Internally consistent thermodynamic dataset for divalent metal sulfate minerals
Final Report Abstract
The main goal of the project "thermodynamics of metal sulfates" was to derive an internally consistent thermodynamic data set for divalent metal sulfate hydrate minerals. In a pilot project, the system MgSO4 - H2O was chosen 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 of the 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 MgSO4 nH2O (n = 1, 2, 6, 7) and derived an internally consistent data set of the system MgSO4 - H2O enabling the calculation of phase diagrams. Additionally, we were able to extend the data set to several other divalent metal sulfate hydrates M2+SO4 nH2O (M = Fe, Zn, Ni, Co, and Cu). During the last year of the project, we obtained the enthalpies of formation of synthetic MgSO4 4H2O (starkeyite) and MgSO4 3H2O as well as the standard entropy of starkeyite which was derived from low-temperature heat capacity measurements using a physical property measurement system (PPMS). Based on new, recently reported equilibrium relative humidities and the standard properties described above, the internally consistent thennodynamic database for the MgSO4 nH2O system was refined. This time, the earlier assumption ∆Cp = 0 could be omitted.
Publications
- (2009): Internally consistent thermodynamic data for magnesium sulfate hydrates. Geochim. Cosmochim. Acta, 73: 6805-6815
Grevel K.-D. & Majzlan J.
- (2011): Internally consistent thermodynamic data for metal divalent sulphate hydrates. Chem. Geol., 286: 301-306
Grevel K.-D. & Majzlan J.
(See online at https://doi.org/10.1016/j.chemgeo.2011.05.016)
