Extensive application of silica nanoparticles (SNPs) in various industrial products has led to the development of silica extraction methodologies out of various waste products. Rice husk is an agricultural waste with a high content of amorphous silica. However, the presence of metal ion impurities and unburned carbon in the rice husk content may present an adverse effect on product color and purity. The purpose of the present study is to optimize silica extraction procedure and improve its purity and eventually produce high quality SNPs. In this regard, nitric, sulfuric and hydrochloric acids were applied to evaluate the effect of different rice husk pretreatments. Silica extraction process was carried out under controlled calcination conditions in an electric furnace at 600 ˚C. The results of XRF and XRD analyses reveal that hydrochloric acid treatment exhibited the highest performance among the other acid treatments. A purity of 95.55% amorphous silica with major impurities of K2O, CaO and P2O5 were obtained indicating a relatively significant portion of it removed by acid treatment. This product was then subjected to chemical precipitation followed by slow gelation to obtain SNPs. The BET specific surface area of 409 m2.g-1, the average particle size of 200±20 nm, the spherical particle shape and purity of 97% indicate the successful production of silica nanoparticles.
