Evaluation of the selective detachment process in froth flotation

Froth flotation is a process that separates particles based on their differences in physical and surface chemistry properties. For fine material that is comprised of particles having wide degrees of floatability, selectivity is based on differences in the flotation rates between particles targeted for recovery in the froth concentrate and those needed to report to the underflow stream. However, selectivity between particles of varying floatability can be significantly enhanced in the froth zone through a reflux mechanism that circulates detached particles back to the collection zone. Selectivity in the detachment process based on the strength of the bubble-particle attachment may also improve separation efficiency.; In this investigation, froth zone and overall flotation recovery values were quantified for particles in an anthracite coal that were characterized as having wide differences in floatability potential. As a result, operating a flotation column to achieve a separation based on only the collection zone flotation rate differences resulted in a relatively high product ash content of 25.64%. By increasing the feed mass flow rate to take the advantage of the added selectivity provided by the internal refluxing and selective detachment, the product ash content was lowered to 19.22%.; A fundamental analysis using well known models describing the froth flotation process revealed that selective detachment in the froth zone provided significant performance improvements under feed mass flux rates near the carrying capacity limit. As the feed mass flux exceeds the carrying capacity limit, differences in the detachment rates between the various components decrease.; Based on the selectivity of the detachment process, a novel concept was conceived which involves the addition of particles having a greater degree of hydrophobicity directly into the froth zone. The hypothesis was that the enhanced competition for limited bubble surface area would increase the detachment rate of more weakly hydrophobic particles, which are high in ash content. After removal of the particles added in the froth, the enriched froth phase reduced the product ash content by 5 absolute percentage points while maintaining the same level coal recovery and enhancing separation efficiency by 4.7 absolute percentage points. This concept has direct commercial application potential.