Preparation of microwave-activated magnetic bio-char adsorbent and study on removal of elemental mercury from flue gas.

In this study, novel activated magnetic bio-char adsorbents were proposed to remove the element mercury (Hg) from flue gas. Microwave activation and Mn-Fe mixed oxides impregnation assisted by ultrasound treatment were applied on the modification of renewable cotton straw chars. The influence of different preparation methods, loading value of Mn-Fe, molar ratio of Mn/Fe, calcining temperature, reaction temperature and individual flue gas ingredients (O, NO, SO and HO) on removal of Hg was investigated in a fixed bed system. The characterization results reveal that microwave activation is advantageous for the development of the pore structure, and ultrasound treatment can optimize the dispersion of Mn and Fe active ingredients. MnFe4%(3/10)/CSWU700 adsorbent exhibits the optimal Hg removing performance. O, NO, low concentration of SO (<600 ppm) and low concentration of HO (<2%) are found to be favourable for the capture of Hg, while high concentrations of SO and HO inhibit the removal of Hg. Chemical adsorption acts a pivotal part in the process of Hg removal. Mn and Fe active ingredients are consumed in large quantities during the Hg capture. In addition, chemisorbed oxygen (O) also plays an indispensable in the oxidation process of Hg. Furthermore, the magnetic adsorbent MnFe4%(3/10)/CSWU700 presents a good regeneration performance and adsorption capacity.