Oxidation and Nanoparticle Formation during Ce(III) Sorption onto Minerals

Area of Science:

• Environmental Science
• Geochemistry
• Materials Science

Background:

• Cerium (Ce) is a rare earth element with environmental relevance.
• Understanding Ce sorption on minerals is crucial for predicting its fate and transport.
• Environmental minerals like goethite, anatase, and birnessite are common sorbents.

Purpose of the Study:

• Investigate the sorption behavior of Cerium(III) on goethite, anatase, and birnessite.
• Determine the influence of mineral type on Ce oxidation state and speciation.
• Characterize the formation of any secondary phases during sorption.

Main Methods:

• Batch sorption experiments using a radioactive ¹³⁹Ce tracer.
• Advanced characterization techniques: High-resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS), X-ray absorption spectroscopy (XAS).
• Theoretical calculations to support experimental findings.

Main Results:

• Sorption kinetics and oxidation state changes differed significantly for birnessite compared to goethite and anatase.
• Ce(III) was oxidized to Ce(IV) on birnessite surfaces, while remaining as Ce(III) on goethite and anatase.
• CeO₂ nanoparticle formation occurred on birnessite, dependent on Ce concentration and pH.

Conclusions:

• Birnessite actively oxidizes sorbed Ce(III) to Ce(IV), forming CeO₂ nanoparticles.
• Goethite and anatase exhibit passive sorption of Ce(III) without significant oxidation.
• Mineralogy plays a critical role in controlling cerium's environmental behavior and transformation.