Total exchangeable cations capacity

Cation exchange capacity (CEC) the sum total of exchangeable cations that a soil can adsorb... 

Important chemical characteristics of the soil include the total exchange capacity for cations, expressed as total meq of cations per 100 gm of soil, and the base status, which is the percentage saturation of the negative charge with cations such as calcium, magnesium and sodium. The more productive soils are about 80% saturated with calcium and magnesium. Excessive hydrogen and aluminum saturation (much over 15%) is termed soil acidity. Excess sodium saturation (12% or more) leads to dispersiveness of the soil and poor productivity. 

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. 

Typically, HPICE separator columns contain a totally sulfonated high-capacity cation exchange resin. The separation mechanism occuring at this stationary phase is based on three phenomena ... 

In the case of vermiculite, the short-chain organic cations do not penetrate into the interlayer space, and are adsorbed only on the external surface of the mineral. This is clearly seen from the analytical measurements, showing that only 0.06 meq/g of Na" " ions is substituted when Na-vermiculite is treated with tetramethylammonium salt solution, the total exchange capacity being equal to 1.5 meq/g. Therefore, the values of specific surface area obtained from water and hexane adsorption isotherms for the initial and [(CH3)4N] modified vermiculite are virtually the same (Table 3). Such a pronounced difference in the... 

The acidity of the soil may conveniently be characterized by the content of metal ions, relative to the total cation exchange capacity of the soil. In the acid types of soil considered here, this base saturation degree is usually below 10%. The degree of base saturation will be reduced when (1) the roots take up exchangeable cations from the soil, and (2) when accumulation of dead plant material increases the amount of humus, and thereby the cation exchange capacity. To a certain degree, both of these processes are reversible, but if plant products are removed from the area without application of fertilizers, manure or lime, this represents an acidification by reducing the available supply of cations. 

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). 

Anions participate in chemical conversions and in the total exchange dynamics in the soil to an essentially lesser extent than cations. The reason for this is that they are less adsorbed on the colloidal complex, since the soil adsorbents are negative rather than positive on their surfaces. The soil exchange capacity increases with the acidity for anions, which is connected with an increase of the positive charge of soil colloids, particularly of hydrated oxides. In cultivated soils of the Temperate Zone, with a pH... 

A total cation exchange capacity CEC=86.2 meq/lOOg of solid has been used. The exchangeable cations are also secondary species and are controlled by the following reactions ... 

CEC and Anion Exchange Capacity (AEC) Test The method used to find the CEC or AEC indicates the total amount of exchangeable cations or anions. Cations could be alkaline earth and alkaline, metals, and organic complexes. Anions comprise cyanides, arsenic, and so on. The purpose of the CEC test is... 

Naturally occurring minerals called zeolites have long been known to be capable of trading cations in their rather open crystalline lattice for others present in a solution in contact with the zeolite. This is an example of ion exchange, which has become a very popular separation process, particularly since, some 55 years ago, synthetic resins which are capable of exchanging cations or anions were developed. These synthetic resins have considerably more exchange capacity than the zeolites, which they almost totally replaced. 

Postanalysis of geochemical data involves robust calculations to account for the total exchange capacity for cations as a result of the cation exchanges. In most cases, ICP-MS and IC are performed in the final extracts due to its low detection limit capacity and their analytical behavior in complex salt matrices. 

Chemical and physical analyses the total organic matter (OM), pH, snlfnr, phosphorns, exchangeable cations, cation exchange capacity (CEC), textnre, and volnme for soil classification... 

Cation exchange capacity (cec) is defined as the amount of exchangeable cations that a clay mineral can adsorb at a specific pH. This is a measurement of the total negative charges present, and it includes (1) isomorphous substitution within the lattice, (2) broken bonds at edges and external surfaces, and (3) the dissociation... 

In tailoring sorbents for rr-complexation, both the cation-sorbate bond strength and the total number of cations are important. The density of cations depends on the cation exchange capacity of the zeolite. Table 8.3 provides useful information on the total cation capacities for a number of zeolites. 

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