The local structures of U(VI) oxide precipitates produced as a functio
n of LiOH concentration have been studied by XAFS. Curve-fitting analy
ses indicate that the solid formed in 0.1 M LiOH is similar to a schoe
pite-like phase where distinct linear uranyl ions (UO22+) are bridged
along the equator by OH. ions. At higher LiOH concentrations, the uran
yl groups become elongated and the precipitate structure resembles tha
t of a uranate salt. We have studied the speciation of Tc in cement wa
ste forms, where it is desirable to stabilize the highly soluble form
of Tc(VII), TcO4-, by in situ reduction to a less mobile form, i.e. Tc
(IV). Using the XANES to measure the oxidation state, our results show
that significant reduction takes place in the presence of the cement
additives blast furnace slag (BFS) and Na2S. In addition, EXAFS data s
how that in situ reduction leads to formation of Tc clusters possessin
g S and Tc coordination.