Coagulation, rate

A dynamic ordinary differential equation was written for the number concentration of particles in the reactor. In the development of EPM, we have assumed that the size dependence of the coagulation rate coefficients can be ignored above a certain maximum size, which should be chosen sufficiently large so as not to affect the final result. If the particle size distribution is desired, the particle number balance would have to be a partial differential equation in volume and time as shown by other investigators ( ). 

The colloidal stability of silica Suspensions in the present work was assessed by sediment volumes and from the optical coagulation rate constant. In the first method, 50 mg of silica was dispersed in 5 cm3 polymer solution (concentration 10-2 g cm 3) in a narrow tube and the sediment height found at equilibrium. Coagulation rates of the same systems were found by plotting reciprocal optical densities (500nm, 1cm cell) against time. When unstable dispersions were handled, the coagulation was followed in... 

The sediment volume of silica in CCl solutions of poly (methyl methacrylate) was approximately 9 cc g-l but variable results were found in solutions of polystyrene, depending on the molecular wt. of the polymer. Lower M.W. samples are poor stabilizers and the dispersions are so unstable that optical coagulation rates could not be measured with confidence. Figure 5 shows the general trend in CCl. All polymers, whatever their composition, are superior to the pure solvent. 

Colloid stability assessments of silica dispersions in CCI4 by sediment volume and coagulation rate are in general concordance and confirm the pattern previously reported by Barron and Howard... 

Figure 8. log(coagulation rate/min-l) of silica 186 in CCI4 solutions of polymers with various styrene contents. Squares, block polymers circles, random copolymers or homopolymers. 

In summary, polymeric flocculants generally increase peri-kinetic flocculation rates compared with perikinetic coagulation rates. This is not necessarily true for orthokinetic flocculation, and experimental results in the literature are seemingly in conflict. Collision rate theory predicts that the polymer adsorption step may become rate limiting in orthokinetic flocculation. The present study was designed to elucidate the relationship between polymer adsorption rates and particle flocculation rates under orthokinetic conditions. 

Flocculation experiments were also performed with half of the latex pretreated with polymer to ensure complete surface coverage. Coagulation rates were determined using aluminum chloride at pH 3. 

It is seen that the flocculation rates are generally considerably lower than the coagulation rate. A "pseudo" optimum flocculation concentration of 6 OFC units is found for short flocculation times, but for longer times it is clear that the suspension is stabilized and no further flocculation occurs. At higher initial doses restabilization becomes even more pronounced. ... 

Summary plot of experimentally derived stability ratios, Wexp, of hematite suspensions, as a function of added electrolyte or adsorbate concentration at pH around 6.5 (pH = 10.5 for Ca2+ and Na+). Hematite concentration is about 10-20 mg/ . The stability ratio, Wexp, was determined from measurements on the coagulation rate it is the reciprocal of the experimentally determined collision efficiency factor, a. 

Fig. 7.11 gives results on coagulation of hematite suspension by fatty acids. As concentration is increased, an influence on hematite coagulation rate becomes notice-... 

Their electrochemical properties serve to regulate the coagulation rates, catalysis behaviour and electron transfer reactions of iron oxides (Mulvaney et ah, 1991). Two major methods of characterizing electrochemical behaviour are potentiometric titration and electrophoresis. 

Calculation of Coagulation Rate. Here we discuss an interaction potential of two charged particles in a liquid within a framework of DLVO theory. Following this theory, the overall interaction potential U, of charged spherical particles of the same radius R and surface distance d is a sum of a coulombic repulsive force of charged particles and a van der Waals attractive force given by the equation (28) ... 

Note that we no longer need the subscripts 1 and 2 on Z and Nb. The coagulation rate for identical particles is then given by ... 

Figure 1. Measurement of perikineHc coagulation rate under various solution...

Figure 3. Hydrolysis of Al(IU) and the effect of hydrolytic Al(III) species upon the coagulation rate...

A) Logarithmic diagram of Al(III) solubility as function of Al concentration and pH, derived from ther-modyn. equilibrium constants. (B) Extent of Al-hydrol-ysis as function of pH. (C) Variation of the coagulation rate, expressed as collision efficieny factor, with pH at constant Al dosage (a values determined from Equation 3)... 

B) Relative colloid stability as a function of the total concentration of coagulant added, Ct, at constant pH—obtained from the measurement of perikinetic coagulation rates according to Equation 3. (Ludox LS = 0.3 gram/liter)... 

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