Selective fabrication of hydrophilic BiOCl deposition layer on bismuthinite surface for efficient molybdenite/bismuthinite separation

Abstract

Molybdenite and bismuthinite are valuable components arising from Mo–Bi sulfide ore, and their recoveries are considerably limited by separation efficiency. Herein, calcium hypochlorite (Ca(ClO)2) was first introduced as bismuth depressant for efficient separation of molybdenite and bismuthinite, and its depression mechanisms were investigated through a series of analytical techniques supplemented with solution chemistry and thermodynamic calculations. Flotation results showed that Ca(ClO)2 had a stronger depressing ability than conventional depressant sodium sulfide and exhibited superior selectivity for bismuthinite against molybdenite. At pH around 8.0, the high-selective separation of Mo–Bi bulk concentrate was realized, where more than 96% of molybdenite was recovered and over 98% of bismuthinite was depressed. Solution chemistry and thermodynamic analysis indicated that the bismuthinite surface was preferentially oxidized by Ca(ClO)2 to SO2- 4 and Bi3+. The former dissolved into solution and existed as stable ions, whereas the Bi3+ further interacted with Cl− and was hydrolyzed as BiOCl precipitates. Surface analysis demonstrated that the deposition of BiOCl on the bismuthinite surface not only made its surface rougher but also enhanced its surface hydrophilicity. In comparison, the surface of molybdenite was slightly oxidized and it remained hydrophobic as confirmed from scanning electron microscopy with energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and contact angle results. The difference in surface characteristics resulted in the selective adsorption of collector on the surface of molybdenite rather than that of bismuthinite, thus improving the floatability of molybdenite and drastically deteriorating the floatability of bismuthinite. This work suggests that Ca(ClO)2 could be a promising depressant for bismuthinite in the flotation separation of Mo–Bi sulfide ore.