Investigation of a Carbon-Based Sorbent Prepared from FeSO4-Flocculated Sludge for Elemental Mercury Removal from Syngas

A novel carbon-based sorbent was prepared from FeSO4-flocculated sludge by one-step pyrolysis. The characterization results indicated that multiple Fe2O3 and sulfur species (S22− and polysulfide) existed over this sludge-derived sorbent. Its performance on Hg0 removal from syngas was evaluated. The sorbent from the sludge pyrolyzed at 710 ℃ could achieve around 86 % Hg0 removal efficiency at 150 ℃ under simulated syngas (400 ppm H2S, 10 ppm HCl, 20 vol% H2, 30 vol% CO, 8 vol% H2O and N2). H2S and HCl exhibited a promoting effect on Hg0 removal, whereas CO, H2 and H2O inhibited Hg0 removal. The analysis of adsorption kinetics manifested that Hg0 adsorption over the sorbent was better described by pseudo-second-order kinetic model, implying that it was a chemisorption process. The Hg0 removal under N2 condition was due to the reaction between absorbed Hg0 and Fe3+–O or S22−/polysulfide over the sorbent surface. In the presence of H2S, multiple sulfur species was produced by the reaction of adsorbed H2S with Fe3+–O. The increased sulfur species (S22− and polysulfide) greatly promoted the formation of HgS. The sorbent has good prospect in engineering applications because of its good Hg0 removal performance, low cost and facile preparation process.