## 6 Conclusions and Perspectives  
Surface roughness refers to the micron- or even nanometer-scale bumps/grooves on the surfaces of materials. It varies greatly depending on the refinement process of the particles. Several measurement methods and equipment, such as the fitting ellipse method, optical profilometer, surface roughness measurer, Brunauer-Emmett-Teller (BET) method, and atomic force microscopy (AFM), have been employed to assess the surface roughness of different minerals and materials. However, these methods come with their own advantages and disadvantages, which can lead to measurement errors. These discrepancies arise from differences in the particle size and shape, measure philosophy, and measure accuracy. Such errors may lead to substantial variations or even inverse conclusions about the surface roughness when measured by different techniques. Therefore, it is crucial to develop a surface roughness measurement tool with better accuracy or to combine various measurement methods to ensure reliable results. Several roughening techniques, including grinding, abrasion/polishing, and acid etching, have been employed to modify the surface roughness of different minerals and materials. The grinding method is the most widely used technique, as it significantly  
Figure 16: (**a**) Interaction energy between 100 \(\upmu\)m methylated glass particle and flat surface of gas bubble normalized per radius of particle; (**b**) effect of asperity height values on total energy profiles for hydrophobic particle–bubble interaction [57]; interaction energy between spherical particles ((**c**) magnesite [37] and (**d**) magnetite [40]) with different size of asperity and bubble; (**e**) interaction energy between hydrophobic coal particles within 143.5 \(\upmu\)m size and air bubble normalized per radius of particle [42]; and (**f**) relationship between surface roughness and interaction energy and flotation kinetics constants. alters the particle shape and size, impacting both the measurement results of the surface roughness and the flotation behavior. In contrast, the abrasion and etching methods adjust the surface roughness without changing the particle shape and size, thereby minimizing the potential influence from these factors. As a result, findings from these methods tend to be more accurate and reliable, although research using them has primarily focused on a limited range of targets, mainly glass beads and quartz particles. Other roughening methods have also been explored, offering more options for altering the surface roughness. Numerous studies have examined the effects of surface roughness on flotation behavior, wettability, and bubble-particle interactions. Most research indicates that an increased surface roughness effectively decreases the interaction energy and attachment time while increasing the adhesion force and collision probability between air bubbles and hydrophobic surfaces. This enhances the hydrophobicity of the hydrophobic surfaces, hence improving flotation recovery and rates. This improvement also enhances the hydrophilicity of the hydrophilic surfaces, hence decreasing their flotation recovery and rates. Based on the above principle, the surface roughness of different minerals can be regulated, making hydrophilic minerals more hydrophilic and hydrophobic minerals more hydrophobic and expanding the hydrophobicity between different minerals to achieve their selective flotation separation. Thus, it is feasible to achieve the flotation separation of different minerals through surface roughness regulation, which has been demonstrated by some scholars. It is suggested that more attention should be focused on the selective flotation separation of minerals through adjusting the surface roughness. Moreover, some scholars have reported contradictory findings, suggesting that the relationship between surface roughness and flotation behavior warrants further investigation in future studies.