【作者】 马立文；

【导师】 陈白珍； 石西昌；

【作者基本信息】 中南大学 ， 冶金物理化学， 2011， 博士

【摘要】 因为在可充电锂电池和其他相关领域的广泛应用,锂资源不断受到人们关注。但目前世界上的锂矿储量已不能满足未来人类对锂的需求。因此,开发适宜的技术从盐湖卤水和海水等液态锂资源中提取锂,具有重要意义。尖晶石型锂锰氧化物前驱体经过酸浸脱锂,获得的锰氧化物被称作“锂离子筛”。锂离子筛因在溶液中对锂具有高选择吸附性而成为目前研究最多、性能最好的无机锂离子吸附剂,并开始应用于锂资源提取领域。然而,尽管锂离子筛已在近几十年被大量研究,但研究还不够广泛、深入和系统,锂锰氧化物的结构与锂离子筛的性能之间的关系还缺乏讨论。为此,有必要对各种锂锰氧化物及其相应的离子筛进行晶体结构和吸附性能的综合研究。本文首先采用固相法和液相法分别在不同温度下制备了尖晶石锂锰氧化物LiMn2O4。酸浸脱锂后通过XRD、SEM分析发现得到的λ-MnO2锂离子筛均能够保持完整的尖晶石结构和形貌。其中采用液相法在550℃下制备的LiMn2O4酸浸脱锂时Li的溶出率为97.25%,Mn的溶出率为15.47%。脱锂后得到的锂离子筛在HCl-LiCl-LiOH溶液中的吸附容量随pH的升高而升高,最大吸附容量为23.75 mg·g-1,吸附行为符合Langmuir模型。为改善LiMn2O4在酸浸过程中Mn溶损较大的缺陷,采用Ni2+、Al3+、Ti4+和Sb5+对其进行掺入改性,并通过TG-DSC. TG-DTA. XRD、SEM、EDS等手段进行表征。利用不同的合成方法和条件分别制备了理论化学式为LiMzMn2_zO4(M=Ni、Al、Ti、Sb,0≤z≤1)的复合锂锰氧化物。当z≤0.5时,Ni、Al和Ti均能完全纳入尖晶石晶格,形成掺入锂锰氧化物。掺入的Ni和Al会导致晶格收缩,掺入的Ti会导致晶格扩张。其中LiNi0.5Mn1.504、LiAlo.5Mn1.5O4并LiTio.5Mn1.5O4在酸浸脱锂前后均能形成完整的尖晶石结构和形貌。LiNi0.5Mn1.5O4酸浸时Li、Mn、Ni的溶出质量百分率分别为28.12%、7.08%和10.14%；LiAlo.5Mn1.5O4的Li、Mn、Al溶出率分别为59.04%、12.70%和14.40%；LiTio.5Mn1.5O4的Li、Mn、Ti溶出率分别为74.71%、29.58%和19.49%。酸浸之后,只有LiAlo.5Mn1.5O4转型得到的锂离子筛在HCl-LiCl-LiOH溶液中具有较高的吸附容量,达到20.21mg·g-1,且吸附符合Langmuir模型。由于晶格存在显著的收缩或扩张,其他各掺入尖晶石锂锰氧化物的酸浸Li溶出率或其离子筛的锂吸附容量均较低。Sb很难掺入尖晶石LiMn2O4晶格形成单一的掺Sb锂锰氧化物,在z=0.5时形成了Sb、Mn互相掺入的LiMn2O4(尖晶石)(?)(?)LiSbO3(钙钛矿)复合相。其Li、Mn和Sb的酸浸溶出率分别为80.55%、34.20%和4.34%。虽然z0.5样品酸浸前后结构稳定、形貌完整,但其锂离子筛的综合性能不佳。采用柠檬酸配合法合成了系列尖晶石富锂锂锰氧化物,理论化学通式为Li2O·rMnO2(1.75≤r≤3.0),并通过XRD、SEM、XPS和IR等检测手段进行表征。其中350℃合成的Li2O·2.25MnO2 (LMO)具有纯相尖晶石锂锰氧化物结构,并且在酸浸过程中具有高Li溶出率和低Mn溶损率,Li、Mn溶出率分别为95.45%和6.01%。其酸浸后转型为锂离子筛MO, MO仍然保持尖晶石的结构和形貌。LMO和MO中Mn的平均价态分别为3.82和3.91。酸浸过程中LMO转变为MO的机理是Li+-H+离子交换机理。此后,对离子筛在HCl-LiCl-LiOH溶液、LiCl-NH3·H2O-NH4Cl缓冲体系以及盐湖卤水中的吸附性能进行全面研究。在LiCl-NH3·H2O-NH4Cl缓冲体系中MO的吸附符合Langmuir模型,计算得到其吸附过程的△Gθ小于零,反应自发进行；△Hθ为3.319kJ·mol-1,△Sθ为11.70J·mol-1·K-1；吸附符合准二级动力学方程；由颗粒扩散和液膜扩散等步骤混合控制。离子筛MO在混合缓冲溶液中对Li+具有选择吸附性能,选择顺序为：Na+<K+<Mg2+<<Li+,吸附机理为H+-Li+离子交换机理。离子筛MO在卤水中吸附容量约为10 mg·g-1,具有一定的循环使用寿命,至少能循环使用6次。首次采用聚氨酯模板法以沥青为粘结剂,制备出了MO泡沫锂吸附剂,并用DTG、XRD、SEM、TEM、EDS、N2吸附-脱附测试等手段对泡沫吸附剂的组成、结构、形貌、孔结构等性质进行全面表征。MO泡沫具有三维互通网络结构,由沥青载体和锂离子筛MO组成,内部呈介孔/微孔分级多孔结构。MO泡沫在HCl-LiCl-LiOH溶液、LiCl-NH3·H2O-NH4Cl缓冲体系以及盐湖卤水中的吸附容量分别为8.73、3.83和1.49mg(Li+)·g-1(Mo泡沫)。MO泡沫对Li+具有吸附选择性,在混合缓冲溶液中对金属离子的吸附亲和顺序为Na+<K+<Mg2+<<Li+。吸附Li+后,MO泡沫中的沥青载体和锂离子筛MO的结合力变差。最后,采用Mn3+和Mn空位两个指标整合了氧化还原和离子交换机理,提出“Mn态定性”模型,并利用该模型创造出直观的机理评价方法——尖晶石锂锰氧化物“Mn态定性”机理判断图,全面讨论了论文涉及的各种锂锰氧化物的脱锂嵌锂机理。更多还原

【Abstract】 Interest in lithium resources has been increasing because of its wide applications in rechargeable lithium batteries and other related fields. But the present lithium mineral reserves in the world cannot meet the requirement of lithium in the near future. Therefore, to develope appropriate technology to recover lithium from liquid lithium resources, such as salt lake brine and sea water, is of great significance. The treatment of spinel lithium manganese oxide with acid causes the removal of nearly all the Li+from its tetrahedral sites and leaves the manganese oxide called "lithium ion-sieve". Lithium ion-sieve can adsorb lithium selectively in solution, so it has been studied extensively as the best inorganic lithium adsorbent, and began to be applied in lithium recovery area. Although the lithium ion-sieve has been researched in recent decades, the study is not comprehensive, thorough and systematic. There also lacks the discussion on the relationship between the structure of lithium manganese oxide and the performance of its lithium ion-sieve. To this end, it is necessary to widely study the crystal structure of various lithium manganese oxides and adsorption performances of their corresponding lithium ion-sieves.Firstly, spinel lithium manganese oxide of LiMn2O4 was prepared by solid method and liquid method at different temperatures, respectively. XRD and SEM analysis showed that the lithium ion-sieve ofλ-MnO2 obtained by acid treating LiMn2O4 maintained the spinel structure and morphology. During the acid treatment, the Li and the Mn extraction ratios of the sample prepared by liquid method at 550℃were 97.25% and 15.47%. The resultant lithium ion-sieve could adsorb lithium in HCl-LiCl-LiOH solution, and the adsorption capacity increased with the increase of pH with the maximum adsorption capacity of 23.75 mg-g-1. The adsorption behavior of this lithium ion-sieve was modeled and fitted for Langmuir isotherm equation.To reduce the Mn extraction ratio of LiMn2O4 during acid treatment, Ni2+, Al3+, Ti4+and Sb5+ were used to substitute the Mn in LiMn2O4. TG-DSC, TG-DTA, XRD, SEM, EDS and other techniques were employed to characterize the relative materials. Various synthetic methods and conditions were adopted to prepare different substituted lithium manganese oxides with their theoretical chemical formula of LiMzMn2-zO4 (M=Ni, Al, Ti, Sb; 0≤z≤1). Ni, Al and Ti were fully integrated into the spinel lattice when z≤0.5. The incorporated Ni and Al induced the lattice contraction, while the incorporated Ti caused the lattice expansion. LiNi0.5Mn1.5O4, LiAl0.5Mn1.5O4 and LiTi0.5Mn1.5O4 maintained their spinel structure and morphology after acid treatment. During acid treatment, the metallic element extraction ratios were w(Li)=28.12%, w(Mn)=7.08% and w(Ni)=10.14% for LiNi0.5Mn1.5.O4; w(Li)=59.04%, w(Mn)=12.70% and w(Al)= 14.40% for LiAl0.5Mn1.5O4; w(Li)=74.71%, w(Mn)=29.58% and w(Ti)=19.49% for LiTi0.5Mn1.5O4, respectively. Only the lithium ion-sieve derived from LiAl0.5Mn1.5O4 had a relatively high adsorption capacity of 20.21 mg·g-1 in HCl-LiCl-LiOH solution and its adorption behavior complied with Langmuir adsorption model. Due to the remarkable lattice contraction or expansion, other substituted spinels showed low Li extraction ratios or their lithium ion-sieves showed adsorption capacities. It was difficult for Sb to enter in the spinel LiMn2O4 to form Sb-substituted lithium manganese oxide. When z=0.5, the sample formed a combined structure of LiMn2O4 (spinel) and LiSbO3 (perovskite) in which manganese and antimony ions diffused mutually into perovskite and spinel to form a composite. The Li, Mn and Sb extraction ratios of sample z0.5 were 80.55%,34.20% and 4.34%, respectively, during acid treatment. After acid treatment, the resultant lithium ion-sieve exhibited the structural stability and morphology integrity, but the general performance of this lithium ion-sieve was not good.A series of spinel lithium-rich manganese oxide with theoretical chemical formula of Li2O·rMnO2 (1.75≤r≤3.0) was synthesized by citric acid complex method. XRD, SEM, XPS and IR were used to characterize the relative materials. The sample of Li2O·2.25MnO2 (LMO) prepared at 350℃presented spinel structure, high Li extraction ratio of 95.45% and low Mn extraction ratio of 6.01% during acid treatment. After acid treatment, LMO transformed to lithium ion-sieve of MO, which maintained spinel structure and morphology. The average valences of Mn in LMO and MO were 3.82 and 3.91, respectively. The transformation from LMO to MO is consistent with the Li+-H+ion exchange mechanism. In addition, the adsorption properties of MO in HCl-LiCl-LiOH solution, LiCl-NH3-H2O-NH4Cl buffer system and the salt lake brine were comprehensively studied. In LiCl-NH3·H2O-NH4Cl buffer system, the lithium adsorption of MO was fit for Langmuir model. The calculated△Gθwas negative, which means the adsorption process occurred spontaneously;△Hθwas 3.319 kJ-mol-1 and△Sθwas 11.70 J-mol-1·K-1. The adsorption process obeyed the pseudo-second-order kinetic model and was controlled by intraparticle diffusion, boundary layer diffusion, etc. Lithium ion-sieve MO showed selectivity for Li+in mixed buffer solution, and the affinity order was Na+<K+<Mg2+Li+. The adsorption mechanism of MO was also H+-Li+ ion exchange mechanism. MO can be recycled at least 6 times in the brine with the adsorption capacity of about 10mg·g-1.MO foam, a foam-type lithium adsorbent, was prepared by polyurethane template method with pitch as binder. DTG, XRD, SEM, TEM, EDS and N2 adsorption-desorption test were employed to characterize the composition, structure, morphology, pore structure and other properties of the relative materials. The MO foam with three-dimensionally interpenetrating network consisted of the lithium ion-sieve of MO and oxygen-containing cross-linked pitch. The bulk of the MO foam presented meso-/microporous structure. The adsorption capacities of MO foam in HCl-LiCl-LiOH solution, LiCl-NH3·H2O-NH4Cl buffer system and salt lake brine were 8.73,3.83 and 1.49 mg(Li+)·g-1(MO foam), respectively. The affinity order for MO foam in mixed buffer solution was Na+<K+<Mg2+<<Li+. The combination of the pitch support and the MO particles in MO foam became loose after Li+ adsorption.Finally, the ion exchange mechanism and the redox mechanism for lithium extraction/insertion process in solution were reorganized according to Mn3+content and Mn defects in spinel lithium manganese oxide. The "Determine by Mn" model was proposed. A comprehensive discussion on the lithium extraction/insertion mechanism of the lithium manganese oxides involved in this thesis was made. A "Determine by Mn" mechanism map was created to visually evaluate the extraction/insertion mechanism of all kinds of spinel lithium manganese oxides.更多还原