Substitution mechanism of rare earths at fluorapatite characteristic sites: experimental and computational calculations

Abstract

Rare earths (REs) containing phosphate rock is a potential REs resource. The unclear occurrence mechanism of REs in phosphorite limits its further development and utilization. Fluorapatite (FAP) is the main REs-bearing target mineral in phosphorite, the microscopic mechanism of REs entering FAP still needs to be further studied from the electronic scale. In this paper, the doping mechanism of REs in FAP was studied by experiment combined with GGA+U calculation. The XRD, SEM, and FT-IR characterization results of hydrothermal synthesis products showed that REs (La, Ce, Nd, and Y) entered FAP crystal, and one of every 20 Ca atoms was replaced by a REs atom. The GGA+U calculation indicated that La-O/F, Ce-O/F, Nd-O/F, and Y-O/F were ionic bonds in general, and the bonding strength of La-O/F, Ce-O/F, Nd-O/F, and Y-O/F increased gradually with atomic number. The substitution difference of La, Ce, Nd, and Y was mainly caused by the gain and loss of electrons in f and d orbitals. The substitution mechanism of REs at the characteristic sites of Fap was studied, which provided a theoretical reference for the selective recovery of REs from phosphorus blocks.

Selective removal of dolomite from rare earth element‐bearing phosphorite by flotation and leaching and the adsorption mechanism of agents on mineral surfaces

“…When the element content was too low, the obtained data had a poor signal‐to‐noise ratio and could not extract useful information. Meanwhile, because all REEs were replaced in the form of isomorphism in Fap, they had similar occurrence forms in phosphorite 31,32 . The changes of yttrium in different phases before and after leaching were similar to other REEs.…”

“…Studies have shown that the contents of REEs increased with the increase of Fap content, 9,29 but there was no evidence to suggest that it increased with the increase of Dolo content 30 . It was currently recognized that REEs mainly replace calcium atoms in Fap in the form of isomorphism, 31,32 and the content of REEs was often positively correlated with the content of Fap. Dolo contained a certain amount of REEs, but compared with Fap, the content of REEs in Dolo was very low.…”