One of the major pollutants in nuclear waste is 99Tc, a redox-sensitive fission product from 235U and 239Pu with a long half-life of 2.14 X 10 5 years. Under environmental oxidizing conditions, 99Tc mainly exists in aqueous solution as pertechnetate, TcO4-, which is a highly water-soluble ion that does not sorb significantly on minerals or sediments , so that, it is considered as inert with high risk to migrate through the environment. Under reducing conditions, Tc mobility is hampered by formation of Tc(IV) with significantly lower solubility . Pyrite, on one hand, is a good sorbent for Tc(VII) due to the presence of the functional groups FeOH and FeSH, and on the other hand, Tc(VII) is reduced to Tc(IV) by the interaction with structural Fe2+ and possibly with sulfur atoms. Moreover, Bruggeman et al.  found considerably increased Tc sorption when adding pyrite to boom clay in the presence of humic substances, which also favor the Tc retention [4,5].
In this work synthetized pyrite nanoparticles  were used to investigate Tc sorption in classical batch sorption experiments.
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