Solubility technetium

Alder, J. C. 1989. Preliminary studies of packaging and disposal of decommissioning waste in Switzerland. AmcZ. Technol. 86(2) 197-206. Bostic, W. D., J. L. Shoemaker, P. E. Osborne, and B. Evans-Brown. 1989. Treatment and disposal options for a heavy metals waste containing soluble technetium-99. ACS Symp. Ser., Volume Date 1989, 422 345-67 cited in Chem. Abstr. CA 113(20) 179992b. 

Technetium is a silvery-gray metal that tarnishes slowly in moist air. The common oxidation states of technetium are +7, +5, and +4. Under oxidizing conditions technetium (Vll) will exist as the pertechnetate ion, TcOr-. The chemistry of technetium is said to be similar to that of rhenium. Technetium dissolves in nitric acid, aqua regia, and cone, sulfuric acid, but is not soluble in hydrochloric acid of any strength. The element is a remarkable corrosion inhibitor for steel. The metal is an excellent superconductor at IIK and below. 

Chemical separation of technetium in soils is not easy, but it is fairly well-known that under aerobic conditions pertechnetate Tc(YII) is readily transferred to plants while under anaerobic conditions insoluble TcCh (or its hydrate) is not transferred to them. Even under aerobic conditions, however, the transfer rate decreases with time [28], indicating that soluble pertechnetate changes to insoluble forms by the action of microorganisms which produce a local anaerobic condition around themselves [29,30]. Insoluble technetium species may be TcOz, sulfide or complexes of organic material such as humic acid. 

With all solvents studied including cyclohexanol, methyl ethyl ketone and cyclohexanone, heptavalent technetium is extracted most effectively from sodium sulfate and weakest from sodium nitrate or sodium perchlorate solutions. The data in Fig. 5 appear to be consistent with those on the solubilities of various sodium salts in pure tri-H-butyl phosphate. For example, the solubility of Na SO in TBP is extremely small compared with NaClO. ... 

As already mentioned in section 2.1 pertechnetate may be efficiently extracted by pyridine from alkaline solutions Since pyridine derivates are less soluble in the aqueous phase than pyridine, they extract technetium more efficiently even from nitrate solutions. For example, the distribution coefficients of technetium in the extraction from a 2 M (NH )2COj solution with a high nitrate concentration by pyridine and 2-methylpyridine are 7.5 and 242, respectively . Higher distribution coefficients can be achieved by using 3-methyl- or 4-methyl-pyridines. The pyridine derivates are the most promising reagents for the extraction of technetium from nitrate solutions. 

Salaria et al. suggest the separation of technetium and rheniiun as cupfer-ronates of pertechnetate and perrhenate which have different solubilities in chloroform. Pertechnetate can partially be extracted from 4 M H SO by shaking the solution with chloroform, which is pre-equilibrated with a solution of 1 % cupfer-ron in 4 M H SO. The main part of perrhenate remains unextracted. 

Nitron-, thallium, cesium-, and silver pertechnetate are appreciably soluble in water and therefore less suitable for precipitation and separation of technetium. From aqueous ammonia solution, pertechnetate can be co-precipitated with MgMH PO ... 

Some precipitation methods have been applied to the separation of technetium from molybdenum when the former occurs as a radio-active daughter-product of the latter. The separation of technetium is performed by co-precipitation with tetraphenylarsonium perrhenate from an alkaline molybdate solution . In this way, also ruthenium remains in solution. Molybdate may be precipitated away from pertechnetate using 8-hydroxyquinoline " or a-benzoinoxim Pb or Ag" ions can also be used . Kuzina and Spitsyn have developed a method for concentrating technetium from ammoniacal molybdate solutions by co-precipitat-ing pertechnetate with the slightly soluble crystalline MgNH PO. ... 

An X-ray fluorescence method has been developed for the determination of technetium in solution . At concentrations of less than 1.0 mg Tc per ml there are not interelement effects. Therefore, it is possible to ascertain technetiiun in its compounds without previous decomposition, provided that the compounds are soluble in water or dioxane. The detection limit is about 4 Tc. 

It should be mentioned that tetraphenylarsonium salts are soluble in alcohol and that the nitron salts dissolve in ethyl acetate. Thus, technetium as well as the organic reagents can be recovered. 

For the rapid determination of Tc in a mixture of uranium fission products. Love and Greendale have used the method of amalgam polarography. It consists in a selective reduction of technetium at a dropping mercury electrode at a potential of —1.55 V vs. SCE in a medium of 1 M sodium citrate and 0.1 M NaOH. Under these conditions, technetium is reduced to an oxidation state which is soluble in mercury. The amalgam is removed from the solution of fission fragments and the amount of Tc determined in nitric acid solution of the amalgam by a y count. For Tc the measurement accuracy is within 1 %, and the decontamination factor from other fission products 10 . 

Throughout this review Tc always relates to the isotope Tc unless otherwise stated. The only form in which technetium is commercially available is [NH4][Tc04], either in aqueous solutions or as a solid. The salt is of medium solubility in water and recrystallization is used for purification. For the alkali-metal series, only the Li+ and Na+ salts show a reasonable solubility in water, the latter being about 68 g per 100 Addition of large organic cations like [NBu4]+ or... 

Technetium dissolves in dilute or concentrated nitric acid to form nitrate, Tc(N03)2. Reaction with concentrated sulfuric acid yields the sulfate TCSO4. Technetium is oxidized by hydrogen peroxide in alkaline solution to form soluble pertechnetate, Tc04 anion. Such pertechnatate anion forms complexes with tertiary or quarternary amines, pyridine and its methyl-substituted derivatives. 

Tracer studies of the chemical properties showed that astatine was soluble in organic solvents, could be reduced to the —1 state, and had at least two positive oxidation states. These studies were made on solutions of 10-11 to KL15 molar astatine (29). The similarity between astatine and iodine was found to be less close than that between technetium and rhenium or that between promethium and the other rare earths (30). 

Tin and americium were so extensively sorbed under all conditions that isotherm data could not be obtained. These elements are not significantly mobile in the Mabton Interbed aquifer. Values of Freundlich constants for technetium, radium, uranium, neptunium, and plutonium are given in Table IV. The Freundlich equation did not fit the selenium sorption data very well probably because of slow sorption kinetics or precipitation. Precipitation was also observed for technetium at 23°C for concentrations above 10 7M. This is about the same solubility observed for technetium in the sandstone isotherm measurements. Linear isotherms were observed only in the case of radium sorption. In general, sorption on the Mabton Interbed was greater than on the Rattlesnake Ridge sandstone. This is probably due to the greater clay content of the Mabton standard. 

Technetium - In oxic seawater 99Tc appears to be present almost exclusively as the pertechnetate ion (TcOij") (Beasley and Lorz, 1986). This highly soluble and... 

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