Ultrasonic standing waves on flotation bubbles

With the increase in coal mining volume and mining mechanization,the yield of low rank coal slime and its ash content increase,which result in some environmental problems and that large amount of low rank coal slime is difficult to be recycled.Ultrasonic flotation is a method that combines various adjustments,which can improve the flotation selectivity and recovery of coal washed.In this study,the processes of bubble aggregation and coal-bubble aggregation were revealed by a high-speed camera system.The processes of generation,effect and selection of microbubble were explored.Combined with the column flotation results and selective exploration of micro bubble in standing wave field,the effects of the 100 kHz standing wave ultrasound on flotation column was investigated and the influence of the standing wave in the column flotation process was analyzed.The results showed that the clean coal yield (21.93%),combustible recovery (30.52%) and flotation improvement index (23.77%) of ultrasonic column flotation were higher than conventional column flotation.The ash content of clean coal was lower than that of conventional column flotation.The bubbles in the standing wave field gathered regularly.After a few times,the bubble aggregates distributed in the whole standing wave field as stripes.This process was the biggest difference between standing wave ultrasound and diffusion ultrasound.The energy generated by ultrasonic standing waves improved the attachment efficiency between fine particles and microbubbles.The microbubbles acted as a “medium” between fine particles and other bubbles to promote their coalescence and form aggregates at a very short time.These coal-bubble aggregates had a favorable effect on flotation.