Investigating hydrodynamic nanobubble enhanced xanthate adsorption on pyrite surfaces

Hydrodynamic cavitation nanobubble flotation has proven to be effective in enhancing flotation performance of fine pyrite particles and reducing the required collector dosage with xanthate used as collector. However, the mechanism of reduced collector dosage in the presence of nanobubble has not been well investigated. This study was performed with the focus on understanding the contribution of nanobubbles to sodium amyl xanthate (SAX) adsorption on pyrite surface. The results have shown that the adsorption of SAX on pyrite surface fits the Freundlich isotherms with or without the presence of cavitation nanobubbles, indicating SAX adsorption can result in single or multilayers. The introduction of cavitation nanobubbles increased the SAX adsorption capacity and kinetics in the form of nonpolar dixanthogen nanodroplets on pyrite surface. Both hydroxyl radicals (⋅OH) and dissolved oxygen (DO) produced by bulk nanobubbles (BNBs) during cavitation contributed to oxidation of SAX to dixanthogen in the bulk phase of slurry with minimal impacts on pyrite surface. The oxidation effect was more pronounced with increased cavitation time. Electrochemical measurements such as cyclic voltammetry (CV) and Tafel polarization analysis confirm that the presence of BNBs enhanced the SAX adsorption on pyrite surface, while the preferential formation of SNBs (surface nanobubbles) on hydrophobic pyrite surface prevented the contact of oxygen species with pyrite, thereby avoiding further oxidation of the surface. The presence of ·OH and DO reduced the induction time for bubble-particle attachment by 100–250 ms and increased the contact angle by 5° −10° in the nanobubble flotation system.