US2951018A - Electrodeposition of neptunium - Google Patents

Description

Aug. 30, 1960 G. T. sEABoRG ETAL 2,951,013

ELECTRODEPCSITION 0F NEPTUNIUM Filed Oct. 29, 1945 F`lE-1 Gle/zz? 7.15.5605 0129,

ELECTRODEPOSITION F NEPTUNIUM Glenn T. Seaborg, Chicago, Ill., and Arthur C. Wahl, Santa Fe, N. Mex., assignors to the United States of America as represented by the United States Atomic Energy Commission Filed Oct. 29, 1945, Ser. No. 625,136

1 Claim. (Cl. 21M-1.5)

This invention relates to a method of separating certain new elements from solutions. More particularly it perrains to a process involving the electrolytic deposition of neptunium from solutions thereof.

It is known that plutonium can be produced in small quantities by the bombardment of natural uranium with neutrons. The designation plutonium or element 94 as used throughout the present description refers to the transuranic element having an atomic number of 94. The expression 94239 means the isotope of element 94 has an atomic weight or mass of 239. Similarly, the terms element 93 or Np refer to the new element known as neptunium having an atomic number of 93.

Uranium is composed of three isotopes, namely, U234, U235 and U238, the latter being present in excess of 99 percent of the whole. When U238 is subjected to the action of slow or 4thermal neutrons, a fourth isotope, U239, is produced having a half-life of 23 minutes-and undergoes beta decay to Np239 which decays further by beta radiation with a halflife of 2.3 days to yield plutonium. In addition to the formation of the transuranic elements, neptunium and plutonium, there are simultaneously produced other elements of lower atomic weight known as fission fragments. These fission fragments are composed of two distinct element groups, i.e., `a light and heavy element group. The light group contains elements having atomic numbers of between about 35 and 46 while the heavier group is composed of elements of atomic numbers varying between about 5l and 60. The elements of these groups as originally produced are considerably overmassed and undercharged, :and hence are highly unstable. By beta radiation, however, they quickly transform themselves into isotopes of these various elements having longer half-lives. The lresulting materials are commonly known as fission products. It is particularly desirable to separate the neptunium and plutonium from the radio` active fission fragments and fission products thereby removing from the mass, subjected to neutron bombardment, the radioactive materials and particularly the light elements such as the Alight metals having very short halflives. Y

It is= 'an object of this invention to provide ra simple and e'icient means of separating neptunium from solutions and particularly carrying out this separation in a quantitative manner.

It is a further object of this invention to accomplish this result by electrolytic means without the use of added reagents and without the necessity of evaporating the solution to dryness.

Another object of the present invention is to provide a simple, rapid, and eicient means for producing a thin ilm of neptunium.

Further objects will be apparent from the accompanying drawing and the description which follows.

Subsequent to the bombardment of uranium with neutrons to produce new elements a's discussed above, the usual procedure is to dissolve the entire mass in a suitable acid, such as nitric acid. This solution contains uranium, neptunium, plutonium, and all of the other products resulting from the fission of U23?.

In view of the relatively short half-life of neptunium, it is important that any method of separation of this element employed be a rapid one involving a minimum consumption of time.

In the study of radioactive substancessuch as neptunium, it is often of great importance to obtain a very thin uniform layer of the substance in question so that its radioactivity can be measured. If the layer is too thick there will be self-absorption phenomena that will seriously interfere with radioactivity measurements.

In accordance with the present invention it has been found that neptunium may be recovered by electrodeposition from solutions thereof. Nonaqueous solutions of neptunitun such as, solutions of neptunium nitrate in absolute ethyl alcohol or other organic solvent capable of supplying a pair of electrons to neptunium'to ,form a coordinate linkage such as, acetone, methyl ethyl ketone, hexone, methanol, n-propanol, ethyl ether, cellosolve, formamid, acetamid, acetic acid or other -solvent containing the group C=O, -N=, -S-, etc., may be used for this purpose.

The aqueous solutions from which neptunium is deposited may vary widely in their hydrogen ion concentration; however, in the majority of instances it is generally preferable to employ a pH of between about 5 and 7. Suitable buffers such as acetic acid-sodium acetate, carbon dioxidesodium bicarbonate buffers, etc. may be used to establish the desired pH.

The process 'of the present invention may be carried out in any standard electrolytic apparatus. A suitable apparatus is shown in Fig. l wherein the electrolyte 1 is contained in a glass cylinder 2 having a silver bottom 3 connected to lead lline 4 which is in turn connected to a negative source of potential. Anode 5 and cathode 3 consist of platinum `or insoluble anode material and silver, respectively and are connected to a suitable source of direct current such as a battery. The connection is made through switches 6 and 7 and variable resistance 8. In order lto measure the amount of current used a milliammeter 9 with a switch connection 10 for low and high scale readings, is placed in the line. In order to measure the voltage with a Very small current loss a microammeter 11 is placed across the line and in series with two fixed high resistances 12 and 13. As actually used resistance 12 is 0.1 megohm and resistance 13 is 1.0 megohm.

When using 4the apparatus the electrolyte consists preferably of neptunium nitrate and lanthanum nitrate in absolute alcohol. The current is passed through the solution and the amperage is adjusted by means of the vari.- yable resistance 8.

It was found that when carrying out such an electrolysis the famp'erage rises continuously with time as shown in Fig. 2.

In effecting the process of the present invention a relatively wide voltage range may be utilized. For themajority of instances, however, voltage of between about 2 and 50 volts have been found adequate for nonaqueous electrolytes and for aqueous medium a somewhat lower voltage, e.g. 2 to about l() volts, is suitable. Likewise, the current densities used may cover a comparatively wide range, however, for most purposes it has been found entirely satisfactory to use current densities of between about 0.001 and 0.6 ampere per square decimeter. The temperatures employed may, in general, vary from `about.

` 30 C. to about 90 C.

The process of the present invention may be further illustrated by reference to the following specific examples.

In all instances the percentages of neptunium plated out was determined in the manner referred to in Example 1.

Example 1 K thus obtained was again dissolved in nitric acid', evaporated to dryness on asteam bath, andy dissolved in absolute alcohol. The precipitate did not entirely dissolve and the solution Was ltered and diluted to cubic centimeters With absolute alcohol. The solution was centriuged to remove the small amount of precipitate still remaining.

Two cubic centimeters of this solution of neptunium nitrate and lanthanum nitrate in absolute alcohol was electrolyzed in an apparatus similar to that illustrated in Fig. 1. The electrolysis was carried eut for forty-live minutes at 510 volts. The current density varied over the time of electrolysis from 1.8 to 4.7 milliamperes per square decimeter as shown in the curve of Figure 2. The electrodeposited neptunium was washed with absolute alcohol. On the basis of determinations of beta radiation from aliquot portions of the initial neptunium solution and the electrolyte after the plating operation, using standard counter tube techniques, it was found that 100 percent of the neptunium in solution was deposited on the cathode probably in the form of an oxide.

Example 2 One cubic centimeter of the solution prepared as described in Example 1, was mixed with 1 cubic centimeter of a solution of lanthanum nitrate in absolute alcohol. The resulting solution was electrolyzed using the apparatus shown in Fig. 1. The electrolysis was carried out for thirty-five minutes at 17 volts and a current density of 3 to 5 milliamperes per square decimeter. Forty-eight percent of the neptunium was plated out. With 2 cubic centimeters of the electrolyte described in Example l, 8l percent of the neptunium was plated out, using a voltage of between 20 and 40 volts and a current of 2-4 milliamperes per square decimeter vfor a period orfY fifteen minutes.

Example 3 A solution of a `small quantity of neptunium prepared tive.

last traces of lanthanum carrier were removed from the neptunium in the process of separating that element from the nitric acid solution of neutron bombarded uranium.

Example 4 A solution containing a small amount of neptunium in one molal ammonium acetate solution was electrolyzed for ftyrninutes. The current density was 0.15 ampere per square decimeter, `at a voltage of from-2.4 to 2.7. The temperature was maintained at from 79 to 84 C. Seventy-four percent ofthe neptunium was removed from this solution probably in the form of oxide.

Examplev 5 An aqueous molal ammonium acetater solution containing .01 mole 4of uranyl ion (UO2-l-}-) and a tracer quality of neptunium was subjected to electrolysis at a current density of 0.15 ampere. per square decimeter and at a voltage of from about 2.4 to 2.7 volts. The temperature of the solution was maintained at from Iabout 79 to 84 C. The electrolysis was carried out for about sixty-live minutes, at the end of which time 97 percent of the neptunium, probably as an oxide, and 98 percent of the uranium had been removed from the solution.

It is to be Istrictly understood that the foregoing examples are merely illustrative and yare in no Way limita- It will be apparent to those skilled in the art that the present invention is susceptible of numerous improvements and modifications without departing from the scope thereof. For example, the current density employed may be substantially higher than speciiied in the foregoing description merely by using a rotating cathode, increasing the rate of agitation, or altering the bath temperature. In general, it may be said that any procedure for the recovery of neptunium based upon the electrolytic deposition thereof from its solution is to be regarded as lying within the scope of this invention.

What is claimed is:

The process of electrodepositing neptunium from solutions thereof, Which comprises conducting the electrodeposition from Ian absolute alcohol bath containing a neptunium nitrate and lanthanum nitrate at a potential of approximately fifty volts and a current density of between labout 1.8 and 4.7 milliarnperes per square decimeter.

References Cited in the tile of this patent UNITED STATES PATENTS Meyer Nov. 3, 1908 Dennis Nov. '3, 1914 OTHER REFERENCES Uranium and Atomic Power by] ack De Ment and H. C. Dake, published by Chemical Publishing Co., Brookyln, New York, 1941, pages 72, 123, 124, 184.

The Heavy Elements, Chem. Eng. News, 24, pages 1193-1198, May 10, 1946.

Plutonium and Other Transuranium Elements, Chem. Eng. News, 25, pages 358-60, 397, Feb. 10, 1947.

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