Solution Cation Exchange

DILUTE SOLUTION CATION EXCHANGE Mechanical Model 

This approach is important historically in that Gregor attributed selectivity to be entirely due to the mechanical work done during exchange against the swelling pressure 11 of the matrix as given by the relationship  

The terms V and V q represent the partial molal volumes of the solvated counter-ions A and B respectively, and therefore for K 1, 

If selectivity were governed solely by interactions of a purely electrostatic (coulombic) nature one could anticipate negative enthalpies and entropies of exchange due to dominant contributions by A and A5ii respectively. This is indeed found for alkali metal cation exchange on styrenic sulfonate resins as illustrated by Table 5.3a. 

For aqueous systems and large r, the terms of the second bracket of equation 5.37 dominate and the free energy of exchange is governed by differences in the free energies of hydration of the counter-ions. Conversely, for small r, the terms of the first bracket in equation 5.37 

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Illustrate solution, cation exchange, and outer- and inner-sphere species around a soil particle. 

DILUTE SOLUTION CATION EXCHANGE Mechanical Model... 

The ability of a resin to exchange one ion for another depends on its affinity for the ion and the concentration of ions in solution. Cation-exchange resins tend to have affinity in decreasing order for calcium, potassium, sodium, ammonium and hydrogen ions. Administered orally, cation-exchange resins effect changes in... 

Bismuth has been separated from other metals, retained on a cation exchange column, by elution with HBr [11]. From dilute HCl solutions cation exchangers retain Bi and other metal cations, whereas Pt is not sorbed [12]. Successive elutions with 0.3 M and 0.6 M HNO3 enables the separation of T1 and Ag from Bi [13]. 

Strongly acid cation-exchangers have been used for the separation of Th from rare-earth elements and other metals [8,9]. From the metal cations retained on the column 3-5 A/ HCl elutes rare-earth- and most other metals except thorium. Thorium is eluted with 10 M HCI or 3 M H2SO4, as well as with 5 MHNO3 [10], ammonium oxalate [11], ammonium carbonate [1] or ammonium sulphate solutions. Cation-exchange chromatography has also been used to separate thorium with the use of media such as HBr [12], formic acid -I- dimethyl sulphoxide [13], and nitric acid -1- methanol -i-TOPO [14]. 

Figure 4.8 Current efficiency versus fixed ion concentration of a cation exchange membrane in the electrolysis of a sodium chloride solution. Cation exchange membrane sulfonated styrene—divinylbenzene type. Anolyte saturated NaCl catholyte 3.0 N NaOH current density 10Adm 2 at 70 °C.

Figure 4.10 Change in electro-osmotic water (tw) with concentration of various salt solutions. Cation exchange membrane MK-40 (heterogeneous type membrane) measured at low current density (0.03-0.06 A cm 2) to reduce the possibility of concentration polarization.

Figure 4.11 Change in electro-osmotic water with concentration of sodium chloride solution. Cation exchange membrane NEOSEPTA CL-25T (homogeneous type membrane) measured at a current density of 20 mA cm 2 at 25.0 °C.

Figure 5.11 Relationship of permeability coefficients of neutral molecules (urea, glucose and saccharose) through the cation exchange membrane NEOSEPTA CM-1 and the same membrane with a polypyrrole layer to the Stokes radius of the solutes. ( ) Cation exchange membrane without the layer (NEOSEPTA CM-1) (O) membrane with a polypyrrole layer facing the dilute side in the measurement (A) membrane with polypyrrole layer facing the concentrated side. One surface of ferric ion form NEOSEPTA CM-1 was in contact with an aqueous pyrrole solution for 10 min to form a polypyrrole layer (polymerization time 10 min.).

Ion exchange is used in the metal plating industry to purify rinse water and spent plating bath solutions. Cation exchangers ranove cationic metal species, such as Cu, from such solutions. Anion exchangers remove anionic cyanide metal complexes, such as Ni(CN), and chromium(VI) species, such as CrOI. Radionuclides can be ranoved from radioactive and mixed radioactive/ hazardous chemical waste by ion exchange resins. 

K. E., Tiirler, A., Czerwinski, K.R., Hannink, N.J., Kadkhodayan, B., Lee, D.M., Nurmia, M.J., Hoffman, D.C. Chemical properties of element 105 in aqueous solution cation exchange separation with -hydroxyisobutyric acid. Radiochim. Acta 57, 85-92 (1992)... 

In most cases multicompartment electrodialyzers divided by cation-exchange and anion-exchange membranes are used for demineralization of sugar solutions. Cation-exchange membranes of the Permaplex C-20 [64, 71], MK-40, MK-102 [69], and other types and anion-exchange membranes of the Permaplex A-20 [64,... 

Solution Cation-Exchange Resin Mesh (U.S. standard) dry Size (mm) Resin conductivity 26.5 1.5°C cm i a b d... 

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