The foundry industry is a major recycler of waste materials (scrap metal). Unfortunately, the recycling of these materials can result in the generation of hazardous wastes. This article focuses on two potentially hazardous waste types in the ferrous foundry industry - calcium carbide desulfurization slag, (potentially reactive) and melt emission control residuals (potentially EP toxic). An overview is given on how foundries have evaluated different waste management options. The ultimate goal is to minimize the amount and degree of hazardous wastes generated while reducing the cost of managing these wastes.
Although there are differences from one foundry to the next, basic foundry processes vary little from one foundry to another. All foundry operations produce castings by pouring molten metal into molds, typically consisting of molding and core sands. Once the casting has cooled and hardened, it is separated from the mold and core materials in the shakeout process. The castings are cleaned, inspected, and then shipped for delivery. Figure 1 (A.T. Kearney Co., Feb. 1971) is a schematic of a typical foundry process.
Foundries are major recyclers of waste materials. Scrap iron and steel comprise 85 percent or more of the ten million tons of ferrous castings produced each year in the United States. Reclaimed copper, aluminum, lead, tin, zinc, and other metals are also extensively recycled in making nonferrous castings.
TYPICAL FOUNDRY PROCESSES
Environmental Protection Agency
Foundry Process Solid Waste
Figure 2 shows a schematic materials balance for a ferrous foundry. Metal for melting and sand for core and mold materials are the major input materials, while product and waste materials make up the output. Most foundries employ internal recycling of core and mold materials; however, these materials eventually lose their basic characteristics, and portions of these materials no longer suitable for use are then disposed in a landfill. Sprue, risers, and reject castings are recycled internally to the melting operations, and many types of slags in ferrous foundries are reclaimed internally for their metal content. Nonferrous foundries often contract for recycling services because slags, dross, and grinding residues may contain metal of sufficient value to be extracted in smelters. The reclaimed metal is then returned to the foundry as an ingot.
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