Abstract
Froth flotation is a process in which hydrophobic particles attach to bubbles forming particle–bubble aggregates, which are transported to the top section of the cell where they overflow to form the concentrate. Particles also reach the concentrate by entrainment, which is a non-selective process that leads to low concentrate grades. The objective of this work was to study and compare the degree of entrainment measured using three methods, in fresh and seawater, and using methyl isobutyl carbinol (MIBC) and DF-250 as frothers. The experimental results indicated that the degree of entrainment decreased in seawater. Besides, water recovery was lower in the experiments with seawater regardless of the frother that was used in the experiments, which correlated with the observed low degrees of entrainment. It is proposed that the reduction of entrainment and water recovery in seawater can be explained by a reduction of air recovery and/or more bubble coalescence in the froth. It is also proposed that surfactant diffusion/convection from the lamellae to the Plateau borders in the froth is reduced in seawater, which reduces the surface tension gradients, and thus the restoring liquid flow from the Plateau borders to the lamellae.
Highlights
Froth flotation is a widely used concentration process that is driven by the differences in the surface properties of valuable and gangue particles
Previous studies showed that the differences in surface activity between polypropylene properties of the frothers used in flotation and their interaction with the ions dissolved in the aqueous glycols (e.g., DF-250) and methyl isobutyl carbinol (MIBC) become more important in NaCl electrolyte solutions, and that finer bubbles are generated in seawater [33]
The experimental results indicate that the absolute values of entrainment measured fluctuate, the relative trends obtained under different experimental conditions allow reaching certain experimental conclusions regarding the effect of seawater on the degree of entrainment in the flotation process
Summary
Froth flotation is a widely used concentration process that is driven by the differences in the surface properties of valuable and gangue particles. Hydrophobic particles attach to ascending bubbles forming particle-bubble aggregates, which are transported to the top section of the cell to form the concentrate. The mechanism by which particles report to the concentrate attached to bubbles is referred to as “true flotation”, but there are particles that, irrespective of their surface properties (hydrophobicity/hydrophilicity), are pushed up by the swarm of ascending bubbles, which is called entrainment. The recovery of mineral particles by entrainment is a non-selective process as both hydrophobic and hydrophilic particles have chances of being recovered, which negatively affects the effective separation of valuable and gangue particles and reduces concentrate grades [1]. To understand the phenomena that drive entrainment in flotation, it is necessary to analyze the physical phenomena that explain the variations of the flow of water that overflows the flotation cell and is carried into concentrate
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