Study On Doping And Coatong Modification And Adsorption Performance Of Li_1.6Mn_1.6O₄ Lithium Ion Sieve

The widespread application of power and energy storage lithium batteries in new energy sources has promoted the continuous increase in global demand for lithium resources.Among the lithium resources that have been identified on the earth,the salt lake brine has the largest lithium reserves.Salt lake brine has high total salt content,complex composition,and low lithium concentration.These factors increase the technical difficulty of separating and extracting lithium from Salt lake brine.Therefore,the method of high selective separation of Liions has attracted much attention,especially the research of lithium extraction using inorganic separation materials such as manganese oxide,titanium oxide and iron phosphate has become a research hotspot.Manganese oxide adsorbents include LiMn₂O₄,Li_1.33Mn_l.67O₄ and Li_1.6Mn_1.6O_4,which exhibit high adsorption capacity and Li⁺selectivity during the Li⁺adsorption process.Because of its stability after multiple adsorption cycles and higher theoretical adsorption capacity,Li_1.6Mn_1.6O₄ is the most representative among all LMO spinel materials.However,the LMO ion sieve adsorbent has obvious manganese dissolution loss during the lithium insertion and extraction process,especially during the extraction process.The dissolution loss of manganese not only causes the attenuation of the adsorption capacity,but also causes water pollution of the raw water and the desorption liquid in practical applications.The purpose of this paper is to reduce the manganese dissolution rate and the stability during the cycle adsorption process through metal doping/coating modification.In this paper,the YLMMO lithium ion sieve was prepared by hydrothermal reaction and further roasting,and the influence of roasting temperature and magnesium doping amount on the adsorption performance of lithium ions was investigated.Finally,we obtained the precursor Li_1.6Mg_xMn_1.6-xO₄(YLMMO)of doped ion sieve with uniform magnesium distribution,and treated the YLMMO with hydrochloric acid to obtain the lithium ion sieve(H_1.6Mg_xMn_1.6-xO₄,YHMMO).The doping modification not only improves the adsorption performance of lithium,but also reduces the dissolution loss of manganese.Through the adsorption cycle experiment of YHMMO in salt lake brine,the selectivity and stability of YHMMO in salt lake brine were studied to evaluate its practical application performance.X-ray diffraction(XRD),scanning electron microscope(SEM),transmission electron microscope(TEM)and X-ray photoelectron spectroscopy(XPS)were used to characterize the chemical properties and morphology of the YLMMO ion sieve.XRD results show that the spinel crystal structure is still maintained after Mg doping.SEM and TEM results show that Mg is uniformly distributed in the precursor.XPS analysis shows that the doping of Mg can reduce the content of Mn³⁺in the precursor and help improve its structural stability.The adsorption capacity of acid-treated YLMMO-6%(YHMMO-6%)is 36.93 mg g^-1,which is greater than that of undoped(YHMO).At the same time,the dissolution loss rates of manganese are 3.22%,respectively,and the structural stability is higher than that of the undoped adsorbent.Adsorption cycle experiments show that YHMMO adsorbent has better adsorption capacity and stronger selectivity for lithium in salt lake brine.The SLMMO lithium ion sieve adsorbent was prepared by solid-phase method,and the adsorption performance and adsorption stability of different doping amounts for lithium ions were studied.The experimental results show that the adsorption capacity of SLMMO-4%reaches 40 mg g-1,and the desorption rate reaches 86%.XRD,EDX,SEM and XPS analyze the crystal phase,morphology and selective stability of the ion sieve.After five cycles of adsorption and regeneration,the adsorption capacity of lithium ions was maintained at about 87%of the initial adsorption capacity,and the manganese dissolution rate dropped to about 0.3%.A series of metal oxide-coated Li_1.6Mn_1.6O₄adsorbents were prepared using Mn₂O₃?LiOH?LiNO₃ and Mn(NO₃)₂ as raw materials.The effects of surface element valence,morphology,pore size,specific surface area and oxide coating on the adsorption performance of the adsorbent were investigated.The experimental results show that LMO-L exhibits good Li⁺adsorption performance.The adsorption capacity of HMO-L on Li⁺reaches 43mg g^-1,and the manganese dissolution rate is 1.3%.After20 cycles of adsorption and desorption tests,the HMO-L ion sieve had a lithium ion adsorption performance of 17mg g^-1.