Study On The Process Of Sodium Aluminate Crystallization By Ultrasonic Field

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.