Copper selenide enhanced magnetic biochar for elemental mercury removal from coal combustion flue gas

With the rapid development of adsorbents for removal of elemental mercury (Hg⁰) from coal combustion flue gas, the preparation of adsorbents with superior performance, lower cost and environmental friendliness remains an important challenge. An incipient wetness impregnation method followed by in-situ selenization was used to load copper selenide (CuSe) onto the surface of optimal magnetic biochar (OMBC). The results showed that CuSe significantly enhanced the Hg⁰ removal performance of the OMBC, and CuSe loading ratio of 10 % (10CuSe/OMBC) had the best Hg⁰ removal performance. 10CuSe/OMBC maintained its Hg⁰ removal efficiency above 95 % for 150 min at 30-150 °C, and it had a good resistance to SO₂. The equilibrium adsorption capacity of 10CuSe/OMBC could reach up to 8.73 mg/g, which was close to the theoretical value 12.99 mg/g, and the adsorption rate was up to 20.33 µg/(g·min) Meanwhile, 10CuSe/OMBC had strong magnetism that is not permanently magnetized, which could be separated from desulfurization gypsum and recycled many times. Characterization results demonstrated that Se₂^2-, Cu²⁺ and O_β played essential roles in the oxidation of Hg⁰, and Se₂^2- and Se^2- can immobilize Hg²⁺ to HgSe. 10CuSe/OMBC has important guiding significance for practical application because of its low cost, high performance and low mercury leaching characteristic to form HgSe.