Thermal Decomposition and Transformation of Pyrite in Coal Combustion

Pyrite (FeS₂) is a ubiquitous sulphide mineral in coal that undergoes a series of complex transformations when exposed to the high temperatures and fluctuating atmospheres of combustion processes. Under inert or reducing conditions, pyrite first decomposes through pyrolysis, yielding pyrrhotite (Fe₁–xS) and releasing sulphur vapours. In oxidising environments, partial oxidation produces intermediate iron sulphates and sulphur dioxide before further conversion to iron oxides (magnetite, haematite) and sulphates. The presence of carbonaceous matter and mineral additives in coal influences these pathways by altering local oxygen partial pressures and providing reducing agents that shift equilibrium towards desulphurisation. Key experimental approaches—thermogravimetric analysis, X-ray diffraction and electron microscopy—have revealed that temperature, heating rate and gas composition jointly determine the onset temperatures of mass loss, the kinetics of solid-state transitions and the morphology of residual ash. Understanding these transformations is critical for controlling SO₂ emissions, optimising slag chemistry in furnaces and designing capture strategies for sulphur pollutants. Recent insights into reaction mechanisms have highlighted the roles of intermediate sulphide phases, sintering and particle agglomeration, with direct implications for burner design and environmental compliance in large-scale power plants.

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Thermal Decomposition and Transformation of Pyrite in Coal Combustion publication trend

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Technical terms

Thermogravimetric analysis: A technique measuring mass changes of a sample as a function of temperature or time under controlled atmosphere, used to characterise decomposition kinetics.

Pyrrhotite: A non-stoichiometric iron sulphide (Fe₁–xS) that forms during partial decomposition of pyrite and influences subsequent oxidation and sintering behaviour.

Shrinking core mechanism: A kinetic model describing reactions of solid particles in which an unreacted core shrinks inward as the reaction front advances through the particle.

Pyrolysis: Thermal decomposition of a compound in an inert or reducing atmosphere, leading to fragmentation into simpler solids, liquids or gaseous products without oxidation.

References

1. A Thermodynamic Analysis on the Roasting of Pyrite. Minerals (2019).
2. The Thermal Decomposition Behavior of Pyrite‐Pyrrhotite Mixtures in Nitrogen Atmosphere. Journal of Chemistry (2022).
3. Effects of Pyrrhotite on the Combustion Behavior and the Kinetic Mechanism of Pyrite‐Pyrrhotite Mixture Powders in the Air. International Journal of Chemical Engineering (2023).