Mineralogical study of phosphate rocks by quantitative rietveld refinement

Abstract

Phosphorites from the Kodjari deposits of Burkina Faso are composite rocks with a fine-grained matrix phase and dispersed larger grains. Chemical analysis by XRF revealed a CaO content of 35.98–41.33 wt% and a P2O5 content of 26.85–30.75 wt%. X-ray diffraction patterns show the abundant presence of carbonate-fluorapatite (Francolite), Hydroxyapatite and Quartz, with the minor phases Wavellite, Maricite and phyllosilicates. The mineralogical compositions by Quantitative Rietveld Analysis shows the presence of 75.41–83.85 wt% of phosphate phases, with carbonate structural groups in Francolite and Hydroxyapatite, while F ions are in the Francolite structure. FTIR analyses also validates the identification of mineral phases with the observation of bands from structural phosphate groups, from carbonate groups and from structural F. This study highlights the effectiveness of Quantitative Rietveld Analysis in quantifying the mineralogical composition of phosphorites. The method is suitable for monitoring the exploitation of mineral deposits.

Keywords

• Phosphate
• Mineralogy
• X-ray diffraction
• Rietveld refinement
• Infra-red spectroscopy