An investigation of nanobubble enhanced flotation for fly ash decarbonization

Abstract

Froth flotation is often employed to remove unburned carbon in the fly ash produced as a coal combustion by-product before it can be utilized in the cement or similar industries. However, with the deterioration of coal quality and environmental regulations getting stricter, fly ash has become increasingly more difficult to be purified by the flotation process and the limitations of traditional flotation techniques have become more obvious for ultrafine particles such as fly ash. Nanobubbles have proven effective in enhancing the flotation performance with fine and ultrafine particles. In this study the effect of nanobubbles on fly ash flotation decarbonization and underlying mechanisms have been investigated with a flotation column under various experimental conditions using a Chinese fly ash sample. The results have demonstrated that nanobubbles are able to significantly improve the efficiency of decarbonization of fly ash flotation. Typically the use of nanobubbles increased the recovery of unburnt carbon by 3–15 % and reduced the fly ash LOI by 0.2 %–3.5 %. It has also been shown that nanobubble flotation reduced the required dosages of frother and collector by approximately one half. New mechanisms of nanobubbles improving fly ash decarbonization flotation performance were explored from the perspectives of bubble-particle interactions and solution surface tensions.