The effect of particle size on coal flotation kinetics: A review

Coal flotation is a complex multiphase process governed by different sub-processes and interphase interactions. The coal cleaning efficiency by flotation is largely affected by many different physical and chemical factors that can be roughly classified into three main group: coal feed properties, pulp chemical and rheological properties, and machine and operational properties. A great number of flotation kinetic model have been proposed in literature but a vast majority uses three parameters to describe the flotation kinetics, which are the ultimate recovery, the flotation rate constant, and flotation time. The models expand on the classical theory of flotation proposed by Zuniga (1935) that is based on the assumption that the particle-bubble collision rate is first-order with respect to the number of particles in the system, while bubble concentration remains constant. The flotation rate constant is directly proportional to available bubble surface area and probability of flotation, which is strongly dependent on particle size. Therefore, particle size is one of the most important parameters in coal flotation because it affects gas bubble mineralization and froth stability, bubble size distribution and air holdup, bubble-particle collision, attachment, and detachment rates, and reagent adsorption. Numerous researchers have studied the effect of particle size on flotation kinetics over years. This paper provides a comprehensive review of coal flotation kinetics models with a special focus on the effect of particle size on coal kinetic rate, recovery, and product quality. A particular emphasis will be put on research findings reported over the last three decades.