Activation Pretreatment and Leaching Process of High-Alumina Coal Fly Ash to Extract Lithium and Aluminum

Shenyong Li,Wenyue Gao,Lianwei Kang,Shenjun Qin,Haigang Guo,Penghui Bo

doi:10.3390/met10070893

Abstract

Experiments were conducted to investigate the process of aluminum and lithium extraction from high-alumina coal fly ash (HCFA) generated from coal-fired power plants located in northern China. The presence of mullite and other aluminosilicates lead to low reactivity of coal fly ash. An activation pretreatment that destroys an inert composition of coal is necessary. The activation roasting of coal fly ash using sodium chloride and a subsequent leaching process were performed in this research. The results showed that almost no aluminum and lithium were dissolved under direct water leaching, while about 7% and 10% of those were leached into the acid solution respectively. Adding NaCl enhanced the atmospheric pressure leaching of aluminum and lithium with a leaching rate around 50%. Phase analysis and equilibrium calculations results showed that the roasting reaction between the HCFA and NaCl occurred, which led to generation of main new phase NaAlSi3O8. The pressure extraction efficiencies of aluminum and lithium were increased to about 93% and 98%, respectively. The implications of the findings provide an alternative process for recovering aluminum and lithium from readily available high-alumina coal fly ash.

Highlights

Coal fly ash (CFA) is the main solid waste generated from coal-fired power plants, and in 2018, more than 550 million tons were discharged into the environment in China [1]
The huge quantities of CFA occupy a large volume in landfills, and lead to environmental pollution risks
Typical high-alumina CFA (HCFA) is released in northern China, and the content of Al2 O3 can be as high as 40–50% aluminum and more than 0.2% lithium [3]; it is considered to be a potential substitute for bauxite in alumina production [4]

Summary

Introduction

Coal fly ash (CFA) is the main solid waste generated from coal-fired power plants, and in 2018, more than 550 million tons were discharged into the environment in China [1]. With the continuous development of industry, the total accumulated CFA has exceeded 3 billion tons [2]. Typical high-alumina CFA (HCFA) is released in northern China, and the content of Al2 O3 can be as high as 40–50% aluminum and more than 0.2% lithium [3]; it is considered to be a potential substitute for bauxite in alumina production [4]. Recovering aluminum from HCFA could meet the great demand for aluminum in future industry needs. A continuous and sharp increase in the demand for lithium is expected in future clean energy technologies [7]. Exploring extraction techniques for aluminum and lithium from HCFA is a promising way to achieve an impact on environmental pollution via recycling and reduction

Methods

Results

Conclusion