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Efficient enrichment of macerals improves the liquefaction efficiency of low-rank coal. The paper studied the characteristics of Shendong low-rank coal, including proximate and ultimate analyses, size and density compositions, and petrographic analysis, as well as the migration regularity of narrow particle size of low-rank coal macerals in the enhanced gravity field. On this basis, a novel classification separation process for low-rank coal macerals using Krebs hydrocyclone and enhanced gravity separator was proposed. The classification size was determined to be 0.074 mm and Krebs hydrocyclone achieved a satisfactory classification effect with a classification efficiency of 84.72%. Based on the enhanced gravity separation results of macerals from hydrocyclone underflow and overflow, the optimal sorting solutions for underflow and overflow were obtained through response surface analysis, respectively. Through the novel classification separation process, the vitrinite content of clean coal has been increased from 46.60% to 61.33% with an outstanding recovery of 77.40%. The novel classification separation process using hydrocyclone and enhanced gravity separator develops an excellent enrichment effect for low-rank coal macerals, which also provides a prospective approach for the cleaner utilization of low-rank coal. [ABSTRACT FROM AUTHOR]

This work innovatively introduced EGS technology into the re-separation process of coking coal middlings based on the dissociation characteristics. The EGS separation characteristics were compared with conventional FF and a novel pre-desliming EGS technology was proposed to achieve clean and efficient separation of coking coal middlings. The density composition and washability of the coking coal middlings crushed under the upper limit size of 6, 3, 1, and 0.5 mm show that the dissociation of the coking coal middlings has been basically completed when crushing to −0.5 mm. The clean coal ash can be reduced to 13.37% with a yield of 42.46% through the pre-desliming EGS technology. The optimal combustible recovery of 71.84% and ash removal rate of 81.36% can be obtained by EGS and pre-desliming EGS methods, respectively, which indicates the superiority of EGS compared to conventional FF. The pre-desliming EGS technology has already demonstrated its great potential in the re-separation of coking coal middlings with the advantages of low-cost, no-pollution and high-efficiency. [ABSTRACT FROM AUTHOR]

The work conducted flow field analysis of a typical hydrocyclone (φ500 type) in the Coal Processing Plant using CFD simulation, including hydrocyclone modeling, flow field development, static pressure distribution, three-dimensional velocity, and air column development. Besides, the effects of influential factors on the classification effect of hydrocyclone were studied. On this basis, a novel hydrocyclone model was developed and simulated for the ultrafine classification of coal slurry. The static pressure and velocity in the typical hydrocyclone have good symmetry and certain regularity. Decreasing the overflow pipe diameter and cone angle, while increasing the underflow pipe diameter, cylindrical section height, and feed rate will increase the classification efficiency of hydrocyclone. The novel hydrocyclone designed of annular feeding, small cone angle, and large cone bottom reduces energy consumption, decreases classification size, and improves classification accuracy. CFD simulation results show that the novel hydrocyclone has higher classification efficiency and smaller classification size over the typical hydrocyclone. The novel hydrocyclone develops an excellent ultrafine classification effect of coal slurry and provides a prospective approach for the industrial application of hydrocyclone in the fine coal ultrafine classification process. [ABSTRACT FROM AUTHOR]

High-efficiency beneficiation of low-grade gold ore becomes an inevitable trend with the depletion of high-grade gold ore. The work innovatively proposed a novel beneficiation process for a typical low-grade gold ore through developing compound collector and discussed the adsorption mechanism. PAX and ADD are most suitable compound collector when the ratio is 3:1 and dosage is 100 g/t. A concentrate with gold grade of 18.40 g/t and recovery of 79.72% is obtained by the novel "one-stage rougher, three-stage cleaner, and two-stage scavenger" closed-circuit process, which has the advantages of low-cost, simple-process, and high-efficiency comparing with the conventional process. The FTIR spectra analysis shows that PAX is a saturated organic compound containing branched chains and ADD is a straight-chain organic compound containing unsaturated bonds. The adsorption of PAX or ADD on the gold ore is chemisorption process and the compound collector has a strong chemisorption capacity. The novel closed-circuit flotation process using compound collector develops an excellent beneficiation effect and provides a prospective and effective approach to concentrate low-grade gold ore. [ABSTRACT FROM AUTHOR]

This study focused on the separation performance of a typical high-ash coal with high-mud content in the enhanced gravity field from the viewpoint of desliming. After necessity analysis of desliming, the EGS results of fine coal before and after desliming were examined. The EGS separation indicators and products were analyzed, and its separation characteristics were compared with FF and STS. The EGS results are unsatisfactory without desliming, and the sorting effect of −0.045 mm PS is inferior to other PSs. After desliming, the EGS performance of fine coal has been improved obviously. The optimal ηa of 97.93%, ηt of 85.99%, ηc of 90.50%, and ηd of 34.67% can be obtained through adjusting RF and RWP. In terms of deashing effect, FF > EGS > STS, but EGS can obtain the lowest clean coal ash of 3.02%, which reflects its advantages of preparing ultra-low ash coal. In terms of desulfurization effect, EGS > STS > FF. EGS is a clean and efficient method on fine coal deashing and desulfurization, and pre-desliming can significantly improve its separation performance. Pre-desliming EGS technology provides a new way for the sorting of fine coal with high-mud content. [ABSTRACT FROM AUTHOR]

This study introduced Krebs hydrocyclone into fine coal EGS process, examined the ultrafine classification effect of Krebs hydrocyclone by single-factor tests and orthogonal tests, and evaluated the fine coal EGS effect after ultrafine classification. Besides, the flow field characteristics in Krebs hydrocyclone were explored by simulation. The optimal grading efficiency of the verification test is 91.32%, and the content of ultrafine particles can be reduced to 1.01%, which prove the excellent ultrafine classification effect of Krebs hydrocyclone. The optimal combustible recovery and ash removal rate are 94.29% and 98.52%, respectively, and when the clean coal ash drops below 10%, the combustible recovery is more than 80%, which reveal that the sorting indexes of fine coal EGS after ultrafine classification are much better than that of unclassified coal. Both the static pressure and velocity in Krebs hydrocyclone have good symmetry and certain regularity. Due to the use of water as a separation medium, the introduction of Krebs hydrocyclone in the fine coal EGS process provides an effective and prospective approach for the industrial application of enhanced gravity separators in the fine coal washing process, especially in the face of increasingly serious environmental problems. [ABSTRACT FROM AUTHOR]

High-efficiency separation of low-grade collophane becomes an inevitable trend with the depletion of high-grade phosphate ore. The work innovatively introduced enhanced gravity separation technology into the pre-separation process of low-grade collophane and discussed the influences of various factors on the enhanced gravity pre-separation effect. The influential significances of parameters, parametric interactions, and performance optimization were investigated using the RSM (Response Surface Methodology). The results showed that the P2O5 grade of the low-grade collophane could be increased from 14.84% to 20.26% with a recovery of 79.55%, and the P2O5 grade of tailings could be reduced to 7.27% under the optimal conditions—f of 44.50 Hz, P of 0.02 Mpa, and V of 22.04 ml/s. Compared with conventional gravity separation, the P2O5 recovery significantly increased by nearly 30%, and the P2O5 grade of tailings has been reduced remarkably. The response surface analysis showed that the influential significances of parameters could be ranked as P > f > V, and parametric interactions could be ranked as fP > PV > fV. The results of verification experiments agreed with the optimization results, which proved the reliability of the prediction model. The enhanced gravity separation technology developed an excellent pre-separation effect of low-grade collophane. [ABSTRACT FROM AUTHOR]

This paper studies the characteristics of Shenhua low-rank coal, including industrial analysis, element analysis, density composition, particle-size composition, maceral characteristics and enhanced gravity. The separation characteristics of Shenhua low-rank coal maceral were examined by manual enrichment, screening enrichment and centrifugal heavy-liquid separation. After manual enrichment, vitrinite content was 31.06% higher than vitrinite content in raw coal, and inertinite content was increased by 13.50% compared with raw coal. The screening results show that vitrinite is easily broken into small pieces to be enriched in coarser particle size (0.125–0.074 mm), and inertinite is easily enriched in fine particle size (−0.045 mm); Centrifugal heavy-liquid separation showed that product in range of −1.30 g/cm3 was taken as pure vitrinite and product in range of 1.36–1.40 g/cm3 was regarded as purer inertinite. Finally, using rod mill products as feed material of enhanced gravity separation to study effect of feed speed, rotation frequency and recoil water on vitrinite recovery, vitrinite recovery of 71.81% and vitrinite content of 68.72% are obtained respectively under the optimal conditions of 30 Hz rotation frequency, 0.03 MPa recoil water pressure and 15 ml/s feed speed. [ABSTRACT FROM AUTHOR]

This study carried out component sulfur composition analysis, electron probe microscopic analysis, and particle size and density composition analysis of coal samples from a coal preparation plant in Liupanshui. The influence of various factors on the indexes of clean coal products under different separation medium conditions by enhanced gravity separation technology, including water medium (WM), magnet powder suspension (MPS), and zinc chloride solution (ZCS), is discussed. The results show that the addition of MPS or ZCS has an obvious improvement on coal deashing and desulfurization compared with the WM separation, especially the separation effect of ZCS, which is better than that of MPS because of better uniformity and stability of ZCS. The addition of MPS or ZCS can help the materials stratify strictly according to the density to enhance the sorting function. The clean coal ash and sulfur content are reduced to 13.24% and 2.51%, while the combustible recovery and desulfurization efficiency are up to 71.46% and 49.27%, respectively, under the optimal condition. [ABSTRACT FROM AUTHOR]

High-efficiency deashing and desulfurization of fine coal is an inevitable trend in the comprehensive utilization of coal resources. This work introducing heavy-medium into the enhanced gravity field to examine the effect of each parameter on the performance of fine coal separation. On this basis, the Response Surface Methodology (RSM) was conducted to study the influential significance of parameters, parametric interactions, and performance optimization of fine coal separation in the heavy-medium enhanced gravity field. The feed dosage and heavy-medium density influence the separation indexes obviously by changing the sorting environment, while the rotational frequency and recoil water pressure affect the separation effect apparently by adjusting the force on particles. The performance optimization results showed that the desired separation indexes – ηt of 81.11%, ηa of 80.00%, β of 44.93%, and λ of 44.76% can be obtained under the optimal combination of parameter levels – M of 27.23 g, ρ of 1.4 g/cm3, f of 30 Hz, and P of 0.03 Mpa. The verification experiments were carried out and the results were consistent with the results of performance optimization. The introduction of heavy-medium provides a new efficient way for the deashing and desulfurization of fine-grained high-sulfur coal in the enhanced gravity field. [ABSTRACT FROM AUTHOR]

Efficient desilication of siliceous phosphate ore is an urgent problem in utilizing phosphate resources. The work evaluated the effect of Falcon centrifuge in separating siliceous phosphate ore and proposed a new combined process of Falcon centrifugal separation and flotation. Three factors were utilized, including rotational frequency, backwash water pressure, and feed rate. The influence model of the three factors on P2O5 recovery was established through orthogonal experimental design, and the optimal prediction index was obtained and proved by laboratory tests. A maximum P2O5 recovery of 86.02% with 27.45% of P2O5 grade was obtained at a rotational frequency of 64.73 Hz, a backwash water pressure of 0.012 Mpa, and a feed rate of 30.51 mL/s. The size analysis revealed that the loss of valuable minerals mainly existed in the −0.045 mm size fractions. The mineral constituent and apparent morphology were analyzed by MLA and SEM-EDS. The optimization experiments of narrow particle size fraction showed that the sorting effect of the particle size between 0.045 and 0.09 mm was optimal. The new process reduced the grinding cost and the feed of flotation, providing a simple and effective new approach to beneficiate siliceous phosphate ore. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The enrichment of vitrinite can enhance the oil yield and conversion rate in low-rank coal liquefaction. The work evaluated the effects of surface modification on the rotary triboelectric separation of macerals. Permittivity and charge–mass ratio analysis of vitrinite and inertinite under various modified conditions demonstrated that kerosene and diesel were excellent modifiers since they keep the permittivity of macerals at a low level. The largest difference in triboelectric charge of vitrinite and inertinite was obtained when 3.0 kg/t kerosene was adopted as modifier. Rotary triboelectric separation of untreated low-rank coal indicated that the optimal separation, i.e., a vitrinite content of 65.45% and a recovery of 69.89%, was obtained at a feed rate of 1.5 g/s, a friction wheel speed of 3000 rpm, and a separation voltage of 30 kV. Under the optimum operating conditions, the optimal rotary triboelectric separation under surface modification, i.e., a vitrinite content of 69.78% and a recovery of 73.52%, was achieved when the coal was treated by 3.0 kg/t kerosene. The results demonstrated that surface modification significantly improved the rotary triboelectric separation by changing the surface electrical properties of macerals, while the excessive dosage of the modified reagent was unfavorable to achieving optimal separation. [ABSTRACT FROM AUTHOR]

In this paper, the enhanced gravity separation of maceral components was studied based on the characteristics of maceral components for low-rank coal from Shendong. Vitrinite and ash content were only 48.42 and 8.77%, respectively. Rod mill grinding showed that the optimal grinding time was 10 min based on the vitrinite content and vitrinite recovery which reached maximum 81.34 and 80.85%, respectively. Maceral separation test conducted with the Falcon concentrator showed that using optimal conditions of rotary frequency 30 Hz, feed dosage 15 ml/s and recoil water pressure 0.03 Mpa, the best vitrinite content, benefication ratio and vitrinite recovery were 67.25%, 1.16, and 72.48%, respectively. With the increase of rotary frequency or decrease of recoil water pressure, the finer particles in each particle fraction became more underflow products, and these finer particles in underflow products were all high-density products with density higher than 1.35 g/cm3. Because the content of vitrinite was higher in the coarser particles, the average particle size of the original overflow product was directly reduced by these fine particles entering the overflow product, which caused the decrease of vitrinite content and the increase of vitrinite recovery. [ABSTRACT FROM AUTHOR]

The liberation characteristics of long flame coal from the Chinese Shenhua were studied by comparison of ball grinding and rod grinding. First, the effects of grinding time on maceral liberation under the different particle size range, including vitrinite content (VC), vitrinite liberation degree (VLD) and vitrinite monomer content (VMC) were researched. Then, the influence of different grinding methods on maceral liberation were compared under same grinding fineness. Test results showed that the vitrinite in rod mill grinding is more concentrated in coarser particles compared with ball mill grinding, which provides favorable conditions for subsequent maceral beneficiation. In addition, in the range of +0.125 mm, all indexes with rod grinding are better than that of ball grinding. Especially, in the range of −0.045 mm, the vitrinite yield obtained by rod mill is always higher than that obtained by ball mill when ash content in each particle size range is almost the same. Analysis results show that the stress area of particles is small for ball grinding to result in random cracks. But rod mill crushes particles by slowly increasing squeeze force greater than stress intensity of particles, the force area of particles is larger to protect particle size decrease to a extent. [ABSTRACT FROM AUTHOR]

The improvement of vitrinite content in low-rank coal can enhance liquefaction efficiency. In this work, an innovative rotary triboelectric separator (RTS) was used to enrich the macerals of low-rank coal. The effects of friction wheel speed (A), separation voltage (B), and feed rate (C) of RTS on the macerals enrichment were investigated, and the interactions of the three factors were explored via the response surface method. By the established model, all the three factors have significant effects on the vitrinite recovery Rv, and the interaction between AC is stronger than AB and BC. Taking the maximum value of Rv as the optimization target, the optimal prediction index was obtained and validated based on laboratory experiments. Under the optimum operating conditions, a maximum Rv value of 74.48% was achieved at a friction wheel speed of 3220.14 rpm, a separation voltage of 30.18 kV, and a feed rate of 1.44 g/s. The average vitrinite content and Rv of the verification experiments were 65.45% and 74.71%, respectively. [ABSTRACT FROM AUTHOR]

The application of gravity separation in flotation process of collophane can reduce the reagent consumption. Aiming at the poor pre-separation performance of conventional gravity separators, this work introduced enhanced gravity separation technology into the flotation process of low-grade collophane. After enhanced gravity separator treating, the P2O5 grade of collophane increased from 14.84% to 20.26% with a recovery of 79.55% under the optimal conditions (GF of 78.56 wt%, FR of 22.04 ml/s, RF of 44.50 Hz, and BWP of 0.02 Mpa). Compared with conventional gravity separators, the P2O5 recovery has been significantly increased by nearly 30%, and the P2O5 grade (7.27%) of tailings has been reduced remarkably, which is a considerable breakthrough in the gravity pre-separation direction of low-grade collophane. On this basis, a novel combined enhanced gravity separation-flotation process was proposed. Compared with the existing research findings, the novel process has the advantages of simplicity and high efficiency, which can not only ensure the separation indexes, but also reduce the beneficiation cost and environmental pollution. The introduction of enhanced gravity separator makes the combined enhanced gravity separation-flotation process become an effective and prospective approach in the separation of low-grade collophane, especially in the face of increasingly serious environmental problems. [ABSTRACT FROM AUTHOR]

This research builds an experimental test platform to verify practicability of theoretical calculation formula and CFD simulation (Fluent software) by comparison of measured value and calculated value, including flow film thickness, recoil water velocity, fluid velocity, and particle velocity. For liquid velocity test, 1 mm polystyrene foam beads are used as tracer particles, while solid velocity test uses fine coal with a density of 1800 kg/m3 and a particle size of 0.5 mm as observation object. Measurement results show that flow film thickness measured value is consisted of that of calculated value, all relative error is less than 5%. But increase of rotational frequency can make relative error increase slightly, this may be caused by instability of flow film due to increasing rotational frequency. In terms of recoil water velocity, its measured value is almost same as calculated value and its relative error is lower. Measurement results of fluid velocity and particle velocity indicate that variation trend of tangential and axial velocity simulation value is basically same as experimental value. However, relative error of axial tangential is greater than that of tangential by 10% for fluid velocity and relative error of axial tangential is greater than that of tangential by 20% for particle motion velocity. The large deviation of axial velocity is that direction of the axial acceleration changes easily relative to the stable tangential velocity, the “relaxation phenomenon” of tracer particles in the experiment and interference from other aspects of flow field make deviation increase slightly. [ABSTRACT FROM AUTHOR]

CFD simulation is carried out for the internal flow field of rotary triboelectric separator by Fluent software, analyzing effects of three factors on airflow field inside rotary triboelectric separator, including feeding airflow speed, friction wheel speed, and assistant airflow speed. The best referenced simulation conditions are obtained by single separation test: the plate voltage of 24 kV, the feed frequency of 22 Hz, the friction wheel speed of 189.95 rad/s. Simulation results of feeding airflow speed show the feeding airflow speed of 4 m/s is a cutoff point of the influence for the maximum airflow velocity in the friction chamber, the sorting effect becomes worse when the feed air speed is greater than 4 m/s. Increases of feeding airflow velocity cause two effects: One is that feeding airflow can reach the surface of the friction wheel and then rotate with the friction wheel. The second is to increase the turbulence of the airflow field in the friction chamber; Simulation results of feeding airflow speed show when the rotational speed of the friction wheel is greater than 189.95 rad/s, the influence of the rotation friction wheel exceeds the airflow of feeding airflow. Under the condition of a certain feeding airflow speed, an increase of friction wheel rotate speed makes internal friction flow field velocity increase with the improve of velocity gradient, which leads to the flow field in the friction chamber is more uniform; Simulation results of assistant airflow speed show the 3 m/s assistant airflow in the sorting chamber is most beneficial to the stability of the material motion. The assistant airflow speed mainly affects the airflow field in the separation chamber, the flow field in the separation chamber is increased with the increase of the assistant airflow speed. [ABSTRACT FROM AUTHOR]

Pulverized coal is separated by rotary triboelectric separation to confirm the best charger rotary speed, separation voltage, and airflow velocity. On this basis, pulverized coal surface is modified by studying four modifiers to explore the effect of pulverized coal surface modification on permittivity, specific-charge, and separation indices, including kerosene, diesel, acetic acid, and sodium stearate. Finally, separation indices of triboelectric separation are compared before and after modification. Experimental results show that kerosene has the best modification effect for pulverized coal. Under the best conditions after modification, ash deash rate is increased by 1.87%, desulfurization rate is increased by 0.44%, clean coal recovery is increased by 6.07%, and ash content is reduced by 1.95%. After the modification of pulverized coal, the specific-charge and permittivity of clean coal and gangue minerals form a greater difference, which indirectly increases the trajectory difference of different minerals in the process of rotary triboelectric separation, achieving better separation of clean coal and gangue minerals. [ABSTRACT FROM AUTHOR]

The macerals effective dissociation is the precondition for the macerals enrichment. The macerals dissociation generally adopts the crushing and grinding process. Selective grinding is achieved by using the differences in mechanical properties between different macerals, and grinding equipment and grinding time are important factors affecting the degree of selective grinding. Hence, it is necessary to choose the suitable dissociation method, control the suitable dissociation time, avoid over-crushing, and then cooperate with the suitable concentration methods to achieve macerals efficient enrichment. In this paper, the low-rank coal studied was produced by Shenhua Shigetai Coal Mine. Coal sample was crushed to less than 1 mm and then was carried out for the grinding test by using the rod mill and the ball mill, respectively. In order to determine the macerals dissociation characteristics of Shenhua low-rank bituminous coal, the size distribution, density level, and macerals of the grinding products under the different grinding equipment and grinding time were analyzed. The test results show that the grinding effect of the rod mill is better than that of the ball mill under the same grinding time, and 10 min rod grinding can obtain the best macerals dissociation. [ABSTRACT FROM AUTHOR]

Jigging is one of the common separation processes in coal beneficiation. The analysis of the impact of jigging operating conditions on the stratification process of the particles inside the model jig wash box has a great guiding significance for improving the performance of the equipment. The experimental results showed that different densities particles exchanging their position in vertical direction mainly occurred during the terminal stage of particle ascending motion and the initial stage of particle descending motion. During this stage, the jig bed was relatively loose, and particles in the bed were conditionally stratified according to their own characteristics (particle size, density, and shape). After the completion of particles stratification, the bed was separated into layers according to particles densities. Material with lower density stayed on top and material with higher density settled at the bottom. Within a bed layer of the same density, the bed was stratified into layers according to particle size. Small particles occupied the upper layer and large particles occupied the lower layer. Experiment of unhindered settling of different particles showed that the terminal settling velocity of large particles was significantly higher than that of small particles of the same density. The terminal settling velocity of large particles with lower density was lower than or equal to that of small particles with higher density. This illustrated that equal settling exists among particles of different densities and sizes. The stratification of materials based on their density could be achieved in a jig, which showed that hindered settling instead of equal setting ratio played a dominant role in jigging process. [ABSTRACT FROM AUTHOR]

This paper studied the macerals enrichment of the low-rank coal which produced by Shigetai Coal Mine, Shenhua Group. The coal sample fed to the Falcon were the product of the rod mill after 10 minutes grinding. Three factors were carried out, rotational frequency, feed rate and water pressure. The orthogonal experiment was designed to investigate the interaction between the three factors and a model was established between the factors and response values. Taking the vitrinite recovery rate as the response value, there was an interaction between the rotational frequency and the water pressure, moreover, the effect of the rotational frequency on the vitrinite recovery rate was greater than the water pressure, while, the feed rate on the vitrinite recovery rate was not significant. Taking the vitrinite enrichment ratio as the evaluation index, the Quadratic model was recommended, there was an interaction between the rotational frequency and the feed rate, moreover, the rotational frequency had better response to the vitrinite enrichment ratio than the water pressure and the feed rate. In order to optimize the experimental conditions, and the vitrinite enrichment ratio was set to 1.2, the vitrinite recovery rate was the larger the better, the optimal separation conditions obtained were the rotational frequency 30Hz, the water pressure 0.03MPa, and the feed rate 15ml/s in the laboratory. [ABSTRACT FROM AUTHOR]

Studies were performed on the particle migration in a compound gravity force field. Significant separation performance differences of narrow size fraction were observed by the distribution rates and ash content difference, response rule of the particle size, and density to the separation environment were analyzed. High weight distribution and high ash content of ultrafine particles in overflow were the main cause of the low selectivity of ultrafine particles, which lead to the contamination of products. Influence of centrifugal force and fluidization water pressure on the sorting process was studied. The essence of the separation was to find the equilibrium point that could achieve the best combination separation behavior of different grain size samples. It was necessary to remove fine particles before separation to improve the overall quality of fine coal separation. The sorting process can be expressed by a simple matrix equation. Thus, the separation performance difference of coal samples can be expressed by sorting function. Influence of centrifugal force, fluidization water pressure, and particle size on distribution rate was analyzed by mathematical model fitting. [ABSTRACT FROM AUTHOR]

Rotary triboelectrostatic separator is employed to remove and recycle unburned carbon from fly ash which are main solid wastes of coal-fired power plants. The products after decarburization can be used for building materials, road construction material and other function materials. In previous works, effects of structural parameters and operating parameters on recovery process of fly ash were studied. The present work shows the inlet airflow velocity, rotating angular airflow velocity and co-flow velocity directly affect the airflow filed and motion characteristics of fly ash particles from the analysis of separation process using numerical simulation methods. The average airflow velocity in rotary triboelectrostatic chamber have a trend of first increase, then decline and increase again with the increase of inlet airflow velocity, and it increases with the rotating angular airflow velocity in the selected range. Vortexes appeared on both sides of the inlet and grew bigger with the increase of inlet airflow velocity and rotating angular airflow velocity. Co-flow velocity only affected the airflow in the electrostatic chamber. Moving in the airflow and colliding with friction walls were main motion characteristics of ash particles and carbon particles. The collision numbers were closely related to the net charge from the comparison of simulation and experiment results, it suggested that the net charge of ash particle would increase with the collision numbers. [ABSTRACT FROM AUTHOR]

The spatial distribution of fine high-sulfur lean coal under different backwash water pressures and rotational frequencies in enhanced gravity field using the Falcon concentrator was investigated. It deals with the distribution characteristics of products, including yield, ash content, sulfur content, and pyritic sulfur content, in overflow, upper groove, and lower groove from the top to the bottom in space. Backwash water pressure had coarse adjustment while rotational frequency had fine adjustment on the Falcon concentration process; meanwhile, the desulfurization and de-ashing results were discussed by combining them. The extensive migration characteristic of pyritic sulfur in space was also studied. [ABSTRACT FROM AUTHOR]

The separation of ultrafine coal is inefficient due to the low settling velocity in centrifugal field. The feasibility of increasing particle size by flocculation to increase the separation efficiency is verified. The effect of flocculant on the size distribution of ultrafine coal was tested. The effect of flocculant dose on deash and desulfurization efficiency was studied to determine the appropriate dosage. Further, influence of the main operating parameters of the concentrator, including centrifugal force and water counter pressure on the separation performance, was studied. In addition, a comparative test was designed to verify the stability of the flocs. Results showed that the size of ultrafine coal particles could be effectively increased by the addition of flocculant, and the yield of −0.045 µm fraction was decreased from 50% to 17% when the flocculant dosage was 10 g/t. The combustible material recovery of clean coal increased from 58% to 66%; meanwhile, the ash content reduced from 16.7% to 14.6%. In addition, combustible matter recovery and desulphurization efficiency decreased with the increase of centrifugal force, while they increased with the water counter pressure. Results of comparison tests of ultrafine coal with flocculant pretreatment and artificial coal with the same size composition showed that the latter had greater combustible recovery and desulfurization efficiency. [ABSTRACT FROM PUBLISHER]

The influence of microwave pretreatment on the heating response, moisture content, surface morphology, grindability, and liberation of coal were investigated. The results show that microwave irradiation has a weak effect on the chemical composition, but can reduce moisture content significantly. Intuitionistic evidence was discovered that microwave energy can induce micron cracks on the interface among different minerals. The results of grinding tests show that microwave pretreatment can remarkably promote the fine grinding of coal. Density analysis shows that the liberation degree of grinding products increases with the microwave pretreatment time due to the auxiliary grinding and selective heating effect of microwave radiation. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM AUTHOR]

Froth flotation is widely used in the coal industry to clean -28 mesh fine coal. A successful recovery of particles by flotation depends on efficient particle‐bubble collision and attachment with minimal subsequent particle detachment from bubble. Flotation is effective in a narrow size range beyond which the flotation efficiency drops drastically. It is now known that the low flotation recovery of particles in the finest size fractions is mainly due to a low probability of bubble‐particle collision while the main reason for poor coarse particle flotation recovery is the high probability of detachment. A fundamental analysis has shown that use of picobubbles can significantly improve the flotation recovery of particles in a wide range of size by increasing the probability of collision and attachment and reducing the probability of detachment.A specially designed column with a picobubble generator has been developed for enhanced recovery of fine coal particles. Picobubbles were produced based on the hydrodynamic cavitation principle. They are characterized by a size distribution that is mostly below 1 µm and adhere preferentially to the hydrophobic surfaces. The presence of picobubbles increases the probability of collision and attachment and decreases the probability of detachment, thus enhancing flotation recovery. Experimental results with the Coalberg seam coal in West Virginia, U.S.A. have shown that the use of picobubbles in a 2″ column flotation increased fine coal recovery by 10–30%, depending on the feed rate, collector dosage, and other flotation conditions. Picobubbles also acted as a secondary collector and reduced the collector dosage by one third to one half. [ABSTRACT FROM AUTHOR]

As the mining of large flake graphite is approaching exhaustion, fine flake graphite becomes the main resource for the future. The fine flake graphite ores in the Heilongjiang area of China are very representative of China. Based on a large amount of fine flake graphite in Luobei, Heilongjiang, China, the characteristics of the fine flake graphite have been studied by process mineralogical analysis. The study shows that the large flake graphite content in the raw ore samples in the Luobei area, Heilongjiang, China is about 16.81%, and most of the graphite exists in the form of fine flakes less than 150 μm. In addition, the main reason why graphite minerals are difficult to liberate is that the graphite flakes in the samples are interlocked with Muscovite. Some graphite flakes are distorted in the ore and it is easy to cause the flakes to be severely crushed during the grinding process which can affect the application value of graphite. A part of graphite minerals or gangue is distributed in the ore in the form of a fine disseminated state, which can result in a low grade of the flotation concentrate. [ABSTRACT FROM AUTHOR]

The recovery and reuse of waste printed circuit boards (PCBs) has attracted more and more attention from global researchers, as recycling of waste PCB metals is of great significance to the rational utilization of metal material resources. This study puts forward a clean and economical method in which enhanced gravity separation and wet high-gradient magnetic separation were combined to recover waste PCBs with heat treatment at a temperature of 240 °C. The heat treatment could improve the metal liberation effect of the PCBs, and the thermal behavior was measured by thermogravimetric analysis (TGA). The pyrolysis of the non-metal fraction (NMF) began around 300 °C, and the glass transition temperature of epoxy resin was 135.17 °C. The enhanced gravity separation technique was used for the separation of metals and NMF under the compound force field. The metals grade of the gravity concentrates fraction (GRF) was 82.97% under the optimal conditions, and the metals recovery reached 90.55%. A wet high-gradient magnetic separator was applied to classify the GRF into magnetic (MA) and non-magnetic (NMA) fractions, which could achieve iron and copper enrichment. After the three stages combined process, the copper and iron grades of the NMA and MA fractions were 70.17% and 73.42%, and the recovery reached 74.02% and 78.11%, respectively. [ABSTRACT FROM AUTHOR]

This paper studies particle motion and flow field characteristics with fly ash as an example and combine the experiments to analyze the separation process of rotary triboelectric separator in detail. Under boundary reference conditions of 22 kV plate voltage, 3 m/s feed flow, and 1815 r/min (189.95 rad/s) friction wheel speed, it simulated single-particle and particle group movement with different plate voltages and different feeding positions. Simulation of particle movement shows that particles may collide with a plate to cause serious particle mixing when plate voltage is higher. The initial velocity direction of particles is vertical downward and particles enter the separation chamber from the middle of the feeding port as much as possible to achieve better separation. The analysis of the flow field shows that the increase of the feeding airflow speed leads to a higher flow velocity inside the friction chamber and increases turbulence intensity; increases in friction wheel speed enhances flow field uniformity in the friction chamber and it is accompanied by an increase in velocity gradient; The co-flow speed mainly affects airflow field in the sorting room, the increase of co-flow speed within a certain range effectively stabilizes airflow field in the sorting room. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

• Hydrodynamic cavitation enhanced the floatability and flotation kinetics of pyrite. • The adsorption of SAX on the pyrite surface increased with cavitation time. • Both of ·OH and dissolved oxygen induced the oxidation of SAX. • Hydrodynamic cavitation did not significantly accelerate pyrite oxidation. Although it is well known that cavitation nanobubbles significantly improve the flotation performance of mineral particles, the effects of nanobubbles on sulfide mineral surface oxidation and reagent adsorption have not been studied sufficiently. The present study was conducted to investigate the effects of cavitation nanobubbles on oxidation characteristics and xanthate adsorption behavior of pyrite surface by means of micro-flotation tests, UV–visible spectroscopy, X-ray photoelectron spectroscopy (XPS) and zeta potential measurements. The experimental results have shown that the presence of cavitation nanobubbles in the pyrite flotation pulp enhanced the floatability and flotation kinetics of pyrite and improved the adsorption capacity of sodium amyl xanthate (SAX) and dixanthogen on pyrite surface as a result of stronger hydrophobic interactions. The reactive species generated by nanobubbles were identified to be dissolved oxygen (DO) and ·OH by quenching experiments. In addition, the zeta potential measurements have demonstrated that the rapid formation of cavitation nanobubbles on pyrite reduced the oxidation of pyrite surface. The results from this study have revealed important new mechanisms of cavitation nanobubbles enhancing sulfide mineral flotation from the perspectives of mineral surface oxidation and collector adsorption capacity and their synergistic effects that originate from unique characteristics of cavitation nanobubbles. [ABSTRACT FROM AUTHOR]

The fine quartz was mixed with gold chloride solution to perform stirring contrast experiment under the condition of with and without iodization. Experimental factors were studied in order to gain the best inhibitory effect of iodization about adsorption effect of quartz on gold chloride, including gold solution concentration, stirring speed, stirring time, and KI-I2 dosage. Adsorption property of quartz on gold chloride was obtained by fitting and calculation of adsorption models. On the basis, the adsorption mechanism of quartz on gold chloride is revealed. Experimental results show that adsorbed amount without iodization is higher than with iodization, which is restrained by iodization. The best condition restrained adsorption is gold chloride of 100 mg/L, stirring speed of 500 r/min, stirring time of 8 min under condition of pH = 6 and 10% pulp density, and the best KI-I2 dosage are C(KI) = 2.5g/L and C(I2) = 2g/L. The fitting and calculation of adsorption models demonstrate that the adsorption of quartz on gold chloride contains favorable chemical adsorption in addition to physical adsorption. The analysis results show the main mechanism of chemical adsorption for inhibiting adsorption with iodization is that the ultrafine gold particles reduced on quartz surface form a coordination complex in the pulp systems, which are dissolved by iodization. [ABSTRACT FROM AUTHOR]

• Enhanced gravity separation was implemented to remove unburned carbon from fly ash. • The decarbonization effect were influenced by the backwash water pressure and rotational angular velocity significantly. • Enhanced gravity separation showed its application potential in industry compared with froth flotation. Fly ash is the by-products of electric power, which has potential application in construction industry after removing the unburned carbon. The density difference and favorable dispersion characteristics of fly ash provide the feasibility using gravity separation method. The present study had investigated the removal of unburned carbon from fly ash using enhanced gravity separation under different operation parameters such as rotational angular velocity and backwash water pressure, and the decarbonization performance was compared with the froth flotation. The results showed that both the rotational angular velocity and backwash water pressure had evident effect on the removal of unburned carbon from fly ash, and the rotational frequency adjusted more accurate relative to the coarse adjustment of backwash water pressure. The enhanced gravity separation could yield qualified Level II and Level III ash products with yield of 12%–23% and 23%–69%, while the froth flotation yield Level I, Level II and Level III ash products. The decarbonization results of enhanced gravity separation was slightly lower than froth flotation, while it provided the application value in industry without complex reagent system and high cost on the premise that met the requirements for Level II and Level III ash products. [ABSTRACT FROM AUTHOR]