Mercury removal performance and mechanism of biochar co-modified with HNO₃ and NH₄Br under oxy-combustion atmosphere

ABSTRACT

In order to meet the demand for mercury removal in the oxy-combustion atmosphere, a new mercury adsorbent was prepared by using rice husk char as raw material and co-modification of acid and halogen. The experimental results indicate that the specific surface area of the combined modified char is smaller than those modified by HNO₃ and NH₄Br alone, but it has better mercury removal performance. X-ray photoelectron spectroscopy (XPS) analysis shows that the co-modification can effectively promote the formation of C-O* and C-Br. The high activity of Br will induce the Hg⁰ adsorption, while C-O* will convert the easily decomposed HgBr₂ into more stable HgO, which may be the reason why the combined modified char maintains high mercury removal efficiency. When the reaction temperature reaches 150°C, the mercury removal efficiency of RHC (Br+N) is almost 100%. Both above and below the optimum reaction temperature will affect the activity of chemical functional groups and inhibit mercury removal. According to the density functional theory (DFT) results, the addition of O and Br atoms can stably combine with the carbonaceous surface to form covalent compounds (C=O, C-Br), both of which can induce the charge transfer of surrounding C atoms, which makes the C atoms have stronger electronegativity and easier to chemically adsorb Hg⁰.

KEYWORDS:

• Mercury
• Oxy-combustion
• Density functional theory
• Rice husk char
• Co-modification

Acknowledgements

The authors sincerely thank Chang Shen for the experimental data and efforts he provided for this article.

Disclosure statement

No potential conflict of interest was reported by the authors.

Author contributions

Qingshan Zeng: Validation, Writing – review and editing, visualization.

Hui Wang: Project administration, Supervision, Funding acquisition.

Hengyuan Ran: Writing – original draft.

Jingmao Wu: Data curation and Investigation.

Kang Yang: Investigation.

Additional information

Funding

This work was supported by the National Natural Science Foundation of China (51706104).

Notes on contributors

Qingshan Zeng

Qingshan Zeng is a student of Nanjing University of Science and Technology, focusing on CO2 emission reduction and comprehensive utilization, coal combustion pollution control.

Hui Wang

Hui Wang is a teacher of Nanjing University of Science and Technology, focusing on CO2 emission reduction and comprehensive utilization, coal combustion pollution control.

Hengyuan Ran

Hengyuan Ran is a student of Nanjing University of Science and Technology, focusing on CO2 emission reduction and comprehensive utilization, coal combustion pollution control.

Jingmao Wu

Jingmao Wu is a student of Nanjing University of Science and Technology, focusing on CO2 emission reduction and comprehensive utilization, coal combustion pollution control.

Kang Yang

Kang Yang is a student of Nanjing University of Science and Technology, focusing on CO2 emission reduction and comprehensive utilization, coal combustion pollution control.