Enhancing flotation selectivity via ultrasonic treatment on the froth: foam characteristics and underlying mechanisms

In flotation, improving selectivity is crucial to reduce concentrate ash content and achieve clean coal utilization; however, nonselective entrainment of fine gangue frequently degrades separation performance. This work innovatively applies ultrasound to the froth to investigate the flotation performance, foam characteristics, and the underlying mechanism of ultrasound-enhanced flotation selectivity. The results show that the introduction of ultrasound into the froth significantly reduces the concentrate ash. Under the optimal ultrasonic parameters (30 kHz, 100% power), the concentrate ash decreases from 17.55% to 12.22%, and the flotation selectivity index increases from 3.43 to 4.75. Ultrasound induces bubble shape oscillations, and the squeezing effect of bubble surface waves accelerates drainage within Plateau borders and promotes bubble coalescence. This significantly weakens foam stability and enables fine gangue minerals to drain out alongside liquid flow in plateau borders, thereby improving flotation selectivity. Under ultrasound, the flotation selectivity index is negatively correlated with the foam time constant and positively correlated with the relative foam decay rate. Notably, flotation selectivity index under 30 kHz ultrasound exhibits the highest sensitivity to variations in foam characteristics. As a physical regulation method, applying ultrasound to the flotation froth is environmentally friendly and non-disruptive to pulp mineralization, thereby offering a novel approach for green and efficient flotation selectivity enhancement.