Intrinsic colloids

Formation of intrinsic colloids in natural waters can be excluded for radioisotopes of elements of groups 0, I and VII, and the probability that they may be formed is small for radioisotopes of elements of other groups as long as the concentration of the elements is low. In general, formation of carrier colloids by interaction of radionuclides with colloids already present in natural waters is most probable. Thus, clay particles have a high affinity for heavy alkali and alkaline-earth ions, which are bound by ion exchange. This leads to the formation of carrier colloids with Cs, Ra and °Sr. Formation of radiocolloids with hydrolysing species has already been discussed (section 13.4). 

Radioactivity (activity) Property of matter exhibiting (radioactive) decay or isomeric transition of atomic nuclei and emission of nuclear radiation [Bq = s ] Radioanalysis Analysis by means of radioactive atoms (radionuclides) Radiocolloids Colloids (i.e. matter in the colloidal state) consisting of the radioactive matter considered (intrinsic colloids) or containing microamounts of radioactive matter (carrier colloids)... 

Two types of colloids are recognized in the literature. Intrinsic colloids (also called true colloids, type I colloids, precipitation colloids, or Eigencolloids ) consist of radioelements with very low solubility limits. Carrier colloids (also known as pseudocolloids, type II colloids or EremdkoIIoides ) consist of mineral or organic phases (in natural waters primarily organic complexes, silicates and oxides) to which radionuclides are sorbed. Both sparingly soluble and very soluble radionuclides can be associated with this type of colloid. In addition, radionuclides can be associated with microbial cells and be transported as biocolloids. 

The simulation results of Fig. 7-8 (Corapcioglu et al., 1999) show that, for this case, the presence of colloids enhances contaminant transport relative to the colloid-free case. If the first-order rate constant for the desorption of the contaminant from the mobile colloids, is small in value, the simulation results for the local equilibrium assumption (LEA) case and the kinetic case are the same. In the case of an intrinsic colloid, K m will be the rate of dissolution of the colloid however, if the rate of desorption of the contaminant is relatively slow (in these cases 0.012 vs. 0.0005 s" ), desorption kinetics has the effect of enhancing colloid-facilitated contaminant transport. Note that in the case of intrinsic colloids, Ks would 0. 

Fig. 7-14. TEM photo of a mixed culture of siilfalo-redueitig liaclcria after 4 li of expoMiiv to I iM iiratiyl acetate illustrating the poMluction of I l(IV) intrinsic colloids. Spear el al. ( )<) ))...

Colloidal suspensions are systems of small mesoscopic solid particles suspended in an atomic liquid [1,2]. We will use the term colloid a little loosely, in the sense of colloidal particle. The particles may be irregularly or regularly shaped (Fig. 1). Among the regular shapes are tiny spherical balls, but also cylindrical rods or flat platelets. As the particles are solid, fluctuations of their form do not occur as they do in micellar systems. Not all particles in a suspension will, in general, have the same form. This is an intrinsic effect of the mesoscopic physics. Of course in an atomic system, say silicon, all atoms are precisely similar. One is often interested in the con-... 

An important reason for this lack of experimental work is that the zeta-potential cannot be easily determined independent of the electrophoretic mobility [284] however, in the case of proteins (as well as some other charged colloids), the intrinsic charge obtained by titration is a parameter that can be measured independent of the electrophoretic mobility. The charge obtained from electrophoretic measurements (i.e., the net charge) via the preceding theories is generally not the same as the charge obtained from titration (i.e., the in-... 

The lack of a method to determine the spatial distributions of permeability has severely limited our ability to understand and mathematically describe complex processes within permeable media. Even the degree of variation of intrinsic permeability that might be encountered in naturally occurring permeable media is unknown. Samples with permeability variations will exhibit spatial variations in fluid velocity. Such variations may significantly affect associated physical phenomena, such as biological activity, dispersion and colloidal transport. Spatial variations in the porosity and permeability, if not taken into account, can adversely affect the determination of any associated properties, including multiphase flow functions [16]. 

In colloid science, colloidal systems are commonly classified as being lyophilic or lyophobic, based on the interaction between the dispersed phase and the dispersion medium. In lyophilic dispersions, there is a considerable affinity between the two constituent phases (e.g., hydrophilic polymers in water, polystyrene in benzene). The more restrictive terms hydrophilic and oleophilic can be used when the external phase is water and a nonpolar liquid, respectively. In contrast, in lyophobic systems there is little attraction between the two phases (e.g., aqueous dispersions of sulfur). If the dispersion medium is water, the term hydrophobic can be used. Resulting from the high affinity between the dispersed phase and the dispersion medium, lyophilic systems often form spontaneously and are considered as being thermodynamically stable. On the other hand, lyophobic systems generally do not form spontaneously and are intrinsically unstable. 

Kim, O.K., Little, R.C., and Ting, R.Y. "The Correlation of Drag-Reduction Effects with Polymer Intrinsic Viscosity," J. Colloid Interface Sci.. 1974, 47(2). 

Ferric hydroxide coprecipitation techniques are lengthy, two days being needed for a complete precipitation. To speed up this analysis, Tzeng and Zeitlin [595] studied the applicability of an intrinsically rapid technique, namely adsorption colloid flotation. This separation procedure uses a surfactant-collector-inert gas system, in which a charged surface-inactive species is adsorbed on a hydrophobic colloid collector of opposite charge. The colloid with the adsorbed species is floated to the surface with a suitable surfactant and inert gas, and the foam layer is removed manually for analysis by a methylene blue spectrometric procedure. The advantages of the method include a rapid separation, simple equipment, and excellent recoveries. Tzeng and Zeitlin [595] used the floation unit that was devised by Kim and Zeitlin [517]. 

The intrinsic germicidal property of the Ti02 support was also tested for natural indoor bioaerosol. A piece of cotton cloth was coated with a colloidal suspension of the nanostructured Ti02. After drying, a circular piece of the cloth was cut and fitted inside the Andersen viable single-stage sampler in such a way... 

Hiemstra, T W. H. van Riemsdijk, and H. G. Bolt (1989), "Muitisite Proton Adsorption Modeling at the Solid/Solution Interface of (Hydr)Oxides, I. Model Description and Intrinsic Reaction Constants", J. Colloid Interf. Sci. 133, 91-104. 

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... 

In the results presented in Table 13.5, the addition of tin affects the kinetic selectivity r differently, depending on the catalyst preparation method. When compared to the monometallic PdO catalyst, r slightly decreases for the coimpregnated PdSn catalyst, but it sharply increases for the PdOSn catalyst prepared via the colloidal oxide synthesis. As the intrinsic kinetic constant rates k do not show significant discrepancies between the different catalysts, the main contribution of the variation of the kinetic selectivity is ascribed to the adsorption constant ratio fBo/ Butenes- In the case of the PdOSn catalyst, formation of but-l-ene is favored compared to its consumption because the X Bo/ Butenes ratio increases, indicating that olefin adsorption is much more destabilized than diene adsorption. Thus, the olefin easily desorbs before being hydrogenated into butane. 

T. Hiemstra, W. H. van Riemsdijk, and G. H. Bolt, Multisite proton adsorption modeling at the solidZsolution interface of (hydr)oxides A new approach 1. Model description and evaluation of intrinsic reaction constants, J. Colloid Interface Sci. 133(1), 99-104 (1989). 

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