Efficient Activation of Coal Fly Ash for Silica and Alumina Leaches and the Dependence of Pb(II) Removal Capacity on the Crystallization Conditions of Al-MCM-41

Abstract

In this study, four different coal fly ashes (CFAs) were used as raw materials of silica and alumina for the preparation of the alumina-containing Mobil Composition of Matter No. 41 (Al-MCM-41) and the exploration of an activation strategy that is efficient and universal for various CFAs. Alkaline hydrothermal and alkaline fusion activations proceeded at different temperatures to determine the best treatment parameters. We controlled the pore structure and surface hydroxyl density of the CFA-derived Al-MCM-41 by changing the crystallization temperature and aging time. The products were characterized by small-angle X-ray diffraction, nitrogen isotherms, Fourier-transform infrared spectroscopy, 29Si silica magic-angle spinning nuclear magnetic resonance, and transmission electron microscopy, and they were then grafted with thiol groups to remove Pb(II) from aqueous solutions. This paper innovatively evaluates the CFA activation strategies using energy consumption analysis and determines the optimal activation methodology and parameters. This paper also unveils the effect of the crystallization condition of Al-MCM-41 on its subsequent Pb(II) removal capacity. The results show that the appropriate selection of crystallization parameters can considerably increase the removal capacity over Pb(II), providing a new path to tackle the ever-increasing concern of aquic heavy-metal pollution.

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

“…These results are validated by the study of Zhang et al [41] who evaluated various activation methods (hydrothermal, microwave assisted and NaOH‐fusion) which showed that sodalite, sodium aluminium oxide silicate and nepheline were acid‐soluble. Ju et al [33] activated the CFA using Na 2 CO 3 and discovered that the resultant phases sodium aluminium oxide silicate (NaAlSiO 4 ), and nepheline are acid soluble.…”

“…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 Na−A (LTA) zeolites [14–16] . It is important to note that aluminium, co‐present in the liquid phase, can be separated from silica by adjusting pH [17–19] …”

“…[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. [17][18][19] The resulting silicate solution serves as the silica source for synthesizing porous materials, with templates such as CTAB (cetyltrimethylammonium bromide), P123 (Pluronic-123), and others often employed in the synthesis process.…”

Kinetics Study of Al Extraction from Desilicated Coal Fly Ash by NaOH at Atmospheric Pressure

“…Alkaline methods used for the Al extraction from bauxite are less efficient for CFA [31]. This is due to the fact that CFA contains a high amount of amorphous glassy silica, which dissolves faster than Al-containing minerals [32].…”