Hazardous Slags

In the production of ductile iron, calcium carbide is often used as a desulfurizing agent. When added to the iron, it reacts with the sulfides and forms calcium sulfide. This material floats on the surface of the molten iron, where it is skimmed off the surface and placed in a hopper. Since excess carbide is employed to ensure removal of the sulfur, the resulting slag contains high levels of unreactive carbide and must be handled as a reactive waste. 

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Hazardous slags Alter feed stock SR Stephens 1988... 

Unfortunately, pyrcmetallurgy has several distinct disadvantages. Greatest among these are the environmental concerns regarding air quality and the disposed, of potentially hazardous slags and residues. Further, pyrcmetallurgy has not been demonstrated to be particularly successful where the feed streams vary widely in chemical composition or where more than a few metals are to be extracted for ccmmercial application. 

If Are hazards eannot be moved to a safe plaee, are guarding deviees used to eonflne heat, sparks, and slag and to proteet the immovable Are hazards [OSHA Referenee, 252(a)(l)(i) and (ii)]... 

Schofield, W.R. Lutzman, John Patterson, Gene W. Use of Chemical Additives to Reduce The Impact of Slag Formation in Hazardous Waste Incineration. Hazardous Materials Control Journal, USA, 1992. 

The processes used in the primary production of lead produce several wastestreams of concern under different regulatory scenarios. The listed RCRA hazardous wastes include smelting plant wastes that are sent to surface impoundments to settle. The impoundments are used to collect solids from miscellaneous slurries, such as acid plant blowdown, slag granulation water, and plant... 

The solid-phase wastes generated by secondary processing are emission control dust and slag. Slag is generated from smelting, and the emission control dust, when captured and disposed of, is considered to be hazardous waste. 

High temperature processes produce a slag, a non-leachable, non-hazardous material suitable for use as construction materials. most cases. 

DeCaF treats soil, sludges, solids (e.g., slag), residues, and sediments contaminated with radioactive elements and other hazardous constituents. The technology has potential applications in the treatment of heavy metals. The technology can treat uranium-contaminated calcium fluoride matrices, rare-earth ore residues, and fluorspar contaminated with uranium. The technology can also extract more complex fluoride by-products. 

Avoidance of ash melting No slagging/fouling and related hazards Modularity... 

Foundries that generate furnace dusts that are EP-Toxic due to lead and cadmium have found that by carefully mixing the dusts with water treated calcium carbide desulfurization slag (which contains calcium hydroxide), they may be rendered non-EP-Toxic. Great care must be taken with this method since at high pH levels the lead may leach out. In addition to this problem, the effect of other hazardous materials in the dust and in the slag may still render this waste as hazardous (Stephens 1988). 

The sum of measured volumes of these gases represented less than 1 percent of the total gas volume generated. However, the solubility of these gases in the reaction water was not accounted for. Any one of these gases (except methane and carbon monoxide), or a combination of them, could contribute to the observed odor. Furthermore, the reaction of the slag with water may give rise to potential health hazards if workers are exposed to excessive concentrations of these gases. 

The first option is to eliminate the generation of the reactive desulfurization slag by substituting calcium carbide with some other material. A few large foundry companies have made major advancements in new desulfurization technologies over the past years. One such process involves the use of a mixture of calcium oxide, calcium fluoride, and two other materials. One foundry reports that, not only is the product quality satisfactory, but the plant has eliminated the generation of a major problem hazardous waste, and the economics of the process are actually better than calcium carbide desulfurization. 

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