Extraction of Potash from Polyhalite IV. Cyclic Production of Schonite and Its Use in the Manufacture of Potassium Sulfate and Syngenite' N.
FRAGISN AKD
EVERETT P.
PARTRIDGE
Nonmetallic hlinerals Experiment Station, U. S. Bureau of hIines, Rutgers Univ-ersity, Yew Brunsw-ick, 1v. J. is obtained by decomposing part The hot extraction of calcined polyhalite with of the syngenite n-ith water a t covering potassium sula solution hkgh in magnesium sulfate and sodium 100' C. (15, 16). fate from the commerchloride yields a n extract liquor f r o m which Experimental data for the n e v cially i m p o r t a n t deposits of steps in processes 7 and 7.A are polyhalite (K2S04l I g S 0 ~ 2 C a - schonife crystallizes on cooling. T h e mother presented in this paper. These liquor, after dilution, m a y be used again in fhe d 0 4 2 H 2 0 ) in Texas and Kern cover the leaching of calcined Mexico have been suggested in hot extraction. This cyclic step is combined polyhalite with solutions conthe l i t e r a t u r e ( 1 , 3, 6, 8-10, with other process steps preciously deceloped by taining potassium sulfate, mag13-16, 17). The present paper this station io f o r m a new process f o r the pronesium sulfate, and sodium chlodescribes a new process, desigduction of potassium sulfate, syngenite, and ride to obtain solutions nhich nated as Bureau of Mines procyield schonite on cooling; the sch&'nite f r o m polyhalite. ess 7 , n-hich produces schonite2 change in c o n c e n t r a t i o n of (K2S04RlgS046H20) from the Extractions of more than 95 per cent were schonite mother liquor in the calcined polyhalite in a cyclic obtained in n single-stage procedure with -60 system potassium sulfate-magoperation by first extracting the and -30 mt'sh calcined polyhalite at 100" C., nesium sulfate-water in the prescalcined p o I y 11a 1i t e with hot and with -60 mesh material at 90" C. Csing ence of varying concentrations schonite mother liquor and then a two-stage procedure, similar high extracfions of sodium c h l o r i d e ; and the cooling the extract so obtained to f o r m a t i o n of solid potassium effect the c r y s t a l l i z a t i o n of were obtained with -20 mesh material at 90' C. s u l f a t e b y d i s s o l v i n g solid schonite. The echonite mother Lower temperatures yielded less desirable results. s c h o n i t e in potassium sulfate liquor may then be heated and Data are presented for the crystallization of solutions. re-used in the e x t r a c t i o n of schonite f r o m the hot extract liquor and for the polyhalite. This cyclic btep is crystallization, of potassium sulfate and schonite made possible by the use of soHOT LEACHISGOF CALCIKED lutions high in sodium chloride. in a subsequent process step. A flow diagram POLYHALITE WITH SOLUTIONS The effect of the sodium chloshows that costly ecaporation steps inherent in CONTAINIKG SODIUM CHLORIDE, ride is t w o f o l d : (1) During hfAGKESICRI SULFATE, AXD oiher processes are eliminated or greatly reduced. e x t r a c t i o n it d e c r e a s e s the POTASSIUM SULFATE rate of formation of secondary solid phases containing potassium sulfate; (2) it changes Extraction data are presented here on the treatment of the solubility relationships of schonite in the system potassium calcined polyhalite by solutions having compositions comsulfate-magnesium sulfate-water so that schBnite will parable to schonite mother liquors in the presence of sodium separate from solutions containing lower concentrations of chloride. Since it is desirable to keep the sodium chloride pot'assium sulfate and magnesium sulfate. concentration of the qchonite mother liquor recirculated for The cyclic extraction and crystallization procedure yielding extraction nearly condant, it is necessary to use polphalite schonite probably has greater significance as a unit in a which is nearly free from .odium ~ h l o r i d e . Storch ~ and more complex process than as a simple complete process in Clarke (14) have shown that calcination is necessary prior itself. By using this cyclic step to modify process 4B pre- to an attempt to leach polyhalite in order to increase the viously described by Storch and Fragen (15,16) a new process rate of extraction. designated as 7A has been developed which greatly reduces Both polyhalite and schonite contain potassium sulfate expensive evaporation steps when potassium sulfate is the and magnesium sulfate in a 1: 1 mole ratio. The leaching only product and completely eliminates evaporation if one- of calcined polyhalite nearly free from sodium chloride by third of the total input of potassium salts is marketed as schonite mother liquor and the subsequent crystallization syngenite (K2SO&aS04,H20). I n process 7A schonite of schonite from the extract liquor n-ould therefore leave a obtained from the cyclic hot extraction and cryst~allization solution having the same composition as the starting mother is dissolved in a hot potassium sulfate solution, and the re- liquor if no water was removed. Actually, hon-ever, in sulting solution is cooled to obtain a crop of potassium the process of crystallization the schonite removes water, sulfate, the mother liquor being then mixed with polyhalite and a n equivalent amount must be added to the liquors to a t approximately 26" C. t o form syngenite as in process 4B. prevent increase in the concentration of sodium chloride. The potassium sulfate solution used to dissolve the schonite Figure 1 represents diagrammatically the production of schonite from polyhalite in a cyclic process. 1 For P a r t I. see literature citation IS; P a r t 11, citation 16; P a r t 111,
V
ARIOUS methods of re-
IND. EXQ. CHEM.,25, 1002 (1933).
* The preferred mineralogical name for this double salt is "picromerite." It has seemed best in this work, hoaever, t o conform t o t h e general usage in t h e exteneive German chemical literature on potash by retaining t h e name "schonite." For t h e same reason t h e name "astrakanite" has been used instead of t h e preferred mineralogical name "bloedite" for t h e double salt NazSOr~MgSO~.4HzO.
Initial liquor A is used for hot extraction of potassium and magnesium sulfates from calcined polyhalite, yielding extract 8 D a t a soon t o be published from this station show t h a t practically all of t h e sodium chloride present in crude polyhalite may be removed prior t o calcination with t h e loss of only a small amount of potassium sulfate.
1153
INDUSTRIAL AND ENGINEERING CHEMISTRY
1154
liquor B, which is separated from the solid residue. Cooling of liquor B produces schonite which is separated from mother liquor C . Water is added to C t o make up for water removed a$ water of crystallization in schonite, yielding initial liquor A for re-use in hot extraction Typical concentrations are indicated. In the extraction of polyhalite the objectives are: (1) to dissolve the maximum percentage of potassium and magnesium sulfates possible in a time which Jyill allow the materials to be handled in a plant-scale process, and (2) t o
Vol. 2 5 , No. 10
solution subsequently decreased, owing t o the formation of secondary solid phases. The solid phases which might have formed are polyhalite, syngenite, and langbeinite (K2S04. 2MgSO4). In those experiments in which high concentrations of magnesium sulfate and sodium chloride were used, langbeinite formation was indicated; when lower concentrations of these salts were employed, the formation of syngenite evidently was the major cawe of the removal of potassium sulfate from solution. TABLE11. EXTRACTION OF CALCIXED POLYHALITE WITH SOLUCOXT.4INISG POTASSIUM SULFATE, MAGNESIUM SULFATE, AND SODIUM CHLORIDE AT 100" C.
TIOiW
POLYHALITE EXPT. Lot Fraction 2A B C D
A
3A B
.I
-60
4-
150
E F
-60
4- 150
C D E
F
I
24 26 Mj%4 CONCENTRATION - GRAM5/100 GRAM5 Hz0
6.4
B
FIGURE 1. CYCLIC PROCESS FOR PRODUCTION OF SCHONITE FROM CALCINED POLYHALITE
lTAFB$' MESH
+ 20 +++ 356528 + 100
- 100
- 150
7% 36.8 18.8 14.6 20.0 7.4 2.4
... __
+
+
+
-20 150(B)
-30 150(A)
-30 150(B)
-60 150(A)
%
%
%
% ...
29:o 24.0 33.4 11.2 1.8
.. -
214 22.0 43.4 12.6 5.8 13.0
-
13:o 37.2 36.2 8.2 4.2
.. __
-60
+ 150
...
...
7.4 48.9 31.0b 12.8
-
Total 100 99.4 99 2 98 8 100.1 Polyhalite A after calcination contained 30 3 per cent potassium sulfate and 0 3 per cent aodium chloride. polyhalite B after calcination contained 29 1 per cent potassium sulfate, i8 8 per cent magnesium sulfate, a n d 0 53 per cent sodium chloride b +150 a
EXTRACTIONS AT 100" C. The first series of polyhalite extractions were made using boiling solutions containing sodium chloride, potassium sulfate, and magnesium sulfate, the temperatures of which were always between 100" and 101.5" C. A weighed amount of solution of known composition was heated to boiling in a Pyrex flask under a reflux condenser, and a definite quantity of calcined polyhalite of knon n composition was added gradually to prevent caking. Boiling was continued and samples were removed a t various intervals and filtered immediately, . and the solution was analyzed. The results of these extractions are shown in Table 11. The experiments listed in Table I1 show that the potassium and magnesium sulfates were initiallv dissolved a t a raDid rate fro& the calcined polyhalite buz that the amount- in
5A B
A
9A B C D
A
86 B C D
A
7A B C D
A
1A B
h
-60
+ 150
C D -30
+ 150
E F
-30
+ 150
E F
-30
+ 60
E F
-30
+ 60
C
D
E
4A B C D
A
-20
+ 150
KzS04
EXTD. % 7915
.. .. .. ..
0 5 10 15 20 26
7.31 11.76 11.45 11.20 11.26 10.82
25.09 28.25 27.61 27.33 27.60 26.80
19.10 19.58 19.54 19.68 19.47 19.65
77:4 72.1 67.7 69.5 61.0
0 5
7.32 12.17 12.00 12.01 11.86
21.91 25.65 25.41 25.55 25.24
16.04 16.20 16.20 16.26 16.32
97:o 94.0 94.0 91
0 5 10 20
8.16 12.76 12.34 12.24
21.92 25.17 24.52 24.45
19.04 19.18 19.30 19.45
92 83.7 82.0
5 10 15 20 30
0
7.38 11.85 12.00 11.90 11.95 11.60
21.90 25.46 25.51 25.32 25.61 25.08
13.2 13.4 13.4 13.4 13.4 13.4
89:4 92.4 90.4 91.4 84.4
0 5 10 15 20 30
7.08 11.68 11.79 11.90 11.60 11.29
21.59 25.31 25.21 25.33 24.92 24.68
15.7 16.3 16.3 16.3 16.3 16.3
92:o 94.2 96.4 90.4 84.2
5 10 15 20 30
0
7.05 10.82 11.35 11.46 11.47 11.16
21.66 24.81 24.99 24.92 24.98 24.54
15.7 16.2 16.2 16.2 16.2 16.2
75: 4 86.0 88.0 88.4 82.2
0 5 10 15 30
7.69 11.86 11.58 11.27 10.85
25.72 28.40 28.25 27.95 27.30
15.6 15.8 15.8 15.9 16.0
0 5 10 20
7.33 11.39 11.35 11.14
23.76 26.34 26.15 25.97
19.38 19.35 19.60 19.62
10 15 20
D E
obtain concentrations of the extracts which \ d l yield a maximum amount of schonite per unit of solution used and thus reduce to a minimum the quantity of solution t o be handled. Figure 1 shows that the greater the concentration a t point B , the greater will be the amount of schonite deposited from a given quantity of solution. The chief factors which may be varied t o obtain optimum conditions in the extraction are (a) the concentration of the salts in solution, (b) the particle size of the polyhalite, ( e ) the time of extraction, (d) the rate of agitation, and ( e ) the temperature of the extraction mixture. TABLEI. FRACTION.4L SCREES ANALYSISO F POLYHALITE USED IN HOT EXTRACTIONS
+
A
C
COKCENTRATIOIV OF SOLUTIONS TIME &SO4 MgS04 NaCl Min. Grams/iOO grams H20 0 7.52 25.90 15.80 5 12.25 29.0 16.30 10 12.10 29.0 16.30 15 11.71 28.5 ... 20 11.42 28.3 ... 30 11.30 28.0 ...
..
63:4
.. ..
.. 81.2 80.4 76.2
For extraction a t 100" C. it seems that the optimum conditions would be those of experiment 8 in which -30 150 mesh polyhalite was used to obtain top concentrations of approximately 12 grams of potassium sulfate, 25.5 grams of magnesium sulfate, and 16.5 grams of sodium chloride per 100 grams of water a t the end of an extraction period of 15 minutes. A shorter time of extraction would probably be difficult to operate on an industrial scale. EXTRBCTIOKS AT TEMPERATURES BELOW IO0 " C. Equilibrium data for the system potassium sulfate-magnesium sulfate-water (6, 12) show that below 89" C. leonite (KPSOI. MgS04,4H20) may appear in equilibrium with langbeinite, and that the concentration of magnesium sulfate in a solution which is in equilibrium with these two double salts increases appreciably with a decrease in temperature. Applying this fact to the system including calcium sulfate and sodium chloride, the deduction was made that in extractions of Dolvhalite a t or below 90 " C. more concentrated solutions miiht be used without causing the formation of langbeinite.
+
INDUSTRIAL AND ENGINEERING
Octoher, 1933
A series of extractions was accordingly made a t temperatures between 60" and 90" C.; the data are listed in Table 111. In these extractions the starting solution was placed in a Pyrex flask equipped with a motor-driven stirrer and immersed in a thermostat maintained a t the desired temperature. Because of the heat evolved on the addition of calcined polyhalite, the solution temperature was kept a few degrees lower than the bath temperature a t the start of the test. Sample's were removed at various intervals and filtered immediately. The solutions were analyzed, .yielding the values shown in Table 111, and the solids, which were washed first with 50 per cent and then xyith 93 per cent ethyl alcohol, were examined petrographically.
TABLE111. EXTRACTION OF CALCIXED POLYHALITE WITH SOLUTIONS
CONTAINING
100"
D
15.1
B C D E F
D E F 11-4
B C D E F
+
Some of the relationships of the various factors which are of importance in the hot extraction are shown graphically in Figures 2 to 4. Figure 2 represents data for extractions of -60 150 mesh calcined polyhalite using solutions of nearly the same concentration a t different temperatures. Figure 3 represents the same type of data for the extraction 150 polyhalite. In the extractions a t temperaof -20 tures between 60" and 90" C. syngenite was the onlysecondary solid phase formed which contained potassium sulfate. The effect of the decrease in the rate of syngenite formation with an increase in temperature may be seen from Figures 2 and 3. The increase in the rate of extraction with temperature is also apparent. Figure 4 represents data for the extraction of various size fractions of polyhalite a t 90" C. with solutions of nearly the same composition, approximately 7.5 grams of potassium sulfate, 26 grams of magnesium sulfate, and 19 grams of sodium chloride per 100 grams of water.
+
+
A
-60
+ 150
18.4
B
A
-60
+ 150
€3
-20
+ 150
A
-60
+ 150
C D
E F 13.4
B C
D E 12.4
A
-60
+ 150
22.4 B
B
-30
+ 150
20.4
B
-30
+ 150
B
-30
+ 150
24.4 B C
B
-30
+ 150
17A B
B
-20
+ 150
16.4
B
-10
+ 150
-10
+ 150
B C D E F
C D E F
R C D E
F
21.1
B C
D
:
80
TO
D
I
10
IO
I:
1:
E x r ~ c ~ aT M hC
-
w
3:
40
45
11
M wTta
FIGURE 3. EXTRACTION OF POTASSIUM SmFATE FROM -20 150 MESH CALCIVED POLY-
+
HALITE AT VARIOUS TEMPERATURES
In an attempt t o increase the percentage extraction of -30 150 mesh polyhalite a t 90" C.. experimtlnt 24 of Table I11 was performed using the same conditions as in experiment 20 except that the rate of rotation of the stirrer was increased from 450 r. p. m., the speed used in all other experiments, t o 670 r. p. m. As a result, the rate of extraction was increased in experiment 24 so that 91 per cent of the potassium sulfate was dissolved in 15 minutes as compared with 87.4 per cent in experiment 20. The data from the extractions a t temperatures below 100" C. show that higher concentrations of sodium chloride and magnesium sulfate may be used than a t 100" C. and still effect the removal of a large percentage of the potassium sulfate and magnesium sulfate from the polyhalite. Extracts
+
70
7.49 12.31 12.36 12.15 11.90 11.57
25.58 29.70 29.83 29.70 29.80 29.60
19.05 19.35 19.57 19.52 19.51 19.35
92.4 93.5 89.5 84.7 78.4
80
7.66 11.46 11.17 10.98 10.74 10.72
22.18 26.30 26.35 26.25 26.10 26.20
16.10 16.25 16.40 16.31 16.32 16.43
74.3 68.6 64.9 59.4 59.2
80
7.65 12.63 12.76 12.65 12.51 12.38
25.95 30.10 29.82 30.00 30.00 29.90
19.15 19.48 19.36 19.48 19.50 19.50
95.5 97.8 95.7 93.0 91.1
0 15 25 35 50 75
80
7.59 11.44 11.80 11.93 11.87 11.67
25.97 28.95 29.35 29.68 29.70 29.75
19.24 19.32 19.37 19.45 19.47 19.50
68.9 75.3 77.8 76.6 73.0
0
90
7.66 12.35 12.27 12.07 11.94
22.18 26.33 26.40 26.33 26.33
16.10 16.37 16.43 16.50 16.55
89.9 88.3 84.5 82.0
0 6 15 22 30 40
90
7.60 12.76 12.77 12.71 12.42 12.15
25.82 30.15 29.85 30.05 29.62 29.60
19.18 19.70 19.70 19.85 19.70 19.78
98.8 99.1 97.9 92.3 87.2
0 15 25 35 50 75
90
7.85 13.30 12.98 12.92 12.62 12.56
22.15 26.92 26.59 26.42 26.30 26.30
19.2 19.66 19.50 19.55 19.54 19.55
87.6 82.5 81.5 76.7 72.4
0 15 25 35 50 75
90
7.49 12.04 12.15 12.04 11.95 11.63
25.50 29.20 29.30 29.20 29.30 29.00
18.92 19.30 19.30 19.27 19.30 19.40
87.4 89.4 87.4 85.7 79.5
0 15 25 35 50 75
90
7.49 12.87 12.87 12.82 12.50 12.28
25.50 29.94 29.95 29.90 29.46 29.20
18.92 19.64 19.49 19.55 19.43 19.50
87.4 87.4 86.6 81.5 77.8
0 15 28 45
90
7.63 12.33 12.42 12.18
25.75 29.15 29.30 29.15
19.25 19.47 19.47 19.47
9i:o 92.6 88.0
0 6 15 22 30 40
90
7.59 11.26 12.17 12.28 12.37 12.35
25.97 28.35 29.10 29.78 29.52 29.62
19.24 19.40 19.46 19.56 19.60 19.60
65.7 82.0 84.1 85.6 85.2
0 6 15 22 30 40
90
7.52 10.30 11.25 11.62 11.76 11.77
2 6 . 15
26.52 28.60 29.25 29.25 29.00
19.20 19.15 19.3 19.5 19.6 19.6
49 165 66.3 73.2 75.3 75.5
0 30 50 75
90
7.59 11.62 11.55 11.60
25.97 28.70 28.60 28.55
19.24 19.35 19.35 19.35
72 70.7 71.6
0 6 15 22 30 40
C D E F
B
C D
E F 19.4
B C
D
0 A
li 22 30 45
F
0
73.9 67.8 55.9
A
E
O0
Y 60
19.40 19.36 19.50
F
#
FIGURE 2. EXTRACTION OF POTASSIUM SULFATE FROM -60 150 MESH CALCINED POLYHALITE AT VARIOUSTEMPERATURES
c.
1 1 . 3 4 29.75 10.82 29.85 1 0 . 4 0 30.00
E
C
$
MAGNESIUM
COXCENTRATION OF
B
I L
SULFATE,
POLYHALITE SOLETIONE KrSOj EXPT Lot Fraction T I M E TEMP. K2S04 MgSOd NaCl EXTD. 0 C . Grams/100 grams Hz0 % Min .. 14.4 h ... 60 7.49. 25.58 19.05 B 11.74 29.12 1 9 . 1 5 8 1 . 6 C 79.5 11.63 29.90 19.50
10.4
x
POTASSIUM
SULFATE, AND SODIUM CHLORIDE AT TEMPERATURES BELOW
c
5
1155
CHEMISTRY
B
6 15 22 30
...
...
,.
,
...
...
...
...
...
...
...
...
containing 12 grams of potassium sulfate, 29 grams of magnesium sulfate, and 19 grams of sodium chloride per 100 grams of water may be obtained a t the lower temperatures as compared with 12 grams of potassium sulfate, 25.5 grams of magnesium sulfate, and 16.5 grams of sodium chloride per 100 grams of water as the maximum concentrations yielding good recoveries a t 100" C. More than 90 per cent
1156
I N D U ST R I A L A N D E N G I N E E R I N G C H E M I ST R Y
extraction may be secured from -60 + 150 mesh polyhalite a t temperatures as low as 70" C. if less than 20 minutes is used for the time of treatment, while more than 85 per cent extraction may be secured from -30 150 and -20 150 mesh polyhalite a t 90' C.if less than 40 minutes is used. Under corresponding conditions the percentage extraction obtained a t 90" was consistently higher than a t lower temperatures or a t 100" C. TWO-STAGE EXTRACTION. The use of polyhalite having a comparatively large average particle size would offer several advantages in the extraction process. The larger
+
100
c
y
\
TABLEIV. TWO-STAGE EXTRACTION OF CALCINED POLYHALITE WITH SOLUTIOKS CONTAIXING POTASSIUM SULFATE, M4GNESIUM SULFATE,AKD SODIUMCHLORIDE AT TEMPERATURES BELOW 100" CXpT
LotP O L Y AFract,on 4LITE
2 3 ~ 1
B
-20
+
150
B 21 2 3
35A1 2 B1 2
TIDrE TEMP,
Mm. 0
a
C.
1; 10 16 20
-20 -b 150
c.
0 14 0 20
90 90
CONCENTRATION OF KzSO1 E X T nlgSOa R A CSOLNS T NaCl
EXTD KzS04
%
Gram4100 grams H i 0 63 25 75 19 2 5 1 1 . 7 0 28 70 19 42 8 42 2 6 . 4 0 19 17 8 57 2 6 . 4 0 19 17 8 86 2 6 . 8 5 19 27 8 . 8 5 26 70 1 9 . 2 3
94.8
7 12 7 9
93 0
78 08 78 21
27.90 31 50 27 90 29 60
19 60 20.12 19 60 19.80
78 0
....
79 5
00
8 ao
5
5
Vol. 25, No. 10
O'
$. 50
FIGURE4. EXTRACTION OF POTASSIUM SULFATE AT 90' C. FROM CALCINED POLYHALITE OF DIFFERENT PARTICLE-SIZE RASGES
Conditions have previously been defined which ill yield high percentage extractions in batch operations a t 70°, 80", 90°, and 100" C. with polyhalite not coarser than -30 mesh. 150 The equally good extractions obtained with -20 mesh polyhalite in the two-stage extractions a t 90" C. point toward the use of countercurrent system in practice.
+
CRYSTALLIZATIOK OF SCHOKITEFROM A SOLUTIONCosSODIUMCHLORIDE,POTASSIUM SULFATE, AND MAGNESIUM SULFATE The observation, that schonite separated from the cold polyhalite extract liquors containing sodium chloride a t concentrations of magnesium sulfate and potassium sulfate much lower than those shown in the equilibrium data at 250 or 300 C. for the system potassium sulfate-magnesium sulfate-natpr, led t o a determination of the amount of this lourering Over a limited range of sodium chloride concentration. The equilibrium data for the system free of sodium chloride have been checked by several investigators ( 2 , 4, 5 , 7, 11, 12) and are in fairly close agreement. The measureTAIKIKG
particles v m l d settle rapidly and thus make possible the separation of the solids from the liquor by settling and decantation, or by mechanical classification. Also, the larger the polyhalite used, the less would be the grinding costs. HoTTever, the attempts to leach -20 -k 150 and -10 $. 1.50 mesh a t 100" C. and lower temperatures in a single batch procedure yielded low percentage extractions as shown in Tables 11 and 111. The initial rate of extraction was fairly rapid, but after approximately 20 minutes it became extremely slow. I n an effort to remove the concentrated solution from the 9 partially extracted solids, but t o provide a further extrac14 tion medium, two-stage countercurrent extractions were made a t 90" using -20 + 150 mesh material. The tests were conducted similarly to the previous ones a t 90°, except 3 that after 14 minutes of agitation in the extraction flask the solids were allowed to settle and the liquid was decanted % 8 through a filter paper. The solids which were carried by the solution and retained on the filter paper represented 14 16 18 20 22 24 26 28 30 32 34 36 38 40 less than 5 per cent of the total solids present. A known MgS& CONCENTRATION - GMMS(100 G R A M 5 H 2 0 weight of solution of the same concentration as the starting 5. EFFECTOF TEMPERATURE AXD SODIUM CHLORIDE solution, previous,y heated to approximately 900 C., was FIGURE CONCENTRATION ON THE COMPOSITION OF SOLUTIONS IN EQUIpoured into the flask containing the solids and agitation LIBRIUM WITH SCHONITE was continued. The time consumed for these operations was 4 minutes. At the end of the extraction the solids were ments presented in this paper are not precise equilibrium filtered. The filter cake was dried and the potassium and values, but are probably close approximations. Equilibrium moisture content determined. The total potassium sulfate was approached only from supersaturation since this would dissolved was calculated from the filter cake data. By correspond to the crystallization of schonite from polyhalite such a procedure the partially extracted solids were further extract solutions. The data are shown in Table V and are leached by a solution more dilute than the final extract, represented graphically in Figure 5. In experiments 25 and 26 sodium chloride, potassium and the rate of diffusion from the inside of the particle was presumably increased. The results of these extractions sulfate, and magnesium sulfate were dissolved a t 70" C. so that the concentrations would approach those of solutions are shown in Table IV. Very little increase in fines was noticed after the second obtained by extracting polyhalite, while in experiments 1 to extraction. The moisture content of 25 per cent in the final 9 the crystallizations were made from solutions actually cake represented approximately 21 pounds of water per 100 obtained from the extraction of polyhalite. The concenpounds of polyhalite used a t the start of the experiment. trations of the initial solutions in Table V are slightly higher Petrographic examination showed that considerable un- than the final concentrations in Table 11, because of evapoextracted material remained in the residue from the first ration during filtration a t the end of the extractions. The stage and that very little syngenite had been formed, while solutions a t the elevated temperatures were cooled rapidly the final residue contained very little unextracted polyhalite to the desired temperature and were seeded with schonite. and only slightly more syngenite than was present after After seeding, the solutions were allowed to stand in a thermostat a t the desired temperature for about 18 hours and the first stage.
3''
s6
I N D T; S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
October, 1933 TABLEV.
CRYSTALLIZATION OF SCHOXITE FROM SOLUTIOSS CONTAINING POTASSIUM SULFATE, MAGNESICM SULFATE, AND SODIUMCHLORIDE 7 -
PREQNAIV LIQUOR T CONCEIVTRATIONbfgs04 NaCl KzS04 hfgso4 NaCl % Grams/lOO gram6 Hz0 %
-------MOTHER
LIQUORCONCENTRATION NaCl KzSO4 MgSOl NaCl % Grams/100 grams H 1 0
Hours
70
18 18 18
7.67 7.87 8.13
18.49 16.51 14.39
12.12 12.36 12.72
12.43 12.43 12.55
30.00 26.10 22.25
19.65 19.55 19.65
K~SOI MgSO4 % % 4.24 17.31 5.03 15.35 5.93 13.40
18 18 18
7.85 8.09 8.37
18.95 16.85 14.78
10.12 10.35 10.66
12.44 12.50 12.54
30.02 26.03 22.32
16.04 16.00 15.96
4.54 5.37 6.33
18.02 15.02 13.82
11.10 11.17 11.26
6.85 7.97 9.23
27.18 23.78 20.17
16.74 16.58 16.44
9
18 18
3
18
7.69 7.88 8.07
18.58 16.59 14.47
12.05 12.44 12.76
12.46 12.48 12.47
30.01 26.27 22.37
19.54 19.70 19.72
4.81 5.56 6.55
17.66 15.66 13.67
13.07 13.14 13.30
7.47 8.47 9.86
27.42 23.87 20.58
20.30 20.04 20.01
B1 2 3
18
7.83 8.03 8.32
18.99 17.02 14.82
10.14 10.43 10.69
12.42 12.45 12.56
30.01 26.40 22.40
16.10 16.16 16.15
5.06 5.95 7.00
18.11 16.16 14.19
10.91 11.03 11.03
7.68 8.90 10.33
27.50 24.18 20.92
16.56 16.50 16.30
7.17 7.37 7.05 7.20 7.88 7.56 7.65 7.94
18.02 18.28 17.50 16,78 16.76 16,63 16.71 17.15
10.42 10.56 12.82 12.68 10.86 11.00 10.92 9.16
11.18 11.56 11.26 11.36 12.21 11.67 11.82 12.08
28.11 28.66 27.95 26.50 26,OO 25.66 25.82 26.08
16.18 16.56 20.47 20.00 16.85 16.97 16.87 13.93 ,..
4.92 4.93 4.61 4.84 5.29 5.50 5.45 5.78 5.54
17.37 17.50 16.72 15.95 15.97 15.89 15.81 16.39 14.24
11.06 11.38 13.64 13.53 11.65 11.59 11.64 9.72 13.12
7.37 7.45 7.09 7.37 7.88 8.21 8.12 8.49 8.26
26.07 26.44 25.7 24.3 23.80 23.71 23.56 24.06 21.22
16.60 17.19 20.97 20.6 17.36 17.29 17.35 14.27 19.55
EXPT.
% 25.41 2 3
TEMP. C.
25
B1 2 3 26.41
30
TIME
18 18 25 25 25 25 25 25 25 25
5
1157
..
..
.. .. .. .. ..
..
IMOI
..
...
.
.
I
..
...
were occasionally shaken. The seeding was found to be necessary since there was a marked tendency to supersaturate for long periods of time even though rapid cooling had been used. During the crystallization the evolution of the heat of crystallization of the schonite cauwd a temporary increase in the temperature of the solution. In Figure 5 equilibrium data for the system potassium sulfate-magnesium sulfate-n-ater containing no sodium chloride are shon-n by the broken lines. The 30" C. data are those of Starrs and Clarke (14); the 26" C. data, those of van Klooster (4); data a t other temperatures used but not plotted were those of Levi ( 5 ) . No data were available a t 20" and 15" C., so the concentrations for point B , representing equilibrium between potassium sulfate and schonite, and point C, representing equilibrium between schonite and epsomite (hIgS04.7H20)for the various known temperatures were plotted against temperature, and the resulting curves were extrapolated. From the extrapolated curves the values of points B and C a t 20" and 16' C. were obtained, and the estimated isotherms for these temperatures vere plotted in Figure 6. A comparison of the curves shows the decided lowering of the potassium and magnesium sulfate concentrations in the presence of sodium chloride. From such curves it is possible to predict the concentration of the schonite mother liquor if the sodium chloride concentration is within the range of the experimental data. To show how rapidly these equilibrium concentrations are reached, a test was made similar to those in Table V but with analyses of the schonite mother liquor 1, 3, and 5 hours after seeding. The seeds used were approximately 5 per cent of the total crystal crop. The results listed in Table VI show that crystallization was practically complete within an hour after seeding. TABLEVI. RATEO F CRYSTALLIZATION O F SCHOSITE FROM A SOLUTION CONTAINING SODIUM CHLORIDE, POTASSIUM SULFATE, AND hl.4GNESIlTM SCLFATE r-
EXPT T E M P TIME KzSOd C . Hours 25 1 4.94 24A 4.89 B 3 4.79 C 5
13.24 13.36 13.46
6.52 7.59 8.82
26.67 23.15 19.94
20.31 20.17 20.02
a t temperatures below 25" C., it is safe to assume that cooling the solutions below this temperature would result in lower concentrations and hence a larger crystal crop. The lower temperature limit for the crystallization would probably be determined by the separation of astrakanite (Na2S04. MgSO4.4Hz0)or mirabilite (Xa2S04 10HzO)with the schonite. It was thought that the crystal crop might also be increased by partially evaporating the mother liquor and then cooling, but, when vacuum evaporation of schonite mother liquor containing 20 grams of sodium chloride per 100 grams of water was tried a t temperatures between 50" and 58" C., a considerable quantity of astrakanite was deposited before 10 per cent of the water had been removed as shown in Table VIII. Such a removal of astrakanite n-ould destroy the balance in the cyclic process producing schonite from polyhalite extracts. TABLEVII. ANALYSES OF SCHONITECRYSTAL CROPS EXPT.
KzS04
Theoretical
1 2 3 4
5 6
26B2
COMPOSITION OF S C B ~ N I T E b'lgSO4 H20
so4
%
%
%
%
43.27 42.42 42.55 42.73 43.31 43.66 43.69 43.87
29.89 29.97 30.01 30.08 30.03 30.03 30.02 30.42
26.84 27.61 27.44 27.19 26.67 26.31 26.29
47.68 47.80 47.48 47.58
...
... ... ... ...
TABLEVIII. EVAPORATION AND CRYSTALLIZATION TESTSON SCHONITE MOTHER LIQUOR FROM PROCESS 7 COMPOSITION OF
EXPT.
TEYP.
270 AI B1 A2 B2
5ok 50-58 25" 25"
c.
Analyses made
COhfPOSITION
OF
SOLIDS
E20 SOLUTION AstraREMOVEDK&OI MgSO4 NaCl kanite Schdnite 9.%_ % % % % % (Approx.) 7:OO 25.00 20.-20 io 7.86 28.10 22.70 9i:4 4:4 2.8 18 8.52 29.35 24.65 91.4 6.62 27.00 23.00 22.0 78.0 69.0 29.9 7.76 27.40 26.10 after 18 hours a t 25' C .
.. ..
- CRYSTALLIZATIOS POTASSIUM SULFATE
M O T H E RLIQUORCONCENTRATION MgSOh NaC1 K2SO4 AfgSOa h'aC1 % % Grarns/lOOiirams H20
16.72 16.71 16.74
12.12 12.14 12.16
7.45 7.38 7.24
25.23 25.22 25.21
18.32 18.32 18.32
Analysis of the schonite crystal crops obtained in several crystallization experiments showed close agreement with the theoretical composition of schonite, as evidenced in Table VII. Petrographic examination likewise indicated that these crops consisted of pure schonite. Although no data are presented showing the schonite mother liquor concentration in the presence of sodium chloride
a
OF BY DISSOLVING SCHONITE IX A POTASSIUM SULFATESOLUTION
Storch and Clarke (14) have suggested that a partial separation of the potassium sulfate and magnesium sulfate in schonite may be made by fractional crystallization. They proposed to dissolve schonite in a solution containing both potassium sulfate and magnesium sulfate until the concentration of the latter was nearly equal to the equilibrium concentration for potassium sulfate and schonite at 30" C. (11). I n the investigation reported here, fractional crystallizations were made by dissolving Echonite in a potassium
1158
I N D U S T R I A L -4N D E N G I N E E R I N G C H E 1LI I S T R Y
sulfate solution a t elevated temperatures and cooling to obtain a crop of solid potassium sulfate. I n these experiments both the concentration of magnesium sulfate and the temperature a t which the crop of potassium sulfate was removed were varied. Inspection of the data for the system potassium sulfate-magnesium sulfate-water indicated that up t o approximately 55" C. an increase in temperature raised the magnesium sulfate concentration of point B for the equilibrium between solid potassium sulfate and schonite more rapidly than it did the potassium sulfate concentration. It was actually found that, by crystallizing potassium sulfate a t a temperature near 50" and then cooling to 30" C. with the attendant deposition of schonite, the final mother liquor would contain more magnesium sulfate and less potassium sulfate than the mother liquor of a single-stage crystallization of potassium sulfate to point B a t 30" C. A comparison of single-stage and two-stage crystallization is shown in Figure 6. Schonite is dissolved in potassium sulfate liquor A obtained by the decomposition of syngenite. A t 80" C. the solution composition will proceed along the line ABD'D. For the singlestage crystallization of potassium sulfate sufficient schonite is added to bring the liquor composition to D' at a magnesium sulfate concentration slightly below the value for the equilibrium between potassium sulfate and schonite at the final crystallization temperature, a s E' for 30" C. For a two-stage crystallization a larger amount of schonite is added t o the initial liquor, A , t o bring the magnesium sulfate concentration up t o D, whence, on cooling to some intermediate temperature, pot,assiumsulfate is obtained. After removal of potassium sulfate the mother liquor as E at 50" C. is cooled t o the final crystallization temerature t o yield a final liquor, such as F, at 30" C . This final Equor has a higher magnesium sulfate and lower potassium sulfate content than E' for the single-stage crystallization and hence represents a higher recovery of potassium sulfate in the crystallization step.
Vol. 23, No. 10
obtained from the decomposition of syngenite according to the method proposed by Storch and Fragen and hence contain a very small amount of dissolved calcium sulfate (16). The schonite was obtained from hot extraction of calcined polyhalite and subsequent cooling of the extract solutions. Experiments 29 and 31 represent the crystallization of potassium sulfate a t 30" C. from solutions having an initial magnesium sulfate concentration nearly equal to the potas-
2 2 30
, I '
3
1
~
I
'
/'
-CRYSTALLIZE
M k Ki50r
I0
Mg%
-
20
30
CONCEKTRATIO~ G R A M ~ I O O'RAM$ bo
FIGURE6. COMPARISON OF SINGLEAND TWO-STAGECRYSTALLIZATION PROCEDURES
sium sulfate-schonite invariant point a t that temperature. In experiment 29 the potassium sulfate solution was heated to 90" C. in a flask immersed in a thermostat; the schonite was added gradually, with stirring, oyer a period of 15 minutes; and the solution was seeded with potassium sulfate As will be noted later, two-stage crystallization should equal to approximately 3 per cent of the resulting crop. prove advantageous because it improves the over-all re- Samples of the solid and solution were taken a t 1.5 and 3 hours (samples h and B). The temperature was then slowly covery of process 7A. dropped to 30.5" C. during a period of 4.5 hours, the rate TABLE IX. CRYSTALLIZATION OF POTASSIUM SULFATE FROM A being held especially slow in the temperature interval 52-32 " MIXTURE OF POTASSIUM SULFATE SOLUTION AND SOLID SCHONITE C.4 Samples of the solid and mother liquor (C) were taken ACCORDING TO PROCESS ?A after st'irring a t 30.5" C. for 8 hours. In experiment 31 the COMPOBITION PETROQR.4PAIC COYPOsITION OF highest temperature during the cryst'allization was 51 ", and OF SOLN. EXAMINATION OF SOLID EXPT. TEMP. KzSOd MgSO4 SOLIDPHASE K ~ S O I !.fgSOa NaCl the solution was cooled to 30" a t the rate of 0.2" C. per ' C. Grams/lOO gram8 Hz0 70 7 0 7 0 minute. Sample 31A was taken after mixing a t 51", and Starting materials: samples B and C after 15 and 60 minutes, respectively, a t 30". KzS04,soIn. ] 9 , 2 0 Schonite 42.4 29.1 0.5 Schonite Experiments 30, 32, 33, and 34 represent the data obtained Equilibrium, KzSOd-schonite: from crystallizations of potassium sulfate a t temperatures 30 15.3 17.4 above 30" C. I n experiment 30 the schonite was dissolved ... .. .. 29A 90 25.41 16.98 KzSOh , .. ... .. . B 90 25.30 16.97 KzSOr a t 72", stirred for 2 hours, and then cooled a t the rate of 97.2 2.54 .. C 30.5 15.34 16.85 0.12" per minute to 45". Samples A and B were taken after KzSOi 31A 51 18.82 17.11 1 and 2 hours of stirring a t 72", and C after 1 hour a t 45". KzSOi B 30 15.34 16.91 KzSO4 C 30 15.36 16.94 The mother liquor decanted from the crystal crop was cooled KzSO4 + leonite . .. ... . .. rapidly to 30" and stirred for 3 hours. The crystal crop of 30A 72 21.76 23.65 21.52 22.93 fleonite B 72 potassium sulfate obtained a t 45" mas contaminated by K&O4 + leonite 78:22 14:44 : C 45 18.71 23.25 13.56 19.25 Schonite 44.11 30.08 , D 30 leonite. The concentration of magnesium sulfate in experi32A 72 22.10 21.35 KzSOi ... ment 32 was lower than that used in experiment 30, and a B 45 17.65 21.10 &SO4 , . , 2:09 : . : pure crop of potassium sulfate resulted. The operations Schonite ... . . .. , 15.06 17.05 C 30 Schonite ... . ... 14.44 19.25 C' 30 were similar in both experiments, but in 32 the mixture was 33A 80 23.43 23.42 KzSOi stirred for only 25 minutes a t 72", and for one hour each a t B 48.5 18.20 23.30 KzSO4 4-schonite (Tr'a'ck) 2 : 6 2 . : : 45" and 30". The rate of cooling between 72" and 45' was C 45 17.06 21.02 KzSO4 + schonite . . . 12.67 . . . D 30 14.27 1 8 . 0 2 Schonite . . . 0.5" per minute. Upon cooling the potassium sulfate mother 34A .. 18.84 23.65 Liquor, a pure crop of schonite crystallized. Because of 14.00 20.75 Schonite B 30 incomplete removal of solid potassium sulfate from its Schonite C 30 14.05 20.75 mother liquor by decantation, t'he potassium sulfate conThe results of crystallization of potassium sulfate both a t centration of the schonite mother liquor, 32C, was higher, 30" C. and a t higher temperatures are given in Table IX. and the magnesium sulfate concentration lower than would Those experiments in which the potassium sulfate was have been obtained by cooling a solution having the comcrystallized a t the higher temperatures also include data for 4 Unpublished crystallization experiments made at this station show that, the subsequent schonite crystallization a t 30" C. The unless the solution is cooled slowly in this range, schonite will precipitate potassium sulfate solutions used in these experiments were with the potassium sulfate as a metastable phase. '
I N D U S T R I A L A N D E N G I R'E E R I N G C H E R.I I S T R Y
October, 1933
position shown in 32B. 32C' shows the calculated concentrations for the schonite mother liquor based on complete removal of solid potassium sulfate in the first step. A higher concentration of magnesium sulfate was used in experiment 33 than in 32. The schonite was dissolved a t temperatures between 80" and 72" C., and the mixture stirred a t 80" for 30 minutes. It was then cooled to 49" during 25 minutes, and the temperature was held between 49" and 48.5" C. for a n additional 25 minutes (sample B). The mixture was then cooled t o 45" t o determine to what extent schonite would separate. A considerable amount of schonite precipitated showing that 48.5" C. is approximately the lowest temperature a t which a pure crop of potassium sulfate would result n-hen the magnesium sulfate concentration is as high as in this experiment. Again incomplete removal of the crop of potassium sulfate a t 45" C. caused the schonite mother liquor (33D) to be higher in potassium sulfate and lower in magnesium sulfate than would be expected from cooling a solution of the composition shown in 33C. T o determine how closely the theoretical concentration of the schonite mother liquor would be approached in an actual crystallization, the synthetic starting solution of experiment 34 having nearly the same composition as 33B was cooled t o 30" C. The resulting mother liquor in contact with the schonite crop had nearly the estimated theoretical concentration, and this concentration was almost the same after one hour of standing a t 30" C. (34B) as it was after 18 hours (34C), showing that crystallization was almost complete within a short time. The preceding data show that nearly pure potassium sulfate may be obtained by fractional crystallization of schonite according to the method proposed by Storch and Clarke (14)or by the modification shown in Figure 6. The latter procedure yields a n end solution with a higher concentration of magnesium sulfate and a lower concentration of potasqium sulfate than the former. TaBLE
x.
REPRESENTATIVE C O M P O S I T I o N O F A C.\RLOAD SEW MEXICOPOLYHALITE"
OF
CONETITUEVT % Polyhalite: 76 64 KzSOk 22.15 MgsOI 35.25 Cas04 34.64 H2O 4 6 8.17 -4nhydrite CaSOd 12.81 Halite ( N a L l ) 0.73 Magnesite ( M g C 0 3 ) 2.29 Rz03 Si02 Calculated from analysis by F. Fraas of this station.
+
A-EW PROCESS OUTLINES The investigations reported in this paper have led to two new process outlines, process 7 for the production of schonite alone and process 7d for the production of both potassium sulfate and syngenite using schonite produced in process i as a n intermediate material. Figure i represents preliminary diagrammatic flow sheets for a plant treating 2000 tons of raw polyhalite p w day by either process i or 7'1. The composition of this polyhalite shown in Table X is based on a representative analysis made on a carload of Texas-Sew Mexico polyhalite a t this station. The crushing, screening, salt-removal, and calcination operations have not lieen shown in Figure 7 . These operations, with the exception of salt removal, are discussed by Wroth (f7). The details of the method of treatment shown in Figure 7 are based on the experimental data presented in the present paper and in that of Storch and Fragen (f6). Process 7A may be considered as composed of three distinct units: The first is the complete process 7 which produces schonite by extracting polyhalite. The second
1159
_-_ FIGCRE7 . FLOWD
I ~ G R ~ FOR M PHOCESSES
7
AVD
y\
(Haeed on polyhalite composition of Table X )
involves the use of the schonite produced in the first unit and a potassium sulfate solution furnished from the third unit to yield a potassium sulfate product for the market, and a potassium sulfate mother liquor for use in the third unit. The third unit treats calcined polyhalite with this mother liquor to produce syngenite ( 1 5 ) . Part of this syngenite is extracted to yield the potassium sulfate solution for the second unit, and the remainder is dried for niarket or is decomposed to produce a solution which, when evaporated, yields a n additional amount of potassium sulfate. TABLEXI. ESTIMATED EFFECTO F SEVERAL FACTORS UPON PERFORIMAKCE O F PROCESS 'iA .4ND COMPARISON WITH PROCESS 4R 4A
+
DISTRIBVTION O F &SOI
F R O M POLYHALITE EVAPOR.ATI~N POLYFINAL O B T A I N E D WITHOUT R E Q U I R E M E N T S H.4LITE CRYSTALCONCN. OF EYAPN. AS: F O R KzSok U S E D IN L I Z . ~ T I O N SYNGEHITE TOT.AL KzS04 Syngenite .AS ONLY SYNGENITE TEMP. Em. LOST product product PRODUCTPRODUCTION Grams R ? S O I / Lb. H z O / % of O C. 100 g r a m s H:.O 7c % % Zb. KzSOI tutal P R O C E S S 7.A W I T H 8 I N G L E - S T A G E C R Y S T A L L I Z A T I O N OF'
25
9.4 10.0
16.2 16.2
49.6 51.0
34.2 32.8
30
9.4 10.0
15.0 15.0
45.9 47.2
39.1 37.8
P R O C E S S 7.A W I T H T W O - S T I G E CRYST.ALLIZATION O F
25 30
9.4 10.0
15.2 15.2
62.0 63.3
22.8 21.5
9.4 10.0
13.9 13.9
56.8 57.9
29.3 28.2
10.0
13.9
PROCESS
25
4B
0.0
+
&SOr
4.3 3.9 4.9 4.4 KiSOk A N D 2.86 2.54
29.9 29.9 31.2 31.2 JCHONITE
22.5 22.5
3.63 3.3
23.8 23.8
10.5
29.4
4.4
0.0
Recent investigations, as yet unpublished, have shown that in the decomposition of syngenite by water at 100" C. a concentration of 9.4 grams of potassium sulfate per 100 grams of water may be obtained in a few hours and that a 10-gram concentration may be reached by agitation for a longer period a t that temperature. The effect of these different liquor concentrations, and of the use of single- or two-stage crystallization with final temperatures of 25 " or
1160
INDUSTRIAL AND ENGINEERING CHEMISTRY
30” C., upon the performance of process 7A are shown in Table X I , and a comparison is also made with a combination of process 4B producing syngenite, and 4A using this syngenite to yield potassium sulfate as the only final product. The use of a two-stage crystallization reduces the loss of potassium sulfate in the syngenite mother liquor. This decreased loss is due to the fact that almost all of the magnesium sulfate appears in the waste liquors after the syngenite formation, and the concentration of potassium sulfate in this solution is almost independent of the concentration of magnesium sulfate. Therefore, for a given amount of magnesium sulfate in process there will be less end solution the higher the concentration of magnesium sulfate and, hence, less potassium sulfate discarded with this solution. The effects of variations in the procedure are shown because it is difficult to predict the most economical operating conditions which might prevail a t the treating plant. Future variations in the markets for schonite, syngenite, or potassium sulfate may make it desirable to alter the method of treatment to meet these demands. The modification of Bureau of Mines process 4B presented here as process 7A offers several advantages over the former method of treatment: 1. As indicated in Table XI, the evaporation necessary in the earlier method is eliminated if part of the potassium sulfate is to be marketed as syngenite, or greatly reduced if the product is to be potassium sulfate alone. Even with no evaporation, as high as 67 per cent of the total potassium sulfate can be produced in the form of potassium sulfate, a high-grade product for which there is a well-established market (6). 2. An additional product, dehydrated schonite or kalimagnesia, is available if desired. 3. The hot extraction of polyhalite may be conducted most advantageously at temperatures below the boiling points of the solutions used, thus not only effecting heat economies but also decreasing the difficulties of material handling inherent in the use of boiling solutions.
Vol. 25, No. 10
4. A procedure for extracting comparatively coarse polyhalite has been devised which may eliminate the necessity for filtering large quantities of hot solutions and allow the use of settling and decantation or of classification in the separation of the solid residue from the hot extract liquors.
ACKXOWLEDGMENT The authors wish to express their appreciation to Alton Gabriel, assistant chemist-petrographer a t this station for the petrographic examination of the solid phases in the various experiments, and to Loyal Clarke, assistant chemist a t this station, for valuable criticisms and suggestions. LITERATURECITED (1) Clarke, Davidson, and Storch, Bur. Mines, Rept. Znvestigations 3061 (1931). (2) Geiger, ‘Dissertation, Friedrich-Wilhelms-Universithtzu Berlin, pp. 23-5 (1904). (3) Hill and Adams, 1x0. EXG.CHEhl., 23, 658-61 (1931). (4) Klooster, H. S.van, J. P h y s . Chem., 21, 513 (1917). (5) Levi, 2. p h y s i k . Chem., 106, 93 (1923). (6) Partridge, IND.EKG.CHEM.,24,895-901 (1932). (7) Precht and Wittgen, Ber., 15, 1671 (1882). (8) Ransom, U. S. Patent 1,812,497 (June 30, 1931). (9) Schoch, U. S.Patents 1,794,561-3 (March 3, 1931). (10) Standard Oil Development Co., French Patent 661,278 (March 4, 1929). (11) Starrs and Clarke, J. P h u s . Chem., 34, 1068-63 (1930). (12) Starrs and Storch, Ibid., 34, 2367-74 (1930). (13) Storch, IND.EKG.CHEM.,22, 934-41 (1930). (14) Storch and Clarke, Bur. Mines, Rept. Investigations 3002 (1930). (15) Storch and Fragen, Ibid., 3116 (1931). (16) Storoh and Fragen, IND.ENG.C H ~ M 23, . , 991-5 (1931). (17) Wroth, Bur. Mines, Bull. 316 (1930). REcmvEn February 28, 1933. Presented before t h e Division of Industrial and Engineering Chemistry a t the 85th Meeting of t h e American Chemical Society, Washington, D . C., March 26 t o 31, 1933. Published b y permission of the Director, U.5. Bureau of Mines. ( N o t subject t o copyright.)
Bromination of Saturated Aliphatic Hydrocarbon Gases W. J. PERELIS, Box 323, Berkeley, Calif.
I
N ENDEAVORING to utilize the constituents of natural gas for the manufacture of alcohols and other chemical compounds, the writer considered the halogenation of the gaseous aliphatic hydrocarbons as a preliminary step. Scientific chemical literature did not give sufficient information on this point. Patent literature recites methods by which mixtures of halogenated products can be obtained. Some of the patents claim the production of pure monohalides (5, 6, 9). Egloff, Schaad, and Lowry (3) described the situation as follows: “Considerable difficulties are encountered in halogenating hydrocarbons * * * chief among these are * * * the production of undesired polysubstitution products where monosubstitution is desired.” Frohlich and Wiezewich (4) state, “The main objection seems to be the difficulty of limiting the reaction to the introduction of only one chlorine atom per molecule of hydrocarbon.” Bedford ( I ) explains why pure monohalides are not produced by stating that the chlorine has more affinity towards chloromethanes than towards methane itself. However, one record claimed that a lower halogen concentration produces a larger proportionate amount of the lower halogenated compounds (’7). From this it is assumed that a sufficiently low halogen concentration could lead to pure
monohalides; also, that the failure to produce the desired monohalogenated products was partly caused by not working with an unchanging halogen concentration. At first, the method indicated by Schroeter (9) was used, but it was found impracticable for large-scale operation. The method worked out is as follows: Dry the bromine and the hydrocarbon gas. Bubble the dried gas through a layer of dried liquid bromine. Use a sufficiently high bromine layer to produce a saturated bromine solution in the gas. Vary the temperature of the gas and the bromine according to the products or product desired. By varying the temperatures, any bromine concentration can be produced; t o each bromine concentration correspond certain products. For pure monohalides, therefore, the proper bromine concentration must be used. Commercial products were used for all the experiments, and the following compounds were isolated: methyl bromide, methylene bromide, ethyl bromide, ethylene bromide, ethylidene bromide, N-propyl bromide, sec-propyl bromide, N butyl bromide, sec-butyl bromide. Table IA shows that a bromine concentration of 6.6 per cent will produce pure butyl bromide; Table IB, bromine concentration of 5.6 per cent gives propyl bromide.
