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

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 Cu-SS 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: Ca-O bond and H-F bonds are formed when SS interacts with the fluorite surface, and Ca-O and hydrogen bonds are formed when SS interacts with the calcite surface. A Ca-Cu bond is formed when the Cu-SS complex interacts with the fluorite surface, but both Cu-O and Ca-Cu bonds are formed when the Cu-SS 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 + Cu-SS complex.

Automated summary

This study investigated the effects and mechanisms of Cu2+ and soluble starch (SS) in the flotation separation of fluorite and calcite. The results show that the combination of Cu2+ and SS can effectively depress calcite, while the impact on fluorite flotation is relatively small. Various analyses revealed that Cu2+ can react with SS to form a Cu-SS complex, leading to differential flotation performance between fluorite and calcite.