Technetium / Pertechnetate / Speciation / ChlorideSummary. The speciation of tetravalent technetium has been studied in HCl solutions ranging from 1.0 to 6.0 M. Tc(IV) exists in 6.0 M HCl as the well characterized TcCl 6 2− chloride complex. In 1.0 M HCl, the chloride ligands of TcCl 6 2− are slowly substituted by other ligands such as H(4−m−2n− p)+ compounds may form with (m + n + p + q) = 6. Several speciation techniques such as UV-visible and Raman spectrometries, X-ray absorption spectroscopy and electrochemistry have enabled to get an insight into this problem. All the results have indicated two most likely species of Tc(IV) after aging for about ten days in 1.0 M HCl to be aquo-chlorocomplexes of technetium and not oxo-chorocomplexes: TcCl 5 · H 2 O − and TcCl 4 · 2H 2 O.
Batch experiments were performed in order to investigate the influence of pH, neptunium concentration, and concentration of carbonate in Solution on the Sorption of Np(V) on a synthetic hydrargilite. The concentration of Np{V) at hydrargilite surface was found to be proportional to the concentration of dissolved Np(V) at equilibrium, within the Np(V) concentration ränge =10"" to 10"' M, in C02-free 0.1 M NaC104 solutions at pH = 7.45±0.05. The sorption of tracer concentration of Np(V) on hydrargilite was strongly pH-dependent. Increasing the total concentration of carbonate from about 0 to 10"^ M in the aqueous phase resulted in a net decrease of the extent of Np(V) uptake in the alkaline pH region. Surface complexation modeling suggested that Np(V) sorption behavior in carbonate solutions resulted mainly from a competition between surface complexation and aqueous carbonate complexation of NpOJ. The surface complexation reactions and conditional constants proposed in this study for the non-electrostatic model allowed an accurate description of the sorption behavior of Np(V) on hydrargilite over a wide ränge of pH and carbonate concentration of the aqueous phase.
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