TY - JOUR
T1 - Synthesis, characterization, and thermochemistry of K-Na-H3O jarosites
AU - Drouet, Christophe
AU - Navrotsky, Alexandra
N1 - Funding Information:
The authors thank Juraj Majzlan, John Neil, and Eric Moloy for interesting discussions and comments; and Sarah Roeske and Peter Schiffman for their assistance in electron probe microanalysis. This work was supported by the U.S. Department of Energy (grant DE-FG0397SF 14749).
PY - 2003/6/1
Y1 - 2003/6/1
N2 - The thermochemistry of well-characterized synthetic K-H3O, Na-H3O and K-Na-H3O jarosites was investigated. These phases are solid solutions that obey Vegard's law. Electron probe microanalyses indicated lower alkali and iron contents than predicted from the theoretical end-member compositions, in agreement with thermal analyses, suggesting the presence of hydronium and "additional" water. The standard enthalpies of formation (ΔH° f) of K-H3O, Na-H3O and K-Na-H3O jarosites were determined by high-temperature oxide melt solution calorimetry. These enthalpies vary linearly with the K/H3O, Na/H3O and K/Na ratio, respectively. The enthalpy of formation of pure hydronium jarosite was also determined experimentally (ΔH°f = -3741.6 ± 8.3 kJ.mol-1), and it was used to evaluate ΔH°f for the end-members KFe3(SO4)2(OH)6 (ΔH°f = -3829.6 ± 8.3 kJ.mol-1) and NaFe3 (SO4)2(OH)6 (ΔH°f = -3783.4 ± 8.3 kJ.mol-1). Finally, enthalpies of dehydration (loss of the "additional" water) of some jarosites were determined and found to be near the enthalpy of vaporization of water, suggesting that the "additional" water is weakly bonded in the structure.
AB - The thermochemistry of well-characterized synthetic K-H3O, Na-H3O and K-Na-H3O jarosites was investigated. These phases are solid solutions that obey Vegard's law. Electron probe microanalyses indicated lower alkali and iron contents than predicted from the theoretical end-member compositions, in agreement with thermal analyses, suggesting the presence of hydronium and "additional" water. The standard enthalpies of formation (ΔH° f) of K-H3O, Na-H3O and K-Na-H3O jarosites were determined by high-temperature oxide melt solution calorimetry. These enthalpies vary linearly with the K/H3O, Na/H3O and K/Na ratio, respectively. The enthalpy of formation of pure hydronium jarosite was also determined experimentally (ΔH°f = -3741.6 ± 8.3 kJ.mol-1), and it was used to evaluate ΔH°f for the end-members KFe3(SO4)2(OH)6 (ΔH°f = -3829.6 ± 8.3 kJ.mol-1) and NaFe3 (SO4)2(OH)6 (ΔH°f = -3783.4 ± 8.3 kJ.mol-1). Finally, enthalpies of dehydration (loss of the "additional" water) of some jarosites were determined and found to be near the enthalpy of vaporization of water, suggesting that the "additional" water is weakly bonded in the structure.
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U2 - 10.1016/S0016-7037(02)01299-1
DO - 10.1016/S0016-7037(02)01299-1
M3 - Article
AN - SCOPUS:0038270622
SN - 0016-7037
VL - 67
SP - 2063
EP - 2076
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
IS - 11
ER -