New insights into the structure-activity relationship of the N containing heterocyclic activators for the lime depressed molybdenite flotation

Abstract

The molybdenite is a typical layered sulfide mineral with extremely high natural hydrophobicity and therefore it is extracted by flotation technology. However, molybdenite is usually depressed by the flotation regulator lime and needs activization. In this study, we introduced 10 kinds of N-heterocycles to systematically study the structure–activity relationship of the N-heterocyclic flotation activators for the lime inhibited molybdenite, mainly through flotation tests, surface detection and DFT calculation. The flotation results showed that the lime almost irreversibly depressed the molybdenite flotation when using kerosene as collector alone, and adding these N-heterocyclic reagents effectively helped molybdenite regain its high flotability. When lime was used as 120 mg/L and kerosene at 30 mg/L, the activator effect could be ranked as: 3MI ≈ 2Phl ≈ 5 MB ≈ 5MI ≈ TTA > IND ≈ BTA ≈ Bzlm ≈ 5PhTH > 2MZ, which was decided by the recovery increment. The surface detection indicated that the depression mechanism of the lime was mainly through the adsorption of the CaOH⁺, Ca²⁺, Ca(OH)₂ on the basal plane of molybdenite crystal, thus the chelating affinity of the N-heterocyclic reagents towards the lime components decided its activation ability. The DFT calculation suggested that the N-heterocycles was also able to interact with the Mo sites exposed by surface oxidation on the basal plane, thus the reactivity towards the Mo as well as the steric configuration also determined the activator effect. Therefore, the chelating ability of the activator towards the lime components/exposed Mo sites and the steric configuration of the rest alkyl group both contribute to the structure–activity relationship.