Removal of Sulfate Ion From AN-107 by Evaporation

Abstract

Sample Description. The sample used in this test was derived from an AN-107 archive sample. This material was collected and processed to remove cesium before its use for the BNFL project (Hendrickson 1997). It was collected as 45 grab samples in 125-mL bottles taken during January 1997. Approximately 5.4 L of in-tank material was transferred to the 222-S laboratory and 0.53 M sodium hydroxide was added to dilute the waste to 5 M sodium and adjust the free hydroxide concentration to "0.24M. Solids were separated from the supernatant by settling. The supematant was decanted and passed through small columns containing cesium-selective crystalline silicotitanate material. Analysis of the waste after cesium removal indicated the free hydroxide concentration to be 0.126 M. Following cesium removal, the sample was transfemed to the Pacific Northwest National Laboratory in five 1-L poly bottles where it has been stored in the Shielded Analytical Laboratory hot cells in the Radiochemical Processing Laboratory. As part of an effort to prepare feed for sulfate-removal tests, a subsample of the AN-1 07 archive sample was further treated to remove Sr/transuranic (TRU) components (Hallen et al. 2000) by precipitation. This activity involved adjusting the subsample to a hydroxide concentration of 0.8 M with the addition of 19 M NaOH. A solution of 1 M strontium nitrate was added to provide a Sr concentration of 0.05 M, and a solution of 1 M sodium permanganate was added to provide a permanganate concentration of 0.03 M. The precipitated solids were separated using a 0.45-micron dead-end filter. "The clarified liquid was used for the tests described in this report.

A Case for Molecular Recognition in Nuclear Separations: Sulfate Separation from Nuclear Wastes

“…58 This fractional-crystallization approach has definite appeal in not adding more mass to the waste and potentially has the ability to bring down sulfate levels to well below the sulfate solubility limit of borosilicate glass. Depending on the waste composition, NaNO 3 and Na 2 CO 3 •H 2 O crystallize also, 58,59 and it has turned out that fractional crystallization by evaporation has been of greater interest recently in terms of a bulk sodium removal from medium Curie waste streams. 60−62 Such a strategy concentrates radionuclides in the liquid supernatant phase, and redissolving the solid salts yields a LAW stream.…”

“…When considered only as a sulfate removal process, though, evaporation is considered to be not sufficiently selective or efficient. 41,59 Nevertheless, it may be expected that burkeite crystallization would be selective from high-sulfate waste compositions, where it would be the first phase to crystallize, especially taking advantage of its retrograde solubility (i.e., decreases with increasing temperature, in contrast to that of NaNO 3 ). 58,60 In general, the classical addition of alkaline earth and certain other divalent metal ions has been widely practiced for analytical to tonnage-scale sulfate separations in which the corresponding sulfate salts or sometimes double salts like ettringite, 63 Ca 3 Al 2 O 3 •CaSO 4 , precipitate.…”

“…This fractional-crystallization approach has definite appeal in not adding more mass to the waste and potentially has the ability to bring down sulfate levels to well below the sulfate solubility limit of borosilicate glass. Depending on the waste composition, NaNO 3 and Na 2 CO 3 ·H 2 O crystallize also, , and it has turned out that fractional crystallization by evaporation has been of greater interest recently in terms of a bulk sodium removal from medium Curie waste streams. − Such a strategy concentrates radionuclides in the liquid supernatant phase, and redissolving the solid salts yields a LAW stream. When considered only as a sulfate removal process, though, evaporation is considered to be not sufficiently selective or efficient. , Nevertheless, it may be expected that burkeite crystallization would be selective from high-sulfate waste compositions, where it would be the first phase to crystallize, especially taking advantage of its retrograde solubility (i.e., decreases with increasing temperature, in contrast to that of NaNO 3 ). , …”