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Synthesis, characterization and thermochemistry of a Pb-jarosite

Forray, Ferenc Lázár and Smith, A.M.L. and Drouet, Christophe and Navrotsky, Alexandra and Wright, K. and Hudson-Edwards, K.A. and Dubbin, W.E. Synthesis, characterization and thermochemistry of a Pb-jarosite. (2010) Geochimica et Cosmochimica Acta, vol. 74 (n° 1). pp. 215-224. ISSN 0016-7037

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Official URL: http://dx.doi.org/10.1016/j.gca.2009.09.033

Abstract

The enthalpy of formation from the elements of a well-characterized synthetic Pb-jarosite sample corresponding to the chemical formula (H3O)0.74Pb0.13Fe2.92(SO4)2(OH)5.76(H2O)0.24 was measured by high temperature oxide melt solution calorimetry. This value (DH f = 3695.9 ± 9.7 kJ/mol) is the first direct measurement of the heat of formation for a lead-containing jarosite. Comparison to the thermochemical properties of hydronium jarosite and plumbojarosite end-members strongly suggests the existence of a negative enthalpy of mixing possibly related to the nonrandom distribution of Pb2+ ions within the jarosite structure. Based on these considerations, the following thermodynamic data are proposed as the recommended values for the enthalpy of formation from the elements of the ideal stoichiometric plumbojarosite Pb0.5Fe3(SO4)2(OH)6: DG f = 3118.1 ± 4.6 kJ/mol, DH f = 3603.6 ± 4.6 kJ/mol and S = 376.6 ± 4.5 J/(mol K). These data should prove helpful for the calculation of phase diagrams of the Pb–Fe–SO4–H2O system and for estimating the solubility product of pure plumbojarosite. For illustration, the evolution of the estimated solubility product of ideal plumbojarosite as a function of temperature in the range 5–45 C was computed (Log(Ksp) ranging from 24.3 to 26.2). An Eh–pH diagram is also presented.

Item Type:Article
Additional Information:Thanks to Elsevier editor. The definitive version is available at http://www.sciencedirect.com The original PDF of the article can be found at Geochimica et Cosmochimica Acta website : http://www.sciencedirect.com/science/journal/00167037
Audience (journal):International peer-reviewed journal
Uncontrolled Keywords:
Institution:Other partners > University of California - UC Davis (USA)
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French research institutions > Centre National de la Recherche Scientifique - CNRS
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Université de Toulouse > Institut National Polytechnique de Toulouse - INPT
Other partners > University of London (UNITED KINGDOM)
Université de Toulouse > Université Paul Sabatier-Toulouse III - UPS
Laboratory name:
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Deposited By:Nihad Lahdifi

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