SOLVENT-EXTRACTION OF PERTECHNETATE AND PERRHENATE IONS FROM NITRATE-RICH ACIDIC AND ALKALINE AQUEOUS-SOLUTIONS

Solvent extraction studies of (TcO4)-Tc-99- and its nonradioactive con gener ReO4- into 1,3-diisopropylbenzene and several other organic solv ents containing the 0.200 M Aliquat-336 nitrate (which is predominantl y methyltrioctylammonium nitrate) from a variety of aqueous solutions led to the following conclusions: (i) ReO4- is a suitable solvent extr action surrogate for (TcO4)-Tc-99- under conditions that model nuclear waste streams at the DOE Hanford site; (ii) distribution ratios (D va lues) greater than 100 can be achieved for TcO4- extraction from aqueo us solutions containing a mixture of 1 M NaOH and 1.5 M NaNO3; (iii) t he addition of 1.5 M NaNO2 or 0.14 M K2CrO4 to the aqueous phase conta ining a mixture of 1 M NaOH and 1.5 M NaNO3 does not significantly aff ect D(TcO4-); (iv) D(TcO4-) values were larger by a factor of 3-5 when ketone solvents with flash points above 60 degrees C were substituted for 1,3-diisopropylbenzene. Initial and final concentrations of TcO4- in the organic and aqueous phases were determined by gamma counting o f solutions of (TcO4)-Tc-99- that contained tracer amounts of (TcO4)-T c-95m- (0.204 MeV). Initial and final concentrations of ReO4- in the a queous phase were determined by ICP-AES.