Green recovery of amorphous silica from silicone waste: Alkali activation and thermal treatment

This study presents a green and sustainable method for recovering high-purity silica from solid silicone by-products derived from industrial silicone oil manufacturing through alkali-assisted sol–gel synthesis, with and without thermal treatment. Sodium hydroxide and sodium carbonate were used to evaluate the effects of alkali type, concentration, and calcination at 800 °C on silica yield, structure, and performance. Sodium carbonate-treated and calcined samples achieved the highest silica yield (up to 90.7 %) and purity (>92 wt% SiO2), while maintaining predominantly amorphous structures with enhanced thermal stability and porosity. In contrast, sodium hydroxide treatments, particularly at higher concentrations, induced partial crystallisation and reduced adsorption capacity. The synthesised silica showed effective methylene blue adsorption, supporting its application in wastewater treatment. This acid-free recovery process provides an environmentally friendly pathway for valorising silicone waste, contributing to circular economy strategies and the development of sustainable functional materials.