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Abstract
The desorption behavior of Tc from active carbon was studied as a fundamental study on separating Tc from high-level radioactive liquid waste. Technetium adsorbed from 0.5 M HNO, solution could be desorbed more effectively with alkaline thiocyanate solution than with HN03. The adsorption behavior of Tc on the active carbon previously treated with alkaline thiocyanate solution was also studied for the purpose of a recycle use of the active carbon.
The distribution coefficient of Tc, Kd, depended sensitively on pH in the presence of KSCN. The value of Kd exceeded 105 ml/g below pH 2 and became less than 10 ml/g above pH 4. It was found by spectrophotometric analysis that this large difference in Kd was due to the change of the chemical form of Tc. Below pH 2, Tc was adsorbed in the form of thiocyanate complexes, [TC(NCS)6]2- and [Tc(NCS)6]3-. Above pH 4, these complexes were hardly formed and TcO4 − was desorbed by anion exchange reaction with thiocyanate ion.
