Cerium anomaly

Contrary to other lanthanide elements, which are only trivalent (with the notable exception of Eu2+), Ce3+ can be oxidized by atmospheric oxygen (O2) to Ce4+ under alkaline conditions.

[1] Sediments deposited under oxic or anoxic conditions can preserve on the long term the geochemical signature of Ce3+ or Ce4+ upon reserve that no early diagenetic transformation altered it.

[3] If the oxygen fugacity is high, more Ce3+ will oxidize to Ce4+ and create a larger positive Ce anomaly in the zircon structure.

[3] Cerium in coal is typically weakly negative, meaning that it is present at slightly lower concentrations than the other rare-earth elements.

[2] In contrast, coal mined in felsic rock regions, such as Guxu Coalfield in China, does have weakly negative Ce-anomalies.

Crystal structure of Ceria-zirconia. Ce 4+ has the same charge and similar ionic radius as Ze 4+ resulting in elemental substitution and therefore a positive cerium anomaly. [ 1 ]