Partitioning of selenium from coal to fly ash: The key roles of Fe-bearing minerals and implications for Se potential recovery

Biao Fu; Guangyu Chen; Yijun Cao; James C Hower; Yukun Huang; Yongda Huang; Luyao Chen; Guangqian Luo; Lu Dong; Hong Yao

doi:10.1016/j.jhazmat.2023.132790

Partitioning of selenium from coal to fly ash: The key roles of Fe-bearing minerals and implications for Se potential recovery

J Hazard Mater. 2024 Feb 5:463:132790. doi: 10.1016/j.jhazmat.2023.132790. Epub 2023 Oct 16.

Authors

Biao Fu¹, Guangyu Chen¹, Yijun Cao¹, James C Hower², Yukun Huang³, Yongda Huang⁴, Luyao Chen⁴, Guangqian Luo⁴, Lu Dong⁴, Hong Yao⁴

Affiliations

¹ School of Chemical Engineering, Zhengzhou University, Zhengzhou 450001, China; Key Laboratory of Extraordinary Enrichment and Extraction of Critical Metal Resources, Ministry of Education, Zhengzhou University, Zhengzhou 450001, China; Zhongyuan Critical Metals Laboratory, Zhengzhou 450001, China.
² University of Kentucky, Center for Applied Energy Research, 2540 Research Park Drive, Lexington, KY 40511, United States; University of Kentucky, Department of Earth & Environmental Sciences, Lexington, KY 40506, United States.
³ School of Chemical Engineering, Zhengzhou University, Zhengzhou 450001, China; Key Laboratory of Extraordinary Enrichment and Extraction of Critical Metal Resources, Ministry of Education, Zhengzhou University, Zhengzhou 450001, China; Zhongyuan Critical Metals Laboratory, Zhengzhou 450001, China. Electronic address: huang90@zzu.edu.cn.
⁴ State Key Laboratory of Coal Combustion, School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan 430074, China.

PMID: 37898091
DOI: 10.1016/j.jhazmat.2023.132790

Abstract

The roles of Ca/Fe phases on selenium (Se) enrichment behavior in fly ash during coal combustion were investigated by examining the Ca/Fe mineralogy of various ash samples, exploring the binding forms of Se in fly ashes, and performing bench-scale adsorption experiments (150-1000 ℃). The results indicated that Se capture by fly ash is a function of flue gas temperature, particle size, and more importantly, the contents and form of Ca/Fe in combustion ash. Physical condensation/adsorption was mainly determined by temperature and particle size, contributing to less than 25% of total Se in fly ash. The remaining Se in fly ash was captured by chemical reactions of Se with ash components. Calcium in ash mostly was present as Ca-aluminosilicates, Ca-silicates, gypsum, or complex Ca-Al-Si-Fe-O mixed phases. Iron mainly occurred as Fe-silicates and some crystalline minerals including hematite, magnetite, and maghemite. Although adsorption experiments found that only CaO was able to capture SeO₂ (g) at high temperature (> 900 ℃), the roles of lime as well as Fe²⁺-/Fe³⁺-silicates (conclusion from previous literature) can be excluded, as inferred from the small amount of CaO in ash and the lack of correlation between Fe-silicate and Se. Sequential extraction experiments and electron microscopy analysis revealed that Fe-bound Se was dominant and iron oxides might be the critical phase for Se retention. Simulated adsorption experiments demonstrated that magnetite had the best Se capture ability among the iron minerals. The extraction of Fe-bound Se from coal fly ash required more stringent conditions than that of physiosorbed-Se and Ca-bound Se. Therefore, pretreatment methods including magnetic separation, flotation, size segregation, etc. were suggested to be used prior to acid leaching. This study can provide scientific basis for developing high-efficiency Se recovery methods or Se emission control techniques for high-Se coal utilization in thermal power stations.

Keywords: Coal power plants; Enrichment mechanisms; High-Se fly ash; Metal recovery; Se speciation.