Etude experimentale des parametres de mise a l'echelle de colonnes de flottation.

摘要

This thesis presents the results of an investigation on three parameters of the flotation column scale-up: the particle residence time, the flotation rate constant and the carrying capacity. The determination procedure, their modeling and the affecting factors, were systematically studied based on the understanding of gas and bubble properties inside the column.; First, an evaluation procedure for particle residence time determination was implemented; then, its value was used for the rate constant estimation, to replace the standard approach of using the nominal or liquid residence time. This was made possible by implementing the on-line measurement of gas hold-up and the particle size determination by laser-based analysis of column product samples.; A new experimental method was developed for the determination of the flotation rate constant, whereby the particle residence time is modified by varying the sparger position in the column instead of changing the tailings flow rate as in the standard method. Experimental results show that more precise rate constant values are obtained with the new method as a result of overcoming the drawbacks of the standard method, such as changes in column hydro-dynamics, which affect the collision and attachment process between particles and bubbles.; The experimental study of the carrying capacity determination method, permitted finding that feed solid density (valuable mineral grade), gas rate, collection zone height and froth height have all a remarkable effect on the carrying capacity value as a result of changes in gas properties and concentrate particle size observed in the column experiments. These results clearly demonstrate the necessity of a “standard” column for the carrying capacity determination in which the fixed height and diameter are appropriately set.; A linear relationship between each of the two scale-up parameters (rate constant and carrying capacity) and the bubble surface area flux S_b was found from the experimental results. These findings allow the calcination of a “true” floatability (considering both bubble and particle concentration). To permit the calculation of this true rate constant, the S_b value should first be experimentally measured. Its use for a more realistic scale-up of flotation columns is obvious.