Spectroscopic characterization of the phosphate mineral florencite-La – LaAl3(PO4)2(OH, H2O)6, a potential tool in the REE mineral prospection

Abstract

We have studied bluish green crystals of the mineral florencite-(La) from Serra dos Carajás, Pará, Brazil. Qualitative chemical analysis shows a La and Al phosphate with traces of Ce, Nd and Pr in substitution for La. Two sharp Raman bands at 987 and 1021cm−1 assigned to the PO43- and HPO42- symmetric stretching modes. Raman bands at 1064, 1112 and 1221cm−1 are attributed to the PO43- and HPO42- antisymmetric stretching modes. Raman bands at 404, 464, 524 and 526cm−1 are assigned to the PO43- ν4 bending modes; An intense Raman band at 614cm−1 with shoulder bands at 680 and 647cm−1 are assigned to the PO43- ν2 bending modes.A sharp Raman band observed at 3649cm−1 is assigned to the stretching vibration of the OH units. Raman bands at 2906, 2988, 3158 and 3440cm−1 and infrared bands at 2808, 2956, 3117 and 3416cm−1 are attributed to water stretching vibrations. The spectra in the OH stretching region support the concept of both hydroxyl and water units in the structure of florencite-La, thus confirming the formula as LaAl3(PO4)2(OH, H2O)6.