Surface vermiculites

Small areas Small puddles of liquid can be contained by covering with absorbent material such as vermiculite, diatomaceous earth, clay, sponges, or towels. Place the absorbed material into containers lined with high-density polyethylene. Larger puddles can be collected using vacuum equipment made of materials inert to the released material and equipped with appropriate vapor filters. Wash the area with copious amounts of an alkaline soap/detergent and water. Collect and containerize the rinseate. Removal of porous material, including painted surfaces, may be required because these materials may be difficult to decontaminate. Ventilate the area to remove vapors. 

Kriegman-King MR, Reinhard M. 1991. Reduction of hexachloroethane and carbon tetrachloride at surfaces of biotite, vermiculite, pyrite, marcasite. In Organic substances and sediments in water, volume 2. Lewis Publishers, Inc. 349-364. 

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. 

If mica-type sites are truly indicative of mica surfaces, and so on for montmoril Ionite etc., then of the clays examined, only the mica could be regarded as pure. The Montana vermiculite contained much montmoril Ionite, the Fithian illite contained mica and montmoril Ionite, the Wyoming bentonite contained some mica,... 

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. 

Cu2+ in the interlayer of smectites would seem to have a stronger covalent bond to H2O than Cu + in vermiculites or aqueous solution. The ESR parameters for Cu(H20)5 + in solution have been reported as g( = 2.39, g L = 2.07, and AN = 142 x 10 cm" (18). One interpretation of this result is based on the different extent of hydrogen bonding between the silicate surface and the coordination water of Cu2+. In smectites, the hydrogen bonding is weak (2), and would be unlikely to perturb the preferred CU-OH2 bonding geometry, which is pyramidal tetrahedral) in Cu + hydrates... 

If we consider three components, the phases will be arranged as in Figure 48a at conditions of initial burial. The solid solution series are somewhat abbreviated for simplicity. The phase relations are dominated by fully expanding and mixed layered minerals which cover a large portion of the compositional surface. Notably two dioctahedral expandable minerals exist as does a large undefined series of trioctahedral phases designated as expanding chlorite, vermiculite and trioctahedral montmorillonite. 

Thus, ion exchange kinetics on heterogeneous surfaces such as vermiculite involve mass transfer (PD and FD) and CR processes (Fig. 5.2). For actual CR to occur, ions must be transported to the active fixed sites of the particles. The film of water adhering to and surrounding the particle and the hydrated interlayer spaces in the particle are both zones of low concentration. These zones are constantly being depleted by ion adsorption to... 

Unlike kaolinite and montmorillonite, there are several sites for ion exchange reactions to occur on mica and vermiculite (Bolt et al., 1963 Sparks and Jardine, 1984). Bolt et al. (1963) studied potassium exchange on mica and proposed three sites for reactivity. Slow reactions were ascribed to interlattice exchange sites, rapid reactions to external planar sites, and intermediate reactions to readily exposed edge sites. Sawhney (1966) found two distinct reaction rates for cesium exchange on a Ca-vermiculite. The first reaction was ascribed to a rapid exchange of cesium with cations on external planar surface sites and interlattice edges, followed by a second, slow reaction in which cesium diffuses into the interlayers. 

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