Ion Exchange Fractionations

Mar hal CN, Douchet C, Nicolas E, Albarede F (2000) The abundance of zinc isotopes as a marine biogeochemical tracer. Geochem Geophys Geosyst 1 1999GC-000029 Marechal C, Albarede F (2002) Ion-exchange fractionation of copper and zinc isotopes. Geochim Cosmochim Acta 66 1499-1509... 

Acid soluble rare earth salt solution after the removal of cerium may be subjected to ion exchange, fractional crystalhzation or solvent extraction processes to separate individual rare earths. Europium is obtained commercially from rare earths mixture by the McCoy process. Solution containing Eu3+ is treated with Zn in the presence of barium and sulfate ions. The triva-lent europium is reduced to divalent state whereby it coprecipitates as europium sulfate, EuS04 with isomorphous barium sulfate, BaS04. Mixed europium(ll) barium sulfate is treated with nitric acid or hydrogen peroxide to oxidize Eu(ll) to Eu(lll) salt which is soluble. This separates Eu3+ from barium. The process is repeated several times to concentrate and upgrade europium content to about 50% of the total rare earth oxides in the mixture. Treatment with concentrated hydrochloric acid precipitates europium(ll) chloride dihydrate, EuCb 2H2O with a yield over 99%. 

Separation of niobium from tantalum and impurity metals is the most important step in its extraction from the ore. It may be achieved by several methods that include solvent extraction, ion exchange, fractional crystallization, fractional sublimation, and other techniques. Solvent extraction is apphed mostly in several large-scale commercial processes. Although the classical fractional crystalhzation method forms effective separation, it is a tedious... 

Estimate of the HETP intradiffusion coefficients, when based on HETP dependence on concentration, has been shown to be close in value to the quantity calculated with the theoretical formula obtained by using the model of centrosymmetrical diffusion in an ion-exchanger bead [89,90]. The values in this formula of r /D, where r is the effective particle radius, were determined in thin-layer kinetic experiments with the same ion-exchanger fraction. 

Let each ion-exchanger fraction in the solution be present in Qj (in equiv) amounts. If the mass of each fraction is m, (kg), Q, = m,C,, where C is again the ion exchange capacity in equiv/kg. For simplicity and in agreement with the experiments described later, the following initial condition at t = 0 is assumed ... 

In the above experiment involving five size fractions the rate curves for Cs uptake by each ion-exchanger fraction was not determined experimentally. This formidable task would have required several interruptions of the kinetic experiment after given periods of time, followed by reproducible separations of the particles by sieving into the five size fractions and subsequent analysis of each fraction. For a two component mixture of particles, however, the above sequence of operations becomes practicable and experimental results are available for such systems (see Sec. B.4, where anomalous ion-exchange kinetics is discussed). Another way to... 

Cs ions to particle fractions 4 and 5, niiich have the higher separation factors and can thus take up more Cs ion. The solution again reaches its equilibrium somewhat faster than the ion-exchanger fractions. 

Examples of successful fractionations of aquatic humic substances where only one fractionation mechanism was operative include utilization of the hydrophobic properties of XAD resins (Mantoura and Riley, 1975 Aiken et al., 1979), hydrogen bonding of weak-acid functionalities of humic constituents to weak-base anion-exchange resins (Kim et al., 1976), and use of ion-exchange celluloses for ion-exchange fractionation of aquatic humic substances without hydrophobic matrix adsorption (Sirotkina et al., 1974). These examples of successful fractionations demonstrate the potential for chromatography of aquatic humic substances when fractionations are designed carefully to avoid undesirable interactions. 

Affinity Precipitation of Avidin from Partially Purified Egg Whites. Following the ion exchange fractionation of egg white solution, described in the experimental section above, fractions of eluted protein solution (obtained from the elution described in Figure 6) were mixed with... 

The various processes available for fuel reprocessing are aqueous solvent extraction, precipitation, ion exchange, fractional distillation, pyrometal-lurgy, and fluoride volatility. Most of the commercial development experience has come from the solvent-extraction method for separation of uranium, plutonium, and fission products. 

PM Spiecker, PK Kilpatrick. Ion exchange fractionation of asphaltenes and their resulting interfacial properties, to be submitted. 

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