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A new method for the preparation of rare earth bromates Robertson, Robert Frank Struan 1948

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£•£3 B 7 A NEW METHOD FOR THE PREPARATION OF RARE EARTH BROMATES Robert F. S* Robertson A Thesis submitted in partial fulfilment of the requirements for the degree of MASTER OF ARTS in the Department, of CHEMISTRY THE UNIVERSITY OF BRITISH COLUMBIA April 1948 AGOOWI-DGEM-HT This work was oarried out under the super-vision of Dr. J. Allen Harris, and i t i s to him that I wish to express my indebtedness for his keen interest and constant sound advice. ABSTRACT The preparation of the oxides of the cerium and yttrium sub-groups is discussed, and a new method is proposed for the preparation of rare earth bromates, involving the use of calcium bromate instead of barium brornate. The solubility of calcium bromate was measured roughly, and was found to be 102 .5 gms per 100 ml of saturated solution at 19°C. T A B L E O F C O N T E N T S Page I. Introduction .... 1 II. -reparation of Materials 1. Hare Earths (a) General 6 C_) Cerium Group 7 (c) Yttrium Group 9 2 . Calcium Bromate Ca) Preparation 14 Ch) Determination of solubility 15 3. Spectrographic Data 17 III. Preparation of Bromates 1. Cerium Group 21 2. Yttrium Group 24 IY. Discussion of Results 28 A FEW METHOD FOR THE PREPARATION OF RARE EARTH BROMATES I. INTRODUCTION The value of the hromates as a method of separation of the rare earths has long been recognised. They are especially useful as a means for the preliminary separation of the elements of the Yttrium Group, and use was made of them during the search for Illinium. 1 The solubilities of the hromates, in order of de-creasing solubility are roughly as follows: Erbium, lanthanum, Praesodymium, Yttrium, Holmiutn, Dysprosium, Neodymium, Terbium, Illinium, Samarium, Gadolinium, and Europium.2 James3 advanced the f i r s t synthesis of the rare earth bromates in 1908 and since then several other methods have been proposed. The main ones are as follows : -1. James* Method-^  The dried earth oxalates are heated with concentrated sulfuric acid, are warmed to expel excess acid and are heated strongly to convert them to the anhydrous sulfates. 2 These are now pulverized and sifted into ice water and the resulting solution is thoroughly stirred with freshly pre-cipitated barium bromate, f i l t e r e d and concentrated. (RE) 2(S0 4)3 + 3Ba(BrO^) 2 — * 3 B a S 0 4 + 2RE(Br0 3)^ 2. Harris 1 Method4 This method is an adaption of James method. The rare earth oxides are slowly digested with successive small portions of dilute sulfuric acid so that the resulting mixture is only feebly acid* The mixture is then evaporated to dryness and ignited to expel the excess acid. The re-sulting sulphates can then be. dissolved in water at room temperature and precipitated with a saturated solution of barium bromate. 3. Pearce's Method** The rare earth oxides are dissolved in dilute hydro-chloric acid, the hydroxides are then precipitated with dilute ammonia washed by decantation, and then dissolved i n just enough dilute sulfuric acid to dissolve the precipitate. The bromates are then prepared by adding solid barium bromate and heating, with constant stir r i n g , u n t i l precipitation is complete. The mixture is f i l t e r e d and concentrated. 4. Moeller and Kremer's Method^ The rare earth oxides are dissolved in perchloric acid and, on the addition of potassium bromate, potassium per-3 chlorate i s precipitated leaving the rare earth bromates in solution* RE (010-4)3 -f- 3 K B r 0 3~^3KC10 4 -f- RE(BrO^)^ In the preparation of a l l rare earth bromate solutions, the solution must be as nearly neutral as possible, otherwise, during fractionation, in the f i n a l concentration, decomposition invariably results i f the solution is at a l l acid. It is for this reason that elaborate precautions are taken in a l l the above procedures to cut down acidity* The f i r s t two methods are time consuming, and com-paratively large volumes of solution have to be used because of the very poor solubility of barium bromate. ILarge quan-t i t i e s of i r r i t a t i n g fumes are also produced. In the third method barium bromate i s added in the solid form, but in the author's experience i t was found that the resultant barium sulfate tended to precipitate around the barium bromate, severely inhibiting the reaction, and necessitating prolonged heating and stirring, or the use of a large excess of expen-sive barium bromate, to bring the reaction to completion. The fourth method is faster, requiring less volume of solution, but even so potassium bromate i s not very soluble. The main advantage of this method i s i t s speed and the fact that potassium .perchlorate occludes salts to a far less extent than does barium sulfate. - This, however, is in part offset by the relative solubility of potassium perchlorate. Reference to Table I shows that calcium bromate is much more soluble than "barium bromate and i t was thought that i f 4 this reagent could he substituted the volumes of solution required would be considerably decreased. Calcium sulphate is.more soluble than barium sulphate but i t w i l l be noticed that i t is less soluble than potassium perchlorate, and (on fractionation) any calcium sulfate that did carry- through would concentrate rapdily in the least soluble fraction. The solubility of calcium brornate i s about 1©3 gms/lOO gms of water at 20°C, so that any carried through should concen-trate with samarium and gadolinium in the less, soluble frac-tions* 3Ca (Br03)2 + (BJO^SO^-^aCaSO^ +- 2RE(Br© 3) 3 An added advantage of this method would be that the acidity of the solution need not be controlled to such a fine extent originally, since, prior to the addition of the calcium bromate the solution of rare earth sulfates can be neutra-lized by the addition of precipitated calcium carbonate. Here the only product is calcium sulfate, and as this is going to be precipitated in the next step, the small amount formed by the neutralization can be f i l t e r e d out with the main bulk of the precipitate. HgSC -^f- Ca CO —»CaS0 4 + 1^0 +C0 2 T 5 TABLE TABLE OP SOLUBILITIES (a) gms of solute in 100 gms H2O 0°C ' 2G°C 25°G 35°c 45°G 100PC BaS04 1.15x10" •4 2.4xl0~ 4 CaS04 1.76x10" •1 2. 0x10"1 1.&X10 KCIO4 7.5 xlO" •1 1 .80 21.8 Ba ( B r 0 3 ) 2 X 2.86x10" •1 6.52x10" 1 54xl0 _ 1 Ga(Br0 3) 2 K^ 103. KBrO^ 3 . 1 6.9 50.© 184.6 363.O 462.1 1061.5 TPrCBrO^)^ 88.55 167.9 196.1 278.5 434.5 Y(Br0 3) 3 168 DyCBrO^)^ v . s . Ncl(Br03)3 ' 66.35 128.6 151.3 205.8 289.9 Tb(Br03)3 66.42 117.1 133.2 172.9 227.1 Sm(Br03)3 49.78 100.6 117.3 157.2 214.1 Gd(Br03)3 50.18 95.58 110.5 144.5 195.6 Gms per 100 gms. saturated solution Own determination. Ca(Br©3)2 H2© ( a) Rare earth solubilities taken from James J. Am. Ohem. Soc. 49 132 (1927) . Remainder from Handbook of Chemistry and Physics 3 0 t h Edition 1947. A l l rare earth bromates are of the form RE(Br03)3 ' 9 H 2 ° 6 II. P R E P A R A T I O N OF M A T E R I A L S 1. Rare Earths The starting material used was Gadolinite from Norway. 1.1 Kg hatches (3 in a l l ) were added slowly to 2^ l i t r e s of hot concentrated hydrochloric acid. The red doughy mass that was.formed was heated for 24 hours, the acid lost hy evaporation being replaced. The mix was then diluted to 3 l i t r e s , f i l t e r e d , and washed v/ith 6 l i t r e s of hot water. The residue was re-extracted with hydrochloric acid and the resultant f i l t r a t e was united with the f i r s t . This f i l t r a t e was now diluted with water un t i l the concentration of free acid was about 0.1N, then was heated to about 8o°C, and hot saturated oxalic acid solution was added un t i l precipitation was complete. The oxalates were f i l t e r e d off, washed thoroughly with hot water, and roasted to the oxides in an electric furnace. The. total yield of oxides from 3 batches was 574- gms. This batch of oxides was now combined with 386 gms of oxides of Gadolinite earths. The combined oxides were then treated with concentrated n i t r i c acid. A vigorous reaction resulted but a large amount of insoluble material was l e f t which would not dissolve, even on repeated extraction with n i t r i c acid and hydrogen peroxide. This v/as f i l t e r e d off and assumed to be Ge ©«. 7 The resultant solution was-brownish in color and i t is of interest to note that i f hydrogen peroxide was added to this solution of nitrate a deep reddish orange solution resulted. This was found to be due to the presence of titanium, and i t was found necessary to reprecipitate the oxalates to free them entirely of this element. This w i l l be further dis-cussed on page 12 . The resultant solution of nitrates had a volume of about 5 l i t r e s , and was ascertained to be about 5 N in free acid by t i t r a t i o n of a 1 ml sample with 0 .1R sodium hydroxide. The solution was diluted to 10 l i t r e s and solid sodium sulfate was slowiy sifted into the cold solution with constant s t i r r i n g . A yellow precipitate soon formed. The addition of sodium sulfate was kept up unti l the 5200 A Neodymium band was only faintly disoernible through a 5 e m layer of the 7 solution, using a hand spectroscope. The spectroscope used was made by Reichert, Austria. The precipitate consisting of cerium group sulfates was f i l t e r e d off, but was not washed. Purification of Sub Groups A. Cerium Group The next task was to remove the cerium completely from the precipitated sulfates. Several methods are available 8 q notably the potassium bromate and the permanganate phosphate'-7 methods. It was decided to use the . latter as i t gave a quantitative separation and was less time consuming. 8 The sulfate precipitate was treated with 1 5 N ammonium hydroxide until the appearance of the precipitate indicated that i t had been converted to the hydroxides. This pre-cipitate was washed hy decantation, was dissolved in dilute n i t r i c acid and the oxalates precipitated. The oxalates were roasted to the oxides and then the oxides were dissolved in dilute n i t r i c acid so that the resultant solution was less than 2N in acid. A solution of disodium hydrogen phosphate was added and i t was noticed that a yellowish gelatinous pre-cipitate appeared almost immediately. This was probably a mixture of eerie and titanium phosphates. Now a 0.5N solution of potassium permanganage was added and the mixture became thick with eerie phosphate. The mixture was heated for one hour and was then f i l t e r e d . The f i l t r a t e was treated with hot concentrated oxalic acid and the resultant oxalates were f i l t e r e d out and roasted to the oxides. It was found necessary to repeat this procedure twice more to remove the cerium completely. The f i n a l oxides which were dark brown in color, weighed 160 gms. A l l the sulfates obtained, incidentally, were not converted to the oxide. It was found that disodium hydrogen phosphate was the best precipitating agent to use here. If phosphoric acid was used a white insoluble basic salt was formed which was very hard to f i l t e r out and was found on analysis to contain other earths besides cerium. The average atomic weight of these earths was found by 9 the method based on the ratios; oxalate/oxide, oxalate/per-manganate.10 Results are tabulated in Table II. The value of 137»0 is slightly lower than the atomic weights of the other members of this group, but this may be explained i f i t is remembered that the "double sulfate s p l i t " is by no means quantitative, and some scandium w i l l remain in the cerium group. B. Yttrium Sub Group The f i l t r a t e from the sodium sulfate precipitation was made basic with ammonium hydroxide and the resultant hydrox-ides were washed by decantation and dissolved in dilute n i t r i c acid. The oxalates were then precipitated and con-verted to the oxides. The cerium was now removed by the same procedure as before, and again i t was found that three precipitations were necessary. For this sub group i t was found that either disodium hydrogen phosphate or phosphoric acid could be used as the precipitant, but that the disodium hydrogen phosphate gave best results* The resulting-oxides weighed 190 gms, and were a light tan color. The results of an average atomic weight determination done on this group are given in Table III. The very low value of IO8.5 is due to the presence of scandium (At. Wt .45.l) or yttrium (At. Wt. 88.92) or, more probably, both. 10 TABLE I I AVERAGE ATOMIC WEIGHT CERIUM GROUP Wt. Oxalate V o l . of T i t r a t e d (Gms) KMTIOA ( m l ) 4 n o r m a l i t y Wt. of of Oxalate KMnOy I g n i t e d Wt. Oxide Obtained 0.1622 0.1518 0.16465 44.75 41.75 45.30 0.0340 .0.0340 0.0340 0.4075 0.4032 0.4087 0.2049 0.2023 O.2052 R e l a t i o n s h i p Used REoO 2U3 3<S2 °3 R e s u l t s 2RE -*-48 216.06 ( i ) RE. = • 136.8 ( i i ) RE = •> 136.9 ( i i i ) RE = • 137.0^  gms oxide obt. gms o x a l a t e i g n i t e d x gms oxa l a t e t i t r a t e d V0I.KM1O4 x M of KMn04 x G.Equiv. ' ' wt. Co 0-j 1000 d 3 Value chosen as Average Atomic Weight 137»0 11 TABLE I I I AVERAGE ATOMIC WEIGHT YTTRIUM GROUP Wt. Oxalate V o l . of Normality Wt.of Wt. Oxide T i t r a t e d (Gms) K M U O 4 o f Oxalate Obtained (ml) KMn04 I g n i t e d . (Gms) (Gms) . Same r e l a t i o n s h i p used as before. R e s u l t s (I) BE : 108,4 ( I I ) RE. : : 108.5 ( I I I ) RE = : 108.5^ 0.2097 56.05 0.0392 0.4115 0.1903 0.2341 62,50 6.0392 0.4262 0.1971 0.22135 59.05 0.0392 0.4989 0,2305 Value chosen as average atomic weight IO8 .5 12 In the f o r e g o i n g procedures i t was n o t i c e d t h a t , i n the e a r l y stages, a f t e r p r e c i p i t a t i o n of the o x a l a t e s w i t h hot s a t u r a t e d o x a l i c a c i d , a y e l l o w c o l o r always remained i n the supernatant l i q u i d . At f i r s t i t was thought t h i s was due to e e r i e cerium which was not reduced hy the o x a l i c a c i d , hut f u r t h e r i n v e s t i g a t i o n showed t h a t t h i s was not the case, and the c o l o r was shown to he due t o the presence of f e r r i c and t i t a n i c s a l t s . T h i s was done as f o l l o w s : Some of the cerium g r o u p . s u l f a t e s were converted to the hydroxides before the removal of the cerium and p r e c i p i t a t e d as the o x a l a t e s . The mother l i q u o r , which was a deep orange y e l l o w c o l o r , was c a r e f u l l y decanted through a f i l t e r and was made b a s i c w i t h ammonium hydroxide. An orange g e l a t i n o u s p r e c i p i t a t e appeared, which was f i l t e r e d out and d i s s o l v e d i n 6K h y d r o c h l o r i c a c i d . H a l f of t h i s s o l u t i o n was d i l u t e d w i t h water u n t i l the a c i d c o n c e n t r a t i o n was about 0*5 N , and on the a d d i t i o n of hot s a t u r a t e d o x a l i c a c i d no p r e c i p i t a t e appeared, showing the absence of cerium or any other r a r e e a r t h . The r e s t of the s o l u t i o n was e x t r a c t e d w i t h e t h e r . The ether l a y e r was evaporated and on t r e a t i n g p a r t of i t w i t h ammonium hydroxide, the t y p i c a l r e d f e r r i c hydroxide appeared. The blue f e r r i c f e r r o c y a n i d e was a l s o obtained w i t h potassium f e r r o c y a n i d e , and the r e d complex w i t h potassium t h i o c y a n a t e , but t h i s was not r e l i e d on because t i t a n i c s a l t s g i v e p r e c i s e l y the same c o l o r i n the l a t t e r case. The water l a y e r was found to c o n t a i n t i t a n i u m only by the f o l l o w i n g t e s t s . The a d d i t i o n of hydrogen per o x i d e produced 13 a red solution, ammonium hydroxide gave only a-white gelatinous p r e c i p i t a t e , and potassium ferrocyanide gave only the brown t i t a n i c ferrocyanide. The oxalate p r e c i p i t a t e was washed thoroughly with b o i l i n g water, was converted to the oxides, and the oxalates were then r e p r e c i p i t a t e d . This time a f a i n t yellow color was apparent i n the mother l i q u o r , and t h i s was found to be due almost e n t i r e l y to titanium. A trace of iron, but no cerium, was found. The oxalates were again washed thoroughly with b o i l i n g water, converted to the oxides and dissolved i n n i t r i c acid* The sol u t i o n was quite yellow, but the addition of hydrogen peroxide to a few drops of t h i s caused the yellow color to vanish completely. This indicates that, while i g n i t i o n of oxides causes the formation of cerium dioxide, subsequent soluti o n i n n i t r i c acid leaves a considerable amount of the cerium i n the eerie condition. On p r e c i p i t a t i n g the oxalates again the mother liquor was now found to be quite col o r l e s s * These tests show d e f i n i t e l y that the yellow color was due to titanium and iron, which seem to be occluded to a considerable extent by the oxalates,' but not to cerium. To ensure com-plete removal of impurities from the oxalates, at least two p r e c i p i t a t i o n s are indicated. 14 2. Calcium brornate (a) Synthesis To prepare the calcium hromate, use was made of the following reactions: 2 HC10 4 + CaCO^ » Ca(C10 4) 2 * HgO + C0 2T Ca(C10 4) 2 •*• 2 KBrO-j * C a t B r O ^ + 2 KC10 4 Method. 1000 ml of 6o# perchloric a c i d i s treated with excess calcium carbonate (about 55° gms) u n t i l a l l reaction has ceased. The s o l u t i o n i s heated and the excess calcium carbonate i s removed by f i l t r a t i o n , C e l i t e f i l t e r a i d being added i f i t tends to run through the f i l t e r . l 8 0 0 gms of potassium brornate are now dissolved i n b o i l i n g water and t h i s solution i s added slowly with constant s t i r r i n g . The mixture i s now cooled to 0°C being s t i r r e d mechanically a l l the time, and the potassium perchlorate i s f i l t e r e d off but i s not washed. The f i l t r a t e i s evaporated on a steam bath and a l i m i t e d series of f r a c t i o n a l c r y s t a l l i -zations i s set up., the least soluble frac t i o n s being d i s -carded as they contain -potassium perchlorate and potassium brornate. . It i s best to cool to 0°C before separating the cr y s t a l s from the mother liquor to ensure as complete a removal of potassium s a l t s as possible. The intermediate fracti o n s are dried i n a vacuum over concentrated s u l f u r i c acid f o r a few days and are stored. Theoretical y i e l d 15 1594 gms. Actual y i e l d about 13OO gms. (b) Determination of S o l u b i l i t y No data on the s o l u b i l i t y of calcium bromate could be found i n any of the l i t e r a t u r e , so i t was decided to deter-mine i t roughly for room temperature. The method used was as follows. A saturated solution of calcium was prepared and was allowed to stand several days to reach equilibrium. A 10 ml portion was pipetted into a cal i b r a t e d volumetric f l a s k and di l u t e d to the mark with d i s t i l l e d water. 10 ml portions of th i s solution were evaporated with 3 mL concentrated hydro-c h l o r i c acid to destroy the bromate, 10 ml water and 30 1 1 1 1 o f 0*5 M ammonium oxalate were added and then, slowly, with constant s t i r r i n g , d i l u t e ammonium hydroxide u n t i l the solut i o n was basic. The pre c i p i t a t e of calcium oxalate was heated to 8o°C on a water bath, allowed to stand f o r one hour and was then f i l t e r e d and washed by decantation u n t i l free from chloride ion. The pr e c i p i t a t e was dissolved completely i n 30 ml of hot 3 N s u l f u r i c acid, the f i l t e r was washed thoroughly with hot water, and the resultant s o l u t i o n was t i t r a t e d with standard permanganate. Results• Flask at 23°C contains 499.30 ml. Temperature at which saturated CaCBrO^^ sample taken 19°C 16 K of KMn04 Vol KM11O4 used for Soly. CatBrO^JgHgO 10.0 ml sample g/lOO ml sat.soln. 0.0260 50.4 ml 102,8 0.0260 50.1 " 102.2 0.0340 38.6 " 103.0 0.0340 38.2 n 102.0 Average Solubility - 102 . 5 g/100 ml sat. soln. at 19°G 17 3* Spectrographic Data v The equipment used was the same as that used by Taylor, the only alterations being: ( i ) The arc and the Point-o-light were mounted on the same o p t i c a l axis. When the poles of the arc were separated by an inch or so the Point-o-light could shine through unobstructed and so do away with the necessity of a r e f l e c t i n g mirror. ( i i ) The arc assembly and the Point-o-light were encased i n a plywood box. This kept d i r e c t l i g h t off the spectroscope and also preserved the operator's eyes. Cut f i l m , instead of plates, was used and excellent re s u l t s were obtained. It was found that Kodak Super Panchro Press gave best r e s u l t s and with t h i s f i l m the ex-posure time for the arc could be cut to a f r a c t i o n of a second and f i v e second's exposure through a 1 cm absorption layer was ample. In making a l l plates the usual standard procedure of converting the sample to the n i t r a t e and then photographing the saturated solutions through a 1 cm layer, giving an ex-posure of f i v e seconds, was followed. Some "Specpure" samples Of the rare earths were obtained from Johnson, Matthey and Mallory of Toronto, and absorbtion spectra of these are shown i n Pig. 1. P i g . 2 shows absorbtion spectra of the n i t r a t e s of the cerium and yttrium groups, whose preparation i s described 18 previously. For the benefit of future operators the optimum settings for the spectroscope are; S l i t 0.005 Telescope .. 13*0 Plate T i l t 2.1 Arc current 3 amps Exposures (Kodak Super Pan Press Film) Arc 1/2 to 1 sec Absorbtion 5 sees If the prism is set at 461.75 the spectra w i l l be centered on the plate. F i g . I P r a e s o d y m i u m N i t r a t e N e o d y m i u m N i t r a t e S a m a r i u m N i t r a t e E r b i u m N i t r a t e H o l m i u m N i t r a t e 20 g i g . I I S p e c t r a of C e r i u m a n d Y t t r i u m G r o u p N i t r a t e s 1 . O r i g i n a l S a m p l e 2. C e r i u m G r o u p 3 . Y t t r i u m G r o u p 21 I I I . PREPARATION OF BROMATES (a) Cerium Group 100 gms o f . c e r i u m group oxides were d i s s o l v e d i n 130 ml of c o n c e n t r a t e d n i t r i c a c i d , g i v i n g a p i n k s o l u t i o n . T h i s was made b a s i c w i t h ammonium hydroxide and the p r e c i p i t a t e d hydroxides were washed by d e c a n t a t i o n w i t h d i s t i l l e d water u n t i l the supernatant l i q u o r was only s l i g h t l y b a s i c . Pearce^ now recommends t h a t the supernatant l i q u o r be decanted o f f , but i t was found t h a t i f the mixture i s f i l t e r e d , a c o n s i d e r a b l e r e d u c t i o n i n the volume of the bulky hydroxides i s e f f e c t e d . I f a l a r g e Buchner f u n n e l and a Genco Pressovac o i l pump, as a source of vacuum, i s used, f i l t r a t i o n i s q u i t e r a p i d . J u s t enough 6 N S u l f u r i c a c i d t o d i s s o l v e the p r e c i p i t a t e , (about 350 ml), was now added and a c l e a r pink s o l u t i o n r e -s u l t e d . I n a d v e r t e n t l y , at t h i s p o i n t , too much a c i d was added and the s o l u t i o n was d i s t i n c t l y a c i d ; however powdered c a l c i u m carbonate was s i f t e d i n and the s o l u t i o n r a p i d l y r e -gained n e u t r a l i t y , w i t h no i l l e f f e c t s . A c o n c e n t r a t e d water s o l u t i o n of 312 gms of c a l c i u m bromate was next added and the mixture was heated on a steam b a t h f o r an hour w i t h constant s t i r r i n g . The p r e c i p i t a t e of c a l c i u m s u l f a t e d i d not come down at once, but only a f t e r about f i v e minutes of h e a t i n g and s t i r r i n g . The c a l c i u m s u l f a t e was f i l t e r e d o f f , washed w i t h 500 ml of b o i l i n g water, and the r e s u l t i n g f i l t r a t e was evaporated on a steam bath. 22 By the color of the calcium sulfate i t could he seen that some occlusion of rare earths had taken place, and, to deter-mine how much, the p r e c i p i t a t e was "boiled with hydrochloric acid u n t i l a l l the bromates had decomposed. The rare earths were precipitated, converted to the oxides, and the weight of oxide was found to be 35 gms, showing that calcium s u l f a t e occluded about 35^ of the o r i g i n a l oxides. This value i s very high, but i t should be pointed out that only 500 ml of wash l i q u i d was used. In preparing the yttrium group bromates more wash l i q u i d was used and l e s s occlusion resulted. The oxides r e s u l t i n g from the occlusion were a very much darker brown color than the others. Their absorbtion spectrum i s shown i n F i g . I l l , Spectrum 1, and i t w i l l be noticed that neodymium and es p e c i a l l y lanthanum seem to be concentrating there. When the f i l t r a t e containing the rare earth bromates had reached a volume of about one l i t r e , i t could be seen that a considerable p r e c i p i t a t e of calcium sulfate had separated. This was f i l t e r e d off and evaporation was continued. When a volume of about 600 ml was reached, the accumulated calcium sulfate was again f i l t e r e d o f f , and when the f i l t r a t e was cooled the bromates started to c r y s t a l l i z e . As there was not enough time' to carry out a complete series of f r a c t i o n a -tions, the bromates were divided into s i x rough f r a c t i o n s and the absorbtion spectrum of a representative sample of each was photographed. The r e s u l t s are tabulated i n Table IV and the spectra are shown i n F i g . I I I . 23 During the e n t i r e course of the c r y s t a l l i z a t i o n a c l o s e check was kept on the. a c i d i t y of the s o l u t i o n , and i f i t showed any s i g n s of hecoming too a c i d powdered c a l c i u m c a r -bonate was s p r i n k l e d i n u n t i l n e u t r a l i t y was r e g a i n e d . A f t e r two of these a d d i t i o n s i t was n o t i c e d t h a t a s l i g h t brown sludge formed, which was f i l t e r e d out and on a n a l y s i s found to be mainly cerium. A b s o r p t i o n s p e c t r a ( F i g - I I I S p e c t r a 2 and 3) showed a s m a l l amount of scandium to be present a l s o . I t was probably the o x i d a t i o n and subsequent h y d r o l y s i s i f t h i s cerium t h a t caused the r i s e i n a c i d i t y of the s o l u t i o n . The amount of cerium was not g r e a t , but the f a c t t h at i t was t h e r e i n d i c a t e s t h a t i t had not been e n t i r e l y removed by the permanganate-phosphate treatment. . However, i f the above procedure i s f o l l o w e d t h i s i s not important, s i n c e , i f an excess of c a l c i u m bromate i s added and the s o l u t i o n i s kept n e u t r a l , any s m a l l amount of cerium w i l l be p r e c i p i t a t e d as the b a s i c e e r i e s a l t and can be removed al o n g w i t h the c a l c i u m s u l f a t e . TABLE IV  CERIUM GROUP F r a c t i o n C o l o r of Oxide Elements i n d i c a t e d by a b s o r p t i o n s p e c t r a 1 2 3 4 5 6 Brown Brown L i g h t Brown L i g h t Brown Cream Cream TPr, Nd, Sm, Ho. Pr,^Nd, Sm, Ho. Pr, Nd, Sm, Ho. Pr, Nd, Sm, Ho. No RE g i v i n g absorp-t i o n spec. Nd ( t r ) , Sm ( t r ) 24 Due to the rough nature of the f r a c t i o n a t i o n not much dat a could he obtained on where the v a r i o u s s a l t s were coming out, but i t was n o t i c e d t h a t as f r a c t i o n 5 was being c r y s -t a l l i z e d the appearance of the c r y s t a l s and t h e i r mode of f o r m a t i o n i n d i c a t e d t h a t c a l c i u m brornate was coming out here i n a d d i t i o n t o the o t h e r s . (b) Y t t r i u m Group 100 gms of the y t t r i u m group oxides were t r e a t e d i n an e x a c t l y analagous manner t o those of the cerium group, u s i n g s t i o c h i o m e t r i c q u a n t i t i e s of reagents, w i t h a s l i g h t excess of c a l c i u m brornate. Again i t was found t h a t , i f the s o l u t i o n was too a c i d upon the f o r m a t i o n of the s u l f a t e s , i t c o u l d be e a s i l y r e s t o r e d t o n e u t r a l i t y by the a d d i t i o n of powdered c a l c i u m carbonate. The p r e c i p i t a t e of c a l c i u m s u l f a t e was washed t h i s time w i t h 2 l i t r e s of b o i l i n g water, and i t was found t h a t only 20 gms of the oxide were occluded, and as these oxides were i d e n t i c a l i n c o l o r to the o r i g i n a l they were not spectrographsd. The s o l u t i o n of bromates was evaporated to a volume of about one l i t r e and the accumulated c a l c i u m s u l f a t e was f i l t e r e d out. As t h i s p r e c i p i t a t e c o u l d be seen by i t s c o l o r to c o n t a i n r a r e e a r t h s , i t was b o i l e d w i t h one l i t r e of water and f i l t e r e d . The water e x t r a c t was found t o c o n t a i n 9 gms of oxide and the r e s i d u a l c a l c i u m s u l f a t e 6 gms of oxide. (water e x t r a c t , spectrum 1; Residue from c a l c i u m s u l f a t e , spectrum 2, F i g . IV). 25 The remaining hromate solution was concentrated further on the water bath and was divided into six rough fractions. It was found necessary to add calcium carbonate only at the last fraction when the solution became slightly acid. A small amount of cerium was found i n Fraction 2. Table V shows the results of each fractionation and absorption spectra are shown in Fig. I V . TABLE V  YTTRIUM GROUP Fraction Color of Oxide Elements indicated by absorption spectra 1 Cream Sm (tr) Ho (tr) 2 Yellow Sm ( t r ) Ho (tr) 3 Yellow Nd ( t r ) , Sm, Ho. 4 Yellow TSd ( t r ) , Sm, Ho* 5 Yellow Kd ( t r ) , Sm(tr), Ho 6 Pale Yellow Ho. 5M F i g . I l l C e r i u m G r o u p F r a c t i o n s E x t r a c t f r o m CaSO^. R e s i d u e s a f t e r t r e a t m e n t w i t h CaCO^ F r a c t i o n 1 5. F r a c t i o n 2 6. • 3 11 4 5 7 . 8. g i g . I V  Y t t r i u m G r o u p F r a c t i o n s 28 I V . DISCUSSION Off RESULTS The foregoing results show that i t is possible to prepare rare earth bromates using calcium bromate in the place of the barium salt. The main advantages of this method are : -1. Calcium bromate is far more soluble than barium bromate and thus the reduction in volume of solution needed is considerable. The use of solid barium bromate is eliminated. 2. Since calcium carbonate may be sprinkled into the solution, the usual stringent precautions taken at the start, to prevent the solution becoming too acid, are eliminated. Of course the solution should be as neutral as possible, but time need not be wasted making, sure i t is entirely neutral. 3« The complete removal of cerium is not essential, as any small amount present w i l l be precipitated as the basic eerie salt. This is in effect the James method for the g removal of cerium . Here again of course most of the cerium should be removed before the bromates are made, but complete removal is not essential. 4. Calcium bromate is cheaper than barium bromate. It is easy to prepare. 29 The main disadvantages are : -- 1. Calcium s u l f a t e i s appreciably soluble. However « i t was noticed throughout t h i s work that nearly a l l of the calcium sulfate tended to separate out before the bromates themselves c r y s t a l l i z e d . 2. Calcium sulfate tends to occlude s a l t s to a high degree, although i t i s doubtful i f i t does so any more than does barium brornate. • Some other conclusions reached during the course of th i s work are : .-1.. To ensure quantitative removal of cerium by the permanganate-phosphate method, care must be taken that the solution i s not over 1 N i n free acid, as,, i n acid concen-tra t i o n s greater than that the s o l u b i l i t y of eerie phosphate i s appreciable. 2. The writer was asked to track down the yellow color that remained i n the solution a f t e r the oxalates were pre-c i p i t a t e d i n i t i a l l y . This was shown to be due to the presence of titanium and i r o n . Suggestions for.further work. Much work remains to be done on th i s problem and the main avenues of approach suggested are : -1. Bromates of the cerium and yttrium groups should be prepared and thoroughly fractionated to determine where • 30 the c a l c i u m s u l f a t e and bromate separate out. 2. F u r t h e r data should be.obtained on the s o l u b i l i t y of c a l c i u m bromate at temperatures ranging from 0°C to 10O°C. 3» The optimum volume of wash water t o be used f o r the washing of the p r e c i p i t a t e d c a l c i u m s u l f a t e should be d e t e r -mined, i n order to ensure the most thorough washing, w i t h l e a s t s o l u t i o n of the p r e c i p i t a t e . 4. The q u e s t i o n whether c a l c i u m s u l f a t e p r e f e r e n t i a l l y absorbs any of the r a r e earths s h o u l d be s t u d i e d f u r t h e r , s i n c e , i f t h i s i s the case, a u s e f u l p r e l i m i n a r y s e p a r a t i o n c o u l d be brought about. BIBLIOGRAPHY 1. Harris J.A. (J. A. G. S.) 43 1858 (1926) 2. James Cand Co-workers (J.A.C.S.) 49 132 (1927) 3. James C. (J. A. C. S . ) 30 182 (1908) 4. Harris J.A. (J. A. C. S.) 53 2475 (1931) 5. Pearce D.W. and Russell R.G. Inorganic Syntheses, Vol. II (W.C.Pernelius) p. 62 6. Moeller T. and Kremers H.E. (JiA.C.S*) 66 1795 (1944) 7. libeller T. and Kremers H.E. Ind. & Eng. Chem. (Anal. Ed.) 17 44 (1945) 8. James C. (J. A. G. S.) 33 1326 (1911) 34 757 (1912) 9. Heckers J.W. and Kremers H.C. (J.A.C.S.) 50 955 (1928) 10. Barthauer G.L., Russell R.G. and Pearce D.W. Ind. & Eng. Chem. (Anal. Ed.) 15 548 (1943) 11. Taylor A.E. Master 1s Thesis, University of B. C. 1946 General References Consulted S- I. ILevy, The Rare Earths D.M.Yost, H.Russell and C.S«Garner The Rare Earth Elements and Their Compounds Inorganic Syntheses, Vol. II. W.C.Pernelius Ed-in-Ghief Articles 11 - 19 B. S. Hopkins, Some Chapters in the Chemistry of the Less Pamiliar Elements. (Chapter on Rare Earths) 

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