Extraction of silicon dioxide from waste colored glasses by alkali fusion using sodium hydroxide

Abstract

A process for extraction of SiO2 from waste colored glasses by alkali fusion using NaOH was investigated. In the present study, glass waste colored bottles of green, blue, brown or black were selected as samples of waste glasses. These colored bottles were qualitatively confirmed to contain elements of Na, Mg, Al, Si, K, Ca, Ti, Mn, Fe and Cu from energy dispersive X-ray spectroscopic analysis. The condition for alkali fusion of NaOH and the waste glasses was optimized, i.e., for each bottle, the composition was NaOH : crushed glass bottle = 90 : 10 mass%, melting temperature was 500°C and melting time was 2 h. For each waste colored bottle, the sodium silicate solution was prepared by using the sodium silicate obtained by alkali fusion. After mixing HCl with the obtained sodium silicate solution, Si(OH)4 was then precipitated by boiling the solution which became to be a very strong acid. After drying the Si(OH)4 separated from the solution, SiO2 powder with purity of 99.9% was obtained. The yield of 98.3 ± 0.9% for the SiO2 powder extracted from the bottles was confirmed from quantitative analysis, indicating that the bottles selected in the present study contained about 60 mass%SiO2. From the results of yield and purity, the established process was found to have a potential applicability as a recycling process of waste glasses; various utilizations of waste glasses were expected by extracting SiO2 which is the main component of the glasses.