Clay minerals adsorption capacity

The clay mineral bentonite (sodium montmorillonite) has an excellent ion exchange and adsorption capacity. Films can be applied to electrode surfaces from colloidal clay solutions by simple dip or spin coating that become electroactive after incorporation of electroactive cations or metal particles 136-143)... 

CEC, cation exchange capacity A measure of the amount of cations that will adsorb to the negatively charged surface of a clay mineral. It is usually measured in units of meq of charge per lOOg of clay mineral. This adsorption is reversible. 

Clay minerals, oxides, and humic substances are the major natural subsurface adsorbents of contaminants. Under natural conditions, when humic substances are present, humate-mineral complexes are formed with surface properties different from those of their constituents. Natural clays may serve also as a basic material for engineering novel organo-clay products with an increased adsorption capacity, which can be used for various reclamation purposes. 

Recent studies have shown that the adsorption capacity of a common organic component (humic acid) can exceed that of clay minerals. A change in pH can cause marked changes in the uptake of metal ions by such humic acids [255] or humic acid-clay mixtures [256]. hi this connection, Slavek et al. [257] examined the effect of various electrolytes on the organic acid-metal ion equilibria, with a view to clarifying the situation. 

Whereas several specific soil attributes are advocated as being responsible for DOC sorption in the mineral soil (Table V), it appears that the greater the clay or aluminum and iron oxide content of a soil, the greater its adsorptive capacity for DOC. For example, there is a positive correlation between m (the measure of the affinity of a substance for the sorbent or the partition coefficient) and soil clay content, dithionite extractable iron (Fej), and oxalate extractable aluminum (Al0) (Moore et al., 1992 Nelson et al., 1993 Kaiser and Zech, 1998). Direct measurements of the surface area of soil particles also correlate very well with DOC adsorption capacity (Nelson et al., 1993). Furthermore, Nelson et al. (1993) report that riverine DOC concentrations are negatively correlated to the clay content of watershed... 

Besides using the EPR to evaluate the binding capacity of NOM for metal ions, it is also possible to use the latter as spin probe (Senesi, 1990a). Analyses of spectroscopic data comprise studying the adsorptive properties, surface interactions, and structural chemistry of soil, synthetic metal oxides, hydrous oxides, and clay minerals (McBride et al., 1984 Coyne and Banin, 1986 Senesi et al., 1991a Spagnuolo et al., 2004). 

The type of clay mineral, depending on its abundance and degree of K+ (or NH4+) saturation, may control the adsorption, phase distribution and thus the mobility and (bio)availabihty of NACs in soils [152], The affinity of adsorption capacity of the clays for NACs increase in the order kaolinite < illite < montmorillonite [152],... 

Natural waters always contain colloid particles. They originate from the rocks and soils and contain mineral particles (clay, sand, silt, etc.) and organic matter (humic substances). Since the size of the particles is small, they have great specific surface area and high adsorption capacity. The concentration of colloids is usually studied by the measurement of turbidity. 

The soil is a dynamic biotic and abiotic system. Pesticides deposited in or on the soil have varying capacities to be adsorbed to clay minerals and organic matter. Such adsorption reduces both the movement and the biological activity of the pesticide. In addition to soil adsorption, several other factors are known to influence the behavior and fate of pesticides after the chemicals are in contact with soil. 

Polarised molecules such as higher molecular-weight hydrocarbons can be adsorbed via electrostatic forces. Organic or inorganic colloids (humic matter and clay minerals) are electrically charged and possess high adsorption capacities. Hydrocarbon gas molecules adsorbed in this way can be released by the addition of more competitive molecules (e.g., dichloromethane) to substitute in the occupied sites. 

Hang, P.T., and G.W. Brindley. 1970. Methylene blue adsorption by clay minerals. Determination of surface areas and cation exchange capacities. Clay Clay Miner. 18 203-212... 

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