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.
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 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.
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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