Estimation of Rate Constants and Mixing Characteristics in Flotation Columns

Chul-Hyun Park

doi:10.3390/app112110084

Abstract

The effect of mixing in a flotation column has long been recognized as an important factor in determining the performance of flotation. The paper presents the effects of mixing on the rate constant in a flotation column, and the establishment of relationships based on vessel dispersion numbers (Nd) that can describe axial dispersion. The rate constants were evaluated using models of plug flow, fully mixed tanks, and axial mixing for a coal cleaning operation. Results showed that fine particles are similar between each model; however, for coarse particles, the deviation is large in the case of perfect mixing, while axial mixing is suitable. It reveals the suitability of using an axial dispersion model for estimating the rate constants, particularly for coarser particles. A regression equation to determine the flotation rate constant was also developed with Nd values between 0.2 to 0.5. The ratio of particles to liquid the residence times time (τp/τL) decreases with particle size from small sizes to coarser sizes. Axial dispersion is increased by the superficial gas velocity while is suppressed by the wash water. The relationship between calculated and observed Nd can be used with a 94% accuracy for the coal cleaning application within the range of operating conditions of superficial gas velocity (0.7–1.6 cm/s), superficial wash water velocity (0.1–0.4 cm/s), and Hc/dc (26.8–32.7). The empirical relationship of Nd with significant variables along with the aspect ratio of the column was found to be applicable for coal beneficiation. It may be useful in terms of design and scale up of the columns.

Highlights

Froth flotation exploits the differences in surface hydrophobicity of the different constituent minerals selectively separates the valuable minerals from gangue by attaching them to air bubbles and recovering them from the mineral laden froth [1,2,3,4]
The trend trend is as expected in flotation cells, in that the recovery is maximal in the range
30–100 is as expected in flotation cells, in that the recovery is maximal in the range 30–100 μm μm and decreases for fine larger particles

Summary

Introduction

Froth flotation exploits the differences in surface hydrophobicity of the different constituent minerals selectively separates the valuable minerals from gangue by attaching them to air bubbles and recovering them from the mineral laden froth [1,2,3,4]. Column flotation has found applicability in the mineral industry owing to its effectiveness in processing fine particles, in cleaning operations where gangue entrainment is reduced [7]. The flotation process requires the hydrophobic particles to collide with air bubbles and subsequent bubble–particle attachment to occur for effective separation [9]. The degree of mixing is relatively high as they process particle sizes that are coarser than those treated in flotation columns. Continuous conventional cells are modelled as fully mixed reactors while batch operations are treated as plug-flow reactors consistent with the residence time of particles being equal [9,10]. The mixing characteristics have been considered to be between that of fully mixed tanks and plug-flow reactors

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Discussion

Conclusion