Investigation of High-Frequency, High-Intensity Ultrasonics for Size Reduction and Washing of Coal in Aqueous Medium

Optimum Preparation Conditions for Highly Individualized Chitin Nanofibers Using Ultrasonic Generator

α-Chitin derived from crab shells was treated with 30% sodium hydroxide to prepare partially deacetylated chitin with a deacetylation degree of 36%. Partially deacetylated chitin nanofibers were prepared by applying weak ultrasonic energy generated by a domestic ultrasonic cleaner. The deacetylated chitin was easily disintegrated into nanofibers with the aid of electrostatic repulsion and osmotic pressure effect of amino cations on the chitin surfaces. The nanofibers were characterized in terms of yield, morphology, crystallinity, viscosity, and dispersibility. After a series of characterizations, ultrasonication with 45 kHz frequency and 20 min treatment was found to be the optimum conditions for obtaining fine nanofibers with a high yield.

Effect of Power Ultrasound on Wettability and Collector-Less Floatability of Chalcopyrite, Pyrite and Quartz

Numerous studies have addressed the role of ultrasonication on floatability of minerals macroscopically. However, the impact of acoustic waves on the mineral hydrophobicity and its physicochemical aspects were entirely overlooked in the literature. This paper mainly investigates the impact of ultrasonic power and its time on the wettability and floatability of chalcopyrite, pyrite and quartz. For this purpose, contact angle and collectorless microflotation tests were implemented on the ultrasonic-pretreated and non-treated chalcopyrite, pyrite and quartz minerals. The ultrasonic process was carried out by a probe-type ultrasound (Sonopuls, 20 kHz and 60 W) at various ultrasonication time (0.5–30 min) and power (0–180 W) while the dissolved oxygen (DO), liquid temperature, conductivity (CD) and pH were continuously monitored. Comparative assessment of wettabilities in the presence of a constant low-powered (60 W) acoustic pre-treatment uncovered that surface of all three minerals became relatively hydrophilic. Meanwhile, increasing sonication intensity enhanced their hydrophilicities to some extent except for quartz at the highest power-level. This was mainly related to generation of hydroxyl radicals, iron-deficient chalcopyrite and elemental sulfur (for chalcopyrite), formation of OH and H radicals together with H2O2 (for pyrite) and creation of SiOH (silanol) groups and hydrogen bond with water dipoles (for quartz). Finally, it was also found that increasing sonication time led to enhancement of liquid temperature and conductivity but diminished pH and degree of dissolved oxygen, which indirectly influenced the mineral wettabilities and floatabilities. Although quartz and pyrite ultrasound-treated micro-flotation recoveries were lower than that of conventional ones, an optimum power-level of 60–90 W was identified for maximizing chalcopyrite recovery.

Effects of Ultrasound on Desliming Prior to Feldspar Flotation

In this study, the effects of ultrasound on removal of impurities from raw feldspar were investigated by testing with a newly developed flotation cell with various frequency and power intensities prior to multistage feldspar flotation. Particularly, the quality of feldspar concentrates, the volume of removed slimes and the content of impurities were taken into account to reveal the impacts. Two representative feldspar ore samples taken from the Milas-Mugla region in Turkey were separately tested for desliming and flotation by conventional and ultrasonic methods under similar conditions and the results were compared to each other in terms of the quantity and the quality of the removed slimes and the final feldspar flotation concentrate. As a result, during desliming stage by using ultrasound, the volume of removed slimes was reduced by approximately 45% when compared to the conventional slime removal methods. Moreover, the impurity contents were doubled inside slimes when ultrasound was used. These outcomes lead to significant success in terms of reducing losses during the desliming stage and production of high quality feldspar concentrates by froth flotation assisted by ultrasound.

Enhancement of flaky graphite cleaning by ultrasonic treatment

In this study, the aim is to simplify the graphite cleaning process. In order to achieve flotation for graphite effectively, ultrasonic treatment was used as a pre-treatment technique. Flotation tests were conducted using different ultrasound power and ultrasonic treatment time. The influences of ultrasonic treatment on particle sizes, morphologies, wettability, the content of surface elements and on the flotation effect of flaky graphite were investigated. The results of ultrasonic treatment for graphite flotation were compared with the results of conventional flotation. The results showed that ultrasonic treatment not only changed the size of flaky graphite, but also eliminated impurities on the graphite surface. Additionally, the ultrasonic treatment improved the hydrophobicity of graphite. It was observed that ultrasound can remove not only silicate impurities but also most other metal impurities. The yield, carbon content and recovery of flotation concentrate were 91.46%, 95.17% and 96.12% after ultrasonic treatment for 4 min with ultrasound power 1600 W, which were 5.83%, 2.86% and 8.84% higher than that of conventional flotation, respectively. The graphite after ultrasonic treatment was conducted only one times flotation, the carbon content in concentrate products had reached 95%. This study indicates that intensifying graphite flotation by ultrasonic treatment can shorten the graphite cleaning process.

Influence of ultrasound pre-treatment on ilmenite surface chemical properties and collectors' adsorption behaviour

In this study, we used flotation tests, Fourier transform infrared spectroscopy (FTIR), zeta potential, X-ray photoelectron spectroscopy (XPS), and microcalorimetry measurements to investigate the flotation and possible adsorption mechanisms of the ilmenite surface before and after ultrasonic pre-treatment. Flotation results show that under optimum conditions, the promotion effect of sonication on ilmenite is remarkable. The maximum recovery is 89.54% for ultrasonicated ilmenite at a pH of 4-5. For pH of 8-9, recovery increased again to 66.34%. Microcalorimetry indicates that the adsorption-driven heat release (-Q_ads) is higher for ultrasonicated ilmenite than for raw one. After pre-treatment, the iso-electric point (IEP) changed from pH 6.2 to pH 4.2. FTIR spectra and zeta potential measurements indicated that metal ions as active sites on the ilmenite surface are probably changed by the ultrasonic treatment. XPS analysis shows that ultrasonic treatment can promotes the oxidation of Fe²⁺ to Fe³⁺ and improves the solubilization of Ca²⁺ and Mg²⁺ in the pH range of 4-5. Under weakly alkaline condition, ultrasound also can make Ca²⁺ and Mg²⁺ re-absorb onto the ilmenite surface as main active sites.

Ultrasonic-assisted flotation for enhancing the recovery of flaky graphite from low-grade graphite ore

The feasibility of low-frequency ultrasound in enhancing the flotability of flaky graphite from low-grade graphite ore was investigated in this present study. This study involves a fundamental understanding of ultrasonic-assisted graphite flotation process and its relative comparison with the conventional flotation process. The flotation experiments were conducted in three stages viz., rougher, cleaner, re-cleaner stage during both convention and ultrasonic-assisted flotation. It was found that the efficiency of ultrasonic-assisted flotation was significantly higher than conventional flotation. The yield, fixed carbon content and percentage recovery of the flotation concentrate products increased significantly under ultrasonic-assisted flotation. Furthermore, the ultrasonic mechanism and its effect responsible for the breakage of graphite-impurities locked particles and particle size reduction were also discussed comprehensively. The raw graphite (RG) and final flotation concentrate products of conventional and ultrasonic-assisted flotation process were characterized by Stereomicroscope, X-Ray Diffraction, Field Emission Scanning Electron Microscope and Raman Spectroscopy to understand the graphite liberation properties, mineralogical properties, surface properties and microcrystalline properties, respectively.

Ultrasonic-assisted coal beneficiation: A review

Limited availability and large industrial demands of high-grade coals have forced many coal-dependent industries to shift their preference towards low-grade coals to meet the feedstock requirements. The low-grade coals due to their poor washability nature do not respond efficiently toward existing coal beneficiation techniques, making the cleaning process challenging. Inefficient cleaning of such coals could potentially lead to environmental problems such as solid waste generation and gaseous emissions during combustion. Therefore, it is important to upgrade the existing coal beneficiation techniques for improving the clean coal quality, and simultaneously enhance the efficiency of the process. In the past few decades, many techniques have been developed to improve existing coal beneficiation techniques. Among them, ultrasound technology has gained significant attention due to its ability to enhance the process performance. The incorporation of ultrasound can significantly increase the clean coal yield under the substantial effect of cavitation and streaming. In this paper, an overview on the recent development in ultrasonic-based coal beneficiation techniques and the role of ultrasound in improving the efficiency of various coal beneficiation techniques are discussed. This includes a critical review of the ultrasound mechanism in enhancing coal demineralization, desulphurization, grindability, slurryability and dewatering.

Effective removal of sulfur components from Brazilian power-coals by ultrasonication (40kHz) in presence of H2O2

The present investigation reports a preliminary attempt of using ultrasonic energy (40kHz) to clean some low rank high sulfur Brazilian power-coal samples in presence of H2O2 solution. All types of sulfur components (i.e. pyritic, sulfate and organic) could be removed from the coal samples by this process. The raw and ultrasonicated coal samples were characterized by chemical analysis, Fourier Transformation Infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), focused ion beam (FIB), high-resolution transmission electron microscope (HR-TEM) with selected area electron diffraction (SAED) and/or microbeam diffraction (MBD), scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectrometer (EDS), and Thermogravimetry (TG-DTG) techniques to evaluate the clean-coal quality. The FT-IR spectroscopic analysis demonstrated the formation of oxidized sulfur species (SO and -SO2) and their subsequent removals after ultrasonication. The XRD profiles supported the presence of mineral matters in the coals. The TG-DTG profiles of the beneficiated coals revealed their improved quality for using in thermal plants with better combustion efficiency.