The potential mobility and availability of trace elements in sediments/soils is commonly assessed via selective extractions. In this work, three contrasting sediments, i.e., Rhine riverbank sediment, alkaline volcanic heavy mineral sand, and mine tailings from a Mississippi-valley type ore deposit, are extracted with an oxalate-based solution and compared in terms of trace element mobility from both amorphous and crystalline Fe-Mn-carrier phases. Major and trace elements are characterized in the supernatants via ICP-OES and (HG-)ICP-MS, whereas the residual material is characterized via XRD. The obtained Fe/Si and Mn/As ratios highlight distinct sediment behavior over time. Overall, our results show a significant kinetic component, increasing concentrations for some elements like Fe, Mn, Ti, Si, Al, Mg, Sr, Na, Ge, Sc, and HREE (for the black sand), and decreasing for Ca, K, Y, REE after reaching supersaturation, e.g., formation of a characteristic whitish precipitate. Even though the protocol was successful at destroying most of the Fe-Mn(-Ti) minerals, the crystallization and sedimentation of oxalate salts may be due to the absence of stabilizing agents in solution. A similar situation occurs in the case of urolithiasis, where supersaturation of calcium oxalate in the kidneys, if not inhibited, promotes precipitation. Thus, the findings of this study not only highlight the environmental mobility of technologically critical elements in aquatic systems, but also their potential retention/accumulation in kidney stones.
Acknowledgements:
This work was funded as part of the Excellence Strategy of the German Federal and State Governments.