Foaming and gas dispersion properties of non-ionic frothers in the presence of hydrophobized submicron particles

• Sub-micron particles tended to increase the gas holdup by preventing bubble coalescence.
• The combination particle–surfactant was important in determining the foaminess of solutions.
• Polyglycols showed some increase in foaminess whereas no improvements were found in alcohol.
• Sub-micron particles strongly improved the structure of the foam phase.

Foams represent an important area of research due to their relevance in many industrial processes. In many systems, particulates and surfactants co-exist and can largely define the stability of the foam. A typical example is froth flotation where hydrophobic particles and frothers are essential to maintain a stable froth. Grinding operations may yield a product containing submicron-size particles, which can affect the flotation process. The present study compares the foaming and gas dispersion properties of the non-ionic surfactants 1-pentanol, tri(propylene glycol) methyl ether, and poly(propylene glycol) 425 in the presence of hydrophobic colloidal silica particles in a column. In all cases, it has been found that the gas holdup increases proportionally with the increase in the concentration of particles in the system although an initial decrease may be observed. The effect of particles on the foaminess seems to be dependent upon the surfactant. With the 1-pentanol, the addition of particles systematically decreased the foaminess of the solutions. This is in contrast to poly(propylene glycol) solutions, which exhibited an increase. Interestingly, low concentrations of particles appeared to improve the foaminess of tri(propylene glycol) methyl ether; however, the froth became less stable with further increases in the number of particles in the column. Visual observation showed that the colloidal particles play a crucial role in defining the quality of the structure of the froth.