Abstract
The solubility of Gd2Ti2O7 ceramic in acidic solutions (HCl and HClO4) was studied at 250°C and saturation vapor pressure within pH 2.5–5.2. The dissolution process occurs mainly via two reactions: 0.5 Gd2Ti2O7(cr) + 3H+ = Gd3+ + TiO2(cr) + 1.5 H2O at pH < 3 and 0.5Gd2Ti2O7(cr) + H+ + 0.5H2O = Gd(OH) +2 TiO2(cr) at pH 3–5. The thermodynamic equilibrium constants were calculated at the 0.95 confidence level as log K o(1) = 4.12 ± 0.47; = −0.97 ± 0.16 at 250°C. It was shown that Gd3+ undergoes hydrolysis in solutions with pH > 3, and the species Gd(OH) +2 dominates up to at least pH 5. At pH < 3, Gd occurs in solutions as Gd3+. The second constant of Gd3+ hydrolysis was determined at 250°C as K o = −5.09 ± 0.5, and the thermodynamic characteristics of the initial Gd2Ti2O7 solid phase were determined: S o298.15 = 251.4 J/(mol K) and ΔfG o298.15 = −3630 ± 10 kJ/mol.
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Original Russian Text © N.D. Shikina, A.V. Zotov, V.A. Volchenkova, 2009, published in Geokhimiya, 2009, No. 4, pp. 393–400.
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Shikina, N.D., Zotov, A.V. & Volchenkova, V.A. The solubility of Gd2Ti2O7 and the hydrolysis of Gd3+ in acidic solutions at 250°C and saturation vapor pressure. Geochem. Int. 47, 372–379 (2009). https://doi.org/10.1134/S0016702909040041
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DOI: https://doi.org/10.1134/S0016702909040041