Preparation Of Manganese-titanium Based Composite Lithium Ion Sieve And Its Lithium Extraction Performanc

With the development of new energy technology and the continuous expansion of human society’s demand for lithium,the traditional method of extracting lithium with low production capacity and high cost can not well meet the demand for lithium in various industrial domains.In contrast,adsorption has demonstrated bright application prospects because of its easy operation,low energy consumption,and high efficiency as well as selectivity.Lithium ion-sieves（LISs）are a class of materials which can selectively adsorb lithium ions.A precursor is first synthesized by introducing a lithium source,and then lithium ions are eluted from the precursor structure,thereby forming a lithium-extracting material（i.e.LISs）with a memory effect.And thus,by using the LISs the adsorption or enrichment of lithium ions can be achieved.Generally encountered LISs include manganese-based lithium ion-sieve（HMO）and titanium-based lithium ion-sieve（HTO）.HMO has high chemical stability and adsorption performance,but the Mn dissolution loss rate from HMO is serious during the pickling process.Comparatively,HTO bears higher chemical stability whereas also with much higher cost of titanium source,which distinctly constrains its practical application.In view of the respective advantages and disadvantages of HMO and HTO,this thesis mainly focus on the following two aspects:Firstly,P25,lithium acetate dihydrate and manganese carbonate were used as the raw materials,and as a result the manganese-titanium composite LISs nanospheres（HMTO）were obtained with relatively uniform spherical morphology,narrow size distribution,small average particle size（ca.55 nm）,large specific surface area(37.7 m²·g^-1)and high surface O^2-content（59.01%）.In particular,via the morphology inheritance of P25 and also its deep mixing with lithium acetate dihydrate,optimization of the morphology and size and specific surface area of the HMTO were enabled.To increase the O^2-content on the surfaces of the LISs,that is,to increase the number of lithium-ion adsorption sites,the molar ratio of manganese to titanium was also modulated within the range of 0.25～4.Secondly,the lithium extraction performance of the as-obtained composite LISs with different manganese-titanium molar ratios was studied in depth.Especially,when the HMTO（Mn:Ti=1:4）was used as the lithium adsorbents,it showed a faster adsorption rate（t_e=6 h）and a higher equilibrium adsorption capacity(q_e=79.5 mg·g^-1)at an initial lithium concentration of 1.8g·L^-1,and the maximum adsorption capacity reached 87.26 mg·g^-1,which was better than most reported LISs.The adsorption process conforms to the Langmuir isothermal adsorption model,and the adsorption behavior belongs to chemisorption according to the fitting results originated from various kinetic models.And the rate-determining step of the adsorption lie in the second stage,which is controlled by the pore diffusion as well as the film diffusion.In addition,the HMTO（Mn:Ti=1:4）also exhibited a high lithium extraction in simulated salt lake brine(q_e=33.85 mg·g^-1)as well as a high selectivity at high magnesium-lithium ratio(=2192.76).Besides,after five adsorption-desorption experiments,the HMTO（Mn:Ti=1:4）can still maintain74%of the adsorption capacity,and the dissolution loss rate of Ti⁴⁺is confirmed as less than1.3%,and the dissolution loss rate of Mn²⁺does not further increase after three cycles.Ultimately,based on a large number of experiments and adsorption model calculations,a probable lithium ion adsorption mechanism at the molecular level and macroscopic morphology was uncovered.To sum up,the HMTO developed in the present work combines the respective advantages of HMO and HTO,thus providing a novel strategy design for lithium recovery by adsorption.This work is highly expected to make great contribution to the theoretical basis and technical support for the research and development of lithium extraction from salt lakes and even the future development of new energy technology.