Fractionation and Risk Assessment of Rare Earth Elements in Drill Cuttings from Petroleum Wells in Ultra-Deep Waters

The mobility and bioavailability of rare earth elements (REE) from anthropogenic activity has aroused environmental interest and concern. In this work, we evaluated the chemical fractionation of REE in drill cutting (DC) samples from oil wells in ultra-deep waters by the European Community Bureau of Reference (BCR) sequential extraction procedure. Sequential extraction in the DC samples showed that the concentration of REE in the fractions followed the order of residual > reducible > weak acid soluble > oxidant. The environmental risk, evaluated by the risk assessment code (RAC), potential ecological risk factor ([Formula: see text]) and potential ecological risk index (IR), indicated, in general, a low ecological risk associated with the REE in DC samples. Furthermore, the mineralogical composition analysis of DC, performed by X-ray powder diffraction (XRD), showed that sample composition is mainly of quartz and calcite, while analysis by X-ray fluorescence spectrometry (XRF) indicated that the perforated rocks are composed of aluminosilicate minerals with high levels of SiO₂ and Al₂O₃.