Cation exchange capacity expression

Here, meq is number of milliequivalents and CEC is the cation exchange capacity, expressed in milliequivalents per 100 g of sediment. According to the Vanselow convention, alternatively, the activity is expressed as the the fraction of the sites occupied by the ion,... 

The methylene blue test can also be used to determine cation exchange capacity of clays and shales. In the test a weighed amount of clay is dispersed into water by a high-speed stirrer. Titration is carried out as for drilling muds, except that hydrogen peroxide is not added. The cation exchange capacity of clays is expressed as milliequivalents of methylene blue per 100 g of clay. 

Anion exchange capacity The ability of a solid substance to adsorb anions. The anion exchange capacity of a material represents the total positive charge on the surface of the material and is generally expressed in miWiequivalents per 100 grams of material (compare with cation exchange capacity). 

The insolubility of Al(OH)3 and the diffusion of C02 to the atmosphere drive this reaction to completion. Also, adsorption of cations onto the colloid complex raises the percentage base saturation (extent to which the colloidal complex is saturated with exchangeable cations other than hydrogen and aluminum, expressed as a percentage of the total cation exchange capacity) of the colloidal complex, increasing the pH of the soil solution accordingly. 

Schematic 1. The structure of 2 1 layered silicates. M is a monovalent charge compensating cation in the interlayer and x is thedegree of isomorphous substitution, which for the silicates of interest is between 0.5 and 1.3. The degree of isomorphous substitution is also expressed as a cation exchange capacity (CEC) and is measured in milli-equivalents/g.

Cation exchange capacity (CEC) Quantity of cations that an anionic colloid can hold or exchange and is expressed in terms of centimoles per kilogram (cmoles/kg). 

The capacity of cation exchange for a given rock is expressed in terms of the cation exchange capacity (CEC), usually given in the unit of milliequivalent per kilogram of rock (meq/kg). The capacity can also be expressed in terms of unit pore volume (PV). The unit conversion is... 

Brownian motion The random movement of a particle as a result of collisions with fluid molecules or other parHcles Catalyst A substance that increases the rate of a chemical reacHon without being consumed. Catalysts usually work by providing a lower acHvaHon energy pathway Cation An ion with a positive chaise Cation exchange capacity In the past, this property has been expressed in milliequivalents per 100 g of material (meq/lOOg). In SI units, it is expressed in moles of posiHve charge (p ) per unit mass. Often in centimole per kilogram, cmol (p )/kg. The old and new units are numerically equivalent... 

Calculate the cation exchange capacity of tire mineral in Problem 12 and express the result in millimoles(+) per kilogram. Compare this value to the value normally given for montmorillonite. 

Cation exchange capacity (CEC). The sum of exchangeable bases plus the total soil acidity at a specific pH value, usually 7.0 or 8.0. When acidity is expressed as salt extractable acidity, the CEC is called the effective cation exchange capacity (ECEC) because this is considered to be the CEC of the exchanger at the native pH value. It is usually expressed in centimoles of charge per kilogram of exchanger. 

The accumulation of substances such as silica, iron, aluminum, carbonate, and other salts can result in cemented layers, which change the physical, chemical, and biological behavior of the soil. For example, a cemented layer retards percolation and restricts root activity. Furthermore, the availability of nutrients for plant growth is reduced, i.e., the cation exchange capacity is reduced. There are accumulations in the soil which show the enrichment of one substance and/or the depletion of another substance. This can be expressed by diagnostic subsurface horizons, which are listed in alphabetically order in Table 14.5. It should be stressed that some characteristics can be measured only in the laboratory and not in the field. 

The extent of isomorphic substitution is dictated by the nature of the clay, and this is expressed by the cation exchange capacity (CEC). The CEC of a clay is the number of charges on the clay (expressed in coulombs pa- kilogram) which can be replaced in solution. It is typically in the range of 10 to 10 C/kg and for a given clay is not sensitive to variables such as pH or concentration of the electrolyte in solution. 

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