Technetium isolation

Gr. technetos, artificial) Element 43 was predicted on the basis of the periodic table, and was erroneously reported as having been discovered in 1925, at which time it was named masurium. The element was actually discovered by Perrier and Segre in Italy in 1937. It was found in a sample of molybdenum, which was bombarded by deuterons in the Berkeley cyclotron, and which E. Eawrence sent to these investigators. Technetium was the first element to be produced artificially. Since its discovery, searches for the element in terrestrial material have been made. Finally in 1962, technetium-99 was isolated and identified in African pitchblende (a uranium rich ore) in extremely minute quantities as a spontaneous fission product of uranium-238 by B.T. Kenna and P.K. Kuroda. If it does exist, the concentration must be very small. Technetium has been found in the spectrum of S-, M-, and N-type stars, and its presence in stellar matter is leading to new theories of the production of heavy elements in the stars. 

Plutonium was the first element to be synthesized in weighable amounts (6,7). Technetium, discovered in 1937, was not isolated until 1946 and not named until 1947 (8). Since the discovery of plutonium in 1940, production has increased from submicrogram to metric ton quantities. Because of its great importance, more is known about plutonium and its chemistry than is known about many of the more common elements. The metallurgy and chemistry are complex. MetaUic plutonium exhibits seven aUotropic modifications. Five different oxidation states are known to exist in compounds and in solution. 

The isolation and identification of 4 radioactive elements in minute amounts took place at the turn of the century, and in each case the insight provided by the periodic classification into the predicted chemical properties of these elements proved invaluable. Marie Curie identified polonium in 1898 and, later in the same year working with Pierre Curie, isolated radium. Actinium followed in 1899 (A. Debierne) and the heaviest noble gas, radon, in 1900 (F. E. Dorn). Details will be found in later chapters which also recount the discoveries made in the present century of protactinium (O. Hahn and Lise Meitner, 1917), hafnium (D. Coster and G. von Hevesey, 1923), rhenium (W. Noddack, Ida Tacke and O. Berg, 1925), technetium (C. Perrier and E. Segre, 1937), francium (Marguerite Percy, 1939) and promethium (J. A. Marinsky, L. E. Glendenin and C. D. Coryell, 1945). 

Erdal, B.R. Aguilar, R.D. Bayhurst, B.P. Daniels, W.R. Duffy, C.J. Lawrence, F.O. Maestas, S. Oliver, P.Q. Wolfsberg, K. "Sorption-Desorption Studies on Granite. I. Initial Studies of Strontium, Technetium, Cesium, Barium, Cerium, Europium, Uranium, Plutonium, and Americium", in "Proceedings of the Task 4 Waste Isolation Safety Assessment Program Second Contractor Information Meeting", Vol. II, Report PNL-SA-7352, Battelle Pacific Northwest Laboratory, 1978, pp. 7-67. 

To transfer the original synthesis to technetium was not very convenient, as it would have to start from TcBr(CO)5 (32a). A preparation has recently been reported which starts from 3a or 19a in refluxing THF and used BH3 as the reducing agent [36]. The complex 31a could be isolated in 60-70% yield, based on Tc, and has been characterized by i.r. specroseopic methods as well as Tc and Cl analysis, and compared to its rhenium congener (Scheme 5). 

Crystals of [Tc(tu)6]Cl3 or [TcCl(tu)5]Cl2 are often employed for the synthesis of technetium(III) complexes. However, since the direct reduction of pertechnetate with excess thiourea in a hydrochloric acid solution yields [Tc(tu)6]3+ in high yield [37], direct use of the aqueous solution of the thiourea complex would be preferable for the synthesis of the technetium(III) complex without isolation of the crystals of the thiourea complex. In fact, technetium could be extracted from the aqueous solution of the Tc-thiourea complex with acetylacetone-benzene solution in two steps [38]. More than 95% extraction of technetium was attained using the following procedure [39] First a pertechnetate solution was added to a 0.5 M thiourea solution in 1 M hydrochloric acid. The solution turned red-orange as the Tc(III)-thiourea complex formed. Next, a benzene solution containing a suitable concentration of acetylacetone was added. After the mixture was shaken for a sufficient time (preliminary extraction), the pH of the aqueous phase was adjusted to 4.3 and the aqueous solution was shaken with a freshly prepared acetylacetonebenzene solution (main extraction). The extraction behavior of the technetium complex is shown in Fig. 6. The chemical species extracted into the organic phase seemed to differ from tris(acetylacetonato)technetium(III). Kinetic analysis of the two step extraction mechanism showed that the formation of 4,6-dimethylpyrimidine-... 

Tribalat, S., et J. Beydon Isolement du Technetium. Anal. chim. Acta 8,... 

Nevertheless, the earth s crust contains technetium. Tc is formed by spontaneous fission of U as well as by slow neutron-induced fission of The first isolation of naturally occurring technetium was reported by Kenna and Kuroda , who isolated about 10" ng Tc from 5.3 kg of pitchblende. 

Among the long-lived isotopes of technetium, only Tc can be obtained in weigh-able amounts. It may be produced by either neutron irradiation of highly purified molybdenum or neutron-induced fission of uraniimi-235. The nuclides Tc and Tc are exclusively produced in traces by nuclear reations. Because of the high fission yield of more than 6%, appreciable quantities of technetimn-99 are isolated from uranium fission product mixtures. Nuclear reactors with a power of 100 MW produce about 2.5 g of Tc per day . 

Technetium compounds of the oxidation states 0 to -1-7 have hitherto been isolated, pertechnetates being the most stable. Also, compounds of quadrivalent technetium are fairly stable. Oxidation states lower than -1-4 can easily be oxidized to the quadrivalent or heptavalent state, whereas penta- and hexavalent technetium readily disproportionate into the hepta- and quadrivalent states. 

Distillation methods using sulfuric acid are the most efficient for isolating technetium produced by neutron irradiation of kilogram amounts of molybdenum. Boyd et al. have used this method to separate technetium from pure molybdenum which had been irradiated for one year. In this case for each gram of molybdenum 6 ml of concentrated surfuric acid are added and about 75 % of technetium is passed into the distillate. When double the amount of acid is added, nearly 90 % of technetium are found in the distillate. More than 98 % of technetium are extracted after two distillations. 

Technetiiun can also be isolated quantitatively from molybdate using Dowex-1 resin in the chloride form . Molybdate can be eluted with 0.1 M hydrochloride acid pertechnetate, however, is firmly adsorbed under these conditions. It can be readily eluted with 4.0 M nitric acid. The only drawback of this separation is the need to recover technetium from nitric acid solution. If the acid is evaporated with great care, losses may be kept quite low. 

An isotope dilution mass spectrometric method involves the addition of a known quantity of Tc followed by chemical separation, purification, and measurement of the Tc/ Tc isotopic ratio . An improved technique has been developed for the analysis of Tc in environmental samples. After spiking with Tc the isolated technetium is concentrated onto anion exchange beads. Determination of as little as 1 pg has been achieved through the enhanced ionization efficiency afforded by the resin bead source ... 

Direct chlorination of powdered technetium metal gives a blue product, not TcClg by reducing the amount of oxygen contamination the amount of blue material produced can be reduced but not eliminated. Chlorination of the metal on porous pot affords a green product which resembles TcCl . Both the blue and green products are, in fact, mixtures of purple TcOCl. and colourless TCOCI3 and these compounds have been isolated pure by vacuum distilla-... 

An unusual reaction pattern has been found for the electrochemical and chemical (by ascorbic acid) reduction of the rhenium(II) thioether complex [Re(9S3)2] " (9S3 = 1,4,7-trithiacyclono-nane). Instead of the formation of the corresponding rhenium(I) complex, C bond cleavage and the release of ethene was observed and the brown rhenium(III) species [Re(9S3)(SC2H4SC2H4S)]" (250) was isolated as a BF4 salt. Lfpon electrochemical reduction of [Re(9S3)(SC2H4SC2H4S)]" further loss of ethene was observed while the analogous technetium complex can be reversibly reduced to [Tc(9S3)(SC2H4SC2H4S)]. 

Existence of technetium was predicted from the vacant position in the Periodic Table between manganese and rhenium. Noddack, Tacke, and Berg reported its discovery in 1925 and named it masurium. The metal actually was never isolated from any source by these workers. Its existence, therefore, could not be confirmed. Perrier and Segre in 1937 produced this element by bombarding molybdenum metal with deuterons in a cyclotron. They named the element technetium derived from the Greek word technetos, meaning artificial. 

Tribalat, S. and J. Beydon, Isolement du technetium, Anal. Chim. Acta... 

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