Influence of excess sulfide ions on the malachite-bubble interaction in the presence of thiol-collector

• The type of sulfidizers (Na2S and (NH4)2S) has negligible effect on the malachite floatability.
• Malachite floatability decreases with increasing sulfidizer concentration.
• The malachite flotation recovery without excess S2− is greater than that with excess S2−.
• Excess S2− largely reduces the adsorbed amount of xanthate onto the malachite surface.

In this study, the effects of the type (ammonium sulfide (NH4)2S and sodium sulfide (Na2S)) and amount (8 × 10−5 mol/L and 2 × 10−3 mol/L) of sulfidizing reagents used in malachite flotation with xanthate as a collector on flotation recovery were investigated in a well-controlled Hallimond tube. The results showed that the average flotation recovery of malachite was similar regardless of the type of sulfidizing agent; however, a significant difference was observed when the amount of sulfidizing agents varied. Specifically, malachite had a higher flotation recovery when sulfidized at a low concentration than at a high concentration. This result was not explained by either the differences in the extent of sulfidization or by the electrostatic interaction between xanthate and malachite, which was supported by XPS and XRD analyses, adsorption tests of sulfidizing agents, and zeta potential measurements. Notably, malachite without excess sulfide ions exhibited significantly greater flotation recovery than that with excess sulfide ions regardless of the type of sulfidizing agent. These results were well supported by the results from the potentiometric titration tests, which showed greater xanthate adsorption onto the surface of malachite without excess sulfide ions than that with excess sulfide ions. Therefore, the excessive use of sulfidizing agents was confirmed to inhibit xanthate adsorption onto the malachite surface, and consequently, to decrease the flotation recovery of malachite.

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