The effect of H2O on formation mechanism of arsenic oxide during arsenopyrite oxidation: Experimental and theoretical analysis

Zou, Chan; Wang, Chunbo; Chen, Liang; Zhang, Yue; Xing, Jiaying; Anthony, Edward J.

doi:10.1016/j.cej.2019.123648

Cited by 31 publications

(20 citation statements)

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“…To further understand the mechanisms of NO oxidation and NO 2 reduction reactions, density functional theory (DFT) calculations were used as a powerful method for obtaining accurate chemical reaction pathways, molecular structures, and energy profiles as well as kinetic and thermodynamic parameters. − In terms of DFT calculations, Li et al determined the mechanisms of the NO oxidation reaction when it is absorbed on a TiO 2 surface and showed that the O-containing groups can serve as an effective reactant to oxidize NO molecules, in agreement with the work of Razavi et al Similar studies have been conducted using DFT calculations on the NOx reduction reaction on different material surfaces, such as carbon, metal catalysts, or others. Jiao et al carried out a DFT study on the NO reduction reaction via a char edge model, and the influence of CO on the NO reduction reaction was also taken into account.…”

Section: Introductionmentioning

confidence: 61%

Formation and Reduction of NO₂ in Fixed Bed Combustion of Coal Char under Oxy–Fuel Conditions: Experimental and Density Functional Theory Analysis

Yue

Wang

et al. 2020

Energy Fuels

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Nitrogen dioxide (NO 2 ) has been attracting a lot of attention because of its toxicity and potential in contaminating land, air, and water. However, research on NO 2 release behavior under oxy−fuel conditions is still insufficient. This paper aims to explore the formation and reduction mechanisms of NO 2 during oxy−fuel combustion of char by using both experimental and density functional theory (DFT) methods. Results showed that with the increase of temperature, the energy barrier of the NO oxidation reaction increases, while that of the NO 2 reduction reaction decreases. These facts lead to a higher peak concentration of NO and lower NO 2 emissions. Because of a larger effect of temperature on the rate constant of the NO 2 reduction reaction than that of the NO oxidation reaction, the NO 2 concentration decreases dramatically and rapidly even if the temperature increases only slightly. As the temperature increases to above 1273 K, the equilibrium constant of the NO oxidation reaction falls to below 10 5 . That is, the oxidation of NO to NO 2 is incomplete and reversible over the temperature range of 1273−1673 K. By contrast, the reduction of NO 2 to NO is complete and irreversible over this temperature range. As a result, almost no NO 2 is observed at high temperatures. In the presence of H 2 O, DFT calculations show that the water-gas-shift reaction is less important in contrast to the H 2 O−carbon reaction, which is consistent with previous research. In this case, NOx emissions under an O 2 /CO 2 /H 2 O atmosphere are lower than those under an O 2 /CO 2 atmosphere. Overall, combined experiments with DFT calculations offer a new approach to study the microcosmic mechanisms of NO 2 formation and reduction under oxy−fuel conditions during isothermal combustion of char.

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Section: Introductionmentioning

confidence: 61%

Formation and Reduction of NO₂ in Fixed Bed Combustion of Coal Char under Oxy–Fuel Conditions: Experimental and Density Functional Theory Analysis

Yue

Wang

et al. 2020

Energy Fuels

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“…An adsorption with E ads < 0.4 eV is regarded as a physical adsorption, and E ads > 0.5 eV is regarded as a chemical adsorption . The Gibbs free energy change of an adsorption process, Δ G ads , was calculated by eqs – where G is the Gibbs free energy, T is the thermodynamic temperature (K), S is the entropy, and R is the gas constant.…”

Section: Methodsmentioning

confidence: 99%

Insight into the Mechanism and Effect of H₂O on CaO Sulfation by Density Functional Theory

et al. 2022

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The CaO sulfation is the main reaction to capture SO2 by limestone in circulating fluidized boilers. The mechanism and effects of H2O on CaO sulfation were investigated by density functional theory and experiments. The reaction paths and energy barriers for SO4 2– forming on CaO and CaSO4 surfaces as well as the outward diffusion of Ca2+/O2– in CaO and CaSO4 crystals were examined. Under conditions without H2O, the outward diffusion of Ca2+ on the CaSO4 surface is the rate-determining step for CaO sulfation because it has the largest energy barrier (3.63 eV) of all steps in the sulfation reaction. Under conditions with H2O, X-ray diffraction analysis indicates that H2O cannot directly accelerate the diffusion of Ca2+ in the CaSO4 layer. However, with the assistance of H2O, the interactions between Ca2+ and SO4 2– on the CaSO4 surface become weaker, the energy barrier for the diffusion of Ca2+ decreases from 3.63 to 1.62 eV, and thus the outward diffusion of Ca2+ on the CaSO4 surface is enhanced. The rate-determining step of the sulfation reaction under conditions with H2O became O2– diffusion in the CaSO4 layer with an energy barrier of 3.42 eV, which means that H2O decreases the largest energy barrier for sulfation by 0.21 eV. In addition, H2O can also enhance the adsorption of SO2 on a CaSO4 surface.

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“…Figure S3 displays the PDOS of bonded O and As atoms on the (101) 42 Additionally, these numbers were smaller than the value of −123.46 kJ/mol, which was obtained for pyrite (surface doping an As atom) by using the GGA + PBE method. 38 This difference might be S3). Table S3 also demonstrates that H 2 O molecules can enhance the dissociation of the O−O bond on the arsenopyrite/pyrite surface.…”

Section: Oxidation Behavior Of Omentioning

confidence: 97%

“…22,34,38−41 The (001) surface of arsenopyrite and pyrite exhibits high stability and the crystal model can be established along this plane for the adsorption and oxidation mechanisms of O 2 /O 2 + H 2 O. 38,39 The oxidation of the FeAsS and the FeS 2 interface is also greatly enhanced in the presence of H 2 O. 34,38 The pyrite surface oxidizes as a result of the multistep complex reactions between the surface and the adsorbed O 2 and water molecules.…”

Section: Introductionmentioning

confidence: 99%

“…38,39 The oxidation of the FeAsS and the FeS 2 interface is also greatly enhanced in the presence of H 2 O. 34,38 The pyrite surface oxidizes as a result of the multistep complex reactions between the surface and the adsorbed O 2 and water molecules. Water can promote the formation of H-bonds, while the proton-coupled electron transport through the H-bond causes ferric hydroxylation reactions.…”

Section: Introductionmentioning

confidence: 99%

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Impact of H₂O on the Microscopic Oxidation Mechanism of Lollingite: Experimental and Theoretical Analyses

et al. 2023

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Lollingite (FeAs2) is considered an arsenic-bearing mineral that is oxidized faster than arsenopyrite. The geometric configuration, chemical valence bond, and microscopic reaction of the oxidation on the surface of lollingite were systematically studied, which are of great significance for understanding the mechanism of oxidative dissolution. X-ray photoelectron spectroscopy (XPS) measurements and density functional theory (DFT) calculations were carried out to characterize the (101) surface oxidation process of lollingite under the O2/O2 + H2O conditions. XPS results confirmed that the participation of water molecules can promote the formation of abundant OH structures on the surface of lollingite, while the relative concentration of O, As(III), and Fe(III) increased. Moreover, the DFT results demonstrated that the (101) As-terminal plane of FeAs2 was the most stable surface with the lowest surface energy. H2O molecules were physically adsorbed onto the Fe atoms of the lollingite surface, while oxygen molecules can readily be adsorbed on the Fe–As2 site by chemical adsorption processes. The oxidation process of the lollingite surface with water includes the following mechanisms: adsorption, dissociation, formation of the hydrogen bond, and desorption. The dissociation of the H2O molecule into OH and H led to the hydroxylation of both Fe and As atoms and the formation of hydrogen bonding. The participation of H2O molecules can also reduce the reaction energy barrier and accelerate the oxidation reaction of the lollingite surface, especially as far as the water dissociation and formation of hydrogen bonds are concerned. According to PDOS data, there is considerable hybridization between the d orbitals of bonded Fe atoms and the p orbitals of O atoms, as well as between the p orbitals of bonded As atoms and the p orbitals of O atoms. Due to a strong propensity for orbital hybridization and bonding between the s orbitals of the H atoms in H2O molecules and the p orbitals of the O atoms on the (101) surface, water molecules have the ability to speed up the oxidation on the surface.

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The effect of H2O on formation mechanism of arsenic oxide during arsenopyrite oxidation: Experimental and theoretical analysis

Cited by 31 publications

References 50 publications

Formation and Reduction of NO₂ in Fixed Bed Combustion of Coal Char under Oxy–Fuel Conditions: Experimental and Density Functional Theory Analysis

Formation and Reduction of NO₂ in Fixed Bed Combustion of Coal Char under Oxy–Fuel Conditions: Experimental and Density Functional Theory Analysis

Insight into the Mechanism and Effect of H₂O on CaO Sulfation by Density Functional Theory

Impact of H₂O on the Microscopic Oxidation Mechanism of Lollingite: Experimental and Theoretical Analyses

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The effect of H2O on formation mechanism of arsenic oxide during arsenopyrite oxidation: Experimental and theoretical analysis

Cited by 31 publications

References 50 publications

Formation and Reduction of NO2 in Fixed Bed Combustion of Coal Char under Oxy–Fuel Conditions: Experimental and Density Functional Theory Analysis

Formation and Reduction of NO2 in Fixed Bed Combustion of Coal Char under Oxy–Fuel Conditions: Experimental and Density Functional Theory Analysis

Insight into the Mechanism and Effect of H2O on CaO Sulfation by Density Functional Theory

Impact of H2O on the Microscopic Oxidation Mechanism of Lollingite: Experimental and Theoretical Analyses

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Formation and Reduction of NO₂ in Fixed Bed Combustion of Coal Char under Oxy–Fuel Conditions: Experimental and Density Functional Theory Analysis

Formation and Reduction of NO₂ in Fixed Bed Combustion of Coal Char under Oxy–Fuel Conditions: Experimental and Density Functional Theory Analysis

Insight into the Mechanism and Effect of H₂O on CaO Sulfation by Density Functional Theory

Impact of H₂O on the Microscopic Oxidation Mechanism of Lollingite: Experimental and Theoretical Analyses