Effect of Nanobubbles on the Flotation Performance of Oxidized Coal

Abstract

In this study, the effects of air bubbles and nanobubbles on flotation performance and kinetics of oxidized coal were investigated. The surface properties of the coal sample before and after oxidation were characterized by a scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). The nanobubbles on highly oriented pyrolytic graphite (HOPG) were observed by an atomic force microscope (AFM). The interaction between coal and conventional bubbles in the absence and presence of nanobubbles was explained by induction time. Flotation results showed that oxidized coal flotation in the presence of nanobubbles resulted in 10% higher combustible matter recovery than conventional air bubble flotation. Moreover, it was found that the flotation of oxidized coal in the absence and presence of nanobubbles can be best described using the first-order model with the rectangular model. AFM images analysis showed that a large number of nanobubbles were produced and attached to the oxidized coal surface. The induction times of the oxidized coal in the absence and presence of nanobubbles were 1000 and 39 ms, respectively, indicating that the existence of nanobubbles effectively promotes the interaction between oxidized coal and macroair bubbles. In addition, the agglomeration between oxidized coal particles also occurred spontaneously in the presence of nanobubbles, which was helpful in improving the combustible matter recovery and flotation rate of oxidized coal.

Nanobubble-Assisted Flotation of Apatite Tailings: Insights on Beneficiation Options

“…The fact that the curves for NB, NBC, and NBF were always above the conventional bubbles’ curves indicated the improved flotation k . This is consistent with the findings reported in the literature where nanobubbles result in an increased flotation rate constant. − From the classical first-order model used (eq ), the correlation coefficients, R 2 , were 0.9958, 0.9989, 0.9853, and 0.9988 for CB, NB, NBC, and NBF, respectively for the −850 μm samples. Whilst the −106 μm samples had R 2 values of 0.9925, 0.9968, 0.9879, and 0.9818 for CB, NB, NBC, and NBF, respectively.…”

“…Studies have been conducted to assess the influence of bubble sizes generated in various hydrodynamic cavitation systems. ,, Additionally, liquid properties have been addressed, namely, temperature, surfactant type, and dosage. Through the NB generation, an increase in the surfactant concentration has been found to reduce bubble sizes and improve their stability. − The change in surface tension explains this as the liquid’s surface tension decreases, and the bubbles formed become finer. , Many NB flotation studies reported improving flotation recoveries, grades, and kinetics and even reduced reagent consumption. ,− In a recent study, Pourkarimi et al indicated that generation of NBs in the presence of selective collectors could significantly increase the flotation efficiency of fine phosphate ore samples. Surprisingly, surface analyses of flotation concentrates indicated that the amounts of flotation collectors adsorbed onto the surface of floated particles were lower in the presence of NBs than in their absence.…”

From Microbubbles to Nanobubbles: Effect on Flotation

“…The zeta-potential value depends on the production time-as shown in Figure 7-and a decrease (as an absolute value) with the processing time was found to increase; in this work bulk nanobubbles with oxygen and air were generated in water by counterflow hydrodynamic cavitation. The effects of air bubbles and nanobubbles on flotation performance and kinetics of oxidized coal were studied [72]. It was found that surface nanobubbles were present on highly oriented pyrolytic graphite surface; coal agglomeration occurred in the presence of nanobubbles, indicated by the shear thinning of coal slurry [64,73].…”

“…The effects of air bubbles and nanobubbles on flotation performance and kinetics of oxidized coal were studied [72]. It was found that surface nanobubbles were present on highly oriented pyrolytic graphite surface; coal agglomeration occurred in the presence of nanobubbles, indicated by the shear thinning of coal slurry [64,73].…”

Effective Separation of High-Ash Fine Coal Using Water Containing Positively Charged Nanobubbles and Polyaluminum Chloride

“…Compared to the flotation using tap water, the use of NBs alone increased the overall combustible recovery from a baseline of 54.2–67.1% in NB water. The beneficial effect of NBs on coal flotation has been widely acknowledged in the literature. − However, after adding PAC to NB water, the ability of NBs to enhance coal flotation was compromised, as suggested by the relatively lower cumulative combustible recoveries in the group of NB water + PAC. A similar decline in combustible recovery using NB water after PAC addition has previously been reported by Li et al, who attributed it to the reduced surface hydrophobicity of coal in the presence of PAC.…”