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

Abstract

In this study, novel activated magnetic bio-char adsorbents were proposed to remove the element mercury (Hg0) 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 (O2, NO, SO2 and H2O) on removal of Hg0 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 Hg0 removing performance. O2, NO, low concentration of SO2 (<600 ppm) and low concentration of H2O (<2%) are found to be favourable for the capture of Hg0, while high concentrations of SO2 and H2O inhibit the removal of Hg0. Chemical adsorption acts a pivotal part in the process of Hg0 removal. Mn and Fe active ingredients are consumed in large quantities during the Hg0 capture. In addition, chemisorbed oxygen (Oβ) also plays an indispensable in the oxidation process of Hg0. Furthermore, the magnetic adsorbent MnFe4%(3/10)/CSWU700 presents a good regeneration performance and adsorption capacity.