THERMAL TRANSFORMATIONS IN PHOSPHORITES

The thermal transformations in phosphorites during flash calcination w ere investigated by FT-IR spectroscopy, X-ray diffraction and chemical analyses. During flash calcination changes occur, both in the composi tion of the phosphorite and in the crystallochemistry of the fluor-car bonate-apatite (francolite). The former changes include: decomposition of a great part of the calcite in the rock and oxidation of organic m atter. The latter changes include: partial removal of the structural c arbonate; partial relocation of the remaining carbonate ions in the ap atite structure; a new arrangement of hydroxyl groups and fluorine on the hexagonal axis; partial condensation of the orthophosphate groups and increase of crystallite sizes. Isomorphous substitution of PO4-3 i n apatite by SO4-2 and SiO4-4 may take place.