Sedimentation differential

Flocculation is accelerated and higher overflow rates are achieved by external or internal recirculation of settled soflds into the feed which leads to the collection of fine particles by interception. Addition of conditioned fine sand to the feed induces separation by differential sedimentation, and sometimes increases overflow rates to 6—8 m/h. 

Glassification. Classification (2,12,26,28) or elutriation processes separate particles by the differences in how they settle in a Hquid or moving gas stream. Classification can be used to eliminate fine or coarse particles, or to produce a narrow particle size distribution powder. Classification by sedimentation iavolves particle settling in a Hquid for a predetermined time to achieve the desired particle size and size distribution or cut. Below - 10 fim, where interparticle forces can be significant, gravitational-induced separation becomes inefficient, and cyclone and centrifugation techniques must be used. Classification also separates particles by density and shape. Raw material separation by differential sedimentation is commonly used in mineral processiag. 

Separation into components can only be achieved by stopping the process when sedimentation of the desired component has occurred. The sediment is then resuspended in fresh solvent and centrifuged at a lower speed, when the heavier particles will sediment leaving the component in suspension. Such a method is known as differential sedimentation and is particularly useful for the fractionation of cellular components. The method outlined in Procedure 3.3 is simple and is designed to separate four main cellular fractions, namely, nuclear, mitochondrial, microsomal and soluble. 

SMITH, T. N. Trans. Inst. Chem. Eng. 45 (1967) T311. The differential sedimentation of particles of various species. 

Note the difference between K, the Mark-Houwink constant, and k defined in Equation 12. The differential sedimentation distribution can be transformed to the differential molecular weight distribution by taking the derivative of Equation 11 with respect to s, to get... 

Figure 6. A plot of g(s), the differential sedimentation distribution pattern with s shown in svedbergs.

Frequently the first step in protein purification is differential sedimentation of broken cell parts. In this way soluble proteins may be separated from organelle-sequestered proteins. 

Following differential sedimentation, proteins may be separated into crude fractions by the addition of increasing amounts of (NH4)2S04. Specific proteins characteristically precipitate in a limited range of salt concentrations. 

Bianchi, T.S., Mitra, S., and McKee, M. (2002b) Sources of terrestrially-derived carbon in the Lower Mississippi River and Louisiana shelf Implications for differential sedimentation and transport at the coastal margin. Mar. Chem. 77, 211-223. 

FIG. 1 Continued. Particle collision mechanisms (c) differential sedimentation. 

In the development above, it has been convenient to consider collisions, via particle transport, and reactions, the probability of particle attachment, as separate steps. There are a number of considerations indicating that this conceptual framework may have outlived its usefulness, as advancements in particle science, analytical capabilities, and supercomputers obviate the necessity of this artificial separation. Adler [4], Han and Lawler [3], and others have demonstrated using trajectory modeling the significant influence of hydrodynamics on particle collisions, and show how the lumped collision efficiency (inclusive of hydrodynamics) is a function of the type of collision mechanism. Thus, for a given particle pair, the collision efficiency will be different depending on whether the collision is a result of Brownian motion, fluid shear, or differential sedimentation. 

Microsomes are small, spherical, membranous vesicles with attached ribosomes. During differential sedimentation, they sediment only in the late stages of a preparation, when very high centrifugal forces are used. They don t appear in electron micrographs of a cell. From whence do they arise ... 

This technique is sometimes referred to as differential sedimentation, and is essentially a process of successive centrifugation (single or repeated steps) with increasing centrifugal force (g). Separation is predominantly dependent on particle mass and size, where heavier particles or cells settle first at lower g values (e.g. intact cells can sediment at around 800 g). However, in many cases, differential centrifugation is used to separate out intracellular matter, and thus this method is important for so-called subcellular fractionation (see Figure 6.7). 

The top orange layer is the result of more flooded conditions. Storm events introduced sediments that became multiple fining upward silt-clay laminae. Water must have been present in the cave to promote differential sediment settling, while also preventing the creation of clay rip-up clasts. The laminae vary in thickness, and may represent an ancient record of storm/flooding events in this watershed during the Quaternary. Like the red layer, increased kaolinite and ferrihydrite indicate a more intensely weathered or more deeply eroded sediment source. 

Gravity, which produces vertical transport of particles and which depends on the buoyant weight of the particles. Large, dense suspended particles can contact smaller or less dense ones in a process termed differential sedimentation (Figure 14.21a). If one of the particles is stationary, as in a packed bed filter, contacts of suspended particles with the fixed particle can be said to occur by convective sedimentation (Figure 14.21b). 

With this formulation, chemical effects on coagulation are included in a and physical effects in Particle contacts are usually considered to be caused by three mechanisms differential sedimentation, shear (laminar and turbulent), and Brownian motion. Differential sedimentation contact occurs when two particles fall through the water at different rates and the faster particle overtakes the slower one. Shear contact occurs when different parts of the fluid environment move at different speeds relative to each other, and thus a particle that is moving with one fluid patch overtakes and collides with a particle in a slower fluid patch. Brownian motion contact occurs when two particles move randomly through their fluid in Brownian motion and collide... 

The coagulation kernel for the rectilinear case of differential sedimentation is... 

All of these calculations have been made with the curvilinear model for the differential sedimentation kernel. Flow through an aggregate should increase the kernel. Using the rectilinear kernel is a way to test the effect that such enhanced flow might have (38, 46). As should be expected, it causes a substantial decrease in the maximum algal population. The effect of increased... 

Here (3Br(ij), Psll(i,j), and PDS(ij) are the transport coefficients for interparticle contacts between particles of diameters d, and dj by Brownian diffusion, fluid shear, and differential sedimentation, respectively kB is Boltzmanns constant T is the absolute temperature p, is the viscosity of the liquid G is the mean velocity gradient of the liquid g is the gravity acceleration and pp and p, are the densities of the particles and the liquid, respectively. 

These effects are illustrated in a comparison of the rectilinear and curvilinear approaches to differential sedimentation presented in Figure 8, adapted from Han and Lawler (24). In both approaches, the upper, larger, faster particle is settling by gravity toward the lower, smaller, slower particle. In the rectilinear or Smoluchowski approach, all small particles with size di that reside below the larger particle (size dp within the area Ar with diameter (d, + dj) come into contact with the larger particle ( DS(ij) is given by equation 3c. 

In the curvilinear case where all hydrodynamic interactions between the two particles are considered, only those small particles in the shaded area denoted as Ac can come into contact with the larger particle. The area Ac can be determined numerically. The result is that the actual collision rate is less than the rectilinear rate, and the actual mass-transport coefficient is equal to t(Ac/Ar)PDS(ij)]. Han and Lawler (24) calculated reductions in the rectilinear transport rate by differential sedimentation ranging from about 0.3 to 0.001, so the effects of hydrodynamic interactions on this transport process can be substantial in many cases. 

Figure 8. Schematic presentation of rectilinear and curvilinear trajectories in particle collisions by differential sedimentation. (Adapted with permission from reference 24. Copyright 1991.)...

C15. Coke, H., The differential sedimentation test in relation to the problems of rheumatoid arthritis. Acta Med. Scand. Suppl. 341, 143-155 (1958). 

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