Coalescence and froth collapse in the presence of fatty acid

Abstract

Bubble coalescence and froth collapse occurred during carbonate/silicate separation tests in a flotation column using a commercial fatty acid. To study this a method of quantifying coalescence is developed using the change in gas holdup in the collection (pulp) zone of the flotation column and the calculated change in bubble diameter. Fatty acid (mainly oleic acid), in 3:1 ratio with lannagol emulsifier, caused significant coalescence. For example, 10 ppm of fatty acid added to 20 ppm of TEB (1,1,3-triethoxybutane), a frother, caused a 55% decrease in gas holdup (corresponding to a 50% increase in bubble diameter) and collapsed the froth completely. Higher concentrations of lannagol stabilized the froth, but failed to prevent bubble coalescence. Solids in the presence of sodium silicate, a dispersant, further enhanced coalescence and froth collapse. It is observed that there was no simple relationship between coalescence and froth collapse as a persistent froth could be maintained even with high coalescence. A mechanism of coalescence is proposed based on hydrophobic coating of the bubble causing water drainage.