Solubility of Calcium Sulfate and Calcium Carbonate at Temperatures between 182" and 316" C. -
-
Partridge (3) clikked HaU's figfhe soirrbilil~, (f m k i i L n 2 su/J"ule uiid cuiciurn ire I . Figure 2 is a plmt,ogra& C&Ori,ate in. t / ~ i , sleniperulure ra",flr is a l s ~given. of the testing bomb completely (ires on the solubility of calcium sulfate tip to 200" C . He calcu~ r o r i tthe datu reporlrd, the ucliz,ilyoj culciur,l, assenibled. Figure 3 shows liovilatcd tlie solubility of calcium sulfa,p l~u,cuiulr,d, tlie bombs :ire assembled in the beating box, while Figure4shiiws carbonate up to 200' (!. using three of the heating boxes i n s o l u b i l i t y values derived by Frear and .Johnston ( I ) at temperatures Idow 100' C. Sir the for~grounii. The boxes are electrically heated by means order to obtain further solubility data at higlier tcrntwa- of resistance wire. Const.ant temperature is maintained 1,s t.ires and to study tile in- means OS aot,oniatic-potentionietcr teniperature regulators. Rilelice of s o l u b l e sults, re- The accuracy of tiie temperature contr,ol was =t15'f'. search has been conducted PKOCEDUI~E. Tire procedure inalong this hie. volved in tbese studies was to put the desired solid phase in t i l e larger sOLUllllrrTY TESTS or bottom bomb. The desired solution was tlren added b o i l i n g hot, In order t o o b t a i n the and the bonih closed by screwiiig on desired data, an extrernely the top. The sinaller or top bornb, large number of s o l u b i l i t y previously cleaned and closed, was test,s h a d t o he r u n . The then attached by means of the conpnicedrire in tlie majority of nections on tlie capillary copper-linad the previous iiivestigations steel tubing to tlie lower bomb. TI:e conducted along this line at valve between the two bombs was lower pressures bas involved closed. The assembled b o m b w a s t h e o p e r a t i o n of a siiinll put in the heating boxes and lieid boiler. Saturally the results a t tlie d e s i r e d temperature iiritil obtained from such tests vcre equilibrium was obtained. In these few in norriber since so rriiicii testii the time in the furnace torcacli time had to be spent in 01,equilibrium was found to bo rather t a i n i i i g equilibrium condi- short-about 6 to 10 hours. Kowtions. T l l e present invosti- erer, the furnaces were run alioiit gation had d e p a r t e d froill 90 hours. Coiiseqiiently, plenty of this metliod of t e s t i n g in time was givcn for eqiiiiibrium c o i l that a large number of sniall ditions to be estaiilislied. steel bombs were used for Wiieri it vas desired to sample tlic the solubility detenninations. bombs, tiie v a l v e w a s o p e n e d 119 Four constant-temperahre b o x e s were constructed to rneans of the h a n d l e exteiidirig hold these bombs. With each through to the outside of the lieatbox a t a different temperature ing boxes. When cool, the top bomb and with six bombs in each was removed, and t h e v o l u m e of box, t,wenty-four s e p a r a t e solution accurately m e a s u r e d and F I G U R E2. BOMB s o l u b i l i t y t e s t s were rim completely analyzed. USED IN SOLIIThe solubility tests reported were BllJTY W O U K si mill t a n e o u s l y , thus ob-
August, 1932
INDIJSTRIAL AND ENGINEERING CHEMISTRY
915
run a t 182", 207 ",244 ",282 ", solution. After boiling about and 316" C., corresponding 20 minutes, the sample was approximately to 150-, 250-, allowed to stand a t least 12 500-, 1000-, and 1500-pound hours, filtered, ignited, and gage pressure. weigh e d in tared porcelain I n determining the s o l u crucibles a$ barium sulfate. bility of c a l c i u m s u l f a t e , The calcium portion was made acid with hydrochloric CaS04.2H20 and CaS04 were ;ec. A used in different tests as the acid; about 20 cc. of a 4 per f solid phase. The results were cent solution of ammonium the same, and it was found oxalate was added; and, after boiling a few minutes, the sothat the stable phase was the anhydrite. H o w e v e r , t h e lution was made slightly alkasolubility was the same irreline with ammonium hydroxspective of which solid phase ide and boiled for 20 minutes. was used a t the beginning. After cooling, about 20 cc. of When calcium carbonate ammonium hydroxide were was desired as the solid phase, added, and the solution was small Iceland spar crystals, allowed to stand for 12 hours Sec.A approximately b e t we e n 20 before filtering. The preciand 100 mesh, were used. pitate m-as washed with dilute The v o l u m e of solution ammonium hydroxide u n t i 1 added to the bombs a t the free from ammonium oxalate; beginning of the tests was the calcium oxalate was dis400 cc. T h e s a l t s a d d e d solved with hot sulfuric acid il solution (about 25 cc. conwere in standard solutions, Sec.B and a g i v e n v o l u m e was centrated sulfuric acid to 1 added to a flask and the soluliter of water), heated to 80" t i o n m a d e up to 400 cc. C., and titrated with approxiwith boiled redistilled mately 0.05 N potassium perwater. T h e s o l u t i o n w a s manganate s o l u t i o n . The then added to t h e b o m b s . amount used for the blank POSITION (about 0.2 to 0.3 cc.) was subT h e v o l u m e of s o l u t i o n FIGURE3. C O N S T A N T - T E M P E R A T U R E B O X , SHOWING OF BOMBS collected in the top bomb was tracted from the amount used about 250 cc. The volume for the other solutions. The was determined in each case with an accuracy of 1 0 . 2 cc. potassium permanganate was standardized a t regular intervals The total sample was removed from the top bomb, the bomb against sodium oxalate obtained from the Bureau of Standards was washed thoroughly, and the resulting solution heated just for standardization work. t o boiling, and filtered. The filtrate was collected in a 500-cc. In order to find the degree of accuracy with which the volumetric flask, cooled, and made up to 500 cc. with re- calcium and sulfate could be determined, solutions of calcium distilled mater, free of carbon dioxide. A blank of 250 cc. of sulfate were made, using pure CaS042H20 and redistilled redistilled water was run parallel with each set of six analyses. water. The solid calcium sulfate used was analyzed by a One 250-cc. portion was taken for calcium analyses, and the separate analyst who determined the calcium as calcium other 250-cc. portion for sulfate analyses. When the sulfate oxalate, igniting to the oxide and weighing. The sulfate was was high, only 100 cc. were used for the sulfate test, and 400 determined as barium sulfate. The results of his duplicate cc. were used for the calcium determination The residue analyses in per cent composition were as follows: from the filtration of the first solution, having some iron WATERand small amounts of calcium and sulfate, was digested FREE T H E O R E T I C ~ L SAMPLE 1 SAhCPLE 2 IVERAGE BASIS C O M P O S I T I O V with hydrochloric acid, made alkaline with :tmmonium 90 CaO 31 31 69 41 6 41 3 31 79 hydroxide, and filtered to remove the iron. Since the 44 94 44 94 58 7 60% 44 94 58 8 0 0 Ignition loss 23 67 23 67 23 67 0 0 calcium and sulfate contents were found to be low in this solution, and since the iron content wap also very low, the X solution was made from a weighed amount of this salt iron was precipitated only once. The filtrate was collected in a 250-cc volumetric flask made up to volume with boiled calculated to have 200 p. p. m. of CaSO,. Samples of Tarious redistilled water when cool; similar aliquots were taken as amounts were taken for analysis for calcium and sulfate. The with the 500-cc. sample and combined with them for the results of these tests are given in Table I. calcium and sulfate tests. The combined portions were RESULTSOF SOLUBILITYTESTS evaporated down to about 7 5 cc. The sulfate portion was made slightly acid with hydrochloric acid, and a 4 per cent This shows that the calcium could be determined within an solution of barium chloride was slowly added to the boiling error of about 1 0 . 2 milligram, and the sulfate within about
r
TABLE I. RESULTSO F
ANALYSES O F STLVDARD SOLUTIONS OF CALCIUM SULFATE
AMOUNTOF Ca VOL. OF
SOLN.USED
cc.
a
KMnOh
USED
cc.
50 3.00 100 5.80 250 14.45 Determined minus theoretical
Detd. from titration Gram 0.0031 0.0059 0.0147
h h l O U S T OF
WEIGHTOF Theoretical Gram 0.0029 0.0058 0.0145
Difference' Gram +o. 0002 +o ,0001 0.0002
+
Bas04 Gram 0.0176 0.0336 0.0858
Detd. from Bas04 Gram 0.0072 0.0138 0.0352
so4
Theoretical Gram 0.0071 0.0141 0.0353
Differencea Gram +0.0001 -0.0003 -0.0001
916
I N 1)
[: s ‘I‘ 1% I
,4 I. 4 i1.)
1.: N I; I iE E: n 1 N ( i
1: t i
E 31 I
Vol.
a i i ~ ~ i i iof i t tlie
x , No. 8
calcium sulfate takes place and that tlie sulfate combines with the iron to form the hydroxide of ferric sulfate; apparently this is adsorbed on the solid phase, reducing the solfate content a small amount. The solutions taken from the srrlilbility tests of the calcium sulfate in water had a pH value of approximately 8.0, ~vliiclialso would indicate hydrolysis of the calcium snlfate. EIowever, siiicc the solubility data being collected were to tic correlated with data obtained in boiler operat,ion where similar reactions rniglit take place, no attempt was made to run tests in containprs free from iron. Table 111 givrs the results (iftests having a solid pliasc [if calcium sulfate to wliielr sirdiuiii sulfate has been added. I n both Tables 11 and 111 the reciprocal of t.Iie mean molality and the ionic strengths are calculated. The ionic streiigth is calcnlateil as follows: For calcium sulfate, p = 2Ca Frcmr: 4. 1 , m o n A m w r wil-ti Tnmp: OF TIXE €IE.ATINI:l3r, X E S 1u 2S04. For calcium sulfate in the prrsrncc FoRE0”o”N” of sodium sulfate, p = 2Ca 2S04 i- Na?. tlie sanie error. Thus, if a solutiori from the bunihs con- ‘rI:eions are iii terms of moles per liter. I n Fignre 5,1/m * is taining about 1 millimole pcr liter of caleiinn sillfate were pjott,ed against p”zfor the various kmperatures. I n Fignre 6 analyzed, there would be approximately 40 p. p. m. cal- the values of the act,isities calculated from these cur\.es are cium and 96 p. p. m. sulfate. With a 250-cc. sample t.o Idotted against theioniestrengtli. The values of tile activities analyae, and using 125 cc. for each, there wonld he 5 milli- are fairly accurate at t,he lower temperatures, but a t the grams of calcium and 12 milligrams of siilfatt. With an 11jgii:lirrtenipemtures are merely approximat,ions. IIowerer, error of about 1 0 . 2 niilligmm in analysis, the resultant they tend to show. tlie trend of t,l;lrechange in the activitir.8 at analyses should agree within +0.04 millimoles per liter for the higher tempmatures. These results would indicate that, 8,s both calcium and sulfate. This error would be about the same we approacli the critical t,emprat.iire, the activiti(>sapproach for all solntions until tlie cont:entrations became lower than wro. 0.2 millimole per liier, wlien it might, l~rci~nie somewhat. grenter. Table I J gives thc results of the solubility tests using calcium siilfat,e as a solid phase. It is to he noted that the sulfate is consistently lower than t,lie calcium. Tiiis iu nut an experimental error since the analyses of samples of calcium sulfate solutions,made a t room temperatures to similureoncentrations, checked within 0.04 millimole per liter. The higher calciuni value may be explained on tlie basis that a small amount of Fc(OH)(W4)may have formed owing to the reaction within t,he bomb a t the high tcmperat.ures. With t.his in tlie solid pliase, there would be a tendency to have a low sulfate coli tent in tlie liquid phase. This appeared to he possible, siiicr tlre remaining solid phase always bad a reddish color and a11 peared to be coat.ed with a thin ret1 film of some iron conpound. If the 400 cc. of solut.ion in contact with tlie solid phase were low (about 0.10 millimole per liter rrf sulfate), this ivonld correspond to about. 0.0038 gram of sulfate retained i n the solid phase. Since about 4 grams of calcium sulfak were used in the solid phase, and since it is almost impossible to remin.e the salt which adheres to the inside \~allsof tlw bombs, analysis of the solid phase at the end gave no check o i i tlie real coniposition of thc solid phase. In order to be certain that there was not a slight excess of calcium in the ealciuin sulfate, such as calcium carbonate or ,o* .ead o* .,e .II .19 .,* * ,. ?.o == .dC +uaTe kmt ffin;c a r e ~ f hpi hydroxide, the salt was di ted with hydrochloric acid and washed thoroughly witli redistilled water. When this washrd Fll;UnS 5. sOLUI3n.ll.U OF cAl.ClUM SULFNrE calcium sulfate was used as the solid phase, the results were! Table I V gires the solubility of calciuiii carbonate. The the same as before. Calcium sulfate made by different manufacturers gave the same results. All of this indicatrs partial pressure of tlie carbon dioxide was not controlled, but that tfiere is undoubtedly a reaction involving the iron from was that corresponding to the equilibrium at the varions the containers. In order ta study the effect of iron, a powdered tempcraturcs. This was found to be 0.00015 atm. at 182“ C. iron was added with the calcium sulfate as a solid phase. Any change in tlie partial pressure of the carbon dioxide would The presence of large excesses of the iron had no apparent nndoubtedly affect the solubility of the calcium. The solubility of calcium carbonate decreases as the temperaeffect on the resulting ealeium and sulfate contents. This appeared to indicate that apparently a hydrolysis of a small t.ure increases. This is in aecord with the work of Frear and
+
+
INDUSTRIAL AND ENGINEERING CHEMISTRY
August, 1932
Johnston ( 1 ) . The results obtained are somewhat higher than the values calculated by Partridge (3).
TABLE
11. SOLUBILITY O F CALCICM SL-LFATE
Ca EO4 Millimole p e r liter 0.93 182 0.85 0.85 0.85 0.71 0.91 0.75 0.87 0.81 0.77 0.75 0.96 0.85 0.92 0 .85 1.02 Average 0 . 9 0 0.81
1170
0.0024
0.058
0 56 0.52
2080
0.0019
0.043
TEMP.
l/mi
.iverage
0 48 0.44
2
P
c.
917
Tests were run in which sodium carbonate was added to the liquid phase with calcium carbonate as the solid phase. The results of these tests were extremely interesting since the calcium dropped t o less than 0.5 p. p. m. (0.01 millimole per liter) and remained this low even when the sodium carbonate was as high as 18 millimoles per liter. This made it almost impossible to calculate the activity of the calcium Carbonate with increased ionic strength, since the solubility was so low that one could not determine it with any degree of accuracy.
.Ol
0.2
03
09.
D5
.Ob
lomc 5 t r r n y f b
FrGLnh Average 316
.irerage
0.34
0.20
0.20 0.26 0.26 0.19 0.21 0.27 0.23
0.09 0.10 0.10 0.05 0.10 0.05 0.08
3850
0.001.1
7400
0.033
0.0006
0.026
TABLE 111. SOLUBILITY O F C A L c I m i SULFATE I S PRESEXCE OF SODIUM SULFATE TEMP.
Ca SO4 .Mtllimoles per lzter 0.81 0.78 0.87 0.69 0.90 0.66 1.49 0.53 1.38 0.54 3.38 0.46 11.90 0.45 11.70 0.49 17.50 0.42 17.90 0.50
c.
182
l / m =t
?
P
1265 1290 1280 1125 1155 805 433 417 368 333
0.0034 0.0034 0.0036 0.0053 0.0051 0.0104 0.0372 0.0369 0,0546 0.0556
0.058 0.058 0.060 0.072 0.071 0.104 0.193 0.192 0.233 0.236
20;
0.41 0.28 0.28 0.32 0.29 0.29
0.41 2.74 3.10 11.20 11.30 17.5
2440 1140 1070 530 555 445
0.0021 0,0098 0.0105 0.0355 0.0357 0.0543
0.046 0,099 0.102 0.188 0.189 0.234
244
0.25 0.24 0.22 0.15 0.17 0.20 0.20
0.27 0.56 1.35 3.28 12.0 13.1 17.8
3850 2740 1840 1430 700 618 530
0.0013 0.0021 0.0044 0.0106 0.0368 0.0391 0.0548
0.036 0.046 0.067 0.103 0.192 0.198 0.234
316
0.08 0.11 0.04 0.02 0.06
0.33 0.94 1.07 3.45 20.4
6180 3120 1525 1200 905
0.0013 0.0033 0.0036 0.0107 0.0587
0.036 0,057 0,059 0.106 0.244
T.4BLE
IF-.
OF
Table T' gives the results of tests using a solid phase of calcium carbonate and adding sodium sulfate to the liquid phase. It is interesting to note that at 182" and 207", as the sulfate increases, the calcium increases so that in the solutions of higher sulfate content the calcium is equal to that when calcium sulfate was the solid phase and the sodium sulfate content was high. TABLE t7, TEMP.
c.
181
PO7
SOLUBILITY O F CALCIVM CARBOXATE IN P R E S E S C E O F SODIUM S U L F A T E
Ca SO& Millimoles p e r liter 0.25 0.00 0.27 3.58 0.32 11.85 0.47 17.8 0.44 17.8 0.14 0.00 0.17 1.18 0.29 3.58 0.25 11.85 0.37 17.8 0.29 17.8
T E m . O
C.
244
316
Ca Millimoles 0.11 0.08 0.11 0.14 0.08 0.07 0.02 0.02 0.02
so4 p e r lifer
0.00 3.17 11.5 16.4 0.00 3.00 2.65 11.60 19.40
COSCLUSIOSS The conclusions to be reached a t present are: 1. The solubility of calcium sulfate d e c r p a s e s with increase in temperature. 2. The activities of calcium sulfate for ionic strengths up to 0.05 and temperatures between 182" and 316" C. have been calculated. 3. The solubility of calcium carbonate decreases with increase in temperature. 4. The solubility of calcium carbonate in t h e presence of sodium carbonate is less than 0.5 p. p. m.
SOLUBILITY OF CALCICM CARBOSATE
TEMP. ' C. 182
Ca Mzllimole per liter 0.25 0.26 0.20 0.25 0.29 0.27 Average 0.25
Average
6 . ACTIFITYCOEFFICIE\T C ~ L C I CSCLFATE M
0.14
TEiw. C. 244
Ca ,Millimole per liter 0.13 0.13 0.11 0.13 0.09 0.10 Average 0.11
Average
0.09 0.06 0.07 0.09 0.11 0.08
LITER.iTURE
CITED
(1) Frear and Johnston, J . Am. Chem. Soc., 51, 2082 (1929). ( 2 ) Hall, R. E., Carnegie Inst. Tech., Bull. 24 (192i). ( 3 ) Partridge, E. P., Dept. Eng. Research, Univ. Mich., Bull. 15 (1930). RECEIVED March 10, 1932. Presented before the Division of Industrial and Engineering Chemistry a t the 83rd Meeting of the American Chemical Society, New Orleans, La., March 28 to .ipril l , 1932. Released b y permission of the Director of the Engineering Experiment Station, University of Illinois. Part of research conducted in the Chemical Engineering Division of the Engineering Experiment Station, and financed by the Utilities Research Commission of Chicago.
