Maximum gas and bubble surface rates in flotation columns

Abstract

Maximum gas rates have been reported in flotation columns. Part of the explanation lies in the properties of the gas-water system. Three phenomena are identified which can define a maximum gas rate: loss of bubbly flow, loss of interface and loss of positive bias. Theoretical estimates and experimental measurements of each are reported. As gas rate was increased, the first phenomenon encountered was loss of positive bias followed by loss of bubbly flow and loss of interface at approximately the same gas rate. As frother dosage increased (i.e. bubble size decreased), the maximum gas rates all decreased; however, the corresponding maximum bubble surface area rate remained approximately independent of bubble size. A drift flux model was applied for the theoretical estimates. Model predictions were in general agreement with the measurements. Loss of bubbly flow was the most difficult to define (theoretically and experimentally); loss of positive bias was the most difficult to predict as the model required parameters which were difficult to estimate.