Structural Characterizations of Aluminosilicates in Two Types of Fly Ash Samples from Shanxi Province, North China

Abstract

In order to determine the structural characterization of aluminosilicates in two types of fly ashes, two samples from Shanxi Province, China were selected for study. One was from a pulverized coal boiler (FA-1), and the other from a circulating fluidized bed boiler (FA-2). FA-1 had a much higher content of silicon dioxide (SiO2) (70.30%) than FA-2(42.19%), but aluminum oxide (Al2O3) was higher in FA-2 (25.41%) than in FA-1 (17.04%). The characterizations were investigated using various methods including X-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR), magic angle spinning nuclear magnetic resonance (MAS–NMR) spectrometry, and X-ray photoelectron spectroscopy (XPS). The XRD analysis showed that FA-1 contained aluminosilicate glass, quartz and mullite, while FA-2 contained significant amounts of amorphous aluminosilicate, quartz and gypsum. The FTIR results showed an increased substitution of Al3+ for Si4+ as the band of asymmetric stretching vibrations Si–O(Si) (1100 cm−1) moved to 1090 cm−1 for FA-2, much lower than for FA-1(1097 cm−1). Moreover, the sharpness of the bands in the 1250–1000 cm−1 region for FA-2 indicates that the silicate structure of FA-2 was more ordered than for FA-1. It can be understood from the 29Si MAS–NMR results that Q4(mAl) (Q4 are connected via 4 bridging O atoms to mAl) is the main structural type in FA-1 and FA-2, and that FA-2 contains more Al, which substitutes for Si in the Q4 structure. 27Al MAS–NMR demonstrated that a combination of tetrahedral, pentahedral, and octahedral Al existed in FA-1 and FA-2. The Si 2p XPS spectra suggested that there were three forms of Si, including bridging Si (Si–O2), non–bridging Si (Si–O), and SiO2 gel. The content of Si–O2 for FA-1 was 37.48% higher than Si–O (28.57%), while the content of Si–O2 was 30.21% lower than Si–O (40.15%) for FA-2. The Al 2p XPS spectra showed that octahedral Al was the dominant form for FA-1 with a content of 40.25%, while the main phase was tetrahedral Al for FA-2 with a proportion of 37.36%, which corresponds well with the 27Al MAS–NMR results.

Novel Application of Mineral By-Products Obtained from the Combustion of Bituminous Coal–Fly Ash in Chemical Engineering

“…Furthermore, the symmetrical stretching variation at 730 cm −1 and the symmetrical stretching variation at 660 cm −1 associated with Si-O-Al and Si-O-Si, respectively, were suggested by Mozgawa et al [43]. Moreover, the band at about 550 cm −1 corresponds to symmetric stretching vibrations of ν s Si-O-Si bridge bonds and bending vibrations of δ O-Si-O as a complex band [15,42,43]. Based on the FT-IR spectrum, the presence of pore openings corresponding to the band at 460 cm −1 in FA and FA-H 2 O 2 can be observed, which can be attributed to the dissolution of the minerals (viz., quartz and mullite) present in the samples [15].…”

“…In the obtained Fourier transform infrared (FT-IR) spectra of FA and FA-H 2 O 2 , there was an observed absorption broadband at 3440 cm −1 , a band at 1630 cm −1 , and an absorption broadband at about 1050 cm −1 (Figure 4, Table 1). Coal fly ash oxidized by H2O2 was more hydrophilic than that of the corresponding unoxidized sample [42,43]. There is a noticeable increase in band intensity in the field of 3440 cm -1 in the spectrum of FA-H2O2.…”

“…The vibration bands of Fourier transform infrared (FT-IR) spectra[15,[41][42][43]. O 2 was more hydrophilic than that of the corresponding unoxidized sample[42,43].…”

Reactivity and Pozzolanic Properties of Biomass Ashes Generated by Wheat and Soybean Straw Combustion

“…The most intense band observed for all ashes is at approximately 1000–1100 cm −1 , and is attributed to the asymmetric stretching vibrations of Si(Al)–O in silica and aluminosilicate phases [ 55 , 56 ]. This band provides information on the degree of crystallinity/amorphicity of a sample [ 57 ].…”

Investigation of glassy phase silica in low calcium content fly ash by X‐ray photoelectron spectroscopy

“…Detailed study on amorphous and crystalline silica from various silica-rich sources has also been done in detail by a few researchers. [23][24][25] The present study investigates the crystalline and glassy phases silica in fly ash from two fly ash sources along with the semi quantitative analysis.…”