Effect of Al_2O_3 mole fraction and cooling method on vitrification of an artificial hazardous material. Part 1: Variation of crystalline phases and slag structures

摘要

This study investigated how Al ions affect slag structure. During vitrification, pure Al_2O_3, CaO, and SiO_2 served as the encapsulation phases with the use of Al mol% as an operating parameter. All specimens with the same basicity (mass ratio of CaO to SiO_2) of 2/3 were vitrified at 1400 ℃ and cooled by air cooling or water quenching. XRD was used to measure the volume fractions of crystalline and amorphous phases. In a non-Al environment, CaSiO_3 was formed in air-cooled and water-quenched slags. With the addition of Al_2O_3, no crystalline phases were observed in water-quenched slags. With the increase of Al mol% in specimens, the Al ions in air-cooled slags initially acted as an intermediate linking one tetrahedron chain to another and reducing the amount of crystalline phase, then behaved as a network former making the slags amorphous, and finally replaced Si ions in silicate frames to generate a large amount of CaAl_2Si_2O_8. Air cooling improved the formation of crystallize structures with more leachable metal ions. A highly crystallized Al-framed structure is not suitable for encapsulating hazardous metals in vitrified slags.