Effect of Dodecane-Oleic Acid Collector Mixture on the Evolution of Wetting Film between Air Bubble and Low-Rank Coal

New Insight into Temperature Effects on Low-Rank Coal Flotation Using Diesel as a Collector

Efficient flotation of low-rank coal is of great significance for the development of green and low-carbon cycles. Temperature is a crucial parameter of flotation, but the mechanism of its effect on flotation lacks understanding. In this paper, the mechanism was studied by kinetic flotation, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy, low-temperature liquid-nitrogen adsorption (LP-N₂A), X-ray photoelectron spectroscopy (XPS), and molecular dynamics simulation. The flotation combustible recovery gradually decreases as temperature rises. Compared with 60 °C, the combustible recovery at 5 °C increases by 18.13%. The desorption energy for oil droplets decreases as the temperature rises. As a result, the oil droplets are easier to desorb at high temperatures. The SEM and LP-N₂A results demonstrate that the pores and fractures of the coal sample are well developed. Also, the oil-water interfacial tension and viscosity of oil droplets decrease as the temperature rises, while the diffusion ability increases. These increase the volume of oil droplets that penetrate into the pores, resulting in poor spreadability of oil droplets on the coal surface. The average volume of bubbles gradually increases as temperature rises, which renders the flotation foam unstable and worsens the flotation. Therefore, the flotation performance is better at low temperatures.

Detachment Force of Air Bubbles Detached from Low-Rank Coal Surface in the Presence of Adsorbed Oleic Acid-Dodecane Collector Mixture

It is well known that mixed collectors can effectively strengthen the flotation of low-rank coal. However, less concern has been paid to the detachment of low-rank coal flotation using mixed collectors. In this study, the force of air bubble detachment from low-rank coal surface treated by oleic acid (OA), dodecane (D), and oleic acid-dodecane (OA-D) collector mixture was investigated using microforce balance. The results showed that the process of bubble detachment from the low-rank coal surface was divided into three stages: relaxation stage, stretching stage, and sliding stage. The equilibrium contact angle and critical contact angle were the transition points between different stages. The order of detachment force required for bubble detachment from the surface of low-rank coal was OA-D > OA > D, indicating a synergistic effect between OA and D. Based on the three parameters of equilibrium contact angle, critical contact angle, and contact line length, a theoretical model was proposed to calculate the detachment force. The calculated results were in agreement with the measured results.