Dynamic hydrothermal synthesis of xonotlite fibers by alkali silica extraction of fly ash

Abstract

The silica leached from coal fly ash using alkali, via the hydrothermal method, can be used as the raw material for the synthesis of xonotlite fibers through the hydrothermal synthesis method. This investigation was made to examine how the fly ash desilicated liquid influences the crystal growth and microstructure of xonotlite fibers. The obtained samples were characterized by X-ray diffraction and scanning electron microscope techniques to investigate their mineralogical composition and morphological characteristics. The results indicated that the pure desilication liquid leached from coal fly ash could be used to prepare xonotlite fibers. Xonotlite fibers with single crystal characteristics and large aspect ratio of 100–400 were successfully fabricated from fly ash desilication liquid, which is used as the silica material, at 240°C for 6 h.

High-End Reclamation of Coal Fly Ash Focusing on Elemental Extraction and Synthesis of Porous Materials

“…In addition, a turbid Ca(OH) 2 solution can be used to obtain Xonotlite fibers using a single precipitation method. 99 Moreover, transformation processes have been observed; during precipitation, the pore structure and shape of samples vary from nonporous to wedge-shaped, slit-shaped, and cylinder-shaped mesostructures with an increase in reaction intensity. 44 Precipitation can be conducted under acidic or basic conditions with the acid and base as precipitators; these two pathways yield differences in the product.…”

“…Similarly, alkalis can be used to extract elements from CFA. However, most hydroxides in CFA cannot be dissolved in water, and alkali dissolution is rarely used for extracting elements from CFA, except for amorphous Si and Al due to their special characteristics. , Our previous study of Si extraction using sodium hydroxide (NaOH) showed that the efficiency of Si extraction increased as the reaction temperature rose from 80 to 110 °C; however, further temperature increases led to the formation of the byproduct hydroxy-sodalite. Other techniques (e.g., ultrasound) have been used to shorten the reaction time and have been reported to improve the extraction efficiency from 34.96% to 54.42% .…”

“…Reprinted with permission from ref . Copyright 2016 American Chemical Society; (5) Xonotlite fibers . Open access (6) MCM-41.…”

“…After extracting of Na 2 SiO 3 from CFA, H 2 SO 4 is used to form a precipitate, yielding a fine silica powder after calcination. In addition, a turbid Ca­(OH) 2 solution can be used to obtain Xonotlite fibers using a single precipitation method . Moreover, transformation processes have been observed; during precipitation, the pore structure and shape of samples vary from nonporous to wedge-shaped, slit-shaped, and cylinder-shaped mesostructures with an increase in reaction intensity …”

High‐Purity Template‐Free Mesoporous Silica Synthesized FROM Coal Fly Ash

“…Our method involves a two‐stage treatment of CFA: (1) a thermal activation phase where CFA is mixed with Na 2 CO 3 at various ratios and subsequently calcined at different temperatures, and (2) an HCl‐based acid reflux process to isolate silica as a residual product after filtration. The utilization of Na 2 CO 3 guarantees the extraction of silica as a residue, in contrast to the NaOH technique described by Peng [10] and Ju et al., [11] which results in solubilization of silica. This approach enhances reactivity, improving the leaching of unwanted components during acid leaching and increasing the purity of the synthesized silica.…”