Isotopic ion exchange

Molecular modelling of transition metal complexes (TMC), reproducing characteristic features of their stereochemistry and electronic structure, is in high demand in relation with studies and development of various processes of complex formation with an accent on ion extraction, ion exchange, isotope separation, neutralization of nuclear waste, and also when studying structure and reactivity of metal-containing enzymes. Solving these techno-... 

Water samples Bromine Bromide/bromate Ion exchange/isotopic dilution 6jug I"1 bromide 30/tg I"1 bromate Diemer and Heumann (1997)... 

A continuous ion-exchange isotope separation process for uranium enrichment has been developed in Japan. Few details of this process have been disclosed. However, it is known that "reflux" is obtained by oxidation and reduction of U " " and U02 . A demonstration plant with a capacity of 2 kSWU/y is in operation at Hyuga. 

The principle used for the counter-current ion-exchange isotope separation by electromigration in a column is the balancing of the hydraulic flow of the ions X, the isotopes of which are to be separated, by the opposite flow of ions Y in an electric field. The X ions should be the more strongly sorbed on the ion exchanger and the Y ions should be the more mobile ones in the field. A sharp boimdary between the two kinds of ions is attained at some place in the column and is maintained there by the balancing of the flows. The steady passage of electric current is equivalent to movement of the sorbed band of X (which is actually... 

The use of larger particles in the cyclotron, for example carbon, nitrogen or oxygen ions, enabled elements of several units of atomic number beyond uranium to be synthesised. Einsteinium and fermium were obtained by this method and separated by ion-exchange. and indeed first identified by the appearance of their concentration peaks on the elution graph at the places expected for atomic numbers 99 and 100. The concentrations available when this was done were measured not in gcm but in atoms cm. The same elements became available in greater quantity when the first hydrogen bomb was exploded, when they were found in the fission products. Element 101, mendelevium, was made by a-particle bombardment of einsteinium, and nobelium (102) by fusion of curium and the carbon-13 isotope. 

Figure 47.6). By choosing which isotope to mea.sure, all of the rare earth elements can be analyzed accurately and quickly following their ion-exchange separation into just two fractions. 

The plutonium usually contains isotopes of higher mass number (Fig. 1). A variety of industrial-scale processes have been devised for the recovery and purification of plutonium. These can be divided, in general, into the categories of precipitation, solvent extraction, and ion exchange. 

Other tritium isotope effects of significant magnitude have been observed in ion exchange (qv) (27) and gas chromatography (qv) (28,29). Many other examples have been described (9). 

Further complications ensue if the isotope decays appreciably during the reaction time or if there are chemically inequivalent exchanging groups. These cases will not be treated here, but references concerning the chloride ion exchange of Pt(NH3)Clj and PtCCiHjjClj- provide a guide.7 8... 

Anderson and Bonner made the first detailed kinetic study on the exchange using the isotopic method ( Cr) and a separation method based on the conversion of Cr(II) into Cr(IIl) oxalate and an ion-exchange treatment. To prevent oxidation of Cr(II) during exchange a hydrogen atmosphere was maintained over the reaction mixture. The rate law found to be obeyed for the concentration ratio range Cr(III)/Cr(II) of between 3.3 x 10 and 2.0 in perchlorate media was... 

Early measurements of " Th were on seawater samples and Th was co-precipitated from 20-30 L of seawater with iron hydroxide (Bhat et al. 1969). This procedure may not recover all of the " Th in the sample, and an alpha emitting Th isotope (e g., °Th or Th) is added as a yield monitor. Following chemical purification of the Th fraction by ion exchange chromatography, the Th is electrodeposited onto platinum or stainless steel planchets. The planchets are then counted in a low background gas-flow beta detector to measure the beta activity and subsequently with a silicon surface barrier detector to determine the alpha activity of the yield monitor. The " Th activity is thus determined as ... 

Measurements of " Th in sediment samples (Aller and Cochran 1976 Cochran and Aller 1979) used much the same approach as outlined above. In this case, the dried sediment sample ( 10 g) was leached with strong mineral acid (HCl) in the presence of a yield monitor (generally Th, an artificial Th isotope resulting from the decay of Th that is produced by neutron capture on Th). Thorium was separated from U and purified by ion exchange chromatography, and electrodeposited onto stainless steel planchets. Counting and determination of " Th activity followed the procedure outlined above. 

Ooi, K., Miyai, Y., Makita, Y, and Kanoh, H., Fractionation of lithium isotopes in ion exchange chromatography with titanium phosphate exchanger, Separation Sci. Technol., 34, 1133, 1999. 

Am from its parent 241Pu and the other isotopes present can be effected by precipitation, ion exchange, or solvent extraction. 

Mercury was determined after suitable digestion by the cold vapour atomic absorption method [40]. Lead was determined after digestion by a stable isotope dilution technique [41-43]. Copper, lead, cadmium, nickel, and cobalt were determined by differential pulse polarography following concentration by Chelex 100 ion-exchange resin [44,45], and also by the Freon TF extraction technique [46]. Manganese was determined by flameless atomic absorption spectrometry (FAA). 

Table 5.6 compares the ICP-AES results with data generated for the same sample by two other independent methods - isotope dilution spark source mass spectrometry (IDSSMS), and graphite furnace atomic absorption spectrometry (GFAAS). The IDSSMS method also uses 25-fold preconcentration of the metals and matrix separation using the ion exchange procedure, following isotope... 

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