Development of Alkaline Oxidative Dissolution Methods for Chromium (III) Compounds Present in Hanford Site Tank Sludges

Krot, NN; Shilov, V. P.; Fedoseev, A. M.; Budantseva, N. A.; Nikonov, MV; Yusov, A. B.; Garnov, A. Yu.; Charushnikova, IA; Перминов, В. П.; Astafurova, L. N.; Lapitskaya, T. S.; Makarenkov, VI

doi:10.2172/8396

Cited by 12 publications

(8 citation statements)

References 27 publications

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“…Studies over the last several years with Hanford tank sludge simulants and with actual Hanford tank sludges indicate that treating water-washed and caustic-leached solids with oxidants indeed can significantly increase the effectiveness of Cr removal Rapko et al 1997;Rapko 1998;Delegard et al 1993;Lumetta et al 1995;Krot et al 1999;Sylvester et al 2001, Rapko et al 2002. Tested oxidants to date include ozone, O 3 Rapko et al 1997;Delegard et al 1993), hydrogen peroxide, H 2 O 2 (Rapko et al 1997;Lumetta et al 1995;Krot et al 1999), permanganate, MnO 4 - Rapko et al 1997;Rapko 1998;Rapko et al 2002;Lumetta et al 1995), oxygen, O 2 (Rapko 1998;Krot et al 1999), persulfate, S 2 O 8 2- (Krot et al 1999), and ferrate, FeO 4 2- (Sylvester et al 2001;Rapko and Vienna 2002).…”

Section: 2mentioning

confidence: 99%

“…Tested oxidants to date include ozone, O 3 Rapko et al 1997;Delegard et al 1993), hydrogen peroxide, H 2 O 2 (Rapko et al 1997;Lumetta et al 1995;Krot et al 1999), permanganate, MnO 4 - Rapko et al 1997;Rapko 1998;Rapko et al 2002;Lumetta et al 1995), oxygen, O 2 (Rapko 1998;Krot et al 1999), persulfate, S 2 O 8 2- (Krot et al 1999), and ferrate, FeO 4 2- (Sylvester et al 2001;Rapko and Vienna 2002). The results of these Cr-dissolution investigations can be summarized as follows:…”

Section: 2mentioning

confidence: 99%

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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%

Section: 2mentioning

confidence: 99%

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

Rapko

Vienna²

2002

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“…The process that was examined was oxidative dissolution of the metal using hydrogen peroxide/ammonium carbonate solutions. Krot et al 1999;Fedoseev et al 2002] may be effective to enhance the oxidation rate afforded by H 2 O 2 .…”

Section: Oxidative Dissolution Of U-metalmentioning

confidence: 99%

Disposition Options for Hanford Site K-Basin Spent Nuclear Fuel Sludge

Mellinger¹,

Delegard²,

Gerber³

et al. 2004

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This report provides summary-level information about a group of options that have been identified for the disposition of spent-nuclear-fuel sludge in the K-Basins at the Hanford Site. This study builds upon a review performed in CY1999 which established the current baseline for sludge retrieval and storage from K Basin. (a) Building upon this study, an expert review team was assembled to consider expert knowledge and project progress which has evolved since that time. The membership of this team is provided in Appendix C. This team outlined a revised set of potentially feasible alternatives which could be broadly classified as ambient and elevated temperature treatment methods. In considering the breadth of these methods, the team concluded that the presence of a high uranium metal content fraction was limiting the feasibility of several candidate methods. In other words, if some mechanism were available to eliminate or significantly reduce the uranium metal content, the range and efficacy of feasible treatment methods would be enhanced. Given these preliminary findings by the team, additional discussions were held with Flour Hanford senior project members to explore both the feasibility of separating a uranium metal stream and the congruence of potentially feasible treatment methods with other program interfaces and objectives. The selection of alternatives given in this report for disposition of the sludge is derived for this team effort. The product of each treatment option would be treated sludge that would meet waste-acceptance requirements for disposal as transuranic waste at the Waste Isolation Pilot Plant. The separated concentrated uranium stream would be treated by one of several methods identified by the team, which are beyond the scope of this report. K-Basin sludge is made up of degraded fuel, corrosion products, dirt, and other material that has accumulated in the basins through the 30-year fuel-storage mission. Sludge can be categorized by its location into pit sludge, floor sludge, canister sludge, knockout pot (KOP) sludge, and settler sludge. Pit sludge can be further categorized in accordance with the specific pit in which it resides. Key characteristics of this sludge that shape the selection of a path forward are: • U-metal (b) content ranging up to 5% for canister sludge (and greater than 50% for KOP sludge) • Plutonium content greater than 100 nci/gm, requiring controls for airborne alpha • Dose rates up to approximately 5 rem/h (higher for KOP sludge) • Fissile content requiring controls for the prevention of nuclear criticality. The treatment options that were considered can be divided into two groups-those that would be performed at ambient temperature and those that require elevated temperatures. The two (a) Sludge Treatment Analysis HNF-4097, Rev. 0, K. L. Pearce, NUMATEC Hanford, 4/27/99. (b) The term "U-metal" is used to distinguish uranium in the mettallic form from uranium that will be present, as, for example, an oxide or hydride. iv ambient-temperature treatment options that were...

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“…Persulfate is of interest because of work completed by Russian scientists on its oxidation of Cr(III) in alkaline systems. Krot et al [1999] indicated that persulfate may be preferred over peroxide and other common oxidants because of its reactivity towards Cr(III) and because it could be applied such that little increase in waste volume occurred. However, for both hydrogen peroxide and persulfate, no mechanistic data were available prior to our work under this EMSP project.…”

Section: Impact Of Speciation On Redox: Oxidation Of Cr(iii) By Peroxmentioning

confidence: 99%