Sorption by Ion Exchange

Ion exchangers can preferentially absorb some types of ions relative to other ions therefore, the ratio between different counterions on an ion exchanger is usually not the same as the ratio between those ions in solution. For example, consider a clay ion exchanger that is selective for calcium. In a groundwater regime that initially contains sodium as the only cation, the clay 

Copper-rich waste disposed of in lagoons behind an electroplating operation has percolated down to the groundwater and dissolved, creating a plume. A sample of the porous medium and associated pore water is taken from the plume area and analyzed. The results are 

Copper concentration in pore water = ICC6 mol/liter Copper concentration on aquifer solids = ICC3 mol/kg Aquifer bulk density = 2.5 g/cm3 Aquifer porosity = 0.3. 

If groundwater seepage velocity is 600 ft/year, how fast will the plume migrate  

By assuming the relationship between dissolved and sorbed copper is reasonably linear, a retardation coefficient can be meaningfully applied. The distribution coefficient, Kd, can be estimated as 

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Electron spin resonance (ESR) data suggest that solution in pyridine does not significantly enhance the content of free radicals in humic substances. Pyridine does, however, significantly enhance their nitrogen contents (Table 5), especially in the cases of the fulvic acids, as was found also for extracts with EDA. Sorption, by ion-exchange and possibly by charge-transfer processes, might provide plausible explanations for the enrichments. 

The experiment begins with first deciding on a mechanism of exchange, as described earlier. Next consider the p of the molecule and the pH of the sample to ensure that sorption by ion exchange will occur. 

Diffbsion-Controlled Sorption by Ion Exchange Resin Beds, Ind. Eng. Chem. Fundam., 8(2), 193-198 (1969). 

This value, C, represents the saturation capacity of protein sorption by ion exchange it appears to be independent of the concentration of the monovalent counterion salt In reality, such a limit is achieved only at low values of Csu,- Unlike other ion exchange systems, where for any counterion i is simply obtained from Cpc and Z,, for proteins/biomole-cules, the steric factor additional complexity. For illustrations of the isothetm (3.3.1220, see Brooks and Cramer (1992), which gives a number of proteins/biomole-cules, e.g. cytochrome-c, a-chymotrypsinogen. 

Unfortunately, cation exchange does not lend itself to simple mathematical description as does idealized sorption of hydrophobic organic compounds. For low concentrations of a contaminant ion in a constant background of other ions, however, the ion exchange process often is treated approximately as a linear partitioning process, and use of a simple retardation factor in a transport model may be justified. Distribution coefficients for ionic contaminants in an aquifer are usually determined experimentally. Typically, a batch test is performed in which the ionic concentration on a fixed volume of aquifer solids and the ionic concentration in the associated pore waters are analyzed the distribution coefficient is taken as the ratio of the concentrations. Because sorption by ion exchange is affected by the concentrations of all other ions in the groundwater, the... 

Ion exchange (IX) is a very useful technique for the concentration, the purification and the separation of chemically similar metallic elements present in an aqueous solution. In its most popular form of application, the metal-bearing aqueous solution is passed through a bed of solid organic resin in a particulate form wherein the sorption of the metal ions on the resin takes place by ion-exchange reactions. The pregnant resin is washed free of the entrapped feed solution and then brought into contact with an eluant of suitable composition and volume so that the resin releases the metal ions back to the eluant. The ratio of the volume of the feed and that of the eluant determines the extent of concentration that can be achieved. Purification and separation are achievable if the resin is selective or specific with respect to the metal ions of interest in comparison to impurity ions. 

The distribution of the major elements (Ca, Mg, Na, K,. ..) in soils is well known to be governed by ion-exchange processes (1). The behaviour of transition elements such as Co, Ni, Cd, Cu, etc. in natural systems (soils, sediments) often results from a combination of different effects such as precipitation, sorption in oxides, exchange in clay minerals and complexation with organic... 

Figure 2.1.6.9 and Table 2.1.6.4 present the N2-sorption isotherms and the results of the characterization of the Al-MCM-41 parent material and of the by ion exchange and impregnation onto Al-MCM-41 immobihzed (S,S)-Co( 11)-Jacobsen complexes. The N2-sorption isotherms of the loaded materials clearly illustrate that (S,S)-Co(II)-Jacobsen complex is deposited in the inner surface of the pores... 

Table 2.1.6.4 Nitrogen sorption data of the Co(ll)-Jacobsen complex immobilized on AI-MCM-41 by ion exchange or impregnation.

The adaptation of zeolites to a particular purpose can be done by ion exchange and by different chemical and physical treatments. Physicochemical characteristics of zeolites often reflect the modifications introduced in the structure. Different methods are used to study the modifications and their correlations with sorption properties and catalytic activity. In this section G. T. Kerr reviews the chemistry involved in the thermal activation of NH4Y zeolites. 

Vne of the major industrial applications of zeolites is in the area of ad-sorption processes. Zeolite adsorbents are not only the most important adsorbents today, but their importance is increasing, mainly because of the following unique adsorptive properties (a) selective adsorption of molecules based on molecular dimensions, (b) highly preferential adsorption of polar molecules, (c) highly hydrophilic surface, and (d) variation of properties by ion exchange. 

RECOVERY OF VALUABLE MINERAL COMPONENTS FROM SEAWATER BY ION-EXCHANGE AND SORPTION METHODS... 

Significant parameters for radium sorption are Na2S04, KC1, and N2H4. Each of these variables decrease sorption of radium by ion exchange competition. The effective ion diameter of Ra2+ is near those of Na and N2H5+ so that they compete for similar sorption sites. 

In Figure 2.5, three isotherms of zinc sorption are shown. The upper figure illustrates a so-called sorption isotherm obtained from total sorbed amount of zinc ion (a ) as a function of the zinc concentration of the solution (c,) the lower figure shows the ion exchange and sorption isotherms obtained after the separation of zinc ion quantities sorbed by ion exchange (alie) and adsorption (alads). 

Since the catalytic, sorption, and ion-exchange properties are strongly dependent on the Al—Si ratio it is important to be able to vary this. The A1 content can be decreased, for example, by treatment with SiCU, which removes Al as A1C13. It can be increased in high silica zeolites by A1C13 vapor ... 

Mamchenko, A. V. and M. S. Novozhenyuk (1997). Sorption of humus substances by ion exchange resin in water softening. Khimiya i Tekhnologiya Vody. 19, 3, 242-253. 

Recovery of Valuable Mineral Components from Seawater by Ion-Exchange and Sorption Methods... 

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