Enhancement of Mo-Pb flotation separation using gallic acid as a molybdenite depressant: Investigating flotation behavior and mechanism

In the flotation separation of Mo-Pb bulk concentrate and the purification process of Pb-containing molybdenite concentrate, depressants are typically added to depress galena or molybdenite, aiming to obtain high-quality flotation products. Previous studies have focused on the depression of galena. In this study, gallic acid (GA) was utilized as a molybdenite depressant during Mo-Pb flotation separation. Single mineral flotation experiments showed that pH notably influenced galena and molybdenite flotation with GA, particularly at pH 10, displaying the most substantial recovery difference. Mixed mineral flotation experiments revealed GA’s selective depression on molybdenite. At the optimal dosage of GA, the Mo recovery was reduced by 76.62 percentage points, while the Pb recovery remained unaffected. The depression and separation mechanisms of GA were investigated using contact angle, infrared spectroscopy, Zeta potential, inductively coupled plasma optical emission spectrometer (ICP-OES), X-ray photoelectron spectroscopy (XPS) analysis, first-principles calculations analysis, and interface interaction free energy calculations. The results indicate that GA treatment significantly reduces the hydrophobicity of molybdenite surfaces; however, it slightly enhances the hydrophobicity of galena surfaces. At pH 10, the primary species in GA solution is HGA^3-. It adsorbs on PbO species of the galena surface as Pb-GA complexes and tends to detach from the surface at high adsorption capacity, resulting in galena not being depressed by GA. Differently, GA adsorbs on the molybdenite surface through hydrophobic attraction force, rendering it hydrophilic. Additionally, after treatment with potassium butyl xanthate (PBX), the hydrophobicity of GA-treated galena is significantly enhanced, while the hydrophobicity of GA-treated molybdenite is not restored. This is because PBX can adsorb stably on GA-treated galena, but its adsorption on GA-treated molybdenite is hindered by the pre-adsorbed GA.