Synergistic effect between starch and sulfuric acid on the separation of galena from chalcopyrite

Galena (PbS) is still hard to separate from chalcopyrite (CuFeS<sub>2</sub>) in China, necessitating more effective depressants. This study investigated a combined depressant system using sulfuric acid (H<sub>2</sub>SO<sub>4</sub>) and starch to selectively depress PbS in a PbS−CuFeS<sub>2</sub> mixture. Single-mineral flotation experiments identified the optimal parameters to depress PbS at pH 3, 6 min reaction time, an H2SO4 to starch ratio of 6:1, and 700 mg/dm<sup>3</sup> of H<sub>2</sub>SO<sub>4</sub>. Under these conditions, PbS recovery has decreased to 9.2%, while CuFeS<sub>2</sub> recovery reached 81.1%, Furthermore, the PbS recovery with this combined depressant was significantly lower than the recovery with 700 mg/dm3 of H<sub>2</sub>SO<sub>4</sub> (83.2%) or 116.7 mg/dm<sup>3</sup> of starch (32.1%). FTIR results also showed that starch molecules could physically adsorb onto the PbS surface. Furthermore, XPS and SEM-EDS analyses revealed that the interaction between H<sub>2</sub>SO<sub>4</sub> and the PbS surface produced oxidative components, i.e., Pb-O and SO<sub>4</sub><sup>2−</sup>. These oxidative species may interact with the OH groups in starch molecules, enhancing the adsorption of starch molecules and thus efficiently producing a hydrophilic PbS surface. This study proposes an effective approach for the depression of PbS using the H<sub>2</sub>SO<sub>4</sub> and starch combination. These combined reagents exhibit outstanding industrial potential, owing to their low prices.