Peilun Shen

Bastnaesite is an important source of light rare earth minerals and is commonly recovered by flotation. Although the traditional collector salicylhydroxamic acid (SHA) exhibits good selectivity, it requires high dosages and is expensive. In this study, sodium lauroyl sarcosinate (SLAS), a green, stable, and inexpensive sarcosine derivative, was combined with SHA and used as a combined collector (SHA/SLAS) for the first time. This combined collector efficiently floated bastnaesite under weakly alkaline conditions (pH 7–9) while reducing the required dosage of SHA used alone. The flotation behavior and adsorption mechanism of the SHA/SLAS combined collector on the bastnaesite surface were investigated through flotation experiments, contact angle measurements, zeta potential analysis, adsorption tests, Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), and X-ray Photoelectron Spectroscopy (XPS). Flotation results demonstrated that the SHA/SLAS combined collector could effectively enrich both bastnaesite single-mineral samples and actual ore. The flotation recovery of bastnaesite single-mineral samples reached a maximum of 90.76% in the weakly alkaline pH range of 7–9, with a reduced dosage of SHA compared to its use as a single collector. For the actual ore, a locked-cycle flotation process comprising one-stage roughing, three-stage scavenging, three-stage cleaner-scavenging, and three-stage cleaning yielded a rare earth concentrate with an REO grade of 51.07% and a recovery of 66.68%. Contact angle, zeta potential, and adsorption capacity measurements indicated that SHA/SLAS underwent multilayer electrostatic adsorption and chemisorption on the bastnaesite surface, accompanied by co-adsorption, which significantly enhanced the surface hydrophobicity. Within the pH 7–9 range, SHA and SLAS predominantly existed as salicylhydroxamic acid anion (SHA⁻) and lauroyl sarcosinate anion (LAS⁻), while Ce ions were primarily present as Ce3⁺, Ce(OH)2⁺, and CeOH²⁺, which facilitated the interaction of SHA⁻ and LAS⁻ anions with the bastnaesite surface through electrostatic forces and chemisorption. ToF-SIMS and XPS analyses revealed that Ce atoms on the bastnaesite surface bonded with O atoms from the hydroxamic group (-CONHOH) of SHA and from the carboxyl (-COO⁻) and amide (-CON-) groups of SLAS, forming Ce–SHA and Ce–LAS hydrophobic species containing Ce–O bonds. Furthermore, the combined use of SHA and SLAS produced a greater abundance of these hydrophobic species, further enhancing bastnaesite floatability.