Vermiculite, properties

This fact may explain the superiority of montmorillonite over vermiculite as an adsorbent for organocations (3, 4). Complicating this description, however, is the fact that a sample of any particular layer silicate can have layer charge properties which vary widely from one platelet to another (j>). By measuring the c-axis spacings, cation exchange capacity, water retention, and other properties of layer silicates, one obtains the "average" behavior of the mineral surfaces. 

It is believed that CuO O) " - orients in vermiculite interlayers (2 water layers thick) as shown in Figure 18B (6). Yet, the smectites with more vermiculite-like properties (high tetrahedral charge, high total charge) showed no evidence of this orientation, even in cases where two layers of water were situated between the plates. It is necessary to conclude that Cud O) " or Cu(H20)5 + ions are found in the two-layer hydrates of the smectites, with the orientation shown in Figure 18C. 

Based on these rate laws, various equations have been developed to describe kinetics of soil chemical processes. As a function of the adsorbent and adsorbate properties, the equations describe mainly first-order, second-order, or zero-order reactions. For example. Sparks and Jardine (1984) studied the kinetics of potassium adsorption on kaolinite, montmorillonite (a smectite mineral), and vermiculite (Fig. 5.3), finding that a single-order reaction describes the data for kaolinite and smectite, while two first-order reactions describe adsorption on vermiculite. 

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. 

Three Hanford sediments were used in the sorption studies. Each of these sediments contained significant quartz, feldspar, vermiculite, mica, and montmorillonite and were typical of the Hanford sediment in which the HLW tanks are located. Properties of the sediments used are given in Table H. 

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-... 

The data on influence of OSR (oxidized rice and oxidized maize corns) on physical-chemical properties of dry architectural mixtures on the base of plaster and vermiculite (ratio plaster vermiculite = 7 3) are presented in Table 4. As it is obvious additives of OSR allow significant increasing of both time of stiffening and samples (arms) strength. 

Table 4. Physical-chemical properties of dry plaster-vermiculite mixtures with the use of OSR...

Equation 6.36 for the adiabatic potential is exact within the framework of the mean field description. However, the structure of the electric part P1 is too complex to disclose its analytic properties. Here we examine the adiabatic potential numerically following the Carlson theory of elliptic integrals [15-21], To proceed with numerical computation, it is necessary to enter a set of parameters designed to describe an experimental situation. It will not surprise the reader who has made it this far that we use values of the chemically fixed parameters specified by the n-butylammonium vermiculite gels [22], namely m+ = 74 mp and m = 36 mp. The average density n0 of the small ions is given by... 

Vermiculite Concentrate (also raw or unexfoliated vermiculite)—The mineralogical name given to hydrated laminar magnesium-aluminum-iron silicate (Mg,Ca,K,Fe(II)3(Si,Al,Fe(III)40io(OH)204H20) minerals, which resemble mica in appearance. This mineral has the unusual property of exfoliating or expanding to a low density, bulky material when heated (see Vermiculite). 

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. 

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. 

Examples of other property modifiers are silicone powder and liquids, fiuoropolymer powders, Pro-maxon (processed calcium silicate), mica, vermiculite, and waxes. 

Vermiculite resembles mica in appearance. In industrial process, vermiculite flakes are rapidly heated at flame temperature approaching 1000°C. Some of the water of hydration is removed and the pressure generated by the water vapor expands (or exfoliates) vermiculite particles which increases in volume by 15 to 20 times. This expansion process must be precisely controlled to achieve the required expansion and to retain its water absorption properties. If the time of heating is extended, vermiculite will no longer absorb water. Thus, different grades may be produced by varying the heating time. 

In these formulas, X denotes a monovalent cation such as Na" and/or Ca ", occupying interlayer exchange sites. The formulas show that beidellite is magnesium-free and montmorillonite magnesium-rich. Other smectite minerals include nontronite, hectorite, saponite, and sauconite (Table 9.1). All the smectites (and vermiculites) have swelling properties. 

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). 

---