Experimental comparison of the pathways and rates of the dehydration of Al-, Fe-, Mg- and Ca-sulfates under Mars relevant conditions

This study reports two sets of dehydration experiments conducted on crystalline alunogen Al2(SO4)3·17H2O and melanterite FeSO4·7H2O under Mars relevant pressure (P) and partial H2O pressure (PH2O) at three temperatures (T). These experimental data are compared with those obtained from a similar set of experiments on crystalline epsomite MgSO4·7H2O, and revealed the differences in the phase transition pathways of the dehydrations of these hydrous sulfates, with different cations and the highest hydration degrees, under Mars relevant conditions. Specifically, the differences in the dehydration rates were discussed, and further compared with the dehydration processes of Ca-sulfate and Fe3+-sulfate of the highest hydration degrees. We found that the dehydrations of Mg-sulfate and Fe2+-sulfate would progress the fastest on Mars.