Adsorbents kaolin

Studies of the adsorption of fulvic acids by clays are very limited but apparently the non-polysaccharide portion behaves much like humic acids. According to Evans and Russell (1959) the order of effectiveness of fulvic acid adsorption on bentonite was acid > Ca > Mg > K and Na systems. Only a small proportion of the fulvic acid carbon, as in the case of humic acid carbon, was adsorbed. Kaolin was also an active adsorbent, the order being acid > Ca > K, as in bentonite systems. 

Very finely divided minerals may be difficult to purify by flotation since the particles may a ere to larger, undesired minerals—or vice versa, the fines may be an impurity to be removed. The latter is the case with Ii02 (anatase) impurity in kaolin clay [87]. In carrier flotation, a coarser, separable mineral is added that will selectively pick up the fines [88,89]. The added mineral may be in the form of a floe (ferric hydroxide), and the process is called adsorbing colloid flotation [90]. The fines may be aggregated to reduce their loss, as in the addition of oil to agglomerate coal fines [91]. 

Adsorbed by CeHte (infusorial earth) or kaolin or carboxymethylceUulose (CMC). 

Cyclopentadiene oligomers have been formed by vapor deposition of CPD on kaolin to afford a sorbant for removal of oil from water (71). They are also employed as coatings for controlling release rates of fertilizers (72). Thermal addition of sulfur to a mixture of DCPD and CPD oligomers has led to a number of beneficial appHcations such as waste water oil adsorbant powdery foams (73), plasticized backing for carpets and artificial turfs (74), and in modified sulfur cements for encapsulating low-level radioactive wastes (75). 

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. 

Urokinase utilized medically is generally purified directly from human urine. It binds to a range of adsorbents, such as silica gel and, especially, kaolin (hydrated aluminium silicate), which can be used initially to concentrate and partially purify the product. It may also be concentrated and partially purified by precipitation using sodium chloride, ammonium sulfate or ethanol as precipi-tants. 

Adsorbents (such as kaolin-pectin) are used for symptomatic relief (see Table 23-4). Adsorbents are nonspecific in their action they adsorb nutrients, toxins, drugs, and digestive juices. Co administration with other drugs reduces their bioavailability. 

Adsorbent powders are nonabsorbable materials with a large surface area. These bind diverse substances, including toxins, permitting them to be inactivated and eliminated. Medicinal charcoal possesses a particularly large surface because of the preserved cell structures. The recommended effective antidiarrheal dose is in the range of 4-8 g. Other adsorbents are kaolin (hydrated aluminum silicate) and chalk. 

The absorption of some drugs may also be reduced if they are given with adsorbents such as charcoal or kaolin, or anionic exchange resins such as colestyramine or colestipol. The absorption of propranolol, digoxin, warfarin, tricyclic antidepressants, ciclosporin and levothyroxine is reduced by colestyramine. 

Locally-acting are all agents that decrease stimulation of receptors in the GI tract. A viscous formulation of local anesthetics such as lidocaine increases the threshold of receptor-activity to vomiting. Adsorbents and mucosa protective agents like kaolin and pectin, activated charcoal, bismuth subsalicylate, attapulgite and cholestyramine have similar effects. Cola Syrup and phosphorylated carbohydrate can decrease GI muscle spasm with consequently less input into the vomiting center. 

Nonspecific antidiarrheal agents may be useful in treating self-limiting diarrhea. Kaolin and pectin or chalk may adsorb noxious compounds but evidence that such adsorbents are effective is unconvincing. Disadvantages can be prolongation of the course of infection and interference with absorption of desired drugs. 

KaoUn powder and other hydrated aluminum silicate clays, often combined with pectin (a complex carbohydrate), are the most widely used adsorbent powders (e.g., Kaopectate). Kaolin is a naturally occurring hydrated aluminum silicate that is prepared for medicinal use as a very finely divided powder. The rationale behind its use in acute nonspecific diarrhea stems from its ability to adsorb some of the bacterial toxins that often cause the condition. It is almost harmless and is effective in many cases of diarrhea if taken in large enough doses (2-10 g initially, followed by the same amount after every bowel movement). The adsorbents are generally safe, but they may interfere with the absorption of some drugs from the GI tract. 

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. 

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. 

Adsorbents such as kaolin, pectin, or attapulgite are administered to take up and hold harmful substances such as bacteria and toxins in the intestinal lumen.44 Theoretically, these adsorbents sequester the harmful products that cause the diarrhea. These products are used frequently in minor diarrhea, although there is some doubt as to whether they really help decrease stool production and water loss. 

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],... 

Figure 3.7. Phenanthrene sorption isotherms on (A) the whole Amherst peat soil humic acid, (B) montmorillonite and a montmorillonite-humic acid complex (5 1 ratio), and (C) kaolin-ite and kaolinite-humic acid complex (5 1 ratio). Insets in parts B and C are the respective isotherms presented on a linear scale. Reprinted from Wang, K., and Xing, B. (2005). Structural and sorption characteristics of adsorbed humic acid on clay minerals. J. Environ. Qual. 34, 342-349, with permission from the Soil Science Society of America.

The culture liquid obtained above was adjusted to phi 3.0 with a saturated oxalic acid solution and the precipitate formed therein collected by filtration. The filtrate was added to 50.0 g each of kaolin and Celite 545 powder (diatomaceous earth), and stirred for 15 h at 4°C and after chromoprotein was allowed to adsorb as much as possible, it was filtered. The resulting filtrate was divided and placed in cellophane bags dry air was blown on them at 27°C for 24 h condensing them to about 600 ml. This concentrated solution at 4°C was desalted by cellophane dialysis for 24 h in distilled water. The yield of desalted concentrated solution from the culture liquid was approximately 80% (867 mkg/ml, 600 ml). 

The most pharmaceutical value of adsorption is that of unwanted active materials in solution onto solids such as activated carbon, kaolin, and tannic acid. In addition, adsorption may cause formulation problems when active drugs or inert excipients (i.e., preservatives) adsorb onto containers or medical devices. 

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