## 4 Conclusions  
By studying the effect of water retention of fluorinated surfactant solutions, a preliminary range of optimum values of fluorinated solutions affecting the water retention of coal dust at different concentrations of different species was derived, leading to the following conclusions.  
1. The water retention of non-ionic fluorinated solutions is significantly better than that of anionic fluorinated solutions, and water retention performance gradually increases with increasing concentration within a certain range. Among the four non-ionic fluorinated solutions, FS-30 solution has the better overall water retention, followed by FS-31 solution, FS-34 solution, and FS-50 solution.
2. To meet the requirements for water retention of coal dust, the optimum concentration of anionic fluoride containing solution FS-30 is preferably 0.05%, and the optimum concentration of anionic fluoride solution FS-31 is 0.03%. The optimum concentration of anionic fluoride solution FS-34 is 0.03%. The optimum concentration of anionic fluoride solution FS-50 is 0.3%. The optimum concentration of 0.07% for non-ionic fluoride solution FS-60. The optimum concentration is 0.3% for non-ionic fluoride solution FS-61. The optimum concentration is 0.08% for non-ionic fluoride solution FS-63.
3. The surface morphology of the coal dust after the solution action can be analyzed, the surface of the coal dust after the action of the non-ionic fluorine solution is more compact and detailed, and with the increase in concentration, the surface of the graininess is less obvious. FS-50 solution showed a better effect among the four non-ionic fluorine solutions, the surface of the coal dust samples showing no obvious cracks or fine lines. This indicates that the wetting and agglomeration properties of the non-ionic fluoride-containing solutions are better than those of the anionic fluoride-containing solutions.
4. The water loss at different time periods shows that the four non-ionic fluoride solutions and the anionic fluoride solutions FS-60 and FS-63 all have the highest water loss in the 24-36 h time period, while the anionic fluoride solution FS-61 has the highest water loss in the 36-48 h time period. Therefore, to prevent the risk of secondary dusting, emphasis should be placed on timely wetting of coal dust agglomerates at 24 h and 36 h after the solution has been applied to the coal dust.
5. Overall, the regularity results show that the concentration and type of fluorinated solution used can significantly influence the water retention of coal dust. The non-ionic fluorinated solution FS-50 with a concentration of 0.3% appears to be the most effective at increasing water retention, likely due to the formation of stable micelles that reduce the surface energy and increase the wettability of the coal dust particles.  
Conceptualization, K.W. and B.Z.; data curation, M.X. and M.Y.; writing--original draft preparation, M.X. and M.Y.; writing--review and editing, M.X.; visualization, X.L.; supervision, Q.Y. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the Key R&D Program of Sichuan (2022 YFS0529), the Key R&D Program of Jiangxi (20212 BBG73010), the Fundamental Research Funds for the Central Universities (2022 JCCXAAQ01), the Science and Technology Foundation of Guizhou Province ([2022]General250), the State Key Laboratory Cultivation Base for Gas Geology and Gas Control (Henan Polytechnic University (WS2021A01) and the College Students' Innovative Entrepreneurial Training Plan Program (202212005).  
Not applicable.  
The data presented in this study are available on request from the corresponding author. The data are not publicly available due to some authors' personal privacy and legal restrictions.  
The authors declare no conflict of interest.