Selective recovery of heavy rare earth elements from apatite with an adsorbent bearing immobilized tridentate amido ligands

• The recovery of heavy rare earth elements (HREEs) from apatite was investigated.
• REEs in an apatite concentrate were leached efficiently at 2 mol/L H2SO4.
• HREEs in the leachate were selectively adsorbed onto a column packed with EDASiDGA.
• Passage through the column enriched HREEs by 10- to 30-fold.
• The eluate contained only small amounts of other elements (e.g., Al, Ca, and Fe).

Apatite, which is used in the production of phosphorus fertilizers, contains small amounts of rare earth elements (REEs; 0.1–1%). Apatite deposits occur all over the world and thus have the potential to be a secure source of REEs. We investigated a method for recovery of REEs from an apatite sample; specifically, REEs were leached from the sample with an H2SO4 solution, the acid that is most commonly used for fertilizer production. At high H2SO4 concentrations, most of the REEs in the solution were lost to precipitation as insoluble gypsum (CaSO4·2H2O). However, at H2SO4 concentrations of <2 mol/L, loss of REEs in the form of gypsum was reduced. To recover the REEs from the pregnant solution (the leachate), we used a column packed with an adsorbent composed of silica gel particles modified with diglycolamic acid groups. Passage through the column enriched the heavy REEs by 10- to 30-fold, and the eluate contained only small amounts of other elements (e.g., Al, Ca, and Fe), even though they were present at high concentrations in the pregnant solution.