Elsevier

Minerals Engineering

Volume 22, Issue 5, April 2009, Pages 513-515
Minerals Engineering

Technical Note
Use of frother with sampling-for-imaging bubble sizing technique

https://doi.org/10.1016/j.mineng.2008.11.004Get rights and content

Abstract

Measurement of bubble size in industrial flotation cells is now often accomplished using the sampling-for-imaging technique. Operation calls for frother in the viewing chamber. In this communication the impact of frother concentration in the chamber is examined. A concentration in excess of the system CCC (critical coalescence concentration) is recommended for field work.

Introduction

Sampling-for-imaging techniques are becoming widely used for sizing bubbles in industrial flotation systems. They employ a sampling tube to collect and direct bubbles to a viewing chamber. The recommended protocol is to add frother to the water in the sampling/viewer assembly (chamber) to limit coalescence (Chen et al., 2001, Hernandez-Aguilar et al., 2002, Grau and Heiskanen, 2002). For situations where frother concentration in the flotation cell is known (usually a laboratory environment) the same concentration is used in the chamber. In industrial situations cell concentration is usually not known. No detail on how much to add in those cases was given, which is the subject of this communication.

Experimentation calls for changing frother concentration in the chamber independent of that in the flotation cell. As water is expelled from the chamber as bubbles accumulate a large volume cell is required. We used a 0.8 m3 cell (on loan from Metso Minerals) as even discharging all the chamber water (ca. 5 L) into the cell (ca. 700 L) would not materially change the cell concentration.

Section snippets

Apparatus and methods

A sketch of the set-up is shown in Fig. 1. We used a McGill bubble size analyzer (MBSA)

Results

Fig. 2, Fig. 3 give results for cell concentration 5.2 ppm (CCC85). As chamber concentration was increased the Sauter mean (Fig. 2) decreased from nearly 1.6 mm at zero frother to a minimum size ca. 1.14 mm above ca. 2–4 ppm. The evolution of the bubble size distribution (Fig. 3) shows a pronounced bi-modality at 0.8 ppm chamber concentration which evolves towards a single mode at 12.8 ppm. The presence of both large and fine bubbles at chamber concentrations <2 ppm indicates coalescence/breakage

Discussion

The observations emphasize the need to add frother to the chamber when using the sampling-for-imaging bubble sizing technique. For plant work, where the volume of flotation cell is large and the frother concentration is usually unknown, the recommendation is to use excess frother in the chamber water, above the CCC for the system. The work here shows this does not introduce error. In typical lab-scale cells the chamber concentration cannot be independently manipulated without contaminating the

Conclusion

In the sampling-for-imaging technique for bubble sizing, tested here using the McGill bubble size analyzer, it is recommended for plant work to use excess frother in the chamber, above the CCC for the system.

Acknowledgements

Funding for this work is under the Chair in Mineral Processing co-sponsored by Vale Inco, Teck Cominco, Xstrata Process Support, Agnico-Eagle, Shell Canada, Barrick Gold, SGS Lakefield Research, COREM and Flottec under the Collaborative Research and Development program of NSERC (Natural Sciences and Engineering Research Council of Canada) and through the AMIRA International P9N project also under the Collaborative Research and Development program of NSERC.

References (13)

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Associate Professor, School of Mining Engineering, University of Tehran: on sabbatical at McGill University.

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