Salt effect on gas dispersion in flotation column – Bubble size as a function of turbulent intensity

Abstract

The present work investigates the role of chloride salts on bubble coalescence properties by average bubble diameter measurement. The tested chloride salts (NaCl, MgCl2 and CaCl2) were dissolved in fresh running water and used as feeding of a three-meter high pilot flotation column. The column was operated in close circuit while the superficial gas rate (Jg) was varied. Gas holdup in the collection zone of the column was measured using pressure sensors. Drift flux model is employed to obtain the mean bubble diameter between two pressure-tapping points. The change of cations of chloride salts has an indisputable effect on bubble coalescence; hence the bubble size in the column varies as a function of chloride salt type. The hydrodynamics factors on bubble coalescence and difference in inhibition behavior of monovalent (NaCl) and divalent cations (CaCl2 and MgCl2) based on the partition of the different hydrated ions at the gas-liquid interface were highlighted. The characterisation of the liquid phase used for flotation separation should not only focus on the concentration of salts but also on the ion-water, ion-ion and water-water properties as a function of hydrodynamic condition.