Laboratory testing of ozone oxidation of Hanford Site waste from Tank 241-SY-101

Delegard, Calvin H.; Stubbs, A.M.; Bolling, Stacey D.

doi:10.2172/10117009

Cited by 17 publications

(15 citation statements)

References 6 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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“…TcO 4 -and I -) may be bound to particle surfaces at pH ranges different than those that bind positively charged ions (e.g., UO 2 2+ and Sr 2+ ). Early experiments on caustic leaching of Hanford tank sludge from several different tanks produced highly variable results [18][19][20][21]. The removal efficiency, for example, varied over a wide range for aluminum (16-85 percent), chromium (48-88 percent), and phosphorus (13-98 percent).…”

Section: B Backgroundmentioning

confidence: 99%

Enhanced Sludge Processing of HLW: Hydrothermal Oxidation of Chromium, Technetium, and Complexants by Nitrate

Buelow¹,

Robinson²

1999

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Executive SummaryThe Office of Economic Management has identified treatment of High Level Waste (HLW) as the second most costly environmental problem facing the DOE. In order to minimize costs of disposal, the volume of High Level Waste (HLW) requiring vitrification and long term storage must be reduced. Methods for efficient separation of chromium from waste sludges, such as the Hanford Tank Wastes (HTW), are key to achieving this goal since the allowed levels of chromium in the high level glass control waste loading. At concentrations above 0.5 to 1.0 wt.% chromium prevents proper vitrification of the waste. Chromium in sludges most likely exists as the extremely insoluble oxides and minerals, with chromium in the +3 oxidation state. In order to solubilize and separate it from other sludge components, Cr(III) must be oxidized to the more soluble Cr(VI) state. Efficient separation of chromium from HLW could produce significant savings.This project sought to lay the foundation for the application of hydrothermal processing for enhanced chromium separation from HLW sludges. Experiments were conducted which examined four areas:a. Oxidation of insoluble Cr(III) solids to soluble Cr(VI) using oxygen, b. Oxidation of insoluble Cr(III) solids to soluble Cr(VI) using nitrates, c. Transport properties and speciation of reducing and oxidizing agents under hydrothermal conditions, d. Reactions of plutonium and americium under oxidizing hydrothermal conditions. From the results of our experiments in these areas, we have developed a fundamental understanding of chromium speciation, oxidation/reduction and dissolution kinetics, reaction mechanisms, and transport properties under hydrothermal conditions in both simple and complex salt solutions.Experimental results show that at moderate temperatures (125-200°C), insoluble Cr(III) hydroxide can rapidly be oxidized to soluble Cr(VI). The rate of reaction increases with increasing oxygen and hydroxide concentration and increasing temperature. Experiments also show that sludge components such as aluminate can slow the oxidation/dissolution rate, and that at higher temperatures, organic components in the waste can consume the oxygen before it reacts with the chromium. Reactions of chromium with nitrate only become important at temperatures above 350°C. At lower temperatures the rates of dissolution are not controlled by transport properties. At higher temperatures, particularly near phase transition points, reagent transport could begin to slow and effect dissolution rates. A global rate expression was developed for the reactions involving oxygen and nitrates. The expression agrees well with the experimental results.Future experiments should examine the reactions of HLW sludges with oxygen at temperatures between 100°C and 200°C at hydroxide concentrations between 1M and 6M. This work should be performed at the Hanford site. Work at Los Alamos will continue, supported by the Nuclear Weapons Program. It will focus on high temperature hydrothermal processes including the oxidation o...

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“…More recently, Delegard et al (1993) again investigated use of ozone to oxidize organic complexants in alkaline salt waste solutions. These investigators took careful pains to design and employ a highly efficient flow device for effecting intimate contact of the dissolved complexants with ozone.…”

Section: Ozonolysis Of Complexantsmentioning

confidence: 99%

“…Once nitrite oxidation was complete, ozone rapidly and vigorously attacked organic complexants. In the test equipment used by Delegard et al (1993) organic complexants were converted to refractory oxalate and acetate ions in as little as eight hours at 22 to 25 "C.…”

Section: Ozonolysis Of Complexantsmentioning

confidence: 99%