The kinetics of iodide oxidation by the manganese oxide mineral birnessite

Fox, Patricia; Davis, James A.; Luther, George W.

doi:10.1016/j.gca.2009.02.016

Cited by 66 publications

(64 citation statements)

References 44 publications

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“…It is unlikely that iron oxides will oxidize iodide to iodine or iodate at the alkaline pH values investigated in this study given the lack of oxidation witnessed in our HFO system. Manganese oxides have been shown to oxidize up to 25% of iodide to iodine (Allard et al 2009;Fox et al 2009), however given the small amount of Mn present in our BIOS samples compared to Allard et al (2009), it is an unlikely iodide oxidation mechanism under the geochemical conditions of our study. The sterilization of BIOS eliminates any active bioaccumulation of iodide to explain the sorption capacity of iodide onto BIOS witnessed in this study and the long half life of 129 I (1.57 × 10 7 years) also eliminates radioactive decay as a removal pathway.…”

Section: Discussionmentioning

confidence: 77%

Retention of Iodide by Bacteriogenic Iron Oxides

Kennedy

Gault

Fortin

et al. 2011

Geomicrobiology Journal

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This study was performed to determine the ability of wetland bacteriogenic iron oxides (BIOS) to immobilize iodide in contaminated groundwater systems near Chalk River, Canada. The sorption of iodide onto synthetic hydrous ferric oxide (HFO) and BIOS was investigated using an autotitrator and an I − ion-selective electrode to generate high-resolution anion sorption data over a pH range of 2.5 to 9. The effect of strontium sorption in the presence of I − was also investigated to determine its effect on iodide retention as it is also a common contaminant near Chalk River. Both HFO and BIOS correspond to 2-line ferrihydrite with surface areas of 227.7 m 2 g −1 and 92.52 m 2 g −1 , respectively. Sorption of I − was found to be pH dependent for both HFO and BIOS and was most strongly immobilized at pH 2.5. The pH at which 50% of the I − was bound to HFO occurred at pH 4.0, whereas BIOS maintained 50% sorption to pH 9. Field data also indicated a 54% decrease for iodine and 75% for 129 I in waters passing over in-situ BIOS at circumneutral pH. Iodide sorption to HFO is best explained by homogeneous functional groups, whereas sorption of I − to BIOS is best explained by heterogeneous functional groups, due to the presence of bacterial functional groups with pKa values that extend to 9.0. The presence of Sr 2+ decreased iodide sorption on HFO by 10-20%, but had no effect on BIOS due to its surface functional groups being reactive over the pH range investigated in this study. These results imply that BIOS is a useful sorbent for natural retention of I − from groundwater and that the amount of organic material present in iron oxides is an important factor when considering remediation strategies for radionuclides in groundwater.

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Section: Discussionmentioning

confidence: 77%

Retention of Iodide by Bacteriogenic Iron Oxides

Kennedy

Gault

Fortin

et al. 2011

Geomicrobiology Journal

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“…Metal (Fe, Mn, Al) oxide phases and soil organic matter are both possible oxidising agents. Soil metal oxides have been shown to oxidise iodide in amounts proportional to their concentration, and inversely proportional to pH, in a reaction that is thermodynamically favourable up to pH 7.5 Fox et al, 2009;Gallard et al, 2009). Humic substances, which contain some electron acceptor sites, also act as oxidising agents for iodide (Blodau et al, 2009;Keller et al, 2009).…”

Section: Iodidementioning

confidence: 99%

Iodine dynamics in soils

Shetaya

Young

Watts

et al. 2012

Geochimica et Cosmochimica Acta

135

118

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We investigated changes in iodine ( 129 I) solubility and speciation in nine soils with contrasting properties (pH, Fe/Mn oxides, organic carbon and iodine contents), incubated for nine months at 10 and 20°C. The rate of 129 I sorption was greater in soils with large organic carbon contents (%SOC), low pH and at higher temperatures. Loss of iodide (I À ) from solution was extremely rapid, apparently reaching completion over minutes-hours; iodate (IO À 3 ) loss from solution was slower, typically occurring over hours-days. In all soils an apparently instantaneous sorption reaction was followed by a slower sorption process for IO À 3 . For iodide a faster overall reaction meant that discrimination between the two processes was less clear. Instantaneous sorption of IO À 3 was greater in soils with high Fe/Mn oxide content, low pH and low SOC content, whereas the rate of time-dependent sorption was greatest in soils with higher SOC contents. Phosphate extraction (0.15 M KH 2 PO 4 ) of soils, $100 h after 129 I spike addition, indicated that concentrations of sorbed inorganic iodine ( 129 I) were very low in all soils suggesting that inorganic iodine adsorption onto oxide phases has little impact on the rate of iodine assimilation into humus. Transformation of dissolved inorganic 129 IO À 3 and 129 I À to sorbed organic forms was modelled using a range of reactionand diffusion-based approaches. Irreversible and reversible first order kinetic models, and a spherical diffusion model, adequately described the kinetics of both IO À 3 and I À loss from the soil solution but required inclusion of a distribution coefficient (k d ) to allow for instantaneous adsorption. A spherical diffusion model was also collectively parameterised for all the soils studied by using pH, soil organic carbon concentration and combined Fe + Mn oxide content as determinants of the model parameters (k d and D/r 2 ). The kinetic model parameters were not directly related to a single soil parameter; inclusion of pH, SOC, oxide content and temperature was necessary to describe the observed behaviour. From the temperature-dependence of the sorption data the activation energy (E a ) for 129 IO À 3 transformation to organic forms was estimated to be $43 kJ mol À1 . The E a value was independent of %SOC and was consistent with a reaction mechanism slower than pore diffusion or physical adsorption, but faster than most surface reactions.

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“…In a study conducted to test iodide sorption to different iron minerals, only magnetite showed significant levels of sorption (Fuhrmann et al, 1998). In addition, Mn is implicated in the redox cycling of iodide, with oxidation of iodine to iodate by δMnO 2 and sorption of iodate to δMnO 2 also possible (Aimoz et al, 2012;Allard et al, 2009;Fox et al, 2009). Organic matter has also shown significant uptake of iodide, and soil humus is considered to be a considerable sink for iodine in soil systems (Shetaya et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

Bioreduction of iodate in sediment microcosms

et al. 2015

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Iodine-129 is a high-yield fission product formed in nuclear reactors and is a risk-driving radionuclide in both contaminated land and radioactive waste disposal due to its high mobility and long half-life. Here, the bioreduction behaviour of iodate was investigated by tracking iodine speciation and concentration in solution during the development of progressive anoxia in sediment microcosm experiments incubated at neutral pH. Experiments with acetate added as an electron donor showed the expected cascade of terminal electron-accepting processes. Analysis of solution chemistry showed reduction of iodate to iodide during the early stages of metal (Mn(IV) and Fe(III)) reduction, but with no significant retention of iodine species on solids. There was, however, a net release of natural iodine associated with the sediments to solution when robust iron reduction / sulfate reduction had developed. In addition, over 210 days, the controls with no electron donor and the sterile controls showed no Mn(IV) or Fe(III) reduction but displayed modest sorption of iodate to the sediments in the absence of bioreduction. Overall these results show that under oxic conditions iodate may be partially sorbed to sediments over extended periods but that development of mildly reducing conditions leads to the reductive release of iodine to solution as iodide.

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The kinetics of iodide oxidation by the manganese oxide mineral birnessite

Cited by 66 publications

References 44 publications

Retention of Iodide by Bacteriogenic Iron Oxides

Retention of Iodide by Bacteriogenic Iron Oxides

Iodine dynamics in soils

Bioreduction of iodate in sediment microcosms

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