Chemical recycling of inorganic wastes by using phase separation of glass

A chemical recycling process using phase separation of glass was applied to a granulated blast furnace slag with high CaO content. Glasses were prepared by adding B₂O₃ to the slag in order to promote phase separation, and the glasses were heat-treated above glass transition temperature. In the subsequent acid-treatment, however, gelation due to the elution of SiO₂ phase containing CaO occurred, not obtaining high SiO₂ solids. Then, pretreatment was introduced to reduce CaO content in slag, where the raw slag was briefly washed in acid. The slag glasses prepared from the pretreated slag were commonly phase-separated by heat-treatment regardless of B₂O₃ content. After subsequent acid-treatment, colorless insoluble solids were successfully recovered. The end products consist of 70-90 mass% SiO₂, and coloring ions such as Mn, Fe and Cr were almost completely removed from the slag glasses. Reutilization as raw materials for glass is expected.