Mixed Ca2+/UO2
 2+/CO3
 2- complex formation at different ionic strengths

Калмыков, С. Н.; Choppin, Gregory R.

doi:10.1524/ract.2000.88.9-11.603

Cited by 149 publications

(106 citation statements)

References 4 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 )…”

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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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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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Erratum to Thermal decomposition of sabugalite

Frost

Kristóf

Martens

et al. 2006

J Therm Anal Calorim

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“…For example, Gudavalli et al (2013) showed that during dissolution of Na-and Ca-autunite, buffered bicarbonate solutions were undersaturated thermodynamically with respect to becquerelite, and uranyl carbonate and Ca-uranyl carbonate complexes were the predominant aqueous species, which were postulated to control mineral dissolution. Uranyl carbonate and alkaline-earth uranyl carbonate complexes are highly soluble and stable species that dominate the uranyl aqueous speciation between pH 7 and 11 (Bernhard et al, 1996;Kalmykov and Choppin, 2000;Bernhard et al, 2001) and also uranyl adsorption onto sediment and soils (Stewart et al, 2010). Indeed, breakthrough of U(VI) was noticeably retarded by sorption to quartz in control columns with low carbonate BPW compared to high carbonate BPW systems (Control 2, Fig.…”

Section: Effect Of Dissolved Carbonate On Dissolution Mechanismmentioning

confidence: 98%

Rates and mechanisms of uranyl oxyhydroxide mineral dissolution

Reinoso-Maset

Steefel

et al. 2017

Geochimica et Cosmochimica Acta

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“…Oxidation states of U within the soil were measured within columns (days 117 and 356) by synchrotron micro-X-ray absorption near edge structure (µ-XANES) spectroscopy 15 . In order to determine the aqueous uranyl species within column effluents, fluorescence spectroscopic and lifetime measurements were conducted 5,16 . Bacterial community dynamics during U-reduction and reoxidation processes were monitored by using both terminal restriction fragment length polymorphism (TRFLP) and high density oligonucleotide array 17 analyses.…”

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“…Calcium from calcite dissolution is effective in releasing U(VI) into solution through formation of Ca 2 UO 2 (CO 3 ) 3 complexes at near-neutral pH 5,16 (Eqs 4-5 in Table 3), which are much less susceptible to bioreduction 20 and sorption 21 . Although the magnitude of Ca 2 UO 2 (CO 3 ) 3 stability is currently unsettled 22 , it is acknowledged that neutral uranyl carbonate complexes with cations are important, and that the reported equilibrium constants 5,16 are useful for guidance. Dissolved Ca concentrations in column effluents were about 1 mM, indicative of equilibrium with calcite.…”

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confidence: 99%