Enhanced synthesis of fly ash-derived hydrated sodium silicate adsorbents via low-temperature alkaline hydrothermal treatment for advanced environmental applications

The fly ash (FA) is one of the large amount of solid wastes stored in China. Because of its low price, large specific surface area, and surface electronegativity, reasonable modification can turn FA into treasure, prepared as an adsorption material with good adsorption performance. In this article, the industrial solid waste FA is used as raw material, and the FA-based sodium aluminosilicate was synthesized by a one-step hydrothermal alkali dissolution method and characterized by X-ray fluorescence, X-ray diffraction, scanning electron microscopy, Fourier transform infrared, Brunauer Emmett Teller, and other test methods. The results show that (1) aluminum silicate sodium hydrate can be synthesized by low-temperature method under atmospheric pressure to form P-type zeolite and calcite structure. (2) Alkali concentration, temperature, and reaction time affect the structure of aluminosilicate sodium hydrate. With the increase of alkali concentration, temperature, and reaction time, the product changes from P-type zeolite to calite structure. (3) The optimal synthesis condition of FA for sodium aluminosilicate hydrate is as follows: the concentration of NaOH solution is 4 mol·L −1 , the dissolution temperature is 80°C, the reaction time is 21 h, and the specific surface area is 60.54 m 2 ·g −1 .