Based on those characterizations, we see that the thermal decomposition behavior of the different M-struvites vary significantly. While Co-struvite transformed in a course of a quick, phase transition to Co-dittmarite with an Tonset,1 = 72 °C, Ni-and Mg-struvite evaporated their volatile compounds at slightly higher temperatures at Tonset,1 = 83°C (Ni) and Tonset,1 = 88°C (Mg) (ESI: Table ). Interestingly, Co-and Co-rich NixCo1-x-struvite show multiple phase transitions indicated by multiple events in DSC (1 st , 2 nd , 3 rd thermal event in Figure ). The resulting order of the 1 st M-struvite decomposition is the following: TCo <TNi ≈ TMg (ESI: Table ). Considering the mass-loss analysis associated with the DSC (ESI: Fig. ) the first thermal event corresponds in all compounds to a major phase of degassing with a release of five water molecules and minorly ammonia. Therefore, since all struvite compounds show their main degassing event at around 90°C, the phase composition of heated M-struvite samples were measured in a time-series t = 10, 20, 40, 60, 90, 120, 150 minutes, and 1 day at this temperature. Due to the broad T-interval of the 1 st thermal event, higher temperatures T =120°C and 150°C were also evaluated for the different M-struvite systems to observe potential differences. At temperatures below T < 200°C, Mg-and Ni-struvite were transforming to amorphous phases in dry air, beginning majorly after t = 40 min and completed at t = 120 min, while Costruvite recrystallized quickly after 20 min to Co-dittmarite (Figure , ESI: Figure ). In fact, the phase transformations in transition metals would manifest themselves, just through simple color changes (photographs of powder in circles, in Figure , Figure and Figure ). When heated, Ni-and Co-phosphates exhibited a color change from green to yellow (Ni) and from pink to purple/violet (Co). In the Ni-system during degassing of volatile components a transitional stability of Ni3(PO4)2•8H2O had been observed which disappeared again upon further heating. At high temperatures, the amorphous Ni-phases showed a high stability up to 500°C while in the Co-system multiple crystalline-crystalline phase transitions were observed (ESI: Figure ).