Vermiculite surface area

In view of the problems associated with the expanding 2 1 clays, the smectites and vermiculites, it seemed desirable to use a different clay mineral system, one in which the interactions of surface adsorbed water are more easily studied. An obvious candidate is the hydrated form of halloysite, but studies of this mineral have shown that halloysites also suffer from an equally intractable set of difficulties (JO.). These are principally the poor crystallinity, the necessity to maintain the clay in liquid water in order to prevent loss of the surface adsorbed (intercalated) water, and the highly variable morphology of the crystallites. It seemed to us preferable to start with a chemically pure, well-crystallized, and well-known clay mineral (kaolinite) and to increase the normally small surface area by inserting water molecules between the layers through chemical treatment. Thus, the water would be in contact with both surfaces of every clay layer in the crystallites resulting in an effective surface area for water adsorption of approximately 1000 tor g. The synthetic kaolinite hydrates that resulted from this work are nearly ideal materials for studies of water adsorbed on silicate surfaces. 

Our approach has been to study a very simple clay-water system in which the majority of the water present is adsorbed on the clay surfaces. By appropriate chemical treatment, the clay mineral kao-linite will expand and incorporate water molecules between the layers, yielding an effective surface area of approximately 1000 m2 g . Synthetic kaolinite hydrates have several advantages compared to the expanding clays, the smectites and vermiculites they have very few impurity ions in their structure, few, if any, interlayer cations, the structure of the surfaces is reasonably well known, and the majority of the water present is directly adsorbed on the kaolinite surfaces. 

For these experiments, some of which were also conducted on the ILL D17 small-angle diffractometer, crystals of n-butylammonium vermiculite exhibiting the fewest obvious structural defects were selected and trimmed to a rectangular cross section with a razor blade. This enabled the surface area, and therefore the applied pressure, to be measured accurately. The samples were then immersed in a dilute solution of n-butylammonium chloride of the desired concentration and allowed to swell freely. After equilibration for at least two days at 7°C, the swollen (or colloidal) gel phase samples were placed into the uniaxial pressure cell shown in Figure 3.1. 

To estimate the degree of polymer adsorption, we first calculate the total layer surface area of the vermiculite in the crystalline state. The formula for the dry sodium Eucatex sample considered in Chapter 1 can be abbreviated as... 

The calculation of the surface area is now straightforward. Each cell has a surface area of 0.515 x 0.89 nm2 on each side, and 996 g of the clay contains 6.02 x 1023 cells (Avogadro s number). Thus, the total surface area of 1 g of n-butylammonium vermiculite is... 

Properties Platelet-type crystalline structure. High porosity, high void volume to surface area ratio, low density, large range of particle size. Insoluble in water and organic solvents soluble in hot concentrated sulfuric acid. Water vapor adsorption capacity of expanded vermiculite less than 1%, liquid adsorption dependent on conditions and particle size, ranges 200-500%. Noncombustible. 

A vermiculite clay has the structural formula K.Mgo.sKMgaoFe sFeJ sXAl, sSi65)02o(OH)4. Calculate its cation-exchange capacity in meq/IOO g and its surface-site density in mol/g. Assuming the surface area of the clay is 30 mVg, what is its surface-site density in nm and /umol/m ... 

In the case of vermiculite, the short-chain organic cations do not penetrate into the interlayer space, and are adsorbed only on the external surface of the mineral. This is clearly seen from the analytical measurements, showing that only 0.06 meq/g of Na" " ions is substituted when Na-vermiculite is treated with tetramethylammonium salt solution, the total exchange capacity being equal to 1.5 meq/g. Therefore, the values of specific surface area obtained from water and hexane adsorption isotherms for the initial and [(CH3)4N] modified vermiculite are virtually the same (Table 3). Such a pronounced difference in the... 

Vermiculites. Vermiculites are 2 1 expanding minerals with a structure similar to micas (Table 7-4). They are considered to be derived from the alteration of micas (Douglas, 1977). Cation exchange capacity is high, as is the surface area. Potassium or NHj in solution tends to be strongly fixed by vermiculites. Upon fixation of these ions, the CEC decreases and the properties of vermiculite become like those of mica. In acid soil, hydroxy aluminum polymers can be fixed in the interlayer position to form an "island-like" structure (Jackson,... 

Abrasion resistance, effect on, 146 Chemical composition, 146 Density, 146 Kaoilinite, 146 Mohs hardness, 146 Moisture content, 146 Montmorillolinite, 146 Oil absorption, 146 Specific gravity, 146 Surface area, 146 Vermiculite, 146 Kaolin, 80, 125, 128, 129, 133 Kaolinite, 146... 

Colloid chemists commonly measure surface area by the adsorption of N2 gas. The adsorption is conducted in vacuum and at temperatures near the boiling point of liquid nitrogen (—196° C). The approach is based on the Brunauer-Emmett-Teller (BET) adsorption equation, and has been adapted to a commercially available instrument. Unfortunately, the technique does not give reliable values for expansible soil colloids such as vermiculite or montmorillonite. Nonpolar N2 molecules penetrate little of the interlayer regions between adjacent mineral platelets of expansible layer silicates where 80 to 90% of the total surface area is located. Several workers have used a similar approach with polar H2O vapor and have reported complete saturation of both internal (interlayer) and external surfaces. The approach, however, has not been popular as an experimental technique. 

Smectites Phyllosilicates Mica and/or vermiculite alteration C High CEC high surface area high shrink-swell capacity... 

Clays with mica-type lattices, especially vermiculite and illite, can also react with many organic compounds to form complexes in which the organic substance is held in the clay lattice. The rate of reaction with vermiculite is fairly rapid but very slow with illite and mica. Differences in behavior of these minerals has been attributed to surface area and to the density of charge on the surface. 

The results for the adsorption of crude oil on columns, and the BET surface area for the studied samples are summarized in Table 8.1. The adsorption factor (AF) is defined here as (oil mass)/(vermiculite mass). For both, expanded and FIV samples, the adsorption studies were performed at two different mass values 2.0 and 4.0 g. However, it was found that the AF values were not affected by the used vermicuHte mass. Adsorption experiments were also performed for hydrated (not expanded) vermiculite samples, and it was observed that the AF for these sample is very low (0.3). All adsorption experiments were performed in triplicate, and it was verified that the results are reproducible. 

Typical results of specific surface area determinations on phyllosilicates by nitrogen gas/water vapor or nitrogen gas/CPB adsorption are listed in Table 1.7. For Mg-vermiculite and Na-montmorillonite, the measured adsorption specific surface area is close to that calculated from the unit cell dimensions and structural formula. For illitic mica, the area is about 14 per cent of the ideal crystallographic value, indicating that this mineral forms particles containing about seven phyllosilicate layers that cannot be penetrated by water vapor or CPB. 

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