Americium Concentrations in Solutions Contacting Americium-Doped Glass

Abstract

Americium-doped glass (0.053 wt% /sup 241/Am) was contacted with dilute salt solutions (0.001 M NaCIO/sub 4/), pH buffers, Permian Basin brine (PBB1), and ten-times-diluted PBB1 to determine the aqueous americium concentrations that can be expected in equilibrium with this glass. The americium concentrations in all of these solutions were similar and decreased with increasing pH; americium concentrations decreased to the detection limit (--10/sup -11.6/ M) at a pH value of --7 and remained at or near the detection limit at pH values > 7. Americium concentrations in glass suspensions with pH >5 were found to be controlled by the dissolution of an americium-solid. The value of the log of the equilibrium constant for the solubility of this americium-solid (Am-solid + 3H/sup +/ = Am/sup 3+/ + H/sub 3/-solid) was determined to be -- 10.3. The americium-solid is found to effectively control aqueous americium to very low concentrations under slightly acidic to alkaline conditions. The high ionic strength and the high CI/sup -/ concentrations in brine are found not to measurably affect the americium-solid solubility. The objectives of the present study were (a) to develop a data base that can be used to predict aqueous americium concentrations in equilibrium with americium-doped more » glass and (b) to determine the influence of high ionic strength and high chloride concentrations, conditions that are expected in salt repositories, on the leachability or solubility of an americium-containing glass. « less