【作者】 曾纪术；

【导师】 尹周澜；

【作者基本信息】 中南大学 ， 冶金物理化学， 2008， 博士

【摘要】 铝酸钠溶液种分过程是整个氧化铝生产过程最重要的工序之一。提高溶液的分解速率,获得粒度分布均匀、强度高的氢氧化铝产品是氧化铝生产工作者孜孜以求的目标。本文采用活化晶种、有机添加剂等方法强化铝酸钠溶液的晶种分解与附聚,着重探讨了氢氧化铝结晶过程的强化机制,为强化铝酸钠溶液的晶种分解研究提供了新的思路和方法。本文以研究铝酸钠溶液晶种分解过程为基础,结合激光粒度分析、红外（IR）、²⁷Al NMR、²⁷Al MAS NMR、XRD、SEM等分析测试手段以及量化计算方法,研究了活性晶种的效能及作用机制;考察了具有笼状结构的15-冠-5-醚的强化作用机制;系统研究了添加剂官能团电荷结构、空间结构对其强化铝酸钠溶液分解能力的影响;研究了油酸等油性添加剂强化附聚的效能与机制;提出了颗粒达到临界附聚条件的临界时间模型;从实验和计算两方面论证了使用添加剂控制氢氧化铝形貌的可行性;采用²⁷Al MAS NMR、分子探针方法对铝酸钠溶液的分解过程进行了跟踪和分析;主要依据本文研究结果,归纳了添加剂设计的一般规则。具体研究结果如下:1.采用蒸馏水蒸煮方法对工业级氢氧化铝晶种进行了活化。发现活化晶种能明显提高溶液的分解速率。在种分附聚实验中,溶液分解率在10 h内最高可提高5.0%左右;种分全过程中（60 h）,提高分解率4.0%左右。晶种被活化的机理是封闭晶种活性点的有机物解吸,从而使显露的活性点增多。2.研究了笼状分子结构的15-冠-5-醚对铝酸钠溶液分解过程的影响。发现其促进了铝酸钠溶液的晶种分解,降低了铝酸钠溶液的稳定性,强化了成核过程。铝酸钠溶液的²⁷AlNMR峰宽随15-冠-5-醚的增大而增加。冠醚可能的作用机理:与钠离子配合,促进了铝酸根离子的缔合以及铝酸根离子的网状结构的形成。3.系统研究了添加剂官能团电荷结构、空间结构对其性能的影响。发现四碳链添加剂1-丁醇,1,4-二氧六环和四氢呋喃提高铝酸钠溶液晶种分解速率的能力与分子中官能团上氧原子净电荷数成负相关关系;浓度较高的乙二醇降低了溶液的分解速率,而空间位阻更大的乙二醇一乙醚则能提高分解速率。4.研究了一系列油性添加剂对附聚过程的影响。发现低浓度的油酸在较高温度下能极大地促进晶种附聚;中等浓度的塔尔油对附聚的强化作用明显;塔尔油与十二醇按一定的配比和浓度添加,可得到分解率高、附聚度好的产品。提出了临界附聚时间概念,并结合铝酸钠溶液种分动力学分形特征,得出晶体颗粒达到临界附聚状态所需时间的定积分模型如下:5.提出并证实了使用添加剂控制氢氧化铝晶体形貌的设想。种分实验结果显示,油酸使种分产品gibbsite晶体（001）面簇显露面积增大;均相成核实验结果表明,十八醇、油酸和十八酸均能明显影响晶体的形貌。油酸与gibbsite晶面相互作用的理论计算结果表明,油酸以一定的方式吸附在晶种（001）面,抑制了附聚,但是使（001）面顽强显露;油酸在（100）面以一定的方式吸附则促进了附聚。6.采用²⁷Al MAS NMR,分子探针方法、理论计算等方法对铝酸钠溶液的分解过程进行了跟踪和分析。首次发现、证明了某些醇类化合物（1,2-辛二醇）能够通过改变溶液结构的方式抑制铝酸钠溶液的分解;发现铝酸根离子的分解、构型转化过程主要在本体溶液（固-液界面）中完成;发现空间结构匹配、电荷结构适当的多元醇能够牢固地吸附在晶种表面,抑制生长基元在晶种表面的析出。7.主要依据本文的研究结果,分别归纳出了结晶强化型、附聚强化型添加剂分子设计一般规则,指出结晶强化型添加剂分子设计可从降低溶液的稳定性和改善固-液界面性质两个基本方面入手;附聚强化型添加剂分子设计则应该重点围绕高分子聚合物与油性添加剂这两类物质展开。更多还原

【Abstract】 The crystallization of Al（OH）₃ from seeded sodium aluminate liquors plays a vital role in alumina production. To promote decomposition of sodium aluminate liquors and get high quality Al（OH）₃ are the eager goals of many alumina producers. In present study, seed activation and organic additives were applied to the enhancement of Al（OH）₃ crystallization, and the mechanisms were extremely emphasized. The results will impregnate some new ideas to the subsequent investigations for the enhancement of Al（OH）₃ crystallization.A series analysis techniques, laser particle size analyzer, IR, ²⁷Al NMR, ²⁷Al MAS NMR, XRD, SEM and quantum chemical calculation were assembled to investigate the crystallization process of seeded sodium aluminate liquors. The effect of activated seed on Al（OH）₃ crystallization were studied. The intensification effect of 15-crown-5-ether was proved to be related to its caged structure. The effects of steric configuration and electronic structure of functional group in the additive molecules was investigated systematically. The effect of oily additives on Al（OH）₃ agglomeration was evaluated and their action mechanism was also probed. A model of critical agglomeration time was established to interpret periodic agglomeration of Al（OH）₃. The control of Al（OH）₃ morphology by additive was proved to be feasible both from experimental results and quantum calculation. Probe molecules were initially applied to investigate the Al（OH）₃ crystallization mechanism. Finally, general rules for additive design are proposed on the basis of present investigations. The main inclusions were drawn as follows:1. Industrial grade Al（OH）₃ was activated by boiling in the distilled water. Either in agglomeration experiment or whole Al（OH）₃ crystallization try, activated seed can accelerate the precipitation rate of Al（OH）₃ significantly. The precipitation ratio was found to be promoted for about 5.0% in the agglomeration process, and for about 4.0% in the whole process of Al（OH）₃ crystallization. It is proposed that the poisonous organic impurities desorb from the active site of seed surface during the actvation process, which leads to the increase of seed activity.2. The effect of 15-crown-5-ether on Al（OH）₃ crystallization was investigated. The stability of sodium aluminate liquors decreases with the addition of 15-crown-5-ether and the Al（OH）₃ crystallization is intensified. The peak width of ²⁷Al NMR of sodium aluminate liquor broadens as the 15-crown-5-ether is introduced. The enhancement mechanism is visualized as follow: the presence of 15-crown-5-ether in the sodium aluminate liquor favors the combination of aluminate ions and the formation of network, and the crystallization is enhanced subsequently.3. The influence of steric configuration and electronic structure of functional group in the additive molecules on the enhancement were evaluated systematically. The enhancement of 1-butanol, 1,4-dioxane, tetrahydrofurane are strongerly correlated with the net charge of oxygen atom in the molecules. High concentration of ethylene glycol inhibits Al（OH）₃ precipitation slightly, while ethylene glycol monoethylether acetate, which has more steric hindrance effect, can enhance Al（OH）₃ crystallization.4. A series of oily additives on Al（OH）₃ agglomeration were studied. Low concentrations of oleic acid and moderate concentrations of tall oil can greatly enhance the agglomeration of Al（OH）₃ . High agglomeration degree Al（OH）₃ can be achieved without the decrease of crystallization rate when tall oil and 1-Dodecanol are mixed and introduced at a certain proportion. The concept of critical agglomeration time was proposed. Taking the fractal characteristic of Al（OH）₃ crystallization kinetics into account, an integral model critical agglomeration time is established as follow:5. Using addtives to control Al（OH）₃ morphology was invented and verified. The SEM observation of seeded crystallization product shows that the （001） surface area of gibbsite under the influence of oleic acid is larger than that of the blank. The homogeneous crystallization results suggest that oleic acid, 1-octadecanol and stearic acid can significantly influence the gibbsite morphology. Result of theoretical calculation indicates that the （001） surfaces appear stubbornly when oleic acid molecules are adsorbed by a reasonable mode.6. The techniques of ²⁷AlMAS NMR and probe molecules were applied to unveil the mechanism of Al（OH）₃ crystallization. Some alcohol compounds were verified to inhibit crystallization by disturbing the structure of sodium aluminate solution. The configuration inversion of tetra-coordinated aluminate is completed in the bulk solutions. The crystallization process is susceptible to some organics, for the attachment energy of growth unit on lattice is relatively small. The crystallization of Al（OH）₃ on seed surface would be severely inhibited by the polyols, which characterized with a matching configuration of functional group to crystal lattice and an electronic structure of charge donor.7. General rules for additive design are proposed on the basis of present investigations. The additive molecule design for crystallization enhancement should emphasize on the decrease of stability of sodium aluminate solutions and the improvement of the nature of interface of solid-solution. While the ones for agglomeration enhancement should pay more attention to the soluble polymers and oily organics.更多还原