The importance of frothers in flotation is widely acknowledged, particularly in terms of their role with respect to bubble size, and the stability and mobility of the froth phase. These factors play a significant role in the kinetic viability of the process, and the overall recovery and the grade that can be achieved from a flotation cell or circuit. About 60 years ago, Wrobel [1] presented a comprehensive review of flotation frothers, their action, properties and structures. However, during recent six decades flotation reagent technology has undergone considerable evolutions and innovations. The aim of the present review is to provide an updated, comprehensive database comprising recent developments in flotation frother technology as well as some historical aspects. Different types of flotation frothers are discussed regarding to their classifications, properties, and preparation methods. New classification schemes have been suggested in parallel with introducing new characterization criteria. New classes of frothers are actually conventional frothers modified by incorporating certain functional "group" or "atoms" into their molecular structure. Like particle surface modifiers, frothers are also influenced by biotechnology, leading to introducing a new class of frothers named as "biofrothers".

This paper reviews recent developments in the fundamental understating of ultrafine (nano) bubbles (NBs) and presents technological advances and reagent types used for their generation in flotation. The generation of NBs using various approaches including ultrasonication, solvent exchange, temperature change, hydrodynamic cavitation, and electrolysis was assessed. Most importantly, restrictions and opportunities with respect to the detection of NBs were comprehensively reviewed, focusing on various characterization techniques such as the laser particle size analyzer (LPSA), nanoparticle tracking (NTA), dynamic light scattering (DLS), zeta-phase light scattering (ZPALS), and zeta sizer. As a key feature, types and possible mechanisms of surfactants applied to stabilize NBs were also explored. Furthermore, flotation-assisted nano-bubbles was reported as an efficient method for recovering minerals, with a special focus on flotation kinetics. It was found that most researchers reported the existence and formation of NBs by different techniques, but there is not enough information on an accurate measurement of their size distribution and their commonly used reagents. It was also recognized that a suitable method for generating NBs, at a high rate and with a low cost, remains a technical challenge in flotation. The application of hydrodynamic cavitation based on a venturi tube and using the LPSA and NTA in laboratory scales were identified as the most predominant approaches for the generation and detection of NBs, respectively. In this regard, neither pilot- nor industrial-scale case studies were found in the literature; they were only highlighted as future works. Although the NB-stabilizing effects of electrolytes have been well-explored, the mechanisms related to surfactants remain the issue of further investigation. The effectiveness of the NB-assisted flotation processes has been mostly addressed for single minerals, and only a few works have been reported for bulk materials. Finally, we believe that the current review paves the way for an appropriate selection of generating and detecting ultrafine bubbles and shines the light on a profound understanding of its effectiveness.

Many reagents are used as frother in flotation process, however, a general reference for their identification and characterization is not available. The present work categorizes the commonly used frothers and evaluates the available methodologies to determine their properties. In this paper, frothers properties such as molecular weight, viscosity, boiling and freezing point, hydrophile-lipophile balance number, solubility, surface activity and critical micelle concentration were discussed. The commonly used measurement methods for froth structure and dynamic and static frothability were also presented along with water recovery index and critical coalescence concentration (CCC). Results showed that the practical identification of frothers properties has not been thoroughly evaluated and therefore, there is a need for developing novel and easy-to-apply experimental methods in this area. For example, it was found that there is no promising single process to measure the CCC value. This review revealed that the 2D froth structure measurement methods are associated with a considerable bias, while 3D techniques can effectively represent the actual froth properties. It was also found that the potential interactions between various frothers properties and how they can influence the flotation performance in an industrial environment are not yet understood and needs further investigation. It was also identified that there is no standard instruction to provide a reliable connection between both manufactures and frothers consumers. In our opinion, the current review paves the path for the elaboration of knowledge and technology to provide promising methods for determining conventionally used and complex frothers properties.

Today, with the ever-increasing concerns about the widespread environmental impact of the mining industry, the movement of the mineral processing sectors, which heavily rely on various chemical and petroleum-origin reagents, to the green industry is imperative. Due to the advantages biotechnological approaches provide, bioprocessing is considered a benign alternative to conventional mineral processing techniques. Recent fundamental research works have directed the attention to the development of biotechnology and using microorganisms in the new field of biobeneficiation, especially bioflotation. The current review categorizes bioflotation methods into direct and indirect processes giving an in-depth insight into their concepts. Furthermore, this study provides a comprehensive review of research on different aspects of bioflotation, such as the effects of operating (mainly solid content and pH) and biotechnological parameters, potential mechanisms, and unexplored points, but from different, and practical viewpoints. Recent studies were summarized by categorizing microorganisms based on their wall structures, and growth temperature. It was disclosed based on the literature data that the nutritional requirement of variant microorganisms was only chemolithotroph. Further, the conducted researches in investigating optimum conditions for maximization of contact angle and adhesion forces to reach the maximum recovery were reviewed. In addition, existing problems and challenges of this field were investigated and it was found that economic barriers and obscurities were the main obstacles of industrial application in mining and mineral processing industries. Finally, new perspectives and suggestions were presented to shed light on future research and help to solve the challenges currently facing its application.

Although column flotation cells have been extensively studied in the literature, the hydrodynamic impact of orifice properties has not been adequately addressed yet. This paper initially investigates the effect of sparger orifice diameter on hydrodynamic behavior of coal particles in a pilot-scale column flotation. The metallurgical responses (i.e., ash, yield and recovery contents) were evaluated for four different sparger orifice sizes including 1, 3, 5, and 7 mm under constant operating conditions by experimental measurements associated with computational fluid dynamics (CFD) simulations. A numerical model of a two-phase air-water flow in the column (3 m × 0.5 m) was chosen and the turbulence patterns inside the collection zone and at the pulp-froth interface were simulated by employing the Volume-Of-Fluid (VOF) model. The experimental results indicated that desiring concentrated product i.e., ash content of 8.8% and yield of 57.2% could be obtained using the 3 mm orifice size. Simulation results revealed that as the sparger orifice size decreased to 1 mm, the reduced carrying capacity of the bubbly regime led to the poor flotation performance. In contrast, the turbulence condition intensified as the sparger orifice size was increased to 7 mm. Another negative consequence of the 7 mm orifice was attributed to the exceeded entrainment of high ash fines due to a bubble swarm mechanism. The 7 mm sparger orifice diameter showed a concentrate of 17.1% ash and 12.5% yield. Finally, according to the obtained results in this work and literature studies, several necessary highlights were suggested for future works in this scope.