Clays vermiculites

The Adsorption of Cs+on Clays - an ion with a simple solution chemistry (no hydrolysis, no complex formation) - can be remarkably complex. Grutter et al. (1990) have studied adsorption and desorption of Cs+ on glaciofluvial deposits and have shown that the isotherms for sorption and exchange on these materials are nonlinear. Part of this non-linearity can be accounted for by the collaps of the c-spacing of certain clays (vermiculite, chlorite). As illustrated in Fig. 4.23 the Cs+ sorption on illite and chlorite is characterized by non-linearity. 

The difference in the composition of these two size fractions is similar to the difference between the two types of clay vermiculite described by Barshad and Kishk. The two sets of data confirm the idea that clay vermiculites developed by mild leaching action of pre-existing sheet structures tend to inherit much of their octahedral and tetrahedral character. Clay vermiculites formed by relatively intense weathering and by diagenetic alterations and in approximate equilibrium with their soil environment will have little if any tetrahedral Al the octahedral sheet can be quite variable in composition and depends on the availability of Al, Fe, and Mg. 

Roth et al. (1969) have demonstrated that clay vermiculites commonly have a surface coating of positively charged Fe203 (approximately 10% A1203 is also present) which causes a decrease in C.E.C. This material can be removed (deferration) by reducing free Fe2 03 with Na2 S04 in the presence of Na citrate and NaHC03. 

Liquid pesticide spills can be further contained by covering the entire spill with absorbent materials, such as spill pads, blankets or pillows, absorbent clay, vermiculite, sawdust, com cobs, expanded silica, or other acceptable material. 

A different clay derives from the layered mineral talc, Mg3(Si40io)(01T)2. If iron(II) and aluminum replace magnesium and silicon in varying proportions and water molecules are allowed to take up positions between the layers, the swelling clay vermiculite results. When heated, vermiculite pops like popcorn, as the steam generated by the vaporization of water between the layers puffs the flakes up into a light, fluffy material with air inclusions. Because of its porous structure, vermiculite is used for thermal insulation or as an additive to loosen soils. 

The three-layer phyllosilicates include talc and pyrophyllite, illite and the smectite group clays, various mixed-layer clays, vermiculite, and the micas (e.g., muscovite, phlogopite, and biotite). We will limit ourselves to a discussion of the more environmentally important of these minerals, which include the micas, the smectites and illites, interlayered (mixed-layer) smectite-illites and vermiculite. 

SPILL CLEAN-UP ventilate area of spill or leak sweep spilled substance into suitable containers, using a method that does not generate dust dilute residues from spills with water, or neutralize with dilute acid such as acetic, hydrochloric or sulfuric absorb neutralized caustic residue on clay, vermiculite or other inert substance and package in a suitable container for disposal. 

Weed control soil DL clay Vermiculite Antibacterial soil Decomposed granite soil Sea sand... 

Organic reactions in the interlayer space of clays Vermiculite/L-ornithine peptide formation Rausell and Fornes (21)... 

Silicates Sheet silicates Clays Vermiculites Vermiculite... 

Based on expanded clay. Based on exp. clay/ vermiculite,... 

Macroscopic vermiculites are invariably trioctahedral, but the minerals that occur in soil clays may be either trioctahedral or dioctahedral. Brown [1953] was the first to report the existence of dioctahedral clay vermiculites, and since then, many, perhaps the majority of, clay vermiculites recorded have been of the dioctahedral type. Clay vermiculites, dioctahedral or trioctahedral, have now been identified in soils and sediments from many parts of the world, including Australia, Canada, Czechoslovakia, England, France, Ireland, Japan, New Zealand, North Africa, Scotland, South Africa, Spain, Sweden, and many states of the U.S.A. The inadequacy of the tests used for distinguishing between clay vermiculites and montmorillonites, discussed in Section CIII, makes it certain that many clay vermiculites have been wrongly identified as montmorillonites, whereas the opposite would occur to a lesser extent. This suggests that clay vermiculites are even more widely distributed in soil clays than is generally believed. M. L. Jackson (private communication) estimates an overall average ratio of 2 1 of montmorillonite to clay vermiculite in soils of all types. 

The development of vermiculite minerals in soils at the expense of micas is now well established as a common phenomenon, more particularly by the work of Jackson and his collaborators e.g., Jackson et al. [1952], Schmehl and Jackson [1956], Jackson [1959,1963], Brown and Jackson [1958]) as well as by others e.g., Fieldes and Swindale [1954], Rich [1958], Cook and Rich [1962], Millot and Camez [1963], Nelson [1963]). In spite of the frequent occurrence of dioctahedral clay vermiculites in soils, dioctahedral clay micas, in general, appear to resist decomposition better than their trioctahedral counterparts and, where direct comparison is possible, the dioctahedral type may remain unaffected, whereas the trioctahedral mica in the same profile is almost completely altered (Mitchell [1955]). Vermiculitelike minerals, however, may also develop in soils by other routes, for example, from montmorillonite (Bundy and Murray [1959], Jackson [1963]) or from chlorite (Droste and Tharin [1958], Brown and Jackson [1958], Droste et al. [1962], Millot and Camez [1963]). Such alterations are reversible, and they depend on a chemical equilibrium between the mineral and the soil solution. Hence clay chlorites, illites, and montmorillonites may develop from clay vermiculites in an appropriate environment, and intermediate types are common. The alteration of clay vermiculites to kaolinite in podzols has also been proposed (Walker [1950], Brown [1953], Jackson et al. [1954], McAleese and Mitchell [1958a]). 

The mechanism of the fixation of the larger monovalent ions in true vermiculites has already been treated in Section BIV3, and a discussion of the use of K in identifying and characterizing clay vermiculites, which follows in Section CIII2, is also relevant in this regard. 

The identification of clay vermiculites in soils rests almost entirely on X-ray diffraction procedures which allow the displacement of the basal spacing, after various chemical and heat treatments, to be measured. Even X-ray diffraction, however, can give misleading results unless used with caution, and the preparative methods employed can materially affect the diffraction data, as Harward andTHEiSEN [1962] and Harward et aL [1962] have clearly demonstrated. 

Although the occurrence of clay vermiculites has been reported frequently in recent years. X-ray data on them are still rather limited, only data for the basal and 060 reflections being usually recorded. There is evidence that the nonbasal reflections can sometimes be indexed hkl, and it is probable that this is a general rule. As with the macroscopic minerals, the basal spacing varies with the nature of the interlayer cation and the hydration state of the specimen. If the 060 reflection lies in the range 1.49 to 1.51 A, the mineral is dioctahedral and, if in the range 1.53 to 1.55 A, trioctahedral (Stevens [1946], Walker [1950]). 

Barshad [1954] introduced a technique involving the use of salted pastes for X-ray diffraction analysis of soil clays that intensifies, in many cases, the basal spacings of the minerals and hence makes identification easier. Later (Barshad [I960]), he modified the technique so as to allow a distinction to be made between clay vermiculites and mont-morillonites (cf Section CIII2). 

Instances where 14 A clay minerals in soils contract to near 10 A when saturated with K and dried in air at room temperature were first reported by Jackson and Hellmann [1941]. At that time, the minerals concerned were regarded as montmorillonites, but we would now refer to them as clay vermiculites, and the existence of such minerals in soil clays has been confirmed by a large number of workers. 

NH4 behaves in a similar fashion to K, and the NH4 contraction has been used to aid in the differentiation of clay vermiculites from montmorillonites and clay chlorites (Walker [1949b, 1961]). Young and Cattani [1962] found that the lattices of hydrated vermiculites and also of some montmorillonites contract when ammonia is adsorbed, and Mortland et al. [1963] have demonstrated by means of infrared spectroscopy that ammonia adsorbed in montmorillonites is present as NH4 ions rather than in the molecular form. 

It will be evident from the foregoing that measurement of the lattice spacing after treatment with K or NH4 does not provide a simple unequivocal test capable of distinguishing clay vermiculites from montmorillonites it can, however, be a valuable supplementary technique. 

Lattice expansion in the presence of organic liquids is frequently used as a means of distinguishing clay vermiculites from montmorillonites. Lattice swelling characteristics can, of course, be measured by means of X-ray diffraction in the presence of other minerals, and, since natural clays are usually mineralogically complex and effective methods of isolating the... 

It will be evident that considerable difficulties may arise in the positive identification of clay vermiculites, particularly in distinguishing them from montmorillonites and clay chlorites. These difficulties will be enhanced when clay vermiculite is but one component of a mixed-layer assemblage, and many examples of such minerals in sedimentary and soil clays have been now recorded (cf Chapter 8). As we have seen in the preceding section, laterally mixed structures also add to the complexities of the situation and make it essential that the detailed expansion-contraction characteristics of the lattice be recorded if maximum information is to be conveyed. 

Puketeraki High country Yellow-brown earth from schist 1270 5.5 10 35 Clay-vermiculite... 

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