Chemical reaction flocculation

The physical chemist is very interested in kinetics—in the mechanisms of chemical reactions, the rates of adsorption, dissolution or evaporation, and generally, in time as a variable. As may be imagined, there is a wide spectrum of rate phenomena and in the sophistication achieved in dealing wifli them. In some cases changes in area or in amounts of phases are involved, as in rates of evaporation, condensation, dissolution, precipitation, flocculation, and adsorption and desorption. In other cases surface composition is changing as with reaction in monolayers. The field of catalysis is focused largely on the study of surface reaction mechanisms. Thus, throughout this book, the kinetic aspects of interfacial phenomena are discussed in concert with the associated thermodynamic properties. 

Hazardous Materials Table, 20 809 Dependent chemical reactions, 21 336-337 Dephlegmators, 3 54-56 10 616 Depleted uranium, 25 421 Depletion allowance, 9 539 Depletion flocculation, 10 122, 123 Depletion provisions, magnesium, 15 347 Depletion region, 14 838 23 35 width, 22 244 Depolarization, in cardiac... 

Flocculation processes are complicated phenomena because of the varieties of both particle morphology and chemical reactions they encompass.34 A few concepts of a general nature have emerged, however, and they will be the focus of this chapter. From the perspective of kinetics, perhaps the most important of these broad generalizations is the distinction that can be made between transport-controlled and reaction-controlled flocculation, parallel to the classification of adsorption processes described in Section 4.5. Flocculation kinetics are said to exhibit transport control if the rate-limiting step is the movement of two (or more) particles toward one another prior to their close encounter and subsequent combination into a larger particle. Reaction control occurs if it is particle combination instead of particle movement (toward collision) that limits the rate of flocculation. 

I. Activation of metallic ions in flocculation process Activation of flocculation by metallic ions is similar to that of mineral flotation using collectors discussed earlier. Metallic ions can activate minerals that do not normally have chemical reaction activity with the functional groups of flocculants, which enhance the flocculation effect. For example, for Cu " " -Si02- polymer system, the reaction can be illustrated as below ... 

Most turbidity occurring in wine is due to the flocculation of colloidal particles caused by chemical reactions that leave the solution clear. It is certain that the presence of natural polysaccharides, with their protective colloid properties, prevent the formation of turbidity and deposits. It is also clear that, in some cases, it may be useful to enhance this protective effect by adding a colloid such as gum arabic. 

Stress development. Generally, solidification is accompanied by development of in-plane tensile elastic stress. This is because departure of solvent from solution, crystallization and vitrification, consolidation of particulates, colloidal flocculation and coagulation, and the chemical reactions of curing almost always tend to produce shrinkage of the... 

We have introduced earlier that the use of silica shells around nanoparticles as a general stabilization technique against flocculation in several media. Apart from this, the silica shells can also be envisaged as chemical stabilizers, meaning that they could slow down or even prevent chemical reactions from occurring at the cores. 

Flocculants can be designed on the basis of certain specific interactions, such as chemical reactions of the flocculant with surface sites or ions present on the surface. For example, poly(acrylic acid) (PAA) can react with calcium sites on surfaces. However, such an approach fails when the cations participating in the complexation reactions on the surfaces are the same or chemically similar. 

Solids contact processes combine chemical mixing, flocculation and clarification in a single unit designed so that a large volume of previously formed floe is retained in the system. The floe volume may be as much as 100 times to in a "flow-through" system. This greatly increases the rate of agglomeration from particle contacts and may also speed up chemical destabilization reactions. 

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