Thermodynamic characterization of boltwoodite and uranophane: Enthalpy of formation and aqueous solubility

Shvareva, Tatiana Y.; Mazeina, Lena; Gorman‐Lewis, Drew; Burns, Peter C.; Szymanowski, Jennifer E. S.; Fein, Jeremy B.; Navrotsky, Alexandra

doi:10.1016/j.gca.2011.06.041

Cited by 38 publications

(24 citation statements)

References 41 publications

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“…The uranium ore minerals found using SEM-and TEM-EDS analyses are a mixture of the calcium uranyl silicate, uranophane, Ca(H3O)2(UO2)2(SiO4)2 · 3H2O and becquerelite Ca(UO2)6O4(OH)6·8(H2O), mixed with illite clay minerals. Becquerelite and uranophane are both secondary minerals formed from the oxidation of uraninite and are commonly found together (Shvareva et al, 2011). Results from automated mineralogy analyses (Fig.…”

Section: Ore Mineralogy At Lost Creekmentioning

confidence: 99%

“…Multiple studies on the alteration of uraninite to form secondary minerals have been conducted (Finch & Ewing, 1992;Shvareva et al, 2011;Wronkiewicz et al, 1992;Perez, 2000). Under oxidizing conditions, the surface of uraninite is host to uranyl silicates (Finch & Ewing, 1992).…”

Section: Differences In Ore Mineralogy At the Lost Creek Project And mentioning

confidence: 99%

“…Under oxidizing conditions, the surface of uraninite is host to uranyl silicates (Finch & Ewing, 1992). However, the direct precipitation of uranyl silicates requires a high concentration of Si in solution (Shvareva et al, 2011;Figs. 2.20 and 2.21).…”

Section: Differences In Ore Mineralogy At the Lost Creek Project And mentioning

confidence: 99%

“…With low to moderate Si in solution, the mixed precipitation of two uranyl hydroxides occurs: schoepite (UO2)8O2(OH)12(H2O)12 and metaschoepite UO3(H2O)2. The precipitation of these minerals is then followed by the dehydration and structural rearrangement forming dehydrated schoepite, calculated at approximately UO3· 0.8H2O (Finch & Ewing, 1992 Shvareva et al, 2011).…”

Section: Differences In Ore Mineralogy At the Lost Creek Project And mentioning

confidence: 99%

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Residence of Uranium in Roll-Front Deposits: A Case Study

Wyatt¹

2016

Geological Society of America Abstracts With Programs

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Despite generally low uranium grades, roll-front uranium deposits are attractive exploration targets as these deposits are amenable to in-situ leaching (ISL) techniques. At the Lost Creek Project, a currently operating uranium mine in Wyoming, head grades were five times higher than pre-operational estimates. Similar mines, such as the Crow Butte mine in Nebraska, have experienced head grades that are in good agreement with pre-operational estimates. Ore samples from the Lost Creek Project and the Three Crow Expansion Area, a satellite deposit to the Crow Butte mine, were analyzed in order to understand their mineralogy and to understand the discrepancy between head grades and pre-operational estimates at the Lost Creek Project.Fission track mapping, quantitative trace element mapping of selected areas using EPMA and high-resolution BSE imaging revealed that the uranium phases at the Lost Creek Project are contained in small (<1 µm) wispy phases. Using SEM and TEM techniques, the U bearing phases were identified as a fine intergrowth of kaolinite with becquerelite (Ca(UO2)6O4(OH)6·8(H2O)) and uranophane (Ca(H3O)2(UO2)2(SiO4)2·3H2O). Initial head grades at Lost Creek of 211 ppm are in good agreement with solubility experiments for highly soluble becquerelite (250 ppm), whereas uranophane solubility peaks at 75 ppm in a bicarbonate concentration of 2.0x10 -2 mol/L, which is in good agreement with bicarbonate concentrations used at the Lost Creek Project and with current head grades of 42 ppm. The large discrepancy of estimates and initial head grades at the Lost Creek Project is partly due to the different gamma ray intensity of uranophane versus primary U ore minerals usually found in U roll-front deposits.Uranophane has a gamma ray response of almost half of both uraninite and coffinite leading to an underestimated resource estimate. Moreover, the mobile nature of the U 6+ ion allowed uranium mineralization of secondary minerals to occur away from the primary ore zone leading to a less well defined, larger ore zone.Ore mineralogy at the Three Crow Expansion area was identified to be primarily coffinite (U(SiO4)1−x(OH)4x) and is in good agreement with previous work and the ore mineralogy at the Crow Butte mine. In contrast, the Lost Creek Project is highly oxidized and primary U ore minerals have been replaced by secondary becquerelite and uranophane.iv

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Section: Ore Mineralogy At Lost Creekmentioning

confidence: 99%

Section: Differences In Ore Mineralogy At the Lost Creek Project And mentioning

confidence: 99%

Section: Differences In Ore Mineralogy At the Lost Creek Project And mentioning

confidence: 99%

Section: Differences In Ore Mineralogy At the Lost Creek Project And mentioning

confidence: 99%

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Residence of Uranium in Roll-Front Deposits: A Case Study

Wyatt¹

2016

Geological Society of America Abstracts With Programs

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“…The code PHREEQC (USGS, Version 2) was applied for modeling calculations and most of the thermodynamic data used were from the WATEQ4f database. Additions to the database were made on the basis of published studies (Guillamont, 2003;Dong and Brooks, 2006;Meinrath and Kimura, 1993; DOE/SC0001389 Final technical report: Investigation of uranium attenuation and release at column and pore scales in response to advective geochemical gradients 4 O' Brien and Williams, 1993;Alwan and Williams, 1980;Gorman-Lewis et al, 2008;Gorman-Lewis et al, 2009;Shvareva et al, 2011;Singh, 2010; , and additional data to describe surface complexation was from Korichi et al (2009), Prikryl et al (2001), and Cheng et al (2004. Some of the information used was compiled by Dr. Masa Kanematsu at the University of California, Merced.…”

Section: Geochemical Modelsmentioning

confidence: 99%

DOE/SC0001389 Final technical report: Investigation of uranium attenuation and release at column and pore scales in response to advective geochemical gradients

Savage¹,

Zhu²,

Barnett³

2013

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Experimental approachColumn experiments were devised to investigate the role of changing fluid composition on mobility of uranium through a sequence of geologic media. Fluids and media were chosen to be relevant to the ground water plume emanating from the former S-3 ponds at the Oak Ridge Integrated Field Research Challenge (ORIFC) site. Synthetic ground waters were pumped upwards at 0.05 mL/minute for 21 days through layers of quartz sand alternating with layers of uncontaminated soil, quartz sand mixed with illite, quartz sand coated with iron oxides, and another soil layer. Increases in pH or concentration of phosphate, bicarbonate, or acetate were imposed on the influent solutions after each 7 pore volumes while uranium (as uranyl) remained constant at 0.1mM. A control column maintained the original synthetic groundwater composition with 0.1mM U. Pore water solutions were extracted to assess U retention and release in relation to the advective ligand or pH gradients. Following the column experiments, subsamples from each layer were characterized using microbeam X-ray absorption spectroscopy (XANES) in conjunction with X-ray fluorescence mapping and compared to sediment core samples from the ORIFC, at SSRL Beam Line 2-3. ResultsU retention of 55 -67 mg occurred in phosphate >pH >control >acetate >carbonate columns. The mass of U retained in the firstencountered quartz layer in all columns was highest and increased throughout the experiment. The rate of increase in acetate-and bicarbonate-bearing columns declined after ligand concentrations were raised. U also accumulated in the first soil layer; the pH-varied column retained most, followed by the increasing-bicarbonate column. The mass of U retained in the upper layers was far lower.Speciation of U, interpreted from microbeam XANES spectra and XRF maps, varied within and among the columns. Evidence of minor reduction to U(IV) was observed in the first-encountered quartz layer in the phosphate, bicarbonate, and pH columns while only U(VI) was observed in the control and acetate columns. In the soil layer, the acetate and bicarbonate columns both indicate minor reduction to U(IV), but U(VI) predominated in all columns. In the ORIFC soils, U was consistently present as U(VI); sorption appears to be the main mechanism of association for U present with Fe and/or Mn, while U occurring with P appears in discrete particles consistent with a U mineral phase. U in soil locations with no other elemental associations shown by XRF are likely uranium oxide phases.

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