[en] An extraction study was performed on technetium in its highest oxidation state as a function of nitric acid concentration at 25, 50 and 70 deg C. A long chain amine (tri-n-octylamine TOA) and an organophosphorus solvent (TBP) have been investigated. Addition of NH₄NO₃ has a salting-out effect on the extraction of TBP in the aqueous phase and therefore decreases the distribution coefficient for heptavalent technetium. The mechanism of extraction is discussed in the light of the results obtained. (author) 11 refs.; 8 figs