Glass Composite Materials for Nuclear and Hazardous Waste Immobilisation
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Glass Composite Materials for Nuclear and Hazardous Waste Immobilisation Michael I. Ojovan and Jariah M. Juoi Immobilisation Science Laboratory, Department of Engineering Materials, University of Sheffield, Mappin Street, Sheffield S1 3JD, UK Aldo R. Boccaccini and William E. Lee Department of Materials, Imperial College London, South Kensington Campus, London SW7 2AZ, UK ABSTRACT Glass composite materials (GCM) are versatile wasteforms for immobilising various types of both radioactive and hazardous wastes. We review current research on the utilisation of GCMs for hazardous and radioactive waste immobilisation. Compared to homogeneous glassy materials GCMs can incorporate larger amounts of waste elements and, in the case of glass matrix composites, they can be produced using lower processing temperatures (by viscous flow sintering) than those of conventional melting. INTRODUCTION Hazardous and nuclear waste vitrification is attractive because of its high versatility, i.e. the large number of elements that can be incorporated in the glass, and the potential for a highly durable and low volume wasteform. Recently, there has been a trend to develop waste host systems which are intermediate between completely glassy or crystalline materials [1-6]. Both hazardous and nuclear waste constituents can be immobilised not only by direct chemical incorporation into the glass structure in a classical vitrification approach but also by the physical encapsulation of the waste in a glass matrix, forming a glass composite material (GCM) consisting of both vitreous and crystalline phases. The major component may be the crystalline phase with a vitreous phase acting as a binding agent or alternatively the vitreous phase may be the major component, with particles of a crystalline phase dispersed in the glass matrix. Standard glass-ceramics, which are obtained by the controlled crystallisation of a parent glass, can be considered a special case of GCMs. There have been significant recent research efforts on the utilisation of GCMs for immobilising both radioactive and non-radioactive wastes, which will be reviewed in this paper. Radioactive waste arises from three main sources, the Nuclear Fuel Cycle (NFC) used for power generation as well as military purposes, non-NFC institutes (including non-nuclear industries, medical and research institutions) and accidents [7]. Non-radioactive wastes include incinerator ashes and air pollution control residues, sewage and dredging sludge, iron and steel industry slag and ashes, Zn hydrometallurgical process effluents and coal ash from power stations [3, 4]. Some of these wastes are highly hazardous containing significant concentrations of heavy metals, and/or organic pollutants. Vitrification to form glassy materials including glass-
ceramics for treatment and recycling of non-radioactive wastes has been recently discussed [3, 4]. Moreover, there have been several recent studies on radioactive waste immobilisation in GCMs [1, 8, 9]. Previous reports have considered manufacturing processes, micr
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