Technical NoteUse of frother with sampling-for-imaging bubble sizing technique
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.
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Associate Professor, School of Mining Engineering, University of Tehran: on sabbatical at McGill University.