Interfacial adsorption mechanism of xanthan gum pre-assembled with calcium ions as an efficient depressant for Cu-S flotation separation under low-alkaline

The reduction of sulfur impurities in copper concentrates typically necessitates a highly alkaline environment generated by excessive lime addition, owing to the analogous surface flotation properties of chalcopyrite and pyrite. In this study, an innovative approach was proposed by pre-combining green reagent xanthan gum (XG) with calcium (II) ions to enhance its efficacy as a selective depressant for pyrite. Micro-flotation tests on mixed minerals revealed that XG alone exhibits no depressive effect, whereas the application of the XG-Ca at pH 9 enhances the Cu grade of the concentrate to 29.70% (from 16.43% in the raw mineral), with the recovery of chalcopyrite and pyrite being 85.31% and 12.60%, respectively. The complexation-enhanced depression mechanism of Ca on XG and the interaction mechanism between XG-Ca and pyrite surfaces were evaluated using techniques such as XPS, FTIR, TOF-SIMS, SEM-EDS, and molecular dynamics simulations. The results indicated that calcium ions primarily coordinate with carboxyl groups, inducing the extension of XG side chains and greater exposure of functional moieties, which facilitates the formation of a uniform and compact adsorption layer on pyrite surfaces. There are primarily two interaction mechanisms between XG-Ca and Pyrite: (1) The coordination of carboxyl groups (–COO − ) from XG-Ca with Fe sites on the pyrite surface; and (2) calcium-mediated electrostatic bridging between surface hydroxyl groups (–OH) of pyrite and functional groups in XG-Ca. This study proposes an innovative approach of pre-combining xanthan gum with calcium ions, offering valuable insights for developing efficient and green depressants for Cu-S separation.