Washing and caustic leaching of Hanford tank sludges: results of FY 1996 studies. Revision

Lumetta, G.J.; Rapko, Brian M.; Wagner, Michael J.; Liu, J.; Chen, Y.L.

doi:10.2172/375594

Cited by 41 publications

(62 citation statements)

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“…While substantial concentrations of Cr(III) hydroxide can exist in high-caustic solutions at room temperature, the heating of such solutions causes guyanaite, syn-(CrOOH), to precipitate. This precipitate does not readily redissolve in aqueous caustic media (Lumetta et al 1998). This observation is consistent with previous reports of low solubility of Cr(OH) 3 in acidic and near-neutral solutions at elevated temperature (Lumetta et al 1997).…”

Section: 2mentioning

confidence: 97%

“…Unfortunately, the direct detection of tetrahydroxochromium(III) is much more difficult by visible spectroscopy since the extinction coefficient at its maximum, ca. 600 nm, is more than two orders of magnitude lower (Lumetta et al 1998). However, the total Cr concentration in solution can be determined with good sensitivity by ICP-AES, so the ratio of chromate to total Cr can be effectively measured.…”

Section: Evaluating the Form Of Chromium In Oxidative Alkaline Leach mentioning

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: 97%

Section: Evaluating the Form Of Chromium In Oxidative Alkaline Leach mentioning

confidence: 99%

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

Rapko

Vienna²

2002

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“…Several gibbsite sources were characterized at PNNL by particle size distribution, X-ray diffraction (XRD), scanning electron microscopy (SEM), surface-area analysis, and caustic leaching. These results were then compared against available data (Lumetta 1996) for actual gibbsite waste, which consisted primarily of crystal size and shape, using XRD and SEM. When more actual waste data from Groups 3 and 4 were available, these results were compared based on caustic leaching, and it was found that the gibbsite source that had been picked matched closely.…”

Section: Success Criteriamentioning

confidence: 99%

“…Caustic-leaching experiments were first performed by PNNL on actual Hanford tank sludge samples in FY 1993. The original caustic-leaching experiments were performed by PNNL as a prelude to acid dissolution of the sludge solids, with the intent that the acid-dissolved fraction would be processed through solvent extraction to separate the very small mass fraction of the radioactive elements (the transuranics [TRUs], 90 Sr, and 137 Cs) from the bulk mass of non-radioactive components (Lumetta et al 1996). In this respect, caustic leaching was meant to remove the large amount of aluminum from the waste, thus reducing the nitric acid demand and simplifying the solvent extraction feed.…”

Section: Introductionmentioning

confidence: 99%

Development and Characterization of Gibbsite Component Simulant

Russell¹,

Smith²,

Rinehart³

et al. 2009

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“…Table 1. Properties were measured during sludge caustic leaching (2 M NaOH at 100°C) and washing (0.01 M NaOH/0.01 M NaNO3 at 50°C) from over fifteen different Hanford tanks 16,17,18,19 . For actual wastes, the standard initial solids loading of …”

Section: Figure 5 Initial Particle Gel Configuration From Brownian Dmentioning

confidence: 99%