Distribution behavior of inorganic constituents in chemical recycling processes of a municipal waste slag

• Distribution behavior of municipal waste slag constituents into solid and liquid phases was examined.
• SiO2, P2O5 and TiO2 were preferentially distributed into solid phase.
• The other constituents were almost completely dissolved in acid.
• We found that the distribution was ruled by dissolution–reprecipitation processes and not by phase separation.

A chemical recycling process of inorganic wastes has been developed, where after vitrifying wastes, the glasses were heat-treated and soaked in an acid, obtaining colorless and transparent SiO2-abundant glasses. In the present study, distribution behavior of the constituents such as Si, P, Ti, Al and so on present in a municipal waste slag was examined. According to compositional analyses, the recovered solids after acid treatment consisted of SiO2, P2O5 and TiO2, suggesting the preferential distribution of P and Ti atoms into SiO2-rich phase during phase separation. In high resolution microscopic analyses, however, it was observed that P and Ti atoms were distributed separately from Si atoms, and they were present in the different particles insoluble in the acid. It was finally concluded that the insoluble solids were produced by a dissolution–reprecipitation process, that is, once all the constituents of the vitrified slag were dissolved in the acid, P2O5 and TiO2 coprecipitated as particles, and TiO2 was indispensable for the precipitation of P2O5. SiO2 also precipitated as particles separately from P- and Ti-containing particles.