Total exchangeable cation

The increase of the mean index of refraction for philhpsites was correlated to a decrease in both the Si/(Si + A1 + Fe ) ratio and the monovalent/total exchangeable cation ratios [72G1]. 

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

In soil analysis, the sample pretreatment varies depending on whether a total elemental analysis or an exchangeable cation analysis is required. In the former, a silicate analysis method (see below) is appropriate. In the latter, the soil is shaken with an extractant solution, e.g. 1 M ammonium acetate, ammonium chloride or disodium EDTA. After filtration, the extractant solution is analysed. Fertilizers and crops can be treated as chemical and food samples, respectively. 

Table IV. Total Exchangeable Base-Cation Content and Potential Increase...

Mass-balance calculations for the first 3 years of acid additions indicate that the principal IAG processes are sulfate reduction and cation production. Specifically, one-third of the total sulfate input (added acid and deposition) was neutralized by in-lake processes. Increased sulfate reduction consumed slightly more than one-sixth and production of cations neutralized somewhat less than one-sixth of the acid added. Of the remaining sulfate, one-third was lost by outflow, and one-third decreased lake alkalinity. Laboratory determinations suggest that sediment-exchange processes occurring in only the top 2 cm of surficial sediments can account for the observed increase in water-column cations. Acidification of the near-surface sediments (with partial loss of exchangeable cations) will slow recovery because of the need to exchange the sediment-bound H+ and neutralize it by other processes. Reactor-based models that include the primary IAG processes predict that... 

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. 

Extraction of soils for analysis of die readily available nutrients include replacement of exchangeable cations by salt solutions, dilute acids, and dilute alkalies such as NaHCCh. Fluoride solutions ate employed to repress iron, aluminum, and calcium activity during the extraction of phosphorus. Extraction of the soil solution is effected by displacement in a soil column, often through the application of pressure across a pressure membrane. The soil solution is analyzed by conductance and elemental analysis methods. Also, the total elemental analysis of soils is made by Na2CC>3 fusion of the soil followed by classical geochemical analysis methods. 

The total salt concentration was 0.100 (to.010) N, known to three significant figures. At the high end of the isotherm, the starting solution contained only the ingoing cation at the low end, the solution contained both of the exchanging cations. The equilibrations were carried out for a minimum of three days in a New Brunswick Scientific Company AQUATHERM Water Bath Shaker at 5°, 25°, and 50°C, with temperature control to i0.5°C. Prior to analysis of the equilibrium solutions, the solid and solution phases were rapidly separated by filtration through a Millipore filter immediately after removal from the constant temperature bath. Lead and sodium analyses of the filtrate were obtained by atomic absorption spectroscopy. The cadmium analyses of the filtrate were obtained by plasma emission spectroscopy. These analyses showed that two Na+ ions entered the solution for every Cd2+ or Pb2+ that left ( 2%). 

Total ion-exchange determinations by Dorothy Carroll exchangeable-cation analyses by W.W. Brannock. 

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. 

In addition to MC and MD simulations, several quantum-chemical studies of hydrated clay minerals with or without exchangeable cations in the interlayer space have been performed at the ab initio and semiempirical level of theory. The total energy of hydrated layered silicates (talc and pyrophyllite) without exchangeable counterions, the position and interactions of interlayer water... 

The relation follows from NA1 / Nhv, that is, the total number of equivalents of exchangeable cations per unit cell, where pVc is the mass of the unit cell. 

In the case of a smectite, each layer comprises two sublayers of tetrahedra with an inserted octahedral layer, where between the layers an interlayer space is formed in which the exchangeable cations are located (see Figure 9.3). That is, the smectite structure can be described on the basis of layers containing two sublayers of silica tetrahedra squeezed into a layer of an octahedra of Al3+ or Mg2+, that is, a 2 1 layered clay [34], The replacement of some of the Al3+ with Mg2+ or Li+, or the isomorphous replacement of tetrahedral Si4+ with Al3+, results in a certain amount of total negative charge on the layer, compensated in turn by the presence of hydrated cations in the interlayer region (see Figure 9.3). 

In montmorillonite, similar to other minerals, when the size of the exchanged cation is similar to the pore sizes in the crystal lattice, cations can build into the crystal lattice and, consequently, they reduce the negative layer charge (Chapter 1, Section 1.3.3.2). Other neutral molecules or cationic substances (Chapter 1, Sections 1.3.3.1 and 1.3.3.2) can also be sorbed in the interlayer space and on the external surfaces as well. They play an important role in defining the internal and total surface area and catalytic properties, and they may have an effect on the hydrophobicity of the mineral, as well as playing an important role in the production of pillared materials, etc. 

Catalytic oxidation-reduction (redox) reactions in zeolites are generally limited to reactions of molecules for which total oxidation products are desired. One important class of such reactions falls under the category of emission control catalysis. This encompasses a broad range of potential reactions and applications for zeolite catalysts. As potential catalysts one may consider the entire spectrum of zeolitic structural types combined with the broad range of base exchange cations which are known to carry out redox reactions. 

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