# Pressure-Driven Water Release from Magnesium Sulfate Hydrates: Thermodynamic and Mechanistic Insights

## TL;DR

This study explores how pressure causes magnesium sulfate hydrates to release water, forming dense ice and influencing planetary and technological processes.

## Contribution

The paper reveals that pressure-induced dehydration in magnesium sulfate hydrates initiates at specific pressures and produces dense ice polymorphs.

## Key findings

- Dehydration becomes favorable at 0.8 GPa for MgSO4·11H2O and 1.1 GPa for MgSO4·7H2O.
- Ice VI is the dominant product of pressure-induced dehydration.
- Interstitial water molecules are the initiation sites for dehydration under pressure.

## Abstract

Understanding the behavior of hydrated salts under pressure
is
essential for interpreting geochemical processes in planetary interiors
and for developing (de)­hydration-based technologies. In this study,
we use density functional theory calculations to investigate the thermodynamics
of pressure-induced dehydration in magnesium sulfate hydrates (MgSO4·nH2O, n = 11 and 7), where compression drives the release of water as dense
ice polymorphs (such as ice II and VI) and the formation of hydrates
with fewer water molecules. Our results show that dehydration becomes
thermodynamically favorable at 0.8 GPa for MgSO4·11H2O and 1.1 GPa for MgSO4·7H2O, with
ice VI emerging as the dominant crystallization product. Interaction
energy analysis identifies interstitial, rather than metal-coordinated,
water molecules as the dehydration initiation sites. Unlike thermal
dehydration of MgSO4·7H2O, which proceeds
via MgSO4·6H2O and water vapor, our calculations
indicate that pressure-induced dehydration yields MgSO4·5H2O and dense ice. These results highlight distinct
mechanisms of dehydration under temperature and pressure and provide
insight into hydrate behavior relevant to both thermochemical technologies
and planetary environments.