Combining Positron Emission Particle Tracking and image analysis to interpret particle motion in froths

Previous research into particle motion in the froth zone has focussed on constructing detailed CFD models that describe the behaviour of particle classes with different properties; density, size and hydrophobicity. These models have been reasonably successful in predicting trends in the separation behaviour and how it can be manipulated. Models of separation sub-processes cannot readily be verified experimentally due to the opacity and fragility of froth systems.Positron Emission Particle Tracking (PEPT) can be applied to particles in froth flotation systems to observe the behaviour of individual particles in a mixed particle–liquid–gas system. However, measuring the particle position alone is not adequate as its behaviour is also affected by instantaneous froth events such as bubble coalescence. To link the observed particle behaviour to the froth behaviour requires multi-modal measurements. Video footage of a rising foam column was recorded simultaneously with PEPT data, so that the PEPT tracer trajectory could be explained in terms of foam structure and events. A time weighting function of cubic splines with kernel width 200 ms was used to remove the effects of signal noise. An ascending 70 μm hydrophilic tracer accelerated within vertical Plateau borders and decelerated in Plateau borders angled away from vertical. The tracer trajectory showed velocity peaks and troughs when it was contained in nodes in a rising foam. When the tracer descended within a foam showing convective roll, coalescence events and subsequent foam deformation directly influenced the tracer trajectory.