Actinide Carbonte Complexes and Their Importance in Actinide Environmental Chemistry

Clark, David L.; Hobart, David E.; Neu, Mary P.

doi:10.1021/cr00033a002

Cited by 510 publications

(556 citation statements)

References 55 publications

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“…Uranium speciation is important in the safety assessment of nuclear waste repositories to predict actinide migration from such sites [24]. According to Clark et al [25], actinide elements released to the environment will eventually come into contact with water, containing phosphate and/or hydrogen phosphate anions which are exceptionally strong complexing agents for actinide ions inclusive uranyl, (UO 2 )…”

mentioning

confidence: 99%

Erratum to Thermal decomposition of sabugalite

Frost

Kristóf

Martens

et al. 2006

J Therm Anal Calorim

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IntroductionLayered uranyl phosphates and arsenates known as autunites or formerly as uranyl micas form one of the largest and most widespread groups of uranium minerals [1]. Many of these minerals may be found in quite widespread parts of Australia [2]. The minerals have a general formula M(UO 2 ) 2 (XO 4 ) 2 ⋅8-12H 2 O where M may be Ba, Ca, Cu, Fe 2+ , Mg, Mn 2+ or 1/2(HAl) and X is As, or P. In this mineral group there are also minerals based upon univalent cations. These include metaankoleite (K), uramphite (NH 4 ), and sodiumuranospinite (Na). Autunites are common minerals, yet have been not often studied in terms of recent thermal analysis techniques or vibrational spectroscopy [3,5,[7][8][9]. The minerals have a layer-like structure [5,10,11]. The minerals lend themselves to thermal analysis because of the low temperatures for the dehydration steps. A characteristic feature of the minerals is their layer structure in which uranium is bound in uranyl phosphate or uranyl arsenate layers. The cations and water are located in the interlayer space. Sabugalite has the formula HAl(UO 2 ) 4 the crystal structure of sabugalite has not been determined. The reason for this is that the energy of the X-ray beam causes the decomposition and partial dehydration of the sabugalite. Thus thermal analysis may provide information on the structure of sabugalite which may not be obtained by single crystal X-ray diffraction procedures. Structural information on different minerals has successfully been obtained recently by sophisticated thermal analysis techniques [12][13][14][15][16][17].Sabugalite was described as having endotherms in the DTA patterns at 191, 244 and 320°C with a broad endotherm in the 380 to 450°C temperature range [3,18]. Thermogravimetry gave mass losses due to dehydration of 9 moles at 150°C, 4.5 moles between 150 and 270°C and 3 moles in the 270 to 440°C temperature range. ejka reported that the anhydrous (dehydrated) sabugalite phase decomposed with loss of oxygen and the resulting phase depended upon the temperature [8]. Ambartsumyan et al. reported dehydration at 100°C (7 moles of water), 200°C (4.5 moles of water) and 300°C (4.5 moles of water) [19]. Vochten and Pelsmaekers reported three endotherms in the DSC curve of synthetic sabugalite at 50, 120 and 175°C corresponding to the water loss of 4 moles at 65°C, 7 moles between 65 and 126°C and 5 moles The mineral sabugalite (HAl) 0.5 [(UO 2 ) 2 (PO 4 )] 2 ⋅8H 2 O, has been studied using a combination of energy dispersive X-ray analysis, X-ray diffraction, dynamic and controlled rate thermal analysis techniques. X-ray diffraction shows that the starting material in the thermal decomposition is sabugalite and the product of the thermal treatment is a mixture of aluminium and uranyl phosphates. Four mass loss steps are observed for the dehydration of sabugalite at 48°C (temperature range 39 to 59°C), 84°C (temperature range 59 to 109°C), 127°C (temperature range 109 to 165°C) and around 270°C (temperature range 175 to 525°C) with mass losses of 2....

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confidence: 99%

Erratum to Thermal decomposition of sabugalite

Frost

Kristóf

Martens

et al. 2006

J Therm Anal Calorim

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“…Three scans were averaged and plotted in Figures 6, 7a and 7b showing the XANES, 3 -weighted EXAFS and their corresponding FT spectra, respectively. The XAFS spectrum of UO 2+ 2 before the electrolysis, shown in curve 1 of Figure 6, agreed with that in HCl as shown in curve 1 of Figure 3.…”

Section: In Nitric Acidmentioning

confidence: 99%

“…Detailed information about the local structure around the atoms of a specific element can be obtained from X-ray absorption fine structure (XAFS). Numerous XAFS studies of the coordination structure of uranium complexes have been conducted and reviewed [2][3][4][5][6][7]. The technique enables the identification of the valence states of uranium during the redox reactions from the X-ray absorption near-edge structure (XANES [8][9][10][11][12][13].…”

Section: Introductionmentioning

confidence: 99%

An in-situ X-ray absorption spectroelectrochemical study of the electroreduction of uranium ions in HCl, HNO₃, and Na₂CO₃ solutions

et al. 2015

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“…The formation of UO 2 OH + is of secondary importance to UO 2 2+ at pH ≤ 5. An important complexing agent for U in oxic fresh surface waters is carbonate [72]. For fresh surface waters (0.3 µg U l -1 ) with low hardness and alkalinity (<40 mg CaCO 3 l -1 ) and very low natural DOM (<0.5 mg C l -1 ), UO 2 CO 3 is calculated to be the most dominant uranyl species from pH 5.5 to 6 (Fig.…”

Section: Speciation Freshwatermentioning

confidence: 99%

Uranium Speciation and Bioavailability in Aquatic Systems: An Overview

Markich

2002

The Scientific World JOURNAL

201

142

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The speciation of uranium (U) in relation to its bioavailability is reviewed for surface waters (fresh-and seawater) and their sediments. A summary of available analytical and modeling techniques for determining U speciation is also presented. U(VI) is the major form of U in oxic surface waters, while U(IV) is the major form in anoxic waters. The bioavailability of U (i.e., its ability to bind to or traverse the cell surface of an organism) is dependent on its speciation, or physicochemical form. U occurs in surface waters in a variety of physicochemical forms, including the free metal ion (U 4+ or UO 2 2+ ) and complexes with inorganic ligands (e.g., uranyl carbonate or uranyl phosphate), and humic substances (HS) (e.g., uranyl fulvate) in dissolved, colloidal, and/or particulate forms. Although the relationship between U speciation and bioavailability is complex, there is reasonable evidence to indicate that UO 2 2+ and UO 2 OH + are the major forms of U(VI) available to organisms, rather than U in strong complexes (e.g., uranyl fulvate) or adsorbed to colloidal and/or particulate matter. U(VI) complexes with inorganic ligands (e.g., carbonate or phosphate) and HS apparently reduce the bioavailability of U by reducing the activity of UO 2 2+ and UO 2 OH + . The majority of studies have used the results from thermodynamic speciation modeling to support these conclusions. Time-resolved laser-induced fluorescence spectroscopy is the only analytical technique able to directly determine specific U species, but is limited in use to freshwaters of low pH and ionic strength. Nearly all of the available information relating the speciation of U to its bioavailability has been derived using simple, chemically defined experimental freshwaters, rather than natural waters. No data are available for estuarine or seawater. Furthermore, there are no available data on the relationship between U speciation and bioavailability in sediments. An understanding of this relationship has been hindered due to the lack of direct quantitative U speciation techniques for particulate phases. More robust analytical techniques for determining the speciation of U in natural surface waters are needed before the relationship between U speciation and bioavailability can be clarified.

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Actinide Carbonte Complexes and Their Importance in Actinide Environmental Chemistry

Cited by 510 publications

References 55 publications

Erratum to Thermal decomposition of sabugalite

Erratum to Thermal decomposition of sabugalite

An in-situ X-ray absorption spectroelectrochemical study of the electroreduction of uranium ions in HCl, HNO₃, and Na₂CO₃ solutions

Uranium Speciation and Bioavailability in Aquatic Systems: An Overview

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Actinide Carbonte Complexes and Their Importance in Actinide Environmental Chemistry

Cited by 510 publications

References 55 publications

Erratum to Thermal decomposition of sabugalite

Erratum to Thermal decomposition of sabugalite

An in-situ X-ray absorption spectroelectrochemical study of the electroreduction of uranium ions in HCl, HNO3, and Na2CO3 solutions

Uranium Speciation and Bioavailability in Aquatic Systems: An Overview

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An in-situ X-ray absorption spectroelectrochemical study of the electroreduction of uranium ions in HCl, HNO₃, and Na₂CO₃ solutions