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 ?
Although the increase of the mass concentration leads to a decrease of slurry's sedimentation, the sedimentation phenomenon of slurry also exists.
It has been suggested that a wide QDSL, i.e., a broad intermediate band, formed during slow sedimentation. The intermediate band in the infrared region will increase the number of minority carriers due to thermal excitation.
Paper mill Waste-water after sedimentation treatment
The sedimentation of Nanofluids, after sonication were recorded using digital camera and shown in the fig.8.
In this paper, the LB-DF/FD method has been adopted to simulate the sedimentation of three particles in a narrow channel.
In performing dextran sedimentation, every 6 mL of blood or PBMC-depleted neutrophil/erythrocyte suspension (if preceding or following low-density Ficoll-Hypaque density gradient centrifugation, resp.) was mixed with 4 mL of 5% (w/v) dextran (MW 266000, Sigma-Aldrich) in 0.9% NaCl [16].
This model can be used as a base to determine sedimentation testing practical procedure.
In our approach, Figure 1(b) is used to assess the status of sedimentation initially, followed by assessing the feasibility of changing the parameters in eq.
The project upon completion will ensure safeguarding the existing capacity of WARSAK Dam for next term, adaptation of climate change especially environmental measures, flood and sedimentation management in the Peshawar region and Kabul river.
This study was conducted for a week in June in two areas of Turkey Creek: one upstream of Turkey Creek Falls and one Downstream of Turkey Creek Falls to investigate the effect of sedimentation on the growth and predation of periphyton.
Sedimentation remains a major problem in reservoirs which not only lessens the useful life of the reservoir but also causes abrasion of turbine units; when the sediment loaded water finds its way into the power house.
It was confirmed by Mosaedi and Mohammadi (2002) to determine the sedimentation rate of Garganrood River [7].