Sedimentation


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sedimentation

[‚sed·ə·mən′tā·shən]
(chemistry)
The settling of suspended particles within a liquid under the action of gravity or a centrifuge.
(geology)
The act or process of accumulating sediment in layers.
The process of deposition of sediment.
(metallurgy)
Classification of metal powders by the rate of settling in a fluid.

Sedimentation

The natural process of depositing sediment.

Sedimentation

 

the settling or surfacing of particles in the dispersed phase, such as solid particles, liquid droplets, or gas bubbles, in a liquid or gaseous dispersion medium as a result of a gravitational field or centrifugal force. Sedimentation occurs if the directional motion of the particles under the effect of gravity or centrifugal force predominates over the random thermal motion (seeBROWNIAN MOVEMENT and DIFFUSION).

The rate of sedimentation depends on the mass, size, and shape of the particles, the viscosity and density of the medium, and the acceleration caused by the force field. For fine spherical partices that do not interact with each other, the sedimentation rate can be determined by Stokes’ law. Sedimentation in dispersed systems—especially in a gaseous dispersed medium—is often accompanied by an increase in the size of the settling particles as a result of coagulation or coalescence.

Sedimentation in nature causes the formation of sedimentary rocks, the clarification of water in large bodies, and the release of liquid drops and solid particles from the atmosphere.

In industry, sedimentation is used in the separation of powders into fractions and the isolation of various products in chemical engineering. (See alsoELUTRIATION and SETTLING.)

Sedimentation (industry)

The separation of a dilute suspension of solid particles into a supernatant liquid and a concentrated slurry. If the purpose of the process is to concentrate the solids, it is termed thickening; and if the goal is the removal of the solid particles to produce clear liquid, it is called clarification. Thickening is the common operation for separating fine solids from slurries. Examples are magnesia, alumina red mud, copper middlings and concentrates, china clay (kaolin), coal tailings, phosphate slimes, and pulp-mill and other industrial wastes. Clarification is prominent in the treatment of municipal water supplies.

The driving force for separation is the difference in density between the solid and the liquid. Ordinarily, sedimentation is effected by the force of gravity, and the liquid is water or an aqueous solution. For a given density difference, the solid settling process proceeds more rapidly for larger-sized particles. For fine particles or small density differences, gravity settling may be too slow to be practical; then centrifugal force rather than gravity can be used. Further, when centrifugal force is inadequate, the more positive method of filtration may be employed. All those methods of separating solids and liquids belong to the generic group of mechanical separations. See Centrifugation, Clarification, Filtration

Particles too minute to settle at practical rates may form flocs by the addition of agents such as sodium silicate, alum, lime, and alumina. Because the agglomerated particles act like a single large particle, they settle at a feasible rate and leave a clear liquid behind.

References in periodicals archive ?
The sedimentation of Nanofluids, after sonication were recorded using digital camera and shown in the fig.
Sedimentation imparts negative impact on the storage capacity of the reservoir as it lessens the active and live storages.
After determining the sedimentation rating relationships for various seasons by the means of mean discharge data in previous stages, sedimentation value has been calculated for different years and different seasons.
Sediment traps (6:1 aspect ratio, n = 4 per site) were deployed and collected monthly (February 2008-August 2009) to estimate sedimentation rates at the three selected sites.
Evaluation of sealed vacuum extraction method (Seditainer) for measurement of erythrocyte sedimentation rate.
The question has therefore been raised if mussel culturing on longlines significantly affects the benthic conditions in the eutrophic Limfjorden or if the environmental impacts are negligible resulting from the high rates of sedimentation enhanced by high pelagic primary productivity and the high pools of organic matter already present in the sediments.
The company president and chief executive officer, Martin Quick, said, 'The construction of the power line and sedimentation pond are essential for the dewatering and rehabilitation of the underground mine workings.
The basic mathematical theory of sedimentation is related to Stokes's Law, which governs the behavior of spherical particles suspended in a liquid.
Kujawski said the town now has received $504,000 for the sedimentation control program over the last three years.
At the ARS National Sedimentation Laboratory, one research area focuses on how erosion, soil runoff, and urban and industrial activities affect water quality.
OBJECTIVE: To develop a micro-erythrocyte sedimentation rate (ESR) system with potential to be self-administered by patients at home using capillary blood.
The relatively small amount of water in syrups or concentrates, together with typical dilution ratios in the range of 1:4-7, requires a highly soluble calcium source in order to prevent sedimentation of the calcium, posing a major challenge to producers and processors alike.