Silica Precipitation from Laterite Solid Waste: A Method for Residue Valorization

This study presents a valorization route for laterite acid leaching (AL) residue as a potential silica source for advanced material synthesis. AL residue, containing 21.4 wt.% Fe and 13.9 wt.% Si, was subjected to alkaline leaching using NaOH at 90 °C to produce a sodium silicate (Na₂SiO₃)-rich solution. The subsequent precipitation of silica was optimized using the response surface methodology (Box–Behnken design) to evaluate the effects of temperature, pH, and reaction time. The optimal conditions (54.6 °C, pH 6.96, and 120 min) yielded a silica recovery of 92%. Analysis of variance (ANOVA) confirmed the adequacy of the quadratic model (R² = 0.9905), with pH identified as the most influential variable. Kinetic analysis based on nonlinear least-squares fitting revealed a reaction order (n) between 2.0 and 2.5 and a rate constant (k) decreasing with increasing temperature, suggesting a temperature-inhibited polymerization–condensation mechanism. The precipitation process involved two stages: rapid polymerization of monomeric silicate followed by diffusion-controlled aggregation. These findings demonstrate that controlled NaOH leaching and acid precipitation can effectively recover high-purity silica from laterite waste, providing a sustainable pathway for residue valorization and circular utilization within the mineral processing industry.