Characterization of vitrified slag from mixed medical waste surrogates treated by a thermal plasma system

Various mixed medical waste surrogates have been vitrified by a plasma system built at Institute of Nuclear Energy Research (INER) in Taiwan, Republic of China. Characterizations of vitrified slag were carried out in order to evaluate the effectiveness of an indirect plasma heating used in the INER system. After vitrification, a monolithic metal nugget was separated from the vitrified slag as a result of the gravity effect, The vitrified slag consisted of mostly amorphous state of SiO2, which in turn dissolved other minor constituents from waste feeds and crucible container. In the slag, dispersive metal-bearing second phases in different shapes were observed. Due to their insoluble nature, these phases were embedded in the slag matrix, and no macroscopic segregation was detected. This observation indicates the presence of mixing state during the vitrification treatment. The formation of second phases was closely related to the metallic waste treated, as evidenced by the increased slag densities for the high metallic feed samples, Leachability analysis results revealed that the encapsulation of these second phases by the slag matrix was very effective. Therefore, with optimal feed compositions, the indirect plasma heating condition used in this study has been shown to be satisfactory for the thermal vitrification of mixed medical wastes. (C) 1998 Elsevier Science B.V.