The Solubility of TcO2 · nH2O in Neutral to Alkaline Solutions under Constant pco2

Eriksen, Trygve E.; Ndalamba, P.; Bruno, Jordi; Caceci, Marco S.

doi:10.1524/ract.1992.5859.1.67

Cited by 65 publications

(75 citation statements)

References 7 publications

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“…Technetium, reduced by hydrazine to Tc(IV), forms the hydroxo compound TcOs.nHzO. The solubility of Tc(IV) hydrous oxide in alkaline solution increases from loq7 M in 0.01 M NaOH to 3x105 M in 4.0 M NaOH Eriksen et al 1992). As shown in Section 3.3.1, solid sodium uranate in alkaline suspension is partially reduced by hydrazine in the presence of technetium to form U308-nH20 or U02-nH20.…”

Section: Coprecipitation Of Tc(vi1) With Sodium Uranate In 05 To 40mentioning

confidence: 96%

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Purification of alkaline solutions and wastes from actinides and technetium by coprecipitation with some carriers using the method of appearing reagents: Final Report

Peretrukhin¹,

Silin²,

Kareta³

et al. 1998

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The coprecipitation of transuranium elements and technetium from alkaline solutions and from simulants of Hanford Site tank wastes has been studied in reducing and oxidizing conditions on uranium(IV,vT) hydroxocompounds, tetraakylammonium perrhenate and perchlorate, and on hydroxides of Fe(m), Co(III), Mn(II), and C r o using the Method of Appearing Reagents (MAR). Coprecipitations in alkaline solution have been shown to give high decontamination factors (DF) at low content of carrier and in the presence of high salt concentrations.Uranium(IV) hydroxide in concentrations higher than 3~1 0 -~ M coprecipitates Pu and Cm in any oxidation state from 0.2 to 4 M NaOH with DFs of 110 to lo00 and Np and Tc with DFs of 51 to 176. UraniumCvI), introduced as a sodium uranate precipitate or the soluble peroxocomplex salt NaUO2(02)3, can be partially reduced in 0.2 to 2 M NaOH by hydrazine to U30~.nH20 in the presence of (1 to 5 )~1 0 -~ M Tc(VII). The Tc(VlI) is first reduced to Tc(IV). The product U308.nH20, at 0.012 to 0.05 M uranium, coprecipitates Np, Pu, Cm, and Tc in any oxidation state with DFs greater than 100 from 0.2 to 1.5 M NaOH. Increasing alkali concentration to 4 M NaOH decreases the DFs slightly for TRU and drastically for Tc. Coprecipitation under the same conditions from simulated tank waste containing 3.2 M NaOH, 0.04 M C1-05-and 11 complex-forming salts yields the following DFs: Np-12, Pu-27, Cm-35, Tc-3. The decrease of DFs in the waste simulant is associated with complex formation and with inhibition of Np and Tc coprecipitation by the Cr(m) hydroxide that is formed before Np(IV) and Tc(IV). Coprecipitated Tc may be effectively leached from U30p-nH20 by oxidation of Tc(IV) to Tc(VII) by use of dilute H202 or by NaOH solution and air bubbling. Under these same conditions, more than 99% of the Pu is retained in the solid phase. iii

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Section: Coprecipitation Of Tc(vi1) With Sodium Uranate In 05 To 40mentioning

confidence: 96%

“…Technetium(VII) and transuranic elements in higher oxidation states are known to be reduced by hydrazine to give poorly soluble hydrous oxides of the type MOznH20 (Eriksen et al 1992;Peretrukhin et al 1996Peretrukhin et al , 1997.…”

Section: Coprecipitation Of Tc(vii) Pu(vi) Np(v) and Cm(1ii) With mentioning

confidence: 99%

Purification of alkaline solutions and wastes from actinides and technetium by coprecipitation with some carriers using the method of appearing reagents: Final Report

Peretrukhin¹,

Silin²,

Kareta³

et al. 1998

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“…nH20 hydroxide in pH 7 to 10 solution in the absence of oxidants and complexing agents is lo-' to 10-*M. 'The solubility increases significantly with increasing pH (Eriksen et al 1992). In 1.0 to 3.6 M NaOH containing 0.02 M N2H4 and in the presence of air, the solubility of TcO,.…”

Section: Precipitation and Copreciipitationmentioning

confidence: 96%

“…In acid and in the absence of oxidants, nitrate, and nitrite, the reduction of technetium to TcO,. nH20 and further to 2.2 metal is possible (Spitsyn and Kuzina 1981;Eriksen et al 1992). The reduction of Tc(VII) to Tc(IV) and the subsequent electrodeposition of TcO,.…”

Section: Electrodepositionmentioning

confidence: 99%

Decontamination of alkaline solution from technetium and other fission products and from some actinides by reductive coprecipitation and sorption on metals

Peretrukhin¹,

Silin²,

Тананаев³

et al. 1997

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SummaryEffective decontamination of alkaline solutions and Hanford Site tank waste simulants from technetium has been accomplished by reductive coprecipitation with iron(II1) hydroxide. Addition of 1 M (NH4),Fe(S04), to 0.5 to 4.0 M NaOH to a final concentration of 0.1 to 0.15 M coprecipitates more than 99% of the technetium from 0.5 to 1.0 &j NaOH and 98 to 96% from 2.0 to 4.0 M NaOH. Similar results were obtained by reduction of Tc(VII) with 0.1 to 0.15 &j hydrazine and subsequent addition of FeCI, to a final concentration of 0.15 M. Inclusion of four complex-fonning agents rO.01 &j phosphate, 0.1 M EDTA (ethylenediaminetetraacetate), 0.03 M citrate, and 0.1 M glycolate (HOCH,CO;)] to the alkaline solution decreases technetium coprecipitation with iron hydroxide to 85% under otherwise similar conditions. Inclusion of 0.04 M NqCrO, drastically decreases reductive coprecipitation of Tc(VII) in 0.5 to 4.0 M NaOH. Iron(I1) salt, added to a 0.07 M excess over that of chromate, completely reduces chromate and provides greater than 99% coprecipitation of technetium with product iron(II1) and chromium(II1) hydroxides. Technetium(VI1) reduction by hydrazine is slow in the presence of chromate in alkaline solution, and technetium coprecipitation is incomplete in these conditions. Decontamination of an alkaline Hanford Site tank waste simulant, containing 0.04 &j chromate and eleven salts and complex-forming agents, by adding 1 M iron(I1) salt solution was studied.Coprecipitation of 15 to 28% of the technetium and more than 99% of the plutonium occurred in the Fe/Cr(III) hydroxide precipitate produced by adding 0.05 to 0.10 _M iron@). Chromate reduction was incomplete. About 75% of the technetium was coprecipitated, and the chromate was completely reduced, after adding 0.2 _M iron@) salt.Technetium(VI1) capture from 0.5 to 4.0 M NaOH was insignificant or incomplete on coprecipitation carriers Pe(OH),, Cr(OH),, Mn(OH),, Co(OH),, Co(OH),J obtained by the Method of Appearing Reagents under conditions providing complete capture of Np(V) and Pu(V1). Under the same conditions, cesium-137 capture is insignificant and strontium-90 capture is incomplete with these metal hydroxide carriers. Sodium diuranate coprecipitation from 0.5 to 4 M NaOH removed about 15 to 60? -of the technetium; sodium uranate coprecipitation removed 98 to 99% of the 90Sr, and 1 to 12% of the l3'CS.Reductive sorption of Tc(VI1) on metals (Zn, Cry Sn, and two Pb alloys) from 0.5 to 4 M NaOH and from alkaline waste simulant provided poor decontamination of these solutions. In contrast, greater than 98% of the plutonium(V1) was sorbed on chromium from 0.5 M NaOH at a surface area to volume ratio of 1.6 cm-'.

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“…In carbonate-containing groundwaters, TcO(OH) 2(aq) is dominant at neutral pH; at higher pH values, Tc(OH) 3 CO 3 -is more abundant (Erikson et al, 1992). However, the solubility of Tc(IV) is low and is limited by precipitation of the hydrous oxide, TcO 2 x nH 2 O.…”

Section: Tcmentioning

confidence: 99%

Environmental Geochemistry of Radioactive Contamination

Siegel

Bryan

2003

Treatise on Geochemistry

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This report attempts to describe the geochemical foundations of the behavior of radionuclides in the environment. The information is obtained and applied in three interacting spheres of inquiry and analysis: 1) experimental studies and theoretical calculations, 2) field studies of contaminated and natural analog sites and 3) model predictions of radionuclide behavior in remediation and waste disposal. Analyses of the risks from radioactive contamination require estimation of the rates of release and dispersion of the radionuclides through potential exposure pathways. These processes are controlled by solubility, speciation, sorption, and colloidal transport, which are strong functions of the compositions of the groundwater and geomedia as well as the atomic structure of the radionuclides.The chemistry of the fission products is relatively simple compared to the actinides. Because of their relatively short half-lives, fission products account for a large fraction of the radioactivity in nuclear waste for the first several hundred years but do not represent a long-term hazard in the environment. The chemistry of the longer-lived actinides is complex; however, some trends in their behavior can be described. Actinide elements of a given oxidation state have either similar or systematically varying chemical properties due to similarities in ionic size, coordination number, valence, and electron structure. In dilute aqueous systems at neutral to basic pH, the dominant actinide species are hydroxy-and carbonato-complexes, and the solubility-limiting solid phases are commonly oxides, hydroxides or carbonates. In general, actinide sorption will decrease in the presence of ligands that complex with the radionuclide; sorption of the (IV) species of actinides (Np, Pu, U) is generally greater than of the (V) species.The geochemistry of key radionuclides in three different environments is described in this report. These include: 1) low ionic strength reducing waters from crystalline rocks at nuclear waste research 4 sites in Sweden; 2) oxic water from the J-13 well at Yucca Mountain, Nevada, the site of a proposed repository for high level nuclear waste (HLW) in tuffaceous rocks; and 3) reference brines associated with the Waste Isolation Pilot Plant (WIPP). The transport behaviors of radionuclides associated with the Chernobyl reactor accident and the Oklo Natural Reactor are described. These examples span wide temporal and spatial scales and include the rapid geochemical and physical processes important to nuclear reactor accidents or industrial discharges as well as the slower processes important to the geologic disposal of nuclear waste.Application of geochemical information to remediating or assessing the risk posed by radioactive contamination is the final subject of this report. After radioactive source terms have been removed, large volumes of soil and water with low but potentially hazardous levels of contamination may remain. For poorly-sorbing radionuclides, capture of contaminated water and removal of radi...

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The Solubility of TcO₂ · nH₂O in Neutral to Alkaline Solutions under Constant pco₂

Cited by 65 publications

References 7 publications

Purification of alkaline solutions and wastes from actinides and technetium by coprecipitation with some carriers using the method of appearing reagents: Final Report

Purification of alkaline solutions and wastes from actinides and technetium by coprecipitation with some carriers using the method of appearing reagents: Final Report

Decontamination of alkaline solution from technetium and other fission products and from some actinides by reductive coprecipitation and sorption on metals

Environmental Geochemistry of Radioactive Contamination

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