Patent Number: 054897351
Section: description

DETAILED DESCRIPTION OF THE INVENTION The present invention will now be described more fully hereinafter. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiment set forth herein; rather, this embodiment is provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. As summarized above, the decontamination composition comprises 40 to 60 percent of a compound selected from the group consisting of oxalic acid, alkali metal and ammonium salts of oxalic acid and mixtures thereof; 5 to 20 percent of a compound selected from the group consisting of citric acid, alkali metal and ammonium salts of citric acid and mixtures thereof; 20 to 40 percent of a compound selected from the group consisting of polyaminocarboxylic acid, alkali metal and ammonium salts of polyaminocarboxylic acid and the combination of a polyaminocarboxylic acid and a neutralizing compound, and mixtures thereof; 0 to 2 percent of a nonionic surfactant; 0 to 2 percent of a dispersant; and 0 to 2 percent of a corrosion inhibitor. The alkali metal and ammonium salts of the oxalic and citric acid can include mono- and disubstituted salts. A particularly preferred salt of oxalic acid is ammonium oxalate. A particularly preferred salt of citric acid is ammonium citrate. Suitable polyaminocarboxylic acids include ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, triethylenetetraamine hexaacetic acid, N-2-hydroxyethylethylenediaminetriacetic acid, propylene1,2-diaminetetraacetic acid, propylene-1,3-diaminetetraacetic acid, nitrilotriacetic acid, the ammonium and alkali metal salts of said acids, and the combination of the polyaminocarboxylic acids with neutralizing compound, and mixtures thereof. The alkali metal and ammonium salts can include mono- and disubstituted salts. A particularly preferred salt of polyaminocarboxylic acid is diammonium ethylenediaminetetraacetic acid. A suitable neutralizing compound is hydrazine. Suitable nonionic surfactants include Triton X-100, an octylphenoxy-polyethoxyethanol with 9 to 10 moles of ethylene oxide surfactant, available from Union Carbide, Danbury, Conn., and Pluronic L-101, a polyoxyethylene-polyoxypropylene block polymer surfactant, available from BASF-Wyandotte, Wyandotte, Mich. A suitable dispersant for organic solids is Tamol SN, a sodium salt napthalenesulfonic acid, available from Rohm & Haas, Philadelphia, Pa. A suitable dispersant for inorganic solids is sodium lignosulfonate. A suitable corrosion inhibitor is Rodine 95, which includes thiourea, formaldehyde, o-toluidine and substituted triazine hydrochloric acid, available from Parker+Amchem, Madison Heights, Mich. In operation, a surface (i.e., a metal surface) contaminated with NORM is contacted with the above-described decontamination compound. The contacting can be conducted at a temperature of about 20.degree. to 150.degree. C., and preferably is conducted at about 80.degree. to 100.degree. C. Agitation in any form (e.g., mechanical or ultrasonic) will increase the rate of removal. The foregoing example is illustrative of the present invention, and is not to be construed as limiting thereof. EXAMPLE The following decontamination composition is blended together: ______________________________________ Component Percent by Weight ______________________________________ Ammonium Oxalate 54.52 Diammonium EDTA 32.72 Ammonium Citrate 11.45 Triton X-100 0.13 Pluronic L-101 0.13 Tamol SN 1.00 Rodine 95 0.05 ______________________________________ A sample S to be decontaminated is a perforated steel plate from an oil refinery distillation tower contaminated with NORMs. The sample is immersed in a bath of the decontamination composition and agitated. The bath temperature is about 95.degree. C. The sample is rinsed in a solution of ESI 635.TM. available from Environmental Scientific, Inc., Research Triangle Park, N.C., to disperse loose particulate. The activity on the sample is measured using a Ludlum Model 2 survey meter available from Ludlum Measurement, Inc., Sweetwater, Tex., with a Model 44-9 pancake probe, and is mapped at several locations designated as A through H which appear to give the highest reading (see FIG. 1). Corresponding measurement are taken at one hour intervals. Referring to FIG. 2 and Table 1, the activity decreases rapidly in the first hour and gradually approaches zero. At three hours, the activity level is only about 18 percent of the initial level. TABLE 1 ______________________________________ cpm vs. time in hours Location 0 1 hr 2 hrs 3 hrs ______________________________________ A 4000 1150 900 B 4000 1200 900 800 C 3500 750 690 D 3000 690 450 E 3000 700 500 F 2800 850 425 G 3000 600 H 2300 400 ______________________________________ In the specification and example, there have been disclosed preferred embodiments of the invention. Although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation, the scope of the invention being defined by the following claims.