Effect of mechanochemical activation on the chemical activity, structural and thermal properties of carbonate-substituted apatite from Syria. Part II. Thermal investigations.

The present paper studies phase transitions of the Syrian phosphorite which have occurred after mechanochemical activation with different in size iron-milling bodies for a period of 30 min. The method of mechanochemical activation is an alternative for using poor in useful component (P2O5) raw materials and eliminating the disadvantages of the traditional technologies which create a negative effect on the environment. The results from the thermal analysis give evidence for the presence of substantial structural and phase transformations which have occurred in the samples of the Syrian phosphorite during the period of activation and which come as a development and supplement of part I. The registered thermal effects are connected with: the thermal decomposition of CaH2P2O7, obtained during the period of activation; release of the in-built carbonate groups in the vacancies of the calcium ions which characterise the transformation of carbonate fluorine apatite type B into carbonate fluorine apatite type A2 or AB during the period of activation; decomposition of the obtained during the period of activation isomorphously-substituted apatites: Ca-10(PO4)(6)(OH) F, Ca-10(PO4)(6)(OH)(2) and Ca-10(PO4)(5)CO3(OH)F and the formation of Ca4P2O9. This result finds out a perspective direction for processing the phosphate raw materials by means of tribo-thermal treatment aiming at obtaining condensed phosphates suitable for application as slowly acting fertilisers.