Sulfidation of lead-loaded zeolite microparticles and flotation by amylxanthate

The possibility of recovering lead-loaded zeolite Y microparticles (PbY) by flotation after sulfidation was investigated using amyl xanthate (AMX) as the collector. The sulfidation process (by aqueous Na2S) was first studied as a function of the medium composition (Na2S concentration, pH), and the solid phases were characterized by various physicochemical techniques (X-ray photoelectron spectroscopy, high-frequency impedance measurements, and electrochemistry). Progressively increasing the sulfidation level resulted in the concomitant transformation of Pb(II) species ion-exchanged in the zeolite into PbS clusters that were mostly located at the external boundaries of the zeolite particles while remaining attached to the aluminosilicate (PbS-Y). Similar to what occurred for galena particles, the zeolite-supported PbS clusters were likely to adsorb the AMX collector, the remaining (nonsulfided) ion-exchanged Pb(II) species being transformed into a Pb(AMX)2 precipitate when using AMX in large excess. Owing to such AMX adsorption on PbS-Y, the zeolite particles were found to flocculate and to float in the presence of air bubbles. If rather high AMX concentrations (>5 x 10(-3) M) were necessary to ensure the flotation of nonsulfided PbY particles (Walcarius, A.; Lamdaouar, A. M.; El Kacemi, K.; Marouf, B.; Bessiere, J. Langmuir 2001, 17, 2258), significantly lower concentrations (down to 1 x 10(-4) M) gave rise to high flotation yields (ca. 95%) upon PbY sulfidation. It is noteworthy that the sulfidation level should be maintained at a value high enough (>10%) to produce the minimal PbS amount ensuring flotation but not too high (<75%) to avoid conditions that are too reducing and are not compatible with the flotation process. Finally, depression tests seemed to indicate that PbS-Y flotation occurs according to a mechanism similar to that described for the galena mineral.