The 17 rare earth elements (REEs) are: lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium (the 15 lanthanides), along with scandium and yttrium. Despite their name, most are relatively abundant in the Earth’s crust, but they are difficult to separate from one another and are not often found in concentrated deposits. Most ree deposits do not have all the rees.
“...difficult to separate from one another...” is an understatement. Often they are chemically very similar to other ree’s, so require strong caustic solvents at high temperature and pressure to separate them. Which produces a lot of very toxic pollutants.
How much separation is needed?
If Company T uses 25%A/25%B/50%C, will a partially refined mix of 18%A/22%B/40%C/12%E/8%F work?