2018 AIChE Annual Meeting

(580e) Secondary Nucleation and Growth Kinetics of Aluminum Hydroxide Crystallization from Potassium Aluminate Solution Using FBRM

Authors

Xue, J. - Presenter, East China University of Science and Technology
Liu, C. L., East China University of Science and Technology
Luo, M., East China University of Science and Technology
Li, P., East China University of Science and Technology
Yu, J., East China University of Science and Technology
Rohani, S., Western University
Jiang, Y. F., East China University of Science and Technology
Aluminate hydroxide crystallization is a significant procedure in extraction and recovery of aluminum from aluminum-containing ore with alkaline method. The alumina-rich potassium aluminate liquor is separated from the leaching solution[1,2], then the alumina is crystallized (precipitated) as hydrate by seeding with aluminate hydroxide. Secondary nucleation and growth are main phenomena in industrial crystallization of aluminum hydroxide.

There are many different experimental techniques that have been used to measure the secondary nucleation and growth kinetics. As a promising apparatus of process analytical technologies(PAT), focused beam reflectance measurement (FBRM) can directly monitor the chord length distribution (CLD) at a very short time interval, such as 2s, so more detailed information can be recorded during crystallization without sampling[3]. A method is developed to calculate the low-order moments from the CLD directly without converting the CLD to PSD[4]. Therefore, secondary nucleation and growth rates were measured by FBRM directly.

In this work, moments of crystal population were estimated from the measured CLD, generated by the FBRM[4], and the supersaturation was calculated from the measured solution concentration by ICP-AES. The moments were uesed to approximate the secondary nucleation and growth rates. Meanwile, the secondary nucleation and growth rates were also generally represented by a power-law function of the main driving force for crystallization process, supersaturation. Therefore, kinetics parameters for secondary nucleation and crystal growth were calculated based on experimental data at different supersaturations and temperatures. Also, the kinetic model was verified in further experiments by comparison of experimental data and predicted data.

Another method was perfomed to estimated gibbsite secondary nucleation and crystal growth using a semiempirical power-law model by BET and ICP-AES[5]. Instead of measuring total particle surface area by BET, moments of crystal population by FBRM were uesed to calculate total particle surface area in this work. And the kinetics calculated by FBRM showed a same trend in comparision with the results by BET.

References:

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[2]Mengjie Luo,Chenglin Liu,Youfa Jiang,Jin Xue,Ping Li,Jianguo Yu.Green recovery of potassium and aluminum elements from alunite tailings using gradient leaching process[J]. Journal of Cleaner Production,2017,168:1080-1090.

[3]Yuzhu Sun, Xingfu Song, Jin Wang,Yan Luo,Jianguo Yu. Determination of seeded supersolubility of lithium carbonate using FBRM. J. Cryst. Growth. 294–300, 311(2010).

[4]Milana Trifkovic,Mehdi Sheikhzadeh,Sohrab Rohani.Multivariable real-time optimal control of a cooling and antisolvent semibatch crystallization process[J]. AIChE Journal, 2009, 55(10): 2591-2602.

[5]Jun Li,Jonas Addai-Mensah, Alagu Thilagam, Andrea R.Gerson.Growth Mechanisms and Kinetics of Gibbsite Crystallization: Experimental and Quantum Chemical Study[J]. Crystal Growth & Design, 2012 Jun, 12(6): 3096-3103.