium brine.