Kaolin adsorption

A tyrosine decarboxylase of animal tissues was separated from other decarboxylases by kaolin adsorption. This treatment separates tyrosine decarboxylase from a very active dopa decarboxylase, which occurs in many tissues. This latter enzyme also attacks certain other hydroxylated phenylalanines. It has been resolved and used for assay of phosphorylated pyridoxal. Crude preparations are sufficiently active to permit the reaction to be followed with conventional manometric apparatus for the determination of liberated CO2. 

Fig. 7). This lower adsorption of the sodium ct-sulfo fatty methyl esters on kaolin is in accord with their somewhat worse detergency. 

A major advantage of the simple model described in this paper lies in its potential applicability to the direct evaluation of experimental data. Unfortunately, it is clear from the form of the typical isotherms, especially those for high polymers (large n) that, even with a simple model, this presents considerable difficulty. The problems can be seen clearly by consideration of some typical polymer adsorption data. Experimental isotherms for the adsorption of commercial polymer flocculants on a kaolin clay are shown in Figure 4. These data were obtained, in the usual way, by determination of residual polymer concentrations after equilibration with the solid. In general, such methods are limited at both extremes of the concentration scale. Serious errors arise at low concentration due to loss in precision of the analytical technique and at high concentration because the amount adsorbed is determined by the difference between two large numbers. 

Figure 4. Data of Bensley (14) for the adsorption of commercial flocculants on a kaolin clay (BET surface area 15 m /g).

The nature section of the BBC Website describes several examples of animals eating kaolin clay to immobilize toxins by adsorption on the clay s surface. For example, see the first entry on the page http //www.bbc.co.uk/nature/weird/az/mo.shtml. Alternatively, read The Life of Mammals by Sir David Attenborough, BBC Books, 2002, p. 170. 

Glucosyl-fructose, 24 237 D-Glucuronic acid, 4 711 Glucuronic pathway, of ascorbic acid biosynthesis, 25 762-763, 763-764 Glue, kaolin application, 6 688t Glueckauf approximation, adsorption, 1 608, 609... 

Freeze RA, Cherry JA (1979) Groundwater. Prentice-HaU Englewood Cliffs, NJ Gapon EN (1933) Theory of exchange adsorption in soils. J Gen Chim 3 144-163 Giese RF, Jr. (1982) Theoretical studies of the kaolin minerals Electrostatic calculations. Bull Mineral 105 417 24. 

The rate of disproportionation increases with decreasing pH and rising temperature and these conditions also favour oxide reduction. To achieve a reasonable rate of dissolution, one has to compromise on the pH. A pH of 3 is used in kaolin bleaching (Jepson, 1988), whereas in soil analysis the system is usually buffered with citrate and bicarbonate at ca. pH 7 (Mehra Jackson, 1960). Citrate also complexes the dissolved Fe " and prevents its precipitation as Fe" sulphide. For the dithionite/EDTA system, Rueda et al. (1992) found a maximum efficiency at pH 5-6 and an activation energy for goethite dissolution of 70 kj mol". They stressed the importance of adsorption of S2O4 on the surface to ensure reduction of Fe ". 

Adsorption isotherms for AMP-QS onto kaolin, titania and calcium carbonate are shown in Figure 4. Viscosity profiles obtained when AMP is used to disperse titania and kaolin are shown in Figures 5-7. 

Figure 4 Adsorption isotherms for AMP-95 onto kaolin, titania and calcium carbonate...

XPS can be used to quantify HPAM adsorption onto minerals at various polymer bulk concentrations. It is seen here that kaolinite has twice the affinity for HPAM than feldspar at pH 9.0 and 50 ppm. Little or no adsorption was monitored on the surface of quartz or mica. Imaging XPS to monitor selective adsorption of mineral mixes proved difficult. Flocculating a mineral mixture of kaolinite, mica and quartz caused the kaolin floes to encapsulate the other minerals. This created a layer of kaolin on the quartz and mica prohibiting polymer mapping on their surfaces. It is shown that the effectiveness of the kaolin recovery is more strongly affected by encapsulation of other minerals during flocculation rather than the selective adsorption process. 

The Nature of Adsorption Sites on Unrefined and Ball Milled Kaolin. A Diffuse Reflectance Infrared Fourier Transform Spectroscopic Study... 

Froth flotation has proven to be an efficient method of removing titaniferous impurities (mainly iron-rich anatase) from kaolin clays. Fatty acid reagent, primarily tall oil, is used extensively in the reverse flotation of these impurities. This flotation collector typically requires divalent cations (usually Ca +) to activate the coloured impurities and enhance collector adsorption. This is not very selective since the tall oil can also absorb on the kaolinite particles. Alkyl hydroxamate collectors are relatively new in the kaolin industry but provide significant advantages. Hydroxamates do not require activators, substantially increase the removal of colored impurities and are very selective. 

Michaelis and Bona loc. cit.) have concluded from an examination of various cases of adsorption, e.g. methylene blue hydrochloride by kaolin and by cellulose and of picric acid by iron hydroxide, that the mechanism is one of ionic interchange and not of promoted hydrolysis. 

The heat curves, themselves, are informative. The kaolin-based pellet catalyst has a few more active sites then attapulgite, but its site activity decreases rapidly and to values only about 3 kcal./mole above the heat of liquefaction of the liquid at maximum coverage. Obviously, a distinction cannot be made between physical adsorption and chemisorption for some of the amine adsorbed at full coverage on the cracking catalyst. On the other hand, attapulgite has a much narrower distribution of adsorption energies, and the lowest heats are about double the heat of liquefaction of butyl amine. Therefore, it appears safe to conclude that the amount remaining after evacuation at 25° is chemisorbed. 

Fia. 5. Differential heats of adsorption of n-butyl amine at 26° versus surface coverage 9. (1) Attapulgite clay. (2) Kaolin-based cracking catalyst. 

The specific area is measured in m2/gramme. Its value can vary from 1-5 m2/g in the case of, for example, coarse kaolin to about 100 m2/ g for certain plastic clay types. The measurement for example takes place by adsorption of gases like nitrogen. The adsorbed amount is measured as a function of the pressure. At a certain N2 pressure nitrogen molecules at the surface of the solid particles are adsorbed and pressed into the pores. Consequently, this method is also suitable for measuring porosity and pore size distribution. 

The emission spectrum of Ru(bpy)21 in HZrP and HexA-ZrP had maxima at 620-625 nm. In both cases, quenching by ferricyanide was used to distinguish between the Ru(bpy)2+ adsorbed on the outer surface and in the interlamellar regions. For HexA-ZrP, the Stern-Volmer plot was nonlinear and this nonlinearity was interpreted as due to the adsorption of Ru(bpy) + at two different places. The Stem-Volmer constant (KSv) for the major component was estimated to be 7200 M 1 and this value is of the same order of magnitude as that of Ru(bpy)f1 -kaolin [85], in which Ru(bpy)21 is known to bind on the external surface, and both values are much smaller than that observed in aqueous solution (23,000 M1) [75b],... 

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