TY - JOUR
T1 - Thermochemistry of jarosite-alunite and natrojarosite-natroalunite solid solutions
AU - Drouet, Christophe
AU - Pass, Katrina L.
AU - Baron, Dirk
AU - Draucker, Sara
AU - Navrotsky, Alexandra
N1 - Funding Information:
This work was supported by the U.S. Department of Energy (grant DE-FG0397SF 14749). The authors also wish to thank greatly Dr. C. Alpers for a thorough review of this contribution.
PY - 2004/5/15
Y1 - 2004/5/15
N2 - The thermochemistry of jarosite-alunite and natrojarosite-natroalunite solid solutions was investigated. Members of these series were either coprecipitated or synthesized hydrothermally and were characterized by XRD, FTIR, electron microprobe analysis, ICP-MS, and thermal analysis. Partial alkali substitution and vacancies on the Fe/Al sites were observed in all cases, and the solids studied can be described by the general formula K1-x-yNay(H3O)xFez Alw(SO4)2(OH)6-3(3-z-w)( H2O)3(3-z-w). A strong preferential incorporation of Fe over Al in the jarosite/alunite structure was observed. Heats of formation from the elements, ΔH°f, were determined by high-temperature oxide melt solution calorimetry. The solid solutions deviate slightly from thermodynamic ideality by exhibiting positive enthalpies of mixing in the range 0 to +11 kJ/mol. The heats of formation of the end members of both solid solutions were derived. The values ΔH°f = -3773.6 ± 9.4 kJ/mol, ΔH°f = -4912.2 ± 24.2 kJ/mol, ΔH°f = -3734.6 ± 9.7 kJ/mol and ΔH°f = -4979.7 ± 7.5kJ/mol were found for K0.85(H3O)0.15Fe2.5( SO4) 2(OH)4.5(H2O)1.5, K0.85(H3O)0.15Al2.5( SO4)2(OH)4.5(H2O)1.5, Na0.7(H3O)0.3Fe2.7(SO4) 2(OH)5.1(H2O)0.9, and Na0.7(H3O)0.3Al2.7( SO4)2(OH)5.1(H2O)0.9 respectively. To our knowledge, this is the first experimentally-based report of ΔH°f for such nonstoichiometric alunite and natroalunite samples. These thermodynamic data should prove helpful to study, under given conditions, the partitioning of Fe and Al between the solids and aqueous solution.
AB - The thermochemistry of jarosite-alunite and natrojarosite-natroalunite solid solutions was investigated. Members of these series were either coprecipitated or synthesized hydrothermally and were characterized by XRD, FTIR, electron microprobe analysis, ICP-MS, and thermal analysis. Partial alkali substitution and vacancies on the Fe/Al sites were observed in all cases, and the solids studied can be described by the general formula K1-x-yNay(H3O)xFez Alw(SO4)2(OH)6-3(3-z-w)( H2O)3(3-z-w). A strong preferential incorporation of Fe over Al in the jarosite/alunite structure was observed. Heats of formation from the elements, ΔH°f, were determined by high-temperature oxide melt solution calorimetry. The solid solutions deviate slightly from thermodynamic ideality by exhibiting positive enthalpies of mixing in the range 0 to +11 kJ/mol. The heats of formation of the end members of both solid solutions were derived. The values ΔH°f = -3773.6 ± 9.4 kJ/mol, ΔH°f = -4912.2 ± 24.2 kJ/mol, ΔH°f = -3734.6 ± 9.7 kJ/mol and ΔH°f = -4979.7 ± 7.5kJ/mol were found for K0.85(H3O)0.15Fe2.5( SO4) 2(OH)4.5(H2O)1.5, K0.85(H3O)0.15Al2.5( SO4)2(OH)4.5(H2O)1.5, Na0.7(H3O)0.3Fe2.7(SO4) 2(OH)5.1(H2O)0.9, and Na0.7(H3O)0.3Al2.7( SO4)2(OH)5.1(H2O)0.9 respectively. To our knowledge, this is the first experimentally-based report of ΔH°f for such nonstoichiometric alunite and natroalunite samples. These thermodynamic data should prove helpful to study, under given conditions, the partitioning of Fe and Al between the solids and aqueous solution.
UR - http://www.scopus.com/inward/record.url?scp=2342575773&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=2342575773&partnerID=8YFLogxK
U2 - 10.1016/j.gca.2003.12.001
DO - 10.1016/j.gca.2003.12.001
M3 - Article
AN - SCOPUS:2342575773
SN - 0016-7037
VL - 68
SP - 2197
EP - 2205
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
IS - 10
ER -