On the thermal stability of manganese(II) sulfate and its reaction with zeolite A to form the sodalite Na6Mn2[Al6Si6O24](SO4)2

Thermal gravimetric analysis and in situ high-temperature powder X-ray diffraction (HT-PXRD) revealed that MnSO4 begins to thermally decompose under air at similar to 625 degrees C, which is significantly lower than the values reported in the literature. The reaction is kinetically sluggish and yields bixbyite, Mn2O3, greater than or similar to 625 degrees C and hausmannite, Mn3O4, greater than or similar to 850 degrees C. Na6Mn2[Al6Si6O24](SO4)(2) was prepared as a novel sodalite-type phase by reacting zeolite A, Na-6[Al6Si6O24], with MnSO4 as a compacted mixed-powder monolith at 650 degrees C under air. In situ HT-PXRD indicated that this reaction commenced at about 620 degrees C. Rietveld refinement of the PXRD data recorded at 20 degrees C showed that Na(6)Ma(2)[Al6Si6O24](SO4)(2) crystallizes with a cubic cell, a = 0.89780(2) nm, and is isostructural (I (4) over bar 3m) with the mineral hauyne, Na6Ca2[Al6Si6O24](SO4)(2). The product material contained traces of Mn2O3 which imparts a purplish-brown coloration; highlighting the problem of preparing Na6Mn2[Al6Si6O24](SO4)(2) as a monophasic material within the narrow temperature 'window' available for this reaction.