Cation fixation montmorillonites

Khaorapapong, N., A. Ontam, J. Khemprasit, and M. Ogawa. 2009. Formation of MnS-and NiS-montmoriUonites by solid-solid reactions. Appl. Clay Sci. 43 238-242. Komadel, P., J. Madejova, J. Hrobarikova, M. Janek, and J. Bujdak. 2003. Fixation of Li+ cations in montmorillonite upon heating. Solid State Chem. Solid State Phenom. 90-91 497-502. 

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 ... 

There appears to be little point in a detailed evaluation of the more ambiguous hypotheses of heavy metal fixation. However, it may be noted that a number of investigators have considered the possibility of either the sorption of complex ions on clay mineral surfaces or reaction of heavy metal cations with clay surfaces in some manner other than simple electrostatic sorption (31, 66, 67, 156, 157, 217), However, the solubility products of Cu(OH)2 and Zn(OH)2 in aqueous suspensions of montmorillonite (19) have been found to be quite similar to those previously found for solutions in contact with only the pure hydroxides. This would indicate that metal ion-clay mineral surface complex formation is not important otherwise the apparent solubility would have been greater in the presence of montmorillonite. 

The cations that may be fixed by clay minerals include Rb and Cs in addition to NH4 and K (Joffe and Levine, 1947). Presumably they are all competitive although Uttle work has been reported with Rb and Cs". In the case of and NH4 it is well established (Bower, 1950) that the addition of either to soil will reduce the fixation of the other added subsequently, and the reduction is nearly proportional to the amount added. This is also shown by the work of Stanford and Pierre (1947). Their work was with a soil in which montmorillonite was the predominant mineral but simular results have been obtained with vermicuhte. The behavior of the ions differs somewhat with concentration, time of contact, and type of clay but these variables are usually of minor importance. 

Some of the modifications for the Nicholas reaction include the fixation of a propargylic substrate onto a solid phase,application of montmorillonite K-10 as acid to generate the propargylic cation, complexation of alkyne with a ruthenium complex, and application of tetrabutylammonium fluoride for decomplexation. ... 

In order to determine the structural factors, concerning host clays, which improve on the catalytic efficiency of pillared clay by the fixation of cations, the following were chosen for comparison with TSM montmorillonite (as smectite, having less of a layer charge than TSM, but an octahedral vacancy like TSM) and taeniolite (as mica, having the same layer charge as TSM, but no octahedral vacancy, unlike TSM). Table 14-2 shows the catalytic activities for cumene... 

FIGURE 41 Schematic drawing of the fixation of cationic dyes in montmorillonite for thermal transfer printing. 

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