The fundamental roles of monovalent and divalent cations with sulfates on molybdenite flotation in the absence of flotation reagents

Due to regional shortage of freshwater, the use of saline/seawater for Cu-Mo sulfide ore flotation has received considerable attention. However, the effects of various salts, especially the cations present in seawater, on molybdenite flotation and the mechanisms involved remain unclear due to the complexity of the solutions applied. In this work, the influence of some common cations (i.e., Na⁺, K⁺, Ca²⁺ and Mg²⁺) with sulfate (SO₄ ^2-) anions on molybdenite flotability was investigated in the absence of flotation reagents (i.e., frothers and collectors) at pH 10. Flotation results indicated a greater depression of molybdenite recovery with increased sulfate salt concentration. The underlying mechanisms responsible for the deleterious effects in the presence of Na⁺ and K⁺ can be attributed to the increased repulsive forces between molybdenite particles and bubbles owing to increased molybdenite oxidation to produce e.g., MoO₄ ^2- and HMoO₄ ^-. However, the increased depression observed in the presence of Mg²⁺ and Ca²⁺ is likely due to the adsorption of precipitated Mg(OH)₂ and CaMoO₄, respectively, onto molybdenite surfaces. These clearly show the different depressing mechanisms due to monovalent and divalent sulfates on molybdenite flotation in the absence of flotation reagents, to reveal the influence of these sulfate salts on its natural flotability.