Flotation performance and adsorption mechanism of sodium lauroyl sarcosinate on lead ion-modified bastnaesite surfaces

Abstract

Bastnaesite is an important source of light rare earth minerals and is often recovered by flotation. In this study, sodium lauroyl sarcosinate (SLAS), a green, stable, and inexpensive sarcosine derivative, was used as a collector for the first time to improve bastnaesite recovery and float bastnaesite before and after Pb ion modification in a wide pH range (pH 3–10). The flotation behaviour and adsorption mechanism of SLAS on bastnaesite with and without Pb ions were investigated via flotation experiments, adsorption tests, zeta potential analysis, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The flotation results showed that SLAS could effectively collect bastnaesite with a recovery of up to 90%, in the pH range of 3–10. Neutral and weak alkaline conditions were more favourable for bastnaesite flotation, and Pb ions promoted bastnaesite collection and reduced the amount of SLAS required. The adsorption and zeta potential experiments indicated that multilayer adsorption of SLAS occurred on the bastnaesite surface. SLAS mainly existed as the LAS anion in the pH range of 3–9, while Ce and Pb ions existed as Ce3+, Ce(OH)2+, and CeOH2+ and Pb2+ and Pb(OH)+, respectively, which favoured the interaction between the LAS anions and the bastnaesite surface via electrostatic forces and chemical adsorption. FTIR and XPS analyses revealed that the adsorption of Pb2+ and Ce–O–Pb complexes on the bastnaesite surface increased the number of active sites. The carboxyl (–COO–) and amide (–CON) groups in the LAS anions interacted with Ce and Pb sites on the bastnaesite surface to form stable Ce–LAS and Pb–LAS five-membered ring chelates. The adsorption of the LAS anions and Pb ions on the bastnaesite surface were mutually favourable, and the non-polar carbon chains in the chelates formed by the LAS anions and Pb2+ in the slurry associated with the non-polar carbon chains in the LAS anions adsorbed on the mineral surface, resulting in a multilayer adsorption, which further enhanced the floatability of bastnaesite.