Removal of rare earth elements by algal flagellate Euglena gracilis

Abstract

Removal of rare earth elements (REEs) from an acid solution by an algal flagellate, Euglena gracilis, was studied. Sixteen kinds of REEs were spiked to the solution at a final concentration of 10 μg L −1 for each element. E. gracilis cells grown in the solution under 12 h light–dark cycles efficiently removed REEs during the 21-day experimental period. Significant removal was observed from days 14 to 21 of incubation. On the last day, concentrations of REEs were less than 0.7 μg L −1 except for Sc. The concentration of Sc was 2.8 ± 0.4 μg L −1, suggesting that Sc removal was relatively difficult compared to the other REEs. Among REEs, the same level of removal was observed for light REEs (La–Eu) but not for heavy REEs (Ga–Lu). Heavy REEs removal tended to decrease with an increase in atomic number. The removal of REEs by E. gracilis were affected by lighting conditions because E. gracilis cells grown in the dark had removed just a small amount of REEs, less than 10% of total, through day 21 of incubation.