Application of Microwave Technique for Dehydration of Sludge Generated in a Stainless Steel Plant

In ironmaking and steelmaking processes, dehydration technology is often recognized to be a key process for the successful operation. That is not an exception in recycling process of valuable elements such as Fe, Ni, Cr and so on by reducing the wasted materials including dust, scales and sludge, generated in each steel works. This investigation basically focused on the availability of microwave technique for dehydration stage of sludge generated in a stainless steel mill. Actually sludge is well-known as a wasted resource difficult to be dehydrated. Unless dehydration of such resource is successful, some problems with slow heating and/or burst of briquettes may arise. In this study, prior to the industrial studies, dehydration experiments of goethite were performed. The results showed that the microwave treatment could heat up the specimen directly from inside of specimen while being heated from the outside by the electric furnace. Thus the dehydration ratio resulted higher in the microwave irradiation, indicating the benefit of the microwave treatment. Thereafter the microwave technique was tried for dehydration of industrial sludge. Consequently, the effectiveness of microwave treatment was confirmed because 34 mass% weight-loss after the microwave treatment corresponded to the complete dehydration while 7 mass% weight-loss after heating in a conventional electric furnace. If application to industrial practice is realized, it is expected that the problems brought by the conventional way will be hopefully solved to prevent burst of agglomerations.