Cation exchange capacity measurements

Because so much of the behavior of suspensions is determined or modified by charge associated with the solid phases, ZPC may be inferred from a wide variety of experiments involving pH as a master variable. For example, coagulation and sedimentation rates are maximum at the ZPC, and anion and cation exchange capacities (measured with nonspecific, symmetrical electrolytes) are equal and minimum at the ZPC. More direct and less ambiguous are electrophoresis and streaming potential, in any of their modifications. One can estimate the IEP(s) by measuring adsorption of H+ and OH" if one is certain that no specific adsorption of other species occurs. 

Equivalent The amount of a substance that will react with one mole of H+ or OH-. The related term equivalent mass ( weight ) refers to a molar mass of a substance divided by the absolute value of its valence state. For anion exchange capacity and cation exchange capacity measurements, the results are usually reported in milliequivalents (1/1000 of an equivalent) per 100 g of material. 

Almost all models can simulate organic, inorganic and metal fate, assuming that a careful calibration via an adsorption coefficient may alter the model output to predict measured/monitored values. However, not all models have by design increased chemistry capabilities (e.g., cation exchange capacity complexation), therefore, the most representative capabilities are indicated. 

Some properties of the rock used in this study were measured The cation exchange capacity (cec) was determined by the barium sulfate method as described by Mortland and Mellor (33). Surface area was measured by using a Digisorb Meter (Micromeritics Instrument Corporation) through nitrogen adsorption. Estimation of mineral composition and indentification of the rock were performed by X-ray diffraction. 

Differential refraction( ) and colorimetric measurements ) were used to determine the amount of carbohydrate polymer adsorbed from solution. A Phillips X-ray diffractometer was used to quantify the degree of interlayer expansion(60. The cation exchange capacity of the peptized sodium and potassium... 

Heavy metals in rice and soils as well as several physicochemical indicators of soils including Organic matter (OM), pH, Cation- Exchange Capacity (CEC) and soil granularity were analyzed. As, Cd, Cr, Cu, Hg, Mn, Ni, Pb, Se, Zn and OM of soils, and As, Cd, Cr, Cu, Hg, Mn, Ni, Pb, Se and Zn of rice were determined at the central chemical lab of the Institute of Geophysical and Geochemical Exploration. The CEC of the soils was measured at the analytical institute of... 

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. 

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. 

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. 

Harada, Y. and Inoko, A. (1980) The measurement of the cation exchange capacity of composts for the estimation of the degree of maturity. Soil Science and Plant Nutrition 26, 127-134. 

Cation Exchange Capacity. Various techniques have been used to measure the cation exchange capacity of the clay samples. Unless otherwise noted, in computation of equilibrium quotients, we shall use a value of 0.78 equivalents/kg clay, determined by a column method (14) on the calcium form of Wyoming montmoril-lonite at pH 5. 

All adsorbents have upper limits to the amount of arsenic that they can adsorb from air, water, or other fluids. That is, there is a finite number of adsorption sites on each gram of adsorbent. The maximum adsorption capacity, which is often measured in molal, represents the highest concentration of a solute (such as arsenic) that can be adsorbed by a given mass of a particular adsorbent. The maximum adsorption capacity is routinely obtained from laboratory experiments and measurements, and is closely related to the cation exchange capacity (cec) or anion exchange capacity (aec) of the materials. The cec or aec provide... 

The determination of surface properties of particles is an important key to understanding interactions of trace elements and organic compounds between particulate and dissolved phases in estuarine and coastal systems. Specific surface area (SSA), cationic exchange capacity (CEC) and heat of immersion (AH) have been measured on native and treated suspended sediment and after oxidation with 15% H202- SSA and A H have also been measured on samples leached with NaOH and Na-dithionite in order to remove amorphous aluminosilicates. 

Cation exchange capacity (CEC) of soil samples taken prior to, and after, EO was analyzed by CLC LABS in Westerville, Ohio according to the method described by Brown and Wamcke (1988). This method uses 1 M ammonium acetate to extract cations from the soil. Cations concentrations were measured with an Atomic Adsorption Spectrometer (AAS). 

Zeolite surface chemistry resembles that of smectite clays. In contrast to clays, however, natural zeolites can occur as millimeter- or greater-sized particles and are free of shrink-swell behavior. As a result, zeolites exhibit superior hydraulic characteristics and are suitable for use in filtration systems (Breck 1974) and as permeable barriers to dissolved chemical migration. Internal and external surface areas up to 800 m2 g have been measured. Total cation exchange capacities in natural zeolites vary from 250 to 3000 meq kg 1 (Ming and Mumpton 1989). External cation exchange capacities have been determined for a few natural zeolites and typically range from 10 to 50 percent of the total cation exchange capacity (Bowman et al. 1995). 

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.

Worked example 5.9 - cation-exchange capacity and % base saturation One method to measure the CEC of a soil is to leach a column containing a known weight of soil with a solution of a salt so that the exchange sites are saturated with the cation (index ion). After washing out the excess salt solution, a different salt solution is leached through the column and the exchangeable ions displaced, collected in a known volume and their concentration measured. 

After treatment with hydrogen peroxide in 0.3 M hydrochloric acid at 70°C for 30 minutes in order to remove adsorbed organic matter, the silt fraction (4 to 74 ym diameter) was washed repeatedly with distilled deionized water to constant conductivity in order to remove any adsorbed acid. The specific surface area of this material was measured using Lawrie s (S) 1,10-phenanthro-line adsorption method. The cation exchange capacity per gram was determined by Chapman s ( ) method, in which the surface is first saturated with sodium by three successive washings with 1.0 M sodium acetate solution, followed by three successive washings with 1 M ammonium acetate, which is saved and analyzed for the displaced sodium. 

Edges and plates require different techniques to determine a°. For the former, the titration technique as used for oxides is appropriate, whereas on the plates only counter ion exchange can be realized, for which the maximum number of exchangeable groups can be established, the cation exchange capacity (c.e.c.). The problem is that one cannot easily measure either the plates only or the edges only, but only their summed responses. This is of course also the case with other techniques like conductometry emd electrophoresis. 

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