Dear Jorge Gonzalez

Actually from my view of point, to settle down thus REE from iron constituent or mineral you might be using the Chlorination or oxychlorides methods as  catalyst or agent to reduces REE species from Iron in certain of high temperature extent at 790K->1300K. But any way this is only old suggestion for more detail you can refer to Boguslawa Jezowska Trazebiatowska et al 1990 in The Rare elements occurrence and Technology. 

Best regard's

Zolhizir bin Daud

Thanks for the answer Zolhizir