Speciation of mercury in sludge solids: washed sludge

Abstract

Does not include a small contribution of soluble supernate Hg to Total Hg, see text. ** Includes a small contribution of soluble supernate Hg, see text.

Review of Mercury in the SRS Tank Waste Storage and Treatment Processes for Applicability to Hanford Waste Processing

“…Several key differences need to be noted before addressing how the SRS results can be used to inform waste processing at Hanford: 1) Mercury amounts in the tank waste at SRS are orders of magnitude higher than the amounts in the Hanford tank waste 2,3 (There is more mercury in just the 3H evaporator feed and drop tanks than in the entire 18 Hanford tank farms).…”

“…The dominant form of mercury in the SRS tank farms is insoluble HgO with some fraction of insoluble HgS with concentrations as high as several weight percent of the insoluble solids in the waste 2 . Soluble mercury was typically close to 100 mg/L in supernate.…”

Speciation of Mercury in Sludge Solids: Unwashed Sludge

“…To date, all processing studies for DWPF have been conducted with simulants that are based on only the addition of HgO. In the washed sludge sample studied previously, 21% of the Hg was present as a nonoxide species 13 . In the unwashed sludge sample studied here, 19% of the Hg was present as a non-oxide species that is now suspected to be a mercury amalgam.…”

“…The Hg species that can be expected in various extraction fractions are described in Table 3-3. The F-3 1M KOH extraction was conducted on this unwashed sludge, whereas the previous washed sludge was not subjected to this extraction, 13 to ensure removal of any calomel (Hg2Cl2) in the sludge, but also to extract calomel in the Kaolin Clay standard, so that it would not co-extract with HgS in the F-5 fraction. Since fraction F-4 was the first acidic extraction that these dried solids materials were exposed to, the HgO was expected to dissolve exclusively into this fraction as it had for the washed sludge.…”

“…13 Table 3-4. This table also includes the results from the washed sludge 13 for comparison. One replicate of the fraction F-5 extractions with Tank 51 insoluble solids had a measured total mercury value that was about four times the average of the other three replicates, so it is not included in the average calculated and given in the table.…”