Inhibiting Mechanism of High pH on Molybdenite Flotation. An Experimental and DFT Study

The inhibiting mechanism of high pH on the molybdenite flotation was studied using an experimental and DFT method. The experimental results found that adverse effects of pH on molybdenite flotation should be attributed to the adsorption of OH− on molybdenite [100] surface (MS100). The DFT results show the adsorption energy of H2O/OH− to molybdenite [001] surface (MS001) and MS100 is −8.61/288.30 kJ·mol−1 and −226.81/−302.44 kJ·mol−1. These indicate that H2O is weakly adsorbed on MS001, while OH− is not. Both H2O and OH− can be adsorbed onto MS100. The adsorption energy of OH− to MS100 is much stronger than that of H2O. The results of state density and charge transfer of the adsorption of OH− on MS100 further show that OH− can be chemically adsorbed on MS100 through the bonding of the O atom of OH− and the Mo atom of MS100. This causes a significant reduction in the MS100 hydrophobicity and deteriorates the fine molybdenite flotation.