1. Field of the Invention
This invention relates to a novel method for treatment of heavy metals, including antimony, arsenic, barium, beryllium, cadmium, chromium, lead, mercury, nickel, selenium and silver. These heavy metals are encountered during diverse industrial processes. More specifically the current invention relates to a technology for decontamination of these heavy metals found in industrial processes and sites where these heavy metals have been used in the past or to prevent future contamination by introducing the technology in the manufacturing process. The present invention is used to render these heavy metal compounds nontoxic and therefor not requiring special handling as toxic waste.
Heavy metals, such as those listed above, are highly toxic to humans. Many of these heavy metals and compounds that contain them can be absorbed through the skin of a person in contact with the heavy metal compound. Additionally, many of these compounds can be ingested if they leach into a water supply and the water is consumed. This type of contamination often occurs when these heavy metal compounds, often the byproduct of industrial processes, are disposed of in inappropriate sites which lack the necessary safeguards to ensure the heavy metal compounds do not leach into the ground and attendant water table.
The heavy metals and the compounds that contain them have been used in a variety of industrial applications and processes. In the last quarter century, the toxicity of these heavy metal compounds has become a major health concern. As this concern has grown, the United States Environmental Protection Agency (hereinafter "U.S.E.P.A.") and state environmental agencies have promulgated testing procedures to detect the amount of heavy metals in a given sample that could pose a health or environmental hazard. The standard test established by the U.S.E.P.A. is the Toxicity Characteristic Leaching Procedure (hereinafter "TCLP"). This test measures the amount of heavy metals released into the environment by water and other environmental factors acting on a given sample. The U.S.E.P.A. has used these testing procedures to set limits on the amount of heavy metals that can be present in a given sample.
2. Description of Related Art
One method for handling such lead contaminated surface coatings is shown in U.S. Pat. No. 5,266,122 (Rapp et al.) The method shown by Rapp involves the addition of abrasive unreacted hydraulic cement to abrasive blasting media. The mixture is then used to blast the contaminated surface coating from a structure. Water is added during the blasting operation to react with the cement and form a surficial silica gel that binds the particulates into a cementicious whole.
A method for in situ treatment of lead contaminated soils using calcium phosphate compounds is shown in U.S. Pat. No. 5,512,702 (Ryan et al.) The technique of Ryan is to mix calcium phosphate compounds with soil to render the lead in the soil nontoxic.
A method for removing coatings that contain hazardous byproducts is shown in U.S. Pat. No. 5,674,108 (Rolle). A chemical compound to neutralize the hazardous compound in the coating to be removed is applied and the coating and chemical compound are removed.
A new and innovative use of calcium phosphate compounds for in situ decontamination of lead contaminated surface coatings is shown in U.S. Pat. No. 5,797,992 issued to Carl L. Huff, the inventor of the current invention. Mr. Huffs '992 patent shows a method for using calcium phosphate compounds such as apatite and synthetic hydroxyapatite to render the resultant lead compound nontoxic.
Consequently, while the use of phosphate compounds to decontaminate heavy metal contaminated materials has been shown previously, none of the prior art methods offer the ability to render a variety of heavy metals and their related compounds nontoxic.