Increasing the utilization of copper tailing and flue gas desulfurization is significant for copper smelters. Copper tailing, derived from the copper production, was applied to flue gas desulfurization and increasing utilization of copper tailing and smelting gas with low concentrations of SO2 by preparing slurries composed of copper tailing and water. The effects of different factors, including the inlet SO2 concentration, the ratio of solid to liquid, the absorption temperature, the O-2 concentration, the gas flow rate, the initial copper tailing slurry pH, and the presence of a coexisting gas were investigated systematically. The resulting products and the mechanism driving the flue gas desulfurization were also studied. The results indicated that desulfurization efficiency was primarily influenced by the inlet SO2 concentration, the ratio of solid to liquid, the absorption temperature, and the gas flow rate. An appropriate amount of NO facilitated the desulfurization. The desulfurization efficiency was maintained at or above 80% for 60 h under optimal conditions. The total weight of the copper tailing was reduced by approximately 8%. Ferric sulfate and magnetite could be recycled through evaporation and magnetic separation. Liquid phase catalytic oxidation by metal ions, including ferric and manganese, played a vital role in the flue gas desulfurization.