Foam growth dynamics in the presence of a rising bubble plume: Effect of surfactant concentration and gas superficial velocity

• Effect of surfactant concentration and gas superficial velocity on foam stability studied. • Bubble size distributions and transient variations in foam heights quantified. • Foam dynamics governed by bubble sizes inherently linked to surfactant chemistry. • Foam equilibrium height, time, foaminess parameter, and half-life quantified. • Better foam stability attained at higher surfactant concentration and lower gas velocity. This study investigates foam formation dynamics in the presence of a rising bubble plume which has significant importance in mineral flotation process. Three surfactant systems − anionic (SDS), cationic (CTAB), and a CTAB-NaCl mixture were used to quantify the foam growth behaviour for different surfactant concentrations and gas superficial velocities (u g ). High-speed imaging was used to measure the bubble size distribution and foam heights. The chemistry of the surfactant systems significantly influenced bubble sizes in the bulk affecting the foam growth behaviour. SDS systems produced smaller bubbles in the bulk compared to the CTAB systems which led to relatively spherical shape and polygonal bubbles in the bulk and foam, respectively. Foam stability was characterised using several parameters – equilibrium foam height, equilibrium time, foamability and foam half-life. In general, enhanced foam stability was observed when surfactant and electrolyte concentration was high, and gas superficial velocity was low up to a system specific threshold.