Predicting gas hold-up in flotation columns from the physical characteristics of rigid spargers

Abstract

Rigid spargers are attracting renewed interest in some applications of flotation columns, such as deinking of recycled paper, deoiling of water and the recovery of metallic ions from hydrometallurgical solutions. The main factors to be taken into consideration in the selection of a sparger are the characteristics of the sparger (material and geometry), the nature of the pulp to be processed (e.g. per cent solids and presence of surfactants) and the dimensions of the column. Lacking so far has been a method of estimating bubble size or gas hold-up (or bubble surface-area flux) for a given combination of sparger, column and pulp, which must account for the formation of a bubble swarm at the sparger and the rise of the swarm against a countercurrent flow of pulp or water. The method now proposed predicts gas hold-up by combining two models: one for bubble formation at the sparger, which relates bubble size to sparger and pulp characteristics; and the second for bubble flow, which relates bubble size to gas hold-up and phase hydrodynamics. Application of the method is illustrated for a set of porous, stainless-steel spargers installed in a column that was run with water and frother.

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