Title: Study on the Effects of the Pyrolysis Atmosphere on the Elemental Mercury Adsorption Characteristics and Mechanism of Biomass Char
Abstract: Biochars prepared in three pyrolysis atmospheres of N2, O2, and CO2 were investigated. The pyrolysis characteristics, pore structures, and functional groups of the biochars were characterized by thermogravimetric analysis (TGA), specific surface area and porosity analyses, and Fourier transform infrared (FTIR) spectroscopy. The adsorption mechanism was further explored by the temperature-programmed desorption (TPD) technique in combination with the adsorption kinetics. The results showed that the Hg0 adsorption capacities of the biochars produced in an O2 pyrolysis atmosphere were worse than those of the biochars obtained in a N2 atmosphere, whereas CO2 significantly promoted the adsorption capacity. The biochar prepared in 20% CO2 had the highest adsorption capacity. Three pyrolysis reaction pathways were possible in the O2 atmosphere. In addition, a critical concentration existed between O2 concentrations of 5 and 7%. Above 750 °C, CO2 could react directly with the biochar through the Boudouard reaction. Mercury adsorbed to the surface of the biochar in various ways in the mercury adsorption process and thus was attached to the surface of the biochar in several forms. The products of chemical adsorption were Hg-OM and HgO, and a "secondary adsorption layer" was proposed to form in the mechanism. In the process of mercury adsorption by the biochar, a small part of the Hg0 chemically adsorbed to the active sites through their functional groups, which were mainly carbonyl and carboxyl groups. At the same time, the formation of a monolayer or multilayer "secondary adsorption layer" occurred, and the remaining Hg0 could further adsorb to this "secondary adsorption layer".
Publication Year: 2018
Publication Date: 2018-05-30
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 33
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