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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]

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]

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]

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]

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]

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]

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]