The sinks of rare earth elements in peloids from hydrothermal, estuarine, coastal, and saline formation environments from Cuba

Abstract

This study investigated the main inorganic sinks of rare earth elements (REEs) in six peloid samples from four geological environments (hydrothermal, estuarine, coastal, and saline). We collected samples from each environment and determined pH, electrical conductivity, redox potential, temperature, elemental concentrations (major, minor, and REEs), mineralogy, and REE speciation. Additionally, principal component, hierarchical cluster, and multivariate analyses were used to investigate any relationship between REEs and phyllosilicates, iron, manganese, aluminum, and inorganic and organic carbon. Results showed that peloids from hydrothermal and estuarine environments presented the highest concentrations of minor elements and REEs (up to 109.78 mg/kg) with mineralogy dominated by quartz (31.6 to 92.4%) and phyllosilicates (49.3%). In contrast, coastal and saline peloids presented low concentrations of minor elements and REEs (up to 6.47 mg/kg) with mineralogy dominated by calcite (up to 74.6%), aragonite (up to 25.8%), and evaporitic minerals. Positive relationships were found between REE concentrations and the percentages of phyllosilicates (r = 0.978) and iron concentration (r = 0.986), which were supported by the operational speciation that showed that REEs were mainly associated with the residual and reducible fractions in hydrothermal and estuarine peloids. In coastal and saline peloids, the lower concentrations of REEs were attributed to their distribution on the reducible and oxidable fractions, from which they can mobilize. The results from this study revealed the inorganic sinks of REEs in peloids from hydrothermal, estuarine, coastal, and saline environments.