Insight into the role of SO2 on selenium conversion during adsorption by CaO: Theoretical calculation and experimental study

Mengzhu Yu; Fumitake Takahashi; Yaji Huang; Zihong Li; Hao Xu; Pu Yang; Zhicheng Zhu; Lu Dong; Conghui Fan; Kunio Yoshikawa

doi:10.1016/j.jhazmat.2023.131742

Insight into the role of SO₂ on selenium conversion during adsorption by CaO: Theoretical calculation and experimental study

J Hazard Mater. 2023 Sep 5:457:131742. doi: 10.1016/j.jhazmat.2023.131742. Epub 2023 May 30.

Authors

Mengzhu Yu¹, Fumitake Takahashi², Yaji Huang³, Zihong Li⁴, Hao Xu², Pu Yang², Zhicheng Zhu⁵, Lu Dong⁶, Conghui Fan⁵, Kunio Yoshikawa²

Affiliations

¹ Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, School of Energy and Environment, Southeast University, Nanjing, Jiangsu 210096, PR China; Department of Transdisciplinary Science and Engineering, School of Environment and Society, Tokyo Institute of Technology, Kanagawa, Yokohama 2268503, Japan.
² Department of Transdisciplinary Science and Engineering, School of Environment and Society, Tokyo Institute of Technology, Kanagawa, Yokohama 2268503, Japan.
³ Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, School of Energy and Environment, Southeast University, Nanjing, Jiangsu 210096, PR China. Electronic address: heyyj@seu.edu.cn.
⁴ School of Chemical Engineering, Dalian University of Technology, Dalian, Liaoning 116024, PR China.
⁵ Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, School of Energy and Environment, Southeast University, Nanjing, Jiangsu 210096, PR China.
⁶ State Key Laboratory of Coal Combustion, School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan, Hubei 430074, PR China.

PMID: 37320897
DOI: 10.1016/j.jhazmat.2023.131742

Abstract

SO₂ can noticeably impact the control of high toxic selenium emissions from flue gas by CaO. Surprisingly, our experiments showed that under certain conditions, SO₂ can promote selenium capture by CaO, rather than hinder it. To elucidate the underlying mechanism, a combination of theoretical calculations and experiments was conducted. Thermodynamic equilibrium analysis revealed that gaseous SO₂ and solid Ca-S reaction products can promote SeO₂ converting to SeO/Se⁰. The Ca-S products facilitated greater SeO₂ conversion compared to SO₂. Experimental results demonstrated that selenium adsorption capacity of incompletely sulfurized CaO (CaO with pre-adsorbed SO₂) was higher than that of completely sulfurized CaO (Ca-S products), highlighting the importance of adsorption sites of CaO. Density functional theory calculations showed that the pre-adsorbed SO₂ hardly affected selenium adsorption energy on the SO₂/CaO surface, while completely sulfurized CaO had low selenium adsorption energy, explaining the experimental phenomenon and proving necessary of CaO. Additionally, SeO/Se⁰ had higher adsorption energy on CaO than SeO₂. Overall, the promotion of SO₂ on selenium adsorption was primarily affected by two factors: 1) sulfur facilitating SeO₂ conversion to SeO/Se⁰ which can be adsorbed more easily by CaO; 2) sufficient adsorption sites on CaO surface existing for SeO/Se⁰ adsorption, despite co-adsorption with sulfur.

Keywords: Density Functional Theory (DFT); Effects of SO(2); Selenium conversion; Theoretical calculations; Thermodynamic equilibrium analysis.