New theoretical and experimental investigations on stability of bubble/particle aggregates in flotation: A theory on the upper particle size of floatability

Abstract

During the last three decades flotation has been developed into the most important separating method for minerals. Nowadays more than two thousand million tons of more than 100 different minerals are annually floated in the world. In the last years the field of applicability of flotation has been considerably extended, above all to the operations of process engineering, such as waste-water purification, the paper industry and inorgano-chemical process engineering. Today a new field of application is developing — the flotation of microorganisms for protein recovery in biotechnological processes. Likewise, the minerals to be processed are becoming poorer on the one hand and on the other it is necessary to reduce the energy consumption of the process considerably. Furthermore, automation of the operations is required. All these requirements cannot be adequately met as long as there is no physically based flotation model allowing for the calculation of probabilities of single process stages and the simulation of the process as a whole. Therefore, investigation of the process, aiming at clearing up the single fundamental phenomena, is a task to be urgently solved today. Recently, we succeeded in presenting the three essential and important fundamental stages of flotation: 1. (1) Approach of solid particles and gas bubbles upon formation of a thin liquid film between them. 2. (2) Formation of three-phase contact (tpc). 3. (3) Stability of the formed aggregates. The present paper deals, above all, with the latter phenomenon. It is shown that by considering the kinetic energy of aggregates in the turbulent field of a flotation machine, their stability, i.e. the upper particle size limit of floatability, can be calculated. The behaviour and the forces acting upon the single particles in the fluid interface are the preconditions. The calculations are based on numerical integration of the Laplace differential equation. Experiments were carried out to confirm the theoretical considerations.