Foam fractionation or ion flotation is a process by which surfactant molecules together with counter-ions are adsorbed onto the gas-liquid interface of rising bubbles within the column. This process results in a foam product known as foamate that is high in surfactant concentration. High extraction rates require a high air injection rate. However, high air injection rates lead to a high rate of concomitant liquid within the foam which results in a relatively low concentration of surfactant in the foamate. Therefore the volume reduction, given by the ratio of the feed flux to foamate flux, should tend to decrease to unsatisfactory levels as the air injection rate increases. Using drift flux theory, an elementary model describing the variation of surfactant recovery with the ratio of the feed to gas flux was developed for a conventional ion flotation system. Incorporated into this model is a simple power law relation for the superficial liquid drainage flux through the foam established by dimensional analysis. Experiments were conducted using a fixed feed to gas flux ratio, the aim being to produce a reasonably constant surfactant recovery. The performance of the process was then assessed in terms of the variation in the volume reduction with the gas flux. The model was found to be consistent with the experimental data. The findings also demonstrated the need to limit the gas flux and hence the feed flux to relatively low values in order to produce satisfactory volume reductions and hence concentration upgrades.
Chemeca2008. Chemeca2008: Towards a Sustainable Australasia (Newcastle, N.S.W. 28 September - 1 October, 2008)