Further Investigations on Simultaneous Ultrasonic Coal Flotation

A Review of Ultrasonic Treatment in Mineral Flotation: Mechanism and Recent Development

Ultrasonic treatment has been widely used in the mineral flotation process due to its advantages in terms of operational simplicity, no secondary pollutant formation, and safety. Currently, many studies have reported the effect of ultrasonic treatment on mineral flotation and shown excellent flotation performance. In this review, the ultrasonic mechanisms are classified into three types: the transient cavitation effect, stable cavitation effect, and acoustic radiation force effect. The effect of the main ultrasonic parameters, including ultrasonic power and ultrasonic frequency, on mineral flotation are discussed. This review highlights the uses of the application of ultrasonic treatment in minerals (such as the cleaning effect, ultrasonic corrosion, and desulfuration), flotation agents (such as dispersion and emulsification and change in properties and microstructure of pharmaceutical solution), and slurry (such formation of microbubbles and coalescence). Additionally, this review discusses the challenges and prospects of using ultrasonic approaches for mineral flotation. The findings demonstrate that the application of the ultrasonic effect yields diverse impacts on flotation, thereby enabling the regulation of flotation behavior through various treatment methods to enhance flotation indices and achieve the desired objectives.

A review of sustainable utilization and prospect of coal gasification slag

Currently, the storage of coal gasification slag (CGS) is continuously increasing, as the coal gasification technology develops, posing significant environmental hazards. Due to its volcanic ash characteristics and rich residual carbon, CGS has great potential for resource utilization, which has attracted the attentions of many scholars. This paper firstly introduces the compositions and properties of CGS. Then, it reviews the existing utilization methods of CGS, including Preparation of building materials, carbon-ash separation technology, ecological restoration, and cyclic blending. The advantages and disadvantages of various methods are compared. Subsequently, some high-value utilization methods of coal gasification slag are introduced, such as the preparation of high-performance activated carbon and zeolite, of which the feasibility and advantages are evaluated. Finally, some suggestions are put forward for future developing technologies. This paper aims to provide some references and inspiration for the utilization and environmental protection of CGS.

Effect of Gas Input Conditions and Ultrasound on the Dynamic Behavior of Flotation Bubbles

Ultrasonic flotation is useful for fine low-rank coal purification; however, the efficiency of ultrasonic flotation still needs to be improved. Because the dynamic behavior of flotation bubbles has significant effects on their flotation efficiency, it was investigated under different gas input conditions with and without ultrasound using the volume of fluid method and h-speed imaging. The results indicated that the gas input method can influence the final kinetic behavior of the flotation bubbles by changing the morphology of the initial bubble. With an increase in the size and aspect ratio of the bubble, the bubble deformation and velocity increased, and the range of motion of the bubble increased and then decreased. Meanwhile, the size of the bubble increased with an increase in the thickness of the vibrating plate of the ultrasonic transducer owing to the aggregation of the bubbles under the influence of ultrasound.

Effect of ultrasonic standing waves on flotation bubbles

Ultrasonic flotation was an effective method to float fine coal. In this study, the effects of the standing waves with different frequencies on ultrasonic flotation were investigated. The dynamic processes of bubble and coal-bubble were revealed by a high-speed camera. The results showed that under the action of Bjerknes force, bubble aggregates were formed within 450 ms and coal bubble aggregates were formed within 20 ms. The bubble aggregates were statistically analyzed by image processing method. The number of aggregates and small bubbles in the ultrasonic field at 100 kHz was greater than those at 80 and 120 kHz. Besides, 100 kHz ultrasonic flotation achieved the highest yields of clean coal (35.89%) and combustible recovery (45.77%). The cavitation bubbles acted as either a "medium" or an "inclusion", entrapping and entraining the coal particles in the flotation pulp. It promoted the aggregation of bubbles with coal particles, so the flotation efficiency was effectively improved in the presence of ultrasonic standing waves.

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.

An Improvement on Selective Separation by Applying Ultrasound to Rougher and Re-Cleaner Stages of Copper Flotation

It has been known that the power ultrasound is used as a pretreatment and rarely applied as a simultaneous method to improve grade and recovery during froth flotation processes. This work aimed at investigating the impact of simultaneously used ultrasonic waves under variant operating configurations on the flotation of representative porphyry copper ore during rougher and re-cleaner stages. For this purpose, four different operating outlines were examined as (I) conventional flotation, (II) homogenizer, (III) ultrasonic bath, and (IV) combination of a homogenizer and an ultrasonic bath. The ultrasonic vibration was generated by the homogenizer (21 kHz, 1 kW) in the froth zone and ultrasonic bath (35 kHz, 0.3 kW) in the bulk zone. The rougher and re-cleaner flotation experiments were conducted using Denver-type mechanically agitated cells with 4.2 and 1 L capacities, respectively. The results showed that using the homogenizer (at 0.4 kW) slightly affected the selectivity separation index of chalcopyrite and pyrite, although it positively increased the grade of chalcopyrite from 21.5% to 25.7%. The ultrasonic-assisted flotation experiments with the ultrasonic bath and its combination with the homogenizer (0.4 kW) (i.e., configurations III and IV) led to an increase of approximately 16.1% and 26.9% in the chalcopyrite selectivity index compared to the conventional flotation, respectively. At the cleaning stage, a lower grade of aluminum silicate-based minerals was obtained desirably in every ultrasonic-treated configuration, which was supported with the water recoveries. Finally, applying the homogenizer and its combination with the ultrasonic bath were recommended for re-cleaner and rougher stages, respectively. Further fundamental and practical knowledge gaps required to be studied were highlighted.

A review of effects and applications of ultrasound in mineral flotation

Ultrasound technology is widely applied in the flotation process. From the perspective of the theory of ultrasound, this article explains the effects and applications of ultrasound in the flotation process. To obtain a clear understanding of ultrasonic effects, we observe the phenomena of ultrasound using a high-speed camera and a CCD camera, and investigate potential applications in flotation. From these different phenomena, the ultrasonic effects are classified into three types of effect: the transient cavitation effect, stable cavitation effect, and acoustic radiation force effect. Based on these effects, the applications of ultrasound to mineral flotation are reviewed, including slime coating removal, oxidation film removal, desulfuration, tiny bubble generation, flotation reagent dispersion, and aggregation. In addition, the ultrasonic equipment and treatment methods applied in flotation are classified and compared based on their characteristics. Finally, we propose some potential directions in the study of the stable cavitation effect and acoustic radiation force effect, which are important, but are seldom mentioned in previous reports.

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.

Effect of Heating Oxidation on the Surface/Interface Properties and Floatability of Anthracite Coal

Oxidation processes of coal surfaces are both fundamental and interesting from academic and engineering points of view. In this work, we comprehensively analyzed the mechanism of heating oxidation at 200 °C on the surface/interface characters and the floatability of anthracite coal. The variations of surface/interface characters were studied using SEM (scanning electron microscopy), FTIR (Fourier transform infrared spectroscopy), and XPS (X-ray photoelectron spectroscopy). The floatability was further identified using Induction Time and Bubble-Particle Wrap Angle. It was found that, after heating oxidation at 200 °C, both surface ravines and oxygen-containing groups were increased. The degradation of hydroxyl on anthracite could be neglected during the heating, while the oxidation of hydrocarbon chains dominated the balance of hydrophobicity and hydrophilicity on coal surface. The induction time significantly increased from 200 ms to 1200 ms and 2000 ms after 10 h and 20 h of heating oxidation at 200 °C, respectively. Additionally, raw coal exhibited the fastest kinetics of bubble-particle attachment and the largest wrap angle, directly proving that the floatability decreased after oxidation.

Effect of ultrasound on bubble-particle interaction in quartz-amine flotation system

In this study, the effect of ultrasound (US) on the quartz-amine flotation system was investigated in detail by considering various surface chemistry techniques. The effect of ultrasound on particle size, shape factor, and surface roughness were characterized by using Brunauer-Emmett-Teller (BET) surface area measurements and scanning electron microscopy (SEM) analyses. The contact angle and bubble-particle attachment time, as well as adsorption density measurements was carried out to evaluate the effect of ultrasound on quartz surface wetting ability. In addition, atomic force microscopy (AFM) analyses were conducted, and finally micro-flotation studies were performed. As a result, it was found that the micro-flotation recovery at 2 × 10^-5 M dodecyl amine hydrochloride (DAH) concentration increased from 45.45% to 63.64% with 30 W ultrasonic application at conditioning step. However, the micro-flotation recovery decreased to 37.50% when the ultrasonic power increased to 150 W. The results showed some effect of ultrasound on particle size, particle shape, and surface roughness in some extent. The increase in the contact angle and the decrease in the bubble-particle attachment time were observed. A slightly high adsorption density was measured. All these show a positive effect of ultrasound on quartz flotation with amine as a collector.

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.