Thermodynamic mixing properties of alunite supergroup minerals: Quantum-mechanical modeling and thermodynamic analysis of sulfate, chromate, selenate, phosphate, and arsenate solid solutions, as well as uranyl incorporation

摘要

In various geological settings, alunite supergroup minerals, including the end members alunite [KAl3 (SO4)(2)(OH)(6)] and jarosite [KFe3(SO4)(2)(OH)(6)], occur in extensive solid solution on the cation and anion sites, enabling them to accommodate a variety of elements. Jarosite is known for scavenging heavy metals on the K site (e.g., Pb in solid solution between jarosite and plumbojarosite) in acid mine drainage settings, while both jarosite and alunite can be important in controlling toxic anions such as selenate, chromate, or arsenate. However, there is no thermodynamic information on the solubility of these important cations and anions as a function of temperature, in part because this information is difficult to obtain experimentally. In this study, thermodynamic mixing properties of sulfate-chromate (S-Cr), sulfate-selenate (S-Se), and sulfate-phosphate-arsenate (S-P-As) solid solutions in alunite supergroup minerals are investigated based on quantum-mechanical modeling and statistical thermodynamic analysis.