Upcycling Hazardous Industrial Waste into Chlorinated Sorbents toward Cost-Effective Mercury Removal from Syngas

Mercury-containing spent catalyst (MCSC) from acetylene hydrochlorination and acidic cupric etchants from printed-circuit-board manufacture are hazardous wastes that retain a porous carbon scaffold and reactive chloride species. Herein, their detoxification and reuse were coupled to produce a chlorine-functionalized carbon sorbent for gaseous elemental mercury (Hg0) capture from syngas. Residual mercury in MCSC was first recovered by thermal desorption, producing mercury-free spent catalyst (MFSC) with a preserved hierarchical porous structure. MFSC was then treated by one-step in situ etching with spent acid (SA), activated by H+, Cu2+, and Cl– components to exert its function. The optimized 20SA-MFSC achieved 99.8% Hg0 removal efficiency within 60 min at 100 °C and maintained >95% Hg0 removal for 8 h under pure N2. In the long-term breakthrough test, the cumulative Hg0 adsorption capacity reached 10.42 mg·g–1 at an outlet-to-inlet Hg0 concentration ratio of 0.8. Mechanism analysis implicated that Cl-containing species, especially surface chloride and covalent C–Cl groups, dominated Hg0 removal by converting Hg0 into HgCl2 species. Techno-economic and life cycle assessments demonstrated that the waste-derived route reduced estimated production cost, global warming potential, and cumulative energy demand by 90.9%, 48.1%, and 63.0%, respectively, relative to a commercial-reagent route. These benefits primarily arose from replacing commercial activated carbon and reagents with waste-derived feedstocks, while residual mercury recovery provided a byproduct credit that partially offset the processing costs. This work provides a sustainable and synergistic route integrating hazardous-waste detoxification, resource utilization, and Hg0 pollution control.