Montmorillonite exchange capacity

FIG. 4 Experimental (vertical bars) and simulated (symbols) values of the d-spacings for aUcy-lammonium-exchanged clay at three different cation exchange capacities (CECs) (a) SWy2 mont-morillonite, CEC = 0.8 meq/g (b) AMS montmorillonite (Nanocor), CEC = 1.0 meq/g (c) fluoro-hectorite (Dow-Corning), CEC = 1.5 meq/g. (Erom Ref. 30.)... 

The data are "normalized" with regard to the ion exchange capacity C of the sorbents. The sorption curves of the illite and of the < 40-pm chlorite are strongly non-linear, whereas that of the montmorillonite approaches linearity. 

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. 

Montmorillonite An iron-rich clay mineral that has a very high cation exchange capacity. Unlike the other clay minerals, a significant amount of sedimentary montmorillonite is hydrothermal in origin. 

The smectite group of clay minerals is also poorly crystalline but perhaps better known because of their cation exchange capacity and their occurrence in the bentonite clays. A general formula for montmorillonite, which is one of the dioctahedral smectites is... 

The dichroic properties of the Li modiEed montmorillonite were followed by orientation of thin films (0-45°) in the IR beam (FTIR Brucker IFS 88). The cationic exchange capacity (CEC) of the samples calcined at 400°C was evaluated. 

FOSTER (M.D.), 1951. The importance of the exchangeable magnesium and cation exchange capacity in the study of montmorillonitic clays. 

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 bentonite with a cation exchange capacity (CEC) of 75 meq/100 g of clay, supplied by Commercial Minerals Ltd., Australia, was used as starting clay material, to prepare samples for SCD and surfactant treatments. Besides, sodium montmorillonite (Kunipia G), from Kunimine Industrial Company, Japan, was used as the starting clay for samples of pore opening modification. CEC of this clay is 100 meq/100 g of clay. 

Ensminger, L. E., and Gieseking, J. E. (1941).The adsorption of proteins by montmorillonitic clays and its effect on base exchange capacity. Soil Sci. 51,125-132. 

The cation exchange capacity (C.E.C.) of the illite minerals is reported to range from 10 to 40 mequiv./lOOg however, illites that afford values larger than 10—15 mequiv./lOOg usually contain some expandable layers. Ormsby and Sand (1954) showed that a good linear relation exists between C.E.C. and percent expandable layers in illites and mixed-layer illite-montmorillonites. They concluded that illite with all layers contracted would have a C.E.C. of 15 mequiv./lOOg. 

Table XXXVIII). Brindley (1955) has suggested that stevensite is a mixed-layer talc-saponite however, Faust et al. (1959) considered it to be a defect structure with a random distribution of vacant sites in the octahedral sheets. A small proportion of domains with few or no vacancies would then be present having characteristics of talc. The layer charge in stevensite is due to an incompletely filled octahedral sheet (Faust and Murata, 1953). This deficiency is minor (0.05—0.10) and the resulting cation exchange capacity is only about one-third that of the dioctahedral montmorillonites (100 mequiv./lOO g.).

As has been noted (Weaver, 1953 Ormsby and Sand, 1954 Bystrom, 1956 Hower and Mowatt, 1966), the cation exchange capacity is closely related to the proportion of expanded layers. If all the exchange capacity is assigned to the mont-morillonite-like layers, values ranging from 96 to 144 mequiv./lOO g are obtained which are within the range of values obtained for pure montmorillonites. 

In a study of Georgia kaolinites Bundy et al. (1965) stated that they believed much of the exchange capacity of kaolinite to be due to the presence of minor amounts of montmorillonite (identified by Mg content). Approximately 0.8 mequiv./lOO g was the highest exchange capacity measured for kaolinites which they believed contained no montmorillonite. This could be accounted for entirely by edge charge. 

Figure 3. Absorbance spectra of the 1985 set of MarSAMs. a) absorbance spectra of five variably Ca/Fe-exchanged materials prepared from SWy montmorillonite of nominal iron substitutions of 0, 20, 50, 80 and 100 % of the exchange capacity. b) absorbance spectra of two replicate samples of the crude parent SWy, a 100% exchanged form of SWy prepared in 1982, the crude parent Otay, and a 100% Fe-exchanged form of Otay.

The cations on the as-made pillared clays are protons. The ion-exchange capacity of the original clay is preserved in the hnal pillared clay. Hence, PILCs can have very large ion-exchange capacities, for example, 140 meq/g for the Arizona montmorillonite. The high ion-exchange capacities of PILCs are potentially useful for ion exchange applications. 

---