Understanding the potential mobility of geogenic metals of concern from heavy mineral sands

Iron oxide and hydroxide minerals are widespread in many aquatic environments and as such, can determine the fate of several metals of concern. Their role on metal mobility is generally studied under controlled conditions using synthetized materials. However, natural systems are complex and present a wide range of conditions, which may release metals differently to laboratory settings. In this study, we aim at understanding the mobility of geogenic, technology critical elements such as vanadium, nickel, cobalt, niobium, and tantalum from black sand sediments. These sediments from the OIB volcanic environment of the Canary Islands are the product of weathering and erosion of relatively geologically recent, ultramafic volcanic rocks composed of basanitic, phonolitic, nephelinitic and, locally, melilitic lavas and tuffs, sources of mafic heavy minerals deposited as a placer. The sediments were extracted through magnetic separation, characterized via XRD and SEM-EDS techniques, and further processed with a series of parallel selective extractions following widely applied protocols. Desorption kinetics during the extraction procedures were also investigated in order to understand the efficiency of the protocol for such sediments. Total element concentrations were quantified via XRF and LA-ICP-MS, whereas dissolved concentrations were determined via ICP-MS. Our results point towards contrasting selectivity during the extractions and different iron oxide mineral fractions in which these metals are bound. This information has a broad application for the potential environmental risk of metal mobility in aquatic systems.

Acknowledgements:

This work was funded as part of the Excellence Strategy of the German Federal and State Governments.