It is widely acknowledged that clay minerals have detrimental effects on the process of flotation, but the mechanisms involved are still not fully understood. In this work, the effects of montmorillonite, kaolinite, and illite on pyrite flotation were investigated from the perspective of various structures of clay minerals. Flotation tests suggested that the detrimental effect of clay minerals on the flotation of pyrite increased as follows: montmorillonite > kaolinite > illite. With the help of rheology measurements, it was found that montmorillonite significantly increased pulp viscosity, which in turn substantially reduced pyrite recovery and grade. Scanning electron microscopy (SEM) images suggested that montmorillonite formed the “house-of-cards” structure by edge-to-edge and edge-to-face contact, while kaolinite and illite platelets were associated mainly in the face-to-face mode. In addition, it was clearly observed by SEM–energy dispersive spectrometry that montmorillonite and kaolinite coat on the pyrite surfaces, which would lower the surface hydrophobicity of pyrite. Kaolinite covered much larger area of pyrite surface than montmorillonite owing to the positive charge occurring at the exposed aluminum–oxygen octahedral sheet of kaolinite. Although illite has a similar 2:1 structure to montmorillonite, it showed little or no effect on pyrite flotation, which was attributed to its poor swelling nature. These findings shed light on the root cause of the adverse effect of clay minerals on pyrite flotation and are expected to provide theoretical guidance for mitigating the negative effects on flotation caused by clays.

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In this study, a novel organic depressant maleyl 5-amino-1,3,4-thiadiazole-2-thiol (MATT) was synthesized and utilized as a galena depressant in the flotation separation of molybdenite and galena. The results of the flotation test indicated that MATT exhibited an excellent depression ability on galena but barely influenced the flotation of molybdenite in the pH range of 6.0–11.0. Zeta potential results suggested that MATT preferentially adsorbed on galena surface. UV-visible spectroscopy analysis indicated that the stoichiometric ratio of lead ion and reagent in the complex compound. XPS analysis demonstrated that the S (-SH) atom and N (1,3,4-thiadiazole group) atom of MATT coordinated with the Pb atom on galena surface.

In order to achieve the effective separation of copper-molybdenum in the presence of xanthate and kerosene, carrageenan was explored as a novel environmentally friendly molybdenite depressant in this work. The flotation behavior of molybdenite was studied by micro-flotation tests, and the depression mechanism was investigated through zeta potential, Fourier Transform Infrared Spectroscopy (FTIR) and atomic force microscope (AFM) analysis. The flotation results showed that molybdenite was significantly depressed by carrageenan in the pH range of 6–12 even in the presence of xanthate and kerosene. Zeta potential, FTIR and AFM measurement demonstrated that carrageenan could adsorb strongly on the molybdenite surface and change the surface wettability of molybdenite, thus significantly reducing the floatability of molybdenite.