The mineral stability, depending mainly on the availability of PGE/reactants and/or differences
in pressure and temperature relative to standard conditions, may have an effect on the equilibrium
constants [26–28]. Although the stability relationships between various phases can be studied using the
experimental method, thermodynamics may give us an approach to the calculation of the Gibbs free
energy and phase diagrams [28]. However, the requirements for the PGM stability and re-deposition
remain still unclear, since the activity-composition models and relevant phase diagrams for PGM are
very limited, and the PGM forming processes in natural systems are complicated