This study was conducted to investigate the mechanisms of enhanced microfine flake graphite (MFG) flotation by nanobubbles generated based on the principle of hydrodynamic cavitation. The effects of nanobubbles on graphite surface properties were characterized in terms of the flotation kinetics, collector adsorption behavior, Zeta potential, IR spectra, contact angle, etc. The results show that the surface nanobubbles increased the hydrophobic attraction and reduced the electrostatic repulsion between the graphite particles and collector molecules, significantly improving the flotation selectivity and the kinetic flotation rate and promoting the agglomeration of MFG.

Effects of nanobubbles on fine coal column flotation and underlying mechanisms have been investigated under different operating parameters including frother dosage, collector dosage, feed flow rate, air flow rate and wash water flow rate with a Chinese sub-bituminous coal sample. Experimental results show that the use of nanobubbles significantly improved the column flotation efficiency with fine coal particles. The collector dosage was reduced by almost one half in the presence of nanobubbles as a result of nanobubbles playing a role as a secondary collector and a similar reduction in the frother dosage was observed due to distinctly different mechanisms of nanobubble generation as compared to traditional bubble formation methods. Nanobubbles generated based on the hydrodynamic cavitation mechanism also reduced required air dosage and improved carrying capacity. The aggregation effect of fine coal particles caused by the preferential formation of nanobubbles on the surface of hydrophobic coal particles in the flotation system improves the rate of mineralization of bubbles. The flotation efficiency enhancement by nanobubbles is a result of multiple benefits to flotation processes brought by nanobubbles that form directly on the surface of coal particles.

The enhanced gravity concentrator with water medium has been used for the low-rank coal maceral enrichment and achieved a favorable effect. This study utilized the magnetite powder as the separation medium in the enhanced gravity separation test. The enhanced gravity separation with different medium was contrasted, the heavy medium separation possessed a more excellent separation mechanism and better effect, and the vitrinite content and recovery of concentrates was increased to 80.40 vol.% and 54.85%. In addition, the results of float–sink test and enhanced gravity separation with heavy medium were compared under the same separation density, the difference of vitrinite content and between the two methods was below 5%, and the vitrinite recovery of enhanced gravity separation was increased to 77.9% with the separation medium of 1.40 g/cm³. The density difference of macerals was proved by the EDS and XRD measurement, the more quantity of polycondensation aromatic rings and tighter microcrystalline structure leads to the higher density of inertinite.

The coupling between ferroelectricity and ion conductivity always presents unique physical and chemical properties, making it crucial to understand their correlation for the development of advanced functional devices. CuInP2S6 (CIPS), a van der Waals “ferroionic” material, serves as an excellent platform to investigate their intercoupling. In this study, we observe a bipolar diode-like rectification behavior in a vertical Pt/CIPS/In capacitor by controlling the migration of Cu ions. The non-uniform distribution of mobile Cu ions is coupled with ferroelectricity, resulting in a switchable imprint field and an enhanced saturation polarization about 12 μC/cm2 in CIPS. Additionally, CIPS exhibits a significant photovoltaic response due to its robust built-in electric field caused by the unbalanced distribution of Cu ions. This work demonstrates a controllable Cu ions migration and its manipulation on the electrical transport and ferroelectricity in CIPS. The dynamically tunable bipolar diode effect, closely coupled with ferroelectricity in CIPS, has promising prospects in self-powered photodetectors, memristors, and neuromorphic computing.

Traditional flotation bubbles with large in size and small in specific surface area have low mineralization efficiency for fine particles in flotation, which makes it difficult to recover ultra-fine particles. Nanobubble flotation and traditional flotation of ultra-fine graphite (UFG) were studied in the study. The effects of nanobubble flotation and conventional flotation on UFG were stated by laser particle size analyzer, optical microscope and flotation kinetics test. The results show that the hydrophobic aggregates of UFG in nanobubble flotation system show floc morphology, increase the average size of hydrophobic aggregates by 17.31 µm, and effectively recover finer graphite particles compared with traditional flotation. In addition, the minimum particle size of nanobubble flotation concentrate (NFC) is 1 µm, while the traditional flotation concentrate (TFC) is about 18 µm, nanobubble flotation enhances recovery effect of UFG. More importantly, nanobubble flotation not only significantly improves the flotation rate of UFG but also increases the grade and recovery of UFG.

In this study, the rotary triboelectrification separation technology is applied to the separation of macerals for low rank coal, which has not been studied by previous researchers. The effects of air humidity and temperature on permittivity and specific-charge were tested to ensure that vitrinite and inertinite were effectively separated under obvious electrical differences. The best separation index of macerals was determined by single factor test, including airflow rate, feed rate, friction wheel speed, and plate voltage. The test results of specific-charge and permittivity showed that the difference is most reasonable when the air humidity is 20% and the temperature is 40°C. Single factor test showed that the optimal conditions are the feed rate of 1.5 g/s, the friction wheel speed of 3000 r/min, the plate voltage of 20 kV and the air flow rate of 6 m/s. Finally, this study obtained the best maceral separation indexes are vitrinite content of 72.03 vol%, vitrinite recovery of 67.86% and benefication ratio of 1.33. Comparison with other maceral separation technologies, the rotary triboelectrification technology is a clean dry and economical process technology, it has inherent advantages in the separation of macerals for low rank coal.