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Volume 114
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Re-mixing of sorted clean coal and gangue particles in air-fluidized bed separator with magnetite powder
Yumeng Zhang, Yongdou Wang, Donghui Liu, Quanhong Zhu *
State Key Laboratory of Advanced Optical Polymer and Manufacturing Technology, College of Chemical Engineering, Qingdao University of Science and Technology, Qingdao, 266042, China
10.1016/j.partic.2026.04.011
Volume 114, July 2026, Pages 155-163
Received 24 January 2026, Revised 17 April 2026, Accepted 20 April 2026, Available online 23 April 2026, Version of Record 30 April 2026.
E-mail: zhuqh87@163.com; zhuqh@qust.edu.cn
Highlights

• Re-mixing of sorted clean coal/gangue particles deepened as gas velocity increased.

• Re-mixing fraction increased as gangue/clean coal particles became smaller.

• Re-mixing fraction decreased as the size of magnetite powder decreased.

• Particles re-mixing into magnetite distributed uniformly in vertical direction.

• New strategy to determine dpRm was built based on allowed level of re-mixing.


Abstract

For the dry beneficiation of raw coal in the air-fluidized bed, the re-mixing of sorted clean coal/gangue particles backward into the magnetite powder was thoroughly explored. It deepened gradually as Ug (gas velocity) was raised from the incipient fluidization point of the magnetite powder. Apparent re-mixing of separated gangue particles occurred long before Ug reached their minimum fluidization velocity, proving that it was induced by the macro-circulation of the magnetite powder. The re-mixing of both particles increased as their sizes decreased for the given magnetite powder, offering a new and unique perspective to disclose why the fine raw coal was difficult to beneficiate. The re-mixing of given clean coal/gangue particles decreased as the magnetite powder became finer, further revealing why it was feasible to raise the efficiency of beneficiating the fine raw coal by using the small magnetite powder. The fact that different Ug must be used for the magnetite powders of distinct sizes explained why their capabilities to beneficiate the same fine raw coal differed. The clean coal/gangue particles re-mixing among the magnetite powder distributed uniformly in the vertical direction. Finally, a new strategy based on the allowed level of re-mixing was established to determine the smallest raw coal for effective beneficiation.

Graphical abstract
Keywords
Dry beneficiation; Fluidized bed; Re-mixing; Magnetite; Minimum size
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