Recent advances in fundamentals and applications of nanobubble enhanced froth flotation: A review

Nanobubbles are tiny in size but huge in importance for many scientific fields and applications in biology, agriculture, medicine, environment and engineering. Literature on nanobubble science and applications has skyrocketed in recent years and a comprehensive review of nanobubble-related literature is beyond the scope of this paper. This review article is dedicated to the nanobubble science and applications associated with froth flotation, which is the separation process most widely used in mineral processing and wastewater treatment, with the emphasis on the literature published in the most recent five years. Fundamental aspects of bulk and surface nanobubbles regarding their generation, characterization, and stability are described and different theories and research results are analyzed with critical comments. Unique nanobubble properties of the greatest importance to flotation, including microscopic contact angle, size and shape, number density, surface charge and tension, etc. and their controlling factors are discussed in correlation to flotation performance indicators such as recovery, grade, and reagent consumption. A systematic description of widely recognized nanobubble enhancement mechanisms for fine particle flotation is provided based on up-to-date research results. Finally, recent applications of nanobubbles to flotation separation of typical coal and mineral particles are summarized and future nanobubble research needs in fundamental understanding and commercial development are suggested.