Vermiculites cation exchange

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. 

Foster (1963) established empirically that the cation exchange capacity of vermiculites could be calculated by multiplying the positive charges carried by the interlayer cations by 200. The calculated range of cation exchange capacities of the macroscopic vermiculite she studied ranged from approximately 80 to 200 mequiv/ 100 g. Nearly half the samples have a C.E.C. less than 140 and more than a third have values less than 120. Because it was not known what proportions of the Mg to assign to the interlayer position and what proportion to the octahedral sheet, these calculated values can only be considered minimum values. Macroscopic vermiculites most com-... 

Barshad, I. 1954. Cation exchange in micaceous minerals. II. Replaceability of ammonium and potassium from vermiculite, biotite, and montmorillonite. Soil Sci. 78 57-76. 

Keay, J. and A. Wild. 1961. The kinetics of cation exchange in vermiculite. Soil Sci. 92 54-60. 

Wild, A. and J. Keay. 1964. Cation-exchange equilibria with vermiculite. J. Soil Sci. 15(2) 135— 144. 

I was lucky to receive some jars of sodium-substituted Eucatex vermiculite and n-butylammonium-substituted Eucatex vermiculite. These synthetic systems had been obtained by cation exchange on the raw minerals. Such cation exchange plays a major role in clay chemistry, and the process is described in detail in standard books on clay colloids, like that of van Olphen [2], Some years later, I was able to obtain the following chemical formula for the dry sodium Eucatex vermiculite [3]... 

Note CEC = cation exchange capacity HISM = hydroxyinterlayered smectite HIV = hydroxyinterlayered vermiculite Kf = Freundlich metal distribution coefficients LSB = lime stabilized biosolids = total aluminosilicates. 

A vermiculite clay has the structural formula K.Mgo.sKMgaoFe sFeJ sXAl, sSi65)02o(OH)4. Calculate its cation-exchange capacity in meq/IOO g and its surface-site density in mol/g. Assuming the surface area of the clay is 30 mVg, what is its surface-site density in nm and /umol/m ... 

Micas lose their structural relatively rapidly by a process of cation exchange with or metal ions in the weathering solution. This initial reaction is an alteration that is not necessarily very sensitive to pH. The pH, however, tends to rise during alteration as H" is adsorbed. The secondary mineral formed directly is a vermiculite, which inherits more or less intact the 2 1 layer structure of the mica parent. An ideal biotite mica might have the formula ... 

Vermiculites. Vermiculites are 2 1 expanding minerals with a structure similar to micas (Table 7-4). They are considered to be derived from the alteration of micas (Douglas, 1977). Cation exchange capacity is high, as is the surface area. Potassium or NHj in solution tends to be strongly fixed by vermiculites. Upon fixation of these ions, the CEC decreases and the properties of vermiculite become like those of mica. In acid soil, hydroxy aluminum polymers can be fixed in the interlayer position to form an "island-like" structure (Jackson,... 

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). 

Data sources Bolt 1979, Brummer 1986, Kabata-Pendias and Pendias 2001, Tan 1998, Schmitt and Sticher 1991, Sparks 1995. Dioctahedral and trioctahedral vermiculites. Amorphous Al-oxides. Amorphous Fe-oxides.CEC, cation exchange capacity. 

Diquat and paraquat are readily adsorbed from aqueous solutions by soil particles 40, 41, 42, 43, 44, 45, 46, 47), montmorillonite (30, 41, 48, 49, 50, 51, 52, 53, 54, 55, 56), kaolinite 41, 50, 52, 53, 54, 55), vermiculite 29, 30, 49,56), biotite 29, 30), muscovite 29, 30), phlogo-pite (29), muck 46, 48, 51), and cation exchange resins 48, 57). Only small or insignificant amounts were adsorbed by charcoal and anion exchange resins 48, 51, 53). The compounds were adsorbed to cation exchange substances through cation exchange reactions for diquat by clay minerals (Equation 1). 

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