Scandium and Rare Earths in Major Rivers in Sweden

Scandium (Sc) is often included in the group of rare earths and yttrium (REY), but in contrast to the REY, knowledge on its behaviour in the hydrosphere is rather limited. However, a better understanding of the distribution and behaviour of Sc is important, as its use in industry is expected to grow exponentially in future, which will likely result in an increasing Sc release into the environment. Here, we report and discuss Sc and REY data for the “dissolved fraction” (<0.2 µm) from twelve pristine rivers in Sweden sampled in May 2019. All rivers are characterised by low conductivity (18-60 µS/cm2), slightly acidic to neutral pH (6.04-7.11) and elevated dissolved organic carbon (DOC) concentrations (5.50-10.3 mg/L). Their shale-normalised REY patterns show a slight enrichment of heavy REY (HREY) compared to light REY (LREY), and negative Ce and positive Y anomalies. Some rivers also show a negative Eu anomaly. The REY distribution in these rivers is controlled by nanoparticles and colloids (NPCs) present in the dissolved fraction. Compared to data from 2014, all rivers show higher REY concentrations and a slightly lower HREY enrichment, suggesting a higher NPCs content in the rivers in 2019. Scandium concentrations vary between 0.363nM and 1.17nM and increase with increasing DOC and Fe concentrations. This suggests that Sc has a strong affinity for NPCs, similar to the REY. The association of Sc with DOC further suggests a significant impact of organic ligands on the behaviour of Sc in the hydrosphere.