预碳化-液相结晶法制备砂状氧化铝的基础研究
文献类型：学位论文
| 作者 | 李艳 |
| 学位类别 | 博士 |
| 答辩日期 | 2011-03-14 |
| 授予单位 | 中国科学院研究生院 |
| 导师 | 杨超 ; 张懿 |
| 关键词 | 结晶动力学 氢氧化铝 反应结晶 MSMPR 结晶模拟 |
| 其他题名 | Fundamental Research on Pre-carbonation Liquid-Liquid Crystallization Process for Preparing Sandy Alumina |
| 学位专业 | 化学工程 |
| 中文摘要 | 砂状氧化铝的大规模应用对于电解铝厂的环保和节能有着重要的意义。烧结法生产氧化铝工艺中的二氧化碳气体分解铝酸钠溶液（碳分）工序为一难以精确控制的气液反应结晶过程，因而该工艺很难得到合格的砂状氧化铝。针对这种工业现状，本论文提出了一个全新的工艺路线，本工艺用碳酸氢钠水溶液代替二氧化碳气体来分解铝酸钠溶液，即用一可精确控制的液液反应结晶过程代替传统的难以控制的气液反应结晶过程。本论文对该液液反应结晶过程进行了系统的研究。利用半间歇实验，研究了利用该液液反应结晶体系生产砂状氧化铝的适宜的工艺条件。主要考察了铝酸钠溶液的浓度、分子比、碳酸氢钠水溶液的浓度、滴加速度、结晶温度、搅拌速度等实验条件对铝酸钠溶液的分解率、氢氧化铝晶体的粒度分布的影响。实验结果表明，该结晶过程得到的氢氧化铝颗粒具有规则的球形形貌，且粒度分布较窄，在优选的工艺条件下得到的产品符合电解铝厂对砂状氧化铝的要求。研究了该反应结晶过程的初级成核动力学和初级核的多晶行为。通过成核诱导期与温度之间的关系，计算出了不同晶相的成核界面能及成核机理。初级核的晶相受温度和过饱和度的影响，70 oC时，本文考察的所有过饱和度下的初级核均为gibbsite； 50oC时均为bayerite；而在60 oC时，初级核的晶相还取决于过饱和度的值，高过饱和度有利于bayerite的形成，而低过饱和度有利于gibbsite的形成。此外，通过实验研究还发现，本体系中氢氧化铝晶相的转变顺序为：铝分子束→boehmite→bayerite→gibbsite。利用MSMPR结晶技术研究了gibbsite在70 oC时的二次成核动力学、生长动力学和团聚动力学。实验结果表明，gibbsite的体积生长速度与过饱和度的2.27次方成正比，这意味着gibbsite基面的生长为螺旋生长。本体系中gibbsite的二次成核速度比种分过程的成核速度大3到4个数量级。Gibbsite的团聚因子与生长速度，停留时间近似成线性关系，与晶浆密度的0.55次方成正比。本体系还被用来制备具有规则的球形形貌、无小颗粒、且粒度分布非常窄的化学品氧化铝——拜耳石颗粒。研究了温度、过饱和度及搅拌速度对拜耳石颗粒的粒度分布的影响。实验结果表明，大颗粒和小颗粒具有不同的生长、团聚和破裂机理。利用粒数衡算模型首次对这种无小颗粒类型的粒度分布进行了模拟，提出的大颗粒和小颗粒的复合模型成功地模拟了拜耳石的粒度分布。 |
| 英文摘要 | Sandy alumina plays an important role in the environmental protection and energy conservation of aluminium refinery. In the sinter process for alumina production, it is difficult to produce sandy aluminium hydroxide by the carbonation of sodium aluminate solution. Therefore, a precisely controllable and feasible process for the precipitation of sandy aluminium hydroxide from the aluminate solution neutralized by sodium bicarbonate aqueous solution was proposed for the first time in this thesis. The aluminate-bicarbonate reactive system was systematically investigated in this work. The preferable operational conditions for the production of sandy alumina from the proposed aluminate-bicarbonate reactive system were determined using a semi-batch crystallizer. The influencing factors of the precipitation, i.e. the caustic concentration and molar ratio of the aluminate solution, the concentration and addition rate of the bicarbonate solution, temperature and agitation rate were investigated. All the aluminium hydroxides precipitated in this work had regular globular morphology and narrow size distribution. The product obtained under the preferable conditions fulfills the requirement of sandy alumina. The nucleation mechanism and the polymorphism of the precipitates from the reactive system were investigated. The interface tensions of gibbsite and bayerite in the solution were measured according to the relationship between temperature and induction time. Temperature and supersaturation affected significantly the polymorph of initial precipitates. Gibbsite solely nucleated at 70 oC while bayerite alone at 50 oC regardless of supersaturation, however, the high supersaturation benefited the nucleation of bayerite, and inversely the nucleation of gibbsite at 60 oC. In addition, the sequence of polymorphic transformation for aluminium hydroxide precipitated from the reactive solution was proposed as Al-containing cluster→boehmite→bayerite→gibbsite. The crystallization kinetics of gibbsite at 70 oC from the reactive system was investigated in a steady-state MSMPR (mixed-suspension mixed-product removal) crystallizer. The volume growth rate order of gibbsite with respect to the relative supersaturation is 2.27, which suggests the spiral growth mechanism for the growth of the basal face of gibbsite. The secondary nucleation rate of gibbsite from the system is three to four orders of magnitude larger than that from the seeded process. The agglomeration kernel of gibbsite in the system increases linearly with growth rate and residence time, and the order of magma density is about 0.55. Uniform spherical bayerite particles with narrow “missing-fines-type” size distribution were also obtained from the reactive system. The evolution of the steady-state particle size distributions at various temperatures, supersaturations and agitation rates were investigated, and different growth and breakup mechanisms for small and large size bayerite aggregates were proposed. The population balance equation coupled with the different growth and breakup models for large and small aggregates was successful in simulating the precipitation process. |
| 语种 | 中文 |
| 公开日期 | 2013-09-24 |
| 页码 | 137 |
| 源URL | [http://ir.ipe.ac.cn/handle/122111/1750]  |
| 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 | 李艳. 预碳化-液相结晶法制备砂状氧化铝的基础研究[D]. 中国科学院研究生院. 2011. |
入库方式： OAI收割
来源：过程工程研究所
浏览0
下载0
收藏0
其他版本
除非特别说明，本系统中所有内容都受版权保护，并保留所有权利。