The Chemical and Radioactive Properties of the Heavy Elements G L E N N Τ. SΕΑΒΟRG 1 , Metallurgical Laboratory, University of Chicago, Chicago, III.
Wartime acceleration in the study or the heavy elements a b o v e N o . 8 8 , which form a transition series of the rare earth t y p e , has re moved them from the unfamiliar.
The discovery of elements 9 5 a n d
9 6 , of a new isotope of neptunium, of the occurrence of plutonium in nature, and its large-scale production at H a n f o r d , are T H E present discussion is concerned with the chemical and radioactive properties of the heavy elements—that is, the elements with a t o m i c number larger than 88—and especially with the newly dis covered t r a n s u r a n i u m elements. Aside from the obvious importance of these ele ments from t h e standpoint of a t o m i c en ergy, they are of great interest from the viewpoint of pure science. T h e general study of the chemical properties of these elements, and especially the properties of those which fall in the t r a n s u r a n i u m re gion, has led to a greatly increased knowl edge of the atomic s t r u c t u r e of elements in this region of the periodic table, a m a t t e r which was of necessity only very poorly understood a few years ago. Likewise, a s t u d y of the radioactive properties of t h e new isotopes in t h i s region has a d d e d greatly to our knowledge of t h e properties of radioactive isotopes, and the n a t u r e of and regularities in these properties have contributed greatly to the knowledge of nuclear structure. T h e new information which has been learned within t h e last few years concerning t h e other nuclear properties of these isotopes, such a s t h e fission properties and neutron absorption cross sections, will n o t fall within the scope of t h e present discussion. Previous to 1940, t h e r e was no experi mental information available concerning the chemical a n d radioactive properties of the t r a n s u r a n i u m elements. Actually, n o t a great deal was k n o w n concerning t h e chemical properties of elements i m m e diately below uranium in t h e periodic t a b l e — t h a t is, the elements actinium, thor ium, and protactinium, 'of atomic n u m bers S9, 90, and 9 1 , respectively. The knowledge of the chemistry of u r a n i u m itself at t h a t time fell into the class of t h a t of t h e less familiar elements. I t was 1 On leave from d e p a r t m e n t of University of California. Berkeley.
2190
chemistry,
possible to m a k e much more definite s t a t e m e n t s as to the a t o m i c structure in this region of the periodic table.
outlined
known t h a t u r a n i u m possesses t h e two oxidation states, VI and IV, and t h a t of these, the VI s t a t e is the more stable under ordinary conditions in aqueous solution. I t was also known t h a t u r a n i u m possesses an oxidation s t a t e of I I I which is p r e p a r e d and m a i n t a i n e d only with difficulty- in aqueous solution. Although t h e r e existed a fair a m o u n t of information about the chemical compounds of t h e V I a n d t h e IV oxidation states, information was almost totally lacking on such e l e m e n t a r y items as the properties of t h e metal. In the case of thorium, it was recognized t h a t there exists only one stable oxidation s t a t e in aqueous solution, with t h e oxida tion n u m b e r I V , b u t not a great deal was known about t h e compounds and practic ally nothing was k n o w n a b o u t t h o r i u m metal. Only a very little work h a d b e e n devoted to the chemical investigation of pure protactinium; a few compounds had been prepared and the existence of the- ox idation s t a t e V had been surmised. O n l y a few experiments of t h e tracer t y p e had been performed with the element a c t i n i u m , these leading t o t h e conclusion t h a t this clement exhibits t h e oxidation s t a t e of I I I and is very similar to t h e trivalent Tare earths in its chemical behavior. Transition G r o u p
T h e sum total of this information was not sufficient t o m a k e it possible t o deduce whether this transition group of e l e m e n t s involved t h e filling of t h e 6d shell or the filling of t h e 5f shell of electrons and, in either case, t h e question as t o which ele ment constituted the beginning of t h e transition series remained unanswered. However, with t h e recent discovery of the t r a n s u r a n i u m elements, together w i t h the greater accumulation of k n o w l e d g e of the chemical properties of t h e o t h e r s of these heavy elements which h a s t a k e n place during t h e last few years, i t is now C H E M I C A L
Neptunium T h e first transuranium e l e m e n t was d i s covered b y E. M . McMillan and P . H . Abelson a t the University o f California in M a y 1940. Using t h e neutrons from t h e cyclotron of E. O. Lawrence, they w e r e able to show, w i t h the help of their c h e m i cal work, t h a t a radioactivity of 2.3 d a y s ' half-life formed d u r i n g t h e irradiation of u r a n i u m with neutrons is due t o the iso tope 93 2 3 9 , which is t h e decay product of the 23-minute U 239 f o r m e d by radiative n e u t r o n capture in U238. Their experi m e n t s on the tracer scale o f investigation showed t h a t element 93 h a s a t least t w o oxidation states, an upper s t a t e (or s t a t e s ) a n d a lower s t a t e (or s t a t e s ) with chemical properties analogous to t h e V I and IV forms of uranium. T h e y found t h a t a greater oxidizing power is required t o oxi dize element 93 from i t s lower t o its u p p e r s t a t e t h a n is the case for t h e corresponding oxidation of u r a n i u m . E l e m e n t 93 w a s given t h e name n e p t u n i u m by McMillan after N e p t u n e , the p l a n e t immediately beyond Uranus, which gives i t s name to uranium. A n o t h e r isotope of neptunium, N p 2 3 7 , was discovered early i n 1942 by Λ. C.Wahl and G. T . Seaborg a t t h e University of California. T h i s isotope is the d e c a y p r o d u c t of the previously known 7 - d a y beta-particle e m i t t i n g U 237 , which is formed as the result of an n, 2n reaction on U 238 . Np 2 3 7 is given particular mention here because it is an a l p h a - e m i t t e r of v e r y long half-life (2.25 X 10 s years) a n d is therefore suitable as material for t h e in vestigation of t h e chemical properties of n e p t u n i u m using weighable amounts a n d ordinary concentrations, provided a m e t h o d for production i n q u a n t i t y is available. Fortunately, t h e large c h a i n reacting units a t Clinton and Hanford have solved this production problem a n d a n u m b e r of milligrams h a v e been m a d e available for chemical studies. Using t h i s material, J. C. Hindman, L. B . Magnusson, a n d T . J. L a Chapelle at the M e t a l lurgical Laboratory a t t h e University of A N D
ENGINEERING
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w a s given t h e name p l u t o n i u m , t o follow t h e convention which w a s used in the n a m i n g of n e p t u n i u m . The isotope of plutonium which is of major importance is, of course, the isotope of mass 239. This isotope, Pu 2 3 9 , which is t h e d a u g h t e r of the 2.3-day Np 2 3 9 , is an a l p h a - e m i t t e r with a half-life of about 24,000 years. Its t r e m e n d o u s importance stems from its property of being fission able with slow neutrons, a property which places it in a class of importance compar able t o t h a t of U 2 3 5 . Since Pu 2 3 9 consti t u t e d the material which was used i n at least o n e of the bombs which were s e t off a t New Mexico, Hiroshima, a n d Nagasaki, i t s importance need n o t be elaborated. I t s importance for t h e p r e s e n t discussion lies in the fact t h a t it is available in weighable quantities, m a k i n g it possible to s t u d y t h e chemical properties of plutonium b y the ordinary methods of chemistry. The first pure chemical c o m p o u n d of plutonium, free from carrier material and a i l other foreign matter, was p r e p a r e d by B . B. Cunningham and L . B . Werner at t h e Metallurgical L a b o r a t o r y in Chicago o n August 18, 1942. T h i s memorable day will go down in scientific history to mark t h e first sight of a synthetic element and, in fact, the first isolation of a weighable a m o u n t of a n artificially produced isotope of any element. T h i s work w a s performed w i t h microgram q u a n t i t i e s using the techniques of ultramicrochemistry, and m a t e r i a l prepared b y the b o m b a r d m e n t of u r a n i u m with neutrons from t h e cyclotron. As i s now well known, l a r g e quantities of plutonium are available as t h e result of t h e operation of t h e chain-reacting units
Chicago have been able to m a k e an in t e n s i v e study of t h e chemical properties of n e p t u n i u m l e a d i n g to the establishment of its oxidation s t a t e s a n d the preparation of a n u m b e r of its c o m p o u n d s . T h i s work h a s s h o w n t h a t neptunium h a s t h e oxida tion s t a t e s VI, V, I V , a n d I I I w i t h a gen eral shift in stability toward t h e lower oxi d a t i o n states a s compared to u r a n i u m . Plutonium
After t h e discovery of neptunium, t h e next t r a n s u r a n i u m element t o be discov ered w a s element 94. This element w a s discovered by G. T . Seaborg, Ε. M. M c Millan, A. C. W a h l , and J. w. Kennedy in Berkeley, late in 1940. The isotope in volved w a s the one of mass 2 3 8 formed by t h e deuteron b o m b a r d m e n t of u r a n i u m in t h e cyclotron of E . O . Lawrence. These investigators were able to show t h a t t h e d e u t e r o n b o m b a r d m e n t of u r a n i u m leads t o a new isotope of n e p t u n i u m , the 2.0-day beta-particle-emitting Np 2 3 8 , formed from a d,2n reaction on U 238 . They found t h a t this isotope of element 93 d e c a y s to an alpha-emitting isotope of e l e m e n t 9 4 — n a m e l y , 94 2 3 8 —and t h a t this a l p h a - e m i t t e r h a s a half-life of a b o u t 50 y e a r s . Their early experiments with tracer a m o u n t s of this m a t e r i a l s h o w e d t h a t element 94 also h a s a t least two oxidation states, a n upper s t a t e (or states) a n d a lower s t a t e (or s t a t e s ) . The experiments indicated t h a t i t r e q u i r e s even s t r o n g e r oxidizing agents t o oxidize element 94 t o the upper from t h e lower state t h a n is t h e case for n e p t u n ium. T h e chemical work of A. C . Wahl was particularly n o t a b l e i n t h i s early period of investigation. E l e m e n t 94
at Clinton and Hanford. Using plutonium from these sources, a number of groups have investigated intensively t h e chemical properties of plutonium. T h e group a t Los Alamos under the direction of J. W. Kennedy a n d C. S. Smith and including A. C. W a h l , C. S. Garner, and I . B. Johns was principally concerned with plutonium chemistry as applied to its purification. W. M. Latimer and E. D . E a s t m a n a t Berkeley with R. E . Connick, J . W. Gofman, a n d others contributed notably to the solution chemistry of plutonium including t h e oxidation states, potentials, and reaction kinetics. F. H. Spedding, together with W. H. Sullivan, A. F . Voigt, a n d A. S. Newton at Iowa State College, contributed to the chemistry of complex ion formation as well as other phases of plutonium chemistry. The group of chemists at t h e Metallurgical Labora tory a t t h e University of Chicago was involved in basic solution and dry chem istry studies as well as in the separations process a n d purification work. Somewhat before t h e Clinton plant was to start operation, a sizable part of this Metal lurgical L a b o r a t o r y staff, u n d e r I. Perlman a n d S. G. English, together with H. S. Brown, V. R. Cooper, R. W . Stoughton, a n d others, moved to the plant site where their principal job concerned further intensive work on the plant sepa ration processes a n d the a c t u a l isolation of p l u t o n i u m decontaminated (separated from fission product radioactivities) in the plant- Remaining in Chicago on basic chemistry a n d purification problems were t h e several groups u n d e r W . M. Manning, E . F . Orlemann, N . R. David-
Periodic Ta ble Showing H z a v y Elements as Members of an A c t i n i d e Series
1
Li
Be
5 Β
6 C
7 Ν
6.940
9,02
10.82
12.010
14.008
3
11 Να
12 Mg
22.997
24.32
13AI
19
26.97
21
22
23 V
4510
47 9 0
5 0 95
Ca 39.096
37 Rb 85.48
55 Cs 132.91
87
40.08
38 Sr
39
40
87.63
88.92
91.22
137.36
86
89
Ra
AC
BEE SWiEl
LANTHAMIDE SERIES;
24
25 Mn
52.01
42 Mo 92.91
74
180.88 92
95
90
57
58
138.92
140.13
89 Ac
90 Th
54.93
43
95 9 5
73
58-71 72 SEE LA L a Hf XRIES 178.G
Bo
14 Si
13 AS
2697-
75
183 9 2
93
94
30 Zn
31 Go
32 Go
6 5 38
69.72
72 6 0
26
27 Co
28 Hi
55.85
58 94
5869
63 57
44 Ru
45 Rh
46 Pd
47 Ag
101.7
102.91
106.7
76 08
77 Ir
78 Pt
?9 Au
193.1
195.23
197.2
200.61
Re 166.31 1 9 0 . 2 Ι 95
29 Cu
107.880
6O Hd
61
14-4.27
50 Sn
16.OOO
He" :
1.008
•4.003
9 F
IO Ne,.
19.00
20.183 J
15 Ρ
16 S
17 Cl
30.98
32.06
35457
39.9441
35 Br
36 Kr 83.7, J 54 Xe. 13Γ.3 1
33 As
34 So
74.91
78.96
51 Sb
52 Te
53 I
7 9 916
48 Cd
49 in
112.4l
114.76
118.70
121.76
12761
126 9 2
80 Hg
81 Tl
82 Pb
83 Bi
84 Po
85
96
*« -
59 Pr
28.06
8 0
2 0 4 39
207.21
2 '1
1 H
18 A
86 I Rn Ί .222 "-'I
209.00
'
62 Sm
63 Eu
64 Gd
65 Tb
66 Dy
67 Ho
68 Er
69 Tm
70 Yb
150 4 3
152 0
156.9
159 2
162.46
163.5
167.2
169 4
173.04
71 Lu 1/4.99
r
ACTINIDE SERIES
V O L U M E
232.12
2 3,
N O .
23
91 Pa 231
.
92 U
93 Np
238.07
237
D E C E M B E R
94 Pa
10,
95
1 9 4 5
96
2191
son, and Β. Β. Cunningham, a n d t h e plutonium separations groups directed b y F . W. Albaugh. J . E. Willard, S. G. Thompson, and G. W. Watt. The latter three men later went t o t h e Hanford plant to continue the separations pro gram investigation. A great deal of work of fundamental importance to the sepa rations program—such as work on fission products and radiation chemistry a n d chemical analyses—was done by other groups in the Metallurgical Project, b u t a doscript ion of their contributions is beyond t h e scope of this discussion. T h e work has established that pluto nium has the oxidation states VI, V, I V , and III and that the lower oxidation states lend to he more stable than is t h e case for neptunium. A large number of compounds of plutonium have been pre pared and their properties determined a n d it is fair to say that the chemistry of plu tonium today is as well understood as, or belter understood than, is that of most of the elements in the periodic system. T h e general conclusions from this work are, then, that plutonium and neptunium are similar in chemical properties t o ura nium with an increase in stability of t h e lower oxidation states in going ward plu tonium. Actinide Series The elements 90 to 94 lie in correspond ing positions just, below the sixth period transition elements Hf to Os (atomic num bers 72 to 7 6 in which the 5d electron shell is being filled. T h e transition ele ments HftoO s are similar in their chemi cal properties to the corresponding 4d transition elements in the fifth period (Zr to Ru, atomic numbers 40 to 44). Al though the first, members (90Th, 91Pa) of the group 90 to 94 show a great resem blance in chemical properties to t h e first members (72Hf, 73Ta) in the 5d transition series and t o the first members (40Zr, 41Cb) in the 4d transition series, t h e later members (93Νp,9 4 P u )show practically no resemblance t o 7 5 R e and 76Os and to 43Ru and 44Ru. This suggests t h a t it is the 5f electron shell which is being filled, although it is not possible to deduce from this chemical evidence alone whether uranium is t h e first element in t h e series for which this is the case. While i t is beyond the scope of this discussion to give all t h e supporting evidence, we would like t o advance the attractive hy pothesis t h a t this rare-earth-like series begins with actinium in the same sense that, the "lanthanido" series begins with lanthanum. On this basis it might be termed the "actinide" series and the first 5f electron might appear in thorium. T h u s t h e characteristic oxidation states— i.e., the oxidation state exhibited by those members containing seven 5f and fourteen 5f electrons—for this transition series is I I I . Elements 95 and 9 6 The oxidation s t a t e of IV demonstrated 2192
by thorium is then analogous to the IV oxidation state of cerium. From the be havior of uranium, n e p t u n i u m , and pluto nium it must be deduced that as m a n y as three of t h e assumed 5f electrons are readily given up, so that t h e failure of tho rium to demonstrate an oxidation state of III is accounted for. On the basis of this hypothesis, elements 95 a n d 9 6 should ex hibit very stable I I I states; in fact, ele ment 96 should exhibit the I I I state al most exclusively because, with its seven 5f electrons, it should have an electron structure analogous t o t h a t of gadolinium, wit h its seven 4f electrons. T h e experiments of G. T . Seaborg, R. A. James, L. O . Morgan, a n d A. Ghiorso in the Metallurgical Laboratory have re cently led to the identification of isotopes of elements 95 and 96, making it possible to study t h e chemical properties of these iso topes b y t h e tracer technique. These in vestigators have studied the products pro duced a s a result of the b o m b a r d m e n t of IT238 a n d Pu 239 with very high energy (40 Mcv) helium ions in t h e Berkeley cyclo tron. This work was m a d e possible by the vital participation a n d cooperation of J. G. Hamilton and h i s group at the University of California, who have re cently rebuilt the 60-inch cyclotron to produce the high energy particles needed and who performed the bombardments. Of course in t h e case of some of the ele m e n t s in t h e series it m a y be something of an academic matter to assign electrons to the of or 6d shells, a s the energy necessary for t h e shift from one shell to t h e other m a y b e within t h e range of chemical bind ing energies. T h e electron configuration m a y differ from compound to compound of an element or even with the physical state of a given compound. T h i s shifting of elec tron configuration would probably be most pronounced with t h e middle members of t h e first half of the series—that is, ura nium, neptunium, and plutonium. Since t h e energy difference between t h e 5f and 6d shells is rather small a n d since the resonance effects should be rather large, t h e latter may predominate in determin ing which energy level lies lowest. I t is probably worth while to make a brief summary at this point with the fol lowing statements. As of today, the peri odic system consists of 96 known, identi fied elements—that is, there is now posi tively known a t least o n e isotope, stable or radioactive, for each of t h e elements from atomic n u m b e r 1 t o atomic number 96, inclusive. T h e evidence points to an a t o m i c structure for the heaviest elements — t h a t is, those elements with atomic n u m b e r greater than 88—corresponding t o a transition series in which t h e 5f shell of electrons is being filled. T h i s series dif fers in chemical properties from the rare earth series (the 14 elements of atomic n u m ber 58 to 7 1 , inclusive, following lanthanum) in which t h e 4f shell of electrons is being filled, in t h a t the first members of this h e a v y series are m u c h more readily oxi C H E M I C A L
dized t o oxidation states greater t h a n I I I . As the atomic numbers of the ele ments in this series increase, the lower o x i dation s t a t e s , and particularly the I I I state, increase in stability. T h e first 5 f electron probably appears in thorium a n d t h e stable configuration consisting of seven 5f electrons probably comes with e l e m e n t 96. There has been a great deal of specula tion as to t h e possibility of the existence in nature of isotopes of the t r a n s u r a n i u m elements. A search for such isotopes h a s been made. G. T . Seaborg a n d M . L . Perlman early in 1942 made a chemical separation of neptunium a n d p l u t o n i u m from a q u a n t i t y of pitchblende ore a n d were able to show t h e presence of a small q u a n t i t y of alpha-activity in this t r a n s uranium fraction which they attributed t o plutonium, t h e isotope Pu 239 . T h e a m o u n t of plutonium in t h e pitchblende c o r r e sponded to a b o u t 1 part in 10 14 , a n a m o u n t which could not possibly have been found h a d t h e chemical properties not b e e n known. T h i s plutonium isotope is p r e s e n t in such uranium-containing ores, in s p i t e of its relatively short half-life, p r o b a b l y because it is continuously formed b y t h e absorption i n U238 of some of the n e u t r o n s which are always present. A p a r t i c u l a r source of neutrons, sufficient in a m o u n t t o account for t h e presence of this a m o u n t o f plutonium, results from t h e s p o n t a n e o u s fission of the isotope U 238 . In most w a y s plutonium is t h e most i n teresting element in this new series a n d therefore it i s worth while t o finish this d i s cussion with a further description of t h e achievements which have been accom plished in t h e chemical field with this ele ment. Since the time of its inception, t h e Metallurgical Project had .as its principal goal a m e t h o d for obtaining in a free s t a t e sizable quantities of Pu 239 . This problem was comprised of two major components, which were to a large extent unrelated. T h e nature of the development programs was as different as were t h e groups of r e search workers charged with their com mission. T h e first major p a r t of t h e p r o gram was t h e development of a chain-re acting structure which would produce t h e Pu 239 in a uranium matrix, while t h e sec ond p a r t w a s the design of a method for separating t h e plutonium from t h e u r a nium and t h e highly radioactive fission products formed concurrently with t h e plutonium. Production of Plutonium The problem of designing a process for separating plutonium was without prece dent from almost every standpoint. Nο one h a d ever seen a n y plutonium at t h e time t h a t p l a n t design was under consid eration. T h e chemical properties a t t r i b uted t o the element a t t h a t time h a d been deduced solely from what might be t e r m e d secondary evidence (experiments on t h e tracer scale). The novelty of the problem was e n AND
ENGINEERING
NEWS
hanced by the fact that not only w a s P a 2 3 ' to b e t h e first artificially produced isotope to b e seen but as an element it fell beyond the confines of t h e classical periodic syst e m . These curious conditions, in themselves, would not necessarily produce serious obstacles were they n o t coupled with other aspects of the problem of an unconventional nature for industrial scale operation. Both the plutonium and t h e fission products from which it was t o be separated would be present in extremtely small concentrations in the uranium. These separations would require specialized techniques. The formidable feature of the undertaking was, however, that these min u t e amounts of the fission product elem e n t s would in t u r n have t o be separated from t h e plutonium to t h e extent t h a t only of the order of one part, per million of each would remain. To add. to the complications, the separations process would have to b e carried out entirely by zremote control because of the staggering lev els of g a m m a ray activit}' associated w i t h the fission products. As a result, it w a s imperative t h a t the process be adaptable to simple equipment that would require a minimum of maintenance and that the limits of control be not too stringentAlthough four types of method for chemical separation were examined—volatility, adsorption, solvent extraction, a n d precipitation—the process finally cliosen was a precipitation process. S. G- Thompson is largely responsible for the conception a n d
early development of t h e process actually used. T h e process depends on the coprecipitation of t h e plutonium along with a "carrier" precipitate, a procedure which has been commonly used in radiochemistry. O n e of the most interesting a n d awe-inspiring aspects in the development of this process was t h e necessity for t h e testing of the process a t a time when onl} r microgram a m o u n t s of cyclotron-produced plutonium were available. It was necessary to test the process a t concentrations corresponding to the full level of Han ford plant operation and therefore the experiments h a d to be conducted on t h e ultramicrochemical scale of operation, which employed volumes of only microliters. T h i s involved a scale-up between these experiments and t h e final Hanford plant by a factor of a b o u t 1010, surely the greatest scale-up factor ever a t t e m p t e d . In spite of these difficulties, t h e chemical separation process a t Hanford was successful from the beginning and its performance exceeded all expectations. High yields a n d decontamination factors (separation from fission p r o d u c t activity) were achieved in the very beginning and h a v e continued to improve with time. T h e precipitation process which is being used involves t h e use of a n alternation between t h e IV and VI oxidation s t a t e s of p l u t o n i u m , as pointed o u t in t h e S m y t h Report. T h e process involves a precipitation of plutonium(IV) with a chemical compound as a carrier, then dissolution
Solid Fuels in G e r m a n y T H B solid fuels, coal and coke, w i t h o u t 1 which there would h a v e been little liquid fuel for t h e German, military m a chine a n d which, of course, furnished carbon necessary for the reduction of ores to metals, wrere the keystone o f the G e r m a n war-making economy, according to t h e Technical Industrial Intelligence Comm i t t e e of t h e J o i n t Chiefs o f Staff of t h e A r m y a n d Navy, acting through t h e F E A . T h e investigative field team sent from t h e United S t a t e s was headed b y H. F. Yancey, supervising engineer, Xorthwest E x p e r i m e n t Station, Bureau of Mines. After the organization had b^en completed a n d liaison established with a similar British intelligence group, tie was joined by L. D . Schmidt, engineer* in charge of C o k e Production Survey, Pittsburgh E x periment Station, Bureau of Mines, H. H. Lowry director, Coal Research L a b o r a t o r y , Carnegie Institute o f Technology, H . J . Rose, director, Bituminous Coal Research, John \V. Buch, mining engineer, Fueh> a n d Explosives Branch, Bureau of Mines, F r a n k H . Reed, chief chemist, Illinois S t a t e Geological Survey, L. L. N e w m a n , gas engineer, Bureau of Mines, a n d T h o m a s Fraser, coal pr-eparation engineer, B u r e a u of Mines. V O L U M E
2 3,
NO-
23
T h e N a z i research organization on coal and coke, membership in which was m a n datory, w a s known as t h e Bergbauverein, with h e a d q u a r t e r s a t Essen. One objective of t h e Bergbauverein was to i n s t i t u t e a control p r o g r a m of t h e coal-washery operation in t h e R u h r and Saar, so t h a t a superclean coal of uniform quality suitable for liquefaction by the h y d r o g é n a t i o n process could be regularly produced. T h i s work was u n d e r the direction of H e r m a n Meyer. Another function was t h e preparation of coal even lower in ash content for use in making electrode carbon, principally for aluminum pot lines. F . L. Kuehlwein was responsible for this g r o u p of German investigators a n d was ordered t o develop processes necessary to accomplish this result. T h e outcome w a s t h e building of a plant a t t h e Queen Elizabeth coal mine in Essen, which, until b o m b e d o u t in M a r c h 1945, h a d for 15 m o n t h s previously p r o duced c o a l t h a t contained a b o u t 0 . 5 % ash. A t t h i s plant coal for t h e m a n u f a c t u r e of electrode carbon w a s prepared by a 2stage cleaning process, consisting of a heavy-medium separation in a suspension of m a g n e t i t e followed b y pulverization of t h e p r o d u c t lowest in ash content a n d its recleaning by froth flotation. Other p r o c -
«DECEMBER
10,
1945
of the precipitate, oxidation of t h e plutonium t o the VI state, and p r e c i p i t a t i o n of t h e carrier compound while the p l u t o n i u m (VI) remains in solution. Fission products which are not carried remain in solution when Pu(IV) is precipitated, and fission products which carry are removed from t h e plutonium when it is in the VI state. Successive oxidation-reduction cycles a r e carried out until the desired decontamination is achieved. These s t a t e m e n t s on the Hanford S e p arations Process, to be sure, r e p r e s e n t a gross oversimplification of the a c t u a l process. T h e r e are carried out in adl some thirty major chemical reactions involving hundreds of operations before t h e plutonium (.'merges from the process*. T h e plants themselves defy description with their massive structures and t h e i r intricate maze of equipment, piping, and remotely operated controls. T h e preliminary design of these plants was u n d e r w a y a t a time when the world s u p p l y of plutonium was invisible to t h e naked eye This remarkable program of investigation with microscopic a n d s u b microscopic quantities m a r k s o n l y o n e of a large number of amazing a n d so far unheralded achievements of the m e n of chemistry who developed the chemical separation processes which were used on t h e Atomic Bomb Project. PRESENTED at t h e Symposium on Nuclear Chemistry at the Fiftieth Anniversary Technical Conference of the Chicago Section, a.% N o r t h western University, Nov. 1G, 1945.
esses used to p r e p a r e carbon were the extraction of t h e mineral c o n s t i t u e n t s from coal previously cleaned h-3r froth flotation, by digestion in a m i x t u r e of hydrochloric and hydrofluoric acids, a n d also b y the Pott-Broche process involving solution of organic constituents a n d separation from inorganic material by filtration, a process expanded during the w a r . Developments in t h e h i g h - t e m p e r a t u r e carbonization processes a p p e a r e d to be few b u t t h e preparation of synthesis gas for liquid fuels b y gasification processes expanded rapidly. A t Boehlen, j u s t s o u t h of Leipzig, some 15,000,000 cubic feet of town gas a day were being m a d e by the Lurgi oxygen-pressure m e t h o d , mtade feasible by the m a n u f a c t u r e of cheaper oxygen by the Linde-Fraenkl process. At L e u n a and several other plants in the vicinity synthesis gas was p r o d u c e d in Winkler generators, using oxygen at norm a l pressures for t h e gasification of fine fuel in suspension. A t Leuna t h e r e were also six slagging gas generators using oxygen a t normal pressure for the gasification of high-carbon-content refuse from standa r d gas generators. T h e K r u p p - L u r g i Lowt e m p e r a t u r e carbonization process was expanded in both the R u h r and t h e Saar. T h e high yield of t a r was used a s marine fuel a n d t h e reactive coke p r o d u c t as fuel for automotive gas producers a n d various other purposes. 2193
