Development of a laboratory-scale flotation column with inlet bubble size measurement

Abstract

This paper presents the development of a small-scale (1 in.) laboratory flotation column with online measurement of bubble size. In contrast to the systems that use sampling-for-image techniques and have the viewing chamber located at the top of the flotation device, the system employed here measures the bubble size via image analysis using a bubble size analyzer located at the bottom of the column using a well-referenced sloped viewing chamber. The main advantage of this configuration is that it allowed the measurement and monitoring of the bubble size during flotation experiments (three-phase system). This was possible because the sizes of the bubbles were determined before they entered the column; moreover, the “cloudy effect” caused by fine particles in the bubble viewing chamber was minimized owing to the use of an expansion chamber (named the bubble injection chamber). The image capture, processing, and analysis were automated, which rendered it possible to determine the bubble size distribution and mean bubble size (D32) of consecutive images every 5 s using a simple image analysis procedure. Two-phase experiments conducted to evaluate the system showed that the mean bubble size (D32) and gas holdup were within the ranges found in the literature. As expected, the holdup was dependent on the bubble size, which was strongly dependent on the frother concentration. Finally, some exploratory experiments were conducted to test the apparatus in a three-phase system. Recovery-particle size curves for different bubble sizes showed that mass recovery increases as the mean bubble size decreases, and the coarser the particles, the greater is the effect of the bubble size on the recovery.