INDUSTRIAL AND ENGINEERING CHEMISTRY
318
where k , is the rate of cracking into coke xc, and kl is the rate of cracking into the sum of other products. The writer does not know of any published experiments carried out with the express view of studying the formation of polymerization and allied products, such as coke. Such experiments, for example, as long cracking runs with a good charging stock, a t two or more different temperatures, would be useful. Literature Cited
1-01. 23.
xo. 3
Lurie and Gillespie, J. A m Chem. SOL.,43, 1146 (1927). (6) Pease, I b i d . , SO, 1779 (1928). (7) Poynting, Phil. Mag., [4]12, 32 (1881). ( 8 ) Sackur, “Thermochemistry and Thermodynamics,” p. 219 (1917). (9) Waterman and Perquin, J. Inst. Petroleum Tech., 11, 36 (1925). (5)
Correction In my article entitled “Distillate Yields in Cracking,” IND. ENG.CHEM.,22, 10 (1930), Formula 11 on page 12 should read as follows:
(1) Hurd and Spence, J . A m . Chem. SOL.,51, 3561 (1929). (2) Kiss, IND. END.CHEM.,22, 10 (1930). (3) Larson and Black, J. Am. Chem. SOL, 47, 1015 (1925). 18, 776 (1926). ( 4 ) Leslie and Potthoff, IND.END. CHBM.,
STEPHEN A. KISS
Extraction of Beryllium, Caesium, and Rubidium from Beryl’ C. James, H. C. Fogg, and E. D. Coughlin U N I V E R S I T Y OF h-EW H A M P S H I R E ,
.
DURHAM,
h‘. H
A simple and economical method has been developed for producing pure beryllium oxide from beryl using ordinary chemicals and apparatus. Any small quantity of caesium and rubidium which may be present in the mineral can be obtained a t the same time. The method is applicable either o n , a commercial or laboratory scale. The finely ground mineral is fused with approximately one-half its weight of lime in a furnace of the blast type. The resulting slag is ground, decomposed with sulfuric acid, and heated t o dehydrate the silica. The mass is stirred with hot water and filtered, and the concentration of t h e filtrate adjusted so t h a t potassium, caesium, and rubidium alums will crystallize out when allowed t o cool.
Ammonium sulfate is added to the hot mother liquor which causes ammonium alum to crystallize upon cooling. After oxidizing the iron in the solution from these crystals by a suitable oxidizing agent such as potassium bromate or nitric acid, the major portion of it is removed by the careful addition of dilute ammonium hydroxide to the boiling liquid. The last traces of iron are removed by hydrogen sulfide under slight pressure. The beryllium is then precipitated from the filtrate by ammonium hydroxide or preferably ammonium carbonate. The principles involved in this method can be adapted to the extraction of these elements from ,other silicate minerals with only a few changes, depending upon the mineral used.
H E methods of separation and decomposition given in this article represent work carried out a t various times covering a period of a number of years.z The processes, which are very simple, permit the worker to obtain several interesting by-products such as caesium, rubidium, and scandium, if these elements are present even to a very small extent in the beryl employed.
stirring. It first softened, then became liquid and boiled (owing to the presence of water in the commercial hydroxide), and afterward hardened to a friable bluish solid. The temperature was then maintained for a short time below that a t which there is a tendency for fusion with the formation of a glass. I n order to obtain the best results it is necessary that the mineral be ground very fine (200 mesh), thoroughly mixed with the caustic, and the temperature kept even throughout the mass. Although this decomposition n’as efficient, it introduced large quantities of sodium salts which interfered with the crystallization of ammonium alum a t a later stage. CALCIUM OurDE-There are two outstanding advantages in using this material rather than sodium hydroxide for opening up beryl: cost, and the removal of calcium sulfate, which is insoluble, along with silica, aiding in the filtration. The decomposition of finely divided beryl can be brought about by intimately mixing it with calcium hydroxide and heating to a temperature just below fusion. Complete fusion, however, gives a better decomposition and is more easily carried out commercially. The furnace for the fusion was given careful consideration since it was realized that the temperature of fusion would be necessarily high, the attack on the container would be rapid, and the cost of fusing large amounts of material must be kept as low as possible. A small blast furnace, which could be charged with the fuel (coke,
T
Decomposition of Mineral The employment of hydroxides and oxides of the alkali and alkaline earth elements has been recommended from time to time for this purpose. SODIUM HYDRoxrDE-This substance is very commonly used in the laboratory and for small-scale production. The usual procedure has been to fuse the mixture of mineral and hydroxide completely in an iron kettle. Unfortunately the fused mass attacks the containing vessel to such an extent that much iron is introduced, making the process of separation more difficult, and in some cases actually perforating and destroying the kettle. It was found that these objections could be overcome and a decomposition of 96 to 98 per cent still be obtained if a mixture of beryl, with 11/* times its weight of sodium hydroxide, was heated to only a low red heat with thorough 1 Received
December 3, 1930. Canadian Patent 305,937; United States patent application pending (Serial 315,595). f
March, 1931
I.YDCSTRIdL d-1-D EiYGINEERING CHEMISTRY
gas, oil, etc.) and beryl-lime mixture, appeared to be desirable This would furnish, a t a low cost, a high temperature in intimate contact with the substance to be fused. Since the product of fusion would flow from the base of the furnace, the process would be continuous. For a rapid decomposition it is essential that 1he beryl be in a fairly fine state of division and thoroughly mixed with the lime. It would, of course, be impossible to use a dry and dusty mixture in a furnace of the above type. Accordingly, the lime was first slaked, then mixed with the ground mineral to the consistency of mortar. The ratio of mineral to lime may be varied within quite wide limits. The best ratios vary with the type of mineral being decomposed. On the average, a ratio of 10 parts of mineral to 6 parts of quicklime gave a very fusable slag which was rapidly attacked by the sulfuric acid. This was spread out in a layer of about 2 inches in thickness and allowed to dry. The product was found to be quite firm and easily withstood the burden of the furnace. Firebricks were used to construct the furnace of the following inside dimensions: 25 cm. diameter a t base, 40 cm. diameter a t middle, 30 cm. diameter a t top, and 110 cm. high. The main furnace was set upon a base of the same material. From the center of the base to one side a gradually sloping channel (5 cm. wide) had been cut to allow the fused product to flow onto a slightly hollowed steel plate 90 cm. K 60 cm. X 1.5 cm. The blast was furnished by a centrifugal blower and introduced by three tuyhres placed symmetrically around the furnace about 10 cm. from the bottom. A brisk fire was started with wood and coke and when the lower part of the furnace had reached a white heat, the charge consisting of the beryl-lime mixture, together with one-half to two-thirds volume of coke, was added. I n a few minutes the slag began to flow from the tapping hole in a very fluid state. The ratio of coke to beryl-lime mixture should be adjusted to keep the temperature high and yet use the minimum amount of coke. With a furnace of this size approximatdy a ton of mineral could be run through in 24 hours. The short flame that emerged from the tappirig hole was examined by means of a spectroscope. Lines of the following elements, arranged in the order of decreasing intemities, were visible: sodium, potassium, caesium, lithium, rubidium. Decomposition of Slag
The melt from the furnace was crushed and ground. -The powder was mixed with an equal volume of water ,md treated with slightly more than the theoretical amount of sulfuric acid. The reaction was vigorous, and the whole inass boiled and gave off fumes of sulfuric acid. The mass was well stirred to prevent the formation of hard lumps, and then added w t h thorough stirring to a \-at of water nhich was raised to the boiling point by mems of steam. After standing for 12 hours it was again heated, stirred. and put through a filter press. The vaqh water was used for dissolvins the next hatch. Since this ground slag was found to be attacked by solutions of aluminum sulfate, etc., any unattacked slag remaining in the center of the small lumps was decomposed by the solution during the stirring, with the result that a little silica was dissolved. The solution, consisting mainly of the sulfates of aluminum and beryllium together with small amounts of iron and alkalies, was evaporated in lead pans by means of lead steam coils. The fused sirupy mass was kept for some time a t 3 25" C., then dissolved in boiling water, filtered through a large lead Buchner funnel, and diluted until no simple sulfates separated upon cooling. This concentration gave a solution with a specific gravity around 1.36. It n-as allowed to stand until the crystallization of the alum
319
derived from the potassium, rubidium, and caesium contained in the beryl had ceased. This alum was carefully removed and saved for caesium and rubidium, the separation of which is described later. Separation of Aluminum
The separation of aluminum from beryllium was brought about by the crystallization of the former as ammonium aluminum sulfate (ammonia alum) in the following way: The mother liquor from the potassium, rubidium, and caesium alums was treated with a 25 per cent excess of ammonium sulfate. It was found that the best results were obtained when the ammonium sulfate, in hot concentrated solution, was added to the boiling mother liquor, after which the whole was set aside to deposit the alum. When the crystallization was completed, the mother liquor was evaporated to about half the volume of the original s o l u t i o n 4 e., before the alum crystallized. At this point the solution was allowed t o cool for 24 hours, then placed in a refrigerator a t approximately 0" C. for 24 to 48 hours. This treatment was found to remove all but a minute amount of aluminum, which was removed during the separation of the major portion of the iron as described below. Unless beryllium exceptionally free from aluminum is desired, the cooling in the refrigerator may be omitted. In order that no beryllium should be lost, the first alum crystals were recrystallized from water, wash water from the beryllium basic carbonate being employed. The crystals were placed aside and the mother liquors used to recrystallize the second crop of alum coming from the refrigerator. This was then treated in a similar manner to the solution and crystals obtained in the first alum crystallization. Removal of Iron
The filtrate from the second alum crystallization was heated in a stoneware vessel, by means of a leaden steam coil, to the boiling point and thoroughly oxidized by means of a little potassium bromate or other suitable oxidizing agent. The liquid was next treated with ammonium hydroxide (about 1 to 1) with very thorough stirring and boiling. The precipitated hydroxides rapidly dissolved a t first. As the addition of ammonium hydroxide was continued, the liquid turned deep red and then finally ferric hydroxide separated as a very finely divided precipitate. The addition of ammonium hydroxide was stopped as soon as the supernatant liquid gave a white precipitate upon dilution with water, indicating that the liquid was basic. At this point the pH of the cold solution was 5.5 to 5.7, determined with a quinhydrorie electrode. The pH of a solution from which the iron was not quite all removed, as shown by a distinct red color, was 5.2. With a little practice, it is possible to judge this point quite accurately, as the precipitate becomes very slightly, though distinctly, lighter in color. I t is very important at this stage of the process to add the ammon'um hydroxide carefully and see that the mass is thoroughly stirred and well boiled. The precipitated hydroxides must be given time to react with the solution so that the beryllium hydroxide redissolves. The final precipitate consists mainly of ferric hydroxide together with aluminum hydroxide, derived from the trace of aluminum which remained from the alum crystallization, and a small amount of beryllium hydroxide. The hydroxides were next removed by filtration through a very large Bt'ichner funnel. Any beryllium accompanying the ferric hydroxide was largely saved by stirring the residue with water, boiling, and treating with sulfuric acid until, after long stirring, the filtered liquid showed the presence of some iron by its reddish tint. This liquid, after filtration,
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was returned to the vessel and carefully treated with ammonium hydroxide as previously described. The basic acetate method can be used for separating iron from beryllium on a large scale. A minute amount of iron usually remains in solution. The introduction of ammonium acetate causes a little more bother in subsequent operations, owing to frothing when the beryllium is thrown out as basic carbonate. It also remains in the ammonium sulfate mother liquors which are used over again for the separation of aluminum. The small amount of iron and any members of the copper group were removed from the basic filtrate from the iron and aluminum hydroxides by treating with hydrogen sulfide under slight pressure. After the precipitated sulfides had been filtered off, the solution was found to give a perfectly clear solution when treated with solid ammonium carbonate and warmed. This clear solution did not become discolored on treatment with hydrogen sulfide, indicating the absence of iron. Should there be a darkening of the solution owing to the presence of mere traces of iron, it would be necessary t o saturate again with hydrogen sulfide. Any difficulty in removing iron a t this stage indicates that the solution mas not made sufficiently basic during the removal of the major part of that element as the hydroxide. Precipitation of Beryllium Basic Carbonate
The iron- and aluminum-free filtrate was heated to remove any hydrogen sulfide and the beryllium precipitated by the addition of ammonium carbonate and ammonium hydroxide in slight excess. Care must be taken not to add too large an excess of ammonium carbonate due to the solubility of basic beryllium carbonate in an excess of that reagent. Sufficient precipitant has been added when a small portion, after filtering off the precipitate, shows no turbidity upon the addition of ammonium carbonate. If the precipitate is not granular, boiling for a short time will cause it to become so, thus making it easy to filter and wash. This first wash water was added to the main filtrate, while that obtained later was used for recrystallizing the crude alum as described earlier, By so using all the wash water no ammonium sulfate was lost, A%1N.4LYSISOF BERYLLIUM BASICCARBONATE-The product resulting from the above treatment was pure white as was also the oxide obtained from the ignition of it. A determination of the impurities likely to be present gave the following results : LOTA
97 Si02
+ Fe203 Ca (spectroscopically) 41203
lTolatilematter h-on-volatile matter
0 015 0 05 h-one 60 25
39.75
LOTB 47, 0 025 0 04 None
59 80 40 20
Approximately 0.25 gram of the original sample contained in the 2 cc. of solution gave barely a perceptible coloration with potassium thiocyanate. Accordingly no attempt was made to determine the iron separately. The above analyses were made on material from two entirely different runs, showing that a product of consistent purity may be obtained by this method. Extraction of Caesium and Rubidium
The material for this work is indicated in Table I a t 7 , potassium, rubidium, and caesium alums. These were submitted to a fractional crystallization, whereupon the caesium with the minute amount of rubidium rapidly accumulated in the least soluble portion. These were separated from each other by further fractionation or/and precipitation of caesium antimony chloride and crystallization of rubidium acid tartrate.
Vol. 23, No. 3
Table I-Schematic
O u t l i n e of Separation (1) Mineral fused with CaO (2) Slag f Hz0 HnSO4 extracted with
+
i.
Residue Si02 and Cas04
4
J.
(4) Solution of sulfates of A1 and Be, etc.. evaporated to render any remaining SiOr insoluble
J.
SiOn
(6) Filtrate allowed to crystallize
K , Cs, i and R b alums
(8) Mother liquorJ
~
3
Alum A V
Alum B
4
Fe(OH13 and Al(0H)a
J.
FeS, CuS, etc.
+
Be basic carbonate
J.
(KHdZSO4
+
Lid203
+ (NHa)zSO4
+
(10) Mother liquor concentrated and cooled i (12) Mother liquor
+ NH4OH
+ H2S4 + Filtrate + NH4OH
(14) Filtrate (16)
-b (NH4)2C03
3
(18) Filtrate evaporated
c + NazCOa
(20) Mother liquor
4
Filtrate discarded
Before the fractionation was started, it was decided that the pink feldspar, which occurred plentifully in the mine from which the beryl came, should be examined for caesium and rubidium. d quantity of this was ground and fused as described under the decomposition of beryl. I n this case the slag did not fuse so readily and the furnace had to be run a t a very high temperature. The ground slag was very easily decomposed by dilute acid or even by solutions of aluminum and iron salts. By using insufficient acid, all the alkalies and only a little of the aluminum were dissolved. The solution gave a strong test for lithium, showing that the feldspar contained this metal in addition to potassium and sodium. After the solution had cooled, the clear liquid was siphoned off. and the crystals scraped out and drained. This alum, which showed only potassium and sodium lines when examined spectroscopically, was recrystallized many times. The alums from 9 kg. of mineral v-ere finally reduced to about 200 grams. These crystals gave no distinct test for caesium. Examination of Ferric Hydroxide for Scandium
Several in\-estigators in the past have pointed out that the arc spectra of many varieties of beryl show scandium lines. If the scandium mere present in beryl, it would be expected to concentrate with the ferric and aluminum hydroxides (see 13 in Table I). This precipitate was dissolved in hydrochloric acid, the boiling solution neutralized by means of ammonium hydroxide, and then thoroughly boiled with an excess of sodium thiosulfate. The precipitate, after filtering and washing with a little water, was heated with dilute hydrochloric acid and oxidized by addition of nitric acid. The free sulfur was removed by filtration and the liquid treated with an excess of sodium hydroxide to remove the aluminum and beryllium. The small quantity of insoluble hydroxides, after being washed, was warmed with water and oxalic acid. This treatment gave an insoluble oxalate that was colored blue from the presence of copper derived from the plates of the filter press. This oxalate was then heated with a slight excess of sulfuric acid to fumes with careful addition of nitric acid to oxidize any organic matter. The sulfates were dissolved in water, treated with hydrogen sulfide, and filtered. The clear filtrate was then warmed with oxalic acid, and a pure white oxalate was precipitated.
