VOLATILIZATION OF TECHNETIUM FROM SIMULATED REPROCESSING SOLUTIONS

Volatilization behavior of technetium was investigated in order to eva luate the decontamination efficiency of an evaporator for reprocessing waste solutions. The gaseous species of technetium volatilized over H TcO4 solutions had been considered as the mixture of Tc2O7 and HTcO4. Estimation of the decontamination efficiency needs to determine whethe r the dominant gaseous species is Tc2O7 or HTcO4. The continuous disti llation of dilute HTcO4 solution was carried out and we obtained the p urification factor (PF) defined as the concentration ratio of techneti um in the concentrate and distillate. The PF was normalized by total p ressure, HTcO4 molarity and mole number in II solution. The normalized PF was reciprocal to the second power of HTcO4 molarity and was propo rtional to the activity of water. These findings suggested the dominan t gaseous species were Tc2O7 and volatilization was the dehydration of HTcO4 forming gaseous Tc2O7. The vapor pressure of Tc2O7 was obtained from PF and the equilibrium constant of volatilization reaction was c alculated considering that the gaseous species was dominantly Tc2O7. T he thermodynamic functions controlling the volatilization reaction wer e obtained from the dependence of equilibrium constant on temperature as. Delta H=82.3kJ . mol(-1) and Delta S=205.4J . mol(-1). K-1, respec tively.