Chemistry of inorganic compounds – With additive
Reexamination Certificate
2002-11-05
2004-01-20
Langel, Wayne A. (Department: 1754)
Chemistry of inorganic compounds
With additive
C423S519200, C568S019000
Reexamination Certificate
active
06680039
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to methods of treating industrial waste, including spent foundry waste, and more particularly to a method of treating such waste to reduce the leachability of certain toxic metals and to process those wastes to make them suitable for use as a raw material.
BACKGROUND OF THE INVENTION
Industrial wastes, such as spent foundry sands and slags, typically contain leachable or extractable metallic contaminants. These wastes are then classified as hazardous or non-hazardous, or toxic
on-toxic, depending on the levels of contaminants indicated by various leach modeling methods, including: 1) Toxicity Characteristic Leaching Procedure (TCLP; EPA method 1311, “Test Methods for Evaluating Solid Waste, Physical/Chemical Methods” SW-846); 2) Synthetic Precipitation Leaching Procedure (SPLP; EPA Method 1312, “Test Methods for Evaluating Solid Waste, Physical/Chemical Methods” SW-846); 3) Multiple Extraction Procedure (MEP; EPA method 1320, “Test Methods for Evaluating Solid Waste, Physical/Chemical Methods” SW-846); and 4) Indiana Leaching Method, Neutral (Indiana NL; 329 Indiana Administrative Code 10-7-4(b)(3)(B)).
When the waste is hazardous or toxic, provisions exist for its disposal at a hazardous waste landfill. Because disposal in a hazardous waste landfill is expensive, hazardous or toxic waste is preferably treated to reduce the levels of contaminants to acceptable levels. The waste can then be disposed of at less expense in a non-hazardous waste landfill.
Although disposal of hazardous or toxic waste made non-hazardous or non-toxic by treatment is less costly than disposal of untreated toxic or hazardous waste, disposal of that waste is still relatively expensive. If the waste could be used in another industrial process, significant savings and environmental benefits could be achieved.
Some wastes have physical characteristics that enable them to be used in other industrial processes. For example, addition of pozzolanic coal ash to portland cement mixtures allows the derived concrete to obtain a much greater compressive and shear strength than concretes derived from portland cements alone. More specifically, addition of pozzolanic fly ash to portland cement is essential in obtaining compressive and shear strengths required for construction of certain articles. Furthermore, several states currently allow the use of foundry wastes as alternate raw materials.
However, many states require the levels of contaminants in foundry sands, slags and other industrial waste to be below certain levels prior to their reuse. Therefore, if they are present above those levels, the leachable and extractable metallic contaminants must first be chemically stabilized before the industrial waste can be utilized in another process.
Typical methods of treating industrial waste include adding to the waste either a phosphate compound in combination with a metal oxide and water or Portland cement (and/or cement kiln dust, quicklime, pozzolanic fly/bottom ash, etc.) and water. These methods result in the waste becoming substantially solid and typically add at least ten percent by weight of other non-useful materials to the waste. Because of the need for subsequent crushing to form aggregate, these methods destroy the useful characteristics of wastes as substitute aggregate. For example, the particle size and shape distribution of foundry sands would be detrimentally altered after being treated by these methods. Moreover, although some prior art methods treat industrial waste with only a phosphate-containing compound, no steps are taken to retain or recover the particle size and shape distribution of the waste so it can be used in other industrial processes.
There is therefore a need for an economical method to treat industrial wastes such as foundry sands or slags. Specifically, there is a need for a method of treating industrial wastes that leave their useful particle shapes and size distributions unchanged so the wastes may be recycled as raw materials useful in other industrial processes.
SUMMARY OF THE INVENTION
Briefly describing one aspect of the present invention, there is provided a method of treating waste contaminated with leachable metallic contaminants by combining the waste with a sulfite such as calcium sulfite. The previously leachable metal contaminants are then complexed as insoluble metal sulfur oxides, and the material is safe for use as a raw material.
In another aspect of the invention, industrial wastes such as foundry sand or slag containing metallic contaminants is treated by first reducing the size of the sand or slag “clumps” or “chunks” until the sand or slag is returned to a particle size that is about the same as the size of the sand or slag particles before it was contaminated. The particles are then combined with a reactant effective for converting the metallic contaminants to a non-leachable form, and the product thus formed is useful as a substitute raw material in the production of, for example, concrete. In a preferred embodiment of this second aspect of the invention, the reactant is comprised of a sulfite such as calcium sulfite.
One object of the present invention is to provide a method for recycling industrial waste, including foundry sands and slags.
Further objects and advantages will be apparent from the following description.
DESCRIPTION OF THE PREFERRED EMBODIMENT
For the purposes of promoting an understanding of the principles of the invention, reference will now be made to preferred embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein, being contemplated as would normally occur to one skilled in the art to which the invention relates.
The present invention relates to a method for reducing leachable levels of metallic contaminants such as antimony, arsenic, barium, beryllium, cadmium, chromium, lead, selenium, silver, nickel, iron, manganese, magnesium, aluminum, bismuth, copper, thallium, and zinc in industrial wastes, and particularly in foundry sands and crushed slags. In the most preferred embodiments the sizes and shapes of the sand or slag particles are returned to the size and shape distributions inherent to those materials before they became wastes. One advantage of the inventive method is that it provides treated wastes that are in a condition such that they are useable as raw materials in other industrial processes.
In one aspect of the present invention, the grain structure and size distribution of typical spent foundry sands are restored or retained to make that material useful as a fine aggregate when added to cement to form concrete. The grain structure allows the use of less portland cement in a concrete mix, while affording an equally strong or stronger end product. The cost reduction obtained by using less raw material, and the added strength imparted by the grain structure, are significant. Thus, foundry sands and crushed slags can be processed so as to make them eminently suitable for use as an aggregate, raw material, or fill material. Ready-mix concrete, brick and block, mortar, bricks, concrete blocks, etc., may all benefit from the inclusion of waste foundry sand that has been processed according to the present invention. Asphalt used in roadways, parking lots, etc., can benefit structurally from the inclusion of processed slag. Moreover, the inventive treatment may be utilized to make wastes more suitable for other uses where certain jurisdictions allow environmentally benign wastes to be used in manners other than as an industrial raw material.
In one aspect of the invention, the size of the waste is first reduced prior to being combined with a reactant. Slags are generally reduced in size for subsequent use as alternate raw material prior to application of the reactant. If the size of the slag is not r
Hale, III Edward Carroll
Wildey John E.
Langel Wayne A.
Woodard Emhardt Moriarty McNett & Henry LLP
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