Holdup Profile and Bubble Size Distribution of Flotation Column Froths

Abstract

Wash water is added at the top of flotation columns to eliminate fine hydrophilic particle recovery. It helps create a deep packed bubble bed (loosely termed “froth”) with a well defined froth/pulp interface. Common industrial practice is to maintain a constant froth depth (about 1–2 m) by regulating the wash water addition rate. This practice is being examined through a systematic study of the froth zone.

A two-dimensional Plexiglass column was used with a two-phase (gas-liquid) froth. Gas holdup and bubble size distribution through the froth were measured as a function of gas rate, water rate and frother dosage. Wash water dramatically increased froth stability and depth. Gas holdup increased with increasing height above the interface; the rate of increase is highest close to the interface. The liquid holdup at the top of the froth column was found to increase significantly with increasing gas or wash water flowrate, and increasing frother concentration.

Mathematical models are developed to describe liquid entrainment and drainage throughout the froth.