Decontamination composition for removing norms and method utilizing the same

A 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; about 0 to 2 percent of a dispersant; and about 0 to 2 percent of a corrosion inhibitor. The present invention also relates to a method of decontaminating a surface whereby contaminants in the form of NORMs are removed therefrom.

FIELD OF THE INVENTION 
This invention relates to a decontamination composition, and more 
particularly to a composition suitable for decontaminating surfaces 
contaminated with naturally occurring radioactive materials (NORMs). 
BACKGROUND OF THE INVENTION 
Naturally occurring radioactive material (hereinafter "NORM") is present in 
varying concentrations in groundwater and the like, in water supply wells, 
oil production wells, gas production wells, and as byproducts in mining 
operations. In the oil field, NORM is the result of material that has been 
extracted from the producing zone and is deposited on the equipment in the 
form of solids, films, pipe scale, sediment, and the like. The radioactive 
material is typically radium 226, radium 228, radon 222, thorium 232, 
uranium 235, uranium 238, lead 210, polonium 210, and other naturally 
occurring radionuclides. Typically these radionuclides are .alpha., .beta. 
and often .gamma. emitters which have a long half life. Such radionuclides 
are believed to be associated with toxic and carcinogenic effects. Strict 
health-based limits thereon have been enacted or are under consideration. 
For example, the process equipment used in various petrochemical plants, 
refineries, and the like, and associated piping is exposed to high levels 
of NORM. The disposal of equipment having a high level of NORM has come 
under increased scrutiny, particularly in oil-producing states such as 
Louisiana and Texas. Thus, many companies are stockpiling equipment which 
will need to either be cleaned for reuse or decontaminated for disposal. 
Thus, currently the most common practice other than stockpiling is to ship 
the equipment to a radioactive waste facility which have their own 
environmental problems. There are also several costly mechanical methods 
on the market for removing NORM. These include ice, sponge, or carbon 
dioxide blasting. These methods have limitations in that these methods are 
more applicable to pipe scale and other solid forms of NORM as compared to 
NORM deposited in solution or as a film which adheres to metal surfaces 
and is difficult to remove. 
Methods are known to remove radioactive materials from surfaces such as 
those found in nuclear reactors. For example, U.S. Pat. No. 4,537,666 to 
Murray et al. describes the typical system as treating the surfaces with 
an oxidizing solution, such as one containing an alkaline permanganate. 
This is followed by treatment with a decontamination solution which is an 
aqueous solution of a chelate, such as ethylenediaminetetraacetic acid 
(EDTA), and a solubilizing agent, such as a mixture of oxalic acid and 
citric acid. The chelate forms a complex with the metal ions from the 
deposits and solubilizes them, and, thus prevents them from precipitating 
out of the solution at another location in the cooling system. The 
decontamination solution is circulated between the cooling system and a 
cation exchange resin. The chelated metal ions are deposited on the cation 
exchange resin, freeing the chelate to solubilize additional metal ions in 
the deposit. 
The difficulty with this decontamination process, according to Murray et 
al., is that both the chelates and the cation exchange resin complete for 
the metal ions. As a result, the metal ions do not readily leave the 
chelate and attach themselves to the ion exchange column. This means that 
long resin contact times are required, and that the ion exchange column 
effluent may contain relatively high metal ion concentrations. Murray et 
al. proposes to remove the metal ions by passing the decontamination 
solution through a porous DC electrode. 
Other exemplary methods for removing nonnaturally occurring radioactive 
materials are proposed in U.S. Pat. Nos. 4,704,235 to Arvesen; 4,729,855 
to Murray et al.; 4,792,385 to Snyder et al.; and 5,111,887 to Morris et 
al. 
Despite the general availability of methods of removing naturally occurring 
and nonnaturally occurring radioactive materials, there continues to be a 
need for removing NORMs from surfaces exposed to the same, and 
particularly NORM deposited as a solution or film and adhered to surfaces. 
SUMMARY OF THE INVENTION 
With the foregoing in mind, it is an object of this invention to provide a 
decontamination composition and a method for decontaminating a surface 
contaminated with naturally occurring radioactive material (NORM). There 
are generally three types of NORM contaminants. One is radioactive scale 
which contains uranium, thorium, radium, and associated decay products 
from the production of oil and associated brines contaminated with NORM. 
The radioactivity in the scale originates principally from radium, which 
coprecipitates with barium and strontium sulfate. Another type is 
NORM-contaminated film, coating, or plating which can form from natural 
gas production or processing. Another type is NORM-contaminated sludge in 
pipelines, processing plants, storage tanks and delivery facilities, 
pigging operations, and gas lines and other filter assemblies. These films 
often contain radon and its decay products (i.e., polonium 210, bismuth 
210, and lead 210). The film, coating, and plating forms are often more 
difficult to remove as compared to scale, and moreover the above-described 
mechanical methods are typically ineffective. 
These and other objects, features, and advantages of the invention are 
provided by the decontamination composition of the present invention. The 
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 with 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 present invention also relates to a method of decontaminating a surface 
whereby contaminants in the form of NORMs are removed therefrom. The 
method comprises contacting the surface (e.g., a metal surface) with a 
decontamination composition comprising about 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; about 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; about 
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 with a neutralizing compound, and mixtures thereof; about 0 to 2 
percent of a nonionic surfactant; about 0 to 2 percent of a dispersant, 
and 0 to 2 percent of a corrosion inhibitor.

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.