New insights into the role of positively charged CO2 nanobubbles in enhancing the flotation of cryptocrystalline graphite

An effective method for enhancing the flotation of cryptocrystalline graphite using positively charged CO 2 nanobubbles (NBs) based on electrostatic driving and NB bridging is proposed, targeting the difficult to float characteristics of cryptocrystalline graphite such as fine particle size, strong electronegativity, and low probability of bubble-particle collision and attachment. The effects of circulation time, gas flow rate and solution pH on the charging properties and size of CO 2 NBs were systematically investigated, and positively charged CO 2 NBs with an average size of approximately 280 nm and a zeta potential of about 13 mV were successfully prepared using a micro-nano bubble generator based on the circulating countercurrent and multiphase vortex gas-liquid shearing technology. Compared with the results of conventional flotation, introducing positively charged CO 2 NBs into the pulp could significantly improve the flotation efficiency of cryptocrystalline graphite. In addition, CO 2 NB flotation could also reduce the amount of kerosene by 58.3 % under the condition of similar separation indicators. The interaction mechanism of positively charged CO 2 NBs enhancing the flotation of cryptocrystalline graphite was elucidated through particle surface electrical properties analysis, flotation kinetics analysis, and particle agglomeration behavior analysis. It was found that positively charged CO 2 NBs mainly promoted particle agglomeration by weakening electrostatic repulsion and strengthening hydrophobic attraction, thereby increasing the apparent particle size and improving the collision efficiency between particles and macro-sized bubbles. Meanwhile, the attachment between particles and macro-sized bubbles was further strengthened based on NB bridging, thus improving the flotation efficiency of cryptocrystalline graphite. This research is of great significance to improve the flotation efficiency of cryptocrystalline graphite and facilitate the application of positively charged micro-nano bubble flotation technology in the field of fine mineral resource separation.