Effect of some operational variables on bubble size in a pilot-scale mechanical flotation machine

Abstract

This work aims to provide a relationship of how the key operational variables of frother type and impeller speed affect the size of bubble (D₃₂). The study was performed using pilot-scale equipment (0.8 m³) that is up to two orders of magnitude larger than equipment used for studies performed to date by others, and incorporated the key process variables of frother type and impeller speed. The results show that each frother family exhibits a unique CCC95-HLB relationship dependent on n (number of C-atoms in alkyl group) and m (number of propylene oxide group). Empirical models were developed to predict CCC95 from HLB associated with other two parameters α and β. The impeller speed-bubble size tests show that D₃₂ is unaffected by increased impeller tip speed across the range of 4.6 to 9.2 m/s (representing the industrial operating range), although D₃₂ starts to increase below 4.6 m/s. The finding is valid for both coalescing and non-coalescing conditions. The results suggest that the bubble size and bubble size distribution (BSD) being created do not change with increasing impeller speed in the quiescent zone of the flotation.

Keywords

flotation / bubble size / operational variables / critical coalescence concentration / hydrophile-lipophile balance / impeller speed

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