Cation exchange capacity chlorites

Chlorites have rather low specific surface areas and cation exchange capacities (see Chapter 3, section 3.2), a result of the blockage of the interlayer regions by hydroxy sheets, and do not expand at all in water. Exchangeable cations are likely to be found only on external surfaces and edges of chlorite particles. 

Chemical Properties. An important chemical property of clays, which directly affects fines migration is the cation exchange capacity (CEC) (6-9). CEC is a measure of the capacity of a clay to exchange cations. It is usually reported in units of milliequivalents per 100 g of clay (meq/100 g). The CEC depends on the concentration of exchangeable cations in the diffuse Gouy-Chapman layer (see later). This concentration depends on the total particle charge, which may vary with pH. Unless stated otherwise, the reported values of CEC are measured at neutral pH. CEC values (meq/lOOg) of common clay minerals are as follows smectites, 80-150 vermiculites, 120-200 illites, 10-40 kaolinite, 1-10 and chlorite, <10 (10). 

With these reservations in mind, the approximate range of cation exchange capacities of the vermiculite group can be written as 120 to 200 meq/100 g air-dry Mg-vermiculite. A more satisfactory basis would be to record the exchange capacity as meq/100 g interlayer-water-free and interlayer-cation-free mineral (Walker [1965]), and on this basis, the vermiculites range approximately from 140 to 240 meq. Values of cation exchange capacity below those quoted above have been reported, but their validity is in considerable doubt. These low values have invariably been obtained, not from pure vermicuUtes, but from mixed-layer minerals such as hydrobiotite or chlorite-vermiculite, a correction being applied for the proportion of non-vermiculite layers estimated to be present. The error involved in such corrections is considerable. 

There are inconsistencies in the model for the calculation of activity products for the "clays. Exchangeable cations are disregarded for the low exchange capacity kaolinite, halloysite, chlorite, and moderate capacity illite. For certain expansible layer silicates and two zeolites, the logjo of the activity of selected cations is added into the sum of the activity products. 

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