Enhanced flotation separation of fluorite and F−-activated calcite by sodium gluconate and sodium silicate

The flotation separation of fluorite and calcite faces challenge due to the adsorption of dissolved F⁻ ions on the surface of calcite to impart similar floatability as fluorite. This study utilized a novel inhibitor comprising both sodium gluconate (SG) and sodium silicate (SS) to effectively suppress the F⁻-activated calcite, significantly reducing its recovery from 88.1 % to 22.3 %, without affecting the flotation recovery of fluorite. The selective depression mechanism was investigated using Zeta potential measurements, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and microcalorimetry. The results revealed that the surface of homogenized calcite was coated with a fluorite film, whereas the incorporation of SG facilitated the removal of this fluorite film, thereby exposing fresh calcite surface and augmenting the adsorption capacity and rate of SS. The DFT calculations further suggested that SG complexes with Ca²⁺ ions in 1-, 2-, 3-, or 4-coordination modes exhibited binding energies ranging from 6.35 to 15.24 times higher than that of Ca-F. This interaction led to the displacement of F⁻ ions from the calcite surface and disruption of chemical bonds between the fluorine film and calcite, ultimately detaching the fluorine film from the calcite surface. The single-bonded O atoms in SG formed 3- and 2-coordination complexes with two adjacent Ca²⁺ ions on calcite (104) surface. Therefore, the aforementioned findings provide a theoretical foundation and pave the way for novel strategies in the flotation separation of homogenized fluorite and calcite.