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Electrokinetic and adsorption effects

Adsorption and Electrokinetic Effects of Amino Acids on Rutile and Hydroxyapatite... [Pg.311]

Adsorption and electrokinetic effects of amino acids, solid-aqueous interface, 311-26 Adsorption density, equilibrium PAA at various pH values, 299f PAA on hematite, 304f SDS with and without polymer, 298f,303f... [Pg.342]

The use of centrifugation to separate the liquid from solid phases in traditional batch or tube techniques has several disadvantages. Centrifugation could create electrokinetic effects close to soil constituent surfaces that would alter the ion distribution (van Olphen, 1977). Additionally, unless filtration is used, centrifugation may require up to 5 min to separate the solid from the liquid phases. Many reactions on soil constituents are complete by this time or less (Harter and Lehmann, 1983 Jardine and Sparks, 1984 Sparks, 1985). For example, many ion exchange reactions on organic matter and clay minerals are complete after a few minutes, or even seconds (Sparks, 1986). Moreover, some reactions involving metal adsorption on oxides are too rapid to be observed with any batch or, for that matter, flow technique. For these reactions, one must employ one of the rapid kinetic techniques discussed in Chapter 4. [Pg.41]

The effect of specific adsorption on electrokinetic behavior of materials is usually presented in form of C(pH) curves at constant initial (total) concentration of a specifically adsorbing salt. The electrophoretic mobility rather than the potential is often plotted as a function of the pH. The mobility (directly measured quantity) is a complicated function involving the C potential on the one hand and particle size and shape, and concentrations of ionic species in the solution on the other (cf. Figs. 3.80 and 3.81), and exact calculation of the potential in real systems (polydispersed and irregularly shaped particles) is practically impossihle. This is a serious difficulty in quantitative interpretation of electrokinetic data obtained in the presence of specific adsorption. On the other hand, the zero electrophoretic mobility corresponds to zero C potential, and the shifts in the lEP along the pH axis can be determined with accuracy on the order of 0.1 pH unit. [Pg.341]

The examples shown is Section D indicate that the shape of calculated uptake curves (slope, ionic strength effect) can be to some degree adjusted by the choice of the model of specific adsorption (electrostatic position of the specifically adsorbed species and the number of protons released per one adsorbed cation or coadsorbed with one adsorbed anion) on the one hand, and by the choice of the model of primary surface charging on the other. Indeed, in some systems, models with one surface species involving only the surface site(s) and the specifically adsorbed ion successfully explain the experimental results. For example, Rietra et al. [103] interpreted uptake, proton stoichiometry and electrokinetic data for sulfate sorption on goethite in terms of one surface species, Monodentate character of this species is supported by the spectroscopic data and by the best-fit charge distribution (/si0,18, vide infra). [Pg.698]

To estimate x, the decrease in equilibrium adsorption and the actual adsorption rate according to the electrostatic phenomena, have to be considered. The application of Boltzmann s law assumes equilibrium condition of the DL and neglects any transport within the diffuse layer. Thus, the classic Boltzmann law cannot be used to describe the distribution of adsorbing ions within the double layer in non-equilibrium systems. The presence of any ionic flux is connected with a non-equilibrium state of the DL and the approach given by Overbeek (1943) in his theory of electrophoresis has to be considered. In that theory, the non-equilibrium of the DL causes non-linear dependencies of electrophoresis on the electrokinetic potential, in contrast to the theory of Smoluchowski where this effect is not allocated for. The importance of the non-equilibrium state of the DL for many other surface phenomena was emphasised by Dukhin Deijaguin (1974), Dukhin Shilov (1974), and Dukhin (1993). [Pg.239]

Systematic studies of bubble hydrodynamics based on the Dom effect were suggested by Dukhin (1983). A comprehensive study, comprising the measurement of adsorption on immobile surfaces with the calculation of the Stem potential and measurements of sedimentation potentials, should be performed with homologous series of ionic surfactant so that the condition (8.97) is fulfilled by higher homologues and the opposite condition (8.101) by the lower ones. With decreasing surface activity the condition (8.97) will be fulfilled at smaller adsorption values. This means that the lower the surface activity, the smaller should be the deviation of the electrokinetic potential from the Stem potential at respective values of adsorption. And finally, when condition (8.97) is not fulfilled the electrokinetic and Stem potentials must coincide over the whole concentration interval. [Pg.300]

The relative importance of surface forces rises significantly in nanoscale fluid transport. Especially the electrokinetic effect plays a very important role in nanoflows of polar liquid, such as water. Even without any extra ions, the solid surface will also be charged by physical and chemical adsorption or dissociation at the... [Pg.2298]

In this paper the use of electroacoustic techniques involving the application of a sonic field and the detection of an electric field, for monitoring coalescence of water droplets in non-polar media will be discussed. This technique was used to evaluate the rate and extent of dewatering in oil continuous emulsions when surface active chemicals were added. The results showed that a combination of an oil soluble demulsifier and water soluble surfactant was substantially more effective in causing droplet coalesence than the individual components. An explanation for these findings were based on studies of time-dependent interfacial tensions at the oil/water interface and electrokinetic properties. The results indicated that a direct relationship exists between the adsorption behavior at the oil/water interface (apparent rate of spreading) and emulsion stability. [Pg.157]

The presence of pre-adsorbed polyacrylic acid significantly reduces the adsorption of sodium dodecylsulfonate on hematite from dilute acidic solutions. Nonionic polyacrylamide was found to have a much lesser effect on the adsorption of sulfonate. The isotherm for sulfonate adsorption in absence of polymer on positively charged hematite exhibits the typical three regions characteristic of physical adsorption in aqueous surfactant systems. Adsorption behavior of the sulfonate and polymer is related to electrokinetic potentials in this system. Contact angle measurements on a hematite disk in sulfonate solutions revealed that pre-adsorption of polymer resulted in reduced surface hydrophobicity. [Pg.291]

For the hydrogen electrode reaction (HER) on different metals, it is predicted that the curve log ja vs. AG ds has a maximum with log j0 decreasing both at positive and negative values of AGads. This is due to the opposite effects of the free energy of adsorption on the geometric and exponential factors in the electrokinetic equation (volcano plots). [Pg.67]

It used to be thought that cations simply precipitated polyanions, but it was recognized later that electrolytes had special valence and solvent-mediated effects on a hydrosol other than neutralization of opposite charges (Holmes, 1922). It is now firmly established that ionization of the carboxyl and sulfuric acid groups in ionic polysaccharides, or adsorption of ions on neutral macromolecules, is an initial step in electrokinetic mechanisms of stabilization and destabilization. [Pg.43]

The ODN adsorption onto cationic microgel poly(N-isopropylacrylamide) particles was reported to be dramatically affected by the salinity of the incubation medium [9] as illustrated in Fig. 6. The observed result was related to (i) the reduction in attractive electrostatic interactions between ODN molecules and the adsorbent and (ii) the drastic effect of ionic strength on the physico-chemical properties of such particles [17, 27]. In fact, the hydrodynamic size, the swelling ability, the electrokinetic properties, and the colloidal stability are dramatically affected by pH, salt concentration, and the medium temperature [27]. [Pg.181]

There is another possibility which was applied for interpretation of adsorption of organic ions [34,74]. One measures the effect of pH on the adsorption of cobalt ions at their different total concentrations. Simultaneous electrokinetic measurements provide the concentrations at isoelectric point so that each experimental run would yield the adsorption amounts and cobalt equilibrium concentration at zero electric potential. Regardless to different... [Pg.874]


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Adsorption effect

Effect, electrokinetic

Effect, electrokinetic effects

Electrokinetic

Electrokinetics)

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