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

doi:10.1016/j.gca.2009.09.033

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

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54 Scopus citations

Abstract

The enthalpy of formation from the elements of a well-characterized synthetic Pb-jarosite sample corresponding to the chemical formula (H₃O)_0.74Pb_0.13Fe_2.92(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 Pb_0.5Fe₃(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(K_sp) ranging from -24.3 to -26.2). An Eh-pH diagram is also presented.

Original language	English (US)
Pages (from-to)	215-224
Number of pages	10
Journal	Geochimica et Cosmochimica Acta
Volume	74
Issue number	1
DOIs	https://doi.org/10.1016/j.gca.2009.09.033
State	Published - Jan 1 2010
Externally published	Yes

ASJC Scopus subject areas

Geochemistry and Petrology

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10.1016/j.gca.2009.09.033

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@article{71082f36f64a4d898de4465c2e9380df,

title = "Synthesis, characterization and thermochemistry of a Pb-jarosite",

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.",

author = "Forray, {F. L.} and Smith, {A. M.L.} and C. Drouet and A. Navrotsky and K. Wright and Hudson-Edwards, {K. A.} and Dubbin, {W. E.}",

note = "Funding Information: This work was funded by the US Department of Energy (Grant DEFG0397SF14749 ) to A. Navrotsky and through the UK Engineering and Physical Sciences Research Council (EPSRC) studentship award (No. 309778) to A.M.L. Smith. We thank A.S. Wills for the GSAS refinement of the original synthetic Pb-jarosite, C. Jones and A. Ball for help with SEM analysis and photography, G. Jones and V. Din for assistance with geochemical analysis, and I. Wood for expert help with the XRD analysis. ",

year = "2010",

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doi = "10.1016/j.gca.2009.09.033",

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T1 - Synthesis, characterization and thermochemistry of a Pb-jarosite

AU - Forray, F. L.

AU - Smith, A. M.L.

AU - Drouet, C.

AU - Navrotsky, A.

AU - Wright, K.

AU - Hudson-Edwards, K. A.

AU - Dubbin, W. E.

N1 - Funding Information: This work was funded by the US Department of Energy (Grant DEFG0397SF14749 ) to A. Navrotsky and through the UK Engineering and Physical Sciences Research Council (EPSRC) studentship award (No. 309778) to A.M.L. Smith. We thank A.S. Wills for the GSAS refinement of the original synthetic Pb-jarosite, C. Jones and A. Ball for help with SEM analysis and photography, G. Jones and V. Din for assistance with geochemical analysis, and I. Wood for expert help with the XRD analysis.

PY - 2010/1/1

Y1 - 2010/1/1

N2 - 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.

AB - 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.

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Synthesis, characterization and thermochemistry of a Pb-jarosite

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