亚熔盐法氧化铝生产中水合铝酸钠结晶动力学研究

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题名	亚熔盐法氧化铝生产中水合铝酸钠结晶动力学研究
作者	游韶玮
学位类别	硕士
答辩日期	2012-05-28
授予单位	中国科学院研究生院
导师	张懿 ; 张亦飞
关键词	水合铝酸钠结晶动力学
其他题名	Research on crystallization kinetics of monosodium aluminate hydrate in alumina production by sub-molten salt process
学位专业	化学工程
中文摘要	作为亚熔盐法氧化铝清洁生产技术中的中间步骤，水合铝酸钠结晶是整个工艺的核心技术之一，在整个清洁生产工艺中发挥着举足轻重的作用。本论文对水合铝酸钠的结晶过程进行了系统的研究，主要考察了铝酸钠溶液中二氧化硅浓度对水合铝酸钠结晶过程的影响和水合铝酸钠的连续结晶过程及动力学研究。利用间歇结晶实验，研究了铝酸钠溶液中SiO2含量对水合铝酸钠结晶过程的影响。实验结果表明，铝酸钠溶液中的杂质SiO2对MAH的结晶过程有着明显的抑制作用。随着溶液中初始SiO2浓度的升高，其抑制作用更加明显，且MAH的结晶反应转化率及MAH晶体产品的平均粒径下降。当溶液中初始SiO2浓度较低时，析出的含硅杂质物相为铝硅酸钠（NaAlSiO4）和硅酸钠（Na2SiO3）；当铝酸钠溶液中SiO2浓度很高时，析出的含硅杂质物相则为硅酸钙钠Na4Ca4Si6O18、无水钙铝榴石Ca3Al2Si3O12和水钙铝榴石Ca3Al2(SiO4)2(OH)4。实验所得MAH晶体产品主要为薄圆片结构。随着溶液中SiO2浓度的升高，MAH晶体产品形貌由不规则的圆片结构转变为片状聚集体。采用连续操作的方式对水合铝酸钠的结晶过程进行研究，考察了平均停留时间、过饱和度、温度及搅拌强度对结晶过程的影响。实验结果表明，体系平均停留时间增大，有利于晶体的生长。随着停留时间的增大，晶体粒径及结晶反应转化率增大，但是停留时间在50 min后，结晶反应转化率增大不明显。结晶温度的升高使得小粒径范围内的晶体数明显增多，不利于MAH的结晶过程。晶体粒径随搅拌速率的增大而减小。此外连续结晶实验得到的MAH晶体粒度均一、结构与形貌规则，均为由截锥体及八边形片状的小晶体组成的球状聚结体。利用MSMPR结晶技术，基于粒数衡算模型，研究了MAH的结晶动力学，主要包括成核动力学、生长动力学及团聚动力学。实验结果表明，MAH晶体的体积生长速率与过饱和度的1.19次方成正比，这意味着MAH晶体生长属于扩散与表面反应机理。二次成核速率与晶浆悬浮密度的1.06次方成正比，表明结晶器内二次成核主要来自于晶体与搅拌桨间的碰撞及晶体与结晶器壁面间的碰撞，且成核速率小于种分过程中gibbsite的成核速率。团聚因子与体积生长速率、成核速率及平均停留时间成正比。随着溶液过饱和度的增加，晶浆的悬浮密度增加而晶体的平均粒径下降。实验结果表明，在本体系中，MAH晶体长大主要源于晶体的生长。
英文摘要	Crystallization of monosodium aluminate hydrate (MAH), a median step in the sub-molten process for alumina cleaner production, is a core technology of the process, which plays a decisive role in the whole process. The crystallization processes, including effects of silica concentration in sodium aluminate solution on MAH crystallization and researches on continuous crystallization processes and kinetics, were systematically investigated. Effects of the content of SiO2 in sodium aluminate solution on MAH crystallization were researched using batch crystallization experiments. The results show that the impurity of silica in solution significantly inhibits MAH crystallization. Moreover, the higher the concentration, the greater the inhibiting effect. The crystallization conversion ratio and the average particle size decrease with increasing SiO2 concentration. The silicate impurity phases which crystallized simultaneously with MAH were identified as NaAlSiO4 and Na2SiO3 from low silica solution, Ca3Al2Si3O12, Ca3Al2(SiO4)2(OH)4, and Na4Ca4(Si6O18) we obtained when there was a high silica concentration. The resultant crystals were found to be round flakes, and changed from irregular round flakes to aggregates of flakes when SiO2 concentration in solution increased. The continuous process of MAH crystallization, including effects of mean residence time, supersaturation, temperature and the intensity of agitation on the process were investigated. The increase of the mean residence time favors the crystal growth. With the increase of the mean residence time, the crystal size and crystallization conversion ratio increase. But the increase of the crystallization conversion ratio become less obvious when the mean residence time is over 50 minutes. The increase of temperature adversely affects the MAH crystallization, and it makes the numbers of crystals in the small size range increase significantly. The crystal size decreases with increasing agitation rate. MAH crystals from continuous crystallization are of homogeneous size and have regular structures and morphologies, and are in a form of sphere-like agglomerates that consist of smaller truncated quadrangular orthopyramid and octagonal plate-shape crystals. The kinetics of MAH crystallization, including nucleation, growth and agglomeration, was studied bases on the population balance in an MSMPR (mixed-suspension- mixed-product-removal) crystallizer. The results show that the order of the relative supersatulation in the volume growth rate expression is 1.19, which indicates the crystal growth has a diffusion and surface integration control mechanism. The order of suspension density in nucleation rate expression is 1.06, which suggests that secondary nucleation is mainly induced by crystal–agitator and crystal–crystallizer collisions. The agglomeration kernel is proportional to the volume growth and nucleation rates and the mean residence time. When the supersaturation degree of the solution increases, the suspension density increases but the mean crystal size decreases. The particle agglomeration is not as important as the growth for the crystal enlargement in MAH crystallization.
语种	中文
公开日期	2013-09-25
内容类型	学位论文
源URL	[http://ir.ipe.ac.cn/handle/122111/1819]
专题	过程工程研究所_研究所（批量导入）
推荐引用方式 GB/T 7714	游韶玮. 亚熔盐法氧化铝生产中水合铝酸钠结晶动力学研究[D]. 中国科学院研究生院. 2012.