Journal
GEOCHEMISTRY INTERNATIONAL
Volume 60, Issue 6, Pages 596-602Publisher
MAIK NAUKA/INTERPERIODICA/SPRINGER
DOI: 10.1134/S0016702922060052
Keywords
IR spectroscopy; thermal analysis; Calvet microcalorimetry; enthalpy of formation; Gibbs energy; alunite; natroalunite
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A natural alunite sample was studied using various analytical techniques, and its thermodynamic properties were determined. The results were compared with different compositions of alunite.
A sample of natural alunite of the composition K0.6Na0.4Al3(SO4)(2)(OH)(6) was studied by powder X-ray diffraction, infrared spectroscopy, electron microprobe, and thermal analysis. The enthalpy of formation of the alunite from elements increment Delta H-f(0)(298.15 K) = -5149 +/- 13 kJ/mol was determined by the method of melt solution calorimetry, using a Setaram (France) Calvet microcalorimeter. The calculated enthalpies and Gibbs energies of formation of the end members of the series alunite KAl3(SO4)(2)(OH)(6) to natroalunite NaAl3(SO4)(2)(OH)(6) are -5164 +/- 13 and -4651 +/- 13 kJ/mol, respectively, for alunite and - 5127 +/- 13 and -4615 +/- 13 kJ/mol, respectively, for natroalunite.
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