Pertechnetate waste

In closing, recovery of technetium from waste solution should be touched upon. Studies of the base hydrolysis of technetium P-diketone complexes revealed that all of the complexes studied decompose in an alkaline solution even at room temperature, until technetium is finally oxidized to pertechnetate. These phenomena are very important for the management of technetium in waste solutions. Since most metal ions precipitate in alkaline solution, only technetium and some amphoteric metal ions can be present in the filtrate [29]. A further favorable property of pertechnetate is its high distribution coefficient to anion exchangers. Consequently, it is possible to concentrate and separate technetium with anion exchangers from a large volume of waste solution this is especially effective using an alkaline solution [54],... 

Extraction of tetrahedral pertechnetate anion from aqueous solutions using several crown ethers is well known. The coextraction of cesium (or strontium) and technetium from nuclear waste by calix[4]arene-crown-6 has been reported from alkaline media. Although technetium in its common pertechnetate form does not complex directly with crown ethers, pertechnetate extraction may be facilitated by crown ethers as the coanion of sodium (for alkaline nitrate waste). Pertechnetate at trace levels in the waste may be more than a 1000-fold more extractable than the smaller nitrate anion in ion-pair extraction processes.87... 

Sample preparation is required to cope with the sample matrix, the interferences, and the speciation of "Tc. The separation processes for isolating "Tc prior to radiometric detection require that the "Tc be in the pertechnetate ("TCO4) state. However, in waste samples with high organic content, much of the "Tc may be present in reduced valence states. Therefore, to determine the total "Tc content, all the "Tc must be oxidized to the pertechnetate state prior to ion-exchange or extraction-chromatographic separation. 

The tren-based heteroditopic receptor 22, featuring a tripodal tetrahedral amide hydrogen-bond anion-recognition site in combination with benzo-15-crown-5 ether cation-binding moieties, has been found to cooperatively bind chloride, iodide, and perrhenate anions via co-bound crown ether-complexed sodium cations. It also can efficiently extract the radioactive sodium pertechnetate from simulated aqueous nuclear waste streams. The anion-binding affinity of 22 is considerably reduced in the absence of a co-bound cation <1999CC1253>... 

Technetium-99 Tc-99 is a reasonably high-yield (6%) FP (similar to Cs-137). The ratio of activities Cs-137 to Tc-99 is calculated (FISPIN) to be 6,000 to 1. Of the selected waste streams in the UK Nirex Inventory, 18 were found to exceed the GQ level for Tc-99 including HPA SPF (high uncertainty), FED and miscellaneous contaminated items (MCI), and HNA FCC, MCI and IX resin. Tc is chemically different to Cs because it will form anionic species (the pertechnetate anion, TCO4 ) whereas Cs will only form cations. Tc-99 will not be retained by the standard resins used to remove Cs. Cs-137 will therefore not be a good marker for Tc-... 

To rather selectively separate pertechnetate, with more than 90 % yield, from solutions of acid fission products it was proposed to use finely divided cadmium sulphide. The overall yield of the radionuclide pure c, finally extracted as [(C(,H5)4As TcC)4, was 68 % [182,183]. In addition, activated carbon was used to efficiently separate pertechnetate from high-level liquid waste. Distribution coefficients of more than 500 were observed when pertechnetate was separated with activated carbon from a 2 M HNO3 solution [184]. Effective separation and recovery of Tc04 from contaminated groundwater with activated carbon have been reported very recently [185. ... 

Figure 26 Pertechnetate distribution ratios versus the weight percent PEG-2000 in the stock solution contacted with three Hanford tank waste simulants to form an ABS. The simulated waste formulations are given in Ref. 51.

Figure 28 Dws for pertechnetate uptake from three Hanford tank waste simulants versus the molecular weight of the grafted polymer for four ABEC resins.

In the area of amidic receptors, the tris-crown-ether tren-based receptor 52. synthesized by Beer and coworkers was recently shown to efficiently extract pertechnetate anions from simulated nuclear waste streams in the presence of sodium cations. ... 

Technetium is one such constituent of radioactive waste where the need for a chemical means of detection exists, but a sensor does not. Technetium is not found in appreciable quantities in nature however, the isotope c is a byproduct of the thermal nuclear fission of U, U, and Pu at 6.1%, 4.8%, and 5.9% yields, respectively (7), and significant quantities of c exist at many DOE sites. Tc exhibits rather weak P decay (Ebuk = 0.292 keV), but it is of particular concern for two reasons its long half life (2.13 x 10 y) and the high solubility of its most common form in aqueous environmental media, pertechnetate (TcO/) (2). Pertechnetate does not readily adsorb to most minerals, and therefore in aqueous form and under suitable conditions, it may rapidly present itself to subsurface waters (3,4). 

Bridges, N.J. Rogers, R.D. (2008). Can kosmotropic salt/chaotropic ionic liquid (salt/salt aqueous biphasic systems) be used to remove pertechnetate from complex salt waste. Separation Science and Technology Vol.43 (No.5) 1083-1090. 

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