## 2 Measurement and Roughening Methods
### Roughening Methods
#### 2.2.2 Laboratory Test Methods  
The abrasion and polishing method involve using fine, hard particles to abrade or polish the target material, creating various degrees of grooves or scratches without altering the shape and size of the particles. [PERSON] et al. [28] demonstrated the effectiveness of this method in producing different surface roughness levels on more than ten different polymers. The most widely used materials for abrading or polishing are alumina powder [1; 57], silicon carbide powder (SiC) [25; 31; 53; 55; 58], and diamond powders [2; 3; 37; 58; 59], often on a micron or nanometer scale. Sandpapers of various grits are also widely utilized [1; 2; 3; 39; 83], although they may partially change the true surface roughness of the particles. The acid-etching method relies on the strong chemical reaction between hydrofluoric (HF) acid and silicon dioxide, producing different surface roughness levels while maintaining the original shape and size of the particles by controlling the etching time and concentration [36]. This technique is commonly applied to the surfaces of smooth glass beads or silicon-containing minerals (such as quartz), using 5-10% HF acid [35; 36; 54; 84] or a mixed acid based on HF acid [57]. [PERSON] et al. [57] observed that the Ra values for smooth glass beads and those treated by polishing and etching range from 1 to 8 nm, 6 to 18 nm, and 28 to 170 nm, respectively. [PERSON] et al. [53; 79] combined the grinding methods with a fine SiC powder (Mohs hardness scale: 9) to generate different surface roughness levels and explored the effects of the varying surface roughness (produced by both the acid-etching and abrasion methods) on the flotation behavior [57]. Apart from being used individually, these methods can also be combined to achieve a varying surface roughness and shape factors in particles. For example, [PERSON] et al. [35] integrated the ceramic ball mill and HF etching methods to study the effect of the surface roughness and shape factors of glass beads on flotation behavior. [PERSON] et al. [53; 80] combined the grinding methods with a fine SiC powder (Mohs hardness scale:9) to generate different surface roughness levels and explored the effects of a varying surface roughness (produced by both the acid-etching and abrading methods) on the flotation behavior [57]. Some researchers have effectively regulated surface roughness by developing new methods. [PERSON] et al. [85] demonstrated that with an increase in ultrasonic power, cracks gradually expanded into gaps, and new cracks and cavities formed on the surface, leading to the increased roughness of the lignite surface. [PERSON] et al. [86] and [PERSON] et al. [87] found that an appropriate ultrasonic treatment increased the surface roughness of pentlandite and quartz particles, while it decreased the roughness of serpentine particles. [PERSON] et al. [88] and [PERSON] et al. [89] observed that a microwave treatment reduced the surface roughness of chalcopyrite and galena particles. [PERSON] et al. [90] observed that an increased surface roughness enhanced the hydrophobicity and floatability of coal particles by depositinghydrophobic nanoparticles onto their surfaces. [PERSON] et al. [91] and [PERSON] et al. [92] found that a low-temperature heating treatment and low-temperature air plasma pretreatment significantly increased the surface roughness of anthracite coal and low-rank coal particles, respectively. [PERSON] et al. [51; 93; 94] proposed a new concept involving sand-blasting quartz and talc particles to produce particles with a different surface roughness. Various methods are employed to generate a different surface roughness, with the grinding method being one of the most widely used techniques. However, the grinding method greatly changes the particle shape and size while producing a different surface roughness. The shapes and sizes of particles greatly affect the measurement results of the surface roughness and flotation behavior, even when the ground particles are classified into narrow size ranges.