| Frothers are surface-active agents used in flotation to decrease bubble size and promote froth stability. The common frothers are alcohols and polyglycols. One means to classify frothers is by the extent of bubble size reduction. Bubble size measurement is labour-intensive and this thesis explores the use of gas holdup as a surrogate for bubble size.;Nine frothers with different chemical structures were tested in a bubble column equipped with instrumentation to measure bubble size and gas holdup. A correlation between frother structure and gas holdup is observed: for alcohols, gas holdup increases with hydrocarbon chain length and whether branched or straight chain does not seem to matter; and for polyglycols, gas holdup increases with number of propoxy groups. The ranking of the frother on the basis of gas holdup is the same as that given by other methods. The assumed unique relationship between gas holdup and bubble size is examined. For a given frother the relationship appears to hold. Evidence is presented that the continued increase in gas holdup at high frother concentration is correlated with a continued decrease in bubble size. When comparing frothers, however, it is shown that for equal gas holdup bubble size can be quite different. The effect is discussed in terms of bubble velocity in the swarm. |
