Internally consistent thermodynamic dataset for divalent metal sulfate minerals

• Applicant: Professor Juraj Majzlan, Ph.D.
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2007 to 2012
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 58467350

Our main goal is to derive an internally consistent thermodynamic data set for divalent metal sulfate hydrate minerals. In a pilot project, we have chosen the system MgS04 - H2O to carefully test our approach. Initially, the proposed project consisted of two principal parts. The first one was the modification and augmentation of a previously developed software package for the derivation of internally consistent data sets for the use in the sulfate system. The second part ofthe project included the determination of enthalpies of formation of several magnesium sulfate minerals by calorimetric techniques. Both parts of the project turned out to be successful - we measured the enthalpies of formation of MgS04·H20 (n = 1, 2, 6, 7) and derived an internally consistent data set of the system MgSO4 - H2O enabling the calculation of phase diagrams. In the last year of the project, we want to close some remaining gaps: 1. The phase starkeyite (MgS04-4H20) will be synthesized and investigated calorimetrically. Additionally, we will attempt to synthesize and characterize the low-7 phase meridianiite (MgS04·H20). 2. In a pioneering study, the entropy of epsomite and hexahydrite will be obtained by low temperature heat capacity (Cp) measurements using a PPMS® system at Salzburg. 3. These data will be used to refine our thermodynamic data set further. 4. Routines capable of calculating ion activities in aqueous solutions with the Pitzer fomialism were already written, but we still have to include a formalism describing the Cp behaviour of the aqueous solution and the solids.

• DFG Programme: Research Grants