A Review of the Distribution, Isolation, and Catalytic Activity of Rare-Earth Elements

Name of Speaker: Robert B. Pace III
September 22, 2017; 2:00PM, CP-114B

The increasing recalcitrance of Rare-Earth elements has generated a renewed focus on the isolation, extraction, and recycling of these elements and the materials that contain them. The National Science Foundation and DOE have recently issued numerous requests for proposals to study more effective recovery methods for these materials in addition to the investigation of new sources of Rare-Earth bearing substances such as coal byproducts. To understand the importance of these materials, their origins and distribution will be discussed, with further emphasis placed upon their isolation along with a discussion of novel sources of these materials. Finally, the catalytic properties of Rare-Earths will be explored through a discussion of the electronic properties from which their catalytic activity arises.

Growth of the utilization of rare-earth materials has begun to outstrip the industrial capability to supply these materials, resulting in unstable prices even as their ubiquity and usefulness continue to increase.1 The Rare-Earth elements, being heavier than iron, are formed primarily by stellar nucleosynthesis in a process of rapid neutron capture (the R process).2 The result of this unique astrophysical origin is that the name Rare-Earth is somewhat misleading as the Rare-Earths are not actually especially rare. However, these materials do not tend to concentrate through geological processes as many other elements do, and they are often found as mixtures in a variety of minerals, leading to difficulty in their extraction and purification.3

The increasing use of Rare-Earth derived materials has expanded into many areas of electronics, batteries, magnetic materials and an impressive array of catalytic processes. Rare-Earth elements and their oxides have been shown to possess properties which allow them to act as catalyst supports, catalytically active metals, and as catalytic promoters in automotive emission catalysis. The modern three-way automotive catalytic system limits the release of NOx, CO, and unburned hydrocarbons by converting them to less harmful compunds.4 Future interest in Rare-Earths is likely to only increase as their usefulness is fully explored.

1. Golev, A.; Scott, M.; Erskine, P. D.; Ali, S. H.; Ballantyne, G. R., Rare earths supply chains: Current status, constraints and opportunities. Resources Policy 2014, 41, 52-59.
2. Mumpower, M. R.; McLaughlin, G. C.; Surman, R.; Steiner, A. W., The Link between Rare-Earth Peak Formation and the Astrophysical Site of the R Process. The Astrophysical Journal 2016, 833 (2), 282.
3. Ujaczki, É.; Zimmermann, Y.; Gasser, C.; Molnár, M.; Feigl, V.; Lenz, M., Red mud as secondary source for critical raw materials–purification of rare earth elements by liquid/liquid extraction. J. Chem. Technol. Biotechnol. 2017.
4. Machida, M.; Eidome, T.; Minami, S.; Buwono, H. P.; Hinokuma, S.; Nagao, Y.; Nakahara, Y., Tuning the electron density of Rh supported on metal phosphates for three-way catalysis. The Journal of Physical Chemistry C 2015, 119 (21), 11653-11661.