Rare earth element mobility in contrasting sediments

Contrasting sediments behave radically differently in aquatic systems, releasing elements of concern. Their behavior is a function of mineralogy, geochemical composition, and the conditions of the medium (e.g., ionic composition, pH). One way of understanding the reactivity of contrasting sediments, but also the operationally defined fraction of the associated elements is to use selective extraction protocols. Nevertheless, these are generally used without verifying the adequacy of the extraction times, in accordance with the sediment characteristics, nor the potential impact of element-specific behavior to the extracting reagents, biasing the final interpretation. This study aims at providing such understanding for the rare earth elements (including lanthanides, yttrium, and scandium). The sediments used originate from modern aquatic sedimentary environments of both terrestrial and marine-transitional origin, associated to either natural (beach and riverbank sediments) or anthropogenic (mine tailings) sources. A qualitative mineralogical determination of the sediments was performed via XRD. Element mobility was studied via selective extraction protocols applied in parallel, with a kinetic approach, and sequentially. Quantitative analysis of the total concentrations of major and trace elements was determined via XRF-EDX, ICP-OES and ICP-MS, to obtain elemental correlations and total REY+Sc sediment content for mass balance purposes. For each extraction solution, the elemental concentrations were quantified via ICP-MS. The information gained in this study provides further experimental results on the unknown aquatic behavior of REY+Sc elements, for which there is currently an increasing demand for major technological applications.

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Funded as part of the Excellence Strategy of the German Federal and State Governments.