The role of copper ion and soluble starch used as a combined depressant in the flotation separation of fluorite from calcite: New insights on the application of modified starch in mineral processing

• Published in: Minerals engineering Vol. 181; p. 107550
• Main Authors: Sun, Ruofan, Liu, Dan, Tian, Xiaosong, Zuo, Qi, Wang, Daqian, Wen, Shuming
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15.05.2022
• Subjects: Calcite; DFT; Flotation; Fluorite; Modified starch; Flotation; Fluorite; Modified starch; DFT; Calcite
• ISSN: 0892-6875; 1872-9444
• DOI: 10.1016/j.mineng.2022.107550

•Cu2+ and soluble starch (SS) together enhance fluorite/calcite flotation separation.•The mechanism was systematically studied from chemical and atomic perspectives.•CuSS complex interacts strongly with calcite but only weakly with fluorite.•Metal-ion modified starches are flotation reagents with great potential. The flotation separation of fluorite and calcite poses a long-standing challenge in the mineral processing industry because of their similar physicochemical characteristics. In this study, the effects of Cu2+ and soluble starch (SS) in the separation of fluorite from calcite by flotation, and the mechanisms behind these effects, were investigated using micro-flotation experiments, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), time of flight secondary ion mass spectrometry (ToF-SIMS) and density functional theory (DFT). The micro-flotation experiments show that the combination of Cu2+ and SS exhibits a stronger selective depression effect on calcite than that produced by SS alone; in contrast, the effect on fluorite flotation is relatively small. The XPS, FT-IR and ToF-SIMS analyses show that Cu2+ can react with SS to form a CuSS complex, which has better selectivity, resulting in the difference in flotation performance between fluorite and calcite. DFT results show that the SS and the Cu-SS complex form different chemical bonds during their interactions with the mineral surfaces: CaO bond and HF bonds are formed when SS interacts with the fluorite surface, and CaO and hydrogen bonds are formed when SS interacts with the calcite surface. A CaCu bond is formed when the CuSS complex interacts with the fluorite surface, but both CuO and CaCu bonds are formed when the CuSS complex interacts with the calcite surface. This causes differences in adsorption energy. The adsorption energies of the interactions between SS or CuSS complex and the surfaces of fluorite and calcite are ranked as: calcite + CuSS complex > calcite + SS > fluorite + SS > fluorite + CuSS complex.