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RISS 인기검색어
- 검색키워드
- 저자 : Qafoku, Nikolla P. (검색결과 2 건)
- 무료
- 기관 내 무료
- 유료
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Cr(OH)<sub>3</sub>(s) Oxidation Induced by Surface Catalyzed Mn(II) Oxidation
Namgung, Seonyi,Kwon, Man Jae,Qafoku, Nikolla P.,Lee, Giehyeon American Chemical Society 2014 Environmental science & technology Vol.48 No.18
<P>We examined the feasibility of Cr(OH)<SUB>3</SUB>(s) oxidation mediated by surface catalyzed Mn(II) oxidation under common groundwater pH conditions as a potential pathway of natural Cr(VI) contaminations. Dissolved Mn(II) (50 μM) was reacted with or without synthesized Cr(OH)<SUB>3</SUB>(s) (1.0 g/L) at pH 7.0–9.0 under oxic or anoxic conditions. Homogeneous Mn(II) oxidation by dissolved O<SUB>2</SUB> was not observed at pH ≤ 8.0 for 50 days. At pH 9.0, by contrast, dissolved Mn(II) was completely removed within 8 days and precipitated as hausmannite. When Cr(OH)<SUB>3</SUB>(s) was present, this solid was oxidized and released substantial amounts of Cr(VI) as dissolved Mn(II) was added into the suspension at pH ≥ 8.0 under oxic conditions. Production of Cr(VI) was attributed to Cr(OH)<SUB>3</SUB>(s) oxidation by a newly formed Mn oxide via Mn(II) oxidation catalyzed on Cr(OH)<SUB>3</SUB>(s) surface. XANES results indicated that this surface-catalyzed Mn(II) oxidation produced a mixed valence Mn(III/IV) solid phase. Our results suggest that toxic Cr(VI) can be naturally produced via Cr(OH)<SUB>3</SUB>(s) oxidation coupled with the oxidation of dissolved Mn(II). In addition, this study evokes the potential environmental hazard of sparingly soluble Cr(OH)<SUB>3</SUB>(s), which has been considered the most common and a stable remediation product of Cr(VI) contamination.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/esthag/2014/esthag.2014.48.issue-18/es503018u/production/images/medium/es-2014-03018u_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/es503018u'>ACS Electronic Supporting Info</A></P>
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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>
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