Preparation Of Manganese-based Lithium Ion-sieve Composite And Its Application In Lithium Extraction

Geothermal water resource in the West of China is a new type of liquid lithium resource,which can be used as high-quality materials for lithium extraction.However,powder adsorbents have problems such as high dissolution loss and difficulty in the real application.In this thesis,the preparation of composite adsorbents and their performance in extracting lithium from geothermal water were studied.The main conclusions are summarized as follows:（1）Synthesis of high-performance Li_1.6Mn_1.6O₄powder adsorbentManganese lithium-ion sieve precursors Li_1.6Mn_1.6O₄（LMO）were synthesized by hydrothermal or high-temperature solid-phase methods.A comparison of the adsorption properties of lithium-ion sieves and the dissolution loss rate of manganese using different synthesis methods showed that the adsorption and elution properties of LMO synthesized by the high-temperature solid-phase method are better than those by hydrothermal methods.The pickling conditions of LMO and the adsorption conditions of HMO were optimized.The results are as follows:Under the pickling process,the hydrochloric acid concentration is 0.25 mol/L,the solid-liquid ratio is 1:100,and the elution time is 12 h.Under the adsorption process,the p H is 12,and the solid-liquid ratio of the adsorbent is 1:1000.（2）Preparation of spinning fiber PVDF/HMO ion sieve and its lithium extraction performanceThe composite spinning solution was prepared using NMP as an organic solvent,PVDF as a binder,and HMO as core material.PVDF/HMO spinning adsorbent was prepared by commercialized spinning apparatus combined with wet spinning technology.The effects of polymer content on dope forming,HMO loading on the adsorption performance and the optimal adsorption/desorption conditions of PVDF/HMO spinning adsorbent were explored.The results are as follows:The proportion of PVDF in the spinning solution is 6%.The more extensive HMO loading,the higher the adsorption capacity of PVDF/HMO spinning adsorbent was.The theoretical adsorption capacity of70%-PVDF/HMO can reach 16.21 mg/g.The adsorption p H is 12,the elution time is 1 h,and the solid-liquid ratio of elution solution is 1:100.（3）Performance of spinning fiber PVDF/HMO composite adsorbent for extracting lithium from geothermal waterThe adsorption selectivity,adsorption kinetics,thermodynamic properties and cycle stability of PVDF/HMO spinning adsorbent in geothermal water were explored.The results are as follows:the PVDF/HMO adsorbent shows high selectivity for Li⁺,and the distribution coefficient of Li⁺can reach up to 1404.96 m L/g.The adsorption by PVDF/HMO spinning adsorbent in geothermal water conforms to the pseudo-second-order kinetics equation,and the correlation coefficient is 0.9998.The molecular diffusion model shows that lithium adsorption proceeds in two stages;the first stage is faster than the second stage.The adsorption capacity increases with temperature,and the thermodynamic parameters are as follows:ΔG<0,ΔH>0,ΔS>0,which indicates the adsorption process is spontaneous and exothermic.The equilibrium time is 2 h,and the adsorption capacity is14.95 mg/g.After five cycles,the adsorption capacity of the adsorbent is 14.21 mg/g,and the dissolution loss rate of Mn is 1.74%.The cycle stability is good,indicating that the adsorbent has the potential to apply for lithium extraction from geothermal water.