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Furnace Environment
The furnace environment can have a detrimental effect on refractories. If the furnace is processing metals other than steel or aluminum (e.g., certain compositions of brass, bronze or alloy steel), the refractory may retain lead, chrome or nickel – metals that are subject to stricter environmental regulations. In glass-melting furnaces and other vessels where sodium is a constituent, accumulation of sodium oxide can cause the refractory’s melting temperature to decline, thereby reducing its value as a recycling feedstock. Spent refractory ceramic fiber (RCF) materials can be a good source of relatively pure aluminosilicates, but these materials can represent a handling hazard due to the presence of crystalline silica, which could pose an inhalation risk.

Uses for Recycled Refractories
The most common re-use for spent refractory is “grog” or “aggregate” in new brick or tile. A certain percentage of ground, pre-fired material is frequently added to such products to reduce shrinkage and improve quality. Other construction uses for recycled refractories include: roofing granules, landscape material, soil stabilization, slag conditioner and fuel source (in the case of carbonaceous refractories).

In some instances, chrome-magnesite brick can be recycled as a feed source of chromium for the production of ferroalloys. Refractories used in high-temperature processing of precious metals (e.g., silver, gold, platinum) are quite often recycled to recover high-value materials that have penetrated into the lining.

Testing Before Shipping
If hazardous constituents (including radioactivity) in the spent refractory are possible, the furnace user should have samples tested before engaging in discussions with recyclers or landfills. Having a shipment rejected by the recipient can add significant unanticipated cost to what could otherwise be a smooth transaction.

From the opposite perspective, a furnace user shouldn’t assume that his spent refractory has only one available fate – disposal at a hazardous-waste landfill. Armed with favorable test results, the user may find that recycling is a much lower-cost option than disposal as a hazardous waste. In fact, materials rich in Al₂O₃ can even bring a substantial return at current market prices.

According to Dr. Manuel Dekermenjian, principal consultant at Environ and co-lecturer at USC with this columnist, “Recycling and re-use options for industrial materials, including spent refractory, are often overlooked despite their financial, regulatory and environmental payback potential. Knowledge of the material’s chemical composition is the most powerful tool in deciding the most favorable fate for spent refractory.”