###### Abstract  
Surface roughness refers to the micron- or nanometer-scale irregularities (bumps and grooves) on material surfaces, and it varies greatly as particles are refined, affecting their flotation behavior, wettability, and bubble-particle interactions. In this paper, the main roughening and measurement methods for surface roughness are summarized, the effects of surface roughness on flotation behavior and wettability are reviewed, and the main wettability models for rough surfaces are also introduced. Grinding is the most commonly used method, while other methods, such as acid etching, abrasion, sand-blasting, ultrasonic pretreatments, and microwave treatments, have also been explored. Most research shows that increasing the surface roughness effectively enhances the hydrophobicity of hydrophobic surfaces and the hydrophilicity of hydrophilic surfaces. This improvement leads to better flotation recovery and kinetics for hydrophobic surfaces, whereas it deteriorates that for hydrophilic surfaces. Moreover, the relationship between surface roughness and bubble-particle interactions, including bubble-particle attachment, interaction energy, and interaction force, is introduced. Most research shows that increased surface roughness effectively decreases the attachment time and energy barrier and increases the adhesion force between air bubbles and rough hydrophobic surfaces. Conversely, these effects can be detrimental to rough hydrophilic surfaces. This paper also addresses existing problems and challenges in the field and offers references and suggestions for future research efforts.  
surface roughness; roughening and measurement; flotation behavior; wettability; bubble-particle interaction 2020  
13 April  
for many years and is expected to continue being relevant for decades or even centuries to come [21; 22; 23]. The grinding process is an essential step before flotation, as it provides particles with suitable sizes for effective separation. During grinding, the surface morphology (including surface roughness and surface shape) undergoes significant changes as the particles are refined. Numerous studies have explored how the surface roughness affects flotation behavior, wettability, and bubble-particle interactions. However, few review papers comprehensively summarize these effects.  
In this paper, we provide a comprehensive introduction to the measurement methods for surface roughness and the techniques for particle roughening. We discuss, in detail, how various roughening parameters influence surface roughness. Next, we address potential sources of errors in both the measurement and roughening processes and offer suggestions for improvement. We then examine how surface roughness affects flotation behavior, particularly in terms of flotation recovery rates, flotation rates, and the flotation separation of different minerals. Additionally, we investigate the impact of surface roughness on wetting properties and explore the underlying mechanisms involved. We introduce several wetting models for rough surfaces and conduct a comparative analysis with conventional wetting models. To further understanding the mechanisms behind surface roughness, we perform an in-depth study of the interaction between bubbles and particles. This includes examining the contact time, interaction energy, and interaction forces, as we explore the relationship between surface roughness and the interactions between bubbles and particles. This paper details how surface roughness influences flotation behavior, wetting properties, and particle-bubble interactions on both macroscopic and microscopic levels.