Technetium-containing radioactive waste

As mentioned before, subsequent phosphate treatment does not affect the stable sulfide, and TCLP results show excellent stabihzation of Cr in any oxidation state. Alternatively, a small amount of reductant in the waste will convert chromate into lower oxidation states. Such methods, however, are not preferred, because the reductant may also affect the solubility of other hazardous compounds. The exception is technetium-containing radioactive waste, in which chromate is also a contaminant. As we shall see in Chapter 17, a reductant is essential for stabihzation of technetium, and that will also help in stabilization of chromium. 

Vandergraaf T. T., Tichnor K. V., and George I. M. (1984) Reactions between technetium in solution and iron-containing minerals under oxic and anoxic conditions. In Geochemical Behaviour of Disposed Radioactive Waste. ACS Symposium Series 246 (eds. G. S. Barney, J. D. Navratil, and W. W. Schultz). American Chemical Society, Washington, DC, pp. 25-44. 

Caution. Technetium-99 is a weak Remitter (0.292 MeV, 7% =2.12 X 10s years). Therefore, all manipulations should be carried out in a laboratory equipped with a monitored fume hood with Fiberglas trays and plastic-lined absorbent pads used to control potential spills. Personnel should wear disposable lab coats and gloves at all times. Radioactive wastes, both solid and liquid, must be disposed of in special receptacles. Samples sent outside the laboratory must be sealed in glass bottles within a nonbreakable outer container with cotton as a filler, and the glass bottle must be wipetested for contamination prior to ship-... 

The reason that nuclear wastes must be isolated from the environment for a very long time is that they contain relatively long-lived radioactive nuclides, such as technetium-99 with a half-life of over 2.1 x 10 years. One proposed solution is to bombard the waste with neutrons so as to convert the long lived nuclides into nuclides that decay more quickly. When technetium-99 absorbs a neutron, it forms technetium-100, which has a half-life of 16 seconds and forms stable ruthenium-100 by emitting a beta particle. Write the nuclear equations for these two changes. 

The waste contains considerable amounts of Ru, Rh, and Pd, all metals in scarce abundance on earth. These elements are used as catalysts in the chemical industry, for catalytic exhaust cleaning in cars, and as corrosion resistant materials. The United States demand exceeds the domestic production by about a factor of 1(X). The United States would be independent of import from year 2000 if these elements were recovered from the yearly generated spent fuel. This is particularly true if technetium is recovered, since it can often replace platinum. Some of the recovered elements would be radioactive, but the activities would be small enough to make the elements easy to handle. 

Technetium, one of the key elements in the treatment of radioactive liquid waste, because of its long half-life and geochemical mobility, was separated from concentrated alkaline solutions by SLMs containing 2-nitrophenyloc-tyl ether (NPOE) [180]. The hollow-fiber SLM, containing bis(2-ethylhexyl)phosphonic acid, was tested for carrier-free separation of from °Sr [181]. 

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