Exploration of pullulan as a new environmentally friendly selective depressant of calcite in fluorite flotation separation

In fluorite flotation, the effective separation of fluorite from the coexisting mineral calcite is challenging due to their highly similar flotation behaviors and physicochemical properties. This study introduces a novel, environmentally friendly selective depressant for calcite, characterized by good solubility at low temperatures and low solution viscosity. Flotation experiments evaluated its depressant performance, revealing that pullulan selectively depresses calcite without compromising fluorite recovery. The mechanism underlying this selective depression was investigated using contact angle measurements, adsorption capacity determination, zeta potential analysis, Fourier-transform infrared spectroscopy (FTIR), and density functional theory (DFT) calculations. The results demonstrate that pullulan selectively adsorbs onto the calcite surface, rendering it hydrophilic, while not interfering with the hydrophobic modification of fluorite by sodium oleate (NaOl). This adsorption onto calcite is chemisorption, primarily mediated by the hydroxyl groups of pullulan. The stronger adsorption energy of pullulan on calcite compared to fluorite arises from a spatial matching effect. Furthermore, the hydroxyl group at the C6 position of the glucose monomer within pullulan is identified as the most probable site for adsorption interaction with calcite.