Investigation of the structural and mineralogical changes of Tunisian phosphorite during calcinations

摘要

The thermal behavior of Tunisian phosphorite was investigated with X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR), and Raman spectroscopies and DTA-TG measurements. The XRD patterns showed that the chief mineral constituents of calcined samples are calcium oxide and fluorapatite, while those in the raw phosphorite are calcite, dolomite, fluorapatite, and carbonate-fluorapatite. Physicochemical transformations result in the oxidation of organic matter, disappearance of calcite and dolomite crystalline phases, and partial dissociation of structural carbonates. The FT-IR and Raman spectra showed modifications of some bands; a decrease in the intensity of the v(2) and v(3) vibrations of carbonate groups and the appearance of new bands at 520 and 926 cm(-1) after calcination of phosphorites at 800 degrees C. These bands were assigned to isomorphous substitutions of PO43- in apatite by SiO44-. Heat treatment alters the qualitative composition of the mineral as a resu the solubility of apatite in dilute citric acid was decreased.