Coagulation, of colloids

Higashitani K and Matsuno Y 1979 Rapid Brownian coagulation of colloidal dispersions J. Chem. Eng. Japan 12 460-5... 

Smoluchowski, M.V., 1916. Three lectures on diffusion. Brownian movement and coagulation of colloidal systems. Physik Zeitung, 17, 557. 

Smoluchowski, M.V., 1917. Mathematical theory of the kinetics of coagulation of colloidal systems. Zeitschrift fur Physikalische Chemie, 92, 129-168. 

Filter aids are widely used in die fermentation industry to improve the efficiency of filtration. It is a pre-coated filter medium to prevent blockage or blinding of the filter by solids, which would otherwise wedge diemselves into the pores of the cloth. Filter aid can be added to the fermentation broth to increase the porosity of the cake as it formed. This is only recommended when fermentation product is extracellular. Filter aid adds to the cost of filtration. The minimum quantity needed to achieve the desired result must be established experimentally. Fermentation broths can be pretreated to improve filtration characteristics. Heating to denature proteins enhances the filterability of mycelial broths such as in penicillin production. Alternatively, electrolytes may be added to promote coagulation of colloids into larger, denser particles, which are easier to filter. The filtration process is affected by the viscosity and composition of the broth, and the cell cake.5... 

A chemical treatment designed to prevent the coagulation of colloids by the provision of a surface coating onto the colloidal particles. 

Schowalter, W. R., Stability and coagulation of colloids in shear fields. Ann. Rev. Fluid Mech. 16, 245-261 (1984). 

Smoluchowski, who worked on the rate of coagulation of colloidal particles, was a pioneer in the development of the theory of diffusion-controlled reactions. His theory is based on the assumption that the probability of reaction is equal to 1 when A and B are at the distance of closest approach (Rc) ( absorbing boundary condition ), which corresponds to an infinite value of the intrinsic rate constant kR. The rate constant k for the dissociation of the encounter pair can thus be ignored. As a result of this boundary condition, the concentration of B is equal to zero on the surface of a sphere of radius Rc, and consequently, there is a concentration gradient of B. The rate constant for reaction k (t) can be obtained from the flux of B, in the concentration gradient, through the surface of contact with A. This flux depends on the radial distribution function of B, p(r, t), which is a solution of Fick s equation... 

H. W. Woodstra, Brownian movement and the coagulation of colloidal solutions, Chemisch Week-blad 15, 679-680(1918). 

To increase the solubility of calcium carbonate and reduce its potential for precipitation and hence membrane fouling, the pH of the feed water is lowered through the addition of acid (Greenlee et al. 2009). Sulphuric acid and hydrochloric acid are most commonly used. Acid treatment can also help to improve the coagulation of colloids and slightly increase the solubility of silica (Bergman 2007). 

Ellis and Powis (1912-15) introduced the concept of the critical zeta potential for the coagulation of colloidal solutions. 

Coagulation of colloidal dispersions (Fig. 1.26h) as a function of salt concentration, pH, or temperature of the suspending liquid medium can also be used to obtain information on the interplay of repulsive and attractive forces between particles in pure liquids as well as in surfactant and polymer solutions. 

Kinetics is concerned with many-particle systems which require movements in space and time of individual particles. The first observations on the kinetic effect of individual molecular movements were reported by R. Brown in 1828. He observed the outward manifestation of molecular motion, now referred to as Brownian motion. The corresponding theory was first proposed in a satisfactory form in 1905 by A. Einstein. At the same time, the Polish physicist and physical chemist M. v. Smolu-chowski worked on problems of diffusion, Brownian motion (and coagulation of colloid particles) [M. v. Smoluchowski (1916)]. He is praised by later leaders in this field [S. Chandrasekhar (1943)] as a scientist whose theory of density fluctuations represents one of the most outstanding achievements in molecular physical chemistry. Further important contributions are due to Fokker, Planck, Burger, Furth, Ornstein, Uhlenbeck, Chandrasekhar, Kramers, among others. An extensive list of references can be found in [G.E. Uhlenbeck, L.S. Ornstein (1930) M.C. Wang, G.E. Uhlenbeck (1945)]. A survey of the field is found in [N. Wax, ed. (1954)]. 

It was previously mentioned that PDADMAC (Cat-Floe) was the first commercial flocculant approved for potable water [26]. Since then, PDADMAC has been continuously used for coagulation/flocculation both in potable water and waste water treatment. A good example of the performance of PDADMAC in the coagulation of colloidal solids is the reduction of turbidity in fresh water of 150 mg L 1 of Ca(OH)2. A reduction of 82% in turbidity is observed with the addition of only 2 mg L 1 of branched PDADMAC [217]. In addition, PDADMAC and copolymers of DADMAC are reported to be effective in the removal of hard-to-elimi-nate impurities in the water treatment industry. Emulsified impurities from streams of a petroleum refinery waste water and an automotive oily effluent water have been removed by the use of water soluble copolymers consisting essentially of DADMAC and small amounts of anionic acrylic monomers [89]. 

The classical treatment of such processes derives from the consideration of the coagulation of colloids (Smoluchowski, 1917), but many accounts have been given of how the same approach can be used for diffusion-controlled reactions (Noyes, 1961 North, 1964 Moelwyn-Hughes, 1971). The starting point is the assumption of a random distribution of the two reactants (here given the symbols X and B) in the solution. Then, if B is capable of reacting on encounter with a number of molecules of X, it follows that such reactions deplete the concentration of X in the neighbourhood of B and therefore set up a... 

Wilkinson, K.J., Negre, J.-C. and Buffle, J. (1997b) Coagulation of colloidal material in surface waters the role of natural organic matter./. Contamin. HydroL, 26, 229-243. 

However, such an attraction occurs at large separation distances, and does not affect much the interactions at low separations, hence the coagulation of colloids. It is also well accepted that the classic PDisson-Boltzmann treatment is inaccurate at concentrations higher than approximately 0.05 M, and in general either additional interactions or unknown fitting parameters had to be employed for quantitative agreement. 

A sustance that coats the particles of the dispersed phase and prevents coagulation of colloidal particles an emulsifier. 

The heat of coagulation of colloidal ferric hydroxide with potassium oxalate has been studied by Doerinckel.7... 

The presence of organic matter (especially particulate organic matter, POM, common in seawater) promotes the coagulation of colloids by serving as binding material that favors their aggregation. Nevertheless, tidal movements re-suspend these settled... 

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