Hydrogen exchange capacity

In Eq. 10.18, C is the difference between hydroxide-ion and hydrogen ion adsorption in the nnit of miliequivalents per solid surface area (m ) that is, C = Cqjj -Ch+- hydrogen exchange capacity (maximum uptake or... 

Direct titration [119,120] In order to know the number of exchangeable hydrogen ions at different dissociation stayes, various salts of weak acids were used. Data observed in Table 8 shows an increase in the exchange capacity with an increase in the pH of the solution, indicating the presence of weak acid capacity [118]. 

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. 

For both cesium and barium sorption, there is reasonable agreement between the total concentrations of desorbed species and the ion-exchange capacities determined by isotopic redistribution. The small differences which exist could easily be due to the precision in the elemental analyses. (Also, the experimental technique would not have detected desorption of hydrogen ions.) The solid-phase concentrations of sodium, potassium, magnesium, calcium. 

A hard water contains 120 ppm of CaC03, 90% of which is to be removed with a hydrogen exchange resin of capacity 5 meq/g. By the method of Example 15.1 it is ascertained that under these conditions 98% of H+ ion of the resin will be replaced by the Ca++ at equilibrium. The minimum amount of resin will correspond to the equilibrium value. That amount will be calculated for treating 100 gpm of water on a 24 hr cycle. The mol wt of CaC03 = 100.06. 

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. 

All ions in the system, whether specifically adsorbed or not, must be expected to saturate partially the ion exchange capacity arising from these relatively pH-independent sources. For this reason an isoelectric point defined in terms of hydrogen and hydroxyl ion adsorption is hypothetical, and in any real system, the pH at which zero surface charge is observed will depend upon the system composition. 

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