Selective separation of very fine particles at a planar air–water interface

A continuous‐flow surface flotation cell for the separation of scanty mineral samples based on wettability contrast

“…These effects were seen during every test to varying degrees, but they were most apparent for the sample feed composed of 80% graphite, for which graphite particles tended to prominently stick to the walls of the column, resulting in 69% of the graphite and 39% of the quartz being recovered in the overflow of the cell. For large graphite proportions, the wall effects have also been accentuated by the zeta potential of graphite that favours the formation of graphite particle agglomerates, [ 12 ] thus preventing a significant proportion of hydrophobic particles from colliding with bubbles and being recovered in the overflow. The important recovery of quartz in the overflow could in turn be explained by the presence of these graphite agglomerates acting as obstacles in the restricted MFC.…”

“…Diao and Fuerstenau [ 17 ] proved from a free energy variation analysis that even for coarser particles (up to 425 μm) the variation of the interface energy was more than 80% of the system. Tran et al, [ 12 ] however, stated that, for their tested grain size, the main active force for a solid at a liquid surface was the capillary force in a system also composed of the buoyancy and the gravity. The capillary force takes into account the surface tension of the liquid and the contact angle of the solid surface, allowing the particles to float or sink depending on their degree of hydrophobicity.…”

“…The surface flotation cell built and used for this study, shown in Figure 2, is an adaptation of the concept presented by Tran et al [ 12 ] to which modifications were made to allow the use of particles larger than 53 μm. As shown in Figure 3, the system is composed of four zones: a buffer zone, a deposit zone, a sinking zone to recover the wetted particles, and a spillway zone to gather the hydrophobic particles.…”

“…[ 6,9,11 ] The main weakness of the methodology usually resides in the small amount of material that can be used, as the experiment normally consists of sprinkled particles at the surface of a liquid in a small container where the mass has to be restrained to avoid particles overlapping. To remediate this limitation, Tran et al [ 12 ] have elaborated a continuous‐flow surface flotation system, allowing more mass to be handled and enabling a scale‐up of the process. Their stated goal was to scale up to industrial size in order to increase recovery of fine particles in coal flotation, but the concept showed itself to be intriguing as a screening and analytical tool at the laboratory scale.…”

“…From this starting point, the present work aimed to develop a new continuous surface flotation cell, inspired by Tran et al, [ 12 ] to analyze and compare the separation behaviour and efficiency of the concept in comparison with the established laboratory methodologies of micro‐flotation and Denver cell flotation, and assess its potential going forward as a precise and reliable tool for the determination of particle hydrophobicity on limited sample mass in different conditions.…”