Dense Medium Separation Research Articles

Dense medium separation of coarse andalusite using waste iron powder as solid medium

Dense medium separation (DMS) using a waste iron powder from a powder metallurgical plant as solid medium was studied to produce a coarse andalusite concentrate from Kuerle andalusite ore. A high-grade, coarse, andalusite concentrate assaying over 92% andalusite was produced by DMS and magnetic separation, which satisfies the market for the production of a high-duty refractory material. It was also found that the viscosity of waste iron powder suspension could be greatly reduced by adding sodium silicate, leading to better DMS efficiency. The main parameters in DMS of Kuerle andalusite ore, namely feed medium density, underflow spigot diameter and feed pressure, have been studied.

Effectiveness of the dense medium and the froth flotation methods in cleaning some Turkish lignites

The feasibility of cleaning three Turkish lignites (Beypazarı, Gölbaşı and Kangal lignites) by the dense medium separation or the froth flotation method has been investigated. Solutions of zinc chloride (ZnCl 2) with specific gravities ranging from 1.1 to 1.75 have been used as the dense medium. In the case of froth flotation, methyl isobutyl carbinol (MIBC), diethyl isohexanol (DEH) and sodium dodesyl sulphonate (SDS) were used as the frother and kerosene was used as the collector. In both methods, each lignite sample was separated into two sub-fractions: the lignite rich part and the mineral matter rich part. The results indicate that the effectiveness of the methods in ash and sulphur removal is appreciably different for the different lignites. An effective pyritic sulphur removal (over 90%) was obtained for Beypazarı or Gölbaşı lignites by the dense medium separation. The effectiveness of the froth flotation was relatively different depending on both the lignite and frother type. The recovery is generally low and changes considerably depending on the frother type and particle size.

Characterisation of Ferrosilicon Dense Medium Separation Material

Ferrosilicon is used in the dense medium separation of iron ore at Kumba resources, Sishen, South Africa. Due to high cost and losses that occur during use, maximum recovery by means of magnetic separation is aimed for. The purpose of this project was to determine the characteristics of the unused Fe-Si and then to characterise the changes that occur during storage and use thereof. Scanning electron microscopy was used to determine the composition of each sample, whilst Mossbauer spectroscopy yielded a two-sextet spectrum with hyperfine magnetic field strengths of 20 and 31 T, respectively, for the fresh samples. Additional hematite oxide peaks appeared in the Mossbauer spectra after use of the Fe-Si over a length of time, but this did not result in a dramatic degradation of the medium. No definite changes occurred during correct storage methods. It was, however, found that the biggest loss of Fe-Si was due to the abrasion of the particles, which resulted in the formation of an oxihydroxide froth, during the process.

The Effect of Magnetic Field on the Performance of a Dense Medium Separator

The application of a vertically oriented magnetic field external to a dense medium cyclone can be used to manipulate the density differential within the cyclone by influencing the cyclone′s internal ferrosilicon distribution. Tests were conducted on a well‐defined dense medium system using a pilot‐plant cyclone equipped with a solenoid magnet. The objective was to determine the yield to the dense medium cyclone underflow of a sample consisting predominantly of quartzite material, as a function of the magnetic field strength of the solenoid magnet, and as a function of solenoid position. It was observed that for a specific selection of magnetic field strength and solenoid position, the concentrate yield was reduced. A decrease in yield to concentrate is advantageous in that it reduces the mass of material to be processed downstream. The yield reduction was found to be a function of the applied magnetic field strength. Furthermore, it was found that a disruption in the ferrosilicon flow pattern inside the cyclone may occur beyond a certain magnetic field strength which leads to impaired cyclone operation.

A plant comparison of the vorsyl separator and dense medium cyclone in the treatment of Indian coals

In India, a major portion of metallurgical coal of desirable ash is produced from the dense medium cyclone (DMC) process. Based on detailed laboratory studies, vorsyl separator (VS), a centrifugal dense medium separator, was established to be a possible alternative to the dense medium cyclone. To establish further at commercial scale, trials were undertaken with 400 and 600-mm vorsyl separators made of mild steel, at the captive washeries of the Tata Iron and Steel. The studies clearly showed that the VS gave about 4% higher combustible recovery compared to a DMC at the same ash rejection level. Generalised E p value of 0.033–0.045 for VS was also found lower compared to 0.043–0.068 for DMC. This clearly established the better sharpness of separation in VS compared to DMC. Vorsyl separator made of suitable wear-resistant material is recommended for regular plant use.

Combination of sink–float separation and flotation technique for purification of shredded PET-bottle from PE or PP flakes

In this contribution, the separation of polyethylene terephthalate (PET)–polyethylene (PE) and polyethylene terephthalate (PET)–polypropylene (PP) mixtures was studied in order to improve the grade of the raw input used in PET bottle recycling. First, PET bottles and their caps (made of PE or PP) were shredded and the floatability of each polymer was tested. Even with the addition of the wetting reagents dodecylamine acetate (DAA) or polyvinyl alcohol (PVA), the results did not suggest that the required 99.995% purity of PET plastic could not be achieved by floatation. Second, the mixtures were separated with a sink–float process using a drum separator. Finally, as the required purity of PET could not be obtained by either technique alone, a system utilising a combination of the two processes was developed. This system easily achieved the desired PET grade. At last, some sink–float experiments were performed with a medium of magnesium sulphate (dense medium separation).

Application of ultrasonics to enhance wet-drum magnetic separator performance

Wet-drum magnetic separators are used extensively for upgrading iron ore and for magnetite recovery in dense-medium separation circuits. In this study, the performance of a continuous, laboratory wet-drum magnetic separator was evaluated both with and without the application of ultrasonic energy when processing dense medium slurries. Test variables included magnetic-to-nonmagnetic ratio, solids concentration and nonmagnetic material. The results indicate that, under certain conditions, the purity of the magnetic material increased after ultrasonic treatment.

Parametric Evaluation of a Dense-Medium Process Using an Enhanced Gravity Separator

Dense-medium separators have proven to be the most efficient processes for removing the undesirable gangue material from run-of-mine coal. A test program has been conducted to evaluate the parametric effects on a magnetite-based dense-medium application in an enhanced gravity separator (EGS), which mechanically generates an enhanced gravity field. Optimization using empirical models developed utilizing data obtained from a statistically designed test program revealed that a complex manipulation of the medium density, bowl speed, and underflow tailings rate is needed to achieve maximum mass recovery over a range of clean coal ash contents. Subsequent experimental results validated the optimum performances predicted from the empirical models. Organic efficiency values greater than 95% were obtained over a wide range of product ash contents for the treatment of a 1000×45 micron coal sample.

Particle movement in non-Newtonian slurries: the effect of yield stress on dense medium separation

The hydrodynamic theory of particle movement in non-Newtonian fluids is addressed from a rheological perspective. The shear rate due to particle-to-fluid relative movement, the particle Reynolds number in non-Newtonian fluids, and a general form of Stokes’ equation for non-Newtonian fluids are proposed. It is concluded that the fluid drag on a sphere moving in a yield-shear thinning or Bingham plastic fluid is jointly determined by the yield stress and viscosity. For fine particles, the influence of the yield stress becomes dominant. From this conclusion it can be deducted that the dense medium separation of fine and/or near density particles is most affected by the medium yield stress.

Rheology of gas–solid fluidized bed

Coal dry beneficiation with gas–solid fluidized beds belongs to dry dense medium separation. It is important for us to study the rheological behaviors of gas–solid fluidized beds. In this paper, the viscosity of fluidized beds was measured by the solid-settling experiments. The rheological characteristics of fluidized beds can be described with Bingham fluid model. The effective viscosity of fluidized beds can be calculated. The plastic viscosity and yield stress of fluidized beds can be obtained by linear regression analysis of the experimental data. The calculated results agree with the experimental data well.

The influence of particle shape on the dynamic dense medium separation of plastics

The separation of post-consumer plastics of different polymeric compositions is becoming an important topic for the reduction of waste and promotion of recycling. The comminution of plastics creates variable particle shapes which cause difficulties in the separation by a cyclone. To study the influence of particle shape, tests have been performed to determine how the partition curve changes with particle shape in cylindrical cyclones. The test results give a complete picture on the influence of particle shape and size on the cut density d 50 and the probable error E p. Coupled with a mathematical description of the partition curve, these parameters can assist in process simulation, selection and design of dense medium separation (DMS) systems devoted to plastic recycling.

Rheology of Low Density Suspensions in Dense Medium Separation of Post-consumer Plastics*

The aim of this paper is to investigate the feasibility of using clay suspensions in dynamic dense medium separation of post-consumer plastics. The Theological behavior of suspensions formed with different commercial clay samples was studied to ascertain that both viscosity and stability could be maintained in the range required by dense medium separation systems. Suspensions made with a selected clay sample were used in a laboratory test rig equipped with a conical cyclone and a cylindrical cyclone with peripheral underflow discharge. Preliminary separation tests were carried out using different density plastic tracers. The results with both separators demonstrated that the separation of two plastics of different densities can be obtained.

Application of dense-medium in an enhanced gravity separator for fine coal cleaning

Dense-medium separators have proven to be the most efficient processes for removing the undesirable gangue material from run-of-mine coal. The application of high-pressure feed injection into dense-medium cyclones to provide an elevated centrifugal force has recently been found to allow efficient separation performances for the treatment of fine coal (i.e., <1000 μm). However, high-pressure injection requires specialized pumps and results in relatively high maintenance requirements. A test prograrn has been conducted to evaluate the potential cleaning of 1000 x 44 μm fine coal using dense-medium in an enhanced gravity separator (EGS), which mechanically generates enhanced gravity field. Test results indicate that the use of dense-medium in an EGS resulted in an 8% weight unit increase in mass yield compared to the use of water-only for the treatment of an easy-to-clean Illinois No. 6 fine coal sample. For a difficult-to-clean coal, the mass yield improvement was significantly greater at nearly 20% by weight. From the treatment offour different coal samples, organic efficiency values greater than 90% were obtained over the entire range of product quality values. These findings are reflective of the highly efficiency, low density separations provided by the dense-medium as indicated by probable error values below 0.05.

The mechanism of magnetics capture in the wet drum magnetic separator

As part of a larger body of work aimed at developing mathematical models of the wet drum magnetic separator in dense medium separation, four factorial experiments, each of sixteen trials, were carried out using magnetite feed to such a separator. This work was done in a purpose built rig based on a small industrial scale (700mm lip length, 900mm diameter) wet drum magnetic separator. The magnetite lost in these trials, that is reporting to the effluent, was universally found to be of lower susceptibility than the feed, but was commonly found to be coarser than the feed. These observations are explained in terms of a conceptual model of the mechanism by which magnetic material is captured. This explanation is supported by both magnetic theory and high speed photography. It is proposed that the capture of magnetic particles in the wet drum magnetic separator is by a flocculation process which proceeds rapidly at high pulp density, but only very slowly with low pulp density feeds.

00/00018 Design Fuels Corporation (DFC)—Apache, Inc. Coal reclamation system for the plant of the future for processing clean coal

The mechanical washing processing and drying portion of the DFC process offers an efficient method for cleaning of pyritic sulfur bearing compounds which represents 25% sulfur reduction from original run-of-mine coal quality. This reduction can be augmented with the use of calcium and sodium based compounds to reduce the sulfur in many coals to produce compliance quality coal. The use of mechanical/physical methods for the removal of the pyritic material found in coal is used by the DFC process as a first step to the final application of a complete coal refuse clean-up technology based on site specific conditions of the parent coal. The paper discusses the use of the DFC process to remediate slurry ponds and tailings piles and to improve coal cleaning by gravity separation methods, flotation, hydrocyclones and spiral separators, dense media separation, water only cyclones, and oil/solvent agglomeration. A typical DFC Project is the Rosa Coal Reclamation Project which involves the development of a bituminous coal waste impoundment reclamation and washery system. The plant would be located adjacent to a coal fines pond or tailings pond and refuse pile or gob pile at a former coal strip mine in Oneonta, Alabama. Design Fuels would provide amore » development program by which coal waste at the Rosa Mine could be reclaimed, cleaned and sold profitably. This feedstock could be furnished from recovered coal for direct use in blast furnaces, or as feedstock for coke ovens at 250,000 tons per year at an attractive price on a 10-year contract basis. The site has an old coal washing facility on the property that will be dismantled. Some equipment salvage has been considered; and removal of the existing plant would be the responsibility of Design Fuels. The paper briefly discusses the market potential of the process.« less

Static and Dynamic Stability in Dense Medium Separation Processes

Static and dynamic stability in dense medium separation processes are defined, and a model for dynamic DMS systems provides the density differential (a measure of dynamic stability) as a function of the static stability and parameters related to the geometry of separatory vessels and operating conditions. A pilot test rig was installed to: (a) study the behaviour of conical and cylindrical dense medium dynamic separators particularly concerning sink and float densities and density differential under different operating conditions; (b) check the correlation model between density differential and static stability. The results provide an interesting description of the different behaviour of conical and cylindrical vessels, regarding the density differential they exhibit, and help explain the differences between the performance of the two types of separators.

The Rheology of Ferrosilicon Dense Medium Suspensions

Medium rheology is important to the efficiency of dense medium separation processes. An impediment to the selection of appropriate ferrosilicon products for a given DMS process in the past has been the lack of a consistent and comprehensive set of data describing the rheology of the range of manufactured ferrosilicon products. Rheological tests have therefore been conducted using Samancor ferrosilicon dense media over a wide range of media properties and densities, with a modified Debex online viscometer. The data have been successfully fitted to the MV-model that allows apparent viscosity to be predicted as a function of particle size distribution and shape, and medium density and temperature. The results from this procedure provide the expected viscosity ranges for uncontaminated ferrosilicon dense media slurries.

Textural properties in density-separated coal fractions

The results presented in this work are part of a more extensive research programme aimed at assessing the impact of coal porous structure on density-based process evaluation and modelling. The coal samples used were obtained from two different density-based cleaning processes, a Vorsyl dense medium separator for treating an anthracite (TW) with a size fraction of 0.5–8.0 mm and a spiral concentrator for treating a bituminous coal (DH) with a size of less than 2 mm. Textural characterisation of the samples was carried out by measuring true (helium) and apparent (mercury) densities and mercury porosimetry up to a maximum pressure of 200 MPa. Adsorption isotherms in CO 2 at 273 K were also determined for both coal series. In the case of the bituminous coal series a linear relationship between porosity and ash level was found. This may have important implications if coal porosity and/or textural parameters need to be incorporated into new density-based simulation models.

Dense medium separation using a teetered bed separator

A Teetered Bed Separator (TBS) was used autogenously, and with a range of media, to study the dense medium separation of a coal feed slurry, −2.00+0.375 mm in size. The feed slurry consisted of separate portions of a clean coal fraction, and a mineral matter fraction. A series of experiments were conducted using (i) the clean coal only, (ii) the clean coal combined with a portion of the mineral matter, (iii) the clean coal and mineral matter combined with dense media such as magnetite, or sand, or barite. These combinations of feeds provided a basis for assessing the benefits gained from using autogenous dense media, and a range of possible dense media. It was conluded that the TBS performance is improved by increasing the suspension density, and that this is best achieved by operating at the lowest possible water fluidization rate, and using a media with a settling velocity of similar magnitude to the settling velocities of the particles to be separated.

Low dense media process: a new process for low-density solid separation

Presented is a new gravity method for separating low-density plastics. Analogous to dense media separation, in this new low-density gravity separation process, instead of the suspension being water+high-density solids, it is water+low-density solids. Using water with suspended cork particles, one may create a medium with a density as low as 0.75 g/ml. Employing the same equipment as used for dense media separation, but with the low-density slurry, two or more materials with densities below 1 g/ml may be economically separated. One can separate the widely used commercial plastics PMP (0.83 g/ml) from HPDE (0.95 g/ml).