Estimated thermodynamic properties of NaFeS 2 and erdite (NaFeS 2 :2H 2 O)

Abstract : The main by-products of a lead-recovery process from waste are scoriaceous sodium–iron sulphides, whose storage is problematic due to their great reactivity with air and water. The objective of this work was to complete thermodynamic databases with a totally new set of properties for the two major components: NaFeS 2 and erdite (NaFeS 2 :2H 2 O). The solubility product of erdite was measured at 20 °C in a batch reactor. It is À38.0 ± 0.3 when the reaction is written as a function of the predominant species at the experimental conditions: NaFeS 2 :2H 2 O þ 0:5H 2 O ¼ HFeO À 2 þ 1:875HS À þ 0:125SO ¼ 4 þ Na þ þ 2:125H þ : The resulting standard Gibbs free energy of formation of erdite from elements is À809.76 kJ/mol at 25 °C and 1 bar. An original calculation procedure, relying on a combination of different theoretical models , then allowed the determination of the standard Gibbs free energies of formation of NaFeS 2 and of the water of hydration for transforming NaFeS 2 into erdite. At 25 °C and 1 bar, they are À322.85 and À243.46 kJ/mol respectively. The other standard thermodynamic properties (enthalpy, entropy, and heat capacity) of erdite are À922.04 kJ/mol, 232.6 J/(mol K) and 175.7 J/(mol K), respectively. For NaFeS 2 , they are À331.33 kJ/mol, 114.3 J/(mol K) and 97.7 J/(mol K), respectively. For the water of hydration they are À295.36 kJ/mol, 59.2 J/(mol K) and 39.0 J/(mol K), respectively.
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Applied Geochemistry, Elsevier, 2014, 45, pp.14-24. 〈10.1016/j.apgeochem.2014.02.015〉
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Soumis le : mardi 23 juin 2015 - 17:26:25
Dernière modification le : mardi 23 juin 2015 - 17:27:45

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Arnault Lassin, Patrice Piantone, Catherine Crouzet, Françoise Bodénan, Philippe Blanc. Estimated thermodynamic properties of NaFeS 2 and erdite (NaFeS 2 :2H 2 O). Applied Geochemistry, Elsevier, 2014, 45, pp.14-24. 〈10.1016/j.apgeochem.2014.02.015〉. 〈hal-01167087〉

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