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.