Ce, Gd and Yb accumulation in microalgae: an L-edge XAS study

The extraction and separation of rare earth elements (lanthanides) can be difficult due to their chemical similarities. Biological processes can have very selective activity towards different elements. We investigated the use of microalgae for this purpose by looking at the interaction of Ce, Gd and Yb with the microalga Chlamydomonas reinhardtii, which has been induced to form polyphosphate granules. X-ray absorption spectroscopy with XANES and EXAFS at the Ce L₃-edge, Gd L₃-edge and Yb L₃-edge was used to characterize the interaction between the lanthanides and the phosphate-containing algae. All three of the lanthanides, added as the chloride salt to the algae, appeared to react to form phosphate compounds. These form both in the presence of phosphate granules or when there is only a low level of P present. CePO₄ could be determined by XANES, but the structures of GdPO₄ and YbPO₄ were determined by EXAFS analysis without reference to the XAS spectra of the standard compounds. It is proposed that C. reinhardtii or other similar microalgae may be useful in the selective removal of rare earths from solution.