Characterization of Glasses in One Type of Alumina Rich Fly Ash by Chemical Digestion Methods: Implications for Alumina Extraction

Lijun Zhao,Baodong Wang,Hanshuang Xiao,Qi Sun

doi:10.1155/2016/8695890

Abstract

In recent years, one type of alumina rich fly ash (ARFA) with about 50 wt% of alumina has been extensively investigated for alumina extraction in China. Due to the silica in ARFA, alumina extraction would have to generate a huge amount of solid waste. There is a growing interest in the glasses in ARFA, because they are composed mainly of silica and could be removed prior to alumina extraction. In this work, the glasses in ARFA have been investigated by chemical methods, that is, acid and base digestions. The chemical compositions have been measured by XRF for ARFA from the digestion processes. The K2O standard, XRD, and FTIR spectroscopies were successfully used to define the digestions processes, and size analysis and SEM-EDX provided rich information on particle transformations. As a result, acid and base digestion methods were found to produce very similar results for the glasses in ARFA. The K2O standard was attributed to the formation of glasses by illites, and TiO2and Fe2O3were proposed to originate from ilmenite in alumina rich coals (ARC). Some implications of the results were also discussed for the alumina extraction from ARFA.

Highlights

China’s alumina industry relies heavily on foreign bauxite, which accounts for more than 60% of its total consumption, according to China Industry Security Guide
The alumina rich fly ash (ARFA) with about 50 wt% alumina has been regarded as a real gift for China short of bauxite and brings about the hope for a self-contained alumina industry
For the many processes under development for alumina extraction from ARFA, silica should be reduced by predesilication to avoid the addition of enormous amounts of lime

Summary

Introduction

China’s alumina industry relies heavily on foreign bauxite, which accounts for more than 60% of its total consumption, according to China Industry Security Guide. For the promising sintering methods, a large amount of lime has to be added to react with silica for the formation of solid wastes like 2CaO⋅SiO2, so that alumina could be extracted. Hot dilute caustic solutions readily dissolve silica in glassy state, and predesilication should be preferably performed for ARFA prior to alumina extraction. For NaOH solution digestion of glasses in fly ashes, three steps should be involved, that is, step Base Dissolution I, step Acid Dissolution (HCl), and step Base Dissolution II [2]. It seems that the glasses in ARFA can be effectively characterized by utilizing chemical methods corroborated by spectroscopic techniques

Procedures for Acid and Base Digestions of ARFA

Results and Discussion

Conclusions