Extraction of Silica from Fly Ash and Modification by Silane Coupling Agent

Abstract

Abstract: In order to improve the added value of comprehensive utilization of fly ash, this paper systematically studied the optimum conditions for extracting SiO₂ from fly ash using the acid base combination method, and a novel method for the preparation of simplified conventional modified silica was proposed based on the optimal extraction conditions. Results show that fly ash is preactivated at 800 ℃ and successfully converted into silicate gel after continuously reacting for 90 min at the temperature of 80 ℃ and the atmosphere of sulfuric acid (solid-liquid ratio (g/mL) of 1∶8, 3 mol/L), and then the silicate gel is dissolved and purified with the action of NaOH with a mass fraction of 30%, and finally, the solution pH value is adjusted to obtain more than 95.7% of SiO₂ extraction and silica with SiO₂ content greater than 93% (mass fraction). In addition, the silane coupling agent KH560 is successfully covered on the surface of the silica after bonding with the formed silica through Si—O—Si chemical bonding in this novel method. The modified silica, which possesses a superior nature in dispersibility, hydrophobicity and particle size, is obtained under the modification conditions of modifier dosage ratio of 2 mL/g, 70 ℃ and 60 min. And SiO₂ content in the resulting product is still above 95.97% (mass fraction), showing a significant improvement in specific surface area (381.97 m²/g, 2.78 times higher than that of unmodified silica), and the Hunter whiteness (91.43%) is close to the standard white board, which meets the relevant standards of Class A industrial grade silica.

Key words: fly ash, modified silica, SiO₂, silane coupling agent modification, combined acid-base method, activation degree

CLC Number:

X752

XIANG Jie, LI Jianhong, WANG Guifang, XUE Qingyuan, HE Jianqiao, LIU Shujun, HU Qingyan. Extraction of Silica from Fly Ash and Modification by Silane Coupling Agent[J]. BULLETIN OF THE CHINESE CERAMIC SOCIETY, 2023, 42(3): 989-1000.

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