Improved Flotation Separation of Barite from Ca-Containing Gangue Minerals via Surface-Specific Adsorption of Sodium Lignosulfonate

Sodium lignosulfonate (SL, a ubiquitous natural organic macromolecule) containing multiple hydrophilic functional groups was widely used in mineral flotation fields to separate valuable minerals and gangues. However, the selective adsorption mechanism of SL on similar mineral surfaces remains not fully elucidated, resulting in the challenges of the precise modulation of mineral flotation separation processes. In this work, SL as an effective depressant was employed in barite flotation systems, realizing the efficient separation of barite from calcite and fluorite. It was found that SL exhibits a strong depressant effect on the floatability of calcite and fluorite but had only a negligible impact on the recovery of barite at pH 6.0-9.0. The recovery gaps were determined as 85.1% for barite, 12.4% for fluorite, and 5.3% for calcite at pH 9.0. Further analysis indicated that the selective adsorption behavior and mechanism of SL stem from the surface specificity of mineral crystals. Due to the fact that the Ca active sites were located at the outermost layer, fluorite can easily form -SO₃-Ca bonds with sulfate groups and cation-π interactions with the aromatic structures in the SL molecules. For calcite and barite, the surface-active sites, i.e., Ca and Ba, cannot directly bond with the SL molecules due to steric hindrance from CO₃^2- and SO₄^2-. Therefore, the electrostatic attraction between the negatively charged SL molecules with calcite and the electrostatic repulsion with barite dominated the surface adsorption process, resulting in significant differences in adsorption behavior. This study provides insights into the surface-specific adsorption mechanisms of organic macromolecules on similar mineral surfaces, which shed light on developing effective strategies for chemical additive design to achieve the selective modulation of target minerals in complex mineral pulps.