1986
INDUSTRIAL AND ENGINEERING CHEMISTRY
and carbonate ions to form the barium carbonate crystal !attice which is apparently a less soluble arrangemerit of the ions. For 99% conversion of barium sulfate to tho carbonate, 4.4 moles of sodium carbonate n-ere sufficient at a tenipcrature of 840" C. for 30 minutes. The relation of the product of molar concentration of the barium ions times the molar concentration of carbonate ions divided by the molar concentration of barium carbonate recovered does not equal a constant. Variat,ion of time of reaction for 0.5, I, and 1.5 hours at temperatures of 840" and 1000" C. on the various mixtures had no effect on the per cent conversion of barium sulfaic to the carbona,te. Quick quenching from 1000" C. of the molten mixtures as 5hov-n in Tables ITr and I7shoJyed lower convcreion. Just above the melting point barium carbonate is the first compound i o become insoluble. I n ot,hei words, i t is thc. least soluble a t t,hai-
Vol. 40,
No. 10
temperature. Therefore. if given opportunity the baiiuin and the carbonate ions unite to form crystals of barium carbonate, but if quenched suddenly from the molten state no opportunity is afforded for thew ions to get together except for the chance to bcx adjacent a t the moment. Under such conditions the conversion to barium carbonate is merely a matte1 of the number of ions which happen to be in contact a t thc moment. LITERATURE CITED
(1) Booth, I-iaiold S., U. S.Patent, 2,013,401 (Sept. 3, 1935) 12) Ibid.. 2.112.903 (4nril 5 . 1938). (3) Bcoth, Haiold S.,&Pollaid,E. F , and ltentuchler, hI. -1.. l u n Esc. CHEM., 40, 1981 (1948). (4) Noffatt, A, Biit. Patent 22,033 (Sept. 22, 1910). ( 5 ) Xloore, G., U. S.Patent 1,388.285 (-4ng. 23, 1921). ( 6 ) Tammann, G., 2. angeu. Chenz., 39, 863 (1926) REcsrvLD
Conversion of Celestite t
AIarch 27 1H47
§trontium
HAROLD STIPI~IBNSBOOTH AND EEISRA FREDERICK POLLARD' Western Reserve L-niversity9Cleveland 6 , Ohia
OXPOCSDS of stron
Strontium sulfate (celestite) is soluble in fused sodium strontium sulfate t o the carchloride. lnsoluble impurities may be separated by bonate was observed at a tium are made either from the natural carbonate settling and decantation, after which addition of sodium temperature of 840" 6. Ex(strontianite) or from the sulcarbonate to the melt, followed by cooling and leaching to periments were run to find fate (celestite). The former, remove soluble salts, leaves a residue of pure strontium the effect of variations in the carhonate. This procedure has the advantage of producrate of cooling on the per though readily acted upon by acids to yield solutions ing in practically one operation a strontium carbonate of cent conversion. Additional of the desired salts, is not high purity, free €rom objectionable sulfur compounds, determinations were carried plentiful. The sulfate, on the out with and without the other hand, is fairly plentiful fused solvent to ascertain the and is either first reduced to the water-soluble sulfide by means effect of temperature at 840" and 1000' 6.and time of heating of carbon or fused with sodium carbonate. From the sulfide and on the per cent conversion. rarbonate other strontium salts are obtained easily. GROUPI. The components, consisting of 5 grams of sodium I n this investigation a study was made of the reaction of stronchloride, 2 grams of strontium sulfate and a calculated amount of tium sulfate and sodium carbonate i n an inert fused solvent (sosodium carbonate, wcre mixed intimately and the mass heated in dium chloride) ( 1 , 2 ) . covered olatinum crucibles in a Hoskins electric furnace for 0.5, hour a t 840" C. The molten produrt \+as allowed to cool in the furnace to room temperature and analyzed for its content of EXPERIMENTAL
The experimental work involves the same ,general procedure as used in the conversion of barytes to barium carbonate (5), I n all experirnents the various mixtures contained 2 grams of .strontium sulfate and a calculated amount of sodium carbonate based on the assumption t'he re.action proceeded according to the equation: SrSO
h
+ Ka&Os
= BrC08 4- NazSO~
s me of the experiments
AT
NaCI, Grams 5
SrSO4, Grama 2 2
5
2
1.1541
5
2
1.0387
5
2
0.8079
5
a
0.5770
6
2
0.3462
5
Present address, Southern Regional Research Labora,tory, U. 9. Department of Agriculture, New Orlea.nr, La.
8.20'e.
(Conversion using fused sodium rhloride as solvent) ~ Ratio _ _ ~ R Cpn- Carbon- Stron~ a z ~ ~ version s , ate tium S ~ C O ~s ~ + x+ COa-Grains SrSOa ions ions peeovered SrCOa 1.2695 IOO.00 ~..( .... .... 1.2118 99.21 1.05 1. 0,9930 1.06 I
5 grams and in
others 10 grams of sodium chloride solvent were used. Determinations were run using dif,feerent equivalents of the calculated amount of sodium carbonate. The effect of dilution with -sodium chloride on the per cent conversion of 1
TARLE 1. COKVERSIOS OF STRONTIUM SULFATE TO STROSTIUM CARBONATE
09.40 94.78 94.46 94.25 85.01 84,74 84.42 65.10 64.99 65.37 45.10 45.00 25.96 26.21
.
1.00
3
0.9462
1.06
0.90
I
0.8487
1.06
0.70
7~
0.6504
1.07
0.50
n
0.4508
1.11
0.30
P.
0.2608
1.15
g
October 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY
OF STRONTIUM SULFATE TO STRONTIUM CARBONATE TABLE 11. CONVERSION
AT
840' C.
(Conversion in dilute solution of fused sodium chloride) Ratio % ConSrS04, NazCOa, version COS SI SrCOa ""+ Grams Grams SrSOa ions ions recovered SrCOs 1 0.9452 1.06 94.52 1.00 1.1541 2 1 0,8450 1.07 0.90 84.50 2 1.0387 1 0.6496 1.07 0.70 64.96 2 0,8079 1 0.4510 1.11 0.50 45.10 2 0.5770
'''--
NaC1, Grams 10 10 10 10
=
K
OF STRONTIUM SULFATE TO STRONTIUM CARBONATE TABLE 111. CONVERSION
AT
NaC1, SrS04, Grams Grams 2 0
840" C.
(Conversion without sodium chloride as solvent) Ratio % C m - Carbon- StronNazCOa, version ate tium SrCOs Grams SrS04 ions ions recovered 1 0.9426 1.00 1.1541 94.21 94.33 1 0.8482 84.94 0.90 1.0387 84.70 1 0.6476 64.65 0.70 0,8079 64.88 0.50 1 0.4525 45.18 0,5770 45.32 1 0.2575 25.92 0.30 0,3462 25.58
x 'OS-SrCOa 1.06
E
K
1987
GROUP 111. These determinations were carried out similarly to those in Group I ; the only variation was that no sodium chloride was used (Table 111). GROUPIV. I n these experiments the cooling process was altered. The sample was heated in the furnace to 840 O C. and held a t this temperature for 0.5 hour. It was allowed to cool in the air for 1 minute and was plunged immediately into a beaker containing 40% alcohol. The compositions of the samples used in the various fusions were the same as those described in Group I (Table IV). GROUPV. This group of experiments was a repetition of those in Group IV, except that 10 grams instead of 5 grams of $odium chloride were used in all the fusions, to determine the effect of dilution of the per cent conversion (Table V). AYA LYTICAL METHOD EMPLOYED AND ITS ACCURACY
The cooled contents of the crucible were washed into a beaker with 150 ml. of 40Ye alcohol. After digestion on a steam bath a t 1.10 0 2 70" C. for 0.5 hour, the solution was filtered 1.16 0 2 through Jena glass filters and the precipitate washed with 100 ml. of 4070 alcohol. The filters then were dried in an electric oven a t 120" C. for OF STROXTIUM SULFATE TO STRONTIUM CARBONATE 1 hour and subsequently weighed. Strontium TABLE IV. COXVERSION AT 840" C. sulfate and strontium carbonate remained on the (Quick quenching of reactants in fused sodium chloride as solvent) filter. The strontium carbonate was removed Ratio from the filter with 50 ml. of 6 N hydrochloric acid. % Cpn- Carbon- StronFollowing this, 50 ml. of 40yGand 50 ml. of 95% NaC1, SrSO4, NazCOa, version ate tium SrCOa g + +x = K Grams Grams Grams SrSOa ions ions recovered SrCOa alcohol were poured over the filter to remove the 1.06 94.65 1.00 1 0.9448 5 2 1.1541 last traces of strontium chloride and hydrochloric 94.31 1.07 84.01 0.90 1 0.8417 5 2 1.0387 acid. The filter then was dried as before and again 84.33 weighed. 65.12 0.70 1 0,6522 1.07 5 2 0,8079 65.33 The substances in this melt were sodium khlo1 0.4510 1.11 44.94 0.50 5 2 0.5770 45.26 ride, sodium sulfate, sodium carbonate, strontium 1.15 26.21 0.30 1 0,2599 5 2 0.3462 chloride, strontium sulfate, and strontium carbon25 78 ate. The solubilities of these substances in alcohol were determined. It is known that alcohol OF STRONTIUM SULFATE TO STRONTIUM CARBONATE decreases the solubility of strontium sulfate and TABLE V. CONVERSION AT 840" C. strontium carbonate. It was found, however, (Quick quenching of dilute solution of reactants in fused sodium chloride) that not more than a 40% aqueous alcoholic R a.t.i.o... ~ solution need be used in the procedure because % Cpn- Carbon- StronSrCOa SF++ x COS-- = ate the solubilities of sodium carbonate and sodium tium version h'aC1, SrYOa, NazCOa, SrS04 ions ions Grams rwovered SrCOa Grams Grams sulfate decreased rapidly above this concentra94.80 1.00 1 0.9480 1.05 1.1541 10 2 tion. Hvdrochloric acid dissolved the strontium 84.79 2 1.0387 0.90 1 0,8479 1.06 10 lo 2 0.8079 64.75 0.70 1 0.6475 1 .os carbonate and did not dissolve an appreciable 44.98 0.50 1 0,4498 1.11 2 0.5770 amount of the strontium sulfate. Washing first with 400/, and then with 95% ethanol removed the remaining strontium chloride TABLEVI. SOLUBILITY OF STRONTIUM CARBONATE IN GRAMS and hydrochloric acid. The strontium sulfate PER 100 M L . AT 20" c. was practically insoluble in the 95% alcohol. Sodium chloKater 22.5% Alcohol 40% Alcohol ride and sodium carbonate were found to be very soluble in 0.0008 0.0011 0.0004 0.0015 ... 0.0006 40% ethanol solution, whereas strontium chloride and hydrochloric acid likewise were found to be appreciably soluble in the 40 and 95% ethanol (Tables VI and VII). The solubility of TABLE VII. SOLUBILITY OF STRONTIUM SULFATE IN GRAMS PER strontium sulfate in hydrochloric acid was determined quanti100 ML. A T 20' c. tatively. I t was found that the solubility in grams per 100 ml. Rater 2 2 . 5 % Alcohol 40% Alcohol 95% Alcohol was not sufficient to be a weighable amount. According to the 0.0112 0.0084 0.0052 0.0004 literature ( 6 )the solubility is practically negligible. 0,0106 0.0083 0.0049 0.0001 A small amount of strontium carbonate was dissolved in the initial treatment with alcohol and water (at most, about 1 mg.). Any other errors owing to solubility would be concerned with the solubility of strontium sulfate. Only about 0.1 mg. would be disstrontium carbonate. Other fusions in which the amounts of solved by the hvdrochloric acid treatment and at most onlv 0.5 sodium carbonate were varied were carried out, under the same conditions. The results are given in Table I. mg. would be dissolved in the final w a s h g . The errors in this GROUP11. Bnother set of experiments analogous to those in method are compensating and reduce the final error to a very Group I except that 10 grams instead of 5 grams of sodium chloride small amount. Loss of strontium carbonate in the fitst washing were used, mas run to determine the effect, of dilution on the conversion (Table 11). would make the conversion appear smaller whereas loss of stron2
0
0
'
2
1.06
1.08
,
INDUSTRIAL AND ENGINEERING CHEMISTRY
1988
tium sulfate in the second and third washings would make the conversion appear to be larger. Obviously the difference in weight beiTyeen the two weighings represents closely the true conversion.
Vol. 40, No. 10
When the per cent conversion of strontium sulfate to the carbonate is plotted against the molar concentration of sodium carbonate, straight lines are obtained. For 100% conversion of the sulfate t o the carbonate, in the fused state, 1.07 moles of sodium carbonate were sufficient to give complete conversion. The experimental evidence points to complete solution and ionization, the strontium carbonate formed, by union of the itrontium and carbonate ions, is the least soluble arrangement of the ions on solidification of the fused inert sodium chloride as solvent. Variation in the rate of cooling has no effect on the per cent conversion 01 the strontium sulfate to the carbonate with or nithout the sodium chloride from 840" C. Quick quenching from 840" C. of the melts as shown has no effect on the per cent conversion of strontium sulfate t o the carbonate. Variation of time of reaction for 0.5 hour, 1 hour, and 1.5 hours a t 840" C., on the various fusions has no effect on the per cent conversion of strontium sulfate into the carbonate. It i e evident, therefore, that the maximum conversion was obtained in somewhat less than 30 minutes a t this temperature and that the reaction is probably instantaneous.
PRACTICAL OPERdTIOY OF PROCESS
The pilot plant operation of this process v.-as carrird out in the same fashion a3 that for the conversion of barium sulfate (3)to carbonate save that the fused melt was quenchd into atm as in the case of the preparation of pure blanc fixe (4) DISCUSSION
The reaction in fused inert solvents has many advantages over other methods of preparing stront ium carbonate. Preparation of pure strontium products from an aqueous solution of strontium sulfide is unsatisfactory because of contamination with sulfur compounds. Methods in which oxides, sulfides, or silicates u e formed prove unsatisfactory because of the loss of strontium sulfate and the length of the method. The reaction in the fused anert solvents has the advantage in that it permits a separation of the impurities (3, 4). I t is evident, that at 840" C., the fused salt, no matter how great the quantity, has no material effect on the per cent conversion and has no noticeable effect on the reaction rate. It is shown in Tables I to V that the relation of the molar concentration of the strontium ions times the molar concentration of the carbonate ions divided by the molar concentration of the strontium carbonate recovered, equals a constant. The calculated values of K agree fairly well in all of the tables excepting those in which a, ION molar concentration of the carbonate ions was used, namely, 0.3 and 0.5 111.
LITERATURE CITED
(1) Booth, Harold S., U. 9. Patent 2,013,401 (Sept. 3, 1935). (2) Ibid., 2,112,904 (April 5, 1938)., (3) Booth, Harold S., and Pollard, E. F., IND. ENG.CHEM.,40, 1983 (1948) (4) Booth, Harold S., Pollard, E. F., and Rentschler, M.J., Ibid., p 1981. ( 5 ) Comey and Hahn, "Dictionary of Solubilities," 2nd ed., p 1025 Kew Yolk, MaoMillan Co., 1921. ~
RECEIVED April 4, 1947
e
e e
0
e
P
a
EFFECT OF ALKALI HALIDES H. AI. BUSIEY'ASD E. F. POLLAdRD2 Tulane Cnizersity, ,Veto Orleans, La,
HE most abundant strontium mineral in t,his country is the sulfate, called celestite, from wiiich niost strontium compounds arp prepared. The natural stront ianite (strontium carbonate) is commercially the most important of the strontium minerals. Ilovvever, not enough stroniimite is mined to meet the demands of indust,ry; furthermore in its natural state it is n o t pure enough for many uses. Reduction of celestite by carbon to the water-scluble sulfide has been the prinripal method employed for the manufacture of etrontium compounds, The preparation of pure stronlium products from aqueous solutions of the sulfide is difficult because of contamination with sulfur compounds. Celestite has been converted to the carbonatr of strontium by fusing the sulfate with an excess of sodium carbonate. The sodium carbonate produced can be converted readily to water-soluble strontium salts. 1 Present address, Los Alamos Scientific Laboratory, P.O. Box 1663, Loa Alamos Kew Mexico. 8 Prarrrut ndilress, Southern Regional Research Laboratory, U. S. Department of Agriculture, Xew Orleans, La.
Alkaline earth carbonates have been produced (3)by dlssolving the sulfates in fused n-ater-solnble salts, such as sodium and potasslum chloride, that do not react a i t h the ore, and adding sodium or potassium carbonate. Proper choice of the incl t salt mixture (4)makes it possible to use a lovier temperature for the fusion. Also a aartinl purification is accomplished by this proces8 ( I ) because the lion sulfide and silicates which contaminate the minerals have low solubility in the fused salts. Khen the material is to be used as a pigment, colored impurities can be converted to colorless compounds ( 2 ) and the particle size can be regulated by the rate of cooling. This investigation mas conducted to determine the effect of alkali halides on the reaction between strontium sulfate and alkali carbonates at an elevated temperature: SrSOc
+ Ka&08 --+SrCOa + SaSOa
MATERIALS AND ANALYTICAL METHODS
The reagents used in this study were of very pure grade. TIir maximum impurities for any salt, used did not exceed 0.2%,
