**5. Conclusions**

This study was based on the kinetics of single particles. The trajectory of the particles was quantitatively analyzed under different rotation speeds and intake air volumes. The following conclusions were obtained:

(1) The grading experiment results for iron ore fines and barite powder materials indicate that the better process parameter combination for the production of 12-μm particles using the KFF series turbo air classifier is a 1800 rpm rotor speed and 8 m/s air inlet velocity.


**Author Contributions:** The author S.Z. provided help in the preliminary investigation of this article. M.L. provided resources such as experimental equipment. Y.Z. (Yang Zhou) conducted in-depth research on the evaluation index of classification performance, then proposed the concept of the relative classification sharpness index, which could be applied in the classification performance tests of actual production. Y.Z. (Yun Zeng) was in charge of the entire research experiment, statistics all the data and sorted it out. Finally wrote and revised the manuscript. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** This project was supported financially by the National Key R&D project (2016YFC0303703), the National Natural Science Foundation of China (No. 51674040 and No. 51904181), and the National Natural Science Foundation of Hubei province (No. 2016CFC740). The authors would like to thank all the members of the project team for their support.

**Conflicts of Interest:** The authors declare no conflict of interest.
