Synthesis, characterization and thermochemistry of a Pb-jarosite

F. L. Forray, A. M.L. Smith, C. Drouet, A. Navrotsky, K. Wright, K. A. Hudson-Edwards, W. E. Dubbin

Research output: Contribution to journalArticlepeer-review

30 Scopus citations

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 (Δ H{ring operator}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: Δ G{ring operator}f = -3118.1 ± 4.6 kJ/mol, Δ H{ring operator}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.

Original languageEnglish (US)
Pages (from-to)215-224
Number of pages10
JournalGeochimica et Cosmochimica Acta
Volume74
Issue number1
DOIs
StatePublished - Jan 1 2010
Externally publishedYes

ASJC Scopus subject areas

  • Geochemistry and Petrology

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