Enhanced Sludge Washing for Pretreating Hanford Tank Sludges

Lumetta, Gregg J.; Rapko, Brian M.; Liu, J.; Temer, D.J.

doi:10.1007/978-1-4899-1543-6_16

Cited by 32 publications

(37 citation statements)

References 13 publications

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“…This result implies that Cr initially in the +3 oxidation state requires oxidation for dissolution. It follows that adding an oxidant might enhance the dissolution of water-insoluble Cr from Hanford tank sludge by facilitating conversion from its poorly alkaline soluble +3 oxidation state to its more alkaline soluble form as chromate, CrO 4 2- (Lumetta et al 2000).…”

Section: 2mentioning

confidence: 99%

Selective Leaching of Chromium from Hanford Tank Sludge 241-U-108

Rapko

Vienna²

2002

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SummaryPretreatment approaches are planned to improve the effectiveness of vitrifying Hanford tank wastes. The presence of chromium in Hanford waste tank solids can interfere with the efficient vitrification of this waste. Therefore, an important pretreatment objective is to remove excess chromium from Hanford tank sludges. A proposed approach to increase the effectiveness of chromium removal from Hanford tank sludge is through oxidative alkaline leaching.Chromium in tank sludge exists in both the +3 and +6 oxidation states. Chromium, when initially present in the +6 oxidation state, is effectively removed from the Hanford tank sludge solids by alkaline washing and caustic leaching. When present in the +3 oxidation state, however, chromium often dissolves poorly in simple alkaline-wash and caustic-leach solutions. Even when initially present in its +3 oxidation state, prior studies have shown that chromium exists only in caustic-leach solutions in its +6 oxidation state. Therefore, adding an oxidant to the sludge might be expected to facilitate conversion of chromium(III) to its more alkaline-soluble form (chromate [CrO 42-]) and so enhance its leaching from the sludge.This study evaluated the oxidants permanganate, MnO 4 -, and peroxynitrite, ONOO -, as selective chromium-leaching agents from washed 241-U-108 tank sludge under varying conditions of hydroxide concentration, temperature, and time. and 85°C in the absence of any added oxidant generated relatively low amounts of chromate in solution by the end of the 24-h contact time. Contacting the sludge with peroxynitrite under conditions of low-hydroxide concentration and low temperature generated chromate more rapidly than in the absence of added oxidant and also did not appear to be complete at the end of the 24-h contact time. Under conditions of high hydroxide and high temperature, peroxynitrite generated a rapid initial formation of chromate followed by a slower increase in the solution's chromate concentration. Permanganate solutions appear to generate chromate extremely rapidly, both under high temperature/high hydroxide and low temperature/low hydroxide leach conditions, with chromate formation complete within 2 hours.The total chromium concentrations in the leach solutions as measured by inductively couple plasmaatomic emission spectroscopy (ICP-AES) were compared with the chromate generated as measured by ultraviolet-visible (UV-vis) spectroscopy. Chromate and total chromium concentrations in the leachates were found to be identical within the reported ± 15% experimental error for the ICP-AES measurements.It is also desirable that transuranic elements not be leached out of the sludge, so the effectiveness of the oxidants at dissolving transuranic elements was also examined. Only the leach solution with added permanganate at 3 M [OH -] and 85°C showed a dramatic increase in plutonium dissolution. No evidence for either americium or curium in any leach solution was detected.Finally, the mass changes and final sludge compositions were evaluated using gl...

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Section: 2mentioning

confidence: 99%

Selective Leaching of Chromium from Hanford Tank Sludge 241-U-108

Rapko

Vienna²

2002

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“…Microscopy . studies done previously indicated that the phases that are difficult to dissolve are generally aluminosilicates (Lumetta et al 1998). …”

Section: Aluminummentioning

confidence: 99%

Washing and Caustic Leaching of Hanford Tank Sludge: Results of FY 1998 Studies

Lumetta¹,

Rapko²,

Liu³

et al. 1998

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DISCLAIMERPortions of this document may be illegible in electronic image products. Images are produced from the best available original document. AbstractSludge washing and parametric caustic leaching tests were performed on sludge samples fiom five Hadord tanks: B-101, . These studies examined the effects of both dilute hydroxide washing and caustic leaching on the composition of the residual sludge solids.the P, and 63 to 99% of the Na from the H d o r d tank sludge samples examined. The partial removal of these elements was likely due to the presence of water-soluble sodium salts of aluminate, chromate, hydroxide, nitrate, nitrite, and phosphate, either in the interstitial liquid or as dried salts.The response of Al to caustic leaching was v~a b l e .When leached with 3 M NaOH for one week at 95 to 100°C, the cumulative Al removals were 62,99,61,95, and 89% for the B-101, BX-110, BX-112, (2-102, and S-101 samples, respectively. For the B-101 and the BX-110 samples, Al dissolution was rapid, with the AI concentrations reaching >SO% of their final values within the first 5 h of leaching.Interestingly, for the BX-112 sample, A I removal decreased with increasing leaching time and temperature-a trend contrary to what was expected. We hypothesize that this is due to the formation of aluminosilicate minerals. For the C-102 sludge, there was clearly a benefit in increasing the NaOH concentration from 1 M to 3 M. Leaching with 1 M NaOH removed -20 to 30% of the Al from the dilute hydroxide-washed solids while 3 M NaOH removed -95% of the Al. Aluminum dissolved slowly from the S-101 sample, which is consistent with boehmite being the predominant Al-containing phase.all the sludge samples examined, Cr removal during caustic leaching was highly time-dependent, but the Cr dissolution did not fit simple zero-, first-, or second-order kinetic models. Consistent trends in the effects of temperature and hydroxide concentration on Cr removal were difficult to discern. P from the sludge samples examined. Except for the Tank C-102 sample, cumulative P removals,were 285%. For C-102, the cumulative P removals were only -60%. Increasing temperature or hydroxide concentration generally did not result in large improvements in P removal; that is, relatively mild conditions tended to be adequate to remove P. 'The projected 137Cs content for the low-level waste (LLW) resulting fiom immobilizing the sludge washinglleaching solutions would range fiom -50 to -540 CVm3 for the samples examined. Although these concentrations are below the U.S. Nuclear Regulatory Commission Class C LLW limit of 4,600 Cum3, they are well above the proposed guideline of 3 Cum3 for the immobilized LLW product fiom the proposed private-processing facilities. Thu, it is likely that I3'Cs will need to be removed fiom the washing and leaching solutions. On the other hand, transuranic and Sr removal would likely not be required for the washing and leaching solutions fiom processing the sludges examined here. An estimate of high-level waste (HLW) glass produced in im...

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“…Caustic leaching is primarily designed to remove a large fraction of the aluminum, based on the amphoteric nature of this element (Lumetta et al 1998). If aluminum is not removed, the minimum amount of HLW glass produced in immobilizing this fraction of the waste will be defined by this element.…”

Section: Introductionmentioning

confidence: 99%

“…Like Cr, there is relatively low tolerance for P in the HLW melter feed, so its removal is important with respect to reducing the HLW volume. Previous experiments conducted with actual tank-waste samples have indicated that caustic leaching is generally effective at removing P from the HLW solids (Lumetta et al 1998 and. However, little effort has been directed at understanding the mechanism of P removal by caustic leaching.…”

Section: Introductionmentioning

confidence: 99%

Mechanism of Phosphorus Removal from Hanford Tank Sludge by Caustic Leaching

Lumetta

2008

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Enhanced Sludge Washing for Pretreating Hanford Tank Sludges

Cited by 32 publications

References 13 publications

Selective Leaching of Chromium from Hanford Tank Sludge 241-U-108

Selective Leaching of Chromium from Hanford Tank Sludge 241-U-108

Washing and Caustic Leaching of Hanford Tank Sludge: Results of FY 1998 Studies

Mechanism of Phosphorus Removal from Hanford Tank Sludge by Caustic Leaching

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