Modes of Occurrence of Fluorine by Extraction and SEM Method in a Coal-Fired Power Plant from Inner Mongolia, China

Abstract

In this study, an extraction method and environmental scanning electron microscopy (SEM) are employed to reveal the changes in the occurrence mode of fluorine in a coal-fired power plant in Inner Mongolia, China. The different occurrence states of fluorine during coal combustion and emission show that fluorine in coal mainly assumes insoluble inorganic mineral forms. The results illustrate that the three typical occurrence modes in coal are CaF2, MgF2 and AlF3. The fluorine in fly ash can be captured by an electrostatic precipitator (EPS) or a bag filter. In contrast, the gaseous fluorine content in flue gas is only in the range of several parts per million; thus, it cannot be used in this study. The occurrence mode of fluorine in bottom ash and slag is inorganic villiaumite (e.g., soluble NaF, KF and insoluble CaF2) which is difficult to break down even at high temperatures. The occurrence mode of fluorine with the highest content in fly ash is physically adsorbed fluorine along the direction of the flue gas flow. The insoluble inorganic mineral fluoride content in fly ash is also high, but the gradually increasing fluorine content in fly ash is mainly caused by physical adsorption. Fluorine in the coal-fired power plant discharges mostly as solid products; however, very little fluorine emitted into the environment as gas products (HF, SiF4) cannot be captured. The parameters used in this study may provide useful references in developing a monitoring and control system for fluorine in coal-fired power plants.

Preliminary Study on Additives for Controlling As, Se, B, and F Leaching from Coal Fly Ash

“…Trace elements that are also classified as heavy metals are transformed into less soluble compounds, which makes these trace elements non-hazardous in the environment. As, Se, B, and F can react with calcium and form relatively insoluble compounds such as Ca 3 (AsO 4 ) 2 , Ca 4 (OH) 2 (AsO 4 ) 2 •4H 2 O [9,13], CaSeO 3 [9], Ca 2 B 2 O 5 , Ca 3 B 2 O 6 [8] and CaF 2 [24,25]. Therefore, calcium addition through the use of high-calcium-content materials in the leaching process could be applied to control the leaching of trace elements.…”

Global Biogeochemical Cycle of Fluorine

“…In modern power plants in the European Union, the main CCRs consist of approximately 66% fly ash, 24% FGD gypsum, 8% bottom ash, and 2% slag (Córdoba, 2015). Because most F is volatized in flue gas (~90%), the majority of F in modern plants is captured in FGD gypsum, with reported F concentrations as high as 2,730 mg/kg (Wang et al, 2015), and typical values averaging about 1,060 mg/kg (Álvarez‐Ayuso et al, 2006; Córdoba et al, 2012; USEPA, 2009). Available data suggest average F concentrations of about 110 ppm for both fly ash and bottom ash and about 9 mg/kg for slag (Álvarez‐Ayuso et al, 2006; Clayton & Dale, 1985; Córdoba et al, 2012; Dai et al, 2014; López‐Vilariño et al, 2003; Meij, 1994; Tsubouchi et al, 2011; USEPA, 2009; Wang et al, 2015).…”

Environmental Protection of Port Logistics Using Phase Analysis

“…In the Republic of Guinea, they also include especially fly ash from flue gas cleaning of high-temperature metallurgical plants. Interest in and the study of the characterization of waste products is growing [5,6].…”