Coagulation and separation

The coagulation of one sol may be effected by mixing an oppositely charged second sol. Thus, when a positive sol of Fe(OH)3 is mixed with an equivalent amount of a negative sol of AS2S3, both get coagulated and separate out. This process is known as mutual coagulation of sols. 

Destabilization of particles or colloid substances in water as well as their subsequent coagulation and separation are determined by chemical parameters of solution such as pH, concentration, and type of both colloid and coagulant etc. Efficiency of collisions leading to particle agglomeration in pe ikinetic coagulation is expressed by the collision efficiency factor (Up) under perikinetic conditions [ 1,2 ]. 

Experimental Procedure. The investigations were performed in scaled-down continuous-flow reactors (with a scale of about 1 40 relative to the size of technical reactors for aggregation and separation. The hydraulic regime was closely controlled in both coagulation and separation units through exact temperature control (T = 20 0.2 °C) and the maintenance of a constant hydraulic throughput. Suspensions were coagulated in tube-type reactors. 

By careful control of conditions, larger particles in a mixture can be preferentially coagulated and separated from smaller ones. For coagulation, a critical number of calcium ions must be adsorbed per square nanometer, of silica surface, independent of particle size but to attain this degree of adsorption, a higher concentration of cal-... 

Tung t al. (1977) prepared alfalfa whole dried juice from high and low saponin alfalfas for feeding experiments using day-old chicks. Unlike most LPCs which are prepared by coagulating and separating the protein from the juice prior to drying these preparations contained all of the soluble components of the leaves as well as the proteins. 

Fig. 4 The effectivity of two slightly different designs of chemical dosing points expressed in terms of resulting electrophoretic mobility and the rate of the coagulation and separation process (measured by reduction in algae and turbidity after [4])...

The repulsion between two double layers is important in determining the stability of colloidal particles against coagulation and in setting the thickness of a soap film (see Section VI-5B). The situation for two planar surfaces, separated by a distance 2d, is illustrated in Fig. V-4, where two versus x curves are shown along with the actual potential. 

Pretreatment of Suspensions. Another important aspect of soHd—Hquid separation is conditioning or pretreatment of the feed suspension to alter some important property of the suspension and improve the performance of a separator that follows. A conditioning effect is obtained using several processes such as coagulation and docculation, addition of inert filter aids, crystalliza tion, freezing, temperature or pH adjustment, thermal treatment, and aging. The first two operations are considered in more detail due to their importance and wide use. 

Samples may separate into two or more phases as they cool in the sample line precipitate, coagulate, and freeze. Laboratory sampling may result in nonrepresentative compositions. Heat tracing may be required and may not be installed on the nonroutine sample locations. 

Oil Expressed as oil or chloroform extractable matter, ppmw Scale, sludge and foaming in boilers impedes heat exchange undesirable In most processes Baffle separators, strainers, coagulation and filtration, diatomaceous earth filtration... 

As two particles approach in a liquid their charge fields may interact and form two minima as depicted in Figure 6.8. If the particles approach to a distance Li, known as the primary minimum they aggregate to form a configuration with minimum energy - and rapid coagulation is said to take place. On the other hand, if the particles remain separated at a distance L2, the secondary minimum, loose clusters form which do not touch. This is known as slow coagulation and is the more easily reversed. 

Filter. A filter is used in some cases when coagulation and sedimentation do not completely separate the solids from the liquid waste in areas where sand and sandstone formations are susceptible to plugging. Filters with a series of metal screens coated with diatomaceous earth or cartridge filters are typically used.27 Where limestone formations with high solution porosity are used for injection, filtration is usually not required. 

In the previous sections, we described the overall features of the heat-induced phase transition of neutral polymers in water and placed the phenomenon within the context of the general understanding of the temperature dependence of polymer solutions. We emphasised one of the characteristic features of thermally responsive polymers in water, namely their increased hydropho-bicity at elevated temperature, which can, in turn, cause coagulation and macroscopic phase separation. We noted also, that in order to circumvent this macroscopic event, polymer chemists have devised a number of routes to enhance the colloidal stability of neutral globules at elevated temperature by adjusting the properties of the particle-water interface. 

In summary, the DLVO theory seems to break down at very close separation where interfacial phenomena such as particle-particle interaction (coagulation) and particle-surface interaction (deposition) are important. 

Several physico-chemical methods are available for the treatment of pulping and pulp bleaching effluents. The most prominent methods are membrane separation, chemical coagulation, and precipitation using metal salts and advanced oxidation processes. 

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