超声波强化铝酸钠溶液结晶机理研究

发布时间：2018-03-15 02:29

本文选题：分子结构　切入点：结晶　出处：《北京化工大学》2015年硕士论文　论文类型：学位论文

【摘要】：氧化铝工业赤泥、粉煤灰等是我国主要的高铝固体废弃物,它们的占地堆存造成了严重的社会和环境问题。但同时它们也是一种优良的非传统提铝资源。采用亚熔盐法处理赤泥、粉煤灰提取氧化铝的方法,能够成功达到对其中Al2O3的经济循环利用,获取了苛性比较高(大于4)的铝酸钠溶液。这种高苛性比的溶液难以采用传统的只适用于苛性比1.5左右铝酸钠溶液的种子分解的方法制备Al(OH)3,但可以使用铝酸钠结晶析出的方法首先降低溶液的苛性比,然后再进行种分分解。目前,在半工业化实践中,结晶过程存在着结晶时间长、影响因素难以有效控制等问题。针对此问题,中国科学院过程工程研究所提出采用超声波强化铝酸钠溶液结晶的新方法,结晶效率大为提升,但强化机理尚不明确。因此,本论文首先通过对比亚熔盐法处理不同原料获得的溶出液结晶过程进行差异研究,获得了影响其溶液结晶的关键因素,随后重点研究了超声波对溶液粘度、浊度等物化性质的影响规律,剖析了结晶过程中超声波的强化机理。论文取得如下创新性成果：(1)通过对比不同来源的粉煤灰溶出液在超声结晶过程中结晶效果的不同,发现溶出液中含量不多的杂质硅、铁等成分会严重影响溶液的超声结晶效果。实验中分别对比了不同的硅、铁浓度以及不同的初始条件(初始碱浓度不同、初始苛性比不同),发现当硅浓度改变0.5-2g/L,铁浓度改变0.4g/L时,结晶率将大大降低。(2)系统研究了铝酸钠溶液杂质种类、杂质浓度等因素对溶液结晶率、苛性比、粘度、浊度、电导率等性质以及产物的晶体形貌的影响。结果表明,铝酸钠溶液中对结晶起主要阻碍作用的因素是杂质硅。(3)深入探究了超声波作用下铝酸钠溶液结构的变化规律,明晰了超声波的作用机理。研究发现,溶液中硅的加入使得其结构变得更加复杂。随着杂质硅的增多,硅氧键的吸收峰逐渐变大变宽,原本溶液中的铝氧键等简单结构逐渐变为Si-O-Al交织而成的复杂的网络状结构。当有超声存在时,硅氧键的吸收峰明显减弱,并且出现峰位偏移。这说明超声过程中,复杂的Si-O-Al等键可被断裂,形成小的碎片形式的结构,进而减小了铝酸钠成核所需的能量,减小了溶液的粘度,从而有助于铝酸钠结晶的析出。
[Abstract]:Red mud and fly ash in alumina industry are the main solid wastes with high aluminum content in China. Their storage has caused serious social and environmental problems, but at the same time they are also a kind of excellent unconventional aluminum resources. The submolten salt method is used to treat red mud and fly ash to extract alumina. Can successfully achieve the economic recycling of Al2O3, Sodium aluminate solution with higher causticity (> 4) was obtained. The solution with high causticity ratio is difficult to be prepared by the traditional seed decomposition method, which is only suitable for caustic ratio about 1.5 sodium aluminate solution, but the sodium aluminate junction can be used. The method of crystal precipitation first reduces the causticity ratio of the solution, At present, in the practice of semi-industrialization, the crystallization process has many problems, such as long crystallization time, difficult to control the influencing factors and so on. The Institute of process Engineering of the Chinese Academy of Sciences proposed a new method for strengthening the crystallization of sodium aluminate solution by ultrasonic wave. The crystallization efficiency was greatly improved, but the strengthening mechanism was not clear. In this paper, the crystallization process of dissolution solution obtained by submolten salt treatment was studied, and the key factors affecting the solution crystallization were obtained, and the viscosity of solution by ultrasonic wave was studied. The effect of turbidity and other physical and chemical properties on ultrasonic hardening mechanism in crystallization process was analyzed. The following innovative results were obtained: 1) by comparing different sources of fly ash dissolving liquid in ultrasonic crystallization process, the effect of crystallization was different. It was found that the concentration of silicon and iron in the solution would seriously affect the ultrasonic crystallization of the solution. In the experiment, different concentrations of silicon, iron and different initial conditions (initial alkali concentration, initial alkali concentration, etc.) were compared. The initial causticity ratio is different. It is found that when the concentration of silicon changes 0.5-2g / L, and the concentration of iron changes 0.4g / L, the crystallization rate of sodium aluminate solution will be greatly reduced. (2) the effects of impurity types, impurity concentration and other factors on the crystallization rate, causticity ratio, viscosity, turbidity of sodium aluminate solution are studied systematically. The results show that the main obstacle to crystallization in sodium aluminate solution is the impurity silicon. 3) the structure of sodium aluminate solution under the action of ultrasonic wave is studied. The mechanism of ultrasonic wave was clarified. It was found that the addition of silicon in solution made its structure more complicated. With the increase of impurity silicon, the absorption peak of silicon oxygen bond became larger and wider. The simple structures such as aluminum and oxygen bonds in the original solution gradually become complex network structures intertwined with Si-O-Al. The absorption peaks of silicon and oxygen bonds are obviously weakened and the peak position is shifted in the presence of ultrasound, which indicates that in the process of ultrasound, The complex Si-O-Al bonds can be broken to form a small fragment structure, thus reducing the energy required for nucleation of sodium aluminate and the viscosity of the solution, thus facilitating the precipitation of sodium aluminate crystals.
【学位授予单位】：北京化工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ133.1

【参考文献】