Thermal and Thermochemical Study of Blödite (Astrakhanite)

Abstract

The natural hydrous sodium−magnesium sulfate blodite (astrakhanite) Na2Mg(SO4)2 · 4H2O from sediments of saline Lake Bai Shagyr (Russia) is studied. The stages of its decomposition on heating are distinguished using thermal analysis, X-ray diffraction, IR and Raman spectroscopy. The enthalpy of formation of blodite from elements ( $${{\Delta }_{f}}H_{{el}}^{0}$$ (298.15 K) = –3845 ± 13 kJ/mol) is determined on a Tian-Calvet microcalorimeter using high-temperature melt solution calorimetry. The values of standard entropy and Gibbs energy of mineral formation are estimated.