Molecular Structure Analysis and Mercury Adsorption Mechanism of Iron-Based Modified Biochar

Abstract

The elemental composition, molecular skeleton vibration mode, and carbon-chain structure of iron-based modified biochar demercuration materials were studied on a microscopic scale using a variety of characterization methods. A three-dimensional molecular structure monomer model of iron-based modified biochar with defective carbon rings doped with high-valence metals was constructed. The reaction path of Hg0 adsorption on the surface of iron-based modified biochar was studied. The activation energy barrier and the rate-determining step of Hg0 adsorption on the surface of iron-based modified biochar were determined. Then, two reaction mechanisms and the corresponding bonding mechanism of Hg0 adsorption on modified biochar were proposed. In addition, the feasibility of regenerating biochar with different load ratios was verified and the regeneration reaction mechanism of inactivated biochar at different adsorption sites was revealed. The results show that the molecular structure of iron-based modified biochar is dominated by polycyclic aromatic carbon, and its molecular formula is C45H24O12NFe. Adsorption sites on iron-based modified biochar surface are not unique. A heterogeneous oxidation reaction occurs between Hg0, a Lewis base, and modified biochar, a Lewis acid. Hg-O-Fe-O x –1 and the complex Hg-OM are the main products of Hg0 oxidation. Oxygen vacancies with electrons are the chemical adsorption sites, and Fe3+, lattice oxygen, and chemisorbed oxygen are the main oxidation sites on the modified biochar. The coupling of these four constituents enables the adsorption and oxidation of Hg0. Inactivated biochar can be regenerated by supplementing the lost lattice oxygen or chemisorbed oxygen with more oxygen. The maximum mercury adsorption efficiency decreased to 90% of the primary mercury adsorption efficiency. This study quantitatively revealed the mercury adsorption mechanism of iron-based modified biochar and the regeneration mechanism of inactivated biochar, laying a foundation for further improvements in the mercury adsorption efficiency of metal-modified biochar.

Perspectives of Engineered Biochar for Environmental Applications: A Review

“…476 A biochar with a high capacity to adsorb N 2 O (0.057−0.30 mg N 2 O/g char) was obtained by Xiao et al 477 Mercury and its compounds are considered toxic and harmful to humans and animals. 478 Mercury emissions are mainly generated from the tail flue gas of coal-fired power plants. 478,479 Biochar loaded with metal oxide composites exhibited high performance for Hg 0 removal.…”

“…478 Mercury emissions are mainly generated from the tail flue gas of coal-fired power plants. 478,479 Biochar loaded with metal oxide composites exhibited high performance for Hg 0 removal. 480−483 Qin et al studied the use of iron-based modified biochar for adsorption of Hg 0 , and the reaction path of Hg 0 adsorption on the surface of iron-based modified biochar was assessed.…”

“…The results indicated that a heterogeneous oxidation reaction took place between Hg 0 and iron-based modified biochar. 478 5.3. Biochar as Catalysts.…”

“…Zhang et al obtained biochar with a high capacity to adsorb CO 2 (58–99.9 mg CO 2 /g char) from the pyrolysis of soybean straw under CO 2 –NH 3 treatment . A biochar with a high capacity to adsorb N 2 O (0.057–0.30 mg N 2 O/g char) was obtained by Xiao et al Mercury and its compounds are considered toxic and harmful to humans and animals . Mercury emissions are mainly generated from the tail flue gas of coal-fired power plants. , Biochar loaded with metal oxide composites exhibited high performance for Hg 0 removal. − Qin et al studied the use of iron-based modified biochar for adsorption of Hg 0 , and the reaction path of Hg 0 adsorption on the surface of iron-based modified biochar was assessed.…”

“…A biochar with a high capacity to adsorb N 2 O (0.057–0.30 mg N 2 O/g char) was obtained by Xiao et al Mercury and its compounds are considered toxic and harmful to humans and animals . Mercury emissions are mainly generated from the tail flue gas of coal-fired power plants. , Biochar loaded with metal oxide composites exhibited high performance for Hg 0 removal. − Qin et al studied the use of iron-based modified biochar for adsorption of Hg 0 , and the reaction path of Hg 0 adsorption on the surface of iron-based modified biochar was assessed. Different adsorption sites were generated during the synthesis of modified biochar, which include iron-based doping sites and oxygen-containing functional group adsorption sites.…”