Nanoporous Silica Aerogels Derived from Tailings via Alkali Fusion Activation and Resin-Free Purification

This study presents a novel method for synthesizing nanoporous silica aerogels from copper–nickel tailings (CTs) via ambient pressure drying using a resin-free purification approach. CTs are an underutilized industrial solid waste rich in silicates, typically landfilled rather than valorized. To address the high raw material costs and complexity of supercritical drying in conventional silica aerogel synthesis, a potentially advantageous method using CT-derived silicon was developed. Box–Behnken design (BBD) was used to guide the alkali-melting and acid-leaching processes. An intermittent ultrasonic washing method instead of resin-free purification realized the removal of most impurity ions as well as optimized the pore structures of the aerogels. Under this technological condition, a silica aerogel with a specific surface area of 738.92 m2/g and a thermal conductivity of 0.03571 W/(m·K) was obtained, showing that the method can lower the production cost of silica aerogel by over 20% compared to organic silicon sources, and with less new solid-waste generation during the process. This work provides a potential and feasible method for transforming silicate-rich industrial waste into high-value-added silica aerogel materials, compliant with the development of the circular economy.