Geochemistry and mineralogy of Ogun phosphate rock

Abstract

Suitability of direct application of phosphate rock as low cost phosphorus fertilizer for crop production must be environmentally safe. Four pellets of Ogun phosphorites labeled OG1, OG2, OG3 and OG4 were randomly selected and subjected to petrographic, X-ray diffraction and X- ray fluorescence analyses. Petrographic results revealed two textural forms: nodular (OG1 and OG3) and granular (OG2 and OG4). Characteristic features like fine grains of phosphorites, geopedal texture with heavy iron staining were found in nodular form while presence of shell fragments and bioclastic materials with burrows were observed in granular form. The diffractogram of different pellets showed poorly crystalline mineral, flourapatite was identified as the major apatite mineral. X-ray fluorescence results showed wide variations in elemental composition among the different forms of Ogun phosphorites. In nodular phosphorites (OG1 and OG3), apatite content were 31.28 and 30.20% P₂O₅ respectively, Granular phosphorites (OG2 and OG4) contain 19.73 and 11.12% P₂O₅. The alkali metals K₂O and Na₂O are variable and low showing its suitability as P source because minimal salt is added to the soil. Radionuclides present have low values (U 19 to 29 ppm; Th 5 to 13 ppm; Ni 41 to 80 ppm) indicating its environmental security.

Key words: Phosphorus, phosphorites, Ogun phosphate rock, x-ray fluorescence analysis, x-ray diffraction analysis, petrography analysis.