Pyrite is widely treated as a non-valuable and problematic mineral by environmental and mineral processing professionals (Jefferson et al, 2023). However, pyrite is known for hosting potentially critical and economically valuable elements (Co, Zn, Cu, Pb, Ni, Se, Au; Steadman et al, 2021; Babedi et al, 2022; Erlandsson et al, 2025; Li et al, 2025) in various deposit types (Carlin, epithermal high- and low-sulfidation, epithermal alkaline, orogenic Au and porphyry Cu; Keith et al, 2018; Babedi et al, 2022). In fact, pyrite contributes 4–8 wt per cent within Cu tailings (Santander and Valderrama, 2019). When oxidised, it is the main contributor for acid rock and metalliferous drainage (AMD; Xu et al, 2025). To reduce environmental risks associated with tailings, pyrite could be selectively recovered as part of a rehabilitation measure. Cobalt Blue’s patented technology – turning pyrite to pyrrhotite through thermal decomposition (Cobalt Blue Holdings, 2025), followed by leaching critical metals, has shown the potential to deliver benefits throughout the entire life-of-mine. They offer the potential to reduce mine waste acid-forming potential whilst enhancing recovery of critical metals, thereby contributing to the principles of a circular economy and sustainable development goals. This research will explain the pyrite-pyrrhotite reaction mechanisms using Cobalt Blue’s patented technology and emerging technologies; identify the intrinsic and physical properties of pyrite and the behaviour of pyrite during the thermal decomposition process; explore the influence of secondary minerals on the mineral processing performance of pyrite and; combine all observed results to establish a pyrite prediction pathway for the thermal decomposition processing method for different deposits. This thermal decomposition-leaching technology enables the recovery of valuable metals to support the green energy transition (eg Co, Ni) and sulfuric acid production.