Thermodynamic properties of Fe-rich smectite-nontronite |
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| Authors: | L P Ogorodova I A Kiseleva L V Melchakova M F Vigasina V V Krupskaya Yu Yu Bugel’skii |
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| Institution: | 1. Geological Faculty, Moscow State University, Moscow, 119991, Russia
2. Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences, Staromonetnyi per. 35, Moscow, 119017, Russia
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| Abstract: | The results of thermochemical studies are reported for nontronite samples from the Pinares-de-Majari (Eastern Cuba) (Sample I) and Kempirsai serpentine massif (South Urals, Kazakhstan) (Sample II). The enthalpies of formation of dehydrated hydroxyl-bearing nontronites from elements were determined by melt dissolution calorimetry using high-temperature heat-flux Tiana-Calvet microcalorimeter: Δ f H el o (298.15 K): ?4958 ± 13 kJ/mol for Mg0.4(Fe 1.5 3+ Mg0.4Ni0.1)Si3.7Al0.3O10](OH)2 (I) and ?5003.6 ± 8.0 kJ/mol for Mg0.3Na0.1Ca0.1(Fe 1.4 3+ Mg0.5Ni0.1)Si3.7Al0.3O10](OH)2 (II). It was determined experimentally that the enthalpy of dehydration (removal of molecular adsorption and interlayer water) of the studied nontronites is 6 ± 2 kJ per 1 mole H2O. The enthalpy of formation of nontronite of theoretical composition Mg0.15Fe 2 3+ Si3.7Al0.3]O10(OH)2 was estimated at ?4750 kJ/mol. The Gibbs free energies of formation of the nontronites were calculated. |
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