A review of bulk nanobubbles and their roles in flotation of fine particles

Abstract

The decreasing size of minerals that need to be separated with flotation technique has posed a rigorous challenge to conventional flotation techniques. It's urgent for the researchers working in the field of minerals processing to develop a kind of new, efficient but economic flotation technique. In the past dozens of years, a mass of reports regarding the application of bulk nanobubbles in flotation has been emerging and the positive effect of bulk nanobubbles has been widely verified by the flotation performance of various minerals. The rapid and brilliant progresses made in this field and the huge potential of application in minerals processing motivated the present work. In this work, we reviewed various techniques to produce bulk nanobubbles and the widely used measurement techniques for bulk nanobubbles and analyzed the disadvantages of them. These measurement techniques fail to identify the real identification of nanoentities, which have resulted in debates about the real identification of the observed nanoentities. Then, we reviewed the methods as in detail as possible that were proposed by many researchers to identify the identification of nanoentities, which should help close the relevant debate. Next, considering it that flotation is usually performed in such a liquid environment with complex physical and chemical properties (pH, salt, surfactant, ultrasonication et al.), we reviewed the responses of bulk nanobubbles to external stimuli including the factors described above. Only the bulk nanobubbles keep stable all the time during a flotation process does it make sense to employ bulk nanobubbles for flotation. In the last section, we reviewed the underlying mechanism of how the flotation performance was improved in the presence of bulk nanobubbles. The aim of this review is to provide researchers who are working in the area of mineral processing with rough information about nanobubbles from the field of interface physics and shed some light on developing new techniques for fine particle separation.