【作者】 孙玉柱；

【导师】 于建国； 宋兴福；

【作者基本信息】 华东理工大学 ， 化学工程， 2010， 博士

【摘要】 锂是一种重要的战略资源,碳酸锂结晶过程是锂工业中一个最基本、最关键的环节。本文旨在通过对碳酸锂结晶过程的研究,为工业生产提供理论指导和技术支持,同时丰富工业结晶的基础理论和研究方法。针对产业发展需求,本文系统地研究了碳酸锂产业链中初级产品制备(LiCl+Na2CO3反应结晶)、高纯产品制备(LiHCO3热分解反应结晶,Li2CO3重结晶,LiOH+CO2气液反应结晶)和超细粉体制备(溶析-反应结晶耦合过程,喷雾分解结晶等)等三方面过程中碳酸锂的结晶过程。采用激光法研究了未添加晶种条件下,碳酸锂在水溶液中的介稳区性质。结果表明温度和Na2CO3流速对超溶解度影响最大。采用FBRM(聚焦光束反射测量仪)研究了添加晶种条件下碳酸锂的介稳区性质。实验发现较大的晶种表面积能够消耗更多过饱和度用于晶体生长,抑制成核发生,提高超溶解度。采用激光法研究了碳酸锂的诱导期和初级成核过程,计算得到了碳酸锂初级成核过程中界面能、接触角、成核级数等重要参数。通过表面熵因子判定碳酸锂晶体生长机理为螺旋生长。采用FBRM和PVM(颗粒录影显微镜)对碳酸锂二次成核过程进行了在线研究,并采用吸附模型很好地解释了晶种大小、添加量等操作参数对诱导期和成核速率的影响。提出了破碎过程与成核过程对比的方法,对磨损成核和表面成核进行定量区分,反映不同成核机理对二次成核的贡献。系统研究了碳酸锂初级产品制备中操作模式和工艺条件的影响,提出了变温反应结晶制备碳酸锂的工艺,这一工艺产率高、粒度大、分布均匀、流动性好,并基本消除了碳酸锂结晶过程中严重的粘壁现象。由于传统的以PBE (population balance equation)方程为基础的结晶动力学研究方法在本实验体系难以适用,本文提出了拉格朗日法和欧拉法两种神经网络模拟的方法,在本体系中有非常好的应用效果,也为其它复杂结晶过程的动力学研究开辟了一条新路。通过研究碳酸锂溶解过程发现,减小粒度、升高温度和引入超声,能够加速溶解速率,搅拌速度对溶解几乎没有影响。采用FBRM和PVM能够在线监测溶解过程中粒度分布和晶体形貌的变化。分别采用Avrami模型和矩量变换方法,关联出碳酸锂溶解动力学模型。实验发现添加适量的晶种、采用较高的进料浓度和保持适度的搅拌速度有利于碳酸锂重结晶过程。提出了碳酸锂重结晶工艺流程并制备出光滑完整的棒状晶体。计算得到LiHCO3的理论分解温度为4.25℃。研究发现提高初始浓度、降低升温速率和添加晶种使LiHCO3表观分解温度降低。提出了采用Labmax表征LiHCO3分解结晶过程热效应的方法,表明90℃以上高温条件有利反应进行。提出了LiHCO3分解反应结晶过程宏观反应动力学的关联式。分别研究了超声协同作用下和微波协同作用下LiHCO3分解反应结晶的结晶动力学,得到了相关动力学参数。提出了超声-微波耦合场协同作用下LiHCO3分解反应结晶的结晶工艺。采用降膜吸收塔和旋转盘气液反应器,系统研究了LiOH气液反应结晶过程。LiOH碳化终点pH值控制在9.5-10为宜。研究了操作条件对LiOH碳化的影响,构建的神经网络模型,能够同时准确描述气体吸收动力学和气液反应结晶动力学。采用正交实验分析了操作条件对旋转盘气液反应结晶的影响,表明引入超声、降低温度和通气流量有利于减小产品粒径。本文探索采用多种方法制备了碳酸锂超细粉体。超声反应结晶工艺是非常简单有效的方法,提出的溶析-反应结晶耦合工艺和溶析-分解-反应结晶耦合工艺,能够获得平均粒度在200 nm的亚微米级碳酸锂超细粉体。采用喷雾分解结晶技术,能够获得多孔中空球颗粒,这些中空球由大量约200 nm的晶体自组装而成,BET比表面积可达7.24 m2／g。更多还原

【Abstract】 Lithium is an important strategic resource, and the crystallization of Li2CO3 is the key process in the lithium industry. The objective of this research is to provide theoretical guidance and technological support for the production as well as to enrich the basic theory and studying method for the industrial crystallization.According to the development demand of the lithium industry, this research systematically investigated the crystallization processes of Li2CO3 in the preparation of primary product (LiCl+Na2CO3), high-purity product (decomposition of LiHCO3, recrystallization of Li2CO3, LiOH+CO2) and ultrafine powders (anti-solvent reactive crystallization, spray pyrolysis).The unseeded metastable zone of Li2CO3 in aqueous solution was studied by laser method, and the results show the temperature and the feeding rate of Na2CO3 are the two critical factors influencing the supersolubility. The seeded supersolubility of Li2CO3 was measured by FBRM, which shows a larger surface area is beneficial to enhace the supersolubility level.The unseeded induction period and primary nucleation of Li2CO3 was examined by the laser method, and a series of nucleation parameters were obtained such as interfacial energy, contact angle, nucleation order etc. The seeded induction period and secondary nucleation of Li2CO3 was investigated by FBRM and PVM. The adsorption model can explain the effect of seed size and seed loading on the secondary nucleation. A method through comparison between pure breakage/attrition and nucleation process was put forward to distinguish the attrition-induced and surface-induced nucleation quantitatively, which can reveal the contributions of different nucleation mechanisms.The effects of operational conditions on the crystallization in the preparation of primary Li2CO3 product were explored. A variable-temperature reactive crystallization was put forward, which features a high yield, a large and homogeneous crystal size as well as good fluidity. Because the traditional method of kinetic research, which based on the PBE, is not fit to this system, so a novel neural-net work simulation method was presented. The neural net work simulation can be divided into Lagrangian method and Euler method, both of them obtained good results in this crystallization. The novel neural-net work simulation is referential for other complex crystallization processes.Results show a smaller crystal size, a higher temperature and the presence of ultrasound advances the dissolution rate, while the stirring speed has nearly no effect. The evolution of chord length distribution and crystal shape of Li2CO3 particles were monitored by FBRM and PVM respectively. Two method, Avrami model and moment transformation, were adopted to describe the dissolution kinetic processes. The introduction of proper seed, a high initial concentration and a moderate stirring speed is preferred in the recrystallization. This research put forward a recrystallization craft of Li2CO3, and by which good rod crystals were prepared.As for the coupled process of decomposition and reactive crystallization of LiHCO3, the theoretical decomposition temperature was evaluated as 4.25℃.A thermal analysis technique was put forward to characterize the reaction thermal effect by using Labmax reactor, which implied that the reaction became more drastic when the temperature was beyond 90℃. The effects of operating parameters on the apparent reaction rate were investigated, through which a novel empirical correlation was presented to describe the apparent reaction rate as a function of temperature, reactant concentration and stirring speed. The ultrasound-assisted and microwave assisted crystallization kinetics in the decomposition of LiHCO3 were investigated respectively, and the kinetic parameters were achieved. A new craft by using the combination of ultrasound and microwave during the decomposition of LiHCO3was carried out and obtained good results.A falling film tower and a spinning disk reactor were used in the gas-liquid reactive crystallization. Results show the carbonation end point of pH should be controlled within 9.5-10. The effects of operating conditions on the carbonation of LiOH were studied systematically. A neural-net work was set up to describe the complex carbonation of LiOH involving both reactive adsorption and reactive crystallization. The neural-net work simulation can simultaneously give the adsorption rate, crystallization rate and crystal size distribution accurately. An orthogonal experiment was conducted to explore the impacts of operational variables on the carbonation of LiOH in a spinning disk reactor. Results show the introduction of ultrasound, a lower temperature and a lower flow rate of CO2 facilitates the formation of small particles.Several technologies were explored to prepare ultrafine powders of Li2CO3. It was found that the ultrasound-assisted reactive crystallization is a simple and effective method. Two novel reactive crystallization processes, anti-solvent reactive crystallization and anti-solvent-decomposition reactive crystallization were studied, both of them can obtain about submicron crystals. Hollow spheres were prepared by spray pyrolysis of LiHCO3, which are composed of about 200 nm primary particles. The BET surface area of the hollow spheres reaches 7.24 m2/g.更多还原