Technetium: Radionuclides

Abstract

This article provides a review of Tc with regards to the basic chemistry, occurrence, speciation, separation, analysis, fate, and transport. Environmental 99 Tc originates from the nuclear fuel cycle, with most of the isotope (>90%) discharged from reprocessing plants in Europe. It has been recognized that 99 Tc is a very important dose contributor in risk assessment, because of its high abundance, long half‐lives, and presumably high mobility. Essentially all the technetium on the Earth has been created by human activities involving fissionable materials. Among 11 metastates of technetium, 97m Tc is the most stable, with a half‐life of 90.1 days. The common oxidation states of technetium include 0, +2, +4, +5, +6, and +7. Depending upon the redox conditions, Tc primarily exists in two (+7 and +4) stable oxidation states in the subsurface. Under oxidizing conditions, technetium (VII) will exist as the mobile pertechnetate ion (TcO 4 − ) in aqueous solution. Reduction of TcO 4 − to Tc(IV) species (TcO 2 · n H 2 O) will decrease Tc mobility, because Tc(IV) species are strongly retarded from mineral sorption and/or precipitation. ICP‐MS is the common analytical method used to quantify Tc levels.