Ferrate Treatment for Removing Chromium from High-Level Radioactive Tank Waste

Sylvester, Paul J.; La, Rutherford; González-Martín, Anuncia; J, Kim; Rapko, BM; Gj, Lumetta

doi:10.1021/es001340n

Cited by 51 publications

(43 citation statements)

References 22 publications

(36 reference statements)

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“…The concentration of SCN -was kept at 1.25 × 10 -4 M and Fe(VI) concentrations ranged from 4.6 × 10 -5 M to 5.08 × 10 -4 M. Thiocyanate concentrations were determined before and after mixing with Fe(VI) using High Performance Ion Chromatography (HPIC) (16,17). Two products of the reactions of Fe(VI) with SCN -, cyanate and sulfate, were also analyzed by using HPIC (16,17). The stoichiometry of the cyanide reaction with Fe(VI) under anaerobic conditions was determined by keeping cyanide constant at 1.25 × 10 -4 M and varying the Fe(VI) concentration.…”

Section: Methodsmentioning

confidence: 99%

Iron(VI) and Iron(V) Oxidation of Thiocyanate

Sharma

Burnett

O'Connor

et al. 2002

Environ. Sci. Technol.

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Thiocyanate (SCN-) is used in many industrial processes and is commonly found in industrial and mining waste-waters. The removal of SCN- is required because of its toxic effects. The oxidation of thiocyanate (SCN-) by environmentally friendly oxidants, Fe(VI) and Fe(V), has been studied anaerobically using stopped-flow and premix pulse radiolysis techniques. The stoichiometry with Fe(VI) was determined to be 4HFeO(4-) + SCN(-) + 5H2O-->4Fe(OH)3 + SO4(2-) + CNO(-) + O2 + 2OH-. The rate law for the oxidation of SCN- by Fe(VI) was found to be -d[Fe(VI)]/dt = k11([H+]/([H+] + Ka,HFeO4)) [Fe(VI)][SCN-] where k11 = 2.04 +/- 0.04 x 10(3) M-1 s-1 and pKa,HFeO4 = 7.33. A mechanism is proposed that agrees with the observed reaction stoichiometry and rate law. The rate of oxidation of SCN- by Fe(V) was approximately 3 orders of magnitude faster than Fe(VI). The higher reactivity of Fe(V) with SCN- indicates that oxidations by Fe(VI) may be enhanced in the presence of appropriate one-electron-reducing agents. The results suggest that the effective removal of SCN- can be achieved by Fe(VI) and Fe(V).

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Section: Methodsmentioning

confidence: 99%

Iron(VI) and Iron(V) Oxidation of Thiocyanate

Sharma

Burnett

O'Connor

et al. 2002

Environ. Sci. Technol.

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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%

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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“…A few studies have been conducted on the oxidation of chromium(III) in nuclear waste sludges by oxygen, ozone, permanganate, 22 and ferrate. 23 The results are useful, to some extent, to the development of sludge washing strategies.…”

Section: Introductionmentioning

confidence: 99%

Oligomerization of chromium(iii) and its impact on the oxidation of chromium(iii) by hydrogen peroxide in alkaline solutions

Rao

Zhang

Friese

et al. 2002

J. Chem. Soc., Dalton Trans.

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Kinetic studies on the oxidation of separated/characterized chromium(III) oligomers by hydrogen peroxide indicate that the degree of oligomerization has a significant impact on the rate of oxidation in alkaline solutions. The oxidation rate constant decreases in the order: monomer > dimer > trimer > aged/unseparated chromium(III) solution where higher oligomers dominate. SummaryMonomeric, dimeric and trimeric chromium(III) species in solution were separated by ion exchange and characterized with UV/Vis absorption and Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS). The kinetics of the oxidation of the separated species by hydrogen peroxide in alkaline solutions was studied by conventional and stopped-flow UV/Vis absorption spectroscopy. Results indicate that the intensity of Cr-Cr scattering in the EXAFS spectra (d Cr-Cr ~ 2.99 Å), a measure of the degree of oligomerization, increases as the solution alkalinity is increased. As the oligomerization proceeds, the rate of oxidation by hydrogen peroxide in alkaline solutions decreases in the order: monomer > dimer > trimer > aged/unseparated alkaline chromium(III) solution where higher 1 oligomers dominate. The dominant redox pathway has an inverse order with respect to C NaOH . The data suggest that the rate-determining step involves the weakening of the bridging bonds in the oligomer and a concomitant release of one hydroxyl group from the chromium(III) moiety upon the attack by hydrogen peroxide.

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Ferrate Treatment for Removing Chromium from High-Level Radioactive Tank Waste

Cited by 51 publications

References 22 publications

Iron(VI) and Iron(V) Oxidation of Thiocyanate

Iron(VI) and Iron(V) Oxidation of Thiocyanate

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

Oligomerization of chromium(iii) and its impact on the oxidation of chromium(iii) by hydrogen peroxide in alkaline solutions

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