Enhanced lignite flotation using interfacial nanobubbles based on temperature difference method

Abstract

Froth flotation is the primary method for the separation and upgrading of fine coal particles. However, this method is ineffective for lignite which is more hydrophilic than other types of coal due to the abundant oxygenated functional groups, cracks, and micropores on its surface. This study develops a new method that introduces interfacial nanobubbles (INBs) based on the temperature difference method for enhancing lignite flotation. The mechanism of lignite flotation enhanced by INBs is systematically explained through the induction time and bubble-particle collision-attachment behavior. The experimental results show that the lignite flotation efficiency is evidently improved using the temperature difference method. AFM imaging of the changes on a highly oriented pyrolytic graphite surface due to temperature difference demonstrate the production of INBs. In the presence of INBs, the induction time of lignite can be reduced from 400 ms to 27.21 ms, the number of bubble-particle collisions from 4 to 3, and the attachment time from 208 ms to 128 ms. When a macroscopic air bubble approaches to a lignite surface with INBs, the air bubble first merges with the INBs, not only decreasing the induction time but also increasing the apparent contact angle and length of three-phase contact line.