通过检查各种灰分样品的Ca/Fe矿物学,研究了Ca/Fe相对煤燃烧过程中粉煤灰中硒(Se)富集行为的作用。探索粉煤灰中硒的结合形式,并进行实验室规模的吸附实验(150-1000℃)。结果表明,粉煤灰对硒的捕集是烟气温度的函数,颗粒大小,更重要的是,燃烧灰中Ca/Fe的含量和形态。物理冷凝/吸附主要由温度和粒径决定,贡献不到粉煤灰中总硒的25%。飞灰中剩余的Se通过Se与灰分组分的化学反应被捕获。灰分中的钙主要以钙硅铝酸盐的形式存在,硅酸钙,石膏,或复杂的Ca-Al-Si-Fe-O混合相。铁主要以铁硅酸盐和一些结晶矿物,包括赤铁矿,磁铁矿,和磁赤铁矿。虽然吸附实验发现只有CaO能够在高温(>900℃)下捕获SeO2(g),石灰以及Fe2+-/Fe3+-硅酸盐的作用(来自先前文献的结论)可以排除,从灰分中的少量CaO以及Fe-硅酸盐和Se之间缺乏相关性推断。顺序萃取实验和电子显微镜分析表明,Fe结合的Se占主导地位,氧化铁可能是保留Se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Se捕获能力。从粉煤灰中提取Fe结合的Se比物理吸附的Se和Ca结合的Se需要更严格的条件。因此,预处理方法包括磁分离,浮选,尺寸隔离,等。建议在酸浸之前使用。该研究可为火电厂高硒煤高效回收方法或硒排放控制技术的发展提供科学依据。
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.