Coagulation reactions

Inorganic salts of metals work by two mechanisms in water clarification. The positive charge of the metals serves to neutralize the negative charges on the turbidity particles. The metal salts also form insoluble metal hydroxides which are gelatinous and tend to agglomerate the neutralized particles. The most common coagulation reactions are as follows ... 

Similarly to blood coagulation, reactions of fibrinolysis occur on the interface of fluid-and solid-phase structures, generally in transiently formed compartments. 

In summary, the carbonate-cycle program provides preferred precipitation and coagulation reactions to prevent hard scale from forming. Key functions are ... 

Limulus Amebocyte Eysate (EAE) Test This test is used to detect the presence of endotoxins in the drug substance. It relies on the coagulation reaction between the endotoxin and the blood of a horseshoe crab. 

Fig. 1. Process flow sheet for the continuous conversion of latex in a counterrotating, tangential twin-screw extruder as it might be arranged for the production of acrylonitrile-butadiene-styrene polymer (Nichols and Kheradi, 1982). Polystyrene (or styrene-acrylonitrile) melt is fed upstream of the reactor zone where the coagulation reaction takes place. Washing (countercurrent liquid-liquid extraction) and solids separation are conducted in zones immediately downstream of the reactor zone. The remainii zones are reserved for devolatilization and pumping.

Exact solution of one-dimensional reversible coagulation reaction A+A A was presented in [108, 109] (see also Section 6.5). In these studies a dynamical phase transition of the second order was discovered, using both continuum and discrete formalisms. This shows that the relaxation time of particle concentrations on the equilibrium level depends on the initial concentration, if the system starts from the concentration smaller than some critical value, and is independent of the tia(0) otherwise. 

The kinetic expressions shown before explain the direct electrochemical processes. However, many of the processes with interest in electrochemical oxidation or coagulation treatments are not direct processes, but simply chemical processes caused by the products generated at the electrode surface (mediated electrochemical processes). In addition, several chemical processes not related to the electrochemical process can occur in the electrochemical cell. Thus, in electrooxidation, the most common case is the mediated oxidation carried out by oxidants electrochemically generated on the electrode surface, such as hydroxyl radicals, hypochlorite, peroxo-sulphates, or peroxophosphates. In electrochemical coagulation, aluminum species formed during the electrochemical dissolution of the anodes are responsible for the later coagulation reactions. 

If the coagulant reaction is simply allowed to take place in one portion of the tank because of the absence of the rapid mix rather than being spread throughout the volume, all four mechanisms for a complete coagulation discussed above will not be utilized. For example, charge neutralization will not be utilized in aU portions of the tank because, by the time the coagulant arrives at the point in question, the reaction of charge neutralization will already have taken place somewhere. 

In addition, coagulation is a process of expending the coagulant. In the process of expenditure, the alum must react to produce its products. This means that what must exist is the forward arrow and not any backward arrow. Portraying the backward arrow would mean that the alum is produced, but it is known that it is not produced but expended. During expenditure, no equilibrium must exist. To reiterate, the coagulation reaction should be represented by the forward arrow and not by the equihbrium arrows. 

The chemical reactions for the ferric coagulants FeCls and Fc2(S04)2 involve precipitations in the form of ferric hydroxide. Calcium bicarbonate is always present in natural waters, so it must first be satisfied before any external source of the hydroxide ion is provided. This hydroxide can be provided using lime, and as in the case of alum, this is the hydroxide that will be utilized in the coagulation reactions to be discussed. The respective reactions for the satisfaction of calcium bicarbonate are as follows ... 

The solids produced from the coagulation reactions are Al(OH)3, Fe(OH)3 and CaCOj. Referring to the reactions of alnm, the equivalent mass of aluminum hydroxide is 2A1(0H)3/6 = 26.0. The ferric hydroxide is produced through the use of copperas and the ferric salts. Its equivalent mass from the use of copperas [Eqs. (12.89) through (12.91)] is Fe(OH)3/2 = 53.4 and from the use of the ferric salts, its equivalent mass is 2Fe(OH)3/6 = 35.6. Calcium carbonate is produced from the reaction of copperas, Equation (12.89). From this reaction, the equivalent mass of calcium carbonate is 2CaC03/2 = 100. 

Healy, T.W. and lellet. V.R., Adsorption-coagulation reactions of Znfll) hydrolyzed species at the zinc oxide-water interface, J. Colloid Interf. Sci., 24, 41,1967. 

The terms oc(i,j)s and A(i,/)s collectively describe a kinetic coefficient for the coagulation or aggregation of suspended particles of sizes i and j. They have analogies with but are not identical to the terms a(p, c) and tj(p, c) used previously in describing the kinetics of particle deposition processes in porous media. Like q p, c), the term l i,j)s incorporates information about various processes of particle transport, although as used here hydrodynamic retardation is not considered. Unlike t/(p, c), X(iJ)s is not a ratio of fluxes. It is a rate coefficient that includes most physical aspects the second-order coagulation reaction. Like a(p, c), the term a(i, j)s incorporates chemical aspects of the interactions between two colliding solids however, as used here, the effects of hydrodynamic retardation are subsumed in ot(iJ)s. The term a(i,j)s is a ratio defined here as follows ... 

Micelles are not frozen objects. They are in dynamic equilibrium with the free (nomnicellized) surfactant. Surfactants are constantly exchanged between micelles and the intermicellar solution (exchange process), and the residence time of a surfactant in a micelle is fmite. Besides, micelles have a finite lifetime. They constantly form and break up via two identified pathways by a series of stepwise entry/exit of one surfactant A at a time into/from a micelle (Reaction 1) or by a series of frag-mentation/coagulation reactions involving aggregates A, and Aj (Reaction... 

Kline, D. Blood coagulation Reactions leading to prothrombin activation. Annu. Rev. Physiol. 27, 285-306 (1965)... 

Fig. 4. Fig. 2 and 3 show the water in water emulsion. The phase of droplets was of PAS and the continuous phase was of PEG, The droplets were about lOy to lOOy in diameter. Fig. 4 shows a coagulated reaction product in which micro dispersion was not observed. 

Muramatsu H, et al. A quartz crystal viscosity sensor formonitoring coagulation reaction and its application to a multichannel coagulation detector. Biosens Bioelectron 1991 6 353-8. 

Fig. 8 The effect of heterogeneous energy dissipation on the progress of the coagulation reaction in geometrically similar systems of different scale the reaction progress is different even if the (microscopically determined) overall energy dissipation is identical (after [8]). There are no numbers given since they depend exclusively on the experimental boundary conditions...

The coagulation reaction, as it occurs in the laboratory, can be described as the result of two mostly independent reaction steps, a more chemically controlled destabilization and a transport step that is more controlled by physical parameters, i.e., fluid dynamics of the system. In large-scale or technical realization of this process there is at least one more reaction step to the considered, the addition and homogeneous mixing of coagulating chemicals. Furthermore, the conceptually very clear separation between the chemically controlled destabilization and the physically controlled transport fails. There are numerous observations on the interaction of physical, mostly fluid dynamics parameters with chemical reactions and vice versa. 

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