Effect Of Frother (MIBC) Addition On The Characteristics Of Microbubbles Generated By Air Dissolved Nucleation
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EFFECT OF FROTHER (MIBC) ADDITION ON THE CHARACTERISTICS OF MICROBUBBLES GENERATED BY AIR DISSOLVED NUCLEATION Estrella Martínez-Ramos1, Roberto Pérez-Garibay1, Jorge Rubio-Rojas2 1 2
CINVESTAV-IPN Unidad Saltillo, Carr. Saltillo-Monterrey km 13, Ramos Arizpe, Coah. México Universidad Federal do Rio Grande do Sul, Porto Alegre, Brasil
ABSTRACT An identification of the characteristics of microbbubles dispersion is presented in this paper, when frother addition (MIBC) is modified in a biphasic system (air-water). Sauter diameter (d32), gas flow rate (Jg), superficial area flow density of the microbubbles (Sb) and air holdup (εg) are the measured variables in this research work. The studied frother additions were 0, 10 and 20 ppm. Similar to conventional bubble sizes, it was observed also, that air holdup increases with the air flow rate. The linear relationship between εg and Sb permits to conclude that superficial area flow density, a variable difficult to measure directly, may be estimated if air gas holdup is known. Furthermore, the experimental results showed that frother addition (MIBC) reduced the Sauter diameter, increasing all other variables.
INTRODUCTION In a manner different from conventional flotation, which uses bubble sizes between 600 and 2500 m, ADF uses bubbles between 30 and 100 m, a size appropriate for floating fine particles. Interest in this process is increasing because the modern exploitation of minerals makes it necessary to develop new processes, to make mining the poorer ores profitable. In this context, the metallurgical industry needs to have access to this technology to facilitate the processing of finely ground ores. Another interesting application of micro-bubble dispersions is in the treatment of contaminated effluents, a very important environmental activity. Several papers treating the characterization of conventional bubble dispersions have been published, but few have addressed fine and microbubble dispersions; the goal of this paper is to contribute to the knowledge of this subject.
Introducing the effect of a frother to the air dissolution process, it decreases the air diffusion from the gas to the drops of water to be saturated. It is known that a monolayer of frother is adsorbed on the air-water interface. Apparently, this effect is inverse for the gas diffusion in a
bubbling reactor, where the frother decreases the bubble diameters, increasing the bubble surface area of contact. For the case in which the frother reduces the diffusion, two theories explain this fact: the barrier effect and the hydrodynamic effect. In the first case, a barrier of surfactant reduces the diffusion of gas through the interface, while in the second case, the surfactant maintains a thick layer, affecting the mass transfer (Gurol and Nekouinaini, 1985). With lightly turbulent conditions, Libra (1993) observed that oxygen dissolution in water decreases with anionic surfactants. This effect is reduced in turbulent conditions; in which case, the bubble surface area generation is promoted, ameliorat
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