Thermal behaviour of Estonian phosphorites from different deposits

Thermal behaviour of shelly Estonian phosphorite ores from Iru, Toolse, Ülgase deposits and their concentrates have been studied. The phosphorus-bearing mineral in Estonian phosphate ore is fluorcarbonate apatite (francolite), originated from brachiopod Obolus apollinis shells that makes it different from all other sedimentary phosphate ores. The experiments on a Setaram Labsys Evo 1600 thermoanalyzer coupled with Pfeiffer Omnistar Mass Spectrometer for evolved gases analysis were carried out under non-isothermal condition at the heating rate of 10 °C min−1 up to 1200 °C in an oxidizing and inert atmosphere containing 79% of Ar and 21% of O2 or 100% Ar, respectively. The results obtained indicated the complicated character of transformations occurring at thermal treatment of Estonian phosphorites and certain differences depending on the mineralogical composition of sample and gaseous environment. The changes in francolite structure, probable substitution of sulphur additionally to carbonate, were studied by FTIR and XRD. The oxygen in gaseous atmosphere suppresses the liberation of carbonate and sulphate from the structure of francolite. The character of CO2 and SO2 release at heating depending on the atmosphere composition was explained. The impact of thermal treatment of phosphorite on the P2O5, CaO and SO4 −2 solubility in 2% citric acid solution and on the particles pore volume, as well as their dependence on each other, was also studied