Mechanism of Alkali-Gelatinized Soluble Starch as a Depressant for Fluorite–Dolomite Flotation Separation

Flotation separation of fluorite from dolomite is challenging due to their similar surface properties. In this study, neutralized alkali-gelatinized soluble starch (NAGS) was used as a flotation depressant. NAGS was prepared by gelatinizing soluble starch in an alkaline solution, followed by pH neutralization. The depressive performance and mechanism of NAGS in the fluorite-dolomite flotation separation were systematically investigated. Microflotation tests showed that, at pH 7 with a sodium oleate (NaOL) concentration of 30 mg/L and NAGS concentration of 100 mg/L, the recovery difference between fluorite and dolomite in single-mineral flotation reached as high as 95.10%. In the flotation concentrate of the artificially mixed mineral, the fluorite grade was 87.09%, and the fluorite recovery was 90.12%. NAGS exhibited a pronounced selective depressive effect on dolomite, which was further confirmed by contact angle measurements. Zeta potential measurements, Adsorption capacity measurements, Fourier-transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS) were combined to elucidate the adsorption mechanism of NAGS. Collectively, NAGS adsorbs on both mineral surfaces via physisorption but with distinct dominant forces: electrostatic interactions predominate on fluorite, while hydrogen bonding is predominant on dolomite. This differential adsorption strength explains the selective depression of dolomite.