Bulk micro-nano-bubbles (BMNBs) have been proven to be effective at improving the flotation recovery and kinetics of fine-grained minerals. However, there is currently no research reported on the correlation between the properties of BMNBs and flotation performance. For this purpose, aqueous dispersions with diverse properties were created by altering preparation time (0, 1, 2, 3, 5, and 7 min), aeration rate (0, 0.5, 1, 1.5, and 2 L/min) and aging time (0, 0.5, 1, and >3 min). Micro- and nano-bubbles were characterized using focused beam reflection measurements (FBRM) and nanoparticle tracking analysis (NTA), respectively. The micro-flotation of quartz particles was performed using an XFG-cell in the presence and absence of BMNBs with Cetyltrimethylammonium bromide (CTAB) as a collector. The characterization of bubble sizes showed that the bulk micro-bubble (BMB) and bulk nanobubble (BNB) diameters ranged from 1–10 μm and 50–400 nm, respectively. It was found that the preparation parameters and aging time considerably affected the number of generated bubbles. When BNBs and BMBs coexisted, the recovery of fine quartz particles significantly improved (about 7%), while in the presence of only BNBs the promotion of flotation recovery was not significant (2%). This was mainly related to the aggregate via bridging, which was an advantage for quartz flotation. In comparison, no aggregates were detected when only nano-bubbles were present in the bulk solution.

Conventional hydrocarbon oil cannot adhere effectively to oxidized coal, resulting in a low yield of clean coal. In this study, a high-speed homogenizer was used to emulsify LDD (laurylamine dipropylene diamine) and kerosene, which enhanced the flotation efficiency of oxidized coal. The flotation results showed an increase from 4.12% (only kerosene) to 23.33% (emulsified oil). An increase in contact angle indicated that the mixture reagent can increase the hydrophobicity of coal particles, which is attributed to the adsorption of LDD onto the coal particle surface and the decrease of the oil droplet A lower surface tension of LDD allows it to produce a stable layer of froth than the layer generated by kerosene alone.

The flotation method is widely used for the preliminary beneficiation of aphanitic (microcrystalline) graphite. However, there is limited literature regarding the effects of flotation reagents on the flotation kinetics of aphanitic graphite. In this study, six commonly used flotation kinetic models were used to fit the flotation experimental data of aphanitic graphite. The classical first-order model was found to be most suitable for describing flotation kinetics of aphanitic graphite. The modified flotation rate constant (K_m) was then applied to evaluate the effects of collector, frother, and inhibitor on aphanitic graphite flotation kinetics. Compared to diesel oil and terpineol oil, kerosene and 2-octanol produced a greater K_m. The highest K_m was obtained at an inhibitor dosage of 15 mg/L.

In this study, we investigated the effect of the scrubbing medium’s particle size distribution on the scrubbing flotation performance of microcrystalline graphite. A simplex lattice mixture design approach using Design-Expert software was employed for proportioning testing of the scrubbing media. Three different sizes of scrubbing medium (A: 1 mm, B: 2 mm, and C: 3 mm) were mixed to obtain different particle size distributions. The results showed that a linear mixture model was suitable for fitting this mixture design, and the particle size distribution of the scrubbing medium was 3 mm. Hence, we studied the effect of scrubbing time on the flotation performance of the scrubbing flotation process. The flotation results indicated that graphite quality was enhanced by increasing the scrubbing time, and the optimum scrubbing time for this graphite was 45 min when maximum enrichment efficiency was acquired. Also, we investigated the effect of the scrubbing medium’s particle size compositions on gangue entrainment in the scrubbing flotation process. It was concluded that the degree of entrainment under the composition of scrubbing size 1 mm (16.67%), 2 mm (16.67%), and 3 mm (66.66%) was reduced compared to the other two compositions (scrubbing size 2 mm (50%) and 3 mm (50%) as well as scrubbing size 3 mm (100%)). This conclusion was proved using analyses of froth bubble size and scanning electron microscopy and energy dispersive x-ray spectroscopy (SEM-EDS).

Inherent limitation of the mechanical flotation cell is the entrainment of hydrophilic particles (gangue) in the water reporting to the froth. In this study, a combine column and cell flotation process was proposed to reduce the entrainment of gangue particles and, ultimately, ash content of coal flotation concentrate in Datun coal preparation plant, Peixian County, Jiangsu, China. The froth collected from the third and fourth cells of the 4-cell flotation machines in this plant was further re-cleaned to obtain qualified clean coal. Laboratory-scale results show that both the mechanical flotation machine and flotation column as re-cleaning flotation devices could produce the clean coal with qualified ash content. However, the yield obtained by the flotation column (84.49%) is significantly higher than that obtained by the mechanical flotation cell (68.21%). Industry-scale tests indicate the combined column and cell flotation process could produce qualified clean coal and run stably.