Mercury in aqueous tank waste at the Savannah River Site: Facts, forms, and impacts

Abstract

Over the past two years, there has been an intense effort to understand the chemistry of mercury across the Savannah River Site's High-Level liquid waste flowsheet to determine the impacts of various mercury species. This effort began after high concentrations of mercury were measured in the leachates from a toxicity characteristic leaching procedure (TCLP) test on the low-level cementitious waste form produced in the Savannah River Saltstone facility. Speciation at specialized off-site laboratories showed the dominant form of leached mercury was the methylmercury cation. Neither the source of the methylmercury nor its concentration in the Saltstone feed was well established at the time of this testing.

Assessment of Methane Generation from the Thermolysis of Organics in Caustic Waste

“…From previous speciation testing of mercury in Tank 38, the concentrations of methylmercury and dimethylmercury were 160-200 mg/L and 0.0525-0.148 mg/L respectively. 32 The HBP simulant had 450 mg/L of Hg(NO 3 ) 2 , and as mentioned above, Hg(II) is rapidly methylated in the presence of organics. It is possible that a methylated mercury species is partially accountable for the methane generated.…”

“…All the tanks evaluated in Table 3-2 have high assumed temperature limits (≥90 °C). Further, most of these tanks (30,32,37,38, and 43) are evaporator system tanks and fall under unique control programs. As can be seen in Table 3-2, none of the times to 5% methane LFL fall below 7 days, which is the response time required for rapid generation rate tanks.…”

Separation and Speciation of Mercury from Hanford 241-AP-107 Tank Waste Supernatant

“…In 2014, the SRS observed high levels of mercury in a TCLP as part of normal monitoring of the lowlevel cementitious waste form produced at SWPF (Jain et al 2015;Bannochie et al 2017). The TCLP value was higher than the LDR treatment standard for mercury of 0.025 mg/L.…”

“…After finding unexpectedly high mercury and methylmercury levels in tank and waste streams, scientists at Savannah River National Laboratory (SRNL) were tasked with conducting mercury speciation measurements on tank wastes and at various points in the waste treatment process. The analytical results of these mercury characterization studies are documented in a series of SRNL sample analysis reports by Bannochie (2015a,b,c,d,e,f,g,h,i;2016a,b,c), and Bannochie and Crawford (2015a,b), and summarized in a peer-reviewed publication by Bannochie et al (2017).…”

“…Secondary solid waste disposal considerations and approvals for items such as spherical resorcinol formaldehyde, grouted Effluent Management Facility (EMF) overheads, and the Hanford Tank Waste Treatment and Immobilization Plant (WTP) low-activity waste (LAW) melters are highly dependent on identification of retained mercury species, retention characteristics, and the associated impact on discharge and disposal permits. Although there is currently no processing of tank waste at Hanford, waste processing is imminent and representative mercury inventory tracking is desired to anticipate and mitigate stack emission and secondary liquid waste disposal issues like those experienced at the Savannah River Site (SRS) (Bannochie et al , 2017.…”