J Sol-Gel Sci Technol (2017) 82:675–681 DOI 10.1007/s10971-017-4366-3 ORIGINAL PAPER: FUNDAMENTALS OF SOL-GEL AND HYBRID MATERIALS PROCESSING Synthesis of high purity silica from low cost water glass via sol–gel process and soxhlet extraction Bongjun Gu 1 ● Dongwook Ko 1 ● Seokhoon Ahn 2 ● Dong Choon Hyun 3 ● Hyun-Kwuon Lee 1 ● Jongbok Kim 1 Received: 29 November 2016 / Accepted: 20 March 2017 / Published online: 29 March 2017 © Springer Science+Business Media New York 2017 Abstract This study describes a strategy to economically synthesize silica with high purity. For economical synthesis, it is critical to choose proper synthetic process and raw material. Here, we have used economical sol–gel process and water glass with low cost to synthesize a silica powder, and adopted extraction process to enhance its purity. Spe- cially, we have first examined where impurities are mainly located. Then we have considered how to enhance cleaning efficiency during extraction process for achievement of high purity. Scanning electron microscope and energy-dispersive X-ray spectroscopy analysis demonstrate that the impurities prefers to locate at the surface of silica aggregates, which indicates that large aggregates in size easily expose most of the impurities into the surface of silica whereas small sized aggregates can trap the impurities between them. Taken together with these results, we have formed large silica aggregates in size via controlling pH condition during the silica synthesis, followed by conducting Soxhlet extraction process for cleaning the impurities out. The use of this approach allows us to synthesize the silica with a purity of 99.95 wt%. Graphical abstract Keywords Silica ● Water glass ● Purification ● Agglomeration 1 Introduction Since discovering useful characteristics of silica such as its abilities to absorb moisture [1], reinforce mechanical strength [2], and insulate electricity [3], many people have paid attention to how to synthesize silica and extend its application. Many approaches have been reported for syn- thesizing silica, including those based on burning of silicon tetrachloride (SiCl 4 )[4] and precipitation of silica from acid dissolution of minerals [5], as well as mining [6]. Synthe- sized silica have found many emerging applications in humidity sensor [7], catalyst [8], a filler of sealing resins * Jongbok Kim jbkim@kumoh.ac.kr 1 Department of Materials Science and Engineering, Kumoh National Institute of Technology, Gumi, Gyeongbuk 39177, Korea 2 Institute of Advanced Composite Materials, Korea Institute of Science and Technology, Wanju, Jeonbuk 55324, Korea 3 Department of Polymer Science and Engineering, Kyungpook National University, Daegu 41566, Korea