Thermophysical and thermochemical calorimetric investigations were carried out on the synthetic analogue of chalcomenite. The synthesis of CuSeO3·2H2O was realized from copper nitrate and sodium selenite solutions heated to 80 °C for 2 to 3 h. The precipitate was characterized by X-ray powder diffraction, X-ray fluorescence, IR spectroscopy, and Raman spectroscopy. The low-temperature heat capacity of CuSeO3·2H2O was measured using adiabatic calorimetry between 5 and 323 K, and the third-law entropy was determined. A value of S°(298 K, CuSeO3·2H2O, cr) = 181.0 ± 1.0 J/(K mol) was obtained with an uncertainty of 0.5%. The enthalpy of formation of CuSeO3·2H2O was determined by solution calorimetry with H2SO4 solution as the solvent, giving ΔfH°(298 K, CuSeO3·2H2O, cr) = −1035.3 ± 4.9 kJ/mol. The Gibbs energy of formation for CuSeO3·2H2O at T = 298 K, 1 atm can be calculated on the basis on ΔfH° (298 K) and ΔfS°(298 K): ΔfG°(298 K, CuSeO3·2H2O, cr) = −835.3 ± 5.3 kJ/mol. Smoothed Cp°(T) values between T = 0 K and T = 320 K for CuSeO3·2H2O (cr) are presented along with values for S° and the functions [H°(T) – H°(0)]and[G°(T) – H°(0)]. These results motivate a re-evaluation of the natural conditions under which selenites and selenates replace selenides, and sulfides in the oxidation zones of sulfide ore deposits or upon weathering of technologic waste. The value of ΔfG° for CuSeO3·2H2O was used to calculate Eh–pH diagrams of the Cu–Se–CO2–H2O system. The behaviour of selenium and copper in the surface environment has been quantitatively explained by variations of the redox potential and the acidity–basicity of the mineral-forming medium. Precisely, these parameters determine the migration ability of selenium compounds and their precipitation in the form of various solid phases.
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Research Article|
May 01, 2017
A calorimetric and thermodynamic investigation of the synthetic analogue of chalcomenite, CuSeO3·2H2O
Marina V. Charykova;
Marina V. Charykova
1
Department of Geochemistry, St. Petersburg State University, 7–9 University Embankment, Saint-Petersburg 199034, Russia
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Maxim I. Lelet;
Maxim I. Lelet
2
Research Institute for Chemistry, Lobachevsky State University of Nizhni Novgorod, 23 Prospekt Gagarina (Gagarin Avenue), Nizhny Novgorod 603950, Russia
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Vladimir G. Krivovichev;
3
Department of Mineralogy, St. Petersburg State University, 7–9 University Embankment, Saint-Petersburg 199034, Russia*
Corresponding author, e-mail: vkrivovi@yandex.com
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Natalya M. Ivanova;
Natalya M. Ivanova
4
Resource Center “Geomodel”, St. Petersburg State University, 1 Ulyanovskaya Street, Saint-Petersburg, Russia
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Evgeny V. Suleimanov
Evgeny V. Suleimanov
2
Research Institute for Chemistry, Lobachevsky State University of Nizhni Novgorod, 23 Prospekt Gagarina (Gagarin Avenue), Nizhny Novgorod 603950, Russia
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European Journal of Mineralogy (2017) 29 (2): 269–277.
Article history
received:
23 May 2016
rev-recd:
29 Jul 2016
accepted:
14 Aug 2016
first online:
17 Nov 2017
Citation
Marina V. Charykova, Maxim I. Lelet, Vladimir G. Krivovichev, Natalya M. Ivanova, Evgeny V. Suleimanov; A calorimetric and thermodynamic investigation of the synthetic analogue of chalcomenite, CuSeO3·2H2O. European Journal of Mineralogy ; 29 (2): 269–277. doi: https://doi.org/10.1127/ejm/2017/0029-2595
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Index Terms/Descriptors
- calorimetry
- cell dimensions
- Eh
- enthalpy
- entropy
- experimental studies
- free energy
- heat capacity
- infrared spectra
- low temperature
- pH
- Raman spectra
- selenites
- selenium
- solution
- spectra
- synthetic materials
- temperature
- thermodynamic properties
- X-ray diffraction data
- X-ray fluorescence spectra
- chalcomenite