Electrodeposition of Tc99 from Aqueous Solution

Abstract

A study has been made to determine the optimum conditions necessary for the electrodeposition of macro amounts of technetium (Tc 99) from an aqueous bath containing about 0.018 mole of NH4TcO4 and 1 mole of (NH4)2SO4 per liter of solution with H2SO4 added to pH about 1: Electrolysis of this solution at 1 to 2 amp/din 2 and room temperature gives a bright, metallic appearing deposit of Tc with a cathode current efficiency of up to 30%. Included in this study are the effects on CCE of such factors as current density, bath pH, concentrations of the various reagents, temperature, and the colored cathode reduction product. Tests made to determine the nature of the deposit showed it to be essentially metallic; however, annealing is necessary to produce metallic crystals. During electrolysis a light pink reduction product forms in the bath; as electrolysis continues this reduction product becomes darker and appears to poison the bath. Addition of small amounts of H202 to the bath during electrolysis can prevent the colored reduction products from forming.Technetium, the first artificial element to be synthesized (1), can be purchased from Oak Ridge National Laboratory as the salt NH4TcO4 for about $90 per gram of activity. This availability suggested to the authors that a study of the electrodeposition of technetium on a macro scale from aqueous solution would be a worthwhile addition to the already extensive literature dealing with the electrochemistry of the element and its compounds. An excellent review article by Boyd (2) and a book by Colton (3) gives information about the production and properties of Tc so detailed information will not be repeated here.Tc 9~ has a half life of about 2.12 x 105 years and emits weak beta rays with a maximum energy of 0.32 Mev (4); thus the walls of ordinary laboratory glassware give sufficient radiation protection when Tc and its compounds are being used. Since information about the physiological effects of Tc is still incomplete, great care should be taken to protect the worker as well as the laboratory from contamination. Several sources of information describing the handling of Tc and its salts (3, 5) are available. Use of rubber gloves, protective clothing, a "film badge," a well-ventilated hood [HTcO4 is fairly volatile (6)], and a covered plating cell are mandatory protections for the laboratory worker.A number of reports of the electrodeposition of technetium from aqueous solutions have appeared in the literature, but most of them necessarily deal with dilute baths in the order of 10 -1~ to 10-5 m/1 (mole per liter). The discoverers of Tc, Perrier and Segr~, reported the deposition of a thin layer on a platinum wire from a very dilute acid solution (7). Other investigators (8) obtained bright cathode deposits from solutions of NH4TcO4 in 2N H2SO4 and NH~HF2. Black or brown cathode deposits were obtained when various pertechnetate salts in H2804 were electrolyzed (9,10). Lietzke and Stoughton (11) obtained semiquantitative data on the electrodeposition of Tc on Pt and Hg catho...

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