Literature review of the potential impact of glycolic acid on the technetium chemistry of srs tank waste

Abstract

This document presents a literature study of the impact of glycolate on technetium chemistry in the Savannah River Site (SRS) waste system and specifically Saltstone. A predominant portion of the Tc at SRS will be sent to the Saltstone Facility where it will be immobilized. The Tc in the tank waste is in the highly soluble chemical form of pertechnetate ion (TcO 4 -) which is reduced by blast furnace slag (BFS) in Saltstone, rendering it highly insoluble and resistant to leaching.Currently, the Defense Waste Processing Facility (DWPF) uses formic acid as a reducing agent. DWPF is investigating the use of glycolic acid in lieu of formic acid for various reasons, including the fact that the byproduct generation of hydrogen gas during decomposition of formic acid is minimized. Although most of the glycolic acid would be destroyed in DWPF, some of it could be returned to the Tank Farm where it would be mixed with other tank waste. Glycolic acid is a chemical reductant and can be a complexant for metal ions. It is thus important to investigate if it reacts in the tank waste to form soluble species that are not pertechnetate and that may not undergo the reduction reaction with BFS.The literature shows several experiments and analyses with SRS tank waste that likely would have indicated if soluble non-pertechnetate forms of Tc were already present in SRS waste. The experiments with SRS tank waste used ion exchange resin that selectively absorbs only pertechnetate. The methods with anion exchange had already been used at Hanford to detect non-pertechnetate. Such analyses with SRS waste were consistent with the presence of only pertechnetate. Secondly, the tank sample analyses that have been done used sample preparation methods that separated pertechnetate and would have shown a difference if non-pertechnetate was present. The results gave no indication that any soluble non-pertechnetate species is currently present in SRS tank waste.The impact of glycolate on technetium was examined by (1) testing which showed that glycolate did not complex with Tc(I) tricarbonyl, which is believed to be the form of non-pertechnetate present in Hanford, (2) testing that showed that glycolate did not interfere with technetium immobilization as Tc 2 S 7 , (3) testing that showed that glycolate in the presence of noble metals caused the reduction of pertechnetate to insoluble Tc dioxide but no soluble complexed species, (4) real waste testing that showed the absence of nonpertechnetate in Hanford tanks (241-AW-101 and 241-AZ-101) that are known to contain glycolate, and (5) testing that showed for a tank 241-AN-105 simulant spiked with both pertechnetate and glycolate at room temperature, the Tc adsorption using the ion exchange resin Purolite ® A530E a is not affected by the presence of glycolate. The literature review of glycolate-pertechnetate interactions relevant to SRS did not reveal indications that glycolate would impact the chemistry of Tc in alkaline tank waste or the behavior of Tc during reduction to Tc dioxide in Saltstone. Rev...

Evaluation of Technologies for Enhancing Grout for Immobilizing Hanford Supplemental Low-Activity Waste (SLAW)

“…Another method has also been developed that uses a special sensor to measure the Tc(I) moiety, but would not sense if other forms of non-pertechnetate exist (Bryan et al 2017). More information on the topic of non-pertechnetate chemistry can be found in a summary report (Nash et al 2017).…”