In this paper, the influence of Ca²⁺ on the flotation of a skarn type molybdenum ore and pure molybdenite mineral at pH 8 was studied using diesel as the collector. It was found that Ca²⁺ had little effect on molybdenum flotation at low concentrations. By further increasing Ca²⁺ concentration, the floatability of molybdenite—especially from the fine size fractions—was depressed even without the presence of fine gangue minerals. The mechanism responsible for the deleterious effect of Ca²⁺ on molybdenite flotation was studied by a range of techniques including zeta potential measurements, Scanning Electron Microscopy, and Energy Dispersive X-ray Spectrometer (SEM-EDS) analyses and molybdenum phase analyses. It was found that Ca²⁺ interacted with molybdenite edges producing CaMoO₄ precipitates which were responsible for the depression of molybdenite flotation of Ca²⁺ by preventing the adsorption of diesel.

Nonpolar hydrocarbon oils are widely used as collectors for floating molybdenite. However, they can only adsorb on molybdenite faces and not on molybdenite edges, resulting in limited molybdenite recovery, especially in processed water containing a high amounts of Ca²⁺. In this study, the influence of Ca²⁺ and pH on the adsorption of polycyclic aromatic hydrocarbons (PAHs), as part of composite collection on molybdenite edges, was studied. It was found that PAHs could only adsorb on molybdenite edges in the presence of Ca²⁺. Ca²⁺ reacted with molybdenite edges to form CaMoO₄ precipitates. Then, CaMoO₄ precipitates interacted with PAHs to form a structure of π–cation–π by (1) the cation–π interaction, (2) the π–π interaction and (3) the electrostatic interaction. It was also found that CaMoO₄ precipitates on molybdenite edges promoted the adsorption of PAHs. The more the CaMoO₄ precipitates, the easier the PAHs adsorption occurred. As a result, the high amount of Ca²⁺and low pH enhanced the adsorption of PAHs on molybdenite edges. This study provides insights into reducing the deleterious effect of Ca²⁺ on fine molybdenite flotation.

Nonpolar hydrocarbon oil (NHO) is one of the most extensively used collectors in the flotation of molybdenite due to its excellent selectivity. However, NHO has low sensibility at pulp temperature. At low temperatures (<283 K), although more kerosene is used, the recovery of molybdenite flotation is still lower than at room temperature. In this study, magnetizing treatment, which is an efficient, low-cost, innovative, and environmentally friendly emulsification method, was used to improve the flotation performance of NHO in low-temperature molybdenite flotation. The test results showed that, compared with unmagnetized kerosene (UMK), the optimum dosage of magnetized kerosene (MK) could be reduced by 11% at 298 K. At the same dosage of kerosene, the flotation recovery of MK was 3% higher than UMK at 278 K. The surface tension measurement results showed that the surface tension of MK rose periodically as the magnetic field intensity increased, and there was a maximum surface tension within each period. Further, the magnetic field intensity had the maximum flotation recovery of molybdenite at the maximum surface tension of MK. Combined with the analysis based on the Girifalco–Good theory and the static drop volume method of interfacial tension, the interfacial tension of kerosene–water was shown to decrease with the increase of the surface tension of kerosene. This finding indicates that the dispersibility of kerosene in pulp could be improved by reducing the size of oil droplets, thereby improving the molybdenite flotation recovery of kerosene at low-temperature pulp. It is helpful to improve the flotation recovery of molybdenite using NHO as a collector for low-temperature pulp (<283 K).