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Nanobubbles are an important means to enhance the flotation of fine refractory minerals. Generally, nanobubbles are preferentially adsorbed on mineral surfaces, which increases the hydrophobicity of the surfaces. For flake graphite ore, nanobubbles coated on graphite surfaces reduce the thickness of the hydrated film on the mineral surface and increase its hydrophobicity. In comparative experiments performed here, short flotation circuits of small flake graphite coated with nanobubbles achieved a 92.81% average fixed carbon grade of graphite concentrate, whereas conventional flotation circuits achieved an average of 88.15%. In addition, the concentrate recovery of short flotation circuits with nanobubbles was higher than that of conventional flotation circuits. This result shows that nanobubbles enhanced graphite particle flotation. Further, in this process, reducing the grinding duration is beneficial to avoid the overgrinding of concentrate, maintain the flake scale size of graphite, and improve the grade of the graphite concentrate. [ABSTRACT FROM AUTHOR]

Coal gasification is a clean and effective method for converting coal into syngas, which is mainly used in fuel and chemical industry. However, the process of coal gasification produces copious amounts of solid waste, that is, coal gasification slag, which is very harmful to the surrounding environment, and then to people's lives and health. The residual carbon is the product of incomplete coal gasification and has high economic utilization value in coal gasification slag. Recovery and utilization of residual carbon is an effective method for the comprehensive treatment of coal gasification slag. This study discusses the current methods of recovering residual carbon from slag, such as the physical, chemical, physicochemical and special separation methods, based on the properties of coal gasification slag, further the advantages and disadvantages of each method are compared. Moreover, the utilization of residual carbon as fuel or for the preparation of materials are discussed in detail. Finally, research and development recommendations for the future study of residual carbon in future are discussed based on existing limitations in the field. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • A combination device of ultrasonic and microbubble generator is developed. • Extraction of carbon by flotation of coal gasification coarse slag. • Ultrasonic can emulsify and disperse the collector agent. • Ultrasonic hydraulic coupled cavitation improves carbon ash separation. Coal gasification coarse slag represents a type of low-value solid waste produced in coal gasification. This study investigated how the pretreatment of the pulp obtained from coal gasification coarse slag affects carbon extraction by flotation. Ultrasonic treatment can promote carbon ash separation. Flotation results revealed that at an ultrasonic action time of 15 min, the ultrasonic power was 90 W and the microbubble generator flow rate was 300 ml/min. Moreover, the best flotation effect was observed under these conditions. Compared with the results obtained for conventional flotation, the concentrate ash content decreased from 36.88 % to 25.51 % and the combustible substance recovery index increased from 79.84 % to 92.91 %. After coupled cavitation treatment, coal gasification coarse slag exhibited a reduced particle size, an increased specific surface area, a smooth and clean surface, a reduced number of surface inorganic elements, an increased number of pores and a remarkable carbon ash separation effect. This study can provide a reference for special methods such as ultrasonic-hydraulic coupling cavitation to strengthen the flotation of coal gasification coarse slag. [ABSTRACT FROM AUTHOR]

In order to investigate bubble size distribution (BSD) in the cyclonic flotation column, a series of tests were conducted to study flow velocity distribution (FVD) and BSD by using the method of particle image velocimetry (PIV). Foaming performance of the n-octyl alcohol is more applicable than both of n-butyl alcohol and terpenic oil. At different circulation volume conditions, BSD range lies in 0–800 μm, and a large number of tiny bubbles (<90 μm) are generated. Besides, the curve presents a normal distribution in 90–180 μm. With the increase in circulation volume, bubble size decreases. BSD determined by cyclonic flow effect plays a crucial role on bubble mineralization with fine particle in cyclonic zone of the flotation column. [ABSTRACT FROM AUTHOR]

The present work has been carried out to investigate the effect of process variables on gas holdup and develop an empirical equation and a neural network model for online process control of the gas holdup based on the operating variables. In this study, the effect of process variables (nozzle diameter, circulation pressure, aeration rate, and frother dosage) on gas holdup in a cyclone-static micro-bubble flotation column of an air/oily wastewater system was investigated. Gas holdup was estimated using a pressure difference method and an empirical equation was proposed to predict gas holdup. A general regression neural network (GRNN) model was also introduced to predict gas holdup for the cyclone-static micro-bubble flotation column. The predictions from the empirical equation and the GRNN are in good agreement with the experiment data for gas holdup, while the GRNN provides higher accuracy and stability compared with that of the empirical equation. [ABSTRACT FROM PUBLISHER]

In order to improve the separation efficiency of fine oil droplets from oily wastewater, a new process utilizing coal adsorption and column flotation has been developed. In this work, anthracite from Jincheng, China was used as an adsorbent for oil removal from wastewater. The effects of adsorption time, coal particle size distribution, the value of pH, and the oil concentration in wastewater on the adsorption capacity of anthracite were investigated by static experiments. A novel device named a cyclone-static microbubble flotation column was developed for the separation of oily wastewater, which combines the conventional hydrocyclone with a conventional flotation column. Coal adsorption-column flotation tests were carried out and scaled-up from a lab-scale (1 m3/day), to a pilot scale (30 m3/day), and to a full-scale (2000 m3/day) unit. Different operating parameters, such as coal dosage, feed rate, circulation pressure, and gas flow rate were studied. In full-scale tests of 2000 m3/day, oil removal of 97.70% with the treated effluent containing an oil concentration of 23.39 mg/L was obtained. [ABSTRACT FROM AUTHOR]

Recovering inner residual carbon is important for fully utilizing coal gasification fine slag (CGFS) resources. In this study, we adopted a combined gravity-separation and flotation process to efficiently recover residual carbon by considering the characteristics of the CGFS and optimizing the operating factors of the process. CGFS is principally a mixture of residual carbon and ash, with low-density particles containing more of the former. Accordingly, residual carbon is preliminarily enriched by gravity separation, in which gas velocity (v g) and water velocity (v w) significantly impact separation efficiency, followed by feed volume (m). The residual carbon in the initial concentrate was preliminarily enriched (i.e., loss on ignition (LOI): 55.90%; combustible recovery (R o): 72.36%) under appropriate operating conditions (i.e., v w = 0.04 m/s, v g = 3 m/s, m = 150 g). Moreover, the quality of the flotation concentrate was most influenced by collector dosage (m c), followed by aeration rate (η), frother dosage (m f), stirring speed (w), and grinding time (t) during flotation of the primary concentrate. The flotation concentrate exhibited LOI and R o values of 90.95% and 50.34%, respectively, under the optimal flotation conditions (i.e., m c = 20 kg/t, m f = 15 kg/t, w = 2600 rad/min, η = 200 L/h, t = 360 s); it has a high residual carbon content and is an ideal raw material for preparing fuels or carbon materials. [Display omitted] • The residual carbon in coal gasification fine slag (CGFS) was enriched. • A combined gravity-separation and flotation process was developed to enrich CGFS. • The operational factors of the combined process were optimized. • Combined process afforded a concentrate with a loss on ignition of 90.95%. [ABSTRACT FROM AUTHOR]

Coal fly ash, which is the solid waste produced during the coal combustion and utilization, causes serious environmental problems. The preparation of concrete from coal fly ash has been proven helpful in potentially improving its value and reducing its environmental impact to a certain extent. However, the presence of unburned carbon components affects the performance of coal fly ash-based concrete. In this study, unburned carbon is separated from coal fly ash by pre-classification and subsequent optimized flotation, wherein the factors influencing are explored. The results show that under the pre-classification function of the inflatable-inclined liquid–solid fluidized bed, the underflow product is enriched in unburned carbon particles, with loss-on-ignition (LOI) and yield (Y o) values of 11.58 % and 72.87 %, respectively. Further, the underflow product is flotated for a cleaner carbon product, which is affected by the stirring rate (W) and the amount of collecting agent (C) and foaming agent (F o). Optimized flotation (i.e., C = 18 kg/t, F o = 6.5 kg/t, W = 1600 rad/min) results in the maximum combustible recovery rate of the flotation concentrate (89.89%), with LOI of 41.80 % and Y o of 18.51 %, yielding unburned carbon products for fuel. After mixing the flotation tailings with the pre-classified overflow production, the LOI of the formed ash-rich product is 1.73% with Y o of 81.49%, prepared into concrete. Thus, the proposed pre-classification and flotation process can improve the quality of coal fly ash. The results provide a theoretical basis for the harmless and resource treatment of coal fly ash. [Display omitted] [ABSTRACT FROM AUTHOR]