Process for removing dissolved uranium from water

Details Process for removing dissolved uranium from water Process for removing dissolved uranium from water

2000-03-06

2002-07-16

Lithgow, Thomas M. (Department: 1724)

Liquid purification or separation

Processes

Ion exchange or selective sorption

C210S716000, C210S717000, C210S724000, C210S725000, C210S727000, C423S011000, C423S012000

Reexamination Certificate

active

06419832

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention.
The present invention relates to a process for removing dissolved uranium from water, and more particularly, such a process which is simple and economical to carry out.
2. Description of the Prior Art.
Uranium is a naturally occurring radioactive element which is commonly found dissolved in water at varying concentrations. The United States Environmental Protection Agency and other state and federal agencies have regulations which establish the maximum permissible levels of soluble uranium that can be contained in different types of waters. Hence, it is often necessary to remove some or most of the dissolved uranium from water to comply with the applicable regulations before the water can be safely discharged or used for human consumption.
A number of processes have heretofore been developed for removing dissolved uranium from water. Such processes include the use of anion exchange resin, activated alumina, granular activated carbon, lime softening, reverse osmosis and under certain conditions, conventional coagulation using aluminum sulfate or iron salts. Many of these prior art processes require that the pH of the water being treated be raised to a very high level (over a pH of 10) or reduced to a very low level (lower than a pH of 3). Other of the processes require some type of pretreatment of the water. As a result, very few of the processes have been converted to practice on a large scale either because of unsatisfactory uranium removal efficiency and/or high costs associated with the implementation of the process technology.
Thus, there is a continuing need for a process for removing dissolved uranium from water which is simple and economical to carry out.
SUMMARY OF THE INVENTION
The present invention provides a process for removing dissolved uranium from water which meets the need described above and overcomes the deficiencies of the prior art. A preferred process of this invention comprises the steps of (a) mixing phosphoric acid with the water, (b) mixing a source of calcium such as calcium hydroxide with the phosphoric acid-water mixture produced in step (a) to thereby form calcium hydroxy apatite (synthetic bone ash) which in turn reacts with and complexes as well as occludes at least a portion of the uranium in the water to form a precipitate thereof and (c) separating the precipitate from the water.
Another process of this invention for removing dissolved uranium from water is comprised of the steps of (a) mixing particulate bone ash (synthetic or natural) with the water to form calcium hydroxy apatite therein, (b) mixing calcium hydroxide with the calcium hydroxy apatite-water mixture formed in step (a) to thereby cause the calcium hydroxy apatite to react with and complex as well as occludes at least a portion of the uranium in the water to form a precipitate thereof and (c) separating the precipitate from the water.
The mixing of particulate bone ash with the water in accordance with step (a) above can include first mixing the bone ash with an aqueous acid solution so that the bone ash is at least partially dissolved in the aqueous acid solution and then mixing the aqueous acid solution containing the bone ash with the water. Also, the flocculating of the precipitate formed in step (b) can be carried out prior to step (c) to facilitate the separation of the precipitate. When the water contains fluoride ion, the process can include the step of mixing aluminum sulfate with the water as a part of step (a) so that the aluminum sulfate hydrolyzes and reacts with and forms a precipitate with the fluoride ion which occludes as well as complexes with some of the dissolved uranium from the water.
It is, therefore, a general object of the present invention to provide a simple and economical process for removing dissolved uranium from water.
Other and further objects, features and advantages of the invention will be readily apparent to those skilled in the art upon a reading of the description of preferred embodiments which follows when taken in conjunction with the accompanying drawings.


REFERENCES:
patent: 2766204 (1956-10-01), Lowe
patent: 2882123 (1959-04-01), Long
patent: 2885258 (1959-05-01), Bain
patent: 2981593 (1961-04-01), Pagny
patent: 3764553 (1973-10-01), Kirby
patent: 5711015 (1998-01-01), Tofe
patent: 5994608 (1999-11-01), Pal et al.
patent: 5994609 (1999-11-01), Luo
Publication entitled Immobilization Of Uranium In Contaminated Sediments By Hydroxyapatite Addition by Arey et al.,Environ. Sci. Technol., vol. 33, pp. 337-342 (1999).

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