Refractories Review: Recycling Refractories
B. Oxnard of Maryland Refractories Co., Irondale, Ohio, gave an overview of the history of refractory recycling, indicating that little had been done until the 1950s. Growth, he said, has been relatively slow due to a lack of incentives, quality concerns, inexpensive landfills, comparatively lax government regulations, and the availability of inexpensive substitutes. But the economic incentives and the technology to increase refractory recycling and minimize waste are increasing, whereby used refractories will have the same bright future as steel scrap, slag, EAF dust and other industrial waste materials.
Recent FindingsJ. Bennett of the U.S. Department of Energy’s (DOE) Albany Research Center discussed several research programs that have shown that refractories can be effectively recycled. In several aluminum industry applications, he reported, used refractory has been recycled as aggregate for roadbed and landscaping, as well as dense and insulating castables. In another example, the rebuild of a carbon-baking furnace had been estimated to cost $9.6 million, but the substitution of recycled materials resulted in a savings of $3.8 million.
The recycling of refractory wastes is not widely practiced in the U.S. steel industry, but several steel plants have reportedly conducted projects where refractories were recycled as landscape aggregate, gunite, blast furnace and basic oxygen furnace (BOF) flux/additive, and filler for a BOF refractory brick product. Bennett noted that environmental regulations or economic incentives are the two main reasons for recycling, and that neither of these has displaced landfilling as the main option for refractory disposal in North America.
The life of EAF refractories can be increased, and the amount of refractory waste reduced, by utilizing foamy MgO-saturated slags, reported J. Kwang, also of the DOE’s Albany Research Center. He discussed work on the recycling of spent basic refractory materials as EAF slag conditioners. A computer model has been developed to aid in understanding and formulating the optimum slag composition.
J. Smith, University of Missouri-Rolla, discussed the recycling of refractories from non-ferrous metal manufacturers in Missouri. A program was conducted to study the types and quantities of spent refractories generated, which showed that 99 wt% of the amount is landfilled. Based on the use of recycling and reprocessing technology, one example of which is the manufacture of a Portland-type cement, it was estimated that the quantity of landfilled spent refractory could be reduced by more than 50%.
Refractory Recycling in JapanInformation from Japan, where the use of landfilling as a disposal option is declining, indicates successes in the recycling of refractories, especially in value-added-type products. For example, one EAF shop in Japan, producing 1.68 million metric tons of steel per year, has been actively involved in the recycling of refractories for at least 10 years. The plant produces 900 metric tons of used refractory each month, of which 250 tons go directly to landfill. The other 650 tons are processed for recycling, and 60% of that amount is successfully recycled.
Refractory recycling at this plant has progressively increased from 9% in 1990 to 44% in 1995 and 60% in 1999. The recycled refractory applications include flux additions to ladle furnaces and EAF, and value-added uses like EAF bricks, repair material for slide gate plates, and monolithic products such as castables and ramming mixes. Lab testing of recycled MgO-C EAF bricks has shown that their corrosion resistance is very similar to new bricks.
Another Japanese steel company has successfully used various spent carbon-containing refractories as additives in virgin products, with little or no reduction in properties or performance and good performance in field trials. For example, up to 30 wt% spent MgO-C refractory was added in MgO-C bricks, and up to 20 wt% recycled alumina-spinel aggregate was added in alumina-spinel castables. Continuous casting nozzles have also been reused by making one re-fabricated nozzle from two used nozzles, based on the development of a special bonding cement that is stronger than the virgin nozzle material.
Changing PerceptionsAn article by L. Sheppard (“Minimizing Refractory Waste,” Ceramic Industry, February 1999, pp. 39-47) provides other details of refractory recycling. It is clear that economics will continue to be a key factor in the decision to recycle refractories. In addition, however, it is also necessary to change the perceptions of refractory users. For example, while most U.S. refractory users think that recycling is a good idea, they will only use virgin materials in their furnaces, despite field trials that have shown the practical viability of using refractories containing recycled material.
So as the needs and the technology for refractory recycling progressively increase, the justification, the incentives and the pressures for refractory recycling will also increase. Stay tuned for further updates about refractory recycling efforts and successes around the world.
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