Solution Anion Exchange

Solvated ion volumes alone, and therefore pressure-volume considerations, fail to account for observed ion affinity sequences even for the simple halide ions. 

As indicated in Table 5.3d, significant negative enthalpies and entropies of exchange for the exchange of halide ions on quaternary ammonium resins could be interpreted in terms of pure electrostatic interactions. However such a coulombic model invoking solvated ion size or distance of closest approach fails to conform to the observed affinity order I Br CI F . If one includes a larger polyatomic anion such as perchlorate, Cl 04 the experimental sequence is Cl 04 I Br Cr F which clearly contradicts any simple coulombic attraction theory. 

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Spectrophotometric studies were used to identify the anionic hexavalent actinide acetate complexes present in aqueous and nonaqueous solutions, anion exchange resins, and amine extracts. The previously unreported tetraacetate complexes, M02(CJd 0i),, were identified in all these systems. The formation constant for the reaction +... 

To overcome these problems use is made of the now available nitrate-selective resins (Chapter 5, Dilute Solution Anion Exchange ) for which the anion affinity sequence is ... 

The calculated concentration profiles in a KC1 solution-anion exchange membrane boundary layer at different times after the start of a constant current of density 5 ma. per sq. cm. are plotted in Figure 5. The diffusion coefficient of KC1 in the solution was taken as 2.0 X 10—5 sq. cm. per second and the thickness of the diffusion layer as 0.03 cm. 

The absence of a dipole moment in U02Cl2(H20)2 with a linear structure of the oxygen ligands explains its superior extractability. In HF solutions, anion exchange takes place (Pershina 1996) according to... 

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. 

The hydrogen ion of this group can be readily released and its place taken by another cation from a neighboring aqueous solution. Anion exchangers use amine groups R3N+OH" to affect a similar exchange of anions. Thus,... 

SO3H) or weakly acidic (-COOH). These resins exchange with cations in solution. Anion exchange resins contain quaternary ammonium groups with replaceable OH groups. Cations replace H from acidic resins e.g. 

Solution Anion-exchange resin is prepared by chloromethylating SFDVB resin using chloromethyl methyl ether (CMME) and then quartemizing it with trimethyl amine (TMA) as follows ... 

When strong acid cation exchangers are used in the Na" form and strong base anion exchangers are used in the CL form, they are regenerated with a 10% sodium chloride [7647-14-5], NaCl, solution. Other concentrations may be used, perhaps with some adjustment in flow rate. 

Uranium ores are leached with dilute sulfuric acid or an alkaline carbonate [3812-32-6] solution. Hexavalent uranium forms anionic complexes, such as uranyl sulfate [56959-61-6], U02(S0 3, which are more selectively adsorbed by strong base anion exchangers than are other anions in the leach Hquors. Sulfate complexes are eluted with an acidified NaCl or ammonium nitrate [6484-52-2], NH NO, solution. Carbonate complexes are eluted with a neutral brine solution. Uranium is precipitated from the eluent and shipped to other locations for enrichment. Columnar recovery systems were popular in South Africa and Canada. Continuous resin-in-pulp (RIP) systems gained popularity in the United States since they eliminated a difficult and cosdy ore particle/leach hquor separation step. 

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