Clay properties Vermiculit

In Chapter 4 we learned that clay is made of minerals, including potassium, aluminum, and silicon oxides. Barium and other metal oxides, vermiculite, and mold controllers are often added to clay to enhance clay properties. If dry clay is mixed with water, large amounts of silica can be released into the air. 

Some of expanding clays in soils have the attributes of vermiculite, some of smectite, and some have features of both. The variation in properties is largely related to the layer charge. The charge is dependent on the original charge on the 2 1 layer of the parent mineral and the amount of ferrous iron in the octahedral sheet. The oxida-... 

Of special significance with respect to their properties as sorbents are the clay minerals (e.g. kaolinite, montmorillonite, vermiculite, illite, chlorite), mainly due to their high exchange capacity. 

Swelling mica-type clay minerals composed of octahedral and tetrahedral sheets are widely utilized in preparing two-dimensional heterostructural nanohybrids, most likely because of their natural ubiquity, high stability, swelling property, and wide applications. In fact, smectite and vermiculite groups have been the preferred layer components to be hybridized with a variety of inorganic and organic components. 

As mixed-layer I/S clays become smectite-rich, their ion exchange and swelling properties approach those of the pure smectites. Other three-layer clays, including the chlorites and vermiculites, also commonly occur in soils in mixed-layer form (e.g., mixed-layer chlorite-smectite [-vermicu-lite]) (cf. Wilson and Nadeau 1985 Drever 1988). 

In a survey of U.S. stream sediments, Kennedy (1965) concluded that the makeup and properties of the stream sediments essentially equaled that of local soils. In the eastern states (50 to 150 cm precipitation), dominant clays in the <4 jum (0.004 mm) fraction were illite, kaolinite, ver-miculite, and interlayered clays, with a CEC of 14 to 28 meq/lOOg. In central and west-central states (25 to 100 cm precipitation) Kennedy found dominant smectite, vermiculite, mixed-layer illite, kaolinite, quartz, and feldspar in the <4 /zm fraction, with a CEC range of 25 to 65 meq/100 g. In California and Oregon, because of the wide range of wet and dry conditions (<25 to >200 cm precipitation), clays were highly variable, and had a range of CEC s from 18 to 65 meq/l(X) g for the <4 /um fraction. 

Chemical Properties. An important chemical property of clays, which directly affects fines migration is the cation exchange capacity (CEC) (6-9). CEC is a measure of the capacity of a clay to exchange cations. It is usually reported in units of milliequivalents per 100 g of clay (meq/100 g). The CEC depends on the concentration of exchangeable cations in the diffuse Gouy-Chapman layer (see later). This concentration depends on the total particle charge, which may vary with pH. Unless stated otherwise, the reported values of CEC are measured at neutral pH. CEC values (meq/lOOg) of common clay minerals are as follows smectites, 80-150 vermiculites, 120-200 illites, 10-40 kaolinite, 1-10 and chlorite, <10 (10). 

It has been verified that the degree of hydration of the vermiculite clay matrix can exert remarkable effects on the magnetic properties of its intercalation compounds. Furthermore, vermiculite has been recently used for studies involving the adsorption of oil-contaminated water samples [1]. 

Ravichandran, J. and Sivasankar, B. (1997). Properties and catalytic activity of acid-modified montinorillonite and vermiculite. Clays and Clay Minerals, 45 854— 858. 

McBride, M.B. and Mortland, M.M. (1973). Segregation and exchange properties of alkylammonium ions in a smectite and vermiculite. Clc s and Clay Minerals, 21 ... 

Other important characterization studies are ion-exchange capacity, especially cationic, and specific surface measurement. CEC is an important parameter in clay characterization and soil behavior, because it affects nutrient availability, among other soil properties. Some clay minerals (smectites and vermiculites) have a high... 

Smectite clay minerals, such as montmorillonite, saponite, nontronite, hectorite, stevensite, vermiculite and haloysite have been known to act as hosts of intercalated compounds [7] and to function as catalysts for various organic reactions [8]. The properties of smectites depend upon the interlayer cations [9], which are easily exchangable for inorganic or organic cations. 

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