Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Reexamination Certificate
1999-03-24
2002-02-19
Cintins, Ivars (Department: 1724)
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
C210S651000, C210S660000, C210S662000, C210S669000, C210S670000
Reexamination Certificate
active
06348153
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the separation of oxides of heavy isotopes of hydrogen, and in particular to a process and apparatus for separating deuterium oxide (HDO, D
2
O), tritium oxide (HTO, T
2
O) and oxides of deuterium and tritium (DTO) from light water (H
2
O) contaminated with heavy isotopes of water. In addition, this process addresses separation of heavy water isotopes, e.g. DTO from D
2
O, and HTO from D
2
O. Separation is effected by passing the contaminated water through a molecular separation material containing hydration sites, i.e., sites with associated waters of hydration. The heavy isotopic water is held at higher concentrations within the waters of hydration than in the contaminated water thus providing a separation effect. Heavy isotopic water can also replace adsorbed light water. Separation of the isotope molecules may also be effected with a separation membrane that selectively allows passage of light water molecules in preference to the other heavy isotope molecules. These two procedures may also be combined.
2. Description of the Prior Art
Nuclear power plants must routinely deal with the replacement and disposal of contaminated water taken from the core reactor that is laden with heavy isotopes of hydrogen, namely deuterium oxides, tritium oxides and deuterium-tritium oxides. Tritium in particular is highly radioactive having a half-life of about twelve and one half years emitting beta rays to form helium.
Periodically, the contaminated water from nuclear reactors must be replaced. It has become industry practice of dispose of the old contaminated water by simply dispersing it over adjacent ground areas or evaporating the contaminated water into the atmosphere. This is stressful to the environment as the deuterium oxides and tritium oxides are now known to have contaminated ground water sources. One alternative is to sequester contaminated water in concrete at a considerable expense.
SUMMARY OF THE INVENTION
In accordance with the present invention, a process and related apparatus are described for separating deuterium oxide (HDO, D
2
O) and tritium oxide (HTO, T
2
O), i.e. heavy water and tritiated water, and deuterium-tritium oxides, from waste water. As used herein, water molecules of the formula H
2
O will be referred to as light water molecules, or simply water molecules, while water molecules in which one or both of the hydrogen atoms have been replaced by one of these hydrogen isotopes will be referred to as isotope water molecules or isotope molecules.
In the described process, a portion of the isotope water molecules are removed from contaminated water, i.e., water containing a small amount of isotope water molecules, through selective adsorption by contacting the contaminated water with a molecular separation material containing hydration sites carrying one or more associated waters of hydration. In the process, isotope water molecules present in the contaminated water selectively replace a portion of the waters of hydration associated with the hydration sites. The molecular separation material can then be separated from the water, reducing the percentage of isotope molecules in the water. After separation, the molecular separation material can be regenerated by removing the isotope molecules for long-term storage, and reused repeatedly to separate isotope molecules.
In order to improve the efficiency of the selective adsorption process, the percentage of isotope molecules in the contaminated water can be increased, thereby increasing the exposure of isotope molecules to hydration sites, by removing a portion of the light water molecules, before or during the selective adsorption, by bringing the contaminated water into contact with a porous film or membrane that exhibits a greater permeability for light water molecules than for the larger isotope molecules. For some purposes, adequate separation may be effected through membrane separation alone.
THE MOLECULAR SEPARATION MATERIAL
Generally, the molecular separation material of the present invention is comprised of a support medium having a plurality of hydration sites, i.e., sites with associated waters of hydration. The effectiveness of the molecular separation material is determined by the number of hydration sites exposed to the contaminated water, and to the number of waters of hydration at each site. The support medium used to carry the hydration sites is not critical to the invention so long as exposure of the contaminated water to numerous sites containing multiple waters of hydration is provided. In general, this objective is preferably achievable with a high surface area support medium having a plurality of hydration attachment sites.
The support medium or medium may be, for example, a polymer, such as polystyrene/divinyl benzene (PSDVB), or polyacrylic/divinyl benzene (PADVB). These polymers are commonly used as supports in ion exchange resins in the preparation of ion exchange resins. The polymer may be functionalized for example, by being sulfonated or phosphonated to provide the sites for attachment of metal or other cations with the required associated waters of hydration. Both strong and weak acid resins have been shown to be effective.
It is important to note that the present invention involves the preferential adsorption or substitution of the waters of hydration associated with the hydration sites, and not the replacement of the cation or anion as is normally practiced in using this type of resin. Thus, while the resins employed are referred to in some instances as ion exchange resins, since this is the purpose for which they are commonly employed, their function in the present invention is to facilitate molecular exchange of isotope water molecules with the associated light water molecules attached to the hydration sites.
Also, while the present invention will be exemplified by the use of the above resins, it will also become apparent that other materials having a large surface area and hydration sites can be used. That is, the present invention involves the interaction between the hydration sites and the isotope molecules, in which one or more light water molecules initially associated with a hydration site are replaced by isotope molecules in the contaminated water. Thus, the support medium serves essentially as a carrier for the hydration sites. Thus, various high surface area materials can be used, so long as they are water insoluble and provide a large number of accessible hydration sites. For example, the support medium can be other kinds of synthetic polymers, or natural materials, such as zeolites, aluminas, silicas, etc.
Each hydration site will have at least one, and preferably from about 7 to about 25 waters of hydration and even higher up to almost 50 waters of hydration. Various molecules that form associations with water molecules, i.e., waters of hydration can be used in the present invention. The cationic portion of the hydration site may be non-metallic, e.g., an ammonium cation (NH
4
+
), or a metallic cation. Of the metal cations, aluminum is especially suitable due to the large number of waters of hydration associated with aluminum salts. However, other cations, such as sodium, magnesium, copper, zinc, cobalt, iron, nickel, manganese, potassium or chromium can also be employed. Depending upon the structure of the support and the manner of its production, the anionic portion of the hydration site molecule can include nitrates, sulfates, chlorides, acrylates, hydroxides, or phosphates. Moreover, a broad array of physical constants for inorganic compounds having varying waters of hydration are to be found in reference handbooks such as
Handbook of Chemistry
N. A. Lange, Ph.D. Revised 10th Edition, or
CRC Handbook of Chemistry and Physics
, D. R. Lide, Ph.D., 77th Edition.
The molecular separation material may be in various physical forms, so long as a large surface area with hydration sites is exposed to the contaminated water. For ease of manufacture and subsequent regeneration, and the
Furlong Louis E.
Gruber Martin J.
Patterson James A.
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