The problem with rare earths is you get a mix of different rare earths in the final concentrate, which then have to be separated from each other using a lot of

The problem with rare earths is you get a mix of different rare earths in the final concentrate, which then have to be separated from each other using a lot of time-consuming steps, since they're vary similar chemically (technically, having identical d- and s-orbital configurations, only differing in f-orbitals). An active area of research: https://www.ornl.gov/news/game-changing-rare-earth-elements-separation-technology-licensed-marshallton https://www.ornl.gov/news/game-changing-rare-earth-elements-...