CAS OpenIR
LiCl-NH3·H2O-CO2气液反应结晶制备电池级碳酸锂研究
田孟华
Subtype硕士
Thesis Advisor王志
2019-07-01
Degree Grantor中国科学院大学
Degree Discipline化学工程
Keyword碳酸锂, 气液反应结晶, 过饱和度, 晶体粒度分布, 成核动力学
Abstract

碳酸锂(Li2CO3)作为一种最基础、最重要的锂化合物,在锂离子电池、材料、医药等行业有着广泛的应用,尤其随着新能源行业的快速发展,碳酸锂在储能、无线设备等领域发挥着至关重要的作用。自然界中的一次锂资源主要包括锂矿石和盐湖卤水,二次资源锂离子电池中锂的回收也逐渐受到关注。工业中矿石和盐湖卤水提锂工艺都是通过添加碳酸钠直接沉淀得到碳酸锂,制备过程粗放、产品纯度低、粒度不可控。针对传统工艺过程不可控、产品质量差等问题,本文提出LiCl-NH3·H2O-CO2气液反应结晶制备Li2CO3的新体系,以过饱和度及成核与生长过程控制机理为核心,通过在线、离线手段对结晶过程进行解耦分析,重点研究体系介稳特征和结晶特性、成核生长动力学规律、粒度调控及机理等问题。主要取得如下结果:(1)研究了LiCl-NH3·H2O-CO2体系气液反应结晶过程特性。结果表明NH3·H2O对结晶过程有明显的缓和效果,且可以抑制Li2CO3晶体的过度碳化。增大NH3·H2O浓度可以显著提高CO2的吸收效率,增大Li2CO3的过饱和度,提高[Li+]转化率;NH3·H2O的存在使得CO2的吸收过程对温度更加敏感。气液反应结晶过程可分为两个阶段,第一阶段,从25 oC至50 oC,温度显著影响Li2CO3的结晶速率,随着温度的提高,结晶速率逐渐增大;当温度增大到60 oC时,结晶速率受到过饱和度的限制从而不再增大,说明温度和过饱和度都是影响结晶速率的重要参数。(2)研究了LiCl-NH3·H2O-CO2体系Li2CO3结晶动力学。通过测定不同温度下的结晶速率,得到表观活化能为23.55 kJ/mol,说明Li2CO3结晶过程由表面反应和扩散混合控制。利用FBRM测定成核速率得到成核活化能为79.15 kJ/mol,表明初级成核速率受温度影响较大。通过相同温度下改变过饱和度,确定生长速率关于过饱和度的级数为6.81;通过过饱和度与成核速率的关系得到Li2CO3的成核界面能为22.03 mJ/m2,通过诱导期与成核速率的关系得到的成核界面能为18.80 mJ/m2,两者相近,表明通过FBRM计算成核速率具有一定的可行性。通过测定生长速率得到生长活化能为26.79 kJ/mol,其明显小于成核活化能,说明成核过程受温度的影响更显著。(3)对Li2CO3在氨水和氯化铵混合体系下的溶解度进行了测定,氨水浓度一定时,其溶解度随着氯化铵浓度的增大而增大;氯化铵浓度较低时,随着温度的升高,Li2CO3的溶解度逐渐减小,与Li2CO3在水中的溶解度规律一致;然而,当氯化铵浓度较高时,Li2CO3溶解度随着温度的升高而增大。(4)探究了Li2CO3粒度与二次成核和生长速率的关系。Li2CO3的超溶解度随着温度的升高而减小,从而二次成核速率减小,生长速率增大,使得温度和Li2CO3平均粒度呈正相关。过饱和度影响二次成核与生长速率,即改变Li2CO3成核与生长的主导机制,从而得到不同粒度分布的Li2CO3产品,过饱和度越大,成核过程占主导,生长过程被削弱,从而晶体粒度越小。(5)通过添加剂与微气泡两种手段调控Li2CO3的粒度和形貌,并对其调控机理进行初步探索。添加聚丙烯酸(PAA)可以改善Li2CO3形貌,得到由一次片状晶体团聚形成的球形簇状Li2CO3颗粒。添加六偏磷酸钠能得到较为密实的一次片状单体团聚成的球状颗粒,并且对Li2CO3成核有更加明显的抑制作用。焦磷酸钠、聚乙烯亚胺(PEI)、十二烷基苯磺酸钠(SDBS)能够减缓反应结晶过程中溶液pH值的下降,使Li2CO3成核延迟,介稳区宽度变大,强化成核过程,从而有效减小晶体粒度;其中,焦磷酸钠的影响最大,使得Li2CO3的平均粒径减小了48 %左右。通过微气泡装置引入微气泡,从纳微尺度增大气液界面从而强化传质及CO2的吸收,提高局部过饱和度;在微气泡气液界面附近形成反应微区,利于成核过程,抑制晶体团聚。微气泡能够有效减小Li2CO3晶体粒度,35 oC条件下得到的晶体平均粒径为13-17 μm,相比常规通气条件减小了47 %-65 %。;As one of the most basic and stable lithium compounds, Li2CO3 has wide industrial applications in lithium-ion batteries, materials and pharmaceuticals. With the rapid development of the new energy industry, Li2CO3 plays a vital role in energy storage and wireless equipment. The primary lithium resources in nature mainly include lithium ore and brines, and the recovery of lithium from secondary resources of lithium-ion batteries has also received increasing attention. In industry, lithium extracting from ore and brines is directly precipitated by Na2CO3 to obtain Li2CO3 and the preparation process is extensive, thus the purity of Li2CO3 is low and the particle size is uncontrollable. In view of the uncontrollable traditional process and the poor quality of product, this study proposes a novel system for preparing Li2CO3 by LiCl-NH3·H2O-CO2 gas-liquid reaction crystallization. Based on the supersaturation with nucleation and growth control mechanism, the decoupling analysis of the crystallization process was carried out by online and offline means. The study focuses on the characteristics of metastable system and crystallization process, kinetics of nucleation and growth and particle size regulation mechanism. Several main conclusions were drawn from this study:(1) The characteristics of crystallization process were studied. NH3·H2O is believed to be able to inhibit the recarbonation of Li2CO3 crystals, thus simplifying the carbonation process. Increasing NH3·H2O concentration can significantly increase the absorption efficiency of CO2, enlarge the supersaturation of Li2CO3 and improve the [Li+] conversion ratio. The existence of NH3·H2O led to more temperature-sensitive absorption of CO2. Both temperature and supersaturation are important parameters that influence the crystallization rate of Li2CO3 significantly.(2) The solubility of Li2CO3 in the combination system of NH3·H2O and NH4Cl was measured. When the NH3·H2O concentration was constant, the solubility increased with the increase of NH4Cl concentration. When the concentration of NH4Cl was low, the solubility of Li2CO3 decreased with the increase of temperature, which was consistent with the solubility of Li2CO3 in water. However, when the concentration of NH4Cl was higher, the solubility of Li2CO3 increased with increasing temperature. (3) The crystallization kinetics of Li2CO3 was studied. The apparent activation energy was found to be 23.55 kJ/mol, which indicates that the crystallization of Li2CO3 was controlled by a combination of surface reaction and diffusion. The activation energy of nucleation was found to be 79.15 kJ/mol, indicating that the primary nucleation rate was greatly affected by temperature. The order of growth rate with respect to supersaturation was determined to be 6.81. The surface energy of Li2CO3 obtained by supersaturation was 22.03 mJ/m2, and the surface energy obtained by induction period was 18.80 mJ/m2, the results prove that it is feasible to calculate the nucleation rate through FBRM. The growth activation energy was found to be 26.79 kJ/mol, which is less than nucleation activation energy.(4) The relationship of Li2CO3 particle size with secondary nucleation and growth rate was investigated. With the increase of temperature, the supersolubility of Li2CO3 decreased, leading to the secondary nucleation rate decreased and the growth rate declined, which caused the temperature positively correlated with Li2CO3 particle size. The supersaturation affected the secondary nucleation and growth rate, that is the dominant mechanism for Li2CO3 crystallization, thereby obtaining Li2CO3 products with different sizes. The greater the supersaturation, the nucleation process was dominant and the growth process was weakened, thus the crystal size was smaller.(5) The particle size and morphology of Li2CO3 were regulated by additives and microbubbles. By adding PAA, spherical clustered Li2CO3 particles formed by agglomeration of flaky monomers were obtained. The addition of (NaPO3)6 could obtain relatively dense spherical particles formed by agglomeration of flaky monomers. The addition of Na4P2O7·10H2O, PEI, SDBS could slow down the declining of pH and delay the nucleation of Li2CO3, thus enlarge the MSZW and strengthen the nucleation process, thereby effectively reduce the crystal size. Among which, Na4P2O7·10H2O had the greatest influence, with the mean size of Li2CO3 reduced by about 48 %. Microbubbles were generated and the gas-liquid interface was increased thus the mass transfer was enhanced from the nano-scale, with the local supersaturation improved as well; In addition, the presence of microbubbles caused the formation of reaction microdomains near the gas-liquid interface, which facilitated the nucleation and inhibited the agglomeration of Li2CO3. As a result, the particle size of Li2CO3 decreased, which was reduced by 47 %-65 % compared to conventional conditions 

Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/40709
Collection中国科学院过程工程研究所
Recommended Citation
GB/T 7714
田孟华. LiCl-NH3·H2O-CO2气液反应结晶制备电池级碳酸锂研究[D]. 中国科学院大学,2019.
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