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Synthesis, characterization and thermochemistry of synthetic Pb-AS, Pb-Cu and Pb-Zn jarosites

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Forray, F.
Smith, A.
Navrotsky, A.
Wright, Kathleen
Hudson-Edwards, K.
Dubbin, William
Date
2014
Type
Journal Article

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Forray, Ferenc Lázár and Smith, A.M.L. and Navrotsky, A. and Wright, K. and Hudson-Edwards, K.A. and Dubbin, W.E. 2014. Synthesis, characterization and thermochemistry of synthetic Pb-AS, Pb-Cu and Pb-Zn jarosites. Geochimica et Cosmochimica Acta. 127: pp. 107-119.
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Geochimica et Cosmochimica Acta
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This is the author’s version of a work that was accepted for publication Geochimica et Cosmochimica Acta. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Geochimica et Cosmochimica Acta, Volume 127, 15 February 2014, Pages 107–119 http://doi.org/10.1016/j.gca.2013.10.043.

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Abstract

The enthalpy of formation from the elements of well characterized Pb–As, Pb–Cu, and Pb–Zn synthetic jarosites, corresponding to chemical formulas (H3O)0.68±0.03Pb0.32±0.002Fe2.86±0.14(SO4)1.69±0.08(AsO4)0.31±0.02(OH)5.59±0.28(H2O)0.41±0.02,(H3O)0.67±0.03Pb0.33±0.02Fe2.71±0.14Cu0.25±0.01(SO4)2±0.00(OH)5.96±0.30(H2O)0.04±0.002 and (H3O)0.57±0.03Pb0.43±0.02Fe2.70±0.14Zn0.21±0.01(SO4)2±0.00(OH)5.95±0.30(H2O)0.05±0.002, was measured by high temperature oxide melt solution calorimetry and gave DHf = 3691.2 ± 8.6 kJ/mol, DHf = 3653.6 ± 8.2 kJ/mol, and DHf = 3669.4 ± 8.4 kJ/mol, respectively. Using estimated entropies, the standard Gibbs free energy of formation from elements at 298 K DGf of the three compounds were calculated to be 3164.8 ± 9.1, 3131.4 ± 8.7, and 3153.6 ± 8.9 kJ/mol, respectively. Based on these free energies, their log Ksp values are 13.94 ± 1.89, 4.38 ± 1.81 and 3.75 ± 1.80, respectively. For this compounds, a log10 {Pb2+}–pH diagram is presented. The diagram shows that the formation of Pb–As jarosite may decrease aqueous arsenic and lead concentrations to meet drinking water standards. The new thermodynamic data confirm that transformation of Pb–As jarosite to plumbojarosite is thermodynamically possible.