Fu Biao, Chen Guangyu, Cao Yijun, Hower James C, Huang Yukun, Huang Yongda, Chen Luyao, Luo Guangqian, Dong Lu, Yao Hong
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.
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.
J Hazard Mater. 2024 Feb 5;463:132790. doi: 10.1016/j.jhazmat.2023.132790. Epub 2023 Oct 16.
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 SeO (g) at high temperature (> 900 ℃), the roles of lime as well as Fe-/Fe-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.
通过研究不同灰样的钙铁矿物学、探索飞灰中硒的结合形式以及进行实验室规模的吸附实验（150 - 1000℃），研究了钙铁相在煤燃烧过程中对飞灰中硒富集行为的作用。结果表明，飞灰对硒的捕获是烟气温度、颗粒大小的函数，更重要的是，是燃烧灰中钙铁的含量和形态的函数。物理冷凝/吸附主要由温度和颗粒大小决定，对飞灰中总硒的贡献小于25%。飞灰中剩余的硒通过硒与灰分成分的化学反应被捕获。灰中的钙主要以钙铝硅酸盐、钙硅酸盐、石膏或复杂的钙铝硅铁氧混合相存在。铁主要以铁硅酸盐以及一些结晶矿物（包括赤铁矿、磁铁矿和磁赤铁矿）的形式存在。尽管吸附实验发现只有CaO能够在高温（> 900℃）下捕获SeO（g），但从灰中CaO含量少以及铁硅酸盐与硒缺乏相关性推断，石灰以及铁/铁硅酸盐的作用（来自先前文献的结论）可以排除。连续萃取实验和电子显微镜分析表明，铁结合硒占主导地位，铁氧化物可能是硒保留的关键相。模拟吸附实验表明，磁铁矿在铁矿物中具有最佳的硒捕获能力。从煤飞灰中提取铁结合硒比提取物理吸附硒和钙结合硒需要更严格的条件。因此，建议在酸浸之前使用包括磁选、浮选、粒度分离等在内的预处理方法。本研究可为开发高效的硒回收方法或火力发电厂高硒煤利用中的硒排放控制技术提供科学依据。
