US 3047434 A
Description (OCR text may contain errors)
This invention relates to solutions and methods for radioactive decontamination.
Radioactive contaminants occur as unstable forms of the elements which in practical situations may be found in pure form but are usually found mixed in any of a wide variety of soils. Effective decontamination involves both stabilization and physical removal of the radioactive contaminant. An object of the invention is to provide improved solutions and methods for achieving this result.
Previous decontamination methods have been based on an attempt to remove the soil from articles to be cleaned in the hope that its radioactive ingredients would be removed in the process. The process is practiced in the specific form required for the removal of the soil. On the other hand, this invention provides a decontamination solution capable of direct action on the radioactive contaminant although in practice it will remove most of the soils as well.
Another object is to provide highly effective solutions for decontamination when the radioactive contaminant is specifically identified; but the provision of solutions which are very effective evenvwhen the radioactive contaminant is not known, is also an object.
Another object of the invention is to provide a solution, for general application to the problem of decontamination, sufiiciently effective to warrant its use for average cases, for those cases in which a variety of radioactive substances are present, and for first decontamination in preparation for specific contamination in special cases.
Another important object is to provide a solution which is sufliciently inexpensive to make practical the decontamination of inexpensive hand tools such as pliers, screwdrivers, and the like which now must be disposed of, often after only a single usage.
These andother objects and advantages of the invention which will hereinafter be apparent, are realized by the provision of a radioactive contaminant comprising a mixture of a detergent liquid, an ion exchange agent soluble in said liquid to form ions charged oppositely of the radioactive contaminant, and adsorbent solids distributed in the liquid. Each of these ingredients has a specific individual function in the decontamination process, the effectiveness of each of which depends upon the function of the other whereby the invention contemplates solutions simultaneously containing all of these substances. The article to be decontaminated is immersed in the solution which advantageously is subjected to forces producing cavitation. 1
In addition to their functional interdependence there is a mechanical cooperation between the substances. The detergent serves as the vehicle by which the exchange agent and adsorbent may move into association with one another and the surface to be cleaned, while the forces exerted by the substances accounts for that movement. Provision for cavitation action aids the movement and intermixing of the constituents of the solvent in addition to providing mechanical force for dislodging contaminants and soil from the article being cleaned and from one another.
The individual functions of the detergent, ion exchange agent, and adsorbent, taken one at a time, are the functions associated with those names by chemists although the action by which the function is provided may not yet have been defined. The detergent, through the applicaa 3,047,434 C3 Patented July e1, 1962 2 tion of hydrophilic, hydrophobic, lipophilic, or lipophobic forces or chelating action, overcomes the mechanical forces and affinities which bind the soil and contaminants to the articlebeing cleaned.
The ion exchange agent, having polarity opposed to the polarity of the charge associated with the instability or radioactivity of the contaminant, has an afinity for the contaminant and joins it to form a discreet particle. The integrity of the union of the exchange agent and contaminant is preserved by their adherence in combination to the adherent which in turn is prevented by the detergent from adherence to the article being cleaned.
When the contaminant is identified, the ion exchange agent is selected in accordance with principles well known in the chemical art so that chemists having at least ordinary skill can select a proper agent. When the contaminants or some of them are not identified, sulfides, carbonates, hydroxides and sulfates can be utilized. The sodium salts of these radicals are preferred in accordance with the invention and a positive ion from this group should be included if there exists a possibility that one of the contaminants is negative.
To augment the action of the exchange agent, the detergent advantageously includes a chelating agent. In the interest of cost reduction as well as for its eflectiveness as a wetting agent in connection with most soils, it is preferred that the detergent consist primarily of water. Advantageously the detergent may comprise a mixture of water and ethylene diam-inc tetra acetic acid.
A wide variety of adsorbents have been used with good results including silicates such as a colloidal cl-ay, talc, and fullers earth, chalk; sulfides of arsenic and antimony; diatomaceous earth; carbon black; and metallic oxides such as alumina, magnesia, iron oxide, and titanium and manganese dioxide.
Of course, the action of solutions made according to the invention may be augmented and hastened by mechanical agitation to insure that fresh solution reaches the surface to be decontaminated and by mechanical actions on the soil itself.
A superior kind of such mechanical action is ultrasonic cavitation of the decontamination solution and the solution found to be most advantageous for general decontamination is entirely compatible with this kind of action. That solution comprises water, ethylene diamine tetra acetic acid, sodium sulfate, sodium hydroxide, manganese dioxide, and carbon black.
By way of example and not of limitation, since other solutions are possible and the relative quantities in this solution may be modified within the scope of the invention and the appended claims, a particularly effective solution for decontamination was made by the mixing of ingredients in the following proportions:
milliliters of water, 1 gram ethylene diamine tetra acetic acid, 0.2 gram sodium sulfate, 0.2 gram sodium hydroxide, 0.1 gram manganese dioxide and 0.1 gram carbon black. A soiled article having radioactive contaminants, especially radioactive cesium 134, was immersed in this solution.
Also, a similarly contaminated article was immersed in a like solution and the latter was activated to produce cavitation bythe action of ultrasonic energy with improved result.
I claim: I
1. A solution for radioactive decontamination comprising a mixture of water, ethylene diamine tetra acetic acid, sodium sulfate, sodium hydroxide, manganese dioxide, and carbon black.
2. The decontamination method which comprises immersing a radioactively contaminated article in a solution comprised of water, ethylene diamine tetra acetic acid, sodium sulfate, sodium hydroxide, manganese dioxide,
3 4 and carbon black, and subjecting said solution to ultra- 2,401,484 Jackson June 4, 1946 sonic vibration forces sufiicient to produce cavitation 2,607,738 Hardy Aug. 19, 1952 therein. 2,672,449 Snell Mar. 16, 1954 2,678,303 Bonewitz May 11, 1954 References Cried 1n the file of th1s patent 5 2,736,640 McGraW Feb- 28 1956 UNITED STATES PATENTS 2,739,882 Ellis Mar. 27, 1956 2,016,265 Doherty Oct. 1, 1935 2,802,758 Kearney Aug. 13, 1957 2,241,984 Cooper May 13, 1941 2,814,575 Lange NOV. 26, 1957