Effect of Sonochemical Treatment on Thermal Stability, Elemental Mercury (Hg⁰) Removal, and Regenerable Performance of Magnetic Tea Biochar

Elemental mercury (Hg⁰) removal from a hot gas is still challenging since high temperature influences the Hg⁰ removal and regenerable performance of the sorbent. In this work, a facile yet innovative sonochemical method was developed to synthesize a thermally stable magnetic tea biochar to capture the Hg⁰ from syngas. A sonochemically synthesized magnetic sorbent (TUF_0.46) exhibited a more prodigious surface area with developed pore structures, ultra-paramagnetic properties, and high dispersion of Fe₃O₄/γ-Fe₂O₃ particles than a simply synthesized magnetic sorbent (TF_0.46). The results showed that TUF_0.46 demonstrated strong thermostability and attained a high Hg⁰ removal performance (∼98.6%) at 200 °C. After the 10th adsorption/regeneration cycle, the Hg⁰ removal efficiency of TUF_0.46 was 19% higher than that of TF_0.46. Besides, at 23.1% Hg⁰ breakthrough, TUF_0.46 achieved an average Hg⁰ adsorption capacity of 16.58 mg/g within 24 h under complex syngas (20% CO, 20% H₂, 5% H₂O, and 400 ppm H₂S). In addition, XPS results revealed that surface-active components (Fe⁺, O^2–, O*, CO) were the key factor for high Hg⁰ removal performance over TUF_0.46 from syngas. Hence, sonochemistry is a promising practical tool for improving the surface morphology, thermal resistance, renewability, and Hg⁰ removal efficiency of a sorbent.