Study of the influence of water and oxygen on the morphology and chemistry of pyritized lignite: Implications for the development of a preventive drying protocol

•A successful drying protocol for pyritized lignite is proposed.•Water is the main factor responsible for the onset of mechanical damage and the oxidation of pyrite in lignite.•Efflorescence develops as soon as lignite is exposed to dry oxygenated conditions.•Organic reduced sulfur compounds are barely oxidized while pyrite turns easily into sulfates.