Dense Media Separation Density

Dense media (or heavy liquids) Fluids used in dense-medium separation of coal and gangue particles by their relative densities. The medium can be any suitable fluid, but in commercial coal preparation operations, it is usually a suspension of fine magnetite in water. 

Density (gravity) separation Separation methods based on differences in density of separated minerals, such as dense-medium separation and jigging. 

Dense-Medium Washing. Dense-medium separations include processes that dean raw coal by immersing it in a fluid medium with a density intermediate between the density of clean coal and that of reject. Most dense-medium washers use a suspension of fine magnetite in water to achieve the desired density. The process is very effective in providing a sharp separation and is relatively low in capital and operating costs. 

Dense-media separation coal-cleaning method based on density separation, using a heavy-media suspension of fine particles of magnetite, sand, or clay. Dense medium dense slurry formed by the suspension of heavy particles in... 

Separation density 5 Actual density of the dense medium. 

The use of liquids of varying density in a simple float-sink test leads to separation of the raw coal into different density fi actions. In a heavy liquid (dense medium), particles having a density lower than the liquid will float, and those having a higher density will sink. The commercial dense-media separation process is based on the same principle. Since the specific gravity of coal particles varies... 

Any suitable fluid can be used as a dense medium, but only fine solid particles in water suspensions have found wide industrial applications. A good medium must be chemically inert, and must resist degradation by abrasion and corrosion, have high inherent density, be easily recovered from the separation products for reuse, and be cheap. 

In a heavy-medium separation process, coal particles whose density is higher than the medium sink while the lower-density coal particles float the separation efficiency and the through put of the separation device depend on the velocity of coal particles in a dense medium. The viscosity of a medium has little effect on the low-density coal particles or the high-density gangue particles, but becomes critical in the separation of material of a density equal to or near that of the medium hence, a low viscosity must be maintained to separate near-density material at a high rate of feed. 

The efficiency of separation (Ep) in dense-medium baths was found to depend on the plastic viscosity of the media, and a high yield stress (to) of the medium is claimed to cause elutriation of the finer particles into the float as they (and near-density particles) are unable to overcome the threshold shear stress required before the movement takes place. When a particle is held in a suspension, the yield stress is responsible for it but when it is moving, its velocity is a function of plastic viscosity. It is understandable then that dispersing agents used to decrease medium viscosity may improve separation efficiency quite significantly. They may also decrease mag-nitite loses. 

Another separation device that may be used is the mineral jig. This unit produces a loose vibrating bed of particles in a Hquid medium. The vibrations segregate the soHds into layers of density. The dense nonferrous metals, primarily lead, 2inc, and copper are at the bottom while organics are at the top. The middle layer is primarily glass. 

Solids of different densities can be separated by immersing them in a fluid of intermediate density. The heavier solids sink to the bottom and the lighter float to the surface. Water suspensions of fine particles are often used as the dense liquid (heavy-medium). The technique is used extensively for the benefication (concentration) of mineral ores. 

The ligules may be physically separated from each other (low density, i.e., not touching), somewhat overlapping (medium density, as in the cultivar Vilmorin ), or very dense (the base of the ligule overlaps the adjacent ligule) (Pas ko, 1973). 

The density and temperature distribution of interstellar matter, contrary to its elemental composition, is strongly inhomogeneous. At least three different phases exist (e.g. Tielens 2005) (i) extended low-density bubbles of hot ionized gas (hot interstellar medium or HIM, mass fraction 0.003, volume fraction 0.5), resulting from series of SN explosions in mass-rich stellar clusters (ii) cold and dense clouds of neutral gas (cold and neutral interstellar medium or CNM, mass fraction 0.3, volume fraction 0.01), resulting from sweeping up of warm gas and (iii) a warm, either ionized or neutral, medium in between (warm interstellar medium or WIM, mass fraction 0.5, volume fraction 0.5). The essential properties of the three phases are indicated in Fig. 2.4. The coolest and most massive of the clouds are the molecular clouds (MC, mass fraction 0.2, volume fraction 0.0005), a separate component, that are the places of star formation, where new stars are formed as stellar clusters with total masses between about 200 and several 106 M0. 

The cyclone, or inertial separation method, is a common industrial approach for segregating a dispersed phase from a continuous medium based upon the difference in density between the phases. The concept takes advantage of the velocity lag which occurs for dense particles with respect to a lower density medium when both phases are subject to an accelerating flow field, such as within a rotating vortex. The larger the acceleration, the smaller the particle which fails to follow the continuous phase streamlines and will migrate to the outer wall of the cyclone for collection. 

Creaming is the separation of dispersed droplets from the continuous phase under the action of gravity. The droplets do not coalesce when they touch. If the dispersed medium is less dense than the continuous phase, the emulsion will cream upwards. Conversely, for a more dense dispersed phase, the emulsion will cream downwards or sediment. Creaming will inevitably occur in any dilute emulsion in accordance with Stokes s law if the phases are not exactly equal in density. Creaming is, therefore, a trivial form of instability that can be avoided by addition of thickeners that confer plastic rheology, and, therefore, yield value to the aqueous phase. 

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