Hematite-Loaded Wood-Based Activated Carbon Constructed via Alkali-Thermal Method for Flue Gas Desulfurization: Performance, Mechanism, and Kinetic Analysis

The limited regeneration stability and high cost of conventional metal-based activated carbons remain major challenges for efficient flue gas desulfurization. In this study, a layered hematite-loaded wood-based activated carbon (FeHAC) was synthesized via a KOH-assisted hydrothermal strategy followed by high-temperature calcination, enabling the effective dispersion and in situ transformation of iron species within the carbon matrix. Under simulated flue gas conditions, the optimized sample (FeHAC-3) exhibited excellent SO2 capture performance over a wide space velocity range (2000–10,000 h–1) and temperature window (80–120 °C), achieving a breakthrough capacity of 127.66 mg·g–1, while the corresponding equilibrium capacity reached approximately 175 mg·g–1. Furthermore, the FeHAC-3 sample showed excellent regeneration stability, as the SO2 adsorption capacity was fully recovered after the first CO-assisted regeneration and still maintained 57% of its initial capacity (73.17 mg·g–1) after five consecutive cycles at 650 °C. Structural and spectroscopic analyses revealed the coexistence of multivalent iron species (Fe0/Fe2+/Fe3+) and their synergistic interaction with K-derived basic sites, which collectively promoted SO2 adsorption, oxidation, and stabilization. A coupled adsorption–oxidation–fixation mechanism was proposed to describe the SO2 capture process. Kinetic analysis indicated that pore diffusion dominated the adsorption rate, while isotherm fitting suggested cooperative adsorption on heterogeneous and homogeneous active sites. This work highlights the feasibility of using natural hematite, in combination with alkali activation, to construct a regenerable and high-performance sorbent for flue gas desulfurization, providing both mechanistic insight and practical guidance for the design of cost-effective SO2 removal materials.