Clays cation exchange capacity

Cetylmethylammonium (CTMA) as the clay exchange cation and decylamine as the co-surfactant were used to form a PCH. A 1.0 wt % suspension of previously prepared saponite was allowed to react at 50°C with a 0.3 M aqueous cetylmethylammonium bromide solution in two fold excess of the clay cation exchange capacity. After a reaction time of 24h, the product was washed with ethanol and water to remove excess surfactant and... 

Leaching Experiment. Three polyethylene columns (4.8 cm ID by 50 cm height) ware employed to investigate the mobility of dicamba, 2,4-D, atrazine, diazinon, pentachlorophenol, and lindane. Each column was packed with 1,080g of fresh soil to a depth of 40 cm (sandy loam soil from Soils Incorporated, Puyallup, Washington pH 5.9 to 6.0 89 percent sand 7 percent silt 4 percent clay cation exchange capacity 7.5 meq/lOOg). 

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. 

FIG. 4 Experimental (vertical bars) and simulated (symbols) values of the d-spacings for aUcy-lammonium-exchanged clay at three different cation exchange capacities (CECs) (a) SWy2 mont-morillonite, CEC = 0.8 meq/g (b) AMS montmorillonite (Nanocor), CEC = 1.0 meq/g (c) fluoro-hectorite (Dow-Corning), CEC = 1.5 meq/g. (Erom Ref. 30.)... 

The main parameters that affect the cost-effectiveness of soil washing include the physicochemical parameters of the soil (grain size distribution, cation exchange capacity, percentage of silt, clay, or organic matter), and the type and concentration of contaminants. 

Acidic solutions tend to dissolve carbonates and clays highly alkaline solutions tend to dissolve silica and clays. Greater pH generally increases cation-exchange capacity of clays. 

The clay ion-exchange model assumes that the interactions of the various cations in any one clay type can be generalized and that the amount of exchange will be determined by the empirically determined cation-exchange capacity (CEC) of the clays in the injection zone. The aqueous-phase activity coefficients of the cations can be determined from a distribution-of-species code. The clay-phase activity coefficients are derived by assuming that the clay phase behaves as a regular solution and by applying conventional solution theory to the experimental equilibrium data in the literature.1 2 3... 

Hedges, R.E.M. and McClennan, M. (1976). On the cation exchange capacity of fired clays and its effect on the chemical and radiometric analysis of pottery. Archaeometry 18 203-207. 

In addition to the crystalline clays described earlier, there are some materials that act like clays but do not have crystalline structure. Amorphous clays do not have a definite X-ray diffraction pattern and are differentiated from the crystalline clays on this basis. They are composed of mixtures of alumina, silica, and other oxides and generally have high sorptive and cation exchange capacities. Few soils contain large amounts of amorphous clays [2],... 

Standard cations used for measuring cation exchange capacity are Na+, NHJ, and Ba2+. NH is often used but it may form inner-sphere complexes with 2 1 layer clays and may substitute for cations in easily weathered primary soil minerals. In other words, one has to adhere to detailed operational laboratory procedures these need to be known to interpret the data and it is difficult to come up with an operationally determined "ion exchange capacity" that can readily be conceptualized unequivocally. 

Another type of reaction that responds to WD cycles is the fixation of K and NH4 ions by smectite (3-7). The fixation of K in smectite has been studied extensively by soil scientists because of its effect on the availability of plant nutrients. The reaction also decreases smectite s ability to swell, decreases its cation exchange capacity (CEC), and modifies its BrjSnsted acidity. Therefore, an understanding of this phenomenon is applicable to many fields of study that are concerned with swelling clays, fields such as soil fertility, soil mechanics, waste disposal, clay catalysis, and the geochemistry of ground and surface waters. 

The sorption behavior of 11 PAH compounds (a training set, Table 11) on various solid phases (e.g., three soils and two sediments) with different properties to relevant sorption (e.g., organic carbon content, clay content, pH, cation exchange capacity CEC Table 12), was determined by batch equilibrium studies [1]. Batch equilibrium tests were designed to determine rates of equilibrium sorption under conditions of high mixing and high surface areas of the solid particles (see Chap. 3). 

The clay minerals carried by rivers into the ocean represent a net annual addition of 5.2 X 10 mEq of cation exchange capacity. Most of these exchange sites are occupied by calcivun. Within a few weeks to months following introduction into seawater, sodium, potassium, and magnesium displace most of the calcium. As shown in Table 21.7, this uptake removes a significant fraction of the river input of sodium, magnesium, and potassium. 

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