Effect of denitration with formic acid on precipitation and volatilization of ruthenium and technetium

It is necessary to investigate the effect of the denitration with formic acid on the precipitation behaviors of Ru and Tc from a simulated high-level liquid wastes, and the effect of the heat-treatments on the volatility behaviors of them from the sludges. The experiments were carried out using radiotracer techniques. Nitrosylruthenium ion was quantitatively converted into RuNO(OH)3 by the denitration at the initial molar ratio of [HCOOH]/[NO3-] from 1.2 to 1.3, and the precipitation rate decreased drastically at the molar ratio over 1.5. Ferric ion was reduced to Fe2+ ion by the denitration. Pertechnetate ion was reduced to TcO2 by Fe2+ ion, and the quantitative yield of coprecipitation was achieved at the [HCOOH]/[NO3-] ratio above 1.8. The volatilities of Ru and Tc from the sludges increased with heating times and temperatures, however, decreased with an increase in the [HCOOH]/[NO3-] ratios. The denitration lowered the volatilization rate of Ru less than 4 % at 1,000 deg C for 3 h in an air flow. The volatilization rate of Tc was about 5 % at 1,000 deg C for 2 h under conditions of the denitration of the [HCOOH]/[NO3-] ratio over 1.8 and the heattreatment in an Ar flow. (author)