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

Abstract

Coal combustion accounts for a large proportion of the global energy supply due to its low cost and high heat value; however, pollution from the large amounts of coal fly ash (CFA) generated during the process causes many environmental problems. CFA has traditionally been used in construction and soil remediation, although there have been attempts to use CFA in response to the developing shortage of mineral resources. Numerous studies have investigated high-end recycling of CFA to obtain valuable products such as critical metals and porous materials, which are widely used in chemical engineering, ecological remediation, and other fields. In this study, we found that various extraction and synthesis methods summarized high value-added treatments of CFA. Dissolution and sintering processes were applied for extraction, while carbothermal and electrolysis techniques offered other unique advantages. The precursors and polymers used in the procedures were the two main factors influencing the synthesis of porous materials, providing a source of elements and inducing the formation of predictable structures. Considering the mechanisms involved, the complex methods used in state-of-the-art CFA recycling could be combed to develop high value-added CFA reclamation techniques.

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

“…[10,11] Alternatively, alkali fusion, often with auxiliary substances like NaOH, CaCO 3 , or NH 4 F, converts insoluble crystalline phases into soluble compounds for subsequent silica extraction. [7,12,13] NaOH utilization in alkali-fusion has yielded various zeolite phases, including sodalite, analcime, cancrinite, and NaÀ A (LTA) zeolites. [14][15][16] It is important to note that aluminium, co-present in the liquid phase, can be separated from silica by adjusting pH.…”

Green Approach for Rare Earth Element (REE) Recovery from Coal Fly Ash

“…However, few studies have addressed the fate of secondary wastes after REE leaching and separation. CFA solid residues might be used to recover other valuable metals (e.g., Cu and Zn) 34 or synthesize porous materials (e.g., zeolite), 35 which might minimize waste production and add extra economic benefits.…”

Conversion of Harmful Fly Ash Residue to Zeolites: Innovative Processes Focusing on Maximum Activation, Extraction, and Utilization of Aluminosilicate

“…Because of their high adsorption capacities, strong thermal stabilities, and other parameters, zeolites have been widely applied in catalytic cracking, 17 − 19 adsorption and separation, 20 , 21 ion exchange, 22 , 23 and many other important functions with a considerable economic value. 24 The solid residue obtained after alumina extraction has a chemical composition suitable for preparation of zeolites 4A, 13X, ZSM-5, and other aluminosilicate zeolites. These materials provide a potential utilization approach for the solid residue obtained after alumina extraction, the original fly ash, and similar solid wastes.…”

“…The most commonly used zeolites are artificial aluminosilicate minerals with uniform pore structures. Because of their high adsorption capacities, strong thermal stabilities, and other parameters, zeolites have been widely applied in catalytic cracking, − adsorption and separation, , ion exchange, , and many other important functions with a considerable economic value . The solid residue obtained after alumina extraction has a chemical composition suitable for preparation of zeolites 4A, 13X, ZSM-5, and other aluminosilicate zeolites.…”