Research on Activation Mechanisms In Situ during Rapid Desorption of Mercury-Absorbing Activated Coke by the Heating Method

The adsorption of active coke is a good method to control mercury in coal-fired power plants, but spent powdered activated coke (SPAC) will cause secondary pollution and waste of resources if it is not properly treated. The purpose of this study was to explore the desorption performance of SPAC when heated in a drop-tube reactor under different atmospheres. The carbon consumption was 0.13%, 0.24%, 0.17%, 0.16%, and 0.14%, under desorption conditions in N₂, O₂, H₂O, CO₂, and SFG (N₂ + 12% CO₂ + 6% H₂O + 6% O₂) atmospheres, respectively. The readsorption performances of PAC-N₂, PAC-CO₂, PAC-H₂O, PAC-O₂, and PAC-SFG were 40%, 72%, 77%, 58%, and 86%, respectively. In particular, compared with the original PAC, the physicochemical properties of PAC-SFG (optimum conditions) changed greatly; the surface area of PAC-SFG and the pore volume increased by 14.1% and 11.6%, respectively, and the average pore diameter decreased by 0.203 nm. Furthermore, the total acid content of PAC-SFG was 0.505, which was greater than those of the other samples. Additionally, the desorption and activation mechanisms in situ were determined under the optimum reaction conditions. The results showed that the activator gas reacted with C to form new functional groups, Lewis acid sites, and developed pore structures, which could increase Hg⁰ adsorption efficiency from 66% to 86% after the adsorption/desorption cycles. This study provides a novel idea for the reuse of SPAC, and this research is expected to provide valuable guidance for Hg⁰ removal and SPAC activated in situ during rapid desorption processes in future large-scale engineering applications.