Study on the Failure of Sulfide Layer on Malachite Surface and the Stability Regulation Mechanism of Ammonium Salt Compensated Sulfide Layer

The efficient flotation of malachite relies on the sulfidation-xanthate flotation method; however, with prolonged sulfidation time, the shedding of the sulfide layer leads to a significant decrease in the floatability of malachite. This study uses 1-pyrrolidinecarbodithioic acid and ammonium salt (PDTC) to accelerate the growth rate of the sulfide layer and strengthen its adsorption strength. Microflotation tests indicate that the addition of PDTC can significantly improve the flotation recovery of malachite under prolonged sulfidation conditions. Contact angle measurements indicate that when PDTC is added for strengthening after 25 min of sulfidation, the contact angle of malachite increases by 11.09°, suggesting that PDTC can improve the hydrophobicity of the malachite. SEM-EDS analysis reveals that during the growth of CuS crystals, they may preferentially grow in a layered manner centered on "nuclei" in highly active regions; when the sulfidation time is extended, the particle size of CuS crystals increases significantly but some detach, exposing the malachite substrate, whereas strengthening with PDTC enhances both the growth rate and adsorption strength of CuS crystals. UV-vis and LEIS tests show that the addition of PDTC can improve the mechanical strength of the sulfide layer to enhance the hydrophobicity. X-ray photoelectron spectroscopy (XPS) tests indicate that compared with 3 and 25 min of sulfidation, the contents of hydrophobic Cu(I) and Sn²⁻ components on the malachite surface decrease by 4.79% and 3.41%, respectively, while after strengthening with PDTC, the contents of Cu(I) and Sn²⁻ components increase by 12.82% and 16.02%, respectively, suggesting that the addition of PDTC can significantly promote the formation of hydrophobic components and improve the hydrophobicity of malachite.