"Modern technologies increasingly rely on a diverse group of materials to enable their functionalities. Those materials which are both essential to system performance and at risk of supply disruptions are deemed critical. The prime examples of current critical materials are the rare-earth elements (REE), which deliver immense value in civilian industries, including in renewable energy, chemical catalysis, metallurgy, and advanced manufacturing, and unmatched performance in a long list of military applications. Development and deployment of new technologies in these areas is constrained by concerns about availability of rare earths, the stability of their supply chains and the environmental damage caused by their production. A key to enhancing and stabilizing rare-earth supplies is technology development that will enhance conventional sources of rare earths, as well as unlock unconventional sources at mines and from manufacturing wastes and in end-of-life products -- in ways that adequately protect the natural environment and human health. Rare earth elements and critical materials, thus, in general, are being viewed often as isolated chemical substances with their fundamental atomic properties that are used in various applications. However, due to the important role they play in the modern technology as well their geographic distribution, they are considered as new spices of the 21st century"-- Provided by publisher.