Chemical, mineralogical and rare earth elements distribution study of phosphorites from Sra Ouertane deposit (Tunisia)

Abstract

The chemical and mineralogical compositions of four layers (A1, A2, B and C) from the Sra Ouertane phosphorite deposit were studied. Chemical characterization of each sample, classified as five size fractions, reveals that the richest samples in P2O5 are the fine fractions 40 μm ˂fSR˂ 125 μm of the layers A2 and C with a P2O5 content of 17%. Mineralogical characterizations of the samples were undertaken by X-Ray diffraction revealed that the main minerals are carbonates, carbonate fluorapatite and quartz. The highest REEs + Y + Sc concentration values were recorded for Y in all samples, followed by La and Ce. Higher concentration of REEs was found in layers A2 and C which are the richest layer in P2O5 indicating that REEs content has a close relationship with the P2O5 concentration. However REEs concentrations are not equally distributed in the different size fractions, the maximum concentrations were found in fraction 40 μm ˂fSR˂ 125 μm. Moreover, REEs in Sra Ouertane deposit have the highest values of all the Tunisian phosphorites. The present work contributes to a better understanding of the relation between the mineralogical and chemical composition (e.g. REEs, Cd, Th and U) in different layers and different size fractions of Sra Ouertane phosphorite.