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
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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%,
INDUSTRIAL AND ENGINEERING CHEMISTRY
October 1948
1989
Molten alkali halides act as solvents for the reaction of OF STRONTIUM SULFATETO STRONTIUM strontium sulfate with sodium carbonate. The effect TABLE I. CONVEESION
CARBONATE
I
Fusion No.
I11
I1
aonverted64.8 65.2 64.9 64.9
7 %
SrSOc n o t converted, subtracted from 100 Sulfate ion8 pptd. tw SrS0, from leaching water Strontium ions pptd. from SrCh solutions a@ SrSOi
65.2 64.9 65.0
64.8
64.9
SOLUBILITY OF STRONTIUM SULFATEIN TABLE11. OBSBRVED FUSEDSALTSAT 850" C. G. of 8rS04 per G. of Fused Salt 0.90 0.03 0.32 0.002 0.81 0.66
Fused Salt NaCl NaBr KC1 KBr LiCl LiBr
of
alkali halides on the reaction was investigated. Sodilim chloride, sodium bromide, and potassium chloride werr found to have no effect on the reaction. Lithium chloride and lithium bromide probably inhibit the reaction to a slight extent. Variation of the rate of cooling, the time of fusion, the substitution of potassium carbonate for sodium carbonate, and the effect of dilution were all studied and found to have no effect on the degree of completion of the reaction. A short method of analysis W B developed. To convert 1 mole of strontium sulfate t a i carbonate, it was found that at least 1.053 moles of sodium carbonate per mole of strontium sulfate must be present At least 0.0363 mole of sodium carbonate per mole of strontium sulfate must be present before there i s a n \ apparent conversion to strontium carbonate.
ON CONVERSION OF TABLE 111. EFFECTO F TIMEO F FUSION STRONTIUM S U L F A TTO ~ STRONTIUM CARBONATE AT 850 O C.
Time of &mion, Min. 30 20 10 5 I/? '/2
NaC1, Grams 10 10 10 10 10 10
8rSO4, Grams
2 2 2 2 2 2
NasCO,, Moles NazCO, Gram per Mole &SO4 0.8079 0.70 0.8079 0.70 0.8079 0.70 0.8079 0.70 0.8079 0.70 0.8079 0.70
Conversion, % 65.2 65.1 65.2 65.0 64.9 65.1
Impurities consisted of alkali halides which were found to be inert to the reaction. The alkali halide was fused in a platinum crucible and 2 grams o f strontium sulfate were dissolved in the liquid. Then a quan-
The low solubility of strontium sulfate in potassium broinida prevented its being tested as a solvent. If a small portion of sodium carbonate is added t o a saturated solution of strontium sulfate in any of these salts a t constant temperature, a precipitate is always formed. I n several case? some of the precipitate was carefully removed with a platinum spoon, and it was found to be strontium carbonate; this proved i t to be the least soluble arrangement of the ions. Some melts were made to find the effect of time of fusion on the conversion of strontium sulfate to strontium carbonate. Sodium chloride was used as the solvent. The time of fusion had no effect on the reaction as is shown in Table 111. To test the effect of each alkali halide on the reaction between strontium sulfate and an alkali carbonate several fusions using the different halides were made. The results are shown in Table T V
tity of alkali carbonate was added and the melt stirred until it became homogeneous. After a 10-minute period of heating a t 850" C., the solution was allowed to solidify and cool t o room temperature. A sample of approximately 10 grams of the solid was crushed to a powder and extracted with 75 ml. of 40% ethanol in water with DISCUSSION AND CONCLUSIONS the aid of mechanical stirring for 10 minutes. The ethanol was used to decrease the solubility of strontium sulfate; in ethanol The presence of the alkali halides, sodium chloride, sodiuni above 40y0 the solubility of the sodium sulfate being extracted bromide, and potassium chloride were found to have no effect OD decreases (5-7). The mixture then was decanted through an alunthe conversion of strontium sulfate to strontium carbonate at dum filter crucible with suction and washed with 50 ml. of 40y0 850" C. When lithium chloride or lithium bromide is present, it ethanol while the residue was on the filter. Finally it was washed once with 25 ml. of distilled water. This last wash water should is necessary to use a greater concentration of sodium carbonate t o give no test for the sulfate ion. The residue was dried a t 120 O C. effect a conversion comparable to that obtained when no foreign and weighed to find the total strontium sulfate and strontium salt is present. carbonate, if the totalstrontium present in the sample for analvsis Neither the time of fusion nor the rate of cooling affected the was not known. Tho strontium sulfate and strontium carbonate mixture then was stirred in the filter crucible with two 25-ml. portions of 2 N hydrochloric acid and washed with 25 ml. of water. This treatOF TABLEIV. EFFECTOF VARIOUSALKALIHALIDESO N COXVERSION ment dissolved and washed out the strontium carSTRONTIUM SULFATE TO STRONTIUM CARBONATE AT 850 a C. bonate present. The final residue of unconverted (Quantity of strontium sulfate was 2.000 grams in every instance; all fusions were for 111 strontium sulfate was dried and weighed. Imminutes) purities in the original strontium sulfate will cause Alkali carbonate NazCOa h'azcoa NazCOs NaeCOa NazC03 NazCOs NazCOs NazCOl KzCOi .tfhisweight to be high. The strontium chloride formed by dissolving the Alkali halidea None NaCl NaCl NaBr SaRr KClb LiCl LiBr KCI carbonate was determined by precipitation of strontium sulfate using 3 A; sulfuric acid. Moles MlCO* Also the sulfate ions in the filtrate from the per mole leaching process can be precipitated as strontium C o n v e r s i 2 410 RrSO4 _____-sulfate to find directly the quantity of original c 26.3 26.0 23.4 26.7 24.9 0.30 26.2 ... 25.9 strontium sulfate converted to the carbonate. 24.0 26.4 22.9 26.1 25.5 45.4 45.2 44.0 41.1 45.4 ... 45.9 0.50 45.0 ... Table I shows that these three methods give com45.2 43.2 parable results. 65.4 64.8 65.0 64.7 59.5 0.70 64.8 65.2 65.0 65.4 ~
64.8 65.3
RESULTS
The solubility of strontium sulfate was determined approximately in several alkali halides a t 850' C. (Table 11). Sodium carbonate and potassium carbonate dissolved in all proportions in these salts at this temperature.
...
64.7 65.0
...
65.1
65.2
...
,
..
65.4
62.5
85.0 94.9 94.7 100.0 SrSO4.
82.6 94.1 92.3 100.0
60.0
79.2 86.2 90.0 95.2 95.4 95.0 89.1 94.7 94.5 98.2 100.0 100.0 1.10 ... ... 100.0 100.0 5 Proportion of alkali halide was 5 grams per 1 gram of b Proportion alkali halide 10 to 1. 6 Molten sample was qu&hed in aqueous 40% ethanol; in all other runs the melt wa? allowed t o cool t o room temperature and crushed before leaching. 0.90 1 .oo
84.9 94.6
94.6 94.9
94.2 96.0
~
1990
INDUSTRIAL AND ENGINEERING CHEMISTRY
per cent of conversion. On slow cooling strontium carbonate was observed to crystallize first from the clear solutiolis proving it to be the least soluble arrangement of the ions. -4plot of the data in columns 1 through 6 and column 9 of Table IV fell along a straight line. Treatment of these data by the method of least squares yielded the equation:
Y
= -3.57
Vol. 40, No. 10
ACKNOWLEDGMENT
The authors wish to acknowledge the advice and suggestions of Thomas B. Crumpler in the development of the prohlrm and in the preparation of this paper. LITER&TUKE CITED
+ 98.3X
where X equals the moles of sodium carbonate per mole of strontium sulfate and Y equals the per cent conversion of strontium sulfate to the carbonate. From this it was shown that there must be a t least 0.0363 mole of sodium carbonate present per mole of strontium sulfate before any of the strontium sulfate is converted to the carbonate. In the same way it was found that a t least 1.053 moles of sodium carbonate per mole of strontium sulfate must be present before all of the strontium sulfate is converted t o the carbonate.
(1) Booth, €1.S.,U. S.Patent 2,013,401 (Sept. 3 , 1945) (2) I b i d . , 2,048,593 (July 21, 1936). (3) Ibid., 2,112,903 ( h p ~ i 5l , 1938). (4) 1 b X 9 2,112,904. ( 5 ) Newman, E. W., J . Am. Chem. Soc., 56, 879 84 (1933). (6) Townley, R. TT., Ibid., 59, 631-33 (1937), (7) Voail'ev, A . M ~Trans. ? Kirot, Inst. Chem. Technol. Kazon., 3$ 37 (1935) ~
RECEIISD December 9, 1946. Based on X S . thesis submitted by a.M. Buaey t o Graduate Chemistry Faculty of Tulane University, ,Illne 1941.
so ENTHALPY, ENTROPY, AND SPECIFIC HEAT F
T h e enthalpy of liquid isopropyl alcohol referred to 0' C. has been determined up to 200' C. by use of a furnace and ice calorimeter. Derived values of specific heat and entropy are also given.
T
HIS report describes measurements which extend the thermal data on liquid isopropyl alcohol into a previously unexplored region; no measurements of specific heat have been reported heretofore above 54" C. The detelmination of enthalpy was accomplished by heating t,he sample enclosed in a capsule to a desired temperature in a furnace, dropping it into an ice calorimeter, and measuring the heat evolved in cooling t,he sample and capsule to 0' C. After the enthalpy was determined a t several temperatures, the specific heat was obtained by differentiation of the enthalpy-temperature funct,ion. EXPERIiMENTAL
O
c.
and 0.860 giam in the low filling experiments a t 155.0" &ndt 200.7" C. Three shields were used above the capsule instead oi the two that m r e used in other measurements ( 1 , s ) . The high filling sciics >vas begun with three experiment&st 200 7" C which gave 933.8,931.5, and 930.8 calories of heat transieii cd t o the calorimeter, respwtivrly. These were followed by rvperiments a t the three lower temperatures which appeared t o show a random scattering of results and then by three more experiments a t 200.7' C. which gave 931.3,929.1, and927.9 calories, respectively. The d o w i m r d tiend in the results a t 200.7" C , over a range of 0.67, n as taken as indicating chemical change of the sample during the time spent in the furnace a t that temperreture. This time was about 1 hour per experiment. With soma arbitrariness, the value of the heat which would ha,ve been transferred in an experiment at 200 7" before any chemical rcactiort had occurred v a s talrcn to be 933 7 calories and the results for the experiments a t the lower temperatures were increased b j
A commercial sample of 99% isopropyl alcohol vas refluxed for 12 hours over freshly calcined calcium oxide. The entire batch distilled a t 82.2" C. (760 mm.), the sample being taken from the middle half. The sample was sealed in a Monel capsule of IO-ml. capacity. S o attempt was made to expel air from the capsule and sample before sealing.
I t is calculated that the error resulting froni the presence of air did not exceed 0.1%. The authors believe that errors resulting from all impurities in the original sample are small in comparison n ith other errors which are mentioned below. The apparatus and experimental technique have been described recently ( 1 , 4 , 4 ) . In the present measurements, experiments were made with a high filling of sample in the capsule (HF) and with a low filling of sample (LF) at four temperatures between 55.0' and 200.7" C. The differences between the two series of results gave the enthalpy of the saturated liquid-Le., liquid which is in equilibrium with its own vapor-after application of a correction described later. The amount of sample was 4.045 grams in the high filling series, 0.538 gram in the low filling experiments a t 55.0" and 110.4' C.,
TEMPERATURE ldea CJ
Figure 1.
Specific Heat of Liquid Isopropyl Alrohol
