Bubble size, gas holdup and bubble velocity profile of some alcohols and commercial frothers

Frothers are used in flotation to reduce bubble size and as a consequence increase gas holdup. For 1-alcohols, C 4 to C 7, and three commercial frothers, MIBC, DF250 and F150, it is shown that at equivalent Sauter mean bubble size gas holdup depends on frother type. The paper explains the gas holdup result by showing the effect of frother type on single bubble rise velocity profile, i.e., local velocity vs. distance (up to 350 cm). For example, a 1.45 mm bubble in 0.4 mmol/L pentanol hardly slows relative to water only while in 0.4 mmol/L hexanol it reaches minimum velocity. This corresponds to the higher gas holdup in 1-hexanol compared to 1-pentanol. To compare frothers we introduce velocity at 300 cm vs. concentration and the concentration to reach minimum velocity, CMV. The CMV illustrates the strong frother effect: for example, CMV for the alcohols decreases by about one order of magnitude for every 1 C increase in chain length. The decrease in CMV with frother type correlates with the increase in gas holdup. It is shown that all frothers tested follow the same minimum velocity-size trend modeled reasonably by the relationship proposed by Karamanev for terminal velocity. (C) 2013 Elsevier B.V. All rights reserved.