Economic recovery of REEs is recognized as one of the greatest challenges of industrial inorganic separation. This challenge originates from the unique mineralogy, occurrence, and physicochemical properties of REEs. Amongst the identified 20 critical raw materials for the entire global economy, the rare earth elements (REE) have the highest risk of secure supply issues. REE are a group of 17 elements comprising 15 lanthanides plus Yttrium (Y) and Scandium (Sc). These elements are strategic and critical for both green-tech (solar/fuel cells, electric vehicles, wind turbines, low emission engines, high-strength magnets, energy-efficient lighting) and high-tech (electronic and electric devices, hard disk drives, advanced alloys, catalysts). REE are also used by the defence sector in precision-guided munitions, smart bombs, sonars, and radars. 

The state-of-the-art of industrial REE extraction is to concentrate REE minerals using froth flotation aided by physical separation methods such as multi-gravity, magnetic and electrostatic techniques. The concentrate is then treated with a mineral acid to leach out REE, followed by further purification using a hydrometallurgical method, typically solvent extraction. Unfortunately, both froth flotation and solvent extraction are the antitheses of green chemistry, which severely limits their future in the 21^st century. However, green surfactants produced from renewable sources or by bioprocesses offer important benefits compared to the conventional (petroleum-based) counterpart, such as biodegradability, better recyclability, and non-toxicity.   

Emerging greener approaches to make REE extraction more environmentally acceptable are presented and discussed, including their advantages and limitations with respect to conventional REE extraction methods. An alternative cutting-edge foam flotation separation method, a proposed hybrid of froth flotation and solvent extraction, (where the organic solvent is replaced by air, the surfactant acts as an extracting agent, and the stripping step is replaced by physical collection of the cation-enriched foam). This technology is environmentally more sustainable than the conventional and emerging methods of REE extraction.