Kinetics of uranium release from Synroc phases

Zhang, Y; Hart, K.P.; Bourcier, William L.; Day, R. A.; Colella, Michael; Thomas, B.S.; Aly, Zaynab; Jostsons, A.

doi:10.1016/s0022-3115(01)00423-8

Cited by 59 publications

(56 citation statements)

References 13 publications

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“…Therefore, important properties like the critical amorphization dose [18,36,[44][45][46] and the leaching behavior [18,[47][48][49][50][51][52][53] have been studied in detail. To obtain better understanding of the behavior of pyrochlore under extreme conditions, combined swift heavy-ion irradiation and high-pressure studies have been performed (see [54]).…”

Section: Hementioning

confidence: 99%

Thermal annealing of natural, radiation-damaged pyrochlore

Zietlow

Beirau

Mihailova

et al. 2016

Zeitschrift Für Kristallographie - Crystalline Materials

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Radiation damage in minerals is caused by the α-decay of incorporated radionuclides, such as U and Th and their decay products. The effect of thermal annealing (400-1000 K) on radiation-damaged pyrochlores has been investigated by Raman scattering, X-ray powder diffraction (XRD), and combined differential scanning calorimetry/thermogravimetry (DSC/TG). The analysis of three natural radiation-damaged pyrochlore samples from Miass/Russia [6.4 wt% Th, 23.1 · 10 18 α-decay events per gram (dpg)], Panda Hill/Tanzania (1.6 wt% Th, 1.6 · 10 18 dpg), and Blue River/Canada (10.5 wt% U, 115.4 · 10 18 dpg), are compared with a crystalline reference pyrochlore from Schelingen (Germany). The type of structural recovery depends on the initial degree of radiation damage (Panda Hill 28 %, Blue River 85 % and Miass 100 % according to XRD), as the recrystallization temperature increases with increasing degree of amorphization. Raman spectra indicate reordering on the local scale during annealing-induced recrystallization. As Raman modes around 800 cm −1 are sensitive to radiation damage . The most radiation damaged pyrochlore (Miass) shows an abrupt recovery of both, its short-(Raman) and long-range order (X-ray) between 800 and 850 K, while the weakly damaged pyrochlore (Panda Hill) begins to recover at considerably lower temperatures (near 500 K), extending over a temperature range of ca. 300 K, up to 800 K (Raman). The pyrochlore from Blue River shows in its initial state an amorphous X-ray diffraction pattern superimposed by weak Bragg-maxima that indicates the existence of ordered regions in a damaged matrix. In contrast to the other studied pyrochlores, Raman spectra of the Blue River sample show the appearance of local modes above 560 K between 700 and 800 cm −1 resulting from its high content of U and Ta impurities. DSC measurements confirmed the observed structural recovery upon annealing. While the annealing-induced ordering of Panda Hill begins at a lower temperature (ca. 500 K) the recovery of the highly-damaged pyrochlore from Miass occurs at 800 K. The Blue-River pyrochlore shows a multi-step recovery which is similarly seen by XRD. Thermogravimetry showed a continuous mass loss on heating for all radiation-damaged pyrochlores (Panda Hill ca. 1 %, Blue River ca. 1.5 %, Miass ca. 2.9 %).

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Section: Hementioning

confidence: 99%

Thermal annealing of natural, radiation-damaged pyrochlore

Zietlow

Beirau

Mihailova

et al. 2016

Zeitschrift Für Kristallographie - Crystalline Materials

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“…Fast reactions have small activation energy and those with large activation energy usually progress slowly. Previous studies showed that pH has a pronounced effect on activation energy (Zhang et al, 2001). Bemer (1978) and reported that the activation energy can help identify the rate-controlling process of dissolution: activation energy values lower than 20 kJ mol ) were reported by various authors for alkaline earth fluorides whose dissolution rates are believed to be surface controlled.…”

Section: Estimation Of Thermodynamic Parameters (Activation Energy Ofsupporting

confidence: 82%

“…The activation energy observed at pH 6 and 7 also suggests that the dissolution process is surface controlled; whereas at higher pH values, the transfer of uranium may be due to adsorption or ion exchange. The calculated activation energies are in good agreement with that reported in the literature for similar materials (Zhang et al, 2001. We next examined the relationship between the pseudo equilibrium constant, K g , and the temperature to estimate the enthalpy of the system:…”

Section: Estimation Of Thermodynamic Parameters (Activation Energy Ofmentioning

confidence: 99%

“…E a is independent of temperature and concentrations; however, E a has exhibited pronounced pH dependence (Zhang et al, 2001). The activation energy can help to explain the rate-controlling process.…”

Section: Estimation Of Thermodynamic Parameters (Activation Energy Ofmentioning

confidence: 99%

“…The effect of bicarbonate ions in the wide range of pH and temperature variations on the activation energy of the dissolution reactions of uranyl-phosphate minerals has not been studied before. The previous studies on uranium-bearing materials suggested a surface controlled dissolution mechanism for estimated activation energies ranging between 12 -60 kJmol -1 (Scott et al, 1977;Zhang et al, 2001;Pablo et al, 1999). …”

Section: Estimation Of Thermodynamic Parameters (Activation Energy Ofmentioning

confidence: 99%

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Effect of pH and temperature on the carbonate promoted dissolution of sodium meta-autunite

Gudavalli¹

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This dissertation, written by Ravi Krishna Prasanth Gudavalli, and entitled, "Effect of pH and temperature on the carbonate promoted dissolution of sodium meta-autunite", having been approved in respect to style and intellectual content, is referred to you for judgment.We have read this dissertation and recommend that it be approved. Release of uranium from Na-autunite, an artificial mineral created as a result of polyphosphate injection in the subsurface at the DOE Hanford Site, takes place during slow dissolution of the mineral structure. Stability information of the uranyl-phosphate phases is limited to conditions involving pH, temperature, and a few aqueous organic materials. The carbonate ion, which creates very strong complexes with uranium, is the predominant ion in the groundwater composition. _______________________________________The polyphosphate technology with the formation of autunite was identified as the most feasible remediation strategy to sequester uranium in contaminated groundwater and soil in situ. The objectives of the experimental work were (i) to quantify the effect of bicarbonate on the stability of synthetic sodium meta-autunite created as a result of uranium stabilization through polyphosphate injection, (ii) calculate the kinetic rate law parameters of the uranium release from Na-autunite during dissolution, and (iii) to compare the process parameters with those obtained for natural calcium meta-autunite.Experiments were conducted using SPTF apparatus, which consists of syringe pumps for

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Ceramic Host Phases for Nuclear Waste Remediation

Lumpkin

2018

Experimental and Theoretical Approaches to Actinide Chemistry

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Kinetics of uranium release from Synroc phases

Cited by 59 publications

References 13 publications

Thermal annealing of natural, radiation-damaged pyrochlore

Thermal annealing of natural, radiation-damaged pyrochlore

Effect of pH and temperature on the carbonate promoted dissolution of sodium meta-autunite

Ceramic Host Phases for Nuclear Waste Remediation

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