Co-melting of heavy metal-containing sludge and silica slag: a case study from lab to pilot

A case study from the lab to pilot was carried out for the disposal of heavy metal-containing sludge (HM-S), a typical kind of hazardous waste, by co-melting with silica slag (SS). The immobilization of heavy metals (HMs) in the water quenched products was the most favorable when the mass ratio of HM-S, SS, and caustic soda was 25:75:5 at 1300°C for 30–60 min. The main compositions in the water-quenched products were completely amorphous in a homogeneous structure. A compact glassy structure (Si–O) formed in the water-quenched products with HMs immobilized in the silicate network matrix. The results verified the stability of the melting products and their potential for use as valuable materials. This study can provide a feasible, inexpensive, and safe method for the entire use of industrial stream applications for hazardous solid wastes.