Dense Medium Separation Research Articles

INVESTIGATION OF SEPARATION PERFORMANCE OF DENSE MEDIUM CYCLONE USING COMPUTER SIMULATION

Dense medium coal processing technology has been widely used in coal preparation industries in the world since it is the most accurate and efficient coal preparation process to obtain clean coal with a highest possible yield. Separation of coal and impurities using this technology is based on density differ- ences. In literature, a number of mathematical models exist for dense medium cyclones. One of the most widely used model in the coal industry was developed by Mineral Technologies, Inc. This model consists of the equation which predicts the operating performance of a well maintained dense medium separator for a given cyclone geometry (including cyclone diameter) and separation density. In this study, MODSIM© (education/demo version) dense medium cyclone model was applied to coal preparation plant owned by Soma Uyar Mining Co. As a result, the float-sink test results at separation density of the dense medium cyclone were predicted.

Application of Dense Media Separation for Beneficiation of Lignite Mining Waste into Combustible Fuel

The main purpose of coal separation is to reduce ash, sulfur, and other mineral contaminants in the coal to increase the calorific value and benefit the environment. Dense media separations have proven to be the most efficient processes for removing the undesirable gangue material from lignite mining in Gurha block of Bikaner, Rajasthan. Experiments have been conducted with cumene and carbon tetra chloride treating coal in the size range -10 mm to +4.75 mm. The low category lignite can be transformed into marketable high calorie carbonaceous fuel with more than 62% recovery, fit for on-site power generation, Lime kilns, manufacture of cement, etc., using dense media separation through a sink and float experiment.

Research on the intelligent control of the dense medium separation process in coal preparation plant

The density of the dense medium separation used to be controlled according to the desired density given by the operators, which depended on the ash data assayed in each hour. Recently, it is indicated through research and practice that the density of the dense medium separation could be controlled intelligently. The control process is implemented through the procedure as follows. The property of the feed coal would be calculated firstly based on the scanned ash of raw coal on line, thus the process parameters, including the density of the dense medium separation, would be forecasted and optimized. The optimized desired density of circulatory medium would be transmitted to the control system. Similarly, the liquid level of the buckets and silo, the amount of the bypass flow, and the added medium would be calculated and controlled intelligently. The research result could reduce the effect of man's activity on the dense medium separation process, shorten the delay time of the process control, and enhance the efficiency of the dense medium separation. The key technology of the intelligent control of the dense medium process is the forecasting process parameters in the dense medium separation process.

Understanding the Effect of Attrition Scrubbing on the Efficiency of Gravity Separation of Six Inorganic Contaminants

Physical separation methods are normally preferred over chemical methods, but their efficiency often fails to meet the remediation targets for various reasons. Attrition scrubbing could possibly be used to improve their effectiveness. The aim of this study was to demonstrate the usefulness of attrition scrubbing prior to a gravity separation technique and to understand the mode of action involved. Contaminated soil divided into three fractions (0.250–1-, 1–2-, and 2–4-mm) and containing six inorganic contaminants was submitted to attrition scrubbing prior to a gravity separation method (shaking table or jig). The proportions and contaminant contents of attrition sludges and separation products were characterized. A dense media separation was realized to predict the efficiency of gravity separation. The shape of particles and the liberation of contaminants for the 0.250- to 1-mm soil fraction were characterized from image analysis. Attrition significantly improved the gravity separation efficiency for five out of six contaminants. However, attrition moderately impacted the gravity separation efficiency of contaminants for coarser soil fractions. Attrition significantly improved the sphericity of particles from the 0.250- to 1-mm fraction of 3 % and significantly reduced their size. The liberation of contaminants was also increased for Pb and Sn together from 17 % for the same soil fraction. However, despite the attrition scrubbing treatment, differences in the removal efficiencies between the dense media separation and the gravity separation remain important for most of the contaminants. This study suggests that the attrition scrubbing effects and mode of action depend on the size of particles.

Preconcentration strategies in the processing of nickel laterite ores part 2: Laboratory experiments

A number of physical separation techniques for nickel (Ni) laterites have been investigated at laboratory and pilot plant scale and reported in the open literature. These included sink–float (or dense media) separation, gravity separation, magnetic separation, electrostatic separation, (roasting) and flotation. The information located so far and reported in the literature review by Quast et al. (2015) suggests that all these techniques, although providing some degree of upgrading, have not been incorporated into full plant operations as yet. The only successful preconcentration technique incorporated into some commercial operations has been the removal of a coarse product containing lower Ni values than the feed. In this work, the application of a number of physical separation techniques (screening, gravity and magnetic separation with and without roasting) has been investigated in the laboratory for upgrading three Western Australian low-grade Ni laterites (goethitic, siliceous goethitic and saprolitic). Roasting of the goethitic laterite caused a noticeable increase in Ni and Co (and corresponding mass) recovery into the magnetic product with temperature up to a certain point, but this effect was reversed at 650°C. Overall, the application of the selected techniques failed to produce any significant Ni grade enhancement for these three laterite ores. These tests confirm that the complex mineralogy of these three Ni laterite ores compromises any significant upgrading in Ni values by standard physical separation techniques.

Dynamic model for a dense medium drum separator in coal beneficiation

Dense medium drum (DMD) separators are unit processes that are typically used to beneficiate coal, iron ore and other minerals by making use of density separation. Some coal dense medium separation plants typically include a DMD separator. The operational management of this unit process is often limited to localised control of medium density and feed mass flow rate. Dynamic models for coal dense medium separation have been developed by the authors with the intention of using them for dynamic control.A suitable dynamic model for a DMD separator could not been found in the available literature. This paper shows how the dynamic model for a dense medium cyclone has been applied to a DMD separator. The model parameters were determined and the performance of the model is evaluated using actual plant data from a Wemco drum. Coal washability and drum partitioning behaviour are used to estimate the grade of the product for model grade simulation and validation.

THEORETICAL ANALYSIS OF HYDRODYNAMIC PARAMETERS OF PARTICLE MOVEMENT IN CENTRIFUGAL DENSE-MEDIA SEPARATION UNIT

A short description of centrifugal dense-media separation unit with two-layered isolation medium designed for improvement in the quality of gravity concentrates is given in dressing crude ore of color, rare, and precious metals; its basic diagram is shown. The solution of differential equations describing the separated particle movement in the working area is considered. As a result, analytical expressions of the most important hydrodynamic parameters of easy and heavy particle movement, i.e. their radial and longitudinal speeds necessary for correct calculations of the basic constructive elements of the separation unit, are obtained. The tests of a laboratory model of the device on artificial mixtures of quartz and galena have shown that the mutual contamination of separation products does not exceed 5 %.

Study on a Sink and Float Test of a Lead-Zinc Ore from Yunnan

The paper analyses problems of a lead-zinc ore from Yunnan with a sink and float test. In the paper, we explored the possibility of pre-discarding about the ore by dense-media process. Dense liquids with the specific gravity of 2.6, 2.7 and 2.8 were used in the test, respectively. -12mm crudes were taken into the test. Finally, it revealed that pre-discarding by dense-media separation can be used in the ore. 2.7 was taken as the best specific gravity of separation. 12~1mm was used as the optimal fraction of pre-discarding by dense-media separation. Pre-discarding rate was 45.53%. The light product with a lead grade of 0.29% and a lead recovery of 4.29% was pre-discarded in which the grade and recovery of zinc were 0.22 and 5.84, respectively.

Process Control of Dense Medium Separation Based on Improved Implicit Generalized Predictive Control Algorithm

In order to solve the model mismatch between density and liquid level of heavy medium suspension during the dense medium separation process, implicit Generalized Predictive Control (GPC) was applied to realize the on-line identification for model parameters and the decoupling control for density and liquid level of heavy medium suspension. And then improving the implicit GPC algorithm, it can ensure good control performance by constraining control increment to avoid solving the inverse matrix and reduce the computational complexity. The simulation result shows that improved implicit GPC is more effective for the model characteristic of the dense medium separation process with large lag and strong coupling, it has strong anti-interference capability, and the system output is still stable in the case of model mismatch.

Particle separation by horizontal deflection in paramagnetic fluid

This paper describes the horizontal deflection behaviour of the streams of particles in paramagnetic fluids under a high-gradient superconducting magnetic field, which is the continued work on the exploration of particle magneto-Archimedes levitation. Based on the previous work on the horizontal deflection of a single particle, a glass box and collector had been designed to observe the movement of particle group in paramagnetic fluids. To get the exact separation efficiency, the method of “sink–float” involved the high density fluid polytungstate (dense medium separation) and MLA (Mineral Liberation Analyser) was performed. It was found that the particles were deflected and settled at certain positions on the container floor due to the combined forces of gravity and magneto-Archimedes forces as well as a lateral buoyancy (displacement) force. Mineral particles with different densities and susceptibilities could be deflected to different positions, thus producing groups of similar types of particles. The work described here, although in its infancy, could form the basis of new approach of separating particles based on a combination of susceptibility and density.

Coal dense medium separation dynamic and steady-state modelling for process control

Coal dense medium separation is a popular beneficiation process used for the upgrading of coal ore into power station and metallurgical coal. The control systems used in coal beneficiation are often limited to localised regulatory control of feed rate and medium density. A coal dense medium separation process can benefit substantially from process control provided that a dynamic model for this process is available as was previously developed by the authors for a fine coal dense medium cyclone (DMC) circuit. In this paper, the previous model is adapted to a coarse coal DMC circuit and validated over a wider range of operating conditions using real plant data. The model is further validated by reducing it to steady-state to form a partition curve. This curve is then compared to one derived from actual production data. The derived model is able to provide an estimate of the DMC overflow coal product that should be sufficient for process control.

Innovative Design for Autogenous Medium Cyclone Based on TRIZ

In order to solve the issues of the separation of the high-density mineral, TRIZ method of technical contradiction inventive principles was utilized to provide ideas to design a new-type dense medium separation equipment. The technical contradiction of the separation of high-density mineral by Dense medium separation technology was described by a pair of general engineering parameters, and the innovative principles were obtained by the technology of contradiction matrix. The concrete implementations of these innovation theories were carried, Combing with the actual situation of the separation. And a new-type Autogenous medium cyclone is developed which shall be more suitable for the separation of the high-density mineral.

Upgrading valuable mineralization and rejecting magnesium silicates by pre-concentration of mafic ores

Amenability of mafic ores to pre-concentration was investigated with respect to ore mineraliza- tion characteristics. For the pre-concentration tests seven ores from various nickel-copper operations at Sudbury, Ontario were subjected to dense medium separation. Size assays of metal values, i.e. distribu- tion of nickel and copper with respect to size fractions, were also determined. The ores were assessed in three categories of valuable mineralization as massive pure sulphides, coarse massive sulphide grains and disseminated sulphides. For ores with massive pure sulphides and coarse massive sulphide grains even a size classification based pre-concentration route could be sought since a clear trend of metal enrichment was identified towards finer fractions. Orebodies of similar mineralogy had similar responses to pre- concentration tests. The best results were for those ore bodies with a distinct differentiation between mineralization and gangue, i.e. the ores with massive pure sulphides, where nickel recoveries of 97% and mass rejections of 38-53% were achieved. Similar results were obtained for ores with coarse massive sulphides. For disseminated sulphide mineralogy relatively lower mass rejection was attained with ac- ceptable recoveries of metals. Rejection of magnesium bearing gangue, such as talc, was identified as another benefit of pre-concentration. The extent of magnesium rejection occurred as a function of ore mineralogy. Clear distinction between valuable mineralization and gangue provided preferential magnesi- um rejection at high levels with no or minor metal losses.

Cleaning study of a low-rank lignite with DMS, Reichert spiral and flotation

The cleaning potential of a low-rank lignite coal has been evaluated via dense medium separation (DMS), Reichert spiral and flotation techniques. The washability characteristic of the lignite was investigated with laboratory sink and float tests. Solutions of zinc chloride (ZnCl2) with specific gravities ranging from 1.3 to 1.9 were used as dense medium liquid. The as-received raw lignite sample was sieved into three size fractions (−100+25mm; −25+1.5mm; −1.5mm) and washability characteristics of the former two fractions were separately investigated. The latter fine fraction was cleaned using both DMS and Reichert spiral techniques under different operational parameters. Flotation tests were conducted using the −150μm fraction. Clean coal characteristics and recoveries were determined after each experiment.Elementary ash and ±0.1 relative specific gravity curves showed that this low-rank coal can be classified as “difficult to clean” due to its high content of near-gravity materials at specific gravities lower than 1.7. However, about 50% and 40% of the raw coal (3571kcal/kg) can be obtained as clean coal with calorific values of 5400kcal/kg for the coarse fraction and 5600kcal/kg for the fine fraction, by DMS and Reichert spiral methods, respectively. The ash contents (14–18%) and calorific values (6022–5582kcal/kg) of the cleaned coarse and fine fractions are suitable for use in industry. Low calorific value (about 2500kcal/kg) middling and tailing can be used in properly constructed thermal electric power plants.

Study on washability of microcrystal graphite using float–sink tests

This article presented an experimental research on washability of microcrystal graphite using float–sink tests. Chemical and X-ray analyses showed that graphite, semi-graphite, meta-anthracite, and anthracite existed together in this microcrystal graphite sample; and the intergrowth relationship between microcrystal graphite and gangues was very complicated based on optical mineralogy research. The results of float–sink tests revealed that: for the −25+0.5mm size fraction, about 68% (by weight) of microcrystal graphite was obtained at the density of 2.0g/cm3, and the float product met the standard of commercial grade W65; for the −0.5mm size fraction, 58% (by weight) of microcrystal graphite was floated at the density of 2.0g/cm3, which met the standard of commercial grade W70. It can be concluded that microcrystal graphite may be upgraded by dense media separation (DMS) providing a float product using as the raw materials of casting or refractories.

Coal petrology characteristics of middlings from Qianjiaying fat coal mine

The objective of this paper is to evaluate the coal petrology characteristics of slack middlings (13–0.5mm) of dense media separation and flotation middlings from Qianjiaying fat coal preparation plant. Phase composition, macerals distribution, microlithotype and mineral occurrence of the two middlings were studied by XRD analysis and polarized light microscopy observation. Macerals distribution and wettability of the float-and-sink products separated from the middlings after grinding was investigated to determine the liberation degree. Studies show that there are more vitrinite and mineral, but less inertinite in slack middlings than in flotation middlings. Macerals associated with mineral in slack middlings is 69.85%, by volume, which is 17.86% higher than that in flotation middlings. Minerals in slack middlings are dominated by pyrite and clay, which are disseminated with the diameter less than 2μm. The main mineral in flotation middlings is clay with size range of 2–20μm. Single macerals in the slack middlings are difficult to liberate due to the fine-grained minerals. After grinding, macerals associated with minerals in the slack middlings decrease to 46.73%, by volume, which is higher than in flotation middlings by 25.89%, by volume. For slack middlings with poor liberation degree, density fractions below 1.8g/cm3 is hydrophobic with contact angle above 71.5°. For the well liberated flotation middlings, there is significant wettability difference among the float-and-sink products. This research is the theoretical basis to realize re-separation of middlings.

Dry Coal Cleaning Based on Dry Dense Medium Separation Using a Gas-Solid Fluidized Bed

Dry Coal Cleaning Based on Dry Dense Medium Separation Using a Gas-Solid Fluidized Bed

Development of Thickener-Modeled Dry Dense Medium Separator for High-Speed and Low-maintenance Separation

Development of Thickener-Modeled Dry Dense Medium Separator for High-Speed and Low-maintenance Separation

Beneficiation of Coarse Coal Ore in an Air-Fluidized Bed Dry Dense-Medium Separator

The beneficiation of different size fractions (+5, −31 mm) of coal using an air-fluidized bed dry dense-medium separator with silica/zircon sands as the fluidizing-bed medium has been studied. Particle size and bed height were found to strongly influence the efficiency of separation with the dry dense-medium separator. An increase in bubble size associated with increase in bed height to 15 cm results in density variations within the bed that increase the probable error for deeper fluidized beds for the smaller particles up to 0.19 from 0.06 for the shallower 10 cm bed. Good agreement was found between the theoretical yield and ash content obtained from washability curves (produced from conventional float/sink tests) and the actual yield from the dry fluid bed separation for the bulk coal sample. A comparison with industrial coal-washing unit operations indicates that dry dense-medium separations are a strong candidate as an energy- and resource-efficient alternative process.

Disassembly and physical separation of electric/electronic components layered in printed circuit boards (PCB)

Although printed circuit boards (PCBs) contain various elements, only the major elements (i.e., those with content levels in wt% or over grade) of and precious metals (e.g., Ag, Au, and platinum groups) contained within PCBs can be recycled. To recover other elements from PCBs, the PCBs should be properly disassembled as the first step of the recycling process. The recovery of these other elements would be beneficial for efforts to conserve scarce resources, reuse electric/electronic components (EECs), and eliminate environmental problems. This paper examines the disassembly of EECs from wasted PCBs (WPCBs) and the physical separation of these EECs using a self-designed disassembling apparatus and a 3-step separation process of sieving, magnetic separation, and dense medium separation. The disassembling efficiencies were evaluated by using the ratio of grinding area (Earea) and the weight ratio of the detached EECs (Eweight). In the disassembly treatment, these efficiencies were improved with an increase of grinder speed and grinder height. 97.7% (Earea) and 98% (Eweight) could be accomplished ultimately by 3 repetitive treatments at a grinder speed of 5500rpm and a grinder height of 1.5mm. Through a series of physical separations, most groups of the EECs (except for the diode, transistor, and IC chip groups) could be sorted at a relatively high separation efficiency of about 75% or more. To evaluate the separation efficiency with regard to the elemental composition, the distribution ratio (Rdis) and the concentration ratio (Rconc) were used. 15 elements could be separated with the highest Rdis and Rconc in the same separated division. This result implies that the recyclability of the elements is highly feasible, even though the initial content in EECs is lower than several tens of mg/kg.