Dense Medium Cyclone Research Articles

Beneficiation process reengineering under the background of green development-- take the full utilization of a low-grade lead-zinc ore as an example

A zero-waste mine is an advanced mine development and resource utilization strategy that aims to encourage the reduction of mine solid waste at source and the utilization of all its components. A low-grade lead-zinc ore in Guangxi, China, contains valuable components like galena, sphalerite, pyrite, barite, etc. and the gangue mineral is primarily dolomite. This paper proposes a flow of “waste pre-discarding by dense medium cyclone - sequential priority flotation of lead and zinc recovery - flotation and gravity combined process for barite recovery” to realize full component utilization. In this technical approach, 38.81% of the waste rock that can be utilized as concrete aggregate was removed from the feed ore through pre-discarding prior to grinding, after that recovers lead and zinc by the sequential priority flotation method with yield of Pb concentrate and Zn concentrate at 7.61%. In order to more efficiently recover barite and pyrite from lead-zinc flotation tailings, the gravity equipment of reflux classifier (RC) was used, which obtained barite concentrate with a yield of 7.97% and pyrite concentrate with a yield of 2.28%. The remaining yield of 43.34% tailings can be used for filling after the recovery of barite concentrate. Utilizing waste rock, lead, zinc, barite, and other resources might help the mine achieve the dynamic balance of “mining-discarding-beneficiation-filling” and realize zero tailings discharge.

Preconcentration of a Medium-Grade Celestine Ore by Dense Medium Cyclone Using a Factorial Design

A semi-industrial scale hydrocyclone with a 250 mm internal diameter was used to concentrate medium-grade celestine ore (75%–85% celestine) from the Montevive deposit of Granada (Spain) using a dense ferrosilicon (FeSi) medium. For this purpose, a Box–Behnken factorial design (BBD) was carried out, with the response variable being the Sr concentration measured by X-ray fluorescence (XRF), as well as the concentration of celestine measured by X-ray diffraction (XRD) of the mineral collected from the under (sunk) stream of the hydrocyclone. The experimental factors to be optimised were the density of the medium in the mixing tank (water, FeSi, and feed mineral) varying from 2.7 to 2.9 kg/L, the hydrocyclone inlet pressure from 0.8 to 1.2 bar, and the hydrocyclone inclination (from 15° to 25° from the horizontal). The range of densities of the dense medium to be tested was determined from previous sink–float experiments using medium-grade ore, in which the distribution of mineral phases with different particle size fractions was determined. To evaluate the separation behaviour, the following parameters were considered: the enrichment ratio (E), the tailings discarding ratio (R), and the mineral processing recovery (ε). From the factorial design and the response surface, the optimum parameters maximising celestine concentration in the under stream (78%), were determined. These optimised parameters were: a density of 2.75 kg/L for the dense medium, an inlet pressure of 1.05 bar, and a hydrocyclone inclination varying from 18° to 20°. Under these conditions, a 94% recovery of celestine (68% Sr) can be achieved. These results show that medium-grade celestine ore, accumulated in mine tailings dumps, can be effectively concentrated using DMS hydrocyclones and that the operating parameters can be optimised using a factorial experiment design. This study can contribute to reducing overexploitation of strategic mineral resources, avoiding blasting and environmentally damaging clearing, by applying a simple and sustainable technique.

Gravity-based pre-concentration strategies for complex rare earth ore containing niobium and zirconium

The Balzhe rare earth mine, renowned for its rich reservoirs of niobium, zirconium, and rare earth elements, poses a unique challenge due to its diverse and interbedded mineral composition. Despite the abundance of these elements, their valuable grade remains notably low, falling short of economic thresholds. To this end, pre-concentration of valuable minerals to discard gangue minerals before flotation would be an economical option. In response, this study delves into the feasibility of gravity-induced pre-concentration, aiming to segregate valuable minerals from gangue for subsequent flotation processes. Conducting float-and-sink tests on varied particle sizes (-2+0.5 mm, -0.5+0.074 mm, and -0.074+0.02 mm) within heavy liquids of specific gravities (ranging from 2.55 to 2.85), the study reveals the effectiveness of gravity separation. Notably, particles sized -2+0.5 mm and -0.074+0.02 mm demonstrated superior separation performance over the -0.5+0.074 mm fraction. Comparative analysis of diverse gravity separation equipment unveiled compelling results. The dense medium cyclone separator showcased impressive recovery rates and high-grade concentrates of Nb<sub>2</sub>O<sub>5</sub>, ZrO<sub>2</sub>, and total rare earth oxides (TREO) at 0.34%, 8.20%, and 0.41%, respectively, surpassing the sand table's performance for -2+0.5 mm particles. Conversely, for -0.5+0.074 mm particles, the shaking table exhibited optimal separation efficiency, yielding grades of Nb<sub>2</sub>O<sub>5</sub>, ZrO<sub>2</sub>, and TREO at 0.37%, 4.08%, and 0.44%, with substantial recovery values. Ultimately, the Knelson centrifugal separator proved most effective for -0.074+0.02 mm particles, yielding notable grades and recoveries of Nb<sub>2</sub>O<sub>5</sub>, ZrO<sub>2</sub>, and TREO. This study underscores the promising potential of gravity-induced pre-concentration techniques for enhancing the recovery of valuable elements from the complex Balzhe rare earth ore, offering critical insights into optimizing mineral extraction processes.

Influence of nose angle on performance of dense medium cyclones with volute inlet

Dense medium cyclones (DMCs) are widely used in coal mine sorting processes to improve the quality of coal products and reduce pollution. The conventional linear inlet DMCs has the problems of unstable flow field, high turbulence density and low separation efficiency. Based on these concerns, the volute inlet DMCs was proposed, however the nose angle as one of the most critical parameters has not yet been investigated in depth. In this paper, a DMC with volute inlet is investigated, and the effect of nose angle is studied by a computational fluid dynamics model in terms of flow field, particle motion and the forces acting on the particles. The performance of the DMC is evaluated with respect to the inlet nose angle. As the nose angle increases from 0 to 180 deg., the separation efficiency has a tendency to increase and then decrease with the inflection point founding when nose angle is 180 deg. Then the flow field, particle distribution and particle force are analyzed respectively. The results show that the symmetry and stability of the flow field can be significantly improved as nose angle increases from 0 to 180 deg., but they remain almost constant when nose angle is 270°. In addition, a quantification method of the short-circuiting flow is established and it has been found that increasing the nose angle can notably reduce the short-circuiting flow. In terms of particle phase, increasing the nose angle causes heavier particle distribution tends to concentrate. During this period, the variation pattern of forces on particles with different nose angles is also analyzed. The DMC with a nose angle of 180 deg. has a longer acceleration zone at the entrance height and an increased radial force on the particles, which results in better performance. This study provides a theoretical basis and reference for the structure optimization of dense medium cyclones.

Research on highly efficient quality improvement process and product blending scheme for fine coal

In this study, a highly efficient quality improvement process for fine coal was proposed and industrial experiment was conducted. The fine coal was classified with 3 mm flip-flow screen (FFS), and then separated to improve quality by dense medium cyclone (DMC). The vibration characteristics of FFS were analyzed and its capacity was optimized during the screening process. Separation performance toward each particle size of coal in DMC was investigated. According to the products structure of optimized process, a product blending scheme was proposed. The results indicated that the vibration intensity of flip-flow screen surface could reach 27.81. When the capacity was 278 t⋅h−1, the 3 mm screening performance was found to be the best. The separation performances toward each particle size of coal worsened with the decrease of particle size in DMC, and the overall probable error was 0.057 g⋅cm−3. The quality of fine coal after process optimization improved significantly compared to that before process optimization. This study indicates that by using this formulated product blending scheme, the product profit of the fine coal system is expected to increase by 52.85 million RMB annually.

Dense Medium Cyclone Separation of Fine Coal: A Discussion on the Separation Lower Limit

The separation of fine coal has been widely discussed in the coal preparation industry due to its high economic potential. Dense medium cyclone (DMC) is the most efficient equipment available for fine coal separation. However, the industrial application of DMC is far from satisfactory due to operational difficulties and maintenance. In this research, particle settling behavior in a dense medium cyclone was analyzed for improved separation. The calculation result about feed pressure and separation lower limit, which fits the experimental data well, might be a guidance for industrial DMC design and operation. According to the calculation result, it is highly recommended that the separation lower limit be set at 0.2 mm rather than 0.1 mm, because the feed pressure head required for the latter (50 D) is three times higher than the former (15 D).

Application of X-ray computed tomography scanning in describing partition curves of dense medium cyclones

The partition curve is an important tool to evaluate the separation performance of mineral separators like dense medium cyclones (DMCs). This curve is constructed by float-and-sink (FaS) analysis which involves the use of heavy liquids and suspensions. This traditional technique is hazardous to the environment, laborious, and time-consuming. Here, a new technique using X-ray computed tomography (XCT) scanning was successfully developed and applied for describing the partition curve of a DMC at an Australia-based lead–zinc mineral processing plant. The DMC feed, concentrate and reject streams were sampled and sieved into several size classes. The chemical assays and averaged densities according to each class were analysed by X-ray fluorescence spectrometry and gas pycnometry, respectively. The partition behaviour was investigated by XCT analysis. A model was proposed to determine the mass yield value – an important parameter to define partition curves – by mass balance and reconciliation, which is generally unknown during the sampling of continuous separation processes. From the reconstructed XCT images, we obtained detailed information on individual particles such as volume, surface area, mass, and density. Cumulative mass distribution curves and partition curves of the DMC for different size classes were then constructed and agreed with the FaS analysis. Using the XCT technology can help overcome the issues of the traditional FaS analysis. Moreover, this technology would allow for evaluating DMC separation efficiency with continuous, online, and real-time monitoring and control.

Performance characteristics of 76 mm dense medium cyclone to wash high ash high NGM coal

ABSTRACT The present paper describes the detailed experiments carried out using 76 mm dense medium cyclone to determine the extent of beneficiation, ash percent reduction, recovery of ash and non-ash components in clean coal product and the effects of design parameters (Vortex finder and Spigot diameters) on the performance of the two separators have been brought out critically. Under the heading qualitative studies, the recoveries of ash (RA) and non-ash (RNA) percentages achieved in the clean coal, have been related to outlet diameters through regression equations. Further to quantify the performance of the separators, the two performance parameters has been named the efficiency index (EI) and separation efficiency index (SE) have been considered in the analysis. The performance of the separator measured using dependent (EI and SI) and the independent (Tromp or partition curves) criteria have also been discussed in detail. From the plotted tromp curves, the two performance parameters SG50 and EP have been estimated and their dependence on outlet diameters and geometric mean sizes have been depicted here. Additionally, to predict the performances of the separators, the concept of plotting generalized partition curves has been adopted for the separation of bulk coal (−3 + 0.5 mm) and the individual size fractions of the coal (1.93 mm, 1.22 mm, 0.86 mm and 0.35 mm), which have been defined mathematically by Gottfried’s model. It has been found that the coarse fraction of feed separated at lower density, whereas finer fraction have indicated to get separated at higher density.

Study on dynamic stability of suspension in dense medium cyclone

ABSTRACT The dynamic stability of dense medium suspension is the premise to ensure the effective separation of mineral particles in the separation equipment. It is usually difficult to directly measure the dynamic stability of the suspension in the separation process of the dense medium cyclone. In this paper, a parameter defined as the density difference value between the underflow and overflow of cyclone is used to characterize the dynamic stability of the suspension in the separation process. Under the conditions of different operating parameters and structural parameters, the influencing factors of the dynamic stability of 1.30–1.60 g/cm3 dense medium suspension are systematically studied. The results show that the parameter value is in the range of 0.20–0.50 g/cm3, which is conducive to the separation of particles. When the suspension density increases, the characteristic value of density difference decreases, the influence of the suspension density, feed pressure, the diameter of underflow and overflow port diameter on the density difference characteristic are also researched. Eventually, the formula for calculating the density difference of the characteristic value of suspension is derived.

Features of near gravitational material tracers in a dense medium cyclone from PEPT

Dense media cyclones are an integral part of circuits employed for coal processing, iron ore beneficiation, and recovery of diamonds. Many techniques have been applied in studying the separation performance of these devices including the use of different density tracers to develop density partition curves. This study focusses on tracking of near-gravity material radioactive tracers using the positron emission particle tracking technology. This near-gravity phase of coal has long been thought to cause separation inefficiencies which makes coal processing difficult. In this work, a slurry containing magnetite-based dense medium, and coal is pumped through a 100 mm Multotec cyclone. By means of the PEPT camera – apparatus with spatial and temporal resolutions of 1 mm and 1 ms respectively – and direct-adsorption-activated coal tracer particles within the medium, particle trajectories are recorded in space and time. The free vortex region is captured and shown to fit the Rankine vortex behaviour with n = 0.60 ± 0.08 overall for the free vortex power law decay. A logarithmic axial velocity model which captures the observed radial gradient around the locus of zero axial velocity is proposed. Radial profiles of turbulence intensity for the near gravitational material as captured by PEPT are presented. • labeled coal NGM particle trajectory in 4in operating DMC imaged using PEPT • resolve axial variability of two-vortex model at cyclone boundary transition • locus of zero vertical velocity captured • quantified turbulence distribution of NGM particle trajectories • demonstrate axial velocity model fit

Simulation and Performance Evaluation of Three Product Dense Medium Cyclone

ABSTRACT The conventional flowsheet of coal washing plants includes sequential units where different coal size fractions are washed. Generally, coal washeries include dense medium vessels/drums and cylones for coarse and intermediate sizes as well as spirals and flotation units for fine/ultrafine fractions. Three product-dense medium cyclones (TPDMC) may replace the traditional flowsheet, enabling coals of a wide size range to be treated at once. TPDMC is widely used in the world, particularly in China, and has many potential advantages, yet there is limited data about its performance and simulation. In this study, the performance of a 70 t/h feed capacity TPDMC used for hard coal washing was investigated and its separation behavior was simulated using two different dense medium separation models. Test results revealed that the separation performance of TPDMC was efficient, yet different geometric designs might be required for the treatment of various coal types.

Effects of the inlet duct length on the performance of a dense medium cyclone: An experimental and numerical study

The effects of the inlet duct length on the performance of the dense medium cyclones were investigated in this study. The pressure drops and separation efficiencies of the dense medium cyclones with different inlet duct lengths were measured in a cold test rig. A numerical simulation using the four-way coupling method was also conducted to estimate the flow field inside the dense medium cyclone. The experimental results show that a longer inlet duct length results in a lower static pressure drop. The overall separation efficiency first increases and then keeps almost unchanged as the inlet duct becomes longer. The simulated results show that the energy loss decreases as the inlet duct length increases. The changing trends of the static and total pressure drops with the inlet duct length are similar. According to the simulated flow fields, lengthening the inlet gas reduces tangential velocity near the vortex finder and therefore reduces the gas swirling loss. The inlet duct length affects the separation performance mainly by affecting the swirling particle roof. A longer inlet duct leads to fewer particles moving in the swirling particle roof in the dense medium cyclone, which accounts for a better separation efficiency. It was also found that the conventional one-way coupling method fails to qualitatively analyze the effects of inlet duct length on the separation performance of the dense medium cyclone.

Simulation of a gravity processing circuit for low-grade chromite ores of the Gaft deposit (Iran)

The purpose of this study was to design and simulate portable processing circuits for low-grade chromite ores with minimal equipment requirements. The studies were conducted using a chromite sample with Cr2O3 = 24 %. The efficiency of various types of process equipment, including dense medium cyclones, spiral separators, and hydrocyclones, for the separation of chromite from associated minerals was investigated, with due account of the difference in particle sizes and density of the major minerals in the sample, including chromite, dunnite, serpentine, peridotite, magnesite, and talc. Dense medium tests for the three particle size ranges of 1–2, 2–4.75, and 4.75–9.5 mm were carried out in solutions of bromoform (2890 kg/m3) and methylene iodide (3300 kg/m3). In all dense medium tests, the highest grade and recovery values were obtained for the solution with a density of 3300 kg/m3. When chromite particles of –1 mm were processed in a spiral separator, the Cr2O3 grade and recovery in the product were 50.51 and 54.40 %, respectively. Fine particle separation in a hydrocyclone rendered the underflow with d50 = 270 μm and Cr2O3 = 41.10 %. As a result of the laboratory-scale tests, a processing circuit with an input capacity of 10 t/h was designed utilizing MODSIM simulation software. The simulated lowgrade chromite ore processing circuit yielded concentrate with a Cr2O3 grade of over 39 % and a recovery of 50 %.

Dense medium separator performance evaluation based on 3D Eulerian-Eulerian multiphase CFD simulation

ABSTRACT The present paper enumerates a CFD model developed for a 76-mm Dense Medium Cyclone (DMC) using Ansys Fluent Software to gain insights into the separation of particles according to their size and density. The simulation used in this paper includes Reynolds stress model to predict the turbulence inside the cyclone body. An Eulerian–Eulerian multiphase CFD model was applied to model a number of physical aspects such as the separation of coal particles and the segregation of magnetite media solids. The experimental results generated in a laboratory-scale DMC were used for the validation purpose, and the predicted results of CFD have been validated for the flow splits of water, magnetite, and coal. The simulation results obtained from the Eulerian–Eulerian multiphase model reveal that the prediction is in good agreement with experimental results and match reasonably well in terms of the mass flow rates of water, magnetite, and coal. Furthermore, the partition curve of the DMC when mapped for the separation of −3.0 + 0.50 mm size also showed to be in agreement with the experimentally obtained curves. The gravity of cut (SG50) has also been predicted by the Eulerian–Eulerian multiphase CFD model and was found to be in the vicinity of observed experimental value of SG50.

Prediction of medium-to-coal ratio effect in a dense medium cyclone by using both traditional and coarse-grained CFD-DEM models

Dense medium cyclone (DMC) is the working horse in coal industry. In practice, it is usually operated under constant pressure and the operational conditions (mainly medium-to-coal (M:C) ratio and operational pressure) need to be adjusted according to coal washability data (mainly coal particle size and density distributions). Nonetheless, until now it is still not well understood how the M:C ratio would affect the performance of DMCs especially under the practical conditions. In this work, the effect of M:C ratio is for the first time numerically studied under conditions similar to plant operation by using both traditional and coarse-grained (CG) combined approach of computational fluid dynamics (CFD) and discrete element method (DEM), called as traditional CFD-DEM and CG CFD-DEM, in which the flow of coal particles is modelled by DEM or CG DEM which applies Newton’s laws of motion to individual particles and that of medium flow by the conventional CFD which solves the local-averaged Navier-Stokes equations, allowing consideration of particle–fluid mutual interaction and particle–particle collisions. Moreover, impulse and momentum connection law is used to achieve energy conservation between traditional CFD-DEM and CG CFD-DEM. It is found that under constant pressure, the M:C ratio affects DMC performance significantly. The specific effect depends on coal washability or coal type. Under extremely low M:C ratio, the phenomenon that high-quality coal product is misplaced to reject is successfully reproduced, which has been observed in plants in Australian coal industry and called as “low-density tail”. Moreover, strategies are proposed to mitigate the “low-density tail” phenomenon based on the model.

Preconcentration of a low-grade betafite ore by dense medium cyclone

Preconcentration of a low-grade betafite ore by dense medium cyclone

Hydrodynamic force analysis of magnetite medium inside dense medium cyclone using multiphase GPU parallelized ASM model

In order to tackle the high compute cost of the multiphase simulations for dense medium cyclones, the development of an open source high fidelity LES based algebraic slip mixture multiphase flow solver is presented. The solver is parallelized on a general purpose GPU using a full load model, which provides around 13 times speed up as compared to a CPU implementation thereby, making design explorations using the current solver more feasible and less time consuming. The traditional ASM model was improved upon using more realistic slurry viscosity model and polydispersed hindered correlation for dense medium operation. The performance of the developed solver for dense medium cyclone operation was validated with the literature based gamma ray tomography (GRT) experimental results. The solver was then used to study the implication of variation in the key aspects of DMC operation such as pressure head, underflow diameter and feed particle concentration. The medium segregation is explained based on a novel non-dimensional force analysis of the drag, shear lift and turbulent dispersion. Finally, the response of the DMC in terms of hydrodynamic force analysis and density differential with the variation in design and operating variables has discussed. Based on the comprehensive force analysis of the medium a justification is provided as to why a lower pressure head is preferred for DMCs used in mineral processing.

Characterization of Cleaning Potential of Khokhar-Bala, Punjab (Pakistan) Coal and Simulation-Based Study for Identification of Best Strategy for its Cleaning

This study involves the characterization of Khokhar-Bala coal of Punjab (Pakistan) coal field to establish its particle distribution data for size, density and floatability through sizing, float-sink tests and release analysis. Khokhar Bala coal contains high amounts of unwanted impurities like ash (35.22%) and sulphur (8.38%). Over 93% of its mass consists of +1.00 mm particles, when run-of-mine coal is crushed to 38 mm. Washability curves, degrees of washing and the S-values show that the coarser fractions (-38+25 mm; -25+13.33 mm; -13.33+3.35 mm) are extremely difficult to clean, whereas the cleaning potential is high for size fractions -3.35+1.00 mm (moderately difficult) and -1.00+0.15 mm (relatively easy). Modelling and simulation of several processing configurations indicate that at 16% target ash content, dense medium cyclone treating 38 x 1 mm coal particles will provide the maximum clean yield of 37.39% with sulphur content of 4.80%.
 

Potential of the dense media cyclone for gold ore preconcentration

ABSTRACTThe dense media cyclone (DMC) has had wide application in beneficiation of coal, iron ore, diamonds and base metals, with limited applications in preconcentrating precious metals such as gold. This paper reports and discusses data from experimental evaluations of the DMC for preconcentrating gold ores. Two ore types were tested in the particle size range from 0.3 mm to 4.75 mm which was considered a pumpable size range. A DMC with a diameter of 100 mm was used to separate the gold ores at separation densities ranging from 2.55 g/cm³ to 2.95 g/cm³. Evaluation of the data confirms the potential of the DMC for gold ore preconcentration, with some ores being more amenable to gangue rejection than others. An optimum density of separation is required for a given type of ore in order to achieve balance between overall mass rejected and gold recovery.

A Detailed study of Applying Gravity Separation to Lead and Zinc Carbonate Ore for Smithsonite Concentration Using DMC

ABSTRACT Gravity separation of a low-grade lead and zinc carbonate ore (case study: Angouran mine, Zanjan, Iran) was investigated based on detailed laboratory and modeling studies. The authors used two types of laboratory sink-float evaluations with single density and multiple densities to demonstrate the effectiveness of Dense Medium Cyclone (DMC) as a new application to separate lead and zinc minerals, in particular, zinc carbonate (Smithsonite) from silica and limestone gangue. The laboratory tests included determining floats from five to six density intervals that descended between the densities of the light and heavy minerals. In addition, the authors used MODSIMTM process simulation software to determine the optimum separating density, zinc grade of concentrate and tailings products, yield and metal recovery. The results showed the possibility of successful gravity separation of the ore. To optimize DMC gravity separation operation in the plant, the circuit was sampled and the effect of important parameters influencing separation performance was studied. The separation efficiency (sharpness) and plant performance to separate valuable minerals were determined by estimating the partition curve for the particle size distribution limited to 0.5–5.6 mm range. The performance indicating parameters including the short circuit fractions to sinks and floats, the separation sharpness and the separating density were estimated to be equal to 0.0116, 1.5885, 20.4 and 3.18, respectively, using the non-linear optimization tool of Excel (Solver) based on least squares method.