The transformation of sulphate minerals during pyrolysis of an Australian lignite has been studied using pure sulphates (CaSO4, FeSO4 and Fe2(SO4)3), a high mineral (HM) lignite sample and a low mineral (LM) lignite sample collected from different locations of the same deposit, and samples of acid-washed LM doped with sulphates (CaSO4+ LM and FeSO4+ LM), respectively. Thermogravimetric analysis and fixed-bed reactor techniques were used for the pyrolysis experimentation and the lignite samples and their chars were analysed using FTIR and XRD. The TGA experiments showed that CaSO4 decomposes between 1400 and 1700 K in nitrogen and a 50/50 N2/CO2 mixture, while in air CaSO4 decomposes between 1500 and 1700 K. Using a TGA–MS it was found that only a small fraction of CaSO4 in CaSO4+ LM decomposed at 653 K, releasing SO2. CaSO4 was still observed in the char recovered at 1073 K as confirmed by the FTIR and XRD analysis. FeSO4·7H2O released the bound water below 543 K and the remaining FeSO4 decomposed between 813 and 953 K. FeSO4 in FeSO4+ LM decomposed at 500 K to release SO2. The inherent sulphates in HM were dominated by iron sulphates which started to decompose and release SO2 at around 500 K and all sulphate had been decomposed at 1073 K. It was observed that during the fixed-bed pyrolysis at 1073 K in nitrogen, approximately 36% of the total sulphur in the CaSO4+ LM decomposed, 88% of the total sulphur in the FeSO4+ LM decomposed and around 76% of the total sulphur in HM decomposed. It was also confirmed that FeSO4+ LM produced more volatile sulphur than CaSO4+ LM during pyrolysis.