Oily bubble formation induced by N-octane and N-octanoic acid compound collector and its effect on low-rank coal flotation

Oily bubble flotation is a proven efficient method for low-rank coal (LRC) separation. The application of multi-component oils in oily bubble flotation is a novel method that may favor oily bubble formation and LRC flotation. In this study, N-octane (NO) and N-octanoic acid (NOA) were applied as the oils, and they were mixed as the compound collector (CC). Oily bubble formation is investigated from the liquid film-thinning and spreading perspectives. Using the Stefan-Reynolds drainage model, the water-film drainage dynamics is accelerated by CC oils for high zeta potential and low repulsive electrostatic force. When oils spread on the air bubble surface, the spreading coefficients and spreading velocity are influenced by the viscosity and interfacial tension properties of oil. The NO component reduces the viscosity of CC and promotes the spreading velocity. The NOA component reduces the interfacial tension of CC and increases the spreading coefficient. It is found that CC of NO and NOA at a mass ratio 8:2 can achieve satisfying flotation results. Oily bubble flotation can achieve much higher clean coal yields and slightly higher ash content. The oily bubble flotation behavior is well justified by the formation mechanism of the oily bubble.