Standard Gibbs free energies of formation at the temperature 303.15 K of four uranyl silicates: soddyite, uranophane, sodium boltwoodite, and sodium weeksite

Nguyen, Son; Silva, Robert J.; Weed, H.C.; Andrews, James W.

doi:10.1016/s0021-9614(05)80155-7

Cited by 96 publications

(75 citation statements)

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“…By far the most widely used technique involves the direct reaction between dissolved silica and uranyl ion species. 10,11,12 This normally involves the aging of the reaction mixture for several hours or even days, with pH adjustment in some cases, followed by isothermal treatment of the mixture at temperatures usually between 80 and 150 °C for several days to enhance the crystallographic features of the synthetic mineral. After thermal treatment and solidliquid separation, the material is washed with distilled and deionized (ultrapure) water and dried at room temperature or at higher temperatures depending on the nature of the silicate being synthesized.…”

Section: Literature Reviewmentioning

confidence: 99%

“…Sodium weeksite is also synthesized at moderate pH conditions at temperatures ranging from 100 to 150 ºC. 10 Uranophane is the only uranyl silicate mineral that can be synthesized at a wide range of pH conditions ranging from pH 1 to 13. The synthesis temperatures for uranophane 11 are between 100 and 150 ºC.…”

Section: H 2 O)mentioning

confidence: 99%

“…10,21 XRD characterization of the 8-hour sample shows that the material produced after 8 hours of synthesis is not crystalline (Figure 3 insert A.), while the 37-hour sample is fairly crystalline (Figure 3, insert C). The overlay of IR spectra, Figure 3, insert B, for both the 8 and 37-hour samples also shows that the 37 hour-sample has more IR spectra features, meaning distinct peaks after 1200 cm -1 , compared to the 8-hour sample, which showed broad absorptions, characteristic of amorphous phases.…”

Section: Sodium Weeksitementioning

confidence: 99%

“…These IR spectra for the low Na + synthetic sodium boltwoodites are almost identical to the published IR spectra for synthetic boltwoodite. 10,13,21 The reference Raman 25 spectrum for the sodium boltwoodite obtained in this synthesis was measured with laser light of a wavelength of 785 nm. This Raman spectrum for sodium boltwoodite is similar to the published Raman spectrum for synthetic sodium boltwoodite, 25 although taken at different laser wave length of 1064 nm.…”

Section: Sodium Boltwooditementioning

confidence: 99%

“…The overlayed of IR spectra for the two products are shown in insert D. The IR spectra for the synthetic uranophane made at low Na + is identical to the published IR spectra for synthetic uranophane. 10,26 The IR spectrum of the high Na + product (clarkeite) is almost devoid of any pronounced IR peaks or features at the characteristic IR "finger print" section for uranophane, below 1200 cm -1 . Table 4 shows a summary of the target uranium silicate minerals, the uranium solids produced and the synthesis conditions.…”

Section: Sodium Boltwooditementioning

confidence: 99%

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Conditions Conducive to Forming Crystalline Uranyl Silicates in SRS Evaporators

Oji¹

2004

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SUMMARYThe laboratory conditions (temperature range of 80-150º C, hydrothermal and oxidizing environment, soluble uranium and silica, atmospheric and pH conditions) under which synthetic uranyl silicates are made are almost identical to SRS evaporator conditions, with the exception of differences in sodium ion (Na + ) concentration. Synthetic uranyl silicates have been made only under low Na + concentration (<0.02 M), while attempts to synthesize uranyl silicates in this study in the presence of high Na + concentration (5.6 M), which are typical of SRS evaporators have proved unfruitful.In the presence of soluble silica and uranyl ion, uranyl silicates (sodium weeksite, sodium boltwoodite and uranophane) have been synthesized at moderately low to high pH in temperature ranges of 80-150 ºC and at less than 0.02 M Na + ion concentration in the reaction mixtures. However, in the presence of high Na + concentration the main product distribution for the same soluble silica-uranium reaction mixture shifts towards the formation of clarkeite (Na[(UO 2 )O(OH)](H 2 O) 0-1 ), a hydrated sodium uranate and not towards the formation of uranyl silicates.There is a threshold Na + concentration requirement above which uranyl silicates are not formed under laboratory conditions that are quite similar to SRS evaporator conditions. This threshold Na + concentration, which is yet to be determined, may be influenced by the sodium-to-uranium ratio in a reaction mixture.Therefore, based on the synthesis information presented in this study the following conclusions are made:• Crystalline uranyl silicates are readily formed in the presence of dissolved uranium and silica.• The presence of high Na + concentration in a reaction mixture of dissolved uranium and silica inhibits the formation of crystalline uranyl silicates.• The reaction path way favors the formation of hydrated sodium uranates over the uranyl silicates in a reaction mixture with high Na + concentration.• Crystalline uranyl silicate minerals are not easily produced under SRS evaporator conditions because of high Na + concentration in the evaporators and in the evaporator feed tanks.• The principal uranium minerals which could be produced under evaporator conditions are sodium uranium minerals or clarkeite, which could also exist in the dehydrated form called sodium uranate.

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Section: Literature Reviewmentioning

confidence: 99%

Section: H 2 O)mentioning

confidence: 99%

Section: Sodium Weeksitementioning

confidence: 99%

Section: Sodium Boltwooditementioning

confidence: 99%

Section: Sodium Boltwooditementioning

confidence: 99%

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Conditions Conducive to Forming Crystalline Uranyl Silicates in SRS Evaporators

Oji¹

2004

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Physico-chemical study of heterogeneous equilibria in salt-aqueous systems of inorganic compounds of uranium(VI)

Черноруков

Нипрук

2006

Czech J Phys

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The report presents results obtained in systematic investigation of the physico-chemical state of heterogeneous equilibrium systems of "aqueous solution -precipitate" in the case of the crystalline mineral-like uranium (VI) compounds with the general formula M k (AnUO 2 ) k ⋅nH 2 O, where positions denoted as "An" are occupied by VO 4 3-, PO 4 3-, AsO 4 3-, HSiO 4 3-, or BO 3 3-anions, and M k are alkaline, alkaline earth, and the 3d-transition elements. Chemical stabilities and solubilities of uraniumvanadates, uraniumphosphates, uraniumarsenates, uraniumsilicates, and uraniumborates have been experimentally determined. Detailed quantitative description of the physico-chemical processes and reactions involved in heterogeneous equilibrium in aqueous solutions of the salts by means of equilibrium thermodynamics is presented. The description gives us the possibility to predict the behaviour of the uranium compounds under different conditions and to calculate Gibbs functions of the formation of the compounds studied.

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Physico-chemical study of heterogeneous equilibria in salt-aqueous systems of inorganic compounds of uranium(VI)

Черноруков

Нипрук

2006

Czech J Phys

View full text Add to dashboard Cite

The report presents results obtained in systematic investigation of the physico-chemical state of heterogeneous equilibrium systems of "aqueous solution -precipitate" in the case of the crystalline mineral-like uranium (VI) compounds with the general formula M k (AnUO 2 ) k ⋅nH 2 O, where positions denoted as "An" are occupied by VO 4 3-, PO 4 3-, AsO 4 3-, HSiO 4 3-, or BO 3 3anions, and M k are alkaline, alkaline earth, and the 3d-transition elements. Chemical stabilities and solubilities of uraniumvanadates, uraniumphosphates, uraniumarsenates, uraniumsilicates, and uraniumborates have been experimentally determined. Detailed quantitative description of the physico-chemical processes and reactions involved in heterogeneous equilibrium in aqueous solutions of the salts by means of equilibrium thermodynamics is presented. The description gives us the possibility to predict the behaviour of the uranium compounds under different conditions and to calculate Gibbs functions of the formation of the compounds studied.

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Standard Gibbs free energies of formation at the temperature 303.15 K of four uranyl silicates: soddyite, uranophane, sodium boltwoodite, and sodium weeksite

Cited by 96 publications

References 6 publications

Conditions Conducive to Forming Crystalline Uranyl Silicates in SRS Evaporators

Conditions Conducive to Forming Crystalline Uranyl Silicates in SRS Evaporators

Physico-chemical study of heterogeneous equilibria in salt-aqueous systems of inorganic compounds of uranium(VI)

Physico-chemical study of heterogeneous equilibria in salt-aqueous systems of inorganic compounds of uranium(VI)

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