| Summary: | At present, the research on flotation separation of cassiterite and gangue minerals is mainly focused on the development of new collectors or depressants, while the research on combined depressants is rare. In this study, the flotation separation of cassiterite and the typical gangue mineral, calcite, was investigated using the metal-inorganic complex depressant AlSS, composed of aluminum sulfate (Al<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub>) and water glass (Na<sub>2</sub>SiO<sub>3</sub>·4H<sub>2</sub>O). The flotation results indicated that, with the assistance of Al<sup>3+</sup>, the inhibition effect of SS (water glass) on calcite is significantly enhanced, while the inhibition effect on cassiterite is almost unchanged. The zeta potential and adsorption measurements proved that the formation of the negatively charged colloidal particles composed of Al<sub>m</sub>(OH)<sub>n</sub><sup>3m−n</sup> and SiO<sub>m</sub>(OH)<sub>n</sub><sup>4−2m−n</sup> tended to adsorb on the positively charged calcite surface, inhibiting the adsorption of sodium oleate (NaOL), while the adsorption of the colloidal particles on the negatively charged cassiterite surface is relatively less. The contact angle measurements indicate that the contact angle of cassiterite in the NaOL + AlSS solution is obviously larger than that of calcite, which indicates that cassiterite has better floatability in this system. The X-ray photoelectron spectroscopy (XPS) analysis confirms the Al and Si species are adsorbed on the surface of calcite, but not on the cassiterite. In addition, the adsorption of AlSS on cassiterite and calcite changes the chemical environment on the calcite surface, indicating that the adsorption of AlSS on the mineral surface is more inclined to be through a chemical reaction.
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