Abstract: To improve the flotation performance of malachite, sulfidation roasting was conducted using industrial waste desulfurization gypsum as the sulfidation agent. The effects of roasting temperature, roasting time, and desulfurization gypsum dosage on the flotation behavior of the roasted samples were investigated. X-ray diffraction （XRD）, X-ray photoelectron spectroscopy （XPS）, contact angle measurements, zeta potential measurements, and collector adsorption tests were used to characterize the sulfidation-induced reconstruction of malachite and the interfacial interaction between the roasted products and sodium butyl xanthate （NaBX）. The results showed that under the conditions of 500 ℃, 30 min, and a desulfurization gypsum dosage of 0.2, the flotation recovery reached 93.86 %. This value was 74.68 percentage points higher than that of untreated malachite. XRD results showed that increasing the roasting temperature promoted the reduction of desulfurization gypsum and the formation of CuS and CaS. At 550 ℃, the diffraction peaks of Cu₃₉S₂₈ and CaO became stronger, indicating further transformation of copper sulfides and calcium-bearing phases at an excessively high temperature. XPS analysis showed that, as the roasting temperature increased from 400 ℃ to 500 ℃, the relative surface content of Cu⁺ increased from 36.42 % to 58.53 %, while that of Cu²⁺ decreased from 63.58 % to 41.47 %. These changes indicated that the degree of reduction and sulfidation of the malachite surface had increased. Without the sulfidation agent, the contact angle of the roasted sample was only 23.71°. After the addition of desulfurization gypsum, the contact angle increased from 59.03° at 400 ℃ to 80.25° at 500 ℃. This result demonstrated that sulfidation-induced reconstruction markedly enhanced surface hydrophobicity, with higher roasting temperatures further promoting this process. After NaBX treatment, the zeta potential of the sample roasted at 500 ℃ was more negative than that of the sample roasted at 400 ℃, indicating a stronger interaction with NaBX. The NaBX adsorption amounts on the samples roasted at 400 ℃ and 500 ℃ were 6.06×10⁻⁵ mol/g and 7.60×10⁻⁵ mol/g, respectively, corresponding to an increase of 25.4 %. During roasting, desulfurization gypsum was reduced to provide active sulfur. This promoted the conversion of oxygen-containing copper species into copper sulfides and generated more surface copper sites for interaction with NaBX. The enhanced collector adsorption increased surface hydrophobicity and improved the flotation performance of the roasted samples. This method not only improves the flotation performance of malachite but also offers a new approach to utilizing desulfurization gypsum.