Hydrated pertechnetates

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. 

All [TcOX4] spedes hydrolyse in aqueous solution and then disproportionate into pertechnetate and Tc(IV) oxide hydrate according to... 

Many compounds of technetium and rhenium are of analogous composition and of corresponding physical and chemical properties. Because of the very similar ionic radii, isotypic crystal structure formation of analogous compounds could often be observed. Technetium remarkably differs from manganese by the high stability of pertechnetate compared with permanganate. Moreover, divalent technetium does not exist as a hydrated ion but only as a stabilized complex. 

Technetium metal can be electrodeposited from an acidic solution of pertechnetate using a platimun, nickel or copper cathode. Electrolysis of neutral, unbuffered solutions, alkaline solutions, and sulfuric acid solutions lower than 2 N yield a black deposit of hydrated TcOj The current efficiencies are generally poor but the deposition is reasonably quantitative. The deposition requires the application of relatively negative cathode potentials and is therefore non-selective. Polaro-graphy indicates that the overpotentials for the evolution of hydrogen on technetium are rather low hence, electrolysis from acidic media will always include concurrent discharge of hydrogen . ... 

For a given ionic strength, //, depends on the nature of the coextracted anion A-. To allow the formation and extraction of the neutral complex, the coextracted mineral anion A- has to lose part (or all) of its hydration shell. The smaller the hydration energy of the mineral anion is, the easier is its transfer to the organic phase, and thus the higher is the affinity of the solvation extractant toward trivalent 4/ and 5/ elements (29, 76), as observed in the series chloride < nitrate < perchlorate < pertechnetate, which inversely follows the anion hydration energy order AG/CI ) > AG/NO3) > AG(,(CI04) > AG/TcO/. 

The reduced species is cationic, more highly hydrated, and prefers the salt-rich phase. Thus far, the reductant of choice has been SnClj, a common reductant in technetium radiotracer applications. The use of biphase-forming salts that are also chelating agents (e.g., citrate) may stabilize the reduced species and enhance stripping. Stripping into a high-base ABS appears to be hampered by incomplete reduction of technetium or reoxidation to the pertechnetate ion [32]. 

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