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Патент USA US3079236

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Feb. 26, 1963
3,079,227
G. M. BRUNNER ETAL
METHOD FOR THE PURIFICATION oF Po'rAssIuM cARBoNATE
’
Filed March 19. 1959
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George M. Brunner
William V Hauck
Albert Adams-
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Patented Feb. 26, 1903Y
l
2
3,079,227
liquid phase, which contains a small proportion of dis
solved potassium chloride, the solid phase may be further
George M. Brunner and William V. Hauch, Niagara Falls,
NX., and Albert Adams, Qarlsbad, N. Men., assignors
tions. To carry out the leaching, the solid phase is first
slu-rried in a wash medium, suitably water or preferably
METHÜD FÜR THE PURE‘ECATKÜN 0F
iPUiCÀSSlUll/i CAi BÜNATE
to International l'if’iflnerals ë.' Chemical Corporation, a
corporation of New Yorlr
Filed Mar. i9, 1959, Ser. No. 800,527
3 Ciairns. (Cl. 23--63)
The present invention relates to the puriiication of
potassium carbonate. More particularly, it relates to the
purification of potassium carbonate containing potassium
chloride and other impurities.
Cure method for the production of potassium carbonate
comprises electrolysis of aqueous potassium chloride solu
tion to form potassium hydroxide containing a small pro
portion of potassium chloride, followed by carbonation of
the aqueous potassium hydroxide solution, suitably with
liue gas, to form potassium carbonate containing a small
proportion of potassium chloride as the major impurity.
One method ot purifying potassium carbonate con
taining potassium chloride as impurity is repeated crystal
lization of the salt from aqueous solution until the de
puritied by selective leaching under controlled condi
an aqueous solution saturated with essentially pure potas
sium carbonate. The proportion of undissolved solids to
the wash medium should be suíñcient to provide a slurry
containing between about 20% and about 35% by weight
of undissolved solids. The resulting slurry is centrifuged
to separate the solid and liquid phases. The liquid phase,
containing ordinarily up to about 90% or more of the
potassium chloride occluded in the solid phase prior to
the washing step, together with a high proportion of
potassium carbonate, is recycled to the original aqueous
slurry of impure potassium carbonate. The washed solid
phase is a purified potassium carbonate product of re
duced chloride content, ordinarily less than about 0.2%
rand in many cases less than about 0.1%.
Depending on the proportion of chloride as impurity
contained in the original potassium carbonate and/or the
desired purity of the iinal product, it may be Iadvantageous
to again subject the washed potassium carbonate to the
selective leaching process generally according to the same
sired purity is attained. This can be achieved by dis
solving the salt in hot water and recrystallizing by evapo
ration and/or cooling. Such a procedure not only re
sults in poor yields of puritied product, but is time
procedure and under the same conditions as described
consuming aud costly.
saturated with potassium carbonate and potassium chlo
ride at the elevated temperature of separation from the
solid phase. The potassium values therein can advan
tageously be recovered in the following manner. The
liquid phase can optionally be evaporated to higher con
An object of the present invention is to provide an im
proved process for the purification of potassium carbonate.
Another object is to provide an integrated process for
the purilication of potassium carbonate wherein all mate
rials used in the process are substantially completely
recovered.
Another object is to provide an improved process for
the separation of potassium chloride and other impurities
from potassium carbonate produced from electrolytic
potassium hydroxide, containing potassium chloride as
impurity.
Other objects and advantages of the present invention
will become apparent upon a fuller understanding of the
invention as hereinafter set forth.
Generally speaking, the present invention effects puri
hereinabove.
The liquid phase from the original aqueous slurry of
impure potassium carbonate is substantially completely
centration if desired. lt is then cooled to a tempera-ture
sufficiently low to produce crystallization of salts there
from. For this purpose, the cooling is ordinarily carried
to room temperature or somewhat below, the precise tem
perature being chosen to effect maximum crystallization
of salts while avoiding production of a slurry which is
too thick for further processing. By this means, a major.
proportion of the potassium chloride content of the liquor
crystallizes in combination with a substantial proportion
of potassium carbonate.
The resulting slurry is subjected to flotation in a con
iication of potassium carbonate by a technique which may
involve (l) selective leaching with water under con
ventional flotation cell, whereby the potassium chloride
is selectively floated therefrom, preferably, without the
trolled conditions, (2) centrifugal washing of the solid
use of a conditioning agent. lf desired, a cationic flota
tion reagent such as a long-chain fatty acid amine (e.g.,
phase, and (3) concentration of the leach liquor to effect
crystallization, followed (4) by flotation of the resulting
distilled octadecylamine acetate) may be employed; how
slurry and (5) appropriate recycle of the ñoat and sink 50 ever, such reagents tend to cause foaming and dissolu
fractions.
tion of a portion of the solid potassium chloride, and their
The invention is applicable to the purification of potas
use is not generally preferred.
sium carbonate containing a small proportion of potas
The float product is withdrawn, washed to remove
sium chloride as impurity (e.g., up to about 5% by
potassium carbonate, and recycled for production of addi
weight of the total solids, dry basis). The starting mate 55 tional potassium hydroxide by electrolysis under conven
rial is slurried in water (unless already existing in the
tional conditions. The sink fraction, containing a major
form of a slurry) and is adjusted to an elevated tem
proportion of the potassium carbonate originally present
perature between about 60° C. and the boiling point,
in the flotation mixture, is recycled to the original aqueous
preferably between about 80 and about 100° C. The
slurry of impure potassium carbonate.
proportion of starting material to water should be suiii 60
For a better understanding of the present invention,
cient to yield a slurry containing between about 30 and
reference may be had to »the drawing which illustrates a
about 70% by weight of undissolved solids at equilibrium.
preferred embodiment of the present invention.
The mixture is agitated,> preferably until equilibrium has
In a preliminary operation, an aqueous solution of
been approached or reached, and is then filtered, centri
potassium chloride is electrolyzed to produce an aqueous
fuged, or decanted to separate the liquid and solid phases. 65 solution of potassium hydroxide containing a small pro
rPhe liquid phase is an aqueous solution substantially
portion of potassium chloride (ordinarily around 15%
completely saturated with potassium carbonate and 0r
of the solution) as impurity. The resulting solution is
dinarily at or near saturation with potassium chloride,
concentrated by evaporation, preferably to about 45%
while the solid phase is potassium carbonate containing
potassium hydroxide by weight, whereby all but about
potassium chloride in a proportion to potassium carbonate 70 1% of the potassium chloride crystallizes. The potas
substantially lower than in the liquid phase.
sium chloride crystals are separated from the solution
Inasmuch as the solid phase occludes a quantity of the
by centrifugation. The liquid phase is treated with ñue
3,979,227
4
gas, comprised essentially'of carbon dioxide, nitrogen,
phase, 3200 pounds, containing 48 pounds of potassium
and‘water vaporyto convert the potassium hydroxide
therein into potassium carbonate.
chloride, was` separatedV from the solid phase‘by decanta
tion While still above 80° C., .and was cooled to 15° C.,
4The resulting solution of potassium carbonate, contain
whereby potassium chloride' and a small proportion of
potassium carbonate crystallized. The resulting slurry
ingiles's Vthan’about 1% potassium` chloride, dry basis, is
subjectedto evaporation '(designatedfor clarity as opera
tion' "1'Y in `the‘drawing)'to about 60% solids to cause the
potassiumwcarbonate to crystallize. The liquid phase,
>6o taining a ’higher proportion of potassium chloride vto
potassiúm carbonate than the solid phase, is separated 10
was subjectedto astandardñotation operation in a Den
ver flotation cell. 41.6% of the potassium chloride pres
ent was selectively ñoated, whereas only 6.0% of the
potassium carbonate floated. `
`
Though the entire process was otherwise carried out on
a continuous basis, treatment of the vfloat fraction (200
fromme slurryby 'decantatiom leaning a solid'phase corn
pounds) was effected' in"a`batcli"oper`atiori'l The first
prised òf»- otè_z'ssium”ca'rbonatel andl to which isV occluded
float fraction was skimmed oiî and Washed with 30 pounds
as "aïliquid less than about 1% potassium chloride. ' i '
i »The solid phase'potassium carbonate is further puriiied
of water down a chute into a receiving tank. A portion
byslurrying Viri an ’aqueous solution'substantially satu 15 of the solid potassium carbonate present in the tloat frac
rated ¿with potassium carbonate; the resulting slurry pref
tion 'was dissolved in the water, thereby yielding a dilute
solution of potassium carbonate .as supernatant liquid in
erably-domains about"30% undissolved solids by Weight.
The'slur?y'iis'subjected _to centrifugation, 2, yielding a
, the receiving tank.
liquid rv’phase containing about '90% of the potassium
YThis liquid was decanted and used
to Wash thenext iioat fraction down the chute, thereby
chloride originally `contained in the slurry, an'd'a solid 20 increasing the potassium carbonate concentration of the
phase comprised 'essentially' of "potassium carbonarteQcon
liquid phase in the receiving tank. This was continued
taining` lessY than about l0.1% potassium chloride, -dry
basis. 'lhe liquid phase is recycled to -the evaporation
until the liquid phase was nearly saturated with potassium
carbonate. The mixture in'thereceiving tank was then
ï-The solid phase is againslurried in an aqueous solu
iiltered'to separate _the solid potassium chloride from the
aquetmsv solution of potassium carbonate. The hsolid
phase was recycled to electrolysis for potassium hydroxide
s'ium"carbonate. The resulting slurry is centrifuged, 3,
separating the "liquid phase, whichis recycled to centrifug
formation.- ` The liquid phase was recycled to the evapo
ing 2. (The solid phase, >comprised essentially of potas
generally less than about 0.005% potassium chloride, is
VFròm the dectantation step, the slurry phase (5,980
pounds) containing 4020 pounds K2CO3, 50 pounds KCl,
and v1910 -pounds of Water Was pumped to centrifuge 2
' The liquid phase decanted from the slurry of evapora
tion step l' is cooled to about 15° C., during which cool
wherein the slurry was spun for 8 seconds, rinsed for
.2 seconds> with a recycle solution saturated with potassium
carbonate, and spun again for 12 seconds. The solid,
stèpL.,
.,
.
_,.
.
tionlsubstantially'.saturated"with essentially pure .potas
ration step 1.'
`sium carbonate containing less than about0.01% and
dried‘to yield potassium carbonateof high purity.
ing essentially all of thepotassium chloride and some of
the potassium Vcarbonate orystallizes. The resulting
35
slurry" is .subiected'tó >aY ystwdard flotation in a Denver
ilotatyion cell," whereby the potassium chloride _crystals
arefsele‘ctiy'elygñoáted Vfrom the kpotassium carbonate crys
fais." VThe sinkfraetion, comprising potassium carbonate
of Vsubstantially reduced potassium chloride content, is
recycled tothe evaporation step, _1. ~The tloat fraction
istr‘ansferred at intervals from the trough of the dotation
40
evaporation step 1.
'
‘
An aqueous 45% potassium hydroxide solution weigh
'
l'
'
'Y
to certain speciiic details, it isl to be understood that `such
limiting. Many adaptations and modifications of the in
vention will be apparent from the foregoing description
to those skilled in the art.
50
The following claimsparticularly specify and distinctly
claim the subject matterof the present invention:
l. `An improved process for the purification of potas
sium carbonate'containing potassium chloride as an im
purity which comprises preparing a slurry `(I) of said
55 impure potassium carbonate in an aqueous medium se
lected from the group 4consisting of Water and 'aqueous
solutions of potassium carbonate, separating the liquid
phase (IDfrorn >the solid phase (III) of said slurry (I)
ata temperature above about 60° C., cooling said liquid
junction vvith theattached iiowsheet, illustrating a con
Example
cedure‘as described 'above ivascarried out. The purified
s'olidpotass'ium`carbonate from centrifuge 3 was dried,
details are illustrative only, and are not intended .to be
fromV` the "following specific example, to be read in con
'
'
While the invention has been described with reference
` '
tinuous process Vdesigned to produce >and purify 1450
'
comprising potassium carbonate With,0.04% KCI, _was
dnloadedwith the aid'of a recycle solution usaturated
with potassium carbonate to a slurry'tanlt'wherein the
0.0034% potassium chloride.V
The present invention may be more fully understood
pounds of potassium carbonate per hour.
`
yielding l4§50""pounds of potassium carbonate containing
thus eticcting’separation of the solid potassium chloride,
which is recycled to the potassium hydroxide electrolytic
process. The liquid phase, essentially saturated with
potássiumcarbouate and containing less than about 1%
potassium chloride, is recycled _to the potassium carbonate
"
mixture Nvas thoroughly agitated;` ` The mixture was then
pumped to centrifuge 3 wherein essentially the same pro
c'ell‘ to aV container wherein the solids are allowed to
settle out. VThe transfer of the ñrst portion of the float
product is eifected with Water, but the subsequent portions
of the float product are transferred by recycling liquid
phase 'from the earlier portions. When the iloat product
liquid phase approaches saturation with potassium car
bonatefthe entire il'oat'product is Withdrawn and iiltered,
"
60
phase (II) to a temperature sutlìciently low to form a
substantial amount of potassium Vchloride crystals and
potassium carbonate crystals therefrom, subjecting the
resultant slurry (EV) of potassium chloride and potas
sium carbonate to dotation, whereby potassium chloride
ing`2600 pounds was treated with an excess of flue gas 65 is Vselectively floated therefrom, withdrawing the iloat
to produce 2890 pounds of a nearly saturated potassium
product, recycling the dotation underflow to said slurry
carbonate solution containing approximately k1% »portas
(I) lot' impure potassium carbonate in said aqueous me
siurnchlorideasimpurity. 4This solution was combined
with recycle solutions, to be described hereinafter, of
dium, >slurrying said solid phase (Ill) with an aqueous
solution of essentially pure `potassium carbonate, separat
varying concentrations containing potassium carbonate 70 ingthe resulting slurryKV) into a liquid phase and'a‘solid
and 'about l1% potassium chloride. The resulting mix
phase (VI), said solid phase (Yi) beingpuriíied potassium
ture, totaling 10,915 pounds and containing 98 >pounds
carbonate of reduced chloride content.
'
"
potassium chloride, was -evaporated atabout 95° C.,
V2.4251 process as in claim 1 wherein the liquid phase
causing potassium carbonate to crystallize, vuntil thesolid
(Il) is separated from the solidphase (-111) of slurry
phase, constituted about60% of the mixture.V The liquid
(I) at a temperature above about 80° C.
3,079,227
5
6
3. A process as in claim 1 wherein said liquid phase
(Il) is cooled to about 15° C.
4. A process according to claim 1 wherein said solid
phase (Vi) is slurried with an aqueous solution of sub
recycling the flotation underflow to said slurry (II),
slurrying said solid phase (I) with a substantially satu
rated aqueous solution of essentially pure potassium car
bonate, centrifugally separating the resulting slurry (V)
into a liquid phase (VI), recycling said liquid phase (VI)
stantially pure potassium carbonate, and the resulting
slurry is subjected to centrifugation to separate the liquid
phase from the solid phase, said solid phase being purified
to said slurry (Il), and a solid phase (VII), said solid
phase (VII) being purilied potassium carbonate of re
potassium carbonate of less than about 0.01% chloride
duced chloride content.
7. A process as in claim 6 wherein the float product is
content.
5. In a process for the separation of ñnely divided, 10 collected and allowed to stratify, the liquid phase is de
crystalline potassium chloride from admixture with iinely
canted therefrom and used for transferring further quanti
divided, crystalline potassium carbonate in an aqueous
ties of said float product to the collection vessel, said
medium saturated therewith, the improvement which com
decantation and transfer are continued until said liquid
prises subjecting said mixture to ñotation in the absence
phase approaches saturation with potassium carbonate,
of a conditioning reagent, whereby said potassium chlo 15 the float product is then separated into a solid phase com
ride is selectively tloated therefrom, and separating and
prising largely potassium chloride and a liquid phase com
withdrawing the float product.
prising potassium carbonate saturated with potassium
6. In a process for the preparation of potassium car
chloride, and said liquid phase is recycled to the original
bonate, which process comprises passing flue gas through
aqueous slurry of impure potassium carbonate.
an aqueous solution of potassium hydroxide containing 20
8. A process as in claim 6 wherein said purified potas'
potassium chloride as an impurity, concentrating the re
sium carbonate of reduced chloride content is slurried
sulting aqueous solution whereby potassium carbonate
with an aqueous solution substantially saturated with es
containing potassium chloride as an impurity is obtained
as a solid phase (I) in aqueous slurry (II), the improve
is centrifugally separated into a liquid phase and a solid
sentially pure potassium carbonate, the resulting slurry
ment which comprises segregating from said slurry (il), 25 phase, said solid phase being purified potassium car
at an undissolved solids content greater than about 30%
bonate of less than about 0.005% chloride content.
References Cited in the lile of this patent
and at a temperature above about 60° C., said solid phase
(I) and a liquid phase (I1-I), cooling said liquid phase
UNITED STATES PATENTS
(III) to a temperature below about 30° C., thereby crys
tallizing a substantial proportion of the potassium chlo 30 Re. 18,393
Pike ________________ __ Mar. 22, 1932
ride therein as potassium chloride crystals and a quantity
2,343,080
Pike ________________ .__ Feb. 29, 1944
of the potassium carbonate contained therein as potas
2,448,191
Pike ________________ __ Aug. 31, 1948
sium carbonate crystals, subjecting the resulting slurry
(iV) to flotation, whereby potassium chloride is selec
tively rlioated therefrom, withdrawing the ñoat product,
35
2,588,443
2,699,377
2,842,489
Weinig ______________ __ Mar. 11, 1952
Dancy _______________ __ Ian. 11, 1955
Svanoe _______________ __ IJuly 8, 1958
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