【作者】 陈金清；

【导师】 张平民； 甘国耀；

【作者基本信息】 中南大学 ， 冶金物理化学， 2004， 博士

【摘要】 铝酸钠溶液种子分解过程是氧化铝生产的一个极其重要的工序,生产流程中的杂质会对种分产品的产量与质量产生影响。有些学者在研究纯铝酸钠和铝酸钾溶液的种分过程时发现,这两种溶液在自发成核、二次成核及晶种的附聚、长大等动力学过程中的行为存在着一定差异,但由于钾与钠是处于同一个主族的碱金属元素,它们的化学性质较为接近,因此,作为铝酸钠溶液中的一种杂质,钾离子的存在并没有引起研究者们足够的重视。事实上,有些氧化铝厂的铝酸钠溶液中钾离子的积累已达到相当高的浓度,它对生产过程的影响目前还不清楚,因此,系统研究钾离子对铝酸钠溶液种分过程的影响具有非常重要的现实意义。 本文系统研究了钾离子对铝酸钠溶液种分过程的分解率、产品及其二次成核、附聚及长大等动力学过程的影响。研究表明,铝酸钠溶液中存在一定浓度的钾离子会对种分过程产生一定的影响。实验得到了如下结论: 1、钾离子的存在有利于铝酸钠溶液种分分解率的提高,但受分解条件的影响,在较低的温度和α_k条件下,钾离子提高分解率的作用较为明显。 2、由于钾离子的存在促进了铝酸钠溶液二次成核,使得分解产品中细粒子的含量有所增加;随着铝酸钠溶液温度、α_k和晶种添加量的升高,钾离子对种分产品中细粒子含量的影响作用降低。 3、钾离子的存在使铝酸钠溶液分解产品中Na₂O的含量有某种程度的降低,K⁺与Na⁺半径的差异可能是引起种分产品中Na₂O含量降低的原因。 4、钾离子的存在并不改变种分产品的物相及其热稳定性,对产品微观结构的影响也不显著。 5、铝酸钠溶液种分反应的二次成核、附聚及长大等动力学过程的研究表明: 钾离子的存在使铝酸钠溶液二次成核过程的诱导期有不同程度的延长; 在一定的成核条件下,钾离子的存在能在一定程度上促进铝酸钠溶液二次成核。铝酸钠溶液温度、α_k和晶种添加量升高,这种作用降低; 由于铝酸钠溶液中的钾离子能在一定程度上促进溶液中细粒子的产生,因此会对不同粒级范围内的晶种附聚产生不同影响。钾离子的存在能在一定程度上促进10～30μm粒级范围内晶体的附聚,这种促进作用随着铝酸钠溶液温度和α_k的升高而降低;但对0～10μm粒级范围内晶体的附聚作用并不明显。 采用自行研制的微分型种分反应器,在较为单一的条件下了研究铝酸钠溶液中的晶体长大动力学。实验结果表明,在恒推动力的条件下,铝酸钠溶液中晶体的长大遵循晶体长大速率与粒度无关的结论;钾离子的存在不影响铝酸钠溶液中更多还原

【Abstract】 Seeded precipitation of sodium aluminate solutions is an important process in alumina production. The yield and the quality of the product in the process are often affected by the impurities exist in the solutions. Potassium ion is one of the impurities in sodium aluminate liquor. Potassium and sodium elements are in the same main group and their chemical properties are very similar. Potassium ions, as an impurity, are not attracted enough attention. However, researchers have already found that there are some differences between potassium aluminate and sodium aluminate solutions in the kinetics of homogeneous nucleation, secondary nucleation and crystal growth during the seeded precipitation. Since the accumulation of potassium ions has come to a considerable high level in some alumina plant, study of the influence of potassium ions on the seeded precipitation process is of great practical significance.In this thesis, the influences of potassium ions on the seeded precipitation process were studied systematically, and conclusions were made as follows:1. During the seeded precipitation process of sodium aluminate solutions, the presence of potassium ions can promote the precipitation process. The decomposition ratio is obviously increased at relatively low temperature and α_k.2. The presence of potassium ions can affect the particle size distribution （PSD） of the product, especially the number of fine particles. The influence is weakened as the temperature, α_k and seed amount are increased. The main reason is that potassium ions could promote the secondary nucleation during the precipitation process of sodium aluminate solutions.3. The presence of potassium ions leads the content of Na₂O in the products decreased. It may be caused by the radius diversity of K⁺ and Na⁺.4. The presence of potassium does not change the phase of crystal, thethermal stability, and the micrographic structure of the product. 5. By the kinetics studies on secondary nucleation, agglomeration and crystal growth, it was found that the presence of potassium ions can prolong the induction period of secondary nucleation process of sodium aluminate solutions; and promote the secondary nucleation process. The effect is decreased as the temperature, a k and seed amount increased. The promotion on the agglomeration of the crystals with the particle size in the range of 0¹0 u m is small, but obvious in the range of 10³0 u m, and will be weakened as the temperature, a k and seed amount increased. As potassium ions can promote the formation of fine particles, it has different effect on the agglomeration of crystals with difference particle sizes. The kinetics of crystal growth was studied with a self-designed differential reactor that can be performed on a relatively single condition. It was found that the growth of crystals obeys the rules that the rate of crystal growth is not related to the crystal size under constant impulsion. The presence of potassium does not affect the kinetics of crystal growth and the crystal growth of sodium aluminate obeys the law of diffusion theory.更多还原