Solid/liquid separation sedimentation

A selection guide for sedimentation centrifuges by Lavanchy et at. (1964), which includes other types of solid-liquid separators, is shown in Figure 10.19, adapted to SI units. 

Sedimentation classifiers, 76 619-620 in depth filtration theory, 11 339 in particle size measurement, 78 142-144 in solid-liquid separation, 76 656-657 Sedimentation rate... 

Solid-liquid mass transfer coefficients in airlift reactors, 15 727t relationships for estimating, 15 719-721t Solid-liquid protein separation, 12 136 Solid-liquid sedimentation, 22 50, 51 Solid-liquid separation (SLS)... 

Sedimentation is also used for other purposes. For example, relative motion of particles and liquid increases the mass-transfer coefficient. This motion is particulady useful in solvent extraction in immiscible liquid—liquid systems (see Extraction, liquid-liquid). An important commercial use of sedimentation is in continuous countercurrent washing, where a series of continuous thickeners is used in a countercurrent mode in conjunction with reslurrying to remove mother liquor or to wash soluble substances from the solids. Most applications of sedimentation are, however, in straight solid—liquid separation. 

The relative suitability of the common kinds of solid-liquid separation equipment is summarized in Table 11.3. Filtration is the most frequently used operation, but sedimentation as a method of pretreatment and centrifugation for difficulty filterable materials has many applications. Table 11.15 gives more detail about the kinds of filters appropriate to particular services. 

Solid-liquid separation by flotation may be achieved by gravity alone or induced by dissolved-air or vacuum techniques. The mechanisms and driving forces are similar to those found in sedimentation, but the separation rate and solids concentration can be greater in some cases. 

Solid liquid separation. The techniques available for the separation of sohds and hquid include filtration, centrifugation, and sedimentation. 

Two simulations of the effects of solid-liquid separation are considered here. From, algae to aquifers, these are, first, a consideration of the effects of coagulation on algal populations and sedimenting algal fluxes in marine waters taken from Jackson and Lochmann (28) and, second, evaluation of the effects of deposition or filtration on the transport of particles in groundwater systems taken from Tobiason (29). 

MANDERSLOOT, W.G.B., SCOTT, K.J. 8c GEYER, C.P. 1986. Sedimentation in the hindered settling regime. In Advances in Solid-Liquid Separation (ed. H.S. Muralidhara), pp. 63—77. Columbus Battelle. 

Removal eflBciency of solid-liquid separation processes is usually based on removal of suspended solids or mass. However, suspended solids might not be an adequate measure, for two reasons. First, some pollutants are characterized better on a particle number or surface area basis. Second, a comparison of Figures 9,14, and 15 shows that the eflFectiveness of the sedimentation and filtration processes is quantitatively diflFerent when the same mass, distributed in diflFerent ways, is treated. The performance of the individual treatment units and the entire system depends on the particle size distribution of the solids to be treated. 

For multicomponent systems the composition of the equilibrium solid phase can be determined indirectly by the so-called wet-residues method, first proposed by Schreinemakers (1893), in which the need for solid-liquid separation before analysis is avoided. In practice, the equilibrium system is allowed to settle and then most of the saturated supernatant solution is decanted off the sedimented solids. A sample of the wet solids is then scooped out and quickly weighed in a closed weighing bottle, to avoid solvent loss, and subsequently analysed by the most convenient analytical technique. 

The crystals have to be separated from the remaining melt (mother liquor) to achieve the intended purification. In case of layer crystallization, this is done by draining the remaining melt, collecting it separately, and melting down the crystal layer afterward (Fig. 8.2-11). In case of suspension crystallization the solid-liquid separation is done either by conventional filtration or by a sedimentation apparatus, with or without support of centrifugal forces. Another device repeatedly discussed in the context of solid-liquid separation is the wash column (Arkenbout 1995). 

Treatment of a suspension with the necessary chemical will produce a ffster settling system with a more bulky and more permeable sediment, but the final liquid content of the shidge or filter cake may well be significantly hi er than if a nontreated suspension had been settled. The benefits therefore tend to be found in flie enhanced settling rate and increased permeabiUty, and sometimes the sediment is of such bulk as to prove troublesome and expensive in disposal Other solid-liquid separation operations such as dissolved air flotation and centrifiigation have different requirements that must be met by the pretreatment system. 

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