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With the deepening of mineral extraction, the quantity of fine–particle minerals is on the rise. The issue of low separation efficiency is increasingly prominent, thereby driving the advancement of new separation equipment. The compound force field separation equipment integrates two or more force fields, including gravity, centrifugal, magnetic, electrostatic, and interfacial forces, offering a promising approach for the high–efficiency separation of fine particles. This paper summarizes compound force field separation equipment in four categories: enhanced gravity separators, gravity & magnetic separators, gravity & flotation separators, and magnetic & flotation separators, focusing on their structure, operation principle, numerical simulation and application effect. These separators take into account a variety of physical and surface properties of mineral particles and strengthen the separation effect of fine particles. The research of these equipment has become one of the future trends, among which computer simulations bring convenience to optimize the equipment structure, and is an effective means to study the flow field of the equipment as well as the particle motion. [ABSTRACT FROM AUTHOR]

To address the challenging issue of achieving high-precision carbon-ash separation in coal gasification fine slag, magnetic separation and flotation techniques were employed to study their respective separation effect. Optimization tests were conducted to determine the optimal magnetic field gradient and magnetic field intensity, and the ash content of magnetic separation concentrates was 72.18%, with a reduction of 7.28% compared to the sample. Additionally, the magnetic separation tailings exhibited an ash content of 93.99%. Through flotation tests, the optimum conditions for kerosene and composite collector was established. The ash content of flotation concentrates decreased by 16.39% compared to the sample, and the ash content of flotation tailings was 95.83%. A comparative analysis revealed that the combined separation process outperforms single separation methods in reducing the ash content of the concentrates, and realize the further quality improvement and separation effect. Detailed analysis of magnetic characteristics and XRD, XPS analysis studies on the sample and the products, indicated that the magnetic separation effectively pre-removes a certain amount of magnetic high ash minerals. Furthermore, the collector treatment significantly increased hydrophobicity difference between residual carbon and ash matter, which ultimately enhancing the flotation effect. [ABSTRACT FROM AUTHOR]

In order to solve problems of subjectivity, hysteresis and extensiveness existed in reagent amount addition of coal slime flotation in coal preparation plant depended on manual intervention, a coal slime flotation foam image classification method based on semi-supervised clustering was proposed. Firstly, coal slime flotation foam images under known reagent-addition ratio and unknown reagent-addition ratio are collected, and the foam images are preprocessed to extract morphological characteristics such as bubble number, bubble area and bubble perimeter. Then, foam image morphological characteristic samples under known reagent-addition ratio are marked, while foam image morphological characteristic samples under unknown reagent-addition ratio are not marked, and the marked foam image morphological characteristic samples and the unmarked foam image morphological characteristic samples are mixed. Finally, semi-supervised clustering method based on Gaussian mixture model is used to cluster the mixed samples, so as to get various clusters, and information of the marked foam image morphological characteristic samples is mapped to the unmarked foam image morphological characteristic samples in various clusters. The application results show that the method can provide guidance for adjustment of reagent-addition amount in coal slime flotation production process, reduce consumption of reagent, and improve flotation automation level and economic benefit of coal preparation plant.

In the process of coal preparation, large particles are often misplaced into the flotation feedings due to poor classification, and thus bring about negative effects on flotation results. In this paper, batch flotation tests of 0.5–2.5 mm were carried out at different reagent dosage to quantitatively analyze the effect of particle size and density on flotation. Flotation partition curves in corresponding conditions were plotted based on sizing analysis and float-and-sink tests of flotation products. Generalized skew-normal distribution model based on quartile was used to fit the experimental data and the variation rules of separation density, probable error and skewness, etc. with particle size and reagents were obtained, and the density-size partition surface mathematical model was established. The results show that floating ratio decreases with density and particle size. The separation density and probable error both decreases with particle size. The values of skewness were negative and tended to 0 with the decreasing of particle size. As the dosage of reagents increased, the separation density increased, the probable error increased slightly, and the difference of absolute values of skewness decreased. The research results put forward the theoretical instruction of expanding the upper limit of floatable size of particles and improving flotation efficiency. [ABSTRACT FROM AUTHOR]

In view of problems of poor accuracy and high medium consumption of manual control of shunt in dense-medium separation process , an automatic shunt control system in dense-medium separation process was designed, and opening prediction model of the shunt valve based on the least squares support vector machines was established. The parameters including suspension density, coal slime content, qualified medium tank level and opening degree of water supply valve are collected by sensors, which are used as input variables of opening prediction model of the shunt valve. Output value of opening degree of the shunt valve is calculated by the model and then is sent to PLC, so as to control operation of the shunt valve and realize automatic shunt control. The application results show that the density fluctuation of suspension liquid can be controlled in the range of ±0.005 g/cm3, and the ton coal dense-medium consumption is reduced by 0.216 kg.

In view of the similarity between the partition curve of coal preparation and the cumulative curve of distribution function, the quartile of random distribution is often used to describe the characteristics of partition curve, the median being the separation density, quartile deviation being the probable error, quartile measure of skewness reflecting the asymmetry of the partition curve. With the help of the properties of linear interpolation and distribution function, a generalized skew-normal distribution model of partition curves based on quartile and other auxiliary parameters was built which have four or five parameters including separation density, probable error and quartile skew coefficient and so on. The introduced auxiliary parameters have a good correction to the tail of the curve. The model shows very good fitness for the partition coefficient data. [ABSTRACT FROM AUTHOR]

Nonpolar oils such as kerosene and diesel oil are common collectors in coal flotation. Surfactants are usually added to the pulp to emulsify the oil collectors. The present study used dodecane as the oil collector and anionic sodium dodecyl sulfonate (SDS) and nonionic tetraethylene glycol monododecyl ether (C12EO) with different headgroups and identical chain alkyls to investigate the effect of the surfactant headgroups on oil‐in‐water emulsion droplet formation. The morphology and stability of dodecane emulsions were determined experimentally. Density functional theory (DFT) and molecular dynamics (MD) simulations were used to explain the microscopic mechanism. The results of DFT indicated a larger interaction between SDS and the water molecules than that between C12EO and water molecules. The results obtained by MD suggested that the SDS headgroup exhibited a loose arrangement and a relatively large gap size, thereby weakening the interaction between SDS and water molecules at the dodecane/water interface. In contrast, the headgroups of C12EO were bent and interwoven with others to form a tight reticulation at the interface. According to the simulation results, the ability of the surfactant to form dodecane‐in‐water emulsion droplets depends on the arrangement of the surfactants at the oil–water interface rather than on the interaction strength between the headgroups of the surfactants and water molecules. The presented microscopic mechanism of the surfactant headgroup formation of oil‐in‐water emulsion droplets offers surfactant selection and design references. [ABSTRACT FROM AUTHOR]

Froth flotation, a prevalent technique for the separation of fine materials, is employed in the decarburization process of coal gasification fine slag (CGFS). This process is known to consume significant quantities of reagents. This study investigates the pronounced variance in collector consumption during the flotation decarbonization of two distinct CGFS samples, where a tenfold difference was observed when the tailings ash content surpassed 95%. A comprehensive set of analyses, including XPS, BET, SEM, wettability tests, LF-NMR and IGC-SEA, was conducted on the residual charcoal from CGFS to elucidate the mechanism behind reagent consumption. The findings reveal that the reagent’s ability to alter the surface hydrophobicity of residual charcoal is contingent upon the adsorption saturation of micropores and transition pores. Furthermore, variations in porosity and surface energy significantly impact collector consumption, independent of differences in the type and quantity of oxygen-containing functional groups. This investigation aims to provide a theoretical framework for reducing the dosage of reagents in the flotation decarburization of CGFS. [ABSTRACT FROM AUTHOR]

As the reserves of high-quality coal resources in China are decreasing, it is imperative to improve the processing and comprehensive utilization of low-rank coal. In this study, NaNO 2 was used for the flotation pretreatment test of the low-rank coal obtained from Majialiang, and the mechanism was discussed by contact angle analysis, zeta potential measurements, and XPS peak fitting analysis. The results showed that when the dosage of NaNO 2 was 2000 g/t and the pretreatment time was 5 min, the flotation effect was the best, the ash contents of concentrate ash and tailings and the combustible recovery were 17.15, 37.12, and 42.23%, respectively; the combustible recovery increased by 12%. The contact angle, surface functional group content, and zeta potential measurements showed that with the change of NaNO 2 dosage, the content of the hydrophobic functional group and the zeta potential value were consistent with the change of combustible recovery. The increase of hydrophobic functional groups can effectively enhance the hydrophobic interaction on the surface of the coal, which is conducive to the combination of collector and coal, and improve the efficiency of the collector. The NaNO 2 pretreatment test can promote flotation efficiency, and the addition of reductant is an effective method for the flotation efficiency of low-rank coal in reducing oxygen-containing functional groups on the surface of low-rank coal to improve the poor floatability. In this study, the method of chemical pretreatment is put forward to provide a new idea for slime flotation., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)