Hanford Tank 241-C-106: Impact of Cement Reactions on Release of Contaminants from Residual Waste Page: 19 of 177
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Except for lindbergite, these minerals were also present in the 1-month water-leached, 82-day water-
leached, and hydrofluoric (HF)-extracted sludge samples. The Ca(OH)2-saturated system will likely
stabilize the carbonate minerals (dawsonite and rhodochrosite) and have little effect on the solubility of
the metal oxide/hydroxide phases (gibbsite, hematite, and bdhmite) because the pH should not change
appreciably. The Mn oxalate solid should dissolve in this system, while the solubility of the Ca oxalate
will depend on the final Ca and oxalate concentrations in the mixture of grout leachate and residual pore
water.
For the CaCO3-saturated system, it is expected that the carbonate minerals (dawsonite and
rhodochrosite) will partially dissolved in the lower pH environment, and the oxalate minerals (lindbergite
and whewellite) will also be soluble because of the lack of oxalate in the leaching solution. The metal
oxide and hydroxide minerals (gibbsite, hematite, and bdhmite) are not expected to dissolve appreciably
in this system because they are relatively insoluble at a pH of 8.
Deionized water leaches were conducted on C-106 sludges for time periods of 1 day, 2 weeks, and
1 month (Deutsch et al. 2005a). In addition to these single step leaches, sequential water leaches were
conducted. In the sequential leaches, the same sludge sample was extracted for periods of 1 to 4 days
repeatedly with fresh deionized water for 5 periods in sequence. These same samples were then
sequentially leached for periods of 43 and 82 days. All of these leach experiments were conducted using
0.3 g of sludge and 30 mL of water. The resulting pH values of the final solutions from the water
leaching tests were in the range of 6.7 to 7.7. The major leachable metals were Na and Mn. The major
leachable anions were oxalate and carbonate. During the planned leaching experiments with Ca(OH)2-
saturated and CaCO3-saturated solutions, it was expected that Na and Mn would again be the most
leachable metals and oxalate would be a major leachable anion. Carbonate is not expected to be very
leachable from the Ca(OH)2-saturated solution, but may be leachable at the lower pH of the CaCO3
system if soluble carbonate minerals are present.
The primary contaminants of concern in the C-106 sludge are 99Tc, 238U, 129I, and Cr because of their
potential mobility in the environment and the long half-lives of the radionuclides. In the deionized water
leaches, it was found that only low percentages (<10%) of these primary contaminants were readily
leachable from the residual waste, probably because of the previous in-tank mobilization and solids
removal with oxalic acid during retrieval.2.3
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Deutsch, William J.; Krupka, Kenneth M.; Lindberg, Michael J.; Cantrell, Kirk J.; Brown, Christopher F. & Schaef, Herbert T. Hanford Tank 241-C-106: Impact of Cement Reactions on Release of Contaminants from Residual Waste, report, September 1, 2006; Richland, Washington. (https://digital.library.unt.edu/ark:/67531/metadc887933/m1/19/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.