May, 191.8
T H E JOURATAL OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
347
KSZ.
FIG. 5-THE
EQUILIBRIUM DIAGRAMA T 75O
TABLE~V-COMPOSITION, IN GRAMSPER 100 SATURATED AT 50 Saturated with NaCl KCl A: NasSOa B4 KzSO4 4i:iz 6 KC1 D4 NaCl 36: 50 E4 NazSO: and glaserite.. F: &SO4 and glaserite.. ... 45: i 4 G4 KC1 and KzS04.. H4 KCl and NaC1.. 29: 09 22.03 14 NaCl and NazS04.. 33.70 35:66 4.68 L4 KzS04. KCI, glaserite. M4 KCl, NaC1, glaserite.. 26.84 22.43 N4 NaC1, NazSOa, glase1-ite 40.15 14.58
.............. ............... ................. ...............
. ...
...
...
...
..... ......
...............
g. OF
FIG. 6-THE
WATER,OF SOLUTIONSTABLE X-COMPOSITION, KzSOa
SP. Gr.
... ...
1.301 1.110 1,198
As
1i:09
45:i3 6.79
9.40 17.36 1.84
Ea
... ... 2.59 ...
1.351 1.307 1.212 1.246 1.223 1.203 1.254
...
1.248
NazSOa 44.84
... ...
7.34
...
3.15 11.74
...
...
1.188
TABLE VI-COMPOSITION, IN MOLS PER 1000 M ~ L OF S WATER,OF SOLUA4 B4 C4 D4 E4 F 4
G4 H4 14
L4 M4 N4
TIONS SATURATED AT 50 NazClz KzCla NazSO: 56.86
Saturated with NazSOn KzS04 KCI NaCl NazSOa and glaserite.. KzS04 and glaserite.. KCl and KzSOa.. KC1 and NaCl. NaCl and NazS04.. KzSOa, KCl, glaserite KCl, NaCl, glaserite.. NaCI, NazSO4, glaserite
.............. ... ............... ... ................. ................ si:i 4 .. ... ... ..... ....... 44:82 .... 51.93 7.21 41.36 40.15
... 52: io ... ...
5i:03 26.61 4i:k 27.01 14.58
EQUILIBRIUM DIAGRAMAT 100’
... ...
58100 8.61
KzSO4
1i:io
... ...
...
2.67
4.00 11.74
Fa
Gs He Is
L6 Me
Ne
...
.................. .................. .................
...
.......
...
.. ...
with which solid glaserite is in equilibrium. Some further details of these diagrams will be described in the following paper. UNIVERSITY O F CALIFORNIA BERKELEY
... ... 9.72
17.95 1.90
9.26
Sum
Be Ce De
MOLSPER 1000 MOLSOF WATER, OF SOLUTIONS SATURATEDAT 100° Saturated with NazClz KzClz NazSOa KzSO4 Sum NazSO4 52.86 52,86 &SO4 ... 2i:07 24.07 KC1 6j:90 ... 67.90 NaCl ................ 60:81 ... 60.81 NazSOa and glaserite.. ... ... 52:88 14:68 66.96 KnSOa and glaserite.. . . . . 17.21 21.21 38.42 KzSOa and KC1 . . . . . 65:?6 ... 2.93 68.69 NaCl and KCI. 42:ZO 42.48 ... ... 84.68 NaCl and NazSOa.. 56.33 8.12 ... 64.45 K ~ S OKCI ~ glaserite. 4.91 60:41 , 3.24 68.56 KCl, NaC1,’glaserite.. 38.25 43.65 4.78 86.68 NaC1, NazS04, glaserite 55.22 12.31 li:37 78.90 IN
~
THE SEPARATION OF T H E CHLORIDES AND SULFATES OF SODIUM AND POTASSIUM BY FRACTIONAL CRYSTALLIZATION
... ... ... ...
By WALTERC. BLASDALE Received March 20, 1918
TABLEVII-COMPOSITION, IN GRAMSPBR 100oG. OF WATER, O F SOLUTIONS SATURATED AT 75 Saturated with NaCl KC1 NazSOa KzSOa Sp. Gr. As NazSO4 43.41 1 286 Bs KZSO4 20:io 1:120 Cs KCl 49:jo 1,204 Dr NaCl.. 3;:j5 1.183 Es NazSO4 and glaserite.. 4i:06 ii:?7 11332 Fs KzS04 and glaserite.. 10.09 18.60 1.183 48:;s 2.12 Gs KCI and KzS04.. Hs KCl and NaCl. 2?:87 29.06 1:i49 Ir NaCl and NazSO4.. 35.46 6.67 1.210 LI KzSOa, KC1, glaserite . 5.71 42:;s , , 2.83 1.223 MI KCl NaCl, glaserite. 25.45 29.38 3.33 1.257 Ns N a d l , NazSO4, glaserite 28.28 15.72 8.88 1.253
Relatively little use has been made in the industries of data similar t o t h a t presented in the preceding article, ................. ... although the possibility of doing SO was indicated by ................. ... ................. ... ... van% Hoff’ and has recently been discussed by Hilde.............. ... ... ... brand2 as applied t o the utilization of the bittern of . . . . ..... ... sea water. I n this paper the data referred t o will be ....... ... ... utilized in suggesting and testing the efficiencies of ... ... . methods for the separation of certain pairs of salts . ... ... which yield a common ion, and for the recovery of TABLE VIII-COMPOSITION, I N MOLS PER 1000 %OLS OF WATER, OF SOLUpotassium salts from two classes of materials which TIONS SATURATED AT 75 are of special importance t o the states of the Pacific Saturated with NazClz KzClz NazS04 KzSO4 Sum As NazS0: . . . . . . . . . . . . . . . . . ... 55.03 55.03 Coast. The first is the ash of kelp, which is already Bs KzS04 . . . . . . . . . . . . . . . . . . ... 2i:io 21.50 ... ... 60.02 Cn KCl. ................ 66102 produced on a large scale in the state of California; DS NaCl ............... 58: i 7 ... ... 58.17 Es NazSO4 and glaserite.. ,.. ... 5i:i4 12.17 65.51 the second includes certain natural brines found in the F r KzSOa and glaserite. . . . . . 12.80 19.23 32.03 desert regions of California, Nevada and Utah. Many Gs KC1 and KzS04 ...... 58’90 ... 2.19 61.09 Hs KC1 and NaCI ........ 42194 35: 11 ... ... 78.05 of the latter contain small amounts of carbonates, I 6 NaCl and NazSO4.. ... 54.64 8.48 ... 63.12 Ls KzSO:, KCl, glaserite.. 8.80 51145 ... 2.93 63.18 bicarbonates and borates which would make i t necesM6 KC1 NaCl glaserite.. 39.23 35.50 4.23 ... 78.96 ... 73.82 N6 N a d l , NarS‘04, glaserite 43.57 18.99 11.26 sary t o modify t o some extent any process based upon TABLEIX-COMPOSITION, IN GRAMSPER 100 G. 2” WATER,OF SOLUTIONSthese d a t a ; others contain such large proportions of SATURATED AT 100 these substances as t o make a n entirely new set of d a t a Saturated with NaCl KC1 NazSO4 KzSO4 Sp. Gr. A6 NazSO4 .............. ... ... 41.68 1.264 necessary. Be &SO4 ............... ...
................. ..............
Cs KC1 De NaCI.. E6 NazS04 and glaserite.. . F 6 KzSO: and glaserite.. Ge KzSOa and KCl He NaCl and KC1.. ...... I e NaCl and NazSOd.. Le KzSO4, KC1, glaserite Me KCl, NaC1, glaserite.,.. NE NaCI, NazSO4, glaserite
39: 40
...
. ...... 2;:...39 .... 36.56 3.19 24.82 35.84
56:i0
... ...
5i:i3 35.16 50:Ol 36.13 10.18
... ...
4 i .’io 13.57
... ...
6.41
2i 44
...
1i:fiz 20.51 2.83
...
...
...
3.24
...
ii:0o
3.77
1.134 1.217 1.175 1.326 1.213 1.225 1.253 1.204 1.233 1.269 1.256
I-SEPARATION
O F POTASSIUM CHLORIDE F R O M SODIUM CHLORIDE
The behavior upon evaporation of solutions containing different proportions of these salts can be easily 1 2
“Zur Bildung der ozeanischen Salzablagerung,” 1906. THIS JOURNAL, 10 (1918). 96.
348
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
followed by means of a diagram based upon the data given in the preceding article. I n this diagram (Fig. I) the weight of sodium chloride in the solution per I O O parts of water is measured along the vertical axis, that of potassium chloride along the horizontal axis. NnUl
If the evaporation is still continued, sodium chloride will continue t o separate and the solution must change its composition in a manner represented by movement of the point q t o &, a t which point potassium chloride will begin t o separate. If the sodium chloride which has separated is removed and the temperature reduced t o zero, the solution becomes supersaturated with potassium chloride, but unsaturated with sodium chloride, and hence potassium chloride will separate out, and t h e composition of the solution will change t o correspond t o t h a t represented by t h e point r . If the potassium chloride is now removed and the solution again evaporated a t IOO', its composition changes t o t h a t represented by the point s, a t which point sodium chloride will again separate. The result of these operations can be calculated by methods similar t o t h a t already used, t o be as follows: Composition of Solution At the outset.. .. At the point 9 . . . At the point Hr.. , . At the point 1 . . A t the points
. ..... . . .. . . .. . .....
CHLORIDE
Let it be assumed that we start with 134g. of the solution referred to above. When q is reached the ratio of NaCl t o HzO must have changed from 2 0 : 100 to 31.8 : 100. If x represents
No. 5
the water which is evaporated, the following relation is true: 20 : 100-x = 31.86 : IOO When solved for x we obtain 37.22 g.
FIG.I-THE SEPARATION OF POTASSIUM CHLORIDEFROM SODIUM
The points D 1 , D2, Ds, Dd and D5 represent the composition of solutions saturated with sodium chloride a t oo, z s 0 , 50°, 7 5 ' and IOO', respectively, the points C1, Ca, C3, C4 and Cs t h a t of solutions saturated with potassium chloride, and the points H1, H2, H3, H4 and Hg t h a t of solutions saturated with both salts. The lines D I H I , etc., represent the composition of solutions saturated with sodium chloride in t h e presence of varying amounts of potassium chloride in solution and the lines CIH1, etc., t h a t of solutions saturated with potassium chloride which contain varying amounts of sodium chloride. It is assumed t h a t all of these lines are straight, and although no actual measurements have been made, it is probable t h a t they are curves which differ but slightly from straight lines. A solution which contains 2 0 g. of sodium a n d 14 g. of potassium chloride per I O O of water is properly represented by the point p on the diagram. Since this point lies within the space included by the broken line C1 HI D1 it is unsaturated, even a t oo, with respect t o both salts. When such a solution is evaporated the proportion of the two salts t o each other does not change, and the process of evaporation corresponds t o movement of the point p in t h e direction O p . If the evaporation is made a t 100' the solution will become saturated with sodium chloride a t the point of intersection of the two lines O p a n d DIH5. The composition of the solution a t this point can be ascertained graphically, t h a t is, by measurement of its position with respect t o the axes of reference, or by formulating the equations representing the two intersecting lines (namely, x = 1.444~ and x = 39.4 - 0.3413~)and solving for the unknown cobrdinates. The latter method gave the values 2 2 . 0 7 KC1 and 31.86 NaC1 per I O O H 2 0 . T h e amount of water which must be evaporated before this point is reached is easily calculated as follows:
Vo1:1o,
.........
NaCl 20 20 ,10.91 10.91 10.91
KCl 14 14 14
HzO 100 62.78
5.14
5.14
39.72 39.72 31.83
Substances eliminated
37.22 g. Hz0 9.09 g. NaCl (23 g.HpO 8.86 g.KC1 7.89 g.HaO
The series of changes representing movement of r t o s, s t o H5, and H6 t o r , constitutes a cycle which can be repeated as long as any solution remains, or the residual solution can be added t o a further quantity of fresh solution. Cooling t o 2 5 " rather t h a n o o would reduce the efficiency of the process but little and might prove t o be more economical. 11-SEPARATION
OF POTASSIUM CHLORIDE FROM POTAS-
S I U M SULFATE
The possibility of separating these salts can be easily shown by reference t o Fig. I1 which is based upon the d a t a given in the preceding article. I n this diagram the weight of KC1 per I O O g. of water is plotted on the horiFonta1, t h a t of KzSOl on the vertical axis, and the lines BIG1, B2G2, etc., represent the solubility of potassium sulfate in the presence of varying amounts li"h0, I
FIG.
11-THE
SEPARATION OF
POTASSIUU CHLORIDE
SULFATE FROM POTASSIUM
of potassium chloride, while the lines C1 GI, etc., represent the solubility of potassium chloride in t h e presence of varying amounts of potassium sulfate. When a solution of the composition p is evaporated a t IOO', K & 0 4 will separate first a t the point q and will continue t o separate in pure form until the solution has the composition Gs a t which point potassium chloride will separate also. If the temperature is now reduced both
May, 1918
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
KC1 and will separate, and the composition of t h e solution will change t o correspond with t h a t represented successively by the points Gd, G3, Gz and GI. This is a consequence of the fact t h a t the solubility of neither salt is increased b y decreasing the temperature as with t h e KC1-NaC1 mixtures. If the solution of composition GI or Gz is again evaporated a t 100' i t will first become saturated with KC1 a t a point on the CbGa line very near t o G5, and very little additional evaporation will suffice t o saturate it with KzS04 as well as KC1 a t the point G5. T h e proportion of KC1 which could be recovered in pure form by this part of the process would be too small t o be of commercial significance, but the mixture obtained by continued evaporation a t the point G5 would contain only about 5 per cent of KZSO4, and might be used for many purposes without further purification. Hence in dealing with these mixtures i t is possible t o recover in pure form only t h a t amount of KzS04 which must be separated before t h e ratio of KzS04t o KCl is changed t o the ratio of I t o 20. 111-THE
SEPARATION
OF
POTASSIUM
SULFATE
FROM
SODIUM S U L F A T E
The changes which take place during the evaporation
of solutions containing t h e two sulfates can be predicted from Fig. I11 which is based upon the data given in the preceding article. The vertical axis represents grams of KzS04,t h e horizontal, grams of NazSO4, per I O O grams of water. The lines BIF1, etc., represent the composition of solutions saturated with KzS04 in the presence of varying amounts of NazS04, the lines FIE^, FzEz, etc.,
zp PIG. 111-THE
la A
A20
SEPARATIONOF
POTASSIm
SULFATE
' 4jXtt'S0.
FROM SODIUU
SULFATE
solutions saturated with glaserite in the presence of varying amounts of KzS04 and NazS04, the lines FlAl and EzAzsolutions saturated with Glauber's salt in the and E3A3, etc., presence of varying amounts of solutions saturated with Na2S04 in the presence of A study of the diagram varying amounts of &Sod. suggests two possible cycles representing possible co mmer ci a1 methods. If a solution containing 20 g. NaZS04, I O g. KzS04 and I O O g. of water, corresponding t o t h e point p , is heated t o 100' and evaporated a t t h a t temperature, glaserite will begin t o separate a t q, and the composition of the solution will change from q t o E5; if the temperature is then dropped t o soo, glaserite will separate along the line E5r, parallel t o the line representing the composition of solutions which contain K & 0 4 and NaZS04 in the same proportions as in glaserite, but no NazSO4 will separate as such since the solution is not saturated with respect t o
349
this salt a t 50' until i t attains t h e composition E*. If the temperature is now dropped t o 2 5 ' a very little glaserite and much sodium sulfate will separate, and all of t h e latter will be in t h e form of Glauber's salt by the time the solution reaches the point Ez; if t h e temperature is dropped t o 0' a little glaserite and much Glaubbut at some stage in the er's salt will separate along EzFI, process all the glaserite should change into potassium sulfate and Glauber's salt, although i t is probable t h a t this change will be slow and perhaps incomplete unless the glaserite separates a s a fine precipitate, and unless i t is agitated with t h e residual solution. I n making use of this cycle i t is evident t h a t a potassium-rich mixture should be removed a t r and a sodium-rich mixture a t El or F1. The second cycle suggested would involve evaporating a t 50' instead of IOO', t h a t is, from s t o E8 and removing the potassium-rich mixture, then cooling t o 25' or o o and removing the separated sodium-rich mixture. The comparative efficiencies of the two methods can be calculated, by the methods already discussed, t o be as follows: SUBSTANCES ELIMINATED BY PROCESS I HzO NazSOa Between p and Q.. 37.5 Between g and E L . . 17.01 1.03 Between Er and 7 . . 0.39 7.16 Between 7 and E z . , ............. 8.60 9.92 Between Ez and Fi.. 13.02 1.50 Left in Solution.. 23.86
.............. ............ ............. ............ ...............
SUBSTANCES ELIMINATED BY PROCESSI1 Hz0 NazSO4 25.37 Between p and s.. Between s and Ea.. 33.54 1.22 Between Ea and Ea., 10.86 9.42 Between Es and Fr.. 11.43 8.18 Left inlSolution.. 18.80 1.19
.............. ............. ............ ............ ...............
&So4
3.79 1.43 1.36 1.26 2.16 KzSOI . .
4.49 3.12 0.69 1.70
These figures show t h a t the total amount of K & 0 4 recovered by Process I in a concentrated form is somewhat greater t h a n t h a t recovered by Process 11, also t h a t the proportion of KzS04 lost with the sodium-rich mixture is less in Process I t h a n in Process 11. It is also probable t h a t under most conditions evaporation a t 100' would be more economical t h a n a t 50'. The treatment of the residual solution by either of the two processes would be more efficient t h a n the treatment of the original solution. The effect of cooling t o 25' only would be t o decrease greatly t h e proportion of KzS04 t o NazS04 in the residual solution and t o increase the amount of water which would have t o be removed by evaporation in t h e treatment of this residual solution. The separation of pure KzS04 from the potassiumrich mixture would involve large wastes of either power or product, but i t is probable t h a t its content could be utilized as such without further concentration. It is doubtful whether the sodium-rich mixture (especially t h a t obtained by cooling t o 0 ' ) could be profitably treated for the recovery of the potash which it contains, since it could not be concentrated t o a greater degree t h a n would be represented by solutions saturated with both sodium sulfate and glaserite, which a t 100' would correspond t o the point E5. IV-THE
SEPARATION OF SODIUM SULFATE FROM SODIUM CHL 0 RID E
The diagram needed for the discussion of this separation is shown in Fig. IV. The horizontal axis repre-
3.50
T H E J O U R N A L OF I N D U 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
Vol.
IO,
No. 5
tions will be expressed in terms of the number of mols of NazClz, K2Cl2, Na2S04and KzS04 per 1000 mols of water. The composition of any of these solutions can be expressed in terms of any three of the four, and the three actually used will be chosen arbitrarily. By plotting the concentration with reference t o two axes, , intersecting a t right angles, as explained in t h e previous paper, it is possible t o prepare diagrams which properly represent the composition of any such solutions. A clearer idea of the uses of such diagrams can be gained from a study of Fig. V which represents the equilibrium conditions for the system here considered a t 2 5 ’ . The formulas which appear on the different areas represented on this diagram indicate the composition of all possible solutions which are saturated with respect t o the salts represented by these formulas. The lines separating these fields represent the composition of solutions saturated with respect t o the two salts of the adjacent field, and the points of intersection of these lines the composition of solutions saturated as t o the two or three salts of the adjacent fields. It should be noted t h a t each area represents the bounding surface of a solid figure, and that all points within the space enclosed by these surfaces represent unsaturated solutions. When such FIG.IV-THE SEPARATION OF SODIUM SULFATE FROM SODIUM CHLORIDE a solution is evaporated the change in its composition corresponds t o the movement of the point representing Glauber’s salt i n the presence of NazS04and NaC1. I t it in a straight line away from the origin. The point will be assumed t h a t a solution which consists of 20 g . a t which this line intersects the surface of the solid Na2S04, I O g. NaCl and IOO g. H 2 0 is t o be treated. figure indicates the salt with which the solution first The composition of this solution is represented by the becomes saturated and the composition of t h e solution point p . When evaporated a t 100’ pure NazS04 would a t t h a t point. If the process of evaporation be conseparate from q t o the crystallization end-point a t IS. tinued the salt continues t o separate, and the composiIf the separated sulfate is removed and the solution tion of the solution changes in a manner represented allowed t o cool t o 2 5 ’ , pure NaCl would separate until by movement of the point of intersection along a line, the solution attains the composition Y , or if allowed t o which is on the intersected surface, in a direction away cool t o o o , both NaCl and Glauber’s salt would separate from the point representing saturation with respect-to until i t attains the composition I1. If the former the salt concerned in water, t h a t is, in the absence of procedure is adopted the separated NaCl could be removed, the solution again evaporated a t IOO’, a further quantity of pure NazS04 recovered, and this cycle of changes repeated as in the separation of KC1 from NaC1, but it is obvious t h a t the amount of pure salt separated would be small, and in view of the cheapness of both salts not commercially feasible. Cooling t o o o would give a residual solution containing a relatively small proportion of NaZSO4 and would also eliminate a large amount of water as water of crystallization. The efficiency of these processes could be calculated quantitatively, but a n approximate idea can also be gained from a study of the diagram. sents grams of Na~S04,the vertical axis grams of ISaC1, per IOO g. of water. The lines DJ1, etc., represent solutions saturated with NaC1 in the presence of varying amounts of Na~S04,the lines 12Jz, LA3, 14A4 and LA5 solutions saturated with Na2SO4in the presence of NaC1, and LA1 and JzAz solutions saturated with
V-THE
SEPARATION
OF
MIXTURES CONTAINING
SALTS
OF
POTASSIUM
PROM
S U L F A T E S A N D CHLORIDES
O F SODIUM A N D POTASSIUM P R E L I M I N A R Y DISCUSSION-In applying the method already used t o the discussion of the more complex mixtures here considered it becomes necessary t o make use of diagrams in which concentrations are expressed in molecular equivalents, since the salts actually presert are in part ionized, and the manner in which the unionized basic elements and the acidic elements or groups are actually combined is both variable and difficult t o ascertain. Hence the composition of all such solu-
FIG. V-THE
SEPARATION OF COMPLEX
MIXTURES AT 25’
all other salts. These lines will not in general be straight lines, but in most cases the error involved in assuming them t o be straight will not be large. The points representing saturation with respect t o NazS04.~oHz0,KzS04, KzClz and NazClz are Az, Bz,CZ and Dz, and the series of lines radiating from these points represent the “crystallization paths” of solutions from which these salts separate during evaporation. The point representing saturation with Na2S04 is found by prolonging the line IzJZ until i t intersects OAt. ’ The assumption is made here t h a t if NaZSO4could exist
M a y , 1918
T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
at 2 j ” in equilibrium with water, and if its solubility were changed b y varying concentrations of NaCl beyond Jz a t the same rate as between IzJz,its solubility in pure water would correspond t o the point R. The point representing saturation with pure glaserite is found by drawing from 0 a line representing solutions containing K2S04and Na2SO4in the ratio of three to one (as in pure glaserite) and finding its intersection with the line EzFz. Here it is assumed t h a t if pure glaserite could exist in equilibrium with water a t 2 j ’, and if its solubility were t o be changed b y varying proportions of KzS04 and NaZS04 uniformly along the line EzF2,the composition of the solution with which it was in equilibrium would be represented by the point S. Having in this manner drawn crystallization paths on all six of the surfaces bounding the figure, i t isreadily possible t o predict the crystallization paths after the lines separating these surfaces have been reached. It is obvious t h a t solutions corresponding t o points on the NzMzline, which are t o the right of the line joining Dz and S must change t o correspond with the point Mz, whereas those t o the left of this line must change t o correspond with the point NZ when evaporated; t h a t is, there are two “crystallization end-points,’’ Mz and Nz. Aside from the fact t h a t the Glauber’s salt field is eliminated, the crystallization paths on the 100’ diagram (Fig. VI) differ from those of the 25’ diagram mainly in the fact t h a t there is only one “crystallization end-point,” namely Mg. This is a result of the fact t h a t both K5 and ME are t o the right of the line joining Dg and S. T H E S E P A R A T I O N O F P O T A S H F R O M T H E A S H O F KELP-
From a study of the analysis of the ash of a typical sample of Macrocystis p y r i f e r a , which is the species of kelp most largely used in California, made by P. L. Hibbard,l i t would appear t o be readily possible b y leaching with water a t 100’ t o prepare from such a n ash a solution containing 3 0 g. KC1, I O g. NaC1, and 6 g. Na2SO4 per I O O g. of HzO. The composition of this solution, expressed in mols of K2C12, NazClz and NaZS04 per 1000 mols of water, can be calculated as follows: 30 i149.12 = 10 +. 116.92 = 6 i142.06 = 100 +. 18 =
0.2012 0.0855 0.0422 5.555
36.20 mols KzClz 15.39 mols NazClz 7 . 6 0 mols NazSO4 1000. mols H20
=
The composition of this solution corresponds t o the point p , of Fig. V I , which represents the equilibrium diagram a t 100’. It is obvious t h a t , when evaporated, glaserite, then glaserite and potassium chloride, will separate until the composition of the solution corresponds t o the point M5. The total amount of HzO, glaserite and KzClz which separate during the evaporation can be calculated as follows: Let x = HzO, y = KiC12, z = glaserite separated. Then the following relations representing changes in the composition of the solution as t o K2, SO4, Clz and Naz are obvious. (1)
ti] (4)
36.20-9 7.60-25 51.59-y 22.99-0.5
5
1.52
: ~OOO-X
: 1000-
= 4 3 . 6 5 : 1000
x = 4.78 : 1000 : lOOO--% = 8 1 . 9 0 : 1000 : 1000 x 43.03 : 1000
-
When solved for x, y and z these equations give the following values in mols: HzO = 495.87, KzC12 = 10.30, glaserite = 2.59 1 University
of California Experiment Station, Bulletin 248, 142.
351
The residual solution could then be calculated t o have the composition in mols: 504.13 HzO, 22.01 KzC12, 2.41 NaZS04, 19.28 NazClz. It is also of some interest t o ascertain the amount of HzO which must be evaporated before any glaserite separates, the water which separates with the pure FkCI.
FIG.VI-THE
SEPARATION OF COMPLEXMIXTURES AT 100°
glaserite, and the water and KzC12 which separate along the line L5M5. These calculations are somewhat long but the methods can be outlined as follows: I-Calculate the ratio which the KzClz separating along the line L6M5 bears t o the HzO and t o the glaserite separating simultaneously, assuming the rate is a uniform one. 2-Calculate by means of these ratios the weights of HzO and glaserite which would separate after the KzCL begins to separate, from the total amount of KzClz separated, and add the amounts of HzO, KzC12, Na~S04and Na2C12 which they represent to the amounts of these salts present at MEto obtain the amounts present at the point r . 3 S u b t r a c t the glaserite lost between r and MS from that lost between q and MEt o find that lost between q and I and add the amounts of KzC12, Na2S04, and Na2Cl2,which it represents, to the amounts of these salts present at r to find the amounts present at q. 4-Determine the intersection of O p with the crystallization path passing through r t o get the coordinates of the point q and from them the amount of water present at q. 5-Subtract the sum of the amounts of water lost between q and r and between r and Mj from that lost between p and Mg to get that lost between p and q . The results of these calculations gave when expressed in mols: Loss between p and q = 182.0HzO Lossbetweenqand r = 151.16HzO 2.955 glaserite Loss between r and M5= 162.71 H z O 0.25 glaserite 10.3 K2ClZ. If the solution is now cooled t o 2 5 ” i t will become greatly supersaturated with respect t o KzClz as is shown by the position of Mg on the 25’ diagram (Fig. V). After the excess of KC1 has separated its composition will be represented by some point on t h e plane C2HzMzLzGz.The determination of the position of this point can be made by the following procedure: I-Calculate the total amount of KZClz, glaserite and HzO which must separate in passing from M6 t o Mz. z-Calculate the ratio which the amount of glaserite separating along the line LMz bears to the amount of K&la and of water separating simultaneously, assuming that the rates are uniform. calculate, by the use of these ratios, the weights of HzO
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and KzCIZ,which separate after the glaserite begins to separate a t the point t, from the total amount of glaserite separated and add the amounts found to the amounts of these substances present at Mz to get the composition of the solution at t. 4-Subtract the HzO and KzC12 lost between t and MI from the amounts lost between Mz and Ma and add to the amounts present at MZto find the amounts present at s. 5-Determine the point of intersection of the crystallization path tL with the horizontal line M6 s, and from the coordinates of this point determine the KzClz present at the point s. 6-Subtract the sum of the amounts of KzClz lost between t and M2 and between s and t from that between M6 and MZto find the amount lost between MSand s. The results of these calculations can be summarized as follows:
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Loss between Ms and s = I O . 28 KzClz ' = 1.25 KzCla f 2 I . 68 HzO 1 . 2 0 KzCla, 28.15 HzO f 0.19 glaserite
Loss between s and t
Loss between t and Mz
It is not probable t h a t these solutions could be evaporated a t a temperature of 25' economically and t h e only reason for calculating the changes which take place in evaporating the solution from s t o Nzwas t o ascertain the composition of the solution a t s, t h a t is, a t the point a t which all the KC1 which can be separated by cooling t o 25', has separated. The most rational procedure would be t o evaporate t h e solution of composition s a t 100' for the purpose of eliminating salts of sodium. By again referring t o Fig. V I it will become apparent t h a t when this evaporation is made glaserite and NaCl must separate, b u t it is not possible t o predict a priori which of the two will separate first. By using methods similar t o those already employed it can be shown t h a t the solution will first become saturated with NaCl at t h e point u , t h a t NaCl and HzO will separate along uv and t h a t HzO, NaCl and glaserite will separate along u M s . These changes can be summarized as follows:
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Loss between s and u = 75.53 Ha0 1,oss between u and D = 101.64 HzO 6 . 0 9 NazClz Loss between u and Ms 79.33 Hz0: 4 . 6 6 NazClz, 0 . 6 1 glaserite
This completes a cycle of changes similar t o that described in the separation of KC1 from NaC1, but one which is less efficient than the former since some potash is necessarily included with the sodium salts separated a t 100'. A comprehensive idea of the entire process as outlined may be gained by summarizing the changes during the three important stages in terms of t h e weights of seDarated salts expressed in grams. Composition of solution at outset 100 HzO, 30 KCl, 10 NaCl, 6 NazSOi Separated during evaporation to Ms 49.59 HaO, 8.53 KCl, 3.36 glaserite 8 . 5 1 KCl Separated during cooling to s Separated during evaporation to Ms 25.67 HaO, 6 . 9 8 NaCl. 0 . 7 9 glaserite Left in residual solution 24.74 H20,8.95 KCI, 6.13 NaC1, 0 . 9 4 NaaS04 T H E SEPARATION O F P O T A S H F R O M A DESERT BRINE-
A sample of brine from a hole near the center of Death Valley which was analyzed by A. R. Merzl will serve as an illustration for the application of the data of t h e preceding article t o this class of substances. The result of the analysis,.expressed in grams per IOO cc. of solution, was 3.06 KC1, 25.97 NaC1, 9.71 Na2S04 and 1.28 g. of undetermined salts. Although the specific gravity is not given, a solution of this composition should give a value not far from 1.24 and the composition of the solution in grams per IOO g. of HzO 1 THIS JOURNAI,,
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can be calculated to be 3.64 KC1, 30.92 NaCl and 1 1 . 5 6 NazS04. Calculated t o mols per 1000 mols of water these values become 4.40 KzClz, 47.60 NazC1z, 14.65 Na2SO4,1000 HzO. A solution of this composition would be represented by the point m on Fig. VI, and when evaporated at 100' sodium sulfate must separate first, then a mixture of sodium sulfate and sodium chloride, and finally glaserite and sodium chloride corresponding roughly t o movement from m t o rt, from f i t o N5, and from N5 t o Mi. The change from va t o Ng can be calculated t o involve the elimination of 814.2 mols of HzO, 39.45 of NazC12, and 12.45 of Na2SO4;the change from Ngt o M5 of 1 1 5 . j H20, 6.79 NaZC12 and 0.886 glaserite. This would leave 70.3 mols of HzO, 3 . 2 7 of NazC12, 3.08 of KzClz and 0.34 of Na2S04, which solutions could then be treated by the cyclic process already described in dealing with the ash of kelp. The chief objection t o this method of procedure is the large amount of evaporation needed; this might be decreased by utilizing solar evaporation t o some extent. If, for example, i t were permitted to evaporate a t 25' the solution would attain a composition corresponding t o Nz of Fig. V as t h e result of t h e elimination of 614 HzO,3 1 . 2 5 Na2C12, and 5.49 Na2SO4. Further evaporation a t this temperature would not change the composition of t h e solution and i t would be necessary t o continue t h e evaporation at a higher temperature (preferably a t 100') in order t o concentrate still further the potassium salts present. A third possible method would involve cooling the brine t o o o for the purpose of eliminating much of the NaZSO4and HzO as Glauber's salt before evaporation. The composition of the original solution on t h e o o diagram (Fig. 3 of the previous article) is represented by a point which shows t h a t i t is supersaturated at this temperature with Glauber's salt and sodium chloride. The composition of t h e solution after the excess of these salts has separated must be represented by a point on t h e line IsN3; it can be established by making use of the following considerations: I-The original solution contains 4.4 KZC12, but (as shown later) the solution loses 138 mols of water with the separated Glauber's salt, hence the &ClZ content at the desired point must be4.4 f (1000 - 138) = 5.1 per 1000 HzO. a-Since the KzCt changes from o to 13.18 between 18 and Na, the desired point must be (5.1 + 13.18) times the distance Is- Ns from Ia. This locates it a t q, which required the presence of 48.5 NazCl2 and 0.97 NaZS04. 3-The Glauber's salt which must separate in order t o cause NazS04 to change from 14.65: 1000 to 0.97: 1000 can be found by trial t o be 13.80. Similarly the NazClzwhich must separate in order to cause the NaZC12 t o change from 47 6 : 1000to 48.5 : 1000, in spite of the loss of 138 mols of water associated with the separated Glauber's salt, can be calculated to be 5.8. This leaves a solution containing 41.8 NaZC12, 4.4 K2C12, 0.85 NazS04 and 862 HzO which can be treated by methods similar t o those used for the ash of kelp. Of t h e three methods suggested for the treatment of t h e brine t h e second gives promise of being the most economical. The application of similar methods of treatment t o
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
May, 1918
the waters of Owens, Searles, Mono and other desert lakes presents a more complex problem, owing t o the fact t h a t these waters contain large percentages of carbonates. It is not improbable t h a t when the diagrams representing the equilibria, which must exist in solutions which contain carbonates as well as sulfates and chlorides of sodium and potassium, have been prepared it will be found possible t o suggest methods by which the salts present in such waters can be profitably separated into commercial products. It is also possible that it may be found commercially feasible t o precipitate most of the COS ion, either a s NaHC03 or C a C 0 3 , from certain of these waters and recover t h e potassium salts in the residual solution by the methods already described. UNIVERSITY O F CALIFORNIA BERKELEY
THE USE OF “MINE RUN” PHOSPHATES IN THE MANUFACTURE OF SOLUBLE PHOSPHORIC ACID B y War. H. WAGGAMAN AND C . R. WAGNER$ Received February 21, 1918
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The increasing price of acid phosphate makes it appear timely, if not absolutely essential, to look t o other methods of producing available phosphoric acid which will not only release t o the munitions industry part of the immense tonnage of sulfuric acid now manufactured a t the fertilizer plants, but will also enable the farmer t o continue t o obtain phosphates a t a cost which will justify their application t o the soil. The method which has received special attention in this Bureau is t h a t based on the smelting in a n electric furnace of a mixture of phosphate rock, sand and coke, whereby the phosphoric acid is volatilized and subsequently collected by means of the Cottrell precipitator. The equations showing this reaction may be represented thus: Ca3(POd)a 3SiO2 gC = g C a S i 0 ~ 2P gC0 2P 5 0 2 = P201 Ross, Carothers and Merz* showed t h a t t h e Cottrell precipitator gave acid of such a high degree of concentration t h a t t h e added cost of production b y the electric furnace method could be overcome in part a t least by the saving in freight charges over the lower grades of commercial phosphates. In order t o obtain more definite d a t a on the cost of producing phosphoric acid by volatilization a n d electrical precipitation this Bureau conducted some work in co6peration with the R. B. Davis Company, of Hoboken, N. J., over a period of several months. I n a recent report on this work Carother9 showed t h a t phosphoric acid (P205) could be produced by this method a t a cost of 3 . 3 7 cents per lb., exclusive of interest on investment, taxes and royalty. By using the phosphoric acid thus obtained, however, t o treat another batch of phosphate rock, double superphosphate is formed, a product containing three times as much phosphoric acid as ordinary acid phosphate,
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The writers wish t o express their thanks t o Prof. Milton Whitney, who suggested the work described in this paper. * THISJOURNAL,9 (1917), 26. a [ b i d . , 10 (19181, 35. 1
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and as Ross, Carothers and M e r d have pointed out, the making of double superphosphate brings down the price of phosphoric acid produced by the volatilization process very materially. I n order t o compare the economic merits of the furnace process with t h a t of the old established sulfuric acid method of making superphosphate, details of the cost of the two processes are given below in Tables I, I1 and 111. I n these estimates i t is assumed t h a t washed rock will contain an average of 34 per cent of phosphoric acid (P20j)and t h a t g o per cent of this is recoverable by the furnace method of treatment. It is also assumed t h a t the proportions of sand and coke necessary t o smelt the high-grade rock from the different localities is practically the same.2 The estimates on t h e cost of the furnace treatment are based on Carothers’ figures3 obtained a t Hoboken, N. J., but they are modified on the assumption t h a t the process is carried on a t the mines. Allowances, therefore, have been made only for the difference in the cost of phosphate rock, sand and coke. While the cost of labor and of power undoubtedly varies considerably in different parts of the country, a uniform charge has been made for these items throughout. I n the case of the labor and repairs necessary in the manufacture of ordinary superphosphate a charge has been made which is 50 per cent higher t h a n t h a t prevailing in the South Atlantic States prior t o the war. Since Carothers gives no estimates on the cost of installing the furnace process, no interest, charges, taxes and insurance are included in t h e cost d a t a for the acid phosphate process. A comparison of the d a t a given in Tables I and I11 show t h a t under the present abnormal conditions the phosphoric acid in double superphosphate produced b y using the acid volatilized in the electric furnace compares favoratly in cost with t h a t of ordinary acid phosphate. This is particularly true when we consider t h a t in shipping such a concentrated product as double acid phosphate the freight rates per ton of phosphoric acid (P206) are considerably reduced. Based on the conditions existing prior t o the war, this saving in freight charges should be more than counterbalanced a t the end of the war by a considerable drop in the price of ordinary acid phosphate, due t o the release of a n immense tonnage of sulfuric acid no longer’ needed for the manufacture of munitions. So in order t h a t the furnace method may permanently compete with the acid process of producing soluble phosphates, the cost of the former must be materially lowered. There is, however, another and a very important factor t o be considered in connection with the furnace method of producing phosphoric acid which makes this method worthy of more serious consideration. This factor is the immense saving t o be effected in low-grade phosphates and phosphatic material wasted 1 LOC.
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While this assumption is not strictly correct, due to the varying composition of the different types of rock, i t serves all practical purposes. a Carothers’ figures are based on a plant of 3000 kw. capacity producing 2347 tons P2O6 annually 2
