http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
Enhanced <sup>99</sup>Tc retention in glass waste form using Tc(IV)-incorporated Fe minerals
Um, Wooyong,Luksic, Steven A.,Wang, Guohui,Saslow, Sarah,Kim, Dong-Sang,Schweiger, Michael J.,Soderquist, Chuck Z.,Bowden, Mark E.,Lukens, Wayne W.,Kruger, Albert A. Elsevier 2017 JOURNAL OF NUCLEAR MATERIALS Vol.495 No.-
<P><B>Abstract</B></P> <P>Technetium (<SUP>99</SUP>Tc) immobilization by doping into iron oxide mineral phases may alleviate the problems with Tc volatility during vitrification of nuclear waste. Because reduced Tc, Tc(IV), substitutes for Fe(III) in the crystal structure by a process of Tc reduction from Tc(VII) to Tc(IV) followed by co-precipitation of Fe oxide minerals, two Tc-incorporated Fe minerals (Tc-goethite and Tc-magnetite/maghemite) were prepared and tested for Tc retention in glass melt samples at temperatures between 600 and 1000 °C. After being cooled, the solid glass specimens prepared at different temperatures at 600, 800, and 1000 °C were analyzed for Tc oxidation state using Tc K-edge XANES. In most samples, Tc was partially (<60%) oxidized from Tc(IV) to Tc(VII) as the melt temperature increased up to 600 °C. However, most of Tc(IV) was completely (>95%) oxidized to Tc(VII) at temperature above 800 °C. Tc retention in glass melt samples prepared using Tc-incorporated Fe minerals were slightly higher (∼10%) than in glass prepared using KTcO<SUB>4</SUB> because of limited and delayed Tc volatilization.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Reduced Tc(IV) can be incorporated within an Fe oxide mineral structure. </LI> <LI> Tc-incorporated Fe minerals can increase Tc retention in glass waste forms. </LI> <LI> Increased Tc retention in glass can reduce the cost of waste treatment. </LI> </UL> </P>
Immobilization of 99-Technetium (VII) by Fe(II)-Goethite and Limited Reoxidation
Um, Wooyong,Chang, Hyun-Shik,Icenhower, Jonathan P.,Lukens, Wayne W.,Serne, R. Jeffrey,Qafoku, Nikolla P.,Westsik, Joseph H.,Buck, Edgar C.,Smith, Steven C. American Chemical Society 2011 Environmental science & technology Vol.45 No.11
<P>During the nuclear waste vitrification process volatilized <SUP>99</SUP>Tc will be trapped by melter off-gas scrubbers and then washed out into caustic solutions, and plans are currently being contemplated for the disposal of such secondary waste. Solutions containing pertechnetate [<SUP>99</SUP>Tc(VII)O<SUB>4</SUB><SUP>–</SUP>] were mixed with precipitating goethite and dissolved Fe(II) to determine if an iron (oxy)hydroxide-based waste form can reduce Tc(VII) and isolate Tc(IV) from oxygen. The results of these experiments demonstrate that Fe(II) with goethite efficiently catalyzes the reduction of technetium in deionized water and complex solutions that mimic the chemical composition of caustic waste scrubber media. Identification of the phases, goethite + magnetite, was performed using XRD, SEM and TEM methods. Analyses of the Tc-bearing solid products by XAFS indicate that all of the Tc(VII) was reduced to Tc(IV) and that the latter is incorporated into goethite or magnetite as octahedral Tc(IV). Batch dissolution experiments, conducted under ambient oxidizing conditions for more than 180 days, demonstrated a very limited release of Tc to solution (2–7 μg Tc/g solid). Incorporation of Tc(IV) into the goethite lattice thus provides significant advantages for limiting reoxidation and curtailing release of Tc disposed in nuclear waste repositories.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/esthag/2011/esthag.2011.45.issue-11/es104343p/production/images/medium/es-2010-04343p_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/es104343p'>ACS Electronic Supporting Info</A></P>
Chang, Seeun,Um, Wooyong,Kim, Won-Seok,Kim, HyunJu R OLDENBOURG VERLAG GMBH 2018 RADIOCHIMICA ACTA Vol.106 No.2
<P><B>Abstract</B></P><P>Batch sorption and column experiments were conducted to investigate and compare sorption and transport behavior of<SUP>90</SUP>Sr on the assumption of seawater intrusion at nuclear power plants. Batch sorption experiments were carried out on fractured rocks and bedrocks using synthetic groundwater and seawater both spiked with<SUP>90</SUP>Sr. In general, higher<SUP>90</SUP>Sr sorption occurred on fractured rock samples than on bedrocks, because of the presence of weathered secondary minerals (iron oxide and clay) on fractured rock surfaces. However, one particular bedrock sample (WSP-B) which has higher porosity and carbon amount than fractured rock samples also showed the higher<SUP>90</SUP>Sr sorption than its comparable fractured rocks. For all batch sorption studies,<SUP>90</SUP>Sr sorption distribution coefficient,<I>K</I><SUB>d</SUB>decreased from groundwater to seawater environment due to the higher ionic strength of seawater (6.4×10<SUP>−1</SUP>-7.7×10<SUP>−1</SUP>M) compared to groundwater (4.0×10<SUP>−3</SUP>-6.0×10<SUP>−3</SUP>M). The three different ionic strength solutions were used in column experiments, and the results showed that transport behavior of Sr through a fractured rock had similar sorption trend to batch sorption results. The highest mobility (or least retardation) for Sr was found for 100% seawater solution compared to the highest retardation (or least mobility) for 100% groundwater solution. These sorption and transport data of Sr on solid materials contacted with various ionic strength solutions corroborate empirically defensible information for assessment of radioactive contamination in groundwater below the NPP sites located nearby shores. In addition, the experimental data will be incorporated to improve transport models of<SUP>90</SUP>Sr in the subsurface environment for severe nuclear accidents.</P>
Wang, Guohui,Um, Wooyong,Wang, Zheming,Reinoso-Maset, Estela,Washton, Nancy M.,Mueller, Karl T.,Perdrial, Nicolas,O’Day, Peggy A.,Chorover, Jon American Chemical Society 2017 Environmental science & technology Vol.51 No.19
<P>The reaction of acidic radioactive waste with sediments can induce mineral transformation reactions that, in turn, control contaminant fate. Here, sediment weathering by synthetic uranium containing acid solutions was investigated using bench-scale experiments to simulate waste disposal conditions at Hanford's cribs (Hanford, WA). During acid weathering, the presence of phosphate exerted a strong influence over uranium mineralogy and a rapidly precipitated, crystalline uranium phosphate phase (meta-ankoleite [K(UO2)(PO4).3H(2)O] was identified using spectroscopic and diffraction-based techniques. In phosphate-free system, uranium oxyhydroxide minerals such as K-compreignacite [K-2(UO2)(6)O-4(OH)(6).7H(2)O] were formed. Single-pass flow-through (SPFT) and column leaching experiments using synthetic Hanford pore water showed that uranium precipitated as meta-ankoleite during acid weathering was strongly retained in the sediments, with an average release rate of 2.67 X 10(-12) mol g(-1) s(-1). In the absence of phosphate, uranium release was controlled by dissolution of uranium oxyhydroxide (compreignacitetype) mineral with a release rate of 1.05-2.42 X 10(-1) mol g(-1) s(-1). The uranium mineralogy and release rates determined for both systems in this study support the development of accurate U-release models for the prediction of contaminant transport. These results suggest that phosphate minerals may be a good candidate for uranium remediation approaches at contaminated sites.</P>
Synthesis of Tributyl Phosphate-Coated Hydroxyapatite for Selective Uranium Removal
Kim, HyunJu,Um, Wooyong,Kim, Won-Seok,Chang, Seeun American Chemical Society 2017 INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH - Vol.56 No.12
<P>Efficient and rapid removal of radioactive contaminants is crucial when they are released into the environment following nuclear accidents. Here, different types of apatite were synthesized using tributyl phosphate (TBP) and tested for the removal of uranium from various solutions using different reaction times and uranium concentrations. The uranium adsorption results showed that uranium adsorption reached a steady state within 24 h in tests open to atmosphere at a slightly alkaline pH in different background solutions. TBP-coated hydroxyapatite removed U better than hydroxyapatite alone did. The U removal mechanism was considered as multilayer adsorption, showing the best fit to the Freundlich isotherm. The maximal U adsorption capacity determined from the Langmuir isotherm is 38 mg of U g<SUP>–1</SUP>. Because of the high U removal efficiency, even at the high pH used in this study, TBP-coated hydroxyapatite appears to be a promising adsorbent for the removal of U from various waste streams as well as for recovery of U from seawater.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/iecred/2017/iecred.2017.56.issue-12/acs.iecr.6b04491/production/images/medium/ie-2016-04491f_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ie6b04491'>ACS Electronic Supporting Info</A></P>