TY - JOUR
T1 - On the thermochemistry of the solid solution between jarosite and its chromite analog
AU - Drouet, Christophe
AU - Baron, Dirk
AU - Navrotsky, Alexandra
PY - 2003
Y1 - 2003
N2 - Minerals of the jarosite group can be a significant environmental sink for hexavalent Cr by substitution of chromate for sulfate. The thermochemistry of the synthetic solid solution between jarosite KFe3(SO4)2(OH)6 and its chromate analog KFe3(CrO4)2(OH 6 was investigated by high-temperature oxide-melt solution calorimetry. The enthalpies of formation (ΔH0f) of the latter, as well as of five intermediate compositions in the series KFe3(S1-zCrzO4 2(OH)6, were determined, where z corresponds to the Cr content. The variation of ΔH0f with Cr content deviates from ideality, and negative enthalpies of mixing between jarosite and its chromate analog are observed, suggesting some ordering of the sulfate/chromate groups in the solid solution. The measured enthalpy of formation from the elements of the end-member KFe3(CrO4)2(OH)6 is ΔH0f = -3762.5 ± 8.0 kJ/mol. In view of this work, and considering literature data, ΔG0f = -3305.5 ± 3.4 kJ/mol, ΔS0f = -1533.6 ± 29.2 J/(mol·K ), and S0= 487.7 ± 29.2 J/(mol·K) are recommended for KFe3(CrO4)2(OH )6.
AB - Minerals of the jarosite group can be a significant environmental sink for hexavalent Cr by substitution of chromate for sulfate. The thermochemistry of the synthetic solid solution between jarosite KFe3(SO4)2(OH)6 and its chromate analog KFe3(CrO4)2(OH 6 was investigated by high-temperature oxide-melt solution calorimetry. The enthalpies of formation (ΔH0f) of the latter, as well as of five intermediate compositions in the series KFe3(S1-zCrzO4 2(OH)6, were determined, where z corresponds to the Cr content. The variation of ΔH0f with Cr content deviates from ideality, and negative enthalpies of mixing between jarosite and its chromate analog are observed, suggesting some ordering of the sulfate/chromate groups in the solid solution. The measured enthalpy of formation from the elements of the end-member KFe3(CrO4)2(OH)6 is ΔH0f = -3762.5 ± 8.0 kJ/mol. In view of this work, and considering literature data, ΔG0f = -3305.5 ± 3.4 kJ/mol, ΔS0f = -1533.6 ± 29.2 J/(mol·K ), and S0= 487.7 ± 29.2 J/(mol·K) are recommended for KFe3(CrO4)2(OH )6.
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U2 - 10.2138/am-2003-11-1238
DO - 10.2138/am-2003-11-1238
M3 - Article
AN - SCOPUS:0346462889
SN - 0003-004X
VL - 88
SP - 1949
EP - 1954
JO - American Mineralogist
JF - American Mineralogist
IS - 11-12 PART 2
ER -