The Lanthanide Problem
Because all rare earth elements are chemically almost identical, they cannot be easily separated. You cannot just precipitate “Neodymium” without also precipitating “Praseodymium.”
How SX Works
Solvent Extraction uses two immiscible liquids (like oil and water). The rare earth solution is mixed with an organic solvent containing a special extractant. The extractant prefers one element slightly more than its neighbor (e.g., it likes Neodymium slightly more than Cerium).
The Battery of Cells
Because the difference is so small, this process must be repeated hundreds or thousands of times. An SX plant looks like a massive maze of “mixer-settler” tanks. The liquid moves through stage after stage, slowly increasing the purity of the target element until it reaches 99.9% or higher.