Distribution coefficients anion exchange

Example. A mixture of ca 0.05 mmole each of chloride and bromide ions is to be separated on an anion exchange column of length 10 cm and 1cm2 cross-section, using 0.035M potassium nitrate as the eluant. The distribution coefficients (Kd) for the chloride and bromide ions respectively are 29 and 65. 

In closing, recovery of technetium from waste solution should be touched upon. Studies of the base hydrolysis of technetium P-diketone complexes revealed that all of the complexes studied decompose in an alkaline solution even at room temperature, until technetium is finally oxidized to pertechnetate. These phenomena are very important for the management of technetium in waste solutions. Since most metal ions precipitate in alkaline solution, only technetium and some amphoteric metal ions can be present in the filtrate [29]. A further favorable property of pertechnetate is its high distribution coefficient to anion exchangers. Consequently, it is possible to concentrate and separate technetium with anion exchangers from a large volume of waste solution this is especially effective using an alkaline solution [54],... 

Tanimizu M, Asada Y, Hirata T (2002) Absolute isotopic composition and atomic weight of commercial zinc using inductively coupled plasma mass spectrometry. Anal Chem 74 5814-5819 Van der Walt TN, Strelow FWE, Verheij R (1985) The influence of crosslinkage on the distribution coefficients and anion exchange behavior of some elements in hydrochloric acid. Solvent Extract Ion Exchange 3 723-740... 

The chromatographic separation of technetium from molybdenum is based on the different extent to which molybdate and pertechnetate are adsorbed from alkaline and acid solutions. The distribution coefficient of molybdate between the anion exchanger Dowex 1-X8 and 3 M NaOH is 12, while it is 10 for pertechnetate under the same conditions. Molybdate is also adsorbed to a much lesser extent from hydrochloric acid solutions than pertechnetate. Thus, molybdemun can be eluted by hydroxide or HCl solutions while nitric acid, perchlorate or thiocyanate are used for the elution of technetium . 

First consider the system in which no diffusion potential is formed in the membrane. The membrane potential is then determined by the conditions at the membrane/aqueous electrolyte solution boundary. In the simplest situation, a salt of a monovalent ion-exchanger ion, anion A", with monovalent determinand cation J is dissolved in the membrane. In order for this system to be the basis for a usable ISE with Nemstian response to the determinand ion in a sufficiently broad activity interval, it is necessary that the distribution coefficient kj be... 

Schugerl 115] has recently furnished a detail analysis of the reactive extraction of penicdlin-G and V and precursors like phenyl and phenoxy acetic acids. Thirty different amines have been studied for reactive extraction of penicillins 116] in various solvents such as butyl acetate, chloroform, di-isopropyl ether, kerosene, dioctyl ether, etc. Tertiary amines in n-butyl acetate were found to be advantageous because of their low reactivity with solvent but the distribution coefficients of their complexes are significantly lower than those of secondary amines. While using quaternary ammonium salts for ion-exchange extraction, re-extraction is difficult and very large amounts of anion (e.g.. Cl ) are needed to recover penicillins. The basic relationship for distribution coefficient and extraction kinetics have now been fairly developed for amine-penicillin systems. 

Figure 12 Volume-distribution coefficients in hydrochloric acid for various elements on the strong-base anion-exchange resin Dowex 1 X-10 (after Krause and Moore, ref. 359)...

As the ratio of organic to aqueous in a mixed solvent is increased, the concentration of water molecules around the cation is reduced, decreasing the size of the hydrated cation. One consequence of this is that metal complex anions will be formed at lower anion concentrations than in pure water. Moreover, because the forces that bind the hydration cloud depend on the charge density of the cation, selective destruction of the hydration cloud starts at lower organic aqueous ratios for larger cations.399 As a result, large cations will penetrate a cation exchanger more easily, and differences in the distribution coefficients of elements of different size will be enhanced. 

Pilot plant studies (flow rates, 1 cm/s) with the SB-1 anion exchange resin (column diameter, 0.3-0.7 cm) yielded distribution coefficients of the order D = 400 cmVg. The boron sorption process was shown to be film diffusion controlled. The equilibrium values of boron loading were reached in 6-8 hr [280]. Boron elution and resin regeneration were carried out with 0.1 M NaOH. The complete elution of boron required 10 column volumes at 10 BV and yielded concentrates of 100 mg/L. This facilitated the eventual reduction to solid concentrates of alkali metal borates [281]. 

A number of years ago Seno and Yamabe [25] derived equations that examined the amounts of adsorbed amino acid on an ion exchanger in the presence of competing ions. More recently HelfEerich [26] derived equations describing the effective distribution coefficients of amino acids on a strong-acid (cation) and strong-base (anion) exchanger as a function of pH, amino acid concentration and added electrolyte. 

The Helfferich equations describing the effective distribution coefficients of amino acids on a strong-acid cation and a strong-base anion exchanger were derived using the following simplifying assumptions [26] ... 

The effective distribution coefficient on cation and anion exchanger... 

When measurements are made to investigate the ion exchange behavior of a cation or anion it is common practice to determine the distribution coefficient, D,, where... 

Traces of titanium in sea water (at concentrations of 1 pg/1) have been preconcentrated by anion exchange from acidified samples in the presence of thiocyanate. Titanium as thiocyanate complex is strongly sorbed on a column of Amberlite CG 400 (SCN ) and can be easily stripped by elution with 2 M hydrochloric acid containing 1.5% hydrogen peroxide. The sea water samples are favourably adjusted to 1 M HC1 and 1 M NH4SCN. Under these conditions the distribution coefficient of titanium was as high as 4000 52). 

Cobalt from acidified sea water is extracted by anion exchange on the strongly basic resin Amberlite CG 400 (SCN ) after complexation of Co2+ with thiocyanate. Distribution coefficients of cobalt(II) up to 1.9 x 104 are attainable in solutions of 1 M NH4SCN and 0.1 M HC1. Cobalt sorbed on the resin column is stripped by elution with 2 M perchloric acid 74). 

Figure 5. Pu(IV) Distribution Coefficients for Three Anion Exchange Resins as a Function of pH.

Calcium(II), which shows no appreciable complexing, has a distribution coefficient of 147 in 0.5 M perchloric acid and 191 in 0.5 M hydrochloric acid. Strelow. Rethc-meyer, and Bothnia [10] also reported data for nitric and sulfuric acids that showed complexation in some cases. Mercury(II), bismuth(III), cadmium(II), zinc(II), and lead(II) form bromide complexes and are eluted in the order given in 0.1 to 0.6 M hydrobromic acid [11]. Most other metal cations remain on the column. Aluminu-m(III), molybdenum(VI), niobium(V), tin(IV), tantalum(V), uranium(VI), tung-sten(VI), and zirconium(IV) form anionic fluoride complexes and are quickly eluted from a hydrogen-form cation-exchange column with 0.1 to 0.2 M HF [12]. 

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