New basis for measuring the size distribution of bubbles

Abstract

The use of air bubbles of varying size distribution in ore and wastewater treatment, including conventional (froth) and dissolved air flotation (DAF), Jameson flotation cell and Microcel (among others), has attracted much interest recently. These flotation processes are governed by the physical characteristics of the bubbles as well as the particles, and therefore it is necessary to investigate accurately the size distribution of bubbles that are generated. A new method was developed to measure the bubble size distribution based on the bubbles’ capture (without movement) combining microscopy with digital image processing procedures. The technique (LTM-BSizer) employs a sampler to draw bubbles, rising in a column, into a special viewing chamber and exposes them to a digital camera after they have decelerated and stopped. Thus common problems related to the movement of bubbles, namely focus, illumination, photographic speed and bubbles overlapping are all overcome. Results obtained are in good correlation with some values reported with the traditional image analysis method and show that using this technique accurate size distributions can be produced conveniently and efficiently. The influence of some operational parameters on the formation of bubbles was studied. It is believed that the bubble size measurement technique developed in this study will assist understanding and improvement of the DAF and conventional fines and ultrafines mineral flotation, from both theoretical and practical viewpoints.