Thermal behavior and phase transformations of nanosized carbonate apatite (Syria)

The phase transformations of Syrian phosphorite upon mechanochemical activation are examined in the present work. The latter is carried out in planetary mill equipped with 20 mm steel milling bodies and duration from 30 to 300 min. The established by means of DTA, DTG, TG analyses transformation of non-activated carbonate fluorine apatite type B into the carbonate hydroxyl fluorine apatite (COHFAp) mixed type A2-B leads to substantial changes in the properties of the activated samples expressed in lowering the degree of crystallinity, strong defectiveness of the structure, and increase of the citric solubility. The thermal analysis gives evidence for the decomposition of the carbonate-containing component within the phosphorite, as from the positions placed in the vicinity of the hexagonal 6₃ axis (type A2), as well as from the positions of the phosphate ion (type B), and from the free carbonates. The data from the thermal analysis, the powder X-ray analysis and the infrared spectroscopy give also evidence for phase transformations of the activated apatite (with admixtures of quartz and calcite) into Ca₁₀FOH(PO₄)₆, β-Ca₃(PO₄)₂, Ca₄P₂O₉, Ca₃(PO₄)₂ · Ca₂SiO₄ and for that one of the quartz—into larnite and wollastonite. The influence of the α-quartz as a concomitant mineral is considered to be positive. The α-quartz forms Si–O–Si–OH bonds retaining humidity in the solid phase thus facilitating the isomorphous substitution OH^? → F^? with the subsequent formation of partially substituted COHFAp. Calcium silicophosphate and Ca₄P₂O₉ are obtained upon its further heating. The presented here results settle a perspective route for processing of low-grade phosphate raw materials by means of tribothermal treatment aiming at preparation of condensed phosphates suitable for application as slowly acting fertilizer components.