Stability of bubble-particle hetero-coagulates accessed by atomic force microscopy to understand the froth flotation of agglomerating hydrophobic fines

Abstract

The key microprocesses, which determine the efficiency in froth flotation are the formation and breakage of particle-bubble hetero-coagulates. Agglomeration can be used to increase the recovery of fine particles < 20 µm. Here the stability of hetero-coagulates consisting of agglomerates and gas bubble determines the process performance. Therefore, the stability of agglomerate-bubble hetero-coagulates was accessed by atomic force microscopy (AFM) on particle-laden gas bubbles, agglomerates and pristine gas bubbles without particles in the interface. The force and work of adhesion from AFM measurements were compared to the detaching force and the detaching energy that act on agglomerate-bubble and particle-bubble hetero-coagulates under turbulent conditions, similar to those in a flotation cell. This comparison provides the maximum size of agglomerates and single particles that can remain attached to the gas bubbles at a given energy dissipation rate. The results suggest that the size of agglomerates attached to gas bubbles can grow beyond the Kolmogorov length, which limits the size of agglomerates under turbulent conditions. The findings are supported by in-line probe images of agglomerate-bubble hetero-coagulates that were captured in an aerated stirred tank under turbulent conditions. It was further shown that the particle detachment from particle-laden bubbles is governed by the deformation of the underlying gas bubble and the local particle coverage.