【作者】 张扬；

【导师】 郭奋； 马淑花； 郑诗礼；

【作者基本信息】 北京化工大学 ， 化学工程（专业学位）， 2013， 硕士

【摘要】 我国优质铝土矿资源短缺,而污染严重的粉煤灰、煤矸石等排放量大,其中蕴藏着丰富的氧化铝,是宝贵的非传统氧化铝资源。中国科学院过程工程研究所成功研发了亚熔盐法粉煤灰/煤矸石提铝新技术,该技术能耗低,资源利用率高,展示了良好的应用前景。铝酸钠结晶是亚熔盐法相分离核心技术之一。本论文针对铝酸钠溶液结晶过程结晶时间长、效率低等问题,提出采用超声场强化铝酸钠结晶过程,并进行了工艺探索研究。论文取得如下创新成果：(1)采用超声场强化铝酸钠溶液结晶过程,显著提高了铝酸钠结晶效率。在不添加晶种的情况下,当结晶时间为3.5h时,超声频率为45kHz时,结晶率由不加超声场的0.8%增加至75.64%,当结晶时间为4h时,超声频率为80kHz时,结晶率增加至77.24%。(2)系统探索了超声场强化铝酸钠结晶的工艺参数,获得了超声场强化铝酸钠溶液结晶的最优工艺条件。研究结果表明,铝酸钠结晶率随超声波频率的提高而下降,随单位容积内超声波功率的提高而升高,随超声时间的延长而升高。在45kHZ、6.94kw/m3、超声时间3.5h时,铝酸钠结晶率达到75.64%,此时溶液苛性比由初始的9.6提高到36；(3)明晰了超声场强化铝酸钠结晶过程的铝酸钠晶体形貌变化规律。在功率为6.94kw/m3时,随着超声波频率的增加,晶体形貌由薄片状的圆形复合结构向八边形片状复合结构转变,晶体的尺寸略有增大；在频率为45kHz时,随着功率的增加,铝酸钠晶体的形貌由单独的片状八边形结构向圆形复合状结构渐变,晶体尺寸变小；(4)初步探索了超声场作用下铝酸钠溶液结晶诱导期以及溶液导电性能变化情况。结果显示,铝酸钠溶液结晶诱导期在超声场作用下降低明显,在45kHZ、6.94kw/m3功率下溶液诱导期缩短了62%；加入超声场强化后铝酸钠溶液中产生空化气泡,电导率不断减小。当诱导期结束,进入二次成核阶段之后,电导率逐渐趋于平稳。更多还原

【Abstract】 There is a shortage of high-quality bauxite resources in China.The serious pollution of fly ash and coal gangue is a kind of non-traditional bauxite resources, which has a large emission that is500million tons annually. Institute of Process Engineering, Chinese Academy of Sciences has successfully developed a sub-molten salt technology for mention aluminum from fly ash and coal gangue, this technology has more lower energy consumption and more higher resource utilization, shows a good application prospect.The crystallization of monosodium aluminate hydrate is a key technology to realize the sub-molten salt phase separation of this production process. This paper being aimed at long crystallization time and low efficiency, propose to enhance the crystallization process by ultrasonic field and explore this process. The achievements and innovative progresses were exhibited as follows:(1) The experimental results show that ultrasound has a significant effect on reducing the crystallization time. Without the seed crystal, when the crystallization time is3.5h, ultrasonic irradiation can reduce the crystallization rate from0.8%to75.64%with a frequency of45kHz, when the crystallization time is4h, ultrasonic irradiation can reduce the crystallization rate from0.8%to77.24%a frequency of80kHz.(2) The process was investigated systematically and the optimal conditions was obtained. The results showed that the rate of crystallization was increased as the ultrasonic frequency was reduced or the ultrasonic power was increased. It was find that we can enhance the crystallization rate by increasing the ultrasonic irradiation time. When the crystallization time was3.5h, the crystallization rate would be75.64%by ultrasonic field with a frequency of45kHz at the power of6.94kw/mj.(3) Crystallization with ultrasound proved to be a good tool to optimise and control sodium aluminate nucleation and crystallization. The average crystal size decreases with an increase of ultrasonic power with the frequency of45kHz. On the contrary, the average crystal size increases with an decrease of ultrasonic frequency at the power of6.94kw/m3.(4) The experimental results show that ultrasound has a significant effect on reducing the induction time and conductivity. The induction time decreases62%by ultrasonic field with a frequency of45kHz at the power of6.94kw/m3. After applying ultrasound to the system, the conductivity decreased because cavitation bubbles were appeared. Conductivity didn’t change after the end of the induction period.更多还原