Sustainable valorization of granite waste powder into hydrophobic SiO2 aerogel via alkali fusion and ambient pressure drying

This study proposes a sustainable strategy for synthesizing SiO 2 aerogel from waste stone powder (WSP), a byproduct generated during granite processing. The synthesis route involves alkali fusion–leaching, sol–gel processing, and ambient pressure drying. The optimal extraction conditions were determined as an alkali-to-material mass ratio of 1:0.8, calcination at 800 °C for 3.5 h, and leaching at 90 °C for 60 min with a solid–liquid ratio of 1:5. Under these conditions, sodium silicate with a modulus close to 1.0 was obtained, accompanied by a silica dissolution rate of approximately 45%. The as-prepared SiO 2 aerogel shows a high specific surface area of 725.99 m 2 /g, a porosity of 93.16%, a pore volume of 1.72 cm 3 /g, an average pore diameter of 7.37 nm, and a bulk density of 0.15 g/cm 3 . Characterizations using SEM, TEM, BET, FT-IR, and water contact angle measurement (138.26°) verify its typical mesoporous structure and superior hydrophobicity. This work validates the feasibility of converting WSP into high-value SiO 2 aerogel with performance comparable to its conventional counterparts, thereby promoting solid waste valorization and the development of green functional materials.