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8/11/2019 The Extraction of Potash and Other Constitutents From Sea Water Nittern
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9 6
T H E
J O U R N A L O F 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
I ORIGINAL PAPERS
THE EXTRACTION
OF
POTASH AND OTHER
CONSTITUENTS FROM SEA WATER
BITTERN
By
JOEL
H. HILDBBRAND
Received December 5 1917
COMPOSITION OF SEA WATER
The main constit uents of sea water, besides sodium
chloride, are magnesium sulfate, magnesium chloride
and potassium chloride, together with a small quantity
of magnesium bromide an d calcium salts. Dur ing
th e evaporation of the sea water t o secure sodium
chloride, the calcium present is almost completely
deposited as calcium sulfate,
so
that calcium salts are
practically absent from the mother liquor. By con-
sidering the various analyses of se a water we ma y calcu-
late the relative amounts of the solid salts that might
be obtained by evaporation. The salt works around
San Francisco Bay, with which we are primarily con-
cerned, produce something over
IOO,OOO
tons of sodium
chloride per annum; the amounts
of
the other salts
associated with thi s amoun t of so dium chloride would
be as follows:
TONS
Sodium chloride (NsCl) ......................... 100,000
Potassium chloride (RCl) ........................ 2,800
Magnesium chloride (MgClz.6HzO). ............... 27,300
Epsom
salts
(MgS04.7HzO).
.....................
16,000
Bromine (Br) extracted from the bromides.. ....... 240
A t
this time, when the country is suffering from an
acu te shorta ge of potassium salt s, th e am oun t of
potassium chloride indicated above is of considerable
importance. During the first half of
1917
the total
potash production of t he country, calculated on
the basis of
KzO,
was 14,000 ons, which amount was
but IO per cent of th e normal amo unt used before the
war. I t is evident th at the amount of potash that
could be extracted from th e bitterns of t he salt works
on San Francisco Bay alone would add about IO per
cent t o the countrys present annu al production of
potash. The amoun t of s alt actually produced in
this region is nearly 140 000 ons per annum, so t h a t
a liberal allowance for losses in working up the bittern
should leave still 3000 to ns of potassium chloride.
By utilizing the bitterns from other regions on the
Pacific Coast, notably San Diego, this amount would
be very greatly increased.
The other materials mentioned in the above table
also represent very considerable values, although they
have less relation to the present national emergency.
After th e removal of most of t he common salt in th e
salt ponds, the other salts would be contained in ap-
proximately IOO,OOO tons of b itte rn, having a volume
of approx ima tely
IOO,OOO
cubic yards.
The values represented by these materials, and their
imp ortance both as a nat ural resource of California
and in supplying the country with potash in t he present
acut e emergency, made th e stu dy of th is problem seem
a proper one to undertake at th is time.
of California.
1 This work has been supported by the Council of Defense of the Stat e
SCIENTIFIC BASIS OF METHODS FOR RECOVERY O F T
CONSTITUENTS OF BITTERN
We are ve ry for tuna te t o possess a vast fund
information upon the solubility relationships of t
various salts obtainable from sea water through t
classic work of van t Hoff and his co-workers. Th
work is described in great detail in ube r die Bildung
verh3ltnisse der ozeanischen Salzablagerungen (Le
zig Verlagsgesellschaft, I91 ). During the progr
of t he work two smaller volumes were published
1905
and
1909
by vant Hoff, entitled Zur Bildu
der ozeanischen Salzablagerungen (Braunschwe
View eg).
Inasmuch as very little of this work has been tran
lated into English, and in view
of
the difficulty
interpreting it in its formidable complexity, it see
desirable to give a general outline of it s nature .
Th e solubi lity of a single salt in its relation
changes in temp erature may be represented by simp
diagram s of the t ype fami liar to all trained chemis
4
s
In
I
0 20 4d 60
8 do
120 dG
/b
>rnperature deyrees
cen yrprode
F I G .
1
Fig. I are represented the solubility curves for t
ma in sa lt s with- which we have t o deal, v i z . sodi
chloride, potassium chloride, potassium sulfate, ma
nesium sulfate and magnesium chloride. I n this figu
solubility is expressed as the number
of
mols
of
a
hydrous salt per
1000
mols of water.
Of
cour
other u nits may be used, such as mols or grams of s
in a certain number of grams of wate r or of solu tio
or in a certain number
of
cubic centimeters in solutio
If we know th e solubil ity expressed in any of the
term s it is possible t o calculate
it
in any other term
the density
of
the solution being required where t
conversion is between a weight and volume bas
Th e laws of dilute solutions may fre quen tly be e
tended t o give a n approxi mate idea of th e behavior
con cent rated solutions. The solubility of a giv
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Feb.,
1918 T H E J O C R N A L O F I N D U S T R I A L A N D E N G IN E E RI N G C H E M I S T R Y 97
salt is varied by th e introd uction in to the solution of
anot her salt. The effect of the second salt can be
predicted qualitatively by remembering tha t where the
salt s possess a common ion the solubility of each is
usually decreased by the presence of t he o ther.
If,
however, there is a strong tendency t o form a complex
salt t 5e solubility of one may be increased by th e
presence of the other.
Again, where there is no com-
mon ion th e solubilit y of one is increased by the pres-
ence of the other owing to t he i nteract ion of
the two
salts.
Ther e are various ways of r epresenting graphically
th e solubility relationships of salt pairs. The method
adop ted by v ant Hoff is t o represent the a mou nt of
each sa lt in the solution in ter ms of mols of a nhyd rou s
salt per
1000
mols of wate r, mea sured along tw o axes
at right angles to each other, as illustrated in Fig.
11.
Each curve here represents the composition of
a
solu-
tion satur ated with one component. The intersec-
tion s of th e cur ves represent t he composition of
a
solu-
tion saturated with both components.
A
point be-
tween these curves an d th e origin denotes the composi-
tio n of a n unsa tur ated sol ution. A point outside of
the cur ves would represent a mixture of a sat ura ted
A 7 2 .
,
\c
23
50 7s /OO
MO/Sa c /
p e r
/OOO mo/s HZ0
FIG.
I1
solution with one or both solid salts, depending upon
its position.
O n evapora tion of a n unsa tur ated solu-
tion the relative amounts of the two salts would re-
main the same until the solution becomes saturated,
so
that, for example, a solution having t he composition
represented b y the point
a
in Fig.
I1
would, on evapora-
tion, change in composition as represented b y th e mo-
tion along the line ab. As soon as the curve A B is
reached, representing in t his case th e composition of
a solution sat urat ed with potassium chloride, solid
potassium chloride will separate and the solution must
bec0m.e relatively richer in sodium chloride,
so
tha t a s
the evaporation proceeds from
b
the solution will
change in composition along the solubility curve to-
wards
B.
Similarly, an unsaturated solution having
the composition represented by c would, on evapora-
tion, change in composition as represented by move-
ment along the line
cd .
At
d
sodium chloride would
begin to crystallize, whereupon the solution would
become richer in potassium chloride, its composition
changing along the line
dB.
It is evident that the
final result in th e eva porati on of an y solution of thes e
two salts would be a saturated solution having the
composition represented by
B
changing into a mixture
of t he t wo solid salts.
The effect of tem pera tur e may be indicated on a
third axis at right angles to the others, giving
a
solid
figure, as represented in perspective in Fig. 111.
Where a double salt may be formed, the solubility
relationships at a given temperature would be repre-
sented by a diagram such as that in Fig. IV. This
diagram represents the solubility at 30 of m ixtures of
sodium sulfate decahydr ate, a nd magnesium sulfate
heptahydrate, which form the double salt, astra-
kan ite , NazMg(S04)2.4HzO. Th e middle por tio n of
the curve seen in this figure represents the composition
of solutions sat ura ted with astr akan ite. Solid astr a-
kanite, which contains equivalent quantities of the
two salts, has a composition lying upon a line bisecting
th e angle between th e tw o axes. The composition
of
the solid salt is represented by a point on this line a t
E
expressing th e numbe r of mols per
1000
mols
of
water in the solid salt . The composition of solid
sodium sulfate, N a2S04. 10Hz0, which lies along t he
line O A is at a distance from th e origin corresponding
to its water content at
F .
Similarly, solid magnesium
sulfate has the composition
represented by the point
FIG.I11
G. When an unsaturated solution containing these
salts is evaporated, its composition will, as in the
previous case, move along a line away from the origin
unti l one of t he curves representing the compositi on
of t he sa turat ed solution
is
reached, when the solution
will change in composition along this line in the direc-
tion aw ay fro m the line representing the composition
of the solid which is separating. Th us a solution having
the composition represented by
a
would, on evapora-
tion, change in composition along the line
ab
when,
on furth er evaporation, sodium sulfate would separate,
and finally, at B both sodium sulfate and the double
salt would separate, the solution remaining consta nt
in composition until it had all disappeared. Similarly
an unsat urat ed solution of composition represented b y
G would change in composition in the direction
c d B
the solids separating being first pure astrakanite and
the n a mixture of astr akan ite and sodium sulfate.
The point B represents, therefore, the end-point of
Crystallization for soluti ons which contain more sodium
sulfate tha n magnesium sulfate.
Fig. V represe nts the sol ubili ty of mixtures of
magnesium chloride an d potassium chloride, from which
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98
T H E J O U R N A L
O F
I N D U S T R I A L A N D E N G I NE E R IN G C H E M I S T R Y
Vol.
I O , N
MO/S YgS
0 per
OOO mo/s H 0
FIG. V
it is possible to crystallize the double salt carnallite,
KMgCls.6H20. Unlike the previous instance, how-
ever, the line
OE
somewhere upon which lies the point
representing the composition of solid carnallite, does
not intersect the curve
BC
which expresses the compo-
sition of solutions sat ura ted with carnallite. This
fact makes the pa th of crystallization, during th e
evaporation
of
solutions of th ese two salts , somewhat
different from that considered above. A solution
having the composition represented by
a
will, on
evaporation, change in composition till
b
has been
reached, whereupon potassiu m chloride begins to
crystallize out, and the solution, becoming richer in
magnesium chloride, will move along bC. When the
solution has reached the composition represented by
C,
carnallite will begin t o sepa rate, bu t since carnallite
contains more potassium chloride than does the sat-
urated solution at C, it is evident that while carnallite
crystallizes, the solution will tend to move along the
line CB instead of remaining at C. The phase rule,
however, requires that while both potassium chloride
and carnallite are present, the solution must remain
constant in composition at C. Therefore, inste ad
of
the liquid phase disappearing a t this point, as was th e
case in th e former salt pair, i t is one of th e solid phases,
potass ium chloride, which will now disa ppear, being
changed over into carnallite.
It
is no t unti l all of th e
potassium chloride has been
so
changed that the solu-
tion can move from C t o B . B will thus represent an
end-point of crystallization, while C will not. It is
evident, therefore, t ha t in o rder t o prepare crystals of
carnallite it is necessary t o use a solution containing
more th an th e equivalent amo unt of magnesium chlo-
ride, the relative amounts of the two salts being such
that, on evaporation, the line BC will be intersected
slightly above
C.
Similar co nsiderations show
US
t ha t
on tre ating solid carnallite with water, instea d of dis-
solving as such, it would tend to change into solid
potassium chloride and a solution whose composition
is th at represented by C .
It
is obvious, therefore, that
I
/67
/
/
I
f l o h Nper
1000
mo/s
H2
fiG. v
it is not difficult to obtain potassium chloride fr
carnallite, a point
of
importance in the treatment
salt bitterns, as will be discussed later. After
remova l of t he potas sium chloride the solution can
evaporated, carnallite separating, while the compo
tion of th e solution changes frofn C t o
B.
This c
nallite can be treated with water, leaving solid pot
sium chloride, etc.
Solutions containing magnesium and potassi
chlorides and sulfates are in equilibrium with so
phases
at 2 5 O
according to the da ta in Table
I
and
TABLE
System, KCl-MgClaKnSOrMgSO4, a t
25
COMPOSITION
OF
SOLUTI
SOLID HASES
Mols of constituents
per 1000 mols HzO
RzCln MgClz
MgSO4
Kz
A
KCI
.................................
. . . . .
B MgCh.6Hz0
............................ 108
..
C M g S 0 ~ 7 H z 0
............................. 55
D
E
F
H
I a)
K
L
M
N
P
Q
R
..
5 5 ii:5
1 105
104
73
. . . . .
. . . .
42
..
25 21
9
55
8
62
4 5
70
2
99
..
..
..
14
15
58 5
22
..
11
16
15
13.5
12
(a)
The composition
of
the solution a t th is point is given by diff
figures in vant Hoffs earlier and late r books, The lat ter are dou b
incorrect,
as
the former agree with those
of
H.
S.
van Klooster,
J .
P
Chem.,
21
(1917), 513.
represented b y van t Hoff along four axes, as in F
V I , each pair of axes representing solutions contain
a common ion. The boundary lines correspond
solutions saturated with the two constituents rep
sented by the enclosing axes. Where salt pairs c
taining no common ion are present it is impossible
represent th e composition by a p oint in th e plan e
this figure.
A
mixture of equ iva lent quan titie s
potassium sulfate and magnesium chloride would e
dently lie a t t he origin 0 and would be indistingu
able from pure water by its position in th e plane.
order to make this distinction it is necessary t o in
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IO0
T H E J O U R N A L O F 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, N
of water remo ved by
s.
We may then represent what
has become of th e original solution during eva poratio n
b y means of the following equa tion :
IOOOHZO
8MgSO4 + IoMgClz + ZKzClz = ~ ( I O O O H ~ O
16MgS04
+
55MgC12
+
9KzClz) + ~o&Mg(S04)~.6HzO)
~(MgS04.7HzO)
+
SHZO
By equat ing coefficients of the various substan ces
present, i t is possible to set u p the following equatio ns:
Coefficients of H10: 1000 = xooop + 6p
+
7 r +
s
Coefficients
of
Mg:
IS =
71p +
p
+ r
Coefficients of Clz: 12 = 6 4 p
Coefficients
of
Kz z =
99
+ s
The solution of these equations gives the following
values
:
p = 0.188;
q =
0.31; Y = 4.38; s
=
779
These values of
q Y
and s represent the amounts
of the respective substances which have sepa rate d
by evaporating the original solution and p represents
the amount of solution left.
If, instead of tak ing the
TABLE 2
System, NaCl-KCl-MgClrMgSO4-NazSO4, t 25'
MOLS
PER
1000 MOLSHzO
NazCls KzCh MgClz-MgSO4 NazSOc
aturation with NaCl an d
A
B
C
D
E
F
G
H
I
L
M
N
P
Q
R
S
T
U
V
W
X
Y
z
MgClz.6HnO. ....................
KC1. ...........................
NazSOd
.........................
MgClz 6HzO Ca rna llite ..
.........
KCI.
darnaliite..
................
KC1: Glaserite..
NazSOc Glaserite..
. .
.........
NazSO4' Astrakani te ..............
MgSOa.'7HaO Astrakanite..
.......
MgS04.7HeO: MgS0~6Hz0.......
MgS04.6Hz0, Kieserite. ..........
Kieserite, MgClz.6HzO. . . . . . . . . . . .
KC1, Glaserite, Schiinite. . . . . . . . . .
KCl, Schonite, Leonite. . . . . . . . . . .
KC1, Leonite, Kainite. ...........
KCl, Kainite, Carnallite.. ........
Carnallite, Kaipite, Kieserite. .....
NaB04. Glaserite. Astrakanite..
...
Glaserite Astrakanite Schonite.
Leonite hstrakanite bchonite..
...
Leon ite' Astrakanit: MgSOc 7Hz0
Leonite' Kainite MgbOd 7Hzb..
...
MgSOd5HzO Kdinite MgSO4 7Hz0
MgS04.6HzO' Kainit; Ries erke.. .
Carnallite, MgCh.BH;O, Kieserit e.
No.
FIELD FORMUGA
1 ALZD
2. BFMNPQE
3 CGSH
4 DZRQE
5 FMTSG
6 SHIVUT
7 VIJXW
8 JXYK
9 KYRZL
10 TUNM
11 NUVWP
12 PWXYRQ
55.5
...
5 1
2
5.5
44 20
44 10.5
46 ...
26 ...
2.5
44.5 15:;
1
:i
4 . . .
2.5 . . .
1 ...
23 14
19.5 14.5
9.5 9.5
2.5 6
0 . 5 1
26 8
27.5 10.5
22 10.5
10.5 7.5
9
7.5
3.5 4
1.5 2
0 0.5
. . .
103
...
ii1i:5
70.5
...
. . .
...
7
67.5
79
102
21.5
25.5
47
68
85.5
16
16.5
23
42
45
65.5
77
100 ,
. . .
. . .
. . .
...
. . .
...
...
1 i : i
34
12
9.5
5
14
14.5
14.5
5
8
1i :5
19
19
19.5
13
10
5
...
12.5
...
:5
14.5
3
...
...
. . .
...
...
...
...
22
...
...
...
...
;.4Ha0
MINERALOGICAL
DESIGNATION
Bischofite
Sylvite
Thenardite
Carnallite
Glaserite
Astrakanite
Epsom salts
Not found
Kieserite
Schonite
Leonite
1
Kainite
am oun t of t he original solution represented 5 y IOOO
mols of water, a different am oun t is take n, propor-
tionate am ounts of th e solids and water are obtained
from the solution on evaporation to the same point.
When we come t o consider the ev aporati on of sea water,
we have in addition to the above components large
amounts of sodium salts. Since during evaporat ion
sodium chloride is always present, it is possible to
represent saturated solutions such as are obtained on
evaporating sea water by solid models similar t o t he
one considered above. By introdu cing sodium chlo-
ride as anothe r comp onent no new degrees of fre edom
are introduced, provided it is stipulated that solid
sodium chloride shall always be present. Van't Hoff
and his co-workers have determined the solubility
relationships at z 5 O and 83 . Fig. VI11 represents th e
results for 2 5
O
contained in Table z ; results for
are found in Table 3 and Fig. IX . The amoun
sodium chloride present is not consi,dered in the p
jection? but is counted in th e to tal number of dissol
mols which would be represented in a solid mod
Sodium sulfate may be expressed in term s of t he o t
salts present, since NazS04
=
Na2Clz
+
MgSOa
MgC12, or, = NazClz
+
KzS04- KzC12. T hu s po
C, Table 2 is represented in Fig. VI11 by coun
I Z / ~ divisions to the left of the origin and 12l / Z
visions along th e axis. Its position in a sp
model would be 63l/2 divisions vertic ally above
point so obtained.
Such a model may be construc
in a way similar to t ha t previously described.
Th e composition of se a water which has been ev
orated until it is saturated with sodium chloride i
follows, expressed in mols of each constituent:
TABLE3
Syst em, NaCl-KC1-MgClrMgSOcNazSO4, a t 83O
MOLS ER
1000 MOLSHzO
Sat ura tion with NaCl and NazClr KsCla MgClz MgSO4 Na
0
A MgClz.6Hz0
....................
B
KC1
...........................
C NarSO4 ........................
D MgClz.6Hz0, Carnallite. . . . . . . . . .
E
KCl Carnallite
. . . . . . . . . . . . . . . . .
F
KCl: Glaserite.. . . . . . . . . . . . . . . . .
G NazSOa, Glaserite
. . . . . . . . . . . . . . .
H NanSO4, Vanthoff ite
. . . . . . . . . . . .
I Vanthoffite Loeweite
K Loeweite Kieserite . . . . . . . . . . . . . .
L Kieserite: MgCla.6HzO., .........
P KCl Glaserite Langbeinite..
....
Q KCl: Carnallit;, Kieserite. ....... 2
R KCl Langbeinite Kieserite.. . . . . 11
S Glaieerite, NaaSOs: Vanthoffite..
.
43
V Loeweite, Glaserite Vanthoffite.. 34. 5
W
Loeweite, Glaserite,'Langbeinite.
,
30
Y Loeweite, Kieserite, Lang beinitq ., 16
Z Carnallite , MgCla.6Hz0, Kieserite
59
1
39
56.5
1
1.5
39.5
43.5
51
35
12.5
1
29.5
1
37
. .
2
10
39
21
..
..
3;:s
12
15
22.5
26.5
24.5
10.5
2
. . .
121
...
117
92
. . .
. . .
4.5
22
61.5
120
13
86.5
76
. . .
8.5
12
42
116
. . .
. . .
. .
8
. .
..
4
11
1615 .
12.5
5.5 .
1 .
10 .
5
.
5
17.5
.
16.5
14
.
7.5 5
1
MINERALOGICA
DESIGNATIONo. FIELD FoRmuLA
ALZD
BFPRQE
CGSH
DZQE
FPWVSG
NSVI
XVWYK
RYRQZL
WPRY
Bishcofite
Sylvite
Thenarditearnallite
Glaserite
Vanthoffite
Loeweite
Langbeiniteieserite
1oooHz0, 47NazC12, 1.03KZCl2, 7.36MgC12, 3.57MgS
By the use of a solid model i t is possible t o deter m
th at this solution, on further evaporation, would int
sect the surface at the point
a
where Epsom s
would begin to separate. Th e composition of
solution at this point
is
approximately 1000H
I INazC12, 6K2Cl2, zoM gS0 4, 41 M g CL Fur th er ev
oration would lead to the boundary between t
field and the kainit e field W X after which these t
salts would separate together.
It
is possible t o cal
late as before the am ount s of each substance remov
from the solution when the latter has the composit
indicated, say, by X . Suppose that
10 000
g. of
original solution are used. Th e number of grams cor
sponding to th e n umber of mols of each substance
the original solution is 24,790, so t h a t 1 0 0 0 0 g. of so
tion would contain, instea d of th e previous num ber
mols of ea ch const itu ent , only 0.404 of these qu an
ties, namely , 404Hz0, IgNa2 Cl2, 0.4zK2Cl2, 3Mg
and 1.44MgS04. On evapora tion this solution wo
yield mols of th e solution satu rate d a t X ontain
its constituents in the proportions indicated in Table
together with qMgS04.7Hz0 + rNazClp + sKC
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MgS01.3H20 + tH2O. We can, therefore, write the
following equation:
404Hz0
+
rgNazClz
+
0.42KaClz 4 3MgClz + I . LFM~SO~
p(1oooH~0+ 3.5 Na ~Cl ~. 4K~C12
+
65.5MgC12
+
13MgS04)
+ pMgSOa.7Hz0
+
rNazClz+ sKCl.MgS04.3HzO + tHz0
By equating corresponding coefficients and solving
th e resulting equation s, we o btain t he following values:
p =
0.0458;
q =
0.37;
r =
18.9;
s
= 0.47; t
=
354
tions it will be possible to determine what will take
place.
I t is evident from the position of point
a
in the
diagram for
2 5 O
t ha t only a small amount of Epso m
salts will have been crystallized by evaporation
of
the
mother liquor from sea water before kainite will begin
to separate.
I t
is true that kainite shows
a
great
tendency to supersaturation, and unless suitable nuclei
ISGHOFITE
L
Feb.,
1918
T H E J O U R N A L O F 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 101
and by the aid of geometric and algebraic considera- separation of th e potassium salts from the magnesium
Keso
FIG.
VI11
Hence we conclude that 354 mols of water have been
evap orated, and 0.37 mol of Epso m salt s, 18.9 mols
of NazClz an d 0.47 mol of kainite are in the solid
portion. Similar calculations may be made to de-
term ine what will happ en during all sor ts of changes.
For example, instead of removing water, a cert ain salt
may bt: added to a solution saturated with other salts,
F I G .
I x
are present this field might not be present, which will
allow th e evaporati on and separati on of Epsom salt s
to continue somewhat further until the potassium
chloride field is reached. The condit ions obta inin g
in solar evapo ration are, however, very favorable to
the crystallization
of
such
a
subst ance because of t he
presence of many impuritie s. I n order to get a good
8/11/2019 The Extraction of Potash and Other Constitutents From Sea Water Nittern
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I 0 2 T H E J O U R NA L O F I N D U S T R I A L
salts in the bitter n of sea water it is not desirable to
carry on the evaporation so as to separate more than
a small amou nt of Epso m salts a t 2.5 . O n comparing
Figs. VI11 and I X it will be seen tha t a t the higher
temperatures it is possible to continue the evaporation
much farthe r before a ny salt containing potassium will
crystallize from the hot solution.
A t
this tempera-
tu re and in the presence of th e magnesium chloride
which exerts a dehydrat ing effect, inst ead of E pso m
salts cryst allizing, kieserite, MgS04.HZ0, is obtain ed.
The fact th at t he solubility of magnesium sulfate tends
to decrease at higher temperatures, while the solu-
bilities of po tassium chloride and magnesium chlor ide,
and hence, carnallite, increase, causes the kieserite
field at 83' to become large at the expense of t he
fields of potassiu m chloride a nd carnallite.
I t
is evi-
den t, therefore, th at most of t he sulfate present in the
solution could be removed as kieserite by evaporating
the bittern at higher temperatures until the carnallite
boundary is approached. During this evaporation,
the solids which separate would be sodium chloride and
kieserite. By removing these from the hot solution
they could be obtained relatively uncontaminated
with potassium.
If,
now, the m other liquor from these
crystals is cooled, the growth of th e carnallite field
as lower temperatures are reached indicates that this
salt would separate as the solution cools, while the
mother liquor from th e carnallite would consist largely
of a solu tion of magnesium chloride. These considera-
tions seem to indicate th e possibility of a satisfa ctory
process for the sep aration of th e bitter n int o three main
constituents: magnesium sulfate, carnallite, and a
solution of magnesium chloride. The re would remain
the necessity, first, of separating magnesium sulfate
from the sodium chloride accompanying it, second,
of treati ng th e carnallite for the recovery of potassium
chloride, according to the principles discussed earlier,
and , third , th e evaporatio n and cooling of the magne-
A N D E N G I N E ER I N G C H E M I S T R Y
Vol.
IO, N
increase is caused by encountering the boundary
the carnallite field shown in Fig. IX , and th e sub
quent separation
of
carnallite.
The crystals which
deposited from the solution after this point is reac
contain a considerable am oun t of potassium in
for m of carnalli te. A calcula tion of t he amo unt
water which should be removed in order to reach
carnallite boundary a t
83 O
gave a figure correspond
very closely with that indicated by the above cur
The original mother liquor at
2 o
s saturated b
with sodium chloride and magnesium sulfate, but si
the solubility of sod ium chloride does not mate ria
change with the temperat ure, whereas th at of mag
sium sulfate does increase during th e first par t of
evaporation, the solution is satura ted with sodi
chloride but not with magnesium sulfate, hence
first crystals t o separa te consist largely of so di
chloride, which was found to be the case with the
bo th of th e microscope an d of a chemical analy
It
is possible, therefore, t o remove a n additiona l amo
of sodium chloride from th e magnesium sulf ate
filtering the hot solution by the aid of the centrif
during th e early stages of the evapo ration. T
procedure simplifies the fu rther purifica tion of
*IJ6
/L 1.3.
I I
I
I
11
IO
2 0
so
IO SO
FIQ.X-WATER EVAPORATED
N
PER
CENT
OF
BITTERN
AKE
0
jza
sium chloride liquor to obtain MgCl2.6H20.
, magnesium sulfate which separates as evaporat
Table 4 gives the results of th e analy sis
roceeds.
E V A P O R A T I O N E X P E R I M E N T S
The process outlined above, on the basis of t he equ i-
librium diagrams, was first tested on a laboratory
scale by evaporatin g weighed qua ntiti es of bi ttern .
I n one set of experiments the evapo ration was carried
on at the boiling point of the solution . Crops of crys-
tals were removed from the solution from time to time
by centrifuging the liquid through a muslin bag. The
density of th e solution was read b y the aid of a hydrom-
ete r made of pyrex glass, th e smal l coefficient of ex-
pansion of which made its readings nearly co rrect in
spite of changes of temp erature.
Th e. boiling point
was read with a thermometer graduated to one-tenth
of a degree.
The a moun t of water, when each reading
of densi ty and boiling point was made, was determined
by weighing the vessel containing th e hot solution.
It will be seen from the results, plotted in Fig. X,
that the density and boiling point rise gradually until
water has been removed amounting to about 36 per
cen t of the weight of the original bit tern. The dens ity
and boiling point from here on increase more rapidly
with the furthe r removal of water. This more rapid
;he crystals remo vedf rom t he solution by th e aid of
centrifuge at the stages of evapora tion indicated
Fig.
X.
TABLE
Crop from
cooled
mother Crop
liquor from
fina
Crop 1 Crop 2 Crop 3 Crop
4
from 4 evaporatio
MgSO4.... 15.1 24.6 20.1 24.1 1.3 3.5
MgCla.. , . . 12.0 12.3 21.8 16.9 39.2 38.2
KC1. . . .
.
4.8
NaCl
...
. 20.3 20.3 13.3 17.0 1.3
HzO
. . . . . .
52.8 36.4
40 5
24.9 54.7 5 7 : 5
6.3
4.4
17.1 3.6
1 1
The centrifuge employed was not very efficie
and some cooling took place during the process,
that the respective crops are contaminated with
salts that should remain in the mother liquor.
is eviden t from t he results of this analysis, togeth
with th e course of the density a nd boiling-point curv
that the process contemplated furnishes the desir
separation. I n a second experiment, based upon t
results of t he first, the solution was evaporated un
the density ha d reached a value of 1.35 at the boili
poin t of th e solution,
121 .
The crystals separati
up to this point were removed and the mother liqu
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Feb.,
1918
T E E J O UR N AL O F I N D U S T R I A L
allowed to cool. Th e crystals separating on cooling
should be carnallite, and it will be seen from the anal-
ysis of these cry stal s in Tab le 5 that their composition
approx imates closely t o th at of carnallite. The mother
liquor from th e carnallit e consists principally of a
solution of magnesium ch loride, as is confirmed by its
analysis. The potassium content of the first two frac-
tions may be attrib uted t o the cooling in the centrifuge
inevitable
3n
working on such a small scale.
A s
is to
be expected, the proportion of Mg S04 .H2 0 to NaC1
is greater in the second crop of crystals th an in th e first.
TABLECOMPOSTTIO TI ON OF
MATERIAL BTAINED T VARIOUS
STAGES
N
PER CENT
Removed :t Removed Theoretical Final
b. p. 121 , from for mother
B. p. 116'
d.
1.35 cooled liquor carnallite liquor
K . . . . . . . . . . .
3 . 1
5 . 7
10.0 14 .1 0 .4
C1. . . . . . . . . . . 3.5 19 .1 36 .6 38 .4 23 .4
SO4
. . . . . . . . . .
16.9
32.2 trace 0 . 0 2 . 7
Mg . . . . . . . . . .
3 . 9 9 . 2
7 .6
8 . 7 7 . 9
The curve given in Fig. XI was obtained by an
evaporation in which no crystals were removed, thus
avoiding the inevitable losses occurring through at-
tempts to remove crystals from the hot solution.
The break in the boiling-point curve in Fig. XI is at
a higher temperature than th at in Fig. X. This is
doub tless due to the use of different samp les of bi tte rn
in the two experiments, so that the carnallite field is
encountered a t different points in the two cases. I t
may be noticed that the break is more pronounced in
th e case where it occurs at the lower tempe ratur e which
is jus t what would be expected on th e basis of t he solu-
bility diagram in Fig. IX . Th e composition of the two
samples of bitte rn used in th e above experiments is
given in Table 6. The sodium content is not given.
TABLG
Bittern used in gettin curves
in Fig. X in Jig. XI
K
.......................
1.48 1.76
C1
.......................
15.82 18.22
so4 ...................... 5.81 3 .88
Mg ...................... 5 . 3 8 6 . 3 2
TABLG
Bittern used in gettin curves
in Fig.
X
in Jig. XI
K
.......................
1.48 1.76
C1
.......................
15.82 18.22
so4 ...................... 5.81 3 .88
Mg ...................... 5 . 3 8 6 . 3 2
O U T L I N E
O F P R O P O S E D P R O C E S S
I . E V A P O R A T I O N O F THE
BITTERN-The .bitterns
from various sources will vary somewhat depending
on th e temperature of the liquid in the last salt pond,
and whether or not any Epsom salts are allowed to
separate. There is, in fact, no reason apparent why
a crop of Epsom sa lts should not be rem oved b y cooling,
either artificially or by storage till winter, before the
subseq uent process of se paration is applied. Th e
process of solar evaporatio n should n ot, ho wever, be
carried far enough to cause any potassium salts to
crystallize, as it is probably not desirable to separate
the potassium content into two portions. Th e varia-
tions in th e composition of th e bitte rn caused by an y
of
the above factors would not cause any serious diffi-
culty, as during the later evaporation the separation
of NaCl and MgS04.H20,kieserite, would take place
in such proportion as to make the resulting liquid
converge towards a fairly uniform composition.
I t
is more important, under present conditions, to
recover all
of
the potassium salts, and hence to pre-
vent their contaminating the NaCl and kieserite frac-
tion, th an i t is to recover all of the Epsom salts, or
t o
A N D E N G I N E ER I N G C H E M I S T R Y I 0 3
obtain pure magnesium chloride from the final liquor.
Such contamina tion would result, if t he evap oration
were continued as far as the carnallite boundar y,
for some cooling during the separatio n of th e kieserite
from the mother liquor is inevitable, and if t he solu-
tion is saturated with carnallite before this separation
begins, some of it will crystallize along with the kieser-
ite. On th e other han d, if the evapo ration is not con-
tinu ed so far, a little of t he su lfate will remain in th e
solution, and will probably pass thro ugh t he succeeding
operations and come down with the magnesium chlo-
ride at the final stage of the process. Since very pur e
magnesium chloride will probably not be desired, the
presence of th is sulfate can do no har m.
Inste ad, therefore, of c ontinuin g the ev aporation
as far as the break in th e boiling-point curves, as in
Figs. X and XI , it will doubtless be better t o evapora te
till the boiling point is about 120 C. This will re-
sult in the recovery of p ractical ly all of th e carnallit e
and still allow leeway for variations in the bitterns
used.
FIG.
XI-WATER EVAPORATEDN PER CENT
OF
BITTERN TAKEN
Th e best typ e of evapora tor for this operation will
doubt less be of t he film type, where a given par t of
the liquid is not boiling for a very long time. Ther e
is a tendency for magnesium chloride to hydrolyze,
giving magnesium hydroxide and hydrochloric acid,
which escapes with the steam. If the liquid is evap -
orat ed in a ke ttle it is boiling for such a len gth of t ime
th at a considerable a mou nt of magnesium hydroxide
is formed. If, on the o ther ha nd, the liquid is allowed
to flow over a heated surface, the evaporation takin g
place ve ry quickly, there is little time for this hydrolysis
to take place. This liquid may then be kept in a
settling ta nk without f urth er loss of hydrochloric
acid, even near the boiling temperature, provided
actu al boiling does no t ta ke place.
I n principle, the n, the process indicated is a s follows:
Evaporate until the boiling point
of
the liquid
is
raised to about 120 C. and the density is approxi-
mately
1.35.
The liquid running off from the evap-
orator should be caught in a steam-jacketed tank
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104
T H E
J O U R N A L
O F
I N D U S T R I A L A N D E N G I N E E R I N G
CHEMISTRY
Vol. IO, N
where i t is allowed t o se ttle. The clear liquor is al-
lowed to run
off
to a cooling tank, in which the car-
nallite will sepa rate . Th e sludge of NaCl and kieserite
is
run in to centrifuges, previously heated, where i t is
separated from the adhering mother liquor, which is
run into th e cooling tank mentioned above. The
separatio n of th e Na Cl from the material remaining
in the centrifuges and th e recovery of Epsom salt s will
be discussed later.
containing the carnallite may be cooled by the fresh
bittern going t o the evaporator, in order to utilize t he
heat conte nt of the latter . After it has been thor-
oughly cooled, the carnallite which has separated is
removed and freed from
its
mother liquor by centri-
fuging. Th e recovery of the potassium chloride from
this carnallite will be discussed later.
CHLORIDE-The mothe r liquor from th e carnall ite con-
tains a very little potassiu m, a little sulfate, a consider-
able amo unt of colloidal organic matte r, the brom ine
cont ent of th e sea water, an d a large amou nt of mag-
nesium chloride. Th e liquid must be evapor ated fur-
ther in order to recover MgC12.6Hz0. During this
evaporation, however, the temperature rises con-
siderably , unless vac uum evapo ration is employed,
charring the organic matter, and strongly darkening
the magnesium chloride which separates
on
cooling.
To destroy this organic matter, therefore, as well as
to recover the bromine, preliminary treatment with
chlorine is desirable. Th e details of this tre atm ent
are now the sub ject of investigation in this labora-
tory. We can only say at the present time th at there
seems to be good prospec t of success.
Th e disposal of th e large quanti ties of m agnes ium
chloride that would be obtained from these bitterns
presents a n economic problem. The possible outlets
seem to be as follows: magnesium oxychloride c ement,
magnesium oxide and hydrochloric acid, and metallic
magnesium. Th e use of magnesium oxychloride ce-
ments might be greatly increased by skilful advertising,
hydrochloric acid might be substituted for sulfuric
acid, for certain purposes, and t here seems to bq good
reason t o anticipat e a large production of magnesium
in the future.
2 .
TH E
R E C O V E R Y O F
THE
CARNALLITE-The l iquor
3 . THE
RECOVERY
O F B R O M I N E A N D MAGNESIUM
4.
THE SEPARATION O F SODIUM CHLORIDE AND
SULFATE-The separation O f the sodium
AGNESIUM
chloride an d the kieserite obtained in the first pa rt of
th e process is complicated b y the possibility of fo rming
astrakanit e, Na2Mg (S04). 4H20, at ordinary t em-
pera tures an d of loeweite, Na4Mg,(S04)4.sH2O1 or
vanthoffite, N S ~ ~ M ~ ( S O ~ ) ~ ,t higher temperatures.
In order to put the separation of the magnesium from
the sodium salts on an exact basis
it
is desirable to
have a knowledge of th e solubility rela tionships of th e
chlorides and sulfates of these two metals. I t has
been found possible, by using data given by vant
Hoff, Seidelll a nd Roozeboom,2 to construct th e equi-
librium diagram for all but two points which are un-
1Am Chem.
J .
27
1902), 52 ; see
also
Schreinemakers and Baat, 2.
2. hysik . Chem. 2 1888). 518.
phys ik . Chem.
67
1909), 5 3 3 .
important for the present purpose. The dat a
are given in Table
7
and are represented graphic
in Fig. XII , giving a diagram similar to that in
V I , where potassium chloride is considered instead
sodium chloride. Th e two undeter mined points h
been add ed more or less at rand om, for the sak
completing the fields, and are denoted by in terroga
marks on th e figure.
Now the material obtained from the first stage
our process contains MgS04 and NaCl in nearly equ
len t amoun ts, and hence, if dissolved in water, w
be represented by a point lying nearly vertically ab
the origin, at a distance increasing as the solutio
evaporated.
It
might, therefore, cut the surface
the solid model in the astrakanite face, which wo
prevent th e separation of the sodium from the m
nesium.
A
little magnesium chloride, however, wo
if added , raise the solution away from the astra ka
field, so that we would have only NaCl and MgS
7Hz 0 to deal with.
Th e solubilities of these two salts ar e affected
differently by t he tem perature th at we may anticip
their separatio n by first cooling, removing Epsom sa
then evaporating partly at higher temperatures,
moving sodium chloride, th en cooling again, etc. T
portion of the equilibrium diagram th at can be c
structed for 8 O from v an% Hoffs data shows th a
that temperature loeweite and vanthoffite intr
themselves between t he magnesium sulfate an d sodi
chloride fields, even when a considerable amount
magnesium chloride is added, so that i t may not
advisable t o evaporate the solution for the remo
of sodium chloride at too high a temperatu re. T
great tenden cy of these double salt s towards su p
saturation might allow the evaporation to proce
without their formation.
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Feb., 1918
T H E J O U R NA L O F I N D U S T R I A L
TABLE
System,
NaCl-MgC1r-MgSO4-NatSO4,
at
2 5 O
Solid phases
NazClz...............................
NazS04.1OH~0..
.....................
MgSO4.7HzO..
........................
hIgClz.6HzO..........................
MgCla.6HzO; N azClz.. . . . . . . . . . . . . . . . . .
NazC1z. NazS04. ......................
NazSO;. NazS04.10HzO(*).. . . . . . . . . . . . .
NazSO4.1OHeO;NaaM (S04)2.4Hzo
.....
MgS04 7Hz0 NazMgfSOa)z.4Hz0.:.
MgSO4.6HzO MgSOa.Hz0.
. . . . . . . . . . . . .
MgS04.6HzO: MgCIa.6HzO.
. . . . . . . . . . . . . . . . . .
NazSO4; NazSO4.1OHzO; NaaMg(S04) ~.4H zO.
NazClz. MgS04 7Hz0. NazM g(S 04) ~.4 H~ 0...
NazClaf MgSO4.HzO; MgCh.6ZO.. .....
MgSO1:7Hz01 MgS04.6HzO.
. . . . . . . . . . . .
NazCb; NmSb4; NazMg(S04)~.4HnO.
. . . . . . .
46
NazClz MgS04:7HzO: MgSO4 6H z0. .
....
NazCIz M gS04.6H z0: MgSO4HzO.
......
26
. . . . 5 5 . 5
. . . . . .
. . . . . .
. . . .
....
i:
.... 51
.... 30
. . . . . .
. . . . . .
. . . . . .
. . . .
.... 4
2.5
. . . . 1
*) From the experimental work of Professor W
still in progress in this laboratory, this point may be
. . . . .
. . . . .
3 5 : 5
. . . . .
1i:5
. . . 58
. .
108
. . . .
103
. .
. . . . .
27
. . .
35
35
. . .
48 26
73
15
Not determined
104
14
. .
Nitdetermined
7 34
67.5 12
, .
71 9 5
102
5 . .
16.5 3
C. Blasdale, which is
considerably in error.
In order to have the desired data it is very important
th at the equilibria here involved should be determined
or temperatu res both lower an d higher th an
2 5 O .
Work on the solubilities at o o s now in progress in
th is laborato ry and will be published as soon as possi-
ble.
It
is planned , also, to include potassium salts
in this work, so that a diagram for o o similar to t ha t
in Fig. VI11 can be constructed, and which might sug-
gest a modification of th e first tr ea tmen t of th e bittern .
CARNALLITE-The recovery of po tass ium chloride
from the carnallite was discussed earlier in connec-
tion with Fig. V. We m ay ask whether h ot or cold
water should be used for this purpose.
A
reference to
th e tables shows th at th e proportion of p otassium
chloride to magnesium chloride in th e solution a t equi-
librium with potassium chloride and carnallite is much
less at 2 5 th an at 83. This makes it obvious th at
a much smaller prop ortion of potassium chloride goes
into solution at the lower temperature . The composi-
tio n of t he solution in equilibrium with potassium
chloride and carnallite at
2 5 O
is as follows:
1oooH2O
+
5.5K2C12
+
72.5MgC12. Fro m thi s i t is possible t o
calculate the a mou nt of water t o be used in extracting
the magnesium chloride from the carnallite at this
temperature.
If I
mol of carnal lite is used we can
write the following equation:
5
T H E
RECOVERY OF P O T A S S I U M CHLORIDE F R O M
XMgCla.6H20 xHzO = yKsCi2 ~ ( I o o o H ~ O 5.jKzClz
+
72 ~MgC12)
From this we find
=
7.8;
y = 0 .425 ; z =
0.0138.
That is , I mol, or
2 7 7 . 5
g. of carnalli te, require s 7 . 8
mols,
or 140.4 . of wate r, or, th e weight of wate r re-
quired is approximately half the weight
of
the car-
nallite. At th e lower temperat ures th at would natu r-
ally be used somewh at more water would be required,
but relatively less KC1 would be dissolved.
The liquor used in extracting the carnallite may
then be partly evaporated and cooled, whereupon
ano the r crop of carn allite crystals will be obta ined .
To obtain the maximu m amou nt of carnallite but no
magnesium chloride the solution should be evaporated
t o such an extent th at on cooling with separatio n of
carnallite its composition will correspond to point
B
in Fig. V, which is 1oooHz0
+
105MgCL
+
K2C12.
Th e amo unt of evapora tion necessary is calculated
from th e following equatio n:
XOOOH~O72.5MgC12 + 5.5KzC12
xHzO +
yKMgC13.6H20+
~ I O Q O H ~ OIogMgClz + K2C12)
A N D E N G IN E E RI N G C H E M I S T R Y
This gives x =
340;
= 9.8 ;
z
=
0.6;
hence 2 5 7 2 0 g.
of solution should lose 6120 g. of water, giving 2 7 2 0 g.
of carnallite on cooling; or,
I
ton of solution should
lose 0.238 ton of water , and deposit 0.107 ton of car-
nallite.
It
will probably not pay, here or in stage
2
of the
process, t o recover the small amo unt of potassium
chloride remaining in the mother liquor from the car-
nallite,
Condensed summary of th e above process:
Evaporate bittern till boiling point becomes about 120 , and density
hot)
Separate solid and liquid while hot (settling tank and centrifuge).
A .
Solid. NaCl and MgSO4.HzO. Dissolve out NaCl wit h cold
water (containing some MgClz?) dissolve residue
in
hot water
and cool with ice machine, getting MgS04.7HaO.
1.35.
B . Liquid. Cool.
leaving
I.
Solid Carnallite. Extract wi th minimum amount cold water,
1. Solid KCl.
2. Solution. Evaporate partly, cool.
a. Solid carnallite, add to
I.
b. Solution of MgClz, add to 11.
Evaporate, cool, recover solid MgClz.6HnO.
11. Solution, mainly MgClz. Bleach with Clz and remove Brn.
The above process is being tested in this laboratory
on a semi-commercial scale under th e d irection of
Professor Merle Randall, and will be described in a
later publication.
I t
may be mentioned, however,
th at an excellent separatio n of a ctua l bitte rn has been
obtained into one lot of mater ial consisting of kieserite
an d sodium chloride, another consisting of carnallite
of a high degree of pu rit y an d whiteness, a nd a mother
liquor consisting of magnesium chloride solution con-
taining bu t very sm all amou nts of su lfate an d of potas-
sium. For example, using
I
5 lbs. of b itter n, and evap o-
ratin g till the boiling poin t was
I I ~
he thre e fractions
of materia l obtai ned had t he following composition:
NaC1, Kieserite
Carnallite Fraction Mother
Fraction Found Theoretical
Liquor
K
. . . . . . . . . . . . . .
1.6
11
.o
14.1 Trace
c1
. . . . . . . . . . . . .
21.1 37.4 38.4 23.4
so
. . . . . . . . . . . . . 22.2 0 .4 0 . 0 1.25
Mg
. . . . . . . . . . . . .
10.0 8 .1 8 .7
...
The writer wishes, in conclusion, to express gre at
apprec iation for the cordial cooperation of t he Oliver
Salt Company, which has given information and has
furnished samples of material and bi ttern .
Generous credit should be given to Messrs.
A. H.
Foster, W .
D.
Coughlan, C.arl Iddings and
W.
D.
Ram age for much of th e experimen tal work herein
described, and to Mr. Iddings for drawing the illus-
trati ons . Professor W. C. Bray has given considerable
time to th e final criticism of th e man uscript an d the
checking of the figures necessitated by t he absence of
the auth or from Berkeley due t o his acceptance of
a
commission in th e army .
Since concluding the abo ve work there ha s appeare d in
C h e m i c a l A b s t r a c t s
Vol. 11
(1917))
2719 ,
a brief outline
of a process by T. Nishimura, J . C h e m . Ind. T o k y o Vol.
20 (1917), 587, for extracting potassium from bittern
which, apart from certain serious errors in translation,
seems to be fundamentally similar to that herein de-
scribed, and which we may welcome, therefore, as
addit ion al evidence of th e feasibility of working up
these bitterns instead of allowing the m to be largely
wasted, as a t present.
BERKELEY,AL.