Behavior of Concentrated Pertechnic Acid

Behavior of Concentrated Pertechnic Acid

Author: Sarah Maier

Technetium is a radioactive metal in group 7 of the periodic table. KMnO4, a heptavalent oxo-salt of technetium’s lighter analogue manganese, is well known as an oxidant. As a rare and radioactive element, technetium is not a common staple of most laboratories. However, like manganese, it is able to form heptavalent oxo-compounds, for example, the KMnO4 analogue KTcO4 and the corresponding acid HTcO4.

John McCloy, Pacific Northwest Laboratory, Richland, and Washington State University, Pullman, both WA, USA, and colleagues have investigated the behavior of aqueous technic acid (HTcO4) solutions upon evaporation of water. A pure pertechnic acid solution was prepared from KTcO4 by a sequence of recrystallization and cation-exchange processes. The technetium content of the resulting solutions was determined by liquid scintillation counting (LSC), making use of technetium’s radioactivity.

The team observed a color change from colorless to yellow to red during the evaporation of water. The concentrated solutions and isolated compounds were analyzed  by 99Tc NMR and UV-Vis spectroscopy, density determination, and thermal analysis. Three different compounds were identified. A colorless solid assumed to be the monohydrate of pertechnic acid, a yellow liquid, probably H5TcO6, and a dark red solid considered to be Tc2O5, which underwent quick disproportionation.

The researchers could show that only a negligible loss of technetium occurred during the evaporation process. They plan to perform X-ray diffraction experiments for the conclusive determination of the structure and composition of the products.


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