Discarded cigarette butt-derived cobalt-based bifunctional catalysts for simultaneous catalytic oxidation of MgSO ₃ and adsorption of Pb(II) in magnesium-based flue gas desulfurization systems

The catalytic oxidation of magnesium sulfite (MgSO 3 ) plays a pivotal role in magnesium-based flue gas desulfurization (Mg-FGD) systems to enable magnesium sulfate (MgSO 4 ) recovery. However, the coexistence of lead ions (Pb 2+ ) in FGD slurries not only compromises MgSO 4 product purity but also poses substantial risks to aquatic ecosystems and human health. To address these dual challenges, a bifunctional Co/AC-Hy catalyst was synthesized via hydrothermal treatment of non-biodegradable cigarette butt-derived activated carbon (AC) as a support. The AC exhibited hierarchical porosity (916.97 m 2 ·g -1 Brunauer-Emmett-Teller (BET) surface area), promoting uniform dispersion of CoO active sites while suppressing low-activity Co(III) formation through hydroxyl-mediated valence control. The optimized catalyst not only achieved a MgSO 3 oxidation rate of 0.085 mmol·L -1 ·s -1 (8.5 times higher than non-catalytic systems and outperforms most reported cobalt-based catalysts on AC, but also delivered a Pb 2+ adsorption capacity of 143 mg·g -1 , exceeding that of commercial ACs. Additionally, the Pb 2+ adsorption data on Co/AC-Hy showed a good fit to the Langmuir isotherm model (R 2 = 0.998), consistent with a monolayer adsorption process. This method effectively reduces organic solid waste and facilitates the recovery of desulfurization by-products, a green strategy with significant environmental benefits.