The detachment of coarse, composite particles from bubbles

Abstract

The detachment of model coarse, hydrophobic composite particles from bubbles was investigated using an electro-acoustic apparatus. Coarse composite particles with both simple and complex locking textures over a range of liberation classes were synthesized using quartz and lead borate. Quartz particles only were used for the model homogeneously hydrophobic (ie fully liberated) particles. The effect of surface heterogeneity, ie the hydrophobic domain surface exposure and distribution, on the mean detachment force was investigated in water ( = 0.9 mPa.s) and in glycerol-water mixture, the latter providing a high viscosity medium ( = 7.6 mPa.s). The results show that the detachment force for particles with simple locking texture was lower compared to particles with complex locking texture for a similar liberation class. This was possibly due to the attachment of the bubble to less hydrophobic lead borate domains in some detachment tests. In the case of particleswith complex locking texture the bubble may attach to several hydrophobic domains. Thus, attachment may result in more stable particle-bubble aggregates for the case of complex locking texture. The detachment force for simple locking texture particles was independentof the media viscosity. For particles with fully liberated and complex locking textures, the detachment force was higher in the glycerolwater mixture, i.e., the bubble-particle aggregates were more stable in high viscosity medium. It is hypothesised that the detachment process is governed by the velocity of movement of the three phase contact line, which, in high viscosity media, is dampened, leading to enhanced stability of the bubbleparticle aggregate.