In order to reduce the release of hazardous waste silicon sludge (WSS) into the environment, we report a novel method to transform the WSS into silica nanoparticles and simultaneously to separate abrasive silicon carbide (SiC) particles. Alkali dissolution and acid precipitation processes were utilized to prepare silica nanoparticles effectively. The alkali dissolution process was carried out by sodium hydroxide to produce sodium silicate solution, from which SiC was separated by filtration. Afterward, the silica nanoparticles were prepared by acid precipitation method using hydrochloric acid. Box-Behnken design (BBD) was used to optimize the process variables affecting the dissolution efficiency, namely, mass ratio of NaOH and WSS, reaction temperature, and reaction time, and to determine the optimum conditions for the reaction process. Ultraviolet-visible spectrophotometer was used to measure the silica concentration in the solution. Characterized by XRD, FTIR, TEM, and BET surface area analysis, the silica with average pore size (10.52 nm), high specific surface area (430.9 m(2)/g) was obtained, and the particle size was about 20-45 nm. (C) 2015 Elsevier B.V. All rights reserved.