Unraveling the Selective Depression of Calcite by κ-Carrageenan in Green Fluorite Flotation: A Multiscale Study from Interfacial Chemistry to Molecular Dynamics.

Flotation separation between fluorite and calcite is difficult because the two minerals show comparable surface chemistry. In this work, κ-carrageenan (CG), a red-algae-derived natural gum, was introduced as a calcite depressant in the sodium oleate (NaOL) system, and its interfacial interaction was examined. Single-mineral and artificial mixed-mineral flotation tests confirmed that CG could selectively depress calcite. Under the optimal conditions, the recovery difference between fluorite and calcite reached 86.55 percentage points, indicating excellent separation performance. Contact angle, ζ-potential, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS), and time-of-flight secondary ion mass spectrometry (ToF-SIMS) analyses showed that CG was selectively adsorbed on the calcite surface, leading to different adsorption behaviors and surface properties between the two minerals. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses further verified the adsorption of CG on calcite and confirmed the competitive adsorption relationship between CG and NaOL. More importantly, molecular dynamics (MD) simulations revealed the different interaction behaviors of CG and NaOL on the two mineral surfaces, as well as the molecular origin of competitive adsorption and selective depression. In this work, CG was demonstrated to be a viable natural depressant for fluorite-calcite flotation, and its selective depression behavior was linked to specific molecular interactions. A practical basis for biobased flotation reagent development was also provided in this work.