Évolution du CO2 lors de la calcination d'un phosphate apatitique suivie d'une carbonatation par CO2 gazeux

The phenomena of decarbonatation and recarbonatation of the apatite have been studied on calcareous phosphate (Kasrik, Turkey) characterized by low contents of phosphate (14.6 % P₂O₅), sulfur (traces), organic matter (0.15 % C), chlorine (0.01 %) and magnesium (0.5 % MgO). The phosphate phase is made up of a carbonatofluoroapatite in which parameter a of the apatite lattice is equal to 9.341 Å. Thermograms show an important endothermicity, due to the loss of water and to the dissociation of carbonate. The exothermicity effect, connected with the burning of organic matter, compensates partly the endothermicity (the ore samples are crushed to a grain size of 400 μm). The calcination is operated in a muffle furnace at 950 ° and 1 000 °C for about 1 h. After roasting, quenching, washing and attriting, the calcined product is treated by gaseous CO₂. During the calcination, parameter a increases from 9.341 to 9.351 Å, and after recarbonatation decreases from 9.351 to 9.347 Å, corresponding to a decrease of the apatitic CO₂ from 3.8 to 1.1 % and then to an increase to 2.1 %. In final analysis, it appears that the phenomena of thermal decarbonatation and, then, of recarbonatation after cooling, present important consequences on ore beneficiation technologies.