Sodium form of montmorillonite

Sr(II), and Ba(II), for the sodium form of montmorillonite. The Sr(II) results are from a different set of measurements than those in Figure 2, but are in good agreement with them. Effects of loading are small up to the several percent of ion-exchange capacity covered. Values of distribution coefficients for these three ions fall in a narrow range. 

Sodium Form of Montmorillonite Alkali metal ions Distri-bution coefficients of Cs as a function of sodium concentration are summarized in Figure 8 for clays from four different sources. 

Figure 8. Adsorption of Cs(I) on the sodium form of montmorillonites from several sources (Loading 2 X lO — 4 X 10 mol Cs(I)/kg, equilibration for 24 hr.).

Figure 1. Effect of loading on distribution coefficients of Cs(I) on the sodium form of Wyoming montmorillonite (0.5M NaCl + 0.07 M NaOAc, pH 5, equilibration for 74 hr)...

The adsorbability of monovalent and divalent ions on either the sodium or calcium form of montmorillonite decreases with supporting electrolyte concentration approximately as expected from... 

Figure 7. Adsorption of Eu(III) on the sodium form of purified Wyoming montmorillonite (trace loading, equilibration for 96 hr).

A large interlayer distance expand was induced by exchanging the sodium catimis of montmorillonite with La M(fsa)2en cations. Lamellar silicate/oxide nanocomposites were formed by heating the Mont/LaxM(fsa)2Cn compounds at temperatures lower than the one necessary to prepare the oxide phases from the heterobinuclear complexes. 

The peculiar layer structure of these clays gives them cation exchange and intercalation properties that can be very useful. Molecules, such as water, and polar organic molecules, such as glycol, can easily intercalate between the layers and cause the clay to swell. Water enters the interlayer region as integral numbers of complete layers. Calcium montmorillonite usually has two layers of water molecules but the sodium form can have one, two, or three water layers this causes the interlayer spacing to increase stepwise from about 960 pm in the dehydrated clay to 1250, 1550, and 1900 pm as each successive layer of water forms. 

Since charged particles involve all these processes, including the formation of edge charges (Equations 2.3-2.5), first, the electric properties of interfaces have to be determined. A simple way to do so is the application of a support electrolyte in high concentration. The electric double layer, in this case, behaves as a plane and, as a first approach, the Helmholtz model, that is, the constant capacitance model, can be used (Chapter 1, Section 1.3.2.1.1, Table 1.7). It is important to note that the support electrolyte has to be inert. A suitable support electrolyte (such as sodium perchlorate) does not form complexes (e.g., with chloride ions, Section 2.3) and does not cause the degradation of montmorillonite (e.g., potassium fixation in the crystal cavities). In this case, however, cations of the support electrolyte, usually sodium ions, can also neutralize the layer charges ... 

The effect of a complex-forming agent on the cation-exchange processes of montmorillonite is well demonstrated in calcium-montmorillonite, manganese(II) ion, and the sodium salt of the ethylene diamine tetraacetic acid (EDTA) system (K6nya and Nagy 1998 Konya et al. 1998). The reactions are illustrated in Figure 2.9. 

FIGURE 2.13 The equivalent fractions of manganese(II) (XMn), calcium (XCa), hydrogen (XH), sodium ions (XNa), and their sum (X total) in the interlayer space of montmorillonite as a function of pH of the solution. The ratio of the total concentrations of EDTA, calcium, and manganese ions is 1 1 1. The equivalent fractions of calcium and hydrogen ions as a function of pH without the complex-forming agent is also shown. 

Clays involved in fabric softening are most often of the montmorillonite type, particularly sodium and calcium montmorillonite. These clays, also referred to as bentonite, are unique in that their particles swell in water, readily forming colloids whose size is between a few hundredths of a micrometer and several micrometers. 

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