Editorial for Special Issue "Leaching of Rare Earth Elements from Various Sources".

Rare earth elements (REEs) have become an important group of metals used in many high-tech industries, including high-strength magnets, plasma TVs, various military applications, and clean and efficient green energy industries. Most of the REE-bearing minerals are refractory in nature, and therefore, in order to extract REEs from them it is necessary to increase the acidity, or they have to be subjected to pre-treatment with lixiviants such as sulfuric acid or sodium hydroxide before subjecting them to leaching. However, the current coal seam clay materials seem to contain REEs mainly as refractory REE-phosphates, and therefore, only the partial recovery of REEs was possible. [Extracted from the article]