Synergistic adsorption of lanthanum ions and fatty acids for efficient rare-earth phosphate recovery: Surface analysis and ab initio molecular dynamics studies

Abstract

Rare earth elements (REE) are indispensable in our daily life but they naturally occur in minerals, which are generally difficult to concentrate by the froth flotation method. Considering the significant affinity of lanthanum ions for phosphate species as well as for carboxylate groups, the influence of a lanthanum salt (LaCl3) on the adsorption of carboxylate species on monazite surface [(La,Ce,Nd)PO4] was investigated by bubble/particle adhesion tests, X-ray photoelectron spectroscopy (XPS), and atomistic simulations based on density functional theory (DFT). Both theoretical and experimental results demonstrated that lanthanum ions adsorb on the phosphate groups of monazite surface under the LaClCO3 form with a significant adsorption energy. Also, the hydrophobization of the monazite surface with fatty acids is considerably improved in presence of LaCl3, which is in accordance with DFT calculations: the lanthanum ions pre-adsorbed on monazite surface act as highly attractive adsorption sites for carboxylate collectors. In particular, these bridging cations significantly increase the adsorption energy of carboxylate collectors, from 344 to 420 kJ·mol−1 in absolute value. This synergistic adsorption will allow developing new methods for efficient monazite recovery from complex ores, a promising step for the recovery of critical raw materials.