Flotation separation of fluorite from calcite using sulfonated lignite as depressant

In this study, sulfonated lignite (SL) was studied as the depressant in the separation of fluorite and calcite with sodium oleate (NaOL) as the collector. The flotation recovery of fluorite and calcite with and without depressant SL was investigated by micro-flotation test. The mechanism of the depressant was studied through Fourier transform infrared spectroscopy (FTIR) analysis, contact angle analysis and X-ray photoelectron spectroscopy (XPS) analysis. The micro-flotation experiment showed that sulfonated lignite had an effective depression effect on calcite. FTIR results illustrated that sulfonated lignite was selectively absorbed on the calcite surface and NaOL could still be absorbed on fluorite surface with depressant sulfonated lignite. Contact angle analysis demonstrated that depressant sulfonated lignite could significantly increase the hydrophilicity of calcite surface with NaOL as the collector. However, the surface of fluorite was still relatively hydrophobic with depressant SL and collector NaOL. XPS results illustrated that sulfonated lignite was adsorbed on the calcite surface through the interaction of the carboxyl groups of the depressant with the Ca atom on the calcite surface. Therefore, sulfonated lignite could be used as a potential depressant in the flotation system of fluorite and calcite.