US2992888A - Process of treating or forming an insoluble plutonium precipitate in the presence of an organic surface active agent - Google Patents

Description

July 18, 1961 J. H. BALTHls 2,992,888

PROCESS OF TREATING OR FORMING AN INSOLUBLE PLUTONIUM PRECIPITATE IN THE PRESENCE OF AN ORGANIC SURFACE ACTIVE AGENT Filed Dec. 29, 1944 Cofo/-med l W rz. ...3,

[ofc/"med 20% Ares/dene l l l I l l 02468/0/2/4/6/6202 77M;- OF QU/fscf/VCE BEFORE CONT/20u50 Cf/v TQM-06,4 770A/ /N M/A/urEs IN VEN TOR.

2,992,888 Patented July 18, 1961 PRocEss F TREATING on FORMING AN 1N- SOLUBLE PLUTONIUM PRECIPITATE 1N THE PRESENCE OF AN ORGANIC SURFACE ACTIVE AGENT Joseph H. Balthis, Wilmington, Del., assignor to the United States of America as represented by the United States Atomic Energy Commission Filed Dec. 29, 1944, Ser. No. 570,419 4 Claims. (Cl. 23--14.5)

This invention relates to a procedure for processing of materials containing the element of atomic number 94, known as plutonium, -for separating the plutonium from extraneous matter such as substances of the kind present in neutron irradiated uranium exemplified by uranium and especially fission products, and the like radioactive contaminants. More particularly, this invention concerns a separatory and concentration procedure involving the use of a iluoride type of carrier wherein certain improved procedure is employed in forming the carrier.

As described herein, the isotope of element 94 having a mass of 239 is referred to as 94239 and is also called plutonium, symbol Pu. In addition, the isotope of element 93 having a mass of 239 is referred to as 93239 Reference herein to any off the elements is to be understood as denoting the element generically, whether in its liree state or in the form of la compound, unless indicated otherwise by the context.

Elements 93 and 94 may be obtained 1from uranium by various processes which do not form a part of the present invention including irradiation of uranium with neutrons from any suitable neutron source, but preferably the neutrons used are obtained from a chain reaction of neutrons with uranium.

Naturally occurring uranium contains a major portion of 92U238, a minor portion of 92U235, and small amounts of other substances such as UX1 and UX2. When a mass of such uranium. is subjected to neutron irradiation, particularly with neutrons of resonance or thermal energies, 92U238 by capture of a neutron becomes 92U239 'which has a half life of about 23 minutes and by beta decay becomes 93239. The 93239 has a half life of about 2.3 days and by beta decay becomesv 94239. Thu-s, neutron irradiated uranium contains both 93239 and 94239 but by storing such irradiated uranium for a suitable period of time, the 93239 is converted almost entirely to 94239.

In addition to the above-mentioned reaction, the reaction of neutrons with iiss-ionable nuclei such as the nucleus of U235 results in the production of a large number of radioactive fission products. As it is undesirable to produce a large concentration of these tission products which must, in view or their rad-ioactivity, be separated from the 94239 and further as the Weight of radioactive ssion products present in neutron irradiated uranium is proportional to the amounts of 93239 and 94239 for-med therein, it is preferable to `discontinue the irradiation of the uranium by neutrons when the combined amount of 93239 is equal to approximately 0.02 percent by weight of the uranium mass. At this concentration of these substances, the concentration of ssion elements which must be removed is approximately the same percentage.

A number of process have already been proposed for accomplishing the separation and concentration of Pu. Certain of these processes are generically known as the bismuth phosphate type process and the wet uoride type of process. These processes are the invention of others and the detailsof the processes are described in copending applications as for example application Ser.

No. 519,714, now U.S. Patent No. 2,785,951, issued March 3, 1957, to be referred to hereinafter, which gives details relative to such processes. Consequently, all of the details of operation of the aforementioned [processes are not described herein.

In some instances, it has been customary to utilize in the same separation and recovery process both the bismuth phosphate treatment and lanthanum uoride treatment. The present invention in its preferred embodiment concerns the formation of the uoride type of precipitates exemplified by a lanthanum lfluoride precipitate carrying Pu. In processes of the aforementioned type, either combination processes Where several dilerent types of carriers are used, including the formation of a uoride precipitate, or processes Where fluoride compounds are more or less directly precipitated, the formation of these fluoride compounds carrying Pu or iission products or comprising a fluoride compound of Pu may present certain diiculties. For example, one carrier precipitate commonly formed is lanthanum fluoride. This precipitate has been formed under acid conditions by adding to the acid solution a source of fluoride ions and a source of lanthanum ions. The characteristics of the precipitates formed are such as to present some diiculty of separation because of the finely divided nature and `dispersion thereof. That is, it has been required to centrifuge these precipitates at relatively hgh speeds for extended periods or to employ a special filtration technique dior separation from the surrounding liquid. It has also been required to precipitate the LaF3 in two portions, separating after each precipitation.

In accordance with the present invent-ion, it has been found that a precipitate of better characteristics may be formed by the use of surface active agents either alone or in conjunction with certain other modifications of precipitation conditions.

The meaning of the terms bismuth phosphate type of process, fluoride type of process, product and byproduct precipitate, coformed, preformed, and similar terms will be apparent as the description proceeds.

The invention has for 'one object, to provide improvements in methods for the separation and recovery of plutonium.

Another object is to provide a method of separating plutonium by procedure wherein certain additions different from those heretofore used are employed.

Another object is to provide improved procedures for forming certain precipitates.

Still another object is to provide a new procedure patn'cularly useful in forming a uoride carrier precipitate containing Pu.

Another object is to provide a new procedure for forming by-product fluoride carrier precipitates.

Still another object is to provide a procedure for forming fluoride carrier precipitates which exhibit improved characteristics.

Another and particularly important object is to improve the centrifuging characteristics of lanthanum fluoride precipitates.

Still Ianother object is to provide a type of process which lends itself to combination with steps already known or practiced.

Another object is to provide a type of process which may employ the materials used in existing processes, but under Vdifferent conditions, and which may be carried out in existing equipment Without change, or with a @t equipment change.

Stili another object is to provide treatments for uoride precipitates which 4do not exert a detrimental effect on subsequent process steps to which the precipitates may usually be subjected.

Other objects will appear hereinafter.

I have found that Pu in admixture with various extraneous material may be separated and concentrated byY the use of the series of steps involving the formation of certain carrier precipitates. These treatments may be generally similar to known practice as respects reagents, temperatures and similar features. However, I have found that the formation of such carrier precipitates may be rendered simpler and more eilicient by rnodication of precipitation conditions, the use of surface active agents and other features as will be described in detail hereinafter. By the formation of the carrier precipitate under the conditions of the present invention, not only are the advantages previously obtained in the processes still obtainable, but there are Ialso obtained advantages such as the production of precipitates having improved centrifuging characteristics.

Illustrations of some of the types of carrier precipitates which may be improved by the present invention are described in application Ser. No. 519,714, filed January 26, 1944, Thompson and Seaborg, and reference is made to that application for further disclosure, details thereof being omitted from the present disclosure except Where necessary to an understanding of the present invention. As set forth in said application, it has been discovered that plutonium has more than -one oxidation state, including a lower oxidation state or states referred to herein as Pu@ in which the element is characterized by forming insoluble phosphates and fluorides and a higher oxidation state or states referred to as Pu@ in which the element forms soluble phosphates and fluorides.

In accordance with the present invention, for example, a fluoride type carrier precipitate such as a LaF3 precipitate as described in the aforementioned application would be formed by procedure involving the use of a surface active agent such as Aresklene or the like.

The solutions containing Pu which may be treated, and in which the fluoride precipitate may be formed by myinvention `are the same type of solutions as heretofore treated. A common type of solution containing Pu subject to separation and recovery procedures is a solution which has been initially processed by the bismuth phosphate type tof treatment. Such type of solution and its treatment are described in detail in application Ser. No. 519,714 aforementioned. These solutions comprise a nitric acid containing liquid having a content of Pu therein. The nitric acid solution may also contain other acids such as a content of phosphoric acid and oxalic acid. The solution may also contain cert-ain extraneous matter such as radioactive materials wh-ich the subsequently applied uoride precipitation treatments may eliminate or reduce. As indicated above, by means of a fluoride precipitation treatment applied to the solution containing the Pu inthe reduced (r) condition, the resultant iiuoride precipitate (product precipitate) carries the Pu away from extraneous matter. By means of a fluoride precipitation applied to the solution having the Pu in the oxidized (o) state (by-product precipitate), extraneous matter is carried away by the fluoride precipitate leaving the Pu@ in the supernatant liquid from this precipitation.

'Ihe formation of fluoride precipitates exemplied by lanthanum fluoride carrier precipitates may be accomplished in several different Ways. A preformed precipitate is produced by incorporating a source of an excess of fluoride ions such as excess hydrogen fluoride into the solution containing Pu in which the carrier precipitate is to be formed. Thereafter a source of lanthanum ions is added to the process solution. In other words, a prieformed precipitate is produced by procedure described as a lanthanum strike.

A coformed precipitate is produced by oper-ation described as a hydrogen fluoride strike. That is, the source of lanthanum ions is rst incorporated in the solution in which the carrier is to 4be formed, thereafter the hydrogen fluoride is added to cause the formation of the lanthanum fluoride precipitate.

Broadly, therefore, my invention may be applied to various type solutions in which the precipitates may be formed in various ways. The solutions to be processed by my invention preferably have -added thereto one or more surface active agents as may be required at substantially any time during the process dependent upon the particular composition and condition of the solution and the nature of the agent added.

For a further understanding of my invention and appreciation of some of the advantages of the invention in improving the characteristics of the precipitates obtainable, by the incorporation of surface active agents, a number of examples are set forth hereinafter. In general, for the purposes of comparison some runs are described in connection with the examples as carried out for the purposes of control. That is, some of the runs were carried out under various conditions as will be discussed but without the use of surface active agents in the process. It will be notedV that some improvement in the precipitate characteristics may be obtained by the control of certain conditions as will be discussed. Then examples were carried out in a manner substantially exactly the same as the particular control run -but with the addition of surface active agents in accordance with the present invention.

In order to make a more denite comparison, tests were made on slurries for determining the rate of settling and sedimentation volume. This was determined by pouring s-lurry (carrier precipitate plus surrounding liquid) into graduated cc. tapered glass tubes and recording the volume of sediment as a function of the time. By comparative tests with the controls and the runs comprising surface active agents an indication of the improvement obtainable `by employing a particular feature of the invention is given.

Another measurement which may be made is referred to herein as the centrifugation improvement factor. This is the ratio of centrifugable product in the supernatent from untreated precipitate (control) to that in the supernatant Afrom treated precipitates (precipitates in which agents in accordance with the presen-t invention have been incorporated). The slurries under such comparison are centrifuged substantially identically.

iIn further detail, this may be accomplished by pipetting, for example, one cc. samples from each of the mechanically stirred slurries to be compared, transferring to 3 cc. :glass tubes constricted at the bottom to retain solids while pouring off the lbulk of the supernatant. These samples are simultaneously centrifuged in these tubes under carefully controlled conditions (for example one minute at 220 G) followed by immediately pouring olf the supernatants into 50 cc. containers. The product content of the supernatants may be determined by measuring their alpha activity.

The term relative centrifugal force (RCF) as used herein is conventionaland refers to the maximum obtained. In the runs described the time indicated for centrifugation includes that required to reach the desired r.p.m. 'but does not 4include the time of coasting to a stop. .As will be observed as the description proceeds, in large scale continuous centrifuges a relative centrifugal force of greater than 1500 G is usually applied in order to cause satisfactory separation of the uoride carrier precipitate. On the other hand, when iluoride precipitates are `formed employing procedure in accordance with the present invention, a force of even below 500 G is in many instances ample to obtain satisfactory centrifugation.

An additional understanding of this aspect that prior procedure :has required thigh speed centrifuging may be had by reference to the following table of data covering continuous centrifugation operations:

In producing the iiuoride precipitates described as centrifuged in the preceding table, oxalic acid reduced solution was made of the normality in HF indicated. There -was then added a quantity of lanthanum ammonium nitrate solution to give a concentration equivalent to about 125 milligrams of Lai'3 per liter. This was added at about 3% per minute. The slurries (lanthanum uoride precipitates plus supernatant liquor) were digested at between 25 C. and 32 C. and then subjected to centrifuging. As may be observed from the table, when centrifuge speeds of greater than 1700 r.p.m. were employed, only about 11i/2% of the Pu was retained in the precipitate remaining unseparated. When the centrifuge speed was reduced to about one-half, namely, when an r.p.m. of about 870 was used the loss increased to about 15%.

It is therefore apparent from the foregoing that fluoride precipitates when prepared in a conventional manner have required relatively high centrifuging speeds to obtain reasonably satisfactory separation.

It has been found that the centrifuging characteristics of such lanthanum fluoride precipitates may be improved somewhat by subjecting them to vigorous agitation during formation. In general under normal conditions lanthanum uoride precipitate remains partially suspended in aqueous medium for one-half to three hours when agitation is interrupted. When the precipitate has been preformed, the almost transparent precipitate ilocculates after several minutes and settles to a relatively large volume of gelatinous sediment. VCoformed lanthanum fluoride is more opaque and settles more slowly to a smaller volume of less occulent sediment.

As indicated, it has been found that the degree of agitation during the formation of such precipitates affects the centrifuging characteristics of both preformed and coformed lanthanum iiuoride. 'Ihe ease of centrifugation for the precipitates obtained increases with'the rate of agitation employed during their process of formation. In carrying out these runs Where agitation was applied, identical paddle agitators were used. The preferred agitation under the particular circumstances involved the use of a bafed tank with the agitator revolving at 220 r.p.h. However, other rates of agitation may be used.

Both the preformed and coformed lanthanum fluoride precipitates were prepared by using 125 milligrams -per liter ofLa+3 and 0.5 N HF. The precipitates were Ydigested for one hour. The solutions treated and in which the precipitates were formed werestandard oxalic acid reduced solutions The effect of the agitation in improving centrifugability is indicated in the next table.

PERCENT OF ORIGINAL Pu IN SUPERNATAN'T AFTER I have found that, in general, by adding surface active agents in processes of forming precipitates of the class described, the characteristics of the resultant precipitates may thereby be substantially improved. The settling rates of such precipitates and other characteristics are improved yet at the same time the ability of the precipitates to carry Pu in the event the Pu is in a reduced condition, or to carry by-p-roducts in the event oxidizing conditions are present, is not impaired. That is, a precipitate of the class described prepared by the best procedure available including such modifications as employing rapid agitation during formation of the precipitate, may be further improved bythe utilization of surface active agents in accordance with the present invention.

The agents which may be used may be cationactive, anionactive, or non-ionic. As is known, there are an extremely large number of such agents available commercially. In the practice of the present invention it is possible to use commercially obtainable agents. Consequently, for convenience and practicability of description, reference will be made herein to the commercial name under which some of these agents are known. No attempt is made herein to enumerate all possible agents. Likewise, the invention is not to be regarded as limited as respects an agent manufactured by some particular method.

One agent which has been found to be quite satisfacf tory is Aresklene 400. This material is commercially obtainable and is stated to be a dibutyl-phenyl-phenol sodium disulfonate. Another agent which has been found to be quite useful is Neomerpin N. Likewise, this is a commercially obtainable compound stated to be an alkyl naphthalene sulfonic acid.

Many other surface active agents are described in Industrial and Engineering Chemistry, Industrial edition, for January 1941, and in a number of other publications. Still another agent which has been found to give good results when used in the present invention in lecithin. The commonly available commercial products are obf tained from soy beans and contain soya oil, free fatty acids and phosphatides. Soya lecithin is available in several different grades. For example Lipoidol is a loW cost technical grade. Yelkin C is a commercial product stated to be a Water dispersable grade of soya lecithin containing Carbitol (diethylene glycol monoethyl ether).

For the purposes of illustrating some of the specific embodiments of my invention, reference is made to the following examples.

ExampleI In this example the species of agent added was soya lecithin. Under this example a number of runs were carried out as will be described wherein the agent Was present during and after the formation of the precipitate. Also in the various different runs, different quantities of agent were added.

Run (a) was a control run. The starting solution was standard oxalic acid reduced nitric acid solution of the ltype already described. The solution contained Pu and had been subjected to prior bismuth phosphate treatment. The solution was in a condition to be subjected to a lanthanum iiuoride carrier precipitation treatment for carrying down the Pu.

A ml. sample of this solution was used for the control. The lanthanum fluoride carrier precipitate was formed therein by an HF strike. That is, approximately 10.4 ml. of a source of lanthanum ions (La+3) were incorporated into the solution. This source contained 2.5 mg. of Lat3 per ml. Thereafter there was added 4.1 ml. of concentrated HF incorporated at the rate of 3% per minute. The resultant precipitate was digested for 11/2 hours at room temperature. The slurry was poured into a l0() ml. tapered glasstube of the type already described under settling and sedimentation tests and permitted to settle, The observed settling as a function of "3 time, was noted and the data plotted as will be referred to in connection with FIG. 1 of the attached drawing forming a part -of vthe present application.

Run :(b) Vwas carried out substantially vthe same -as the preceding run excepting that there was present during the precipitate formation a content of soya lecithin. The amount added was approximately 22% weight based on the weight of lanthanum. Likewise in this run after digestion of the precipitate the slurry was poured into a 100 cc. bottle and the settling observed, the data being recorded as illustrated in FIG. 1.

Run (c) was carried out substantially identical with the preceding runs excepting that in this run the quantity of soya lecithin agent incorporated was 50%. This was incorporated before precipitation, and consequently was present during the precipitate formation. The settling data with respect to this run was recorded as indicated in FIG. l.

Run (d) was likewise similar to the preceding methods excepting that 22% soya lecithin was added after the lanthanum uoride precipitate had formed. In other words, the primary difference in this run over run (b) was merely the point or time of addition in the process, namely after the lanthanum fluoride precipitate had formed. The settling rate was observed and the data recorded as illustration in FIG. l.

Run (e) likewise Vwas generally similar to the preceding runs excepting `that in this run 40% lecithin was added .after "the precipitate had formed. The settling rate was noted and recorded as illustrated in FIG. l.

Referring now to FIG. 1 of the drawing, by reference to the control and comparison of `this curve with the other curves, it will be observed that the addition of the agent either before or after vprecipitate formation im proves the settling rate. It may be further noted that in the case of the particular agent under description, and the other conditions of the runs, that the addition of the agent after the precipitate formation gave a greater irnprovement in the settling rate. While this is significant with respect to the lparticular example described, it is desired 4to point out that in the instance of some agents, the greatest improvement may be obtained by having the agent present during the precipitate formation. In general, however, in all instances whether the agents be added before, during, or after precipitation, improvement may be obtained. Hence, it is not desired to limit the present invention as respects the exact time and point of agent addition.

Example :Il

In this example `the species of agent added to improve the fluoride carrier precipitate was agar-agar. This is a well known and vreadily available material, consequently, further description thereof is not required. Likewise, in this example a number `of runs were carried out wherein various amounts of the agar were incorporated under a variety-of' conditions. However, for the purposes of this example it appears satisfactory to describe merely a few of these runs illustrative of the action thereof.

`Run (f) constituted the .control.run. 100 ml. of starting solution-was employed for the control. This starting solution comprised an oxalic Lacid reduced nitric acid solution containing Pu which had been freed of at least a part of its contamination by preliminary treatments. There was incorporated in-to the solution approximately ml. of solution containing 2.5 mg. of La+3 per ml. Thereafter there was incorporated 0.8 ml. of concentrated HF added at the rate of 3% per minute. The resultant slurry was digested in a conventional manner and .poured into a container for observing `the settling in the manner comparable to that already described. The settling `of the control was observed and Vthe .data plotted as illustrated in FIG. 2.

Run (g) was exactly similar to the preceding runex- 1cepting that the solution was madeapproximately11%fin agar before forming the precipitate. That is, approximately 1.25 ml. of a 0.02 percent agar solution was added so that the agar wouldV be present during the formation of the lanthanum fluoride precipitate. After digesting 'in a manner comparable to the control, the slurry was poured into the graduated container for observing the settling rate. The data concerning this run is recorded in FIG. 2.

Run (h) was similar to the preceding examples excepting that the solution was made 10% in agar prior to precipitation. That is, approximately 12.5 ml. of the agar solution was incorporated. After precipitate formation and digestion, theslurry was poured into a container for observing the settling. The data on this run is recorded in FIG. 2.

A number of other runs were carried out wherein other concentrations of agar were tried. Since the data observed is to a large extent merely cumulative, inclusion herein is considered unnecessary.

Referring to FIG. 2, it will be noted that the incorporation of even the 1% agar improved the settling. The incorporation of the 10% of an agent still further increased the settling rate. The agar addition caused the rapid settling of the precipitate into a slimy oc somewhat on the voluminous side. The supernatants from the processes in which agar was used were not as clear as supernatants from operations where other agents were used. For example, as will be described. Aresklene not only gives rapid settling, but the resultant supernatant very quickly becomes completely clear.

Example Ill -In this species the agent used was Aresklene. Likewise under this example a number of runs were carried out for vpreparing iboth preformed and coformed precipitates. In addition the variation was made in the process of..permitting the slurries to undergo a period of quiescence prior to centrifuging. lIn all of the runs described in this example, the lanthanum fluoride precipita-te was formed by using .a concentration of La+3 of 125 mg. per liter. The concentration of hydrogen fluoride was 0.5 N. The type of solution treated was oxalic acid reduced nitric acid solution containing Pu of the type as already described.

yCertain data noted in respect to the several runs, is set forth inthe table which follows, .relative to the `percent of `product in supernatant after one minute of centrifugation at 220 G.

Y control.

It will be observed from the data set forth in the table .thatathe percentage of `product remaining in the supernatant in the runs where the agent hadbeenincluded was much smaller than in the control runs. This signifies that the addition of the agents permitted the centrifuging out `of a much larger quantity of product in the oneminute centrifugation at 220 G. Asindicated, a number of runs were conducted andthe results averaged, this information being recorded as illustrated in FIG. 3. Y It will be observedthat under the same circumstances the centrifugation loss when ani-.agent is present may be considerably less than half as maybe noted by comparison with the QA large number of other examples have been carriedout along the same general lines as have been `described in detail above. In these examples various vagents have been incorporated at various stages in the process of forming both preformed and coformcd precipitates. Likewise the liquids treated were of usual types. For convenience of consideration, the infomation respecting these further examples is summarized below in the following table IMPROVEMENT IN OENTRIFUGABILITY AOHIEVED BY SURFACE ACTIVE AGENTS AGENTS ADDED BEFORE PRECIPITATION OF Lara Centrimg./1. HF ugation Example Type of Flocculating agent of norim- No. precipitate La mality provement factor IV Coformed-.- 20% Aresklene 125 0. 5 8.0 V- do 20% Neomerpin N-. 125 0.5 4.0 VI do 50% Fixanol 125 0. 5 1. 0 VII- Preformed. 20% Aresklene 125 0. 5 1. 6 VIII... do 20% Neomerpln N-- 125 0. 5 2. 4

AGENTS ADDED AFTER PRECIPITATION AND ONE HOUR DIGESTION F LaFg IX Coformed.-- 20% Aresklene 125 1. 0 4. 3 d 20% Yelkin C 125 1.0 3.0 20% Aresklene 125 0. 5 4.3

20% Yelkin C 125 0. 5 3. 2

20% Neomerpin N 125 0.5 5. 0

20% Aresklene 125 1. 0 2. 2 d0 125 0. 5 1.2

As indicated above, the operation of the invention is not limited to a specific type agent. Satisfactory results have been obtained with anion-active, cation-active, and non-ionic agents. Information illustrating these different groups is set forth in the table set forth below. All of the agents added produced substantially improved results.

Agent present during Agent added after LaF3 LaF3 precipitation (testprecipitation (testing ing method: Add agent method: Coform LaFa in Classification tosolution,coform LaFg 0.2 N HF, add agent, of agents in 0.2 N HF, compare compare rate of settling rate of settling and sediand sediment volume to ment volume to that of that of untreated control) an untreated control) Aresklene 40G-rapidly Neomerpin N.

settling tlocs. Agar-rapid settling of Aresklene 400. Amon-active.- llocs occupying a large volume. Duponol G-larger sedi- Duponol G.

ment volume.

Duponol ME. Agar. Fixanol-rapld settling at high concentration of (lation-active- Slln'ine Kw rapd Soya lecithin (Yelkln C).

settling at high concentration of agent. Nonionic Tergitol Penetrant 04- some coagulation.

Example XX In this example soya lecithin lwas added -in a mannen the same as described, in three runs, using a centrifuge having a 12 bowl, to flocculate the LaFS-product precipitate produced by precipitation in 0.2 N HF. Twoy of the treated precipitates (slurries) were centrifuged at 410 G, the other at 1510 G. Product losses in the centrifuge efliuents were normal (1.9%, 1.3%, and 0.6%). It is apparent from the foregoing that by the use of the present invention it was possible to run the centrifuge at about one-third of the usual speed and obtain a separation substantially as good and in some instances better than in prior conventional operations. The separated precipitate was then solubilized by metathesizing to lanthanum-plutonium hydroxides by treatment with aqueous KOH. Metathesis waste losses -were normal. A nitric acid solu- 10 tion of the metathesized product behaved satisfactorily in a concentration cycle thereafter carried out.

Example XXI An aqueous nitric acid solution containing oxidized plutonium and radioactive fission products was provided with suicient bismuth in the form of nitrate to yield in the final mixture a bismuth concentration of 21/2 grams per liter. Sufficient phosphoric acid solution was Iadded to provide a `0.1 molar HgPO.,l solution upon precipitation of the bismuth as bismuth phosphate. The mixture was digested for one `hour at 75 C., then an amount of Neomerpin N equal to 20% by weight of the bismuth present was added and the mixture was digested for an additional half houJ.` during which the solution cooled to room temperature. 'Ihe mixture was then centrifuged to separate the bismuth phosphate precipitate and radioactive fission products. After the separation, the solution contained less than one-half as much residual fission products as contained in similar solutio-n formed in a control test ornitting the surface active agent but carried out under otherwise similar conditions.

Example XXII A solution containing oxidized plutonium and radioactive fission products was treated with suflicient hydrogen iiuoride solution to provide a final concentration of 0.2 N HF after precipitation. Sufficient lanthanum was -added as a 1% HNO3 solution of lenthanum ammonium nitrate to provide mg. of lanthanum per liter of solution. The mixture was digested at room temperature for 1/2 hour with agitation. 20% by weight of Aresklene, based on the weight of lanthanum present, was then added and the mixture was digested for one hour more at room temperature. It was then centrifuged to separate solid matter. IIhe centrifuging time for removing 4the precipitate was approximately one-fourth the time required for a corresponding separation in a control test under similar conditions but omitting the surface active agent.

The use of an -kyl-aryl alkali metal sulfonate, exempliiied by Aresklene, is preferred. However, various other agents also give materially improved results such as the use of Neomerpin N and soya. lecithin. In general, under average conditions around 15-30% by weight of the agent based on the weight of lanthanum is a satisfactory quantity to use either singularly or in the aggregate in the event more than one lagent is used. However, amounts from 1% to 200% have been tested and found to give improved results. In processes of the present type Where it is desired to obtain concentration, and it is desired to keep quantities to a minimum, the use of excess is preferably avoided but is not precluded. The use of large excesses might carry over into succeeding steps and require added steps for effecting their removal. In some instances, the improvement obtainable by the use of agents in `accordance with the present invention may be taken advantage of to permit reduction in the number of precipitations and centrifugations required for satisfactorily recovering all of the valuable component contained in lthe solution being treated.

In general, one of the advantages obtainable by the use of the present invention is to permit the obtaining of satisf-actory separation by using lower centrifuging speeds. This is illustrated by the ability, by the use of the present invention, to reduce the centrifugation speed of around 1700 G heretofore used in processes of the class described to about 420 G and still obtain satisfactory separation.

While in a number of the examples the preferred oper- `ation has been to incorporate the agents after the formi-ation of the precipitate, the invention is not limited in this respect. It is, however, generally preferred to employ La+3 strike and follow this operation by the addition of the agent. When using Aresklene, however, it has been noted that maximum improvement is usually obtainedrby an HF strike in the presence of the agent.

The use of agents in accordance with the present invention in processes for recovering the Valuable product, Pu, apparently does not adversely affect existing procedures to which the invention may be applied. That is, the addition of the agents does not strip the Pu from lanthanum iluoride carrier precipitates, and apparently does not inhibit the carrying of the Pu under process conditions. In instances where small quantities of the agents may be carried through the subsequent steps of the process by the carrier precipitate as, for example, through the metathesis into the solution of metathesized product, this residuum apparently does not interfere with the oxidation of Pu and has no yadverse effect upon subsequent concentration cycles which may be applied for concentrating or segregating Pu.

While my invention has been described as employed in preparing the fluoride type of precipitate, illustrated by lanthanum fluoride, since this constitutes the preferred embodiment as well as a type of precipitate frequently encountered in plant processes, my invention is not limited thereto. Similar procedure may be applied in the formation of other precipitates exemplified by the formation of potassium plutonium fluoride and plutonium peroxide precipitates or to BiPO4, CeF3, or other carrier precipitates containing Pu. In certain other instances precipitates which do not occulate or otherwise present difficulties of formation and separation may be improved by the application of the principles of my invention; for example, radioactive fission elements may be more completely separated with a BiPO4 by-p-roduct precipitate when a surface active agent is used, or the agents may also be used to flocculate LaFa by-product precipitates.

The process may be applied to solutions containing Pu from tracer amounts to several hundred milligrams per liter. The concentration of Lai3 ion may be from about 50 to 300 mg. per liter, added in several additions if desired. The concentration of HF may be within the range of about 0.2 to 2 N. While HF has been referred to as .the source of fluoride ions, other reagents such as NaF, KF, and the like may be used. Such details are described in other copending applications and form no part of the present invention excepting that in the present invention it has been possible in many instances to use lower concentrations and obtain satisfactory results. However, my invention is not limited in these respects as the concentrations of the reagents suggested lare merely guides to preferred practice. Likewise, metathesis refers to an .operation customarily Yemployed in processes of the pres ent type and involves the use of alkali metal hydroxides and/or carbonates in a process of converting uoride precipitates to .acid solutions thereof. Since such processes are described in detail in other applications, description herein is unnecessary.

It is to be understood' that all matter contained in the above description and examples shall be interpreted as illustrative and not 'limitative of the scope of this invention, and it is intended to claim the present invention as broadly as possible in view of the prior art.

I claim:

l. In a process for the separation of plutonium from a solution containing la compound of plutonium and compounds of other elements, in which an insoluble precipitate is form-ed in said solution and the precipitate together with its associated plutonium is thereafter separated from the supernatant solution, the improvement which comprises subjecting said precipitate to the action of dibutyl-phenylphenol `sodium sulfonate prior to separating said precipitate from said supernatant solution.

2. In a process lfor the separation of plutonium from a solution containing a compound of plutonium and cornpounds of other elements, in which 4an insoluble precipitate is formed in said solution and the precipitate together with its associated plutonium is thereafter separated from the .supernatant solution, the improvement which comprises forming said precipitate in the presence of dibutyl-phenylphenol sodium sulfonate.

v3. In a process in which lanthanum fluoride is precipitated in an laqueous solution and thereafter separated from the supernatant solution, the improvement which comprises effecting said precipitation in the presence of `dibutyl-phenylphenol sodium sulfonate.

4. In a process in which bismuth phosphate is precipitated in an aqueous solution and thereafter separated from the supernatant solution, the improvement which comprises etfecting said precipitation in the presence of dibutyl-phenylphenol sodium sulfonate.

References Cited in the tile of this patent UNITED STATES PATENTS 1,697,543 Seidler Ian. l, 1929 1,792,863 Peet l Feb. 17, 1931 2,099,079 Rumscheidt et al. Nov. 16, 1937 2,408,059 -Gareld et al. Sept. 24, 17946 OTHER REFERENCES AEC Report No. CN-1409, semimonthly report for period ending March 31, 1944p-age 7, declassiiied March 19, 1957, 11 pages.

Claims (3)

1. IN A PROCESS FOR THE SEPARATION OF PLUTONIUM FROM A SOLUTION CONTAINING A COMPOUND OF PLUTONIUM AND COMPOUNDS OF OTHER ELEMENTS, IN WHICH AN INSOLUBLE PRECIPITATE IS FORMED IN SAID SOLUTION AND THE PRECIPITATE TOGETHER WITH ITS ASSOCIATED PLUTONIUM IS THEREAFTER SEPARATED FROM THE SUPERNATANT SOLUTION, THE IMPROVEMENT WHICH COMPRISES SUBJECTING SAID PRECIPITATE TO THE ACTION OF DIBUTYL-PHENYLPHENOL SODIUM SULFONATE PRIOR TO SEPARATING SAID PRECIPITATE FROM SAID SUPERNATANT SOLUTION.

3. IN A PROCESS IN WHICH LANTHANUM FLUORIDE IS PRECIPITATED IN AN AQUEOUS SOLUTION AND THEREAFTER SEPARATED FROM THE SUPERNATANT SOLUTION, THE IMPROVEMENT WHICH COMPRISES EFFECTING SAID PRECIPITATION IN THE PRESENCE OF DIBUTYL-PHENYLPHENOL SODIUM SULFONATE.

4. IN A PROCESS IN WHICH BISMUTH PHOSPHATE IS PRECIPITATED IN AN AQUEOUS SOLUTION AND THEREAFTER SEPARATED FROM THE SUPERNATANT SOLUTION, THE IMPROVEMENT WHICH COMPRISES EFFECTING SAID PRECIPITATION IN THE PRESENCE OF DIBUTYL-PHENYLPHENOL SODIUM SULFONATE.

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