A novel recycling process of blast furnace slag was developed in order to obtain colorless silica-rich solids by using phase separation of borosilicate glass. B(2)O(3) was added to blast furnace slag to promote the phase separation. The slag glasses were heat-treated above glass transition temperatures. The slag glass prepared from blast furnace slag gelled after the heat treatment and the subsequent three types of acid treatment. The ratios of SiO(2) component in the gels were 40 – 60mass%. On the other hand, phase separation was observed on the surface of the slag glasses prepared from pre-treated slag by 2.5N HCl after the heat treatment. After soaking in acid, they did not gel and changed to insoluble colorless solids. According to compositional analyses, it was found that the insoluble colorless solids contained 70 - 90mass% SiO(2). No colored ions such as Cr, Mn, and Fe were confirmed in the remaining insolubles by optical absorption measurement. Therefore, the colorless silica-rich solids were successfully obtained in the present process. The end products obtained in the present process are expected as material of glass.
Blast furnace slag
Colorless silica-rich solids