Recycling processes of waste glasses such as cathode-ray tubes (CRTs), beverage and food containers have been studied. For the CRT glasses containing metal oxides (e.g., PbO, NiO, Co_3O_4, Fe_2O_3 etc.), the process was investigated from view points of thermal, chemical and optical properties. On the other hand, the processes of the beverage containers have been already established. For example, in Japan, the glass bottles of beer, milk and sake were collected from consumers and utilized as a recycling bottle after washing, because colors and shapes of the bottles were standardized by Japanese beverage companies. However, other bottles, like the colored bottles of the imported alcoholic beverages (e.g., beer, whisky and wine), were difficult to be utilized as the recycling bottle, because these bottles have a variety of colors and shapes. It is known that silicon dioxide (SiO_2) is the main component in the above waste glasses, e.g., glass bottles contain 60-70 wt% SiO_2. In addition, SiO_2 has been demanded from glass and ceramic industries. From this, it was expected that various utilizations of the waste glasses would result from extraction of SiO_2 from the glasses. The purpose of the present study was to establish a process of extraction of SiO_2 from waste colored bottles by alkali fusion. In the present study, the waste bottles of green, blue, brown and black colors were selected. Potassium hydroxide (KOH) was used as an alkali flux, because silicate glasses pan be melted by alkali fusion using KOH at a lower temperature (360°C) compared with that for alkali fusion using NaOH (500°C). In addition, to discuss a potential applicability as a recycling process of waste glasses, the yield and purity of the extracted SiO_2 were also analyzed.
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