Less than one part per million remains during-low cost gas purification
impurity
PRODUCTION
Rare Earths-
with
Switch t o Solvents?
D E O X O purifiers
Solvent extraction may offer some a d v a n t a g e s over îon 125° CENTIGRADE: Conversion of C O to C O a AT 250° CENTIGRADE: Methanation of C O t o CH4 AVAILABLE CAPACITIES: 25 C F H to 5 0 0 , 0 0 0 CFH a n d l a r g e r . S p e c i a l units d e s i g n e d f o r specific r e q u i r e m e n t s .
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OUR NEW CATALOG— Listing 75 gases, gives the gas user complete information on: • CYLINDER PRESSURE, f o r each gas, a t 7 0 ° r. · GAS PURITY · CYLINDER DIMENSIONS · RECOMMENDED PRESSURE A N D FLOW CONTROLS · VALVE OUTLET TYPES • AVAILABLE MIXTURES
On Separating
individual
rar*e earths, b u t wlien t h e present boom in rare earths star-ted most commercial producers adoptecl t h e ion exchange resin column method, At t h e 17th Midwest Regional ACS meeting—held at Iowa State Collègue, Ames, Iowa—commercial rare earth chemists showed more than am aca?deitiic interest in research r e p o r t s on solvent extraction. Solvent extraction h a s some advantages over i o n exchange separation. L. IK, Kriapp, Morton Smutz, and Frank H. Spedding of t h e A m e s Laboratory have used b o x type contactors in pilotplant solvent extraction separations. Staige efficiency is: close t o theoretical. Transfer in a solvent stage is almost instantaneousA 14-stage contactor is about three fee* long a n d 10 inches square. Work at Ames has sometimes involved four of these units connected together. An i o n exchantge column m a y b e equivalent t o , say, a thousand theoretical stages. S o ion exchange would be preferable f o r obtaining highly purified rare earth compommds. B u t flow rate is often hmited. Although some people worry about t h e large number of stages which might conceivably be required for solvent extraction, Smutz believes higher capacities per unit investment coold b e obtained with solvent extraction for rare earrJh compounds of less than "spectrograpnic" purity. • Radioactive &are Earths. Not ores, but materials which have been exposed in nuclear reactors, a r e t h e source of radioactive rare e a r t h isotopes. Ion exchange separation processes used for these fission products are similar to those used for ordinary rare earths. Nerw uses for radioactive rare earth isotopes a r e growing and production facilities are h e i n g expanded a t Oak Ridge National Laboratory, IProrQethiurxî-14'7 is one of t h e more promising radioactive rare earths, says Roscoe S. Pressly of O a k Ridge. If it can be sufficiently purified it would b e useful as a low-energy x-ray source;* sin«ce i t is a pure b e t a emitter. A platinum target could be used to obtain the x-rays. One company i s already experiment-
after 18 years as president of Crows
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DEC.
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1956
phosphors for watch dials. It is less hazardous than the rather toxic strontium-90 n o w used. A radioactive rare earth use—which has apparently not been adopted hy any commercial producers—is for proc ess control in a plant producing ordi nary rare earths. A radioactive tracer added to a mixture from which a par ticular element is being extracted would indicate w h e n the desired element ap peared in the process stream. • Europium, Latest rare earth to be prepared in pure form by reduction of the oxide with lanthanum is europium. It had previously been prepared only in semimicro quantities, or mixed with the reduction mixture. But Joseph J. Hanak, of the Ames Laboratory, has prepared larger quantities using a method developed b y Spedding and co-workers for ytterbium and samarium. L a 2 0 3 has a high heat of formation, but lanthanum metal has a low volatil ity. Europium, on the other hand, is one of the most volatile rare earth metals. This makes it possible for the metal to b e distilled off from the reduc tion mixture and obtained in high purity. The mixture of E u 2 0 3 and lanthanum metal was heated under high vacuum in a tantalum crucible. Temperature was about 1200° C. About 36 grams of pure metal could b e obtained in five hours. Progress of the reaction could b e determined by radiographic pictures of the sealed crucible using a eobalt-60 source. Europium metal is malleable and soft enough t o be cut with a knife. It is rapidly attacked by moist air and water. Melting point is 826 ± 10° C.
For Drying Refrigerants Latest use for Linde Air Products' Molecular Sieves (C&EN, Nov. 27, 1954, page 4 7 8 6 ) is in drying of re frigerants. According to extensive tests carried out b y Linde with prospective users, these synthetic zeolites have a relative capacity advantage over other desiccants now in use for water ad sorption. This advantage is striking for drying of Freon-12 and Freon-22, Linde claims, particularly at low rela tive humidities and temperatures around 140° F. and higher. Use of Molecular Sieves in automo bile air conditioners means smaller units, Linde adds. The high capacity of the desiccant leads to smaller de hydrates. ^r τ -ν > American Agile has set up a test station at Cleveland, Ohio, to test ef fects of weather on polyethylene coated metals.
