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

Xu Peng

doi:10.1177/1558925019890340

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.

Highlights

Xonotlite is an excellent thermal insulation and refractory material, with distinct physical and chemical properties, such as thermal stability, low heat conductivity, low density, fibrous form, and environmental friendliness
The X-ray diffraction (XRD) patterns of the sample shows that the purification of silicon raw materials used in preparation of coal fly desilication liquid have little influence on the crystalline phases of the products
The main crystalline phases prepared by hydrothermal synthesis method with fly ash desilicated liquid are xonotlite fibers, corresponding to 6CaO·6SiO2·H2O

Summary

Introduction

Xonotlite is an excellent thermal insulation and refractory material, with distinct physical and chemical properties, such as thermal stability, low heat conductivity, low density, fibrous form, and environmental friendliness. The main process involves using sodium hydroxide solution mixed with coal fly ash, and dissolving silica under certain conditions to obtain fly ash desilicated liquid, and after lime causticization reaction, the active calcium silicate byproduct is obtained (Figure 1). The fly ash desilicated liquid developed from fly ash was used as raw material for synthesis of xonotlite fibers.

Results

Conclusion