Unraveling the role of a novel XG-SS combined depressant in the flotation separation of barite from specularite and quartz: Insights from experiments and DFT calculations

Traditional separation of barite, specularite, and quartz relies mainly on magnetic and gravity-based methods. In this study, a composite depressant, XG-SS (xanthan gum/sodium silicate), was introduced for the first time for the selective flotation separation of this mineral system. Under optimal conditions (pH 9, with NaOL and XG-SS dosages of 20   mg/L), a floatability difference of 83.89 percentage points among the three minerals was achieved. Open-circuit flotation tests on actual ore further produced a high-quality barite concentrate with a BaSO 4 grade of 95.68%. The separation mechanism was elucidated using contact angle measurements, zeta potential analysis, FTIR, and XPS. The results show that the depressive effect of XG-SS on barite is weaker than the collecting ability of NaOL, whereas XG-SS strongly suppresses specularite through hydrogen bonding and chemisorption associated with hydroxylated Fe(III) surface sites (Fe-OH/FeOOH-like species). In contrast, only weak physical adsorption occurs on quartz. Density functional theory calculations further identify the hydroxyl and carboxyl groups in xanthan gum as the primary active sites, with Mulliken charge and frontier molecular orbital analyses confirming their strong nucleophilicity and high reactivity. Based on these findings, a mechanistic model for the selective flotation separation of barite, specularite, and quartz in the NaOL-XG-SS system is proposed.