US2918700A

US2918700A - Radioactive concentrator and radiation source

Info

Publication number: US2918700A
Application number: US522187A
Authority: US
Inventors: Loranus P Hatch
Original assignee: Individual
Current assignee: Individual
Priority date: 1955-07-14
Filing date: 1955-07-14
Publication date: 1959-12-29
Anticipated expiration: 1976-12-29

Description

Dec. 29, 1959' L. P. HATCH RADIOACTIVE CONCENTRATOR AND mmmqxon SOURCE Filed July 14; 1955 p\5z 93 I06 INVENTOR. LORANUS R HATCH United States Patent RADIOACTIVE CONCENTRATOR AND RADIATION SOURCE Loranus P. Hatch, Brookhaven, N.Y., assignor to the United States of America as represented by the United States Atomic Energy Commission Application July 14, 1955, Serial No. 522,187

17 Claims. (Cl. 18-475) become an ever-increasing problem as the'atomic energy industry has developed. Various methods have been developed for concentrating and ultimately disposing of these radioactive materials. One method of disposing of radioactive liquid wastes has been disclosed in U.S. Patent 2,616,847, issued November 4, 1952, to Ginnell. This method takes'advantage of the well-known property of Montmorillonite clays to exchange cations with a solution, and to some extent also to adsorb cations. The sum of the two processes is generally referred to as adsorption and no distinction is made herein between these two processes.

The Ginnell process consists of bringing into contact a cation exchange mineral of the Montmorillonite group and a solution containing radioactive cations. The resultingsuspension is shaken until there is no change in the radioactivity of the solution as measured by determining .its specific activity.

selective filtration or other complex means, and heat treated to a temperature in the range 750 to 1000 C, to

fix the adsorbed radioactive cations.

I have found the above described method has limited value in large-scale use for several reasons. First of all, the method of batch contacts is inelficient and diflicult to handle, particularly for treating large volumes having high radioactivity. Secondly, for each batch contact only one equilibrium. stage is possible to adsorb the radioactive ions on the clay. Frequently further contact and separation steps are necessary to eifect a complete adsorption and separation of the resultant radioactive clay' from the supernatant liquids. These additional steps present serious problems when processing large quantities of radioactive liquids.

It is therefore an object to eliminate the difliculties of a bath process by providing a continuous method of bringing an aqueous solution containing radioactive cations into uniform contact with a composition consisting essentially of a permeable clay aggregate to bring about efficient adsorption of said radioactive cations onto the clay, separating the solution from the clay, and subsequently heating the clay to a temperature in the range 750 to 1000 C. to fix the radioactive cations in the clay structure. Another'object of the invention is to provide a method of forming a chemically stable radioactive bed suitable for flowing. liquids therethrough, thereby to i'rradi'ate said liquids. A further objectof the present Thereafter the suspended clay is separated from the solution by centrifugatiomf invention is to provide a method of rendering a bed of Montmorillonite clay permeable to ,allow free flow; of

liquids containing radioactive cations through said bedthereby to adsorb said radioactive ions on said clay bed.

Another object is to provide a composition which .is a source ofnuclear radiation and is suitable for flowing liquids therethrough to irradiate the liquids.- Still' a further object is to provide a method of disposinglof' radioactive cations in solution by passing the solution through a bed of the kind described herein. 7

With these and other objects in mind the method of this invention, broadly speaking, comprises forming a paste consisting essentially of a mixture of Montmoril-'.

lonite clay, water and a material that combines with the clay to form a stable aggregate in the presence of water, passing said paste through a small aperture into a volume: of water to form a bed of permeable clay rods, displacing said volume of water with a solution containing radioactive cations to adsorb the cations from said solution, separating the rods from the solution and heating the bed of clay rods to a temperature in the range750 1000 C. q I I Because of its largesurface area, a packed bed of wet Montmorillonite clay is impervious to. fluids, as is typical of clayey masses. Thus, methods of utilizing the cation exchange capacity of Montmorillonite have until now been limited to batch contact of finely divided clay with V cation-containing liquids followed by separation ofliquid and solid phases. This method is cumbersome when large, quantities of solutions are involved, particularly when'. treating radioactive solutions. Further, when suspended in water, fine particles jofclay do not settle .out'readily,

even under quiescent conditions, and filtration is di flicult Complete separation of solid and liquid phases is impera-.,

tive, because after treating radioactive solutions, the clay;

becomes highly radioactive. U

My method, which produces stable aggregations'fo fi Montmorillonite clay, permit continuous processing ofliquids containing radioactive ions with complete separa tion of solid and liquidphases, According to this method,

, Montmorillonite clay is mixed wtih a material that combines with the clay to form clay aggregates that are stable in the presence'of water. Water-soluble synthetic polyelectrolytes mixed with clay particles form -stable clay aggregates even in the presence of water.. I have discovered that these materials, contrary to expectations,

do not reduce the cation exchange capacity of the clays. Moreover, the stable, aggregated clay composition in the form of extruded clay rods is: highly permeable to liquids passing through a bed prepared therefrom. While,- the action of these polyelectrolytes is not completelyf understood, it'isbelieved that the polymer molecules are;

sutficiently long to form a bridge that binds the indie vidual ultimate, clay particles. This process is probably one of ion exchange. Suitable, water-soluble polymers; of this type are readily available under a variety of trade names.

The preparation ,and composition,

In practicing the invention water is added to-a mixture of clay and an aggregative material of the type defined, above to form a paste. This paste is then extruded,

, Patented Dec. 2 1

I have found that one of these that may I be used with advantage is the commercially available product Krilium. i I I of Krilium type resins suitable for use in practicing the J present invention are disclosed in U.S. Patent No toform a permeable bed. The small clay rods retain their form in water and in solutions containing radio active ions. Even with the aggregating agent adsorbed not impaired.

The clay aggregates are surprisingly stable in Water moving over them. This permits continuous ion exon the clay, the cation exchange capacity of the clay is change with a solution containing radioactive cations fiowing'through the clay bed. Equilibrium is attained.

with complete separation between the solid clay phase and the efiluent. After the process has been in operat on for some time the clay rods reachv their maximum capacity for adsorption of the radioactive ions. The clay' rods are separated and then heated to a temperature in the range-750 to 1000 C. to fix the radioactive cations in the clay- The fired clay containing the fixed radioactive cations may thenbe stored for permanent disposition. I

I have also found that the fired clay is extremely useful as source of gamma or beta radiation. Since the clay rodsslargely hold their shape after heat-treatment, the mass of material remainshighly permeable to fluids. The fired clay consists essentially of closely packed ceramic rods with the radioactive cations fixed therein. The clay aggregative material is believed to be volatilized by the heat treatment.

When the clay paste is extruded into a container made of a refractory material, all the further steps of the process may be performed without handling the clay further. The container with the bed of ceramic rods con-' taining radioactive cations contained therein, is useful as a; convenient packaged source of radioactivity; When used as a gamma'source, the material to be irradiated does not have to be in direct contact with the clay, although. it may be. When used as a beta source, direct contact is necessary because of the relatively low penetrating power of the beta, radiation.

Liquids to be irradiated, such as pharmaceuticals or food products, may

. thus be flowed directly through the clay bed to expose the material to beta or gamma irradiation without fear of chemical contamination.

The inventionwill be more clearly understood by refe'rence to the accompanying drawing which is a representation, partly in section, of an ion exchange column containing a packed bed in accordance with this invention.

The following examples illustrate the effectiveness of my invention 'in providing a method and composition permitting the processing of radioactive fluids. It is not intended to limit the scope of the invention by the details set forth in these examples. 1

Example I and/or calcium salt of partially hydrolyzed polyacrylonitrile. The clay and the Krilium were mixed with 35 millilit ers. of water to produce a paste-like mass. This paste was then placed in the chamber of an extrusion press, and anozzle having a diameter of was put in place. The extrusion chamber was evacuated with a vacuum pump. With the vacuum stillapplied the piston was advanced until a small quantity, of clay passed through the nozzle. At this point the vacuum was broken, and the clay was continuously extruded into a water-filled container. As

- the clay entered the water it broke into short discrete rods, which packed loosely and randomly to form a bed.

' the sea water.

The radioactive cesium chloride was then passed continuously through the column, initially displacing the water. The activity in the column effluent was determined periodically by measuring the activity of aliquot samples of the efiluent during the flow period. When the clay reached its maximumcapacity for adsorption, the water was removed from the column, and the clay was heated to a temperature in the range 750 to 1000" C. A

synthetic sea water solution was then flowed through the column to provide an accelerated determination of the effect of leaching from the column. The sea water had a composition approximatelyv the same as that from the Atlantic Ocean. Over a period of 52 days it was found that less than .1% of the adsorbed cesium was leached by The exchange capacity of the clay was calculated to be 1.1 milliequivalents per gram. In another identical experiment except that the caly was prepared without the Krilium,'the exchange capacity of the clay was 1.06 milliequivalents .per gram. This illustrates the fact that the clay 'aggregative materialdoes not impair the cation exchange capacity of the clay rods; in fact specific activity of 197x105 counts per milliliter per in this case there was an increase in the ion exchange capacity even though the additional material was present.

Example II In this experiment two columns were prepared by the procedure described in Example I. The first column was prepared with extruded clay rods containing .5% Krilium by' weightof clay, while the second column was made up without Krilium. .A solution containing .04 molar of the clay bed prepared according to the method of the present invention.

7 Example 111 A solution of mixed fission products from which the major part of uranium was. removed was found to have a minute. A clay column was prepared by the extrusion of a mixture of 200 grams of dried Montmorillonite clay (Filtrol Corporation lot #R-2532), 1.75 grams of Krilium and milliliters of water, by the procedure described in Example I. The solution was flowed through the column, after which the column was drained and the clay heated to a temperature in the range 750 to 1000 C. Thereafter the clay was leached by flowing a solution of a synthetic sea water through the column to provide an accelerated determination of the effect of leaching. The sea water had acomposition approximately the same as that from the Atlantic Ocean. Leaching over a period. of 52 days released less than .1% of the radioactivity- In carrying out the method, it is preferable that the pH of the solution be maintained in the range 4 to 9. When the solution is more acid or basic than. this, there appears to be a decrease in the amount adsorbed so the a larger volume of clay is required per volume of solution processed. The time of contact and ratio of clay to solution treated may. easily be found by simple experimental procedures well known in the art.

The composition of the clay before extrusion is quite important. I have found that by preparing a composition. having 4010 45% by weight of water and. from. .2% to 1% of a synthetic polyelectrolyte. by weight of clay an op-.

timum mixture is obtained. The concentration of the polyelectrolyte used depends somewhat on the particular compound usd.- In the case of Krilium. .5 by weight.

5. of clay is preferred. At a concentration above 1% by weight of clay no substantial benefit is obtained.

While it is preferable, it is not necessary to heat the clay to constant weight before preparing the extruded clay. Where the clay is not subjected toa preliminary heat treatment, its water content should be known for optimum composition requirements.

I have found that clay rods having diameters in the range & inch to A; of aninch may conveniently be used in the preparation of the clay beds. I prefer to use rods having a diameter of approximately inch. This dimension provides the most favorable conditions for ion exchange and mechanical strength of the aggregated clay rods.

The process may be carried out in equipment such as that shown in the drawing. With reference to the figure, the ion exchange assembly includes a cylindrical stainless steel casing 89 formed of separable upper and

lower portions

88 and 90 having mating flanges 102 and a pair of bolted clamping rings 100 therefor. Casing 89 is in two parts to provide easy access to the interior, and, when held together by the clamping rings 100 bearing on the flanges 102, the casing forms a continuous cylinder.

The casing 89 encloses an inner impervious cylindrical container 80 of a refractory material such as silicon carbide. The inner container 80 has a smaller outside diameter than the inside diameter of the casing 89, and is centered therein by an outwardly directed flange 84 on the upper end of container 80 and by a guide ring 112 on the upper end of casing portion 90. Thereby an-annular space 70 is formed between the inner container 8 and the casing 90.

The outer ends of casing 89 are capped with

heads

91 and 93. The upper head 91 has an annular ring 92 sealed to upper casing portion 88. On its under surface the ring 92 is provided with a gasket 104 against which a boss 108 on flange 84 is caused to bear in order to seal theinner container from the annular space 7 0. The lower head 93, in turn, has an annular ring 94 sealed to the lower casing portion 90. On its upper surface the ring 93 has a gasket 106 against which an annular boss 110 is caused to bear to seal the lower end of the inner container from the annular space 70.

A flanged pipe fitting 124 fills the central opening in the upper head ring 92. The fitting 124 is flanged and held in fluid-tight relation by spaced screws 132 causing the fitting to bear on an O-ring gasket 105. The central opening in the lower ring 94 is threaded to receive a ball check valve 146. The check valve permits filling the container with liquid before beginning the flow of the radioactive solution to the column.

To support the packed bed and to distribute the incoming liquid through the bed, a porous disk 86 of a refractory material, such as silicon carbide, is supported on an inner shoulder 82 at the lower end of the container.

'When the material being treated is flowing upward, only one such disk is required. When the liquid being treated flows down, it is necessary to provide an additional disk or similar distribution means across the upper end of container 80. In the latter event, the ball check valve is replaced by a manually operated valve.

When the liquid being treated is flowed upward through the column, the ball valve 146 is connected by

pipes

72 and 56 to a feed storage tank 60.

Valves

50 and 52 are inserted in

pipe lines

72 and 56 to control the flow of fluid. A pump 54 transfers fluid from the storage tank 60 to the column. The outlet fitting 124 may be connected to a waste receiver.

The equipment is prepared for use by inserting a silicon, carbide container 80 fitted with a porous silicon carbide disk 86 into the lower portion 90 of the cylindrical casing. The upper portion 88 of the casing (with head 91) is placed on the lower portion 90 and the clamping rings 100 are placed on adjacent flanges 102 and tightened on the flanges by means of bolts to draw the two portions 6 of the casing together. This action forces the annular" bosses 108 and 110 against the

gaskets

104 and 106 respectively, to seal the interior of the container from the annular space 70 surrounding it. The container 80 is then partly filled with water. Any water that-passes through the porous disk 86 is retained in the space below it by the valve ball 146. The Montmorillonite clay mixture is extruded in rod form intothe container 80 to fill it and keep the clay rods covered with water as shown in the drawing. When the container is filled, the fitting 124 is secured in place by screws 132. The column is now ready for use.

Then, after the desired adjustments have been made to it, the solution containing radioactive cations enters the column from storage tank 60 through the feed pipe 72.- As the solution passes upwards through the bed of clay rods, the radioactive cations are adsorbed on the clay. After the process has been in operation for some time the clay reaches its adsorptive limit and radioactivity will be detected in the effluent solution. When saturation has been reached, the upper casing portion 88 is removed, and the container 80 with its load of clay is removed from the lower housing 90. The container 80 with its bed of clay rods is drained and is then placed in a furnace where it is heated to a temperature in the range 750 to 1000 C. to fix the adsorbed cations in the clay.

The impervious refractory container 80 with its bed of ceramic rods is a convenient packaged source of radiation for use in irradiation of liquids. This source has several unique advantages. The labyrinthine passages between the rods in the clay bed insure that all of the liquid passing through will come in close contact with the radiation. A further advantage of this radiation source is that the clay rods are physically and chemically stable, permitting a wide variety of liquids to be irradiated without risk of radioactive or chemical contamination.

Since many embodiments can be made of the present invention and since many changes can be made in the embodiment described above, it is to be understood that the above description is to be interpreted as illustrative only and not in a limiting sense.

I claim:

1. A method of preparing a clay bed which comprises forming a paste consisting of water, Montmorillonite clay, and a synthetic water-soluble polyelectrolyte having a weight average molecular weight of at least 10,000 and having a structure derived by the polymerization of at least one mono-olefinic compound through the aliphatic unsaturated group, said structure being substantially free of cross-linking, shaping said paste into rods and passing said rods into a volume of water to form a permeable clay bed. T

2. A method of preparing a clay bed which comprises forming a paste consisting of water, Montmorillonite clay and a synthetic water soluble polyelecetrolyte having a weight average molecular weight of at least 10,000 and having a structure derived by the polymerization of at least one mono-olefinic compound through the aliphatic unsaturated group, said structure being substantially'free' of cross-linking to aggregate the clay in water and extruding said paste into a volume of water to form a permeable bed of short clay rods.

3. A method of preparing a clay bed comprising the steps of forming a paste consisting of water, Montmorillonite clay and the sodium salt of a partially hydrolyzed polyacrylonitrile and extruding said paste into a volume of water to form a permeable bed of short clay rods.

4. A method of preparing a clay bed which comprises forming a paste consisting of a mixture of water, Montmorillonite clay and the calcium salt of a partially bydrolzed polyacrylonitrile and extruding said paste into a volume of water to form a permeable bed of short clayrods.

5. A method of preparing a clay bed which comprises forming a paste consisting of Montmorillonite clay, a

- synthetic water-soluble polyelectrolyte having a weight average molecular weight of at least 10,000 and having a structure derived by the polymerization of at least one mono-olefinic compound through the aliphatic unsaturated group, said structure being substantially free of cross-linking, in the amount of .2 to 1% by weight of clay'and water in the amount of 40 to 45% of the total weight of the paste mixture, and extruding said-paste into a volume of water to form a permeable bed of short clay rods.

6. A method of preparing a clay bed which comprises forming a paste consisting of Montmorillonite clay, about .5 by weight of the sodium salt of a partially hydro- .lyzed polyacrylonitrile and water in the amount of 40 to 45% of the total weight, and extruding said paste into a volume of water to form a permeable bed of short clay rods.

7; A method of preparing a clay bed which comprises forming a paste consisting of Montmorillonite clay, about I .5% by weight of the calcium salt of a partially hydrolyzed polyacrylonitrile and Water, equal to 40 to 45% of the total weight of the paste mixture.

8. A method of preparing a clay bed which comprises forming a plastic mixture consisting. of Montmorillonite clay, 40 to 45% by'weight of water and a synthetic watersoluble polyelectrolytehaving a weight average molecular weight of at least'10,000 and having a structure derived by the polymerization of at least one monoolefinic compound through the aliphaticunsaturated group, said structurebeing substantially free of cross-linking, and extruding said paste into a volume of water reform a permeable bed of short clay rodshaving diameters of ,4, inch to 1A; inch,

9. A. method of preparing a clay bed which comprises forming a plastic mixture consisting of Montmorillonite I clay, 4.0 to 45% by weightof water and a synthetic water-soluble polyelectrolyte having a weight average molecularweight of at least 10,000 and having a structure derived by the polymerization of at least one mono olefinic compound through the aliphatic unsaturated group,ysaid structure being substantially free of crosslink-ing and extrudingsaid paste into a volume of water to form a permeable bed of short clay rods having diameters of about & inch.

, 10. Clay rods consisting essentially of a mixture of water, Montmorillonite clay and a watersoluble synthetic polyelectrolyte having a weight average molecular weight of at least 10,000 and having a structure derived by the polymerization of at least one mono-olefinic compound through the aliphatic unsaturated group, said structure being substantially free of cross-linking.

11. A method of preparing a chemically resistant radiation bed suitable for irradiation of liquids flowing therethrough which comprises forming a plastic mixture consisting essentially of water, Montmorillonite clay and a.

synthetic water-soluble polyelectrolyte having a weight average molecular weight of at least 10,000 and having a structure derived by the polymerization of at least one mono-olefinic compound through the aliphatic unsaturated group, said structure being substantially free of cross-linking, shaping said mixture into rods and forming said rods into a volume of water to form a permeable bed of randomly oriented clay rods, flowing a solution containing radioactive cations through said bed, thereby toabsorb said cations on said clay rods, separating the clay rods from the solution and thereafter heating the rods to a temperature in the range 750 to 1000 C. to fix the ions chemically in the clay.

12. A method of preparing a chemically resistant radiation bed suitable for irradiation of liquids flowing therethrough which comprises forming a paste consisting of water, Montmorillonite clay and a synthetic watersoluble. polyelectrolyte having, a weight average moles-- ular weight of at least 10,000 and havinga structure; den rived by the polymerization of at: least one monorolefinic compound, through the aliphatic unsaturated group, said structure being substantially free of cross-linking, extruding said mixture into a volume of water to formga. permeablebed of randomly oriented clay rods, flowing: a. solution containing radioactive cations through said. bed, thereby to adsorb said ions on said clay rods, separating the rods from the solution,- drying said rods and there" after heating the dry rods to a temperature in the range: 750 to 1000 C.

13. :A method of preparing a chemically resistant. radiation bed which comprises forming a plastic mixture consisting of Montmorillonite clay, 40 to 45 by weight. water and .2 to 1% of a synthetic water-soluble polyelectrolyte having a weight average molecular weight of at least 10,000 and having a structure derived by the polymerization ofat: least one mono-olefinic compound through the aliphatic unsaturated group, said structure; being substantially free of. cross-linking, extruding said: mixture into avolume of water to form a permeable bed of randomly oriented clay rods, flowing a. solution containing radioactive. cations through said bed thereby to adsorb said-ions on said clay rods, separating the rods from the solution, drying said bed and then heating it to a temperature in therange 750 to 1000 C.

j 14. The method according to claim 13 in which thepaste is extruded into rods having diameters girl the range ,6 inch to inch.

15. The method accordiugto claim 13 in which the paste is extruded into rods having diameters of about.

/32 inch.

16. A composition suitable for irradiating liquids flowing therethrough which comprises a permeablebed ofrandomly oriented short ceramic rods formed from. Montmorillonite clay anda synthetic water-soluble polyelectrolyte having a weight average molecular weightof at least 10,000 and having a structure derived by the polymerization of at least one mono-olefinic compound through the aliphatic unsaturated group, said structure. being substantially free of cross-linking, having small diameters and having a radioactive material chemically bound with the clay.

17. A composition suitable for irradiating liquids flowing therethrough which comprises a permeable bed of randomly oriented ceramic rods formed from Montmorillonite clay and a synthetic water-soluble polyelectrolyte having a weight average molecular weight of at least 10,000 and having a structure derived. by the polymerization of at least one mono-olefinic compound through the aliphatic unsaturated group, said. structure being substantially free of cross-linking, having diameters of about of an inch and having a radioactive; material chemically bound with the clay.

References Cited in the file of this patent UNITED STATES PATENTS 1,239,227 Saubermann Sept. 4, 1917 1,296,472 Brand Mar. 4, 1919 1,817,329 Wichmann Aug. 4, 1931 2,025,762 Malinovsky Dec. 31, 1935 2,072,460 Malinovsky Mar. 2, 1.937 2,193,570 Seaton Mar. 12, 1940 2,373,468 Glenn Apr. 10, 1945 2,440,743 Gary May 4, 1948. 2,477,386 McCarter July 26, 1949 2,616,847 Ginnell Nov. 4,, 19521 2,637,890 Ramsay May 12, 1953 2,749,590 Kilpatrick June 12,. 1956-- 2,759,899 Hanson Aug. 21, 1956)

Claims

11. A METHOD OF PREPARING A CHEMICALLY RESISTANT RADIATION BED SUITABLE FOR IRRADIATION OF LIQUIDS FLOWING THERETHROUGH WHICH COMPRISES FORMING A PLASTIC MIXTURE CONSISTING ESSENTIALLY OF WATER, MONTMORILLONITE CLAY AND A SYNTHETIC WATER-SOLUBLE POLYELECTORLYTE HAVING A WEIGH AVERAGE MOLECULAR WEIGHT OF AT LEAST 10,000 AND HAVING A STRUCTURE DERIVED BY THE POLYMERIZATION OF AT LEAST ONE MONO-OLEFINIC COMPOUND THROUGH THE ALIPHATIC UNSATURATED GROUP, SAID STRUCTURE BEING SUBSTANTIALLY FREE OF