Cation exchange capacity montmorillonites

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.)... 

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. 

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. 

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. 

The mineralogical phase composition of the sample SW [86] (in wt %) is 90% 5% clinoptilolite and 10% 5% others, which include montmorillonite (2-10 wt %), quartz (1-5 wt %), calcite (1-6 wt %), feldspars (0-1 wt %), magnetite (0-1 wt %), and volcanic glass (3-6 wt %). Employing this sample and a pure clinoptilolite, whose TCEC fluctuates between 2.0-2.2 mequiv/g depending on the Si/Al relation of the clinoptilolite monocrystal, it is possible to indirectly evaluate the total cation-exchange capacity of the sample SW as follows ... 

Basal (d00i) Spacing, Internal and Total Specific Surface Area, and Cation-Exchange Capacity of Natural Bentonite-Montmorillonite Samples... 

Some basic properties, such as basal spacing (d001), internal and total specific surface area, and cation-exchange capacity (CEC) of some natural montmorillonite or bentonite with high montmorillonite samples are listed in Table 2.1. Similar characteristics of different cation-exchanged montmorillonites are given in Section 2.3. 

When montmorillonite is suspended in the acetoneous solution of FeCl3, the iron content of the clay obviously increases. The increase of iron concentration is proportional to the quantity of iron(III) added to montmorillonite, and it can even surpass the cation-exchange capacity. However, no excess of iron salt can be observed by Mossbauer spectra or x-ray diffraction. 

Bentonite rocks have many uses in the chemical and oil industries and also in agriculture and environmental protection. The usefulness of bentonite for each of these applications is based on its interfacial properties. These properties are determined by geological origin, chemical and mineral composition (especially montmorillonite content), and particle size distribution, and they include the specific surface area (internal and external), cation-exchange capacity (CEC), acid-base properties of the edge sites, viscosity, swelling, water permeability, adsorption of different substances, and migration rate of soluble substances in bentonite clay. 

Aggregation of dissolved humic substances can also occur with particulate materials in the estuarine water column. Preston and Riley (1982) showed that the adsorption of riverine humic substances onto kaolinite, montmorillonite, and illite increased with increasing salinity and dissolved humic substance concentration. Adsorption increased in the order kaolinite < illite < montmorillonite, which they ascribed to increasing cation-exchange capacity of the clays. They found considerable quantitative differences between the extent of adsorption of riverine versus extracted sedimentary humic substances, indicating the importance of using materials of proper origin in experiments of this type. 

Although there is no bulk liquid with which adsorbed cations can be exchanged in the experiments made in atmospheres of controlled relative humidity, successive experiments can be made with different adsorbed cation populations, and it is found that the succession of dehydration steps varies with size and hydration energy of the cation (Posner and Quirk, 1964). There is also a dependence upon the type and extent of substitution in the aluminosilicate framework White (1958), for example, observed that two montmorillonites with the same cation-exchange capacity, loaded with the same cation, may have different water sorption and swelling properties. 

Sakurai, K., Teshima, A., and Kyuma, K., Changes in zero point of charge (ZPC), specific surface area (SSA), and cation exchange capacity (CEC) of kaolinite and montmorillonite, and strongly weathered soils caused by Fe and Al coatings. Soil Sci. Plant Nutr, 36, 73, 1990. 

Hehny, A.K., Ferreiro, E.A., and de Bussetti. S.G., Cation exchange capacity and condition of zero charge of hydroxy-Al montmorillonite, Clavs Clay Miner., 42, 444, 1994. 

The direct distillation of soil in an alkaline medium may lead to partial breakdown of organic matter thus introducing a possible error with most surface soils. Also if cation exchange capacity is large, the final titration will consume too much titrant if 10 g soil is taken. Hence for direct distillation of heavy clay soils mainly montmorillonite, it is better to take 5 g soil for analysis. 

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