A method for removing a wide variety of radioactive contaminants from a contaminated surface sufficient for the surface to be classified as a low-level waste or as free release. Contaminated surfaces may be classified as Class C, Class B, Class A, or high-level radioactive wastes prior to treatment. An aqueous solution having a wetting agent and a complex substituted keto-amine is provided. The aqueous solution is left on the surface for a time sufficient to remove the radioactive contaminants into the aqueous solution which is then removed. Depending on the type and condition of the surface, an acid may be added to the aqueous solution to aid in the contaminant removal process. However, typical metals surfaces may often be treated effectively without the use of concentrated acids or with dilute concentrations of such acids. The method of the present invention has the effect of removing substantially all of the radioactive contaminants from a variety of previously contaminated surfaces.
BACKGROUND OF THE INVENTION
The present invention. relates generally to a method for decontamination of surfaces. More particularly, the present invention relates to using an aqueous solution having particular compositions to remove radioactive contaminants from a given area, location or surface.
Contamination of various areas or surfaces from radioactive or other unwanted materials is a common problem. The contamination of an area or surface may occur as a result of contact with a radioactive isotope during transport, storage, use in a nuclear reactor, mining operations, or a variety of other industrial, medical, or military activities. Current Nuclear Regulatory Commission (NRC) classifications refer to these types of waste as low-level wastes. The NRC has outlined three general categories of low-level radioactive waste: Class A, Class B, and Class C. Class B and C wastes involve significant restrictions and licensing in order to handle and dispose of such wastes. However, Class A wastes are much less restrictive to dispose of and present reduced environmental hazards. In recent years, methods have been explored to reduce or remove such contaminants from various areas or surfaces and equipment so that such items or areas may be put back into use and the contaminants may be disposed of safely. These methods have met with varying degrees of success and often present trade-offs between decontamination of the surface or area and the toxicity of the waste product containing the radioactive contaminant.
One method of removing radioactive materials is to physically wash the contaminated area or surface with water and an optional surface-active agent. However, such methods are generally limited to physical separation of contaminants that are not strongly physically or chemically adhered to surfaces or areas. Thus, this method does not work well where the contaminants are chemically bound or strongly physically adhered to a solid surface or structure.
For example, a number of methods have been developed to remove radioactive contaminated scale or rust deposits from metal surfaces that are partially successful. The radioactive substances are removed in a solution that is transported at safe levels for disposal. However the concentrated radioactivity found in scale or rust adhering to surfaces presents increased danger and cost in removal and disposal. Depending on the type of scale or rust deposit either acidic or basic removal treatments may be appropriate. U.S. Pat. Nos. 5,200,117; 5,049,297; and 5,824,159 illustrate typical approaches to removing radioactive substances in these situations.
Another method for removing contaminants from surfaces or areas, which are not necessarily limited to deposited scales, is known generally as acid leaching. In acid leaching methods, a strong acid is used to dissolve radioactive contaminants from the surface into solution. The resulting solution is removed and disposed of leaving a clean, or at least a reduced amount of radioactive contaminants, on the surface. Such acid leaching processes may or may not use chelating agents.
Chelating agents have been the subject of much research in this area and include ligand or binding agents such as oxalate, citrate, gluconate, picolinate, EDTA, hydrazines with carboxylic acids, and hydroxamic acids. Acidic and basic solutions containing a chelating agent are used to dissolve and bind contaminants depending on the characteristics of the surface and the contaminants. When used to remove radioactive substances from contaminated areas, the chelating agent is thought to have the effect of stabilizing certain dissolved radioactive contaminants to keep them in solution. Several of these methods use concentrated carbonate solutions to recover uranium, thorium, radium, technetium, and other actinides.
With several of these methods, a separate ion-exchange process is used to purify the resulting solution to make disposal of the radioactive contaminants easier.
In addition to these challenges, other considerations include providing a decontaminating agent and method which is not excessively corrosive and is easy to prepare and use. Further, the solution containing removed contaminants should preferably be easily disposed of in compliance with state and federal regulations. It would therefore be a significant advancement and contribution to the art to provide a method which is a simple, economic, and effective way of removing substantially all of the radioactive contaminants from various surfaces or areas.
SUMMARY OF THE INVENTION
While many methods for removing radioactive or other unwanted contaminants have been developed there remains the need for improved decontamination methods which speed up the decontamination process and remove substantially all of the radioactive contaminants. The present invention relates to the removal of radioactive contaminants from a surface or area using an aqueous solution which includes a wetting agent and an active agent which is a complex substituted keto-amine. The aqueous solution is applied to a radioactively contaminated surface and retained on the surface for a period of time sufficient to allow at least a portion of the radioactive contaminants to migrate into the aqueous solution. The contaminant rich aqueous solution is then removed from the surface for further treatment or disposal. In accordance with the present invention, many Class B and Class C wastes, as defined by the NRC, may be converted to Class A or free release wastes through treatment using the present invention.
In one aspect of the present invention the active agent is a complex substituted keto-amine having the molecular formula C.sub.33 H.sub.45 NO.sub.2.Cl H.
In a more detailed aspect of the present invention the wetting agent is a member selected from the group consisting of water, lower alcohols, glycols, surfactants, and mixtures thereof.
In another aspect of the present invention, the aqueous solution includes a concentrated acid such as hydrochloric acid, hydrofluoric acid, sulfuric acid, phosphoric acid, sulfurous acid, bromic acid, iodic acid, nitric acid, perchloric acid, oxalic acid, aqua regia, citric acid, sulfamic acid, glycolic acid, ascorbic acid, and mixtures thereof. In a more detailed aspect, the concentration of one or more of the above acids is up to about 10% by weight of the aqueous solution. In a yet more detailed aspect, the concentration of one or more of the above acids is up to about 5% by weight of the aqueous solution. In yet another detailed aspect, the aqueous solution is substantially free of an acid.
In accordance with yet another more detailed aspect of the present invention, the method is used to remove radioactive contaminants, and particularly those found in the actinide and lanthanide series such as thorium, uranium, and plutonium. Exemplary of radioactive contaminants, some of which are in the actinide and lanthanide series, are: Actinium-227, Americium-241, Americium-242, Americium-243, Americium-244, Antimony-124, Antimony-125, Barium-133, Beryllium-7, Bismuth-207, Cadmium-109, Calcium-45, Carbon-14, Cerium-139, Cerium-141, Cerium-144, Cesium-134, Cesium-135, Cesium-137, Chromium-51, Cobalt-56, Cobalt-57, Cobalt-58, Cobalt-60, Copper-64, Copper-67, Curium-242, Curium-243, Curium-244, Curium-245, Curium-246, Curium-247, Curium-248, Curium-249, Europium-152, Europium-154, Europium-155, Gadolinium-153, Germanium-68, Gold-195, Hafnium-181, Hydrogen-3(Tritium), Iodine-125, Iodine-126, Iodine-129, Iodine-131, Iodine-133, Iridium-192, Iron-55, Iron-59, Iron-65, Lead-2.10, Manganese-52, Manganese-54, Manganese-56, Mercury-203, Neptunium-237, Neptunium-239, Nickel-59, Nickel-63, Niobium-94, Niobium-95, Plutonium-236, Plutonium-238, Plutonium-239, Plutonium-240, Plutonium-241, Plutonium-242, Plutonium-243, Plutonium-244, Polonium-210, Potassium-40, Promethium-147, Protactinium-231, Radium-223, Radium-224, Radium-226, Radium-228, Ruthenium-106, Samarium-151, Scandium-46, Selenium-75, Silicon-31, Silver-108 m, Silver-110 m, Sodium-22, Sodium-24, Strontium-85, Strontium-89, Strontium-90, Sulfur-35, Tantalum-182, Technetium-99, Thallium-204, Thorium-natural, Thorium-228, Thorium-230, Thorium-232, Tin-113, Uranium-232, Uranium-233, Uranium-234, Uranium-235, Uranium-236, Uranium-238, Uranium-natural, Uranium-depleted, Yttrium-88, Yttrium-91, Zinc-65, Zinc-69, Zirconium-95, and isotopes and associated decay products of these contaminants.
In accordance with a detailed aspect of the present invention, the method is used to remove transuranic radioactive contaminants.
In accordance with another aspect of the present invention, the method is applied to a solid surface or area as defined above which comprises metal, plastic, glass, concrete, wood, fiberglass, soil, natural or synthetic fabrics, or any other material.
In general, the method comprises applying the aqueous solution, as hereinafter defined, in such a manner as to contact the radioactive contaminant and remove it from the surface or area to which it is associated into the solution. Such application techniques may be by wetting, spraying, wiping, soaking, immersing, and the like. Once applied to a surface it is important that the solution be removed before the solution dries on the surface. Otherwise, the radioactive contaminant would not be removed. Hence, the time the solution is on the surface may be relatively short or long, depending on the wetting time and application process. It may be desirable to sequentially perform more than one application and removal step to adequately remove the radioactive decontaminant from the surface. Additionally, the length of time between the application and removal steps may vary from a few seconds to several minutes depending on the condition of the surface and the amount radioactive contaminant to be removed. Any suitable removal technique, such as a squeegee, wiper blade, vacuum, gravity flow, wringer, centrifuge, and the like may be used to remove the solution from the surface.
In yet another more detailed aspect of the present invention, the application and removal steps may be repeated more than once to remove further portions of the contaminants from the surface. Consecutive treatments may use the same aqueous solution composition or different compositions including linear alcohol alkoxylates, ethoxylated alkyl amines, and mixtures thereof.
Finally, in accordance with another aspect of the present invention the collected aqueous solution containing the removed radioactive contaminant may be treated to neutralize the pH. Collected aqueous solution may be treated by adding sodium hydroxide or any other suitable neutralizing agent to obtain a pH of greater than about 5.5, and preferably about 7 to about 9 to form a waste solution.
Additional features and advantages of the invention will be apparent from the detailed description which follows.
For a license agreement and protocol on how to decontaminate a specific project. contact us Include specific information concerning specific radioactive contaminate amount of radioactivity and location of project. We will determine the best Enviroworx™ High Performance Solution and method to complete the decontamination.