Abstract
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 v2 and v3 vibrations of carbonate groups and the appearance of new bands at 520 and 926 cm−1 after calcination of phosphorites at 800 °C. These bands were assigned to isomorphous substitutions of PO4 3− in apatite by SiO4 4−. Heat treatment alters the qualitative composition of the mineral as a result; the solubility of apatite in dilute citric acid was decreased.
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