The melting treatment of wastes, compared with the conventional incinerating method, helps reduce the burdens on final disposal sites since wastes are made harmless, less bulky and reusable as useful resources. Of various types of melting waste, the gasifying and melting technologies are recently attracting attention. This is because, unlike incineration residue melting furnaces, the melt-solidified products are obtained without passing the state of ash, hence simplifying the equipment concerned. More than twenty years ago, Nippon Steel developed the gasifying and melting technology for a shaft furnace and has steadily refined the commercial furnace as the "direct-melting resource-recovery system." The system does not simply "treat" wastes. It positively "produces" useful resources from wastes and contributes to the promotion of a recycling-oriented society. Starting with the melting furnaces commissioned in Kamaishi City, Iwate Prefecture and in Ibaraki City, Osaka Prefecture, Nippon Steel has pursued studies on waste reutilization jointly with civil engineering and construction companies. At the currently operating facilities, nearly the entire amount of molten slag has come to be reused as aggregate in civil engineering and construction companies. This paper describes the outline of the utilization technology of molten slag.
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