铝酸钠溶液分解制备砂状一水软铝石的机理研究
文献类型：学位论文
| 作者 | 张娟 |
| 学位类别 | 硕士 |
| 答辩日期 | 2010-05-27 |
| 授予单位 | 中国科学院研究生院 |
| 授予地点 | 北京 |
| 导师 | 王志 ; 郭占成 |
| 关键词 | 铝酸钠溶液 分解 一水软铝石 结晶 |
| 其他题名 | Mechamism research of sandy boehmite precipitation from sodium aluminate solutions |
| 学位专业 | 环境工程 |
| 中文摘要 | 我国氧化铝生产的传统工艺为烧结法和混联法，平均能耗约是国外拜耳法的2-4倍。在铝酸钠溶液分解阶段以一水软铝石取代传统的三水铝石产物，由于二者焙烧焓变的不同可以在后续的焙烧阶段实现氧化铝生产的节能，其实质是用“低温结晶脱水”代替“高温焙烧脱水”。中科院过程工程研究所提出了“铝酸钠溶液碳分-种分耦合分解制备一水软铝石”的新思路，前期对分解可控结晶过程进行了深入研究。由于砂状氧化铝是今后铝工业的发展方向，这要求作为前驱体的一水软铝石也必须是砂状的。本文针对铝酸钠溶液分解析出砂状一水软铝石进行了基础研究，重点对一水软铝石晶体的生长、附聚，以及NaHCO3和有机添加剂强化分解过程的机理问题进行了研究。 (1) 生长是晶体形成的动力学过程，采用光学显微镜在线观测一水软铝石晶体的生长。结果表明，一水软铝石晶体生长速率范围为0.08-2.4 μm/h，集中分布在0.5 μm/h左右，比三水铝石的生长速率慢4-10倍，且升高温度有利于提高生长速率，同一温度下一水软铝石晶体的生长速率与起始晶种的粒径大小没有关系。 (2) 附聚是提高分解产物粒度的主要手段，除采用附聚效率来衡量一水软铝石的附聚效果外，还引入磨损指数来判断附聚过程的有效性。晶种添加量越少或分解率越高，新析出的物质可以把颗粒粘结的更牢固，使分解产物磨损指数越低。研究范围内一水软铝石的最佳有效附聚条件为晶种系数SR=1.0，温度T=75℃，分子比MR=1.6，铝酸钠溶液浓度C(Na2O)=155 g/L。 (3) 基于分解结晶中反应传递过程匹配耦合调控原理，研究了NaHCO3对铝酸钠溶液晶种分解制备一水软铝石过程的强化作用与规律。晶种系数和NaHCO3添加方式均会影响分解过程，相同条件下添加NaHCO3使分解率提高了3倍，晶种系数SR在0.0-1.0范围内NaHCO3添加量到151.2 g·L-1时分解率均高于80%，恒定SR时NaHCO3添加速率越慢分解率越高。NaHCO3的添加方式改变了铝酸钠溶液的瞬时过饱和度，因而改变了产物的组成和粒度。采用逐步增加NaHCO3添加速率的方式有利于提高产物中一水软铝石的含量和粒度。 (4) 基于添加剂对结晶过程固-液界面特性调控的作用原理，研究了有机添加剂对调控铝酸钠溶液分解结晶的影响，并结合溶液的红外光谱分析了作用机理。不同有机添加剂对铝酸钠溶液分解有不同的作用机制，聚丙二醇PPG改变了溶液中的氢键，使铝酸钠溶液分解率提高，而且可以促进颗粒二次附聚的进行，所以有利于产物粒度的增加。1, 2丙二醇也改变了溶液中的氢键使分解率升高，但抑制了部分细粒子的附聚。正丙醇、丙三醇、正辛醇和甘露醇对铝酸钠溶液分解率和产物粒径均起到抑制的作用。结晶助剂(Alclar CM 5159)改变了铝酸钠溶液的结构，分解率随着结晶助剂添加量的增加而升高，但产物中>45 μm粒子的含量却随之降低，因为其对细粒子的附聚没有促进作用。 |
| 英文摘要 | Owing to the conventional sintering process and combinational process in our country, the production of alumina consums 2-4 times energy as much as abroad country for bayer process. Energy savings can be achieved through the precipitation of boehmite in place of gibbsite from sodium aluminate solutions in the subsequent calcinations step because of different enthalpy. Its essence is dehydration in the crystallization process with low temperature instead of the calcination process with high temperature. A new coupling of carbonization-seeded precipitation technology was proposed to prepare boehmite from sodium aluminate solutions by Institute of Process Engineering, Chinese Academy of Sciences. In addition, the precipitation and crystallization were studied. Sandy alumina is the development direction for alumina refining requiring sandy boehmite. The precitation mechanism of sandy boehmite from sodium aluminate solutions was studied in this paper, whose contents include the crytal growth and agglomeration of boehmite and improving the precipitation process by NaHCO3 and organic additives. (1) Growth is the kinetic process of crystallization. Crystal growth of boehmite was determined using in situ optical microscopy. The results indicated that the growth rates of boehmite single crystals range from 0.08 μm/h to 2.4 μm/h, mostly distributed in 0.5 μm/h. The growth rate of boehmite is 4-10 times low than gibbsite. High temperature can improved the growth rate of boehmite, whereas the size of initiate seed can’t affect the growth rate directly. (2) Agglomeration is the major means to enhance the particle size of precipitation products. The agglomeration efficiency of boehmite were investigated using agglomeration degree and attrition index. Adding less seed or improving precipitation ratio can make enough precipitated boehmite cement particles tightly, resulting in the lower attrition index of products. The effective conditions for boehmite agglomeration is SR=1.0, T=75℃, MR=1.6 and C(Na2O)=155 g/L. (3) Based on the adjustment mechanism of reaction transfer and coupling in the precipitation process, boehmite was precipitated with seeds from sodium aluminate solution intensified by NaHCO3, and the influence of SR and adding NaHCO3 methods on precipitation process was studied. The results show that NaHCO3 can intensify the precipitation process of sodium aluminate solution and the precipitation ratio can be enhanced by 3 times under the same condition. When SR=0.0-1.0 and the mass of adding NaHCO3 comes to 151.2 g·L-1, precipitation ratio is all higher than 80%. With the constant SR the slower rate of adding NaHCO3, the higher precipitation ratio can be got. The instantaneous surpersaturation of sodium aluminate solutions was changed by the adding NaHCO3 methods, so the content and size of boemite, which were both affected by adding NaHCO3 methods, can be improved by slowing down the initial rate of adding NaHCO3. (4) On account of the effect of additives on solid-liquid interfaces in crystallization process, the effects of organic additives on controlling precipitation process from sodium aluminate solutions were studied, and the mechanisms were proposed using IR. PPG changed the hydrogen bond in the solution, which promoted the precipitation ratio and secondary agglomeration of particles and increased the size of products. 1, 2-propanediol also changed the hydrogen bond in the solution and improved precipitation ratio, but inhibited the agglomeration of fine particles. N-propanol, glycerol, n-octyl alcohol and mannitol inhibited both precipitation and the size of products. Crystallizing agent(Alclar CM 5159), changing the structure of sodium aluminate solution, improved the precipitation ratio, but inhibited the agglomeration of some fine particles and leaded to the decrease of >45 μm particles in the products. |
| 公开日期 | 2013-09-17 |
| 页码 | 96 |
| 源URL | [http://ir.ipe.ac.cn/handle/122111/1534]  |
| 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 | 张娟. 铝酸钠溶液分解制备砂状一水软铝石的机理研究[D]. 北京. 中国科学院研究生院. 2010. |
入库方式： OAI收割
来源：过程工程研究所
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