Sorption of Rare Earth Elements by Synthetic Hydroxyapatite

The sorption capacity of synthetic hydroxyapatite with respect to rare earth cations in aqueous solutions at pH 2.5 and 7.0 was studied. It was shown that, at pH 2.5, the most exhaustive recovery (up to 99%) of the rare earth elements from the solutions was achieved. Modeling the process using sorption isotherms and kinetic curves indicates the dominance of chemical sorption mechanisms. Scanning electron microscopy, IR spectroscopy, and X-ray diffraction analysis revealed structural and morphological changes in hydroxyapatite after sorption, confirming the chemical nature of the sorption of the lanthanum cations, accompanied by ion exchange with the calcium cations of hydroxyapatite.