Aug. 1, 1967 W. C. MAZEN ET AL
RECOVERY OF ACIDS
3,333,924
Filed Jan. 10, 1964 4 Sheets-Sheet 1
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INVENTOR.
WAYNE C. HAZEN
ANGUS V HENRICKSON
BY
S~-J~~
ATTORNEYS
Aug. 1, 1967
Filed Jan. 10, 1964
W. C. HAZEN ETAL
RECOVERY OF ACIDS
3,333,924
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INVENTOR.
WAYNE C. HAZEN
ANGUS V. HENRICKSON
8Y
S~-J7?~
ATTORNEYS
Aug. 1,1967
Filed Jan; 10, 1964
W. C. HAZEN ETAL
RECOVERY OF ACIDS
3,333,924
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INVENTOR.
WAYNE C. HAZEN
ANGUS V. HENRICKSON
BY
s~~i9~
ATTORNEYS
Aug. 1, 1967 W. C. HAZEN ETAL 3,333,924
RECOVERY OF ACIDS
Filed Jan. 10, 1964 4 Sheets-Sheet 4
RECOVERY OF H2S04 FROM
AMINE SOLVENT WITH WATER
ALONE AND WATER AND S02
WATER ALONE
WATER PLUS S02
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IMPURE ACID
RAFFINATE
WASTE
LOADED SOLVENT
REGENERATED SOLVENT
STEAM
STRIPPED SOLVENT
CONTAINING 502
'-------5°2---------+---------1
PURE ACID
CONTAINING S02
STEAM --"~I D1STI L~ATION r-SO,
:::J:£9"=----- 8 PURE ACID
INVENTOR.
WAYNE C. HAZEN
ANGUS V. HENRICKSON
BY
J~...J-~~
ATTORNEYS
United States Patent Office 3,333,924
Patented Aug. 1, 1967
1 2
factors render present solvent extraction processes for
recovery of acids uneconomical.
Accordingly, it is an object of this invention to provide
a process for the recovery of acids from solutions which
is economically feasible for commercial production of
high purity acids.
It is another <object of this invention to provide a process
for the recovery of acids by solvent extraction in
which a high purity acid is recovered and the solvent can
be regenerated in a substantially pure state.
10 It is still another object of this invention to provide a
process for the recovery of acids in which the reagents
used can be regenerated and continuously recycled for
use in the process.
15 It is a further object of this invention to provide an
economical method for stripping the acid from an acid
loaded extraction solvent and recovering it in a relatively
pure form.
It has been found that the above and other objects can
20 be accomplished by treating the solution containing the
acid with an organic solvent in a solvent extraction process
to extract the acid followed by stripping the acid from
the solvent with sulfur dioxide and water, and recovering
the sulfur dioxide for reuse from both the stripped
25 solvent and the produced acid, thereby regenerating the
solvent for reuse and producing a concentrated acid product.
The process of the invention is not limited by the
conventional extraction step but in its broadest form comprises
the stripping of acid from an acid loaded solvent
30 extractant with water and sulfur dioxide.
The invention will now be described in conjunction with
the accompanying drawings in which:
FIG. 1 is a graph presenting the data of Example 1
as an extraction isotherm and showing the effectiveness
35 of amine solvent as an extraction agent for phosphoric
acid;
FIG. 2 is a graph of stripping isotherms based on the
stripping of acid from amine solvent with water and 802
and in which acid in the organic phase is plotted against
40 acid in the aqueous strip phase;
FIG. 3 is a graph plotted similarly to FIG. 2 of the
results of an example using water alone as the stripping
agent for stripping acid from an amine solvent and showing
the graph of FIG. 2 for comparative purposes;
FIG. 4 is a graph plotted similarly to FIG. 2 showing
the effect of temperature on stripping acid from an amine
solvent with sulfur dioxide and water;
FIG. 5 is a graph plotted similarly to that of FIG. 2
showing the effectiveness of sulfur dioxide and water in
50 stripping acid from various amine solvents;
FIG. 6 is a graph plotted similarly to that of FIG. 2
showing the effectiveness of 802 and water in stripping
acid from a 20 percent amine solvent;
FIG. 7 is a graph plotted similarly to that of FIG. 2
55 showing the effectiveness of water alone and water and
sulfur dioxide in stripping sulfuric acid from an amine
solvent, and
FIG. 8 is a flow diagram showing the adaptation of the
process to a continuous circuit.
60 The acids which are recoverable by this process are
acids which are unreactive with sulfur dioxide, including
phosphoric and sulfuric acid. The acids must be compatible
with the solvent which is used and preferably should have
a lower vapor pressure than sulfur dioxide to permit its
3,333,924
RECOVERY OF ACIDS
Wayne C. Hazen, Denver, and Angus V. Henriel,son,
Golden, Colo., assignors, by mesne assignments, to 5
Hazen Research, Inc., a corporation of Colorado
Filed Jan. 10, 1964, Ser. No. 336,914
14 Claims. (Cl. 23-165)
ABSTRACT OF THE DISCLOSURE
The invention relates to the recovery of sulfuric and
phosphoric acids from solutions of acids by solvent extraction
and comprises extracting the acids with an organic
extractant, such as an amine, and stripping acid
from the acid-loaded solvent with sulfur dioxide and
water, the novelty being based on the stripping feature.
A modification is the recovery of sulfur dioxide after
stripping by adding an organic base, such as lime, to convert
it to a sulphite and heating the sulfite.
This invention relates to a process for the recovery of
acids from solutions, including such recovery from solvent
extractants; more particularly, it relates to improvements
in acid recovery processes utilizing solvent extraction
techniques providing for regeneration and reuse of
reagents including the solvent.
The invention will be illustrated principally by its application
to the recovery of phosphoric and sulphuric
acid; however, its application is not limited to the recovery
of these acids as it is likewise applicable to the
recovery of other strong acids.
Processes for the recovery of phosphoric acid from
phosphate ores in which the ore is treated with sulfuric
acid to form phosphoric acid are well known. When the
insoluble matter is separated from the liquid phosphoric
acid by filtration or decantation the impure phosphoric
acid is used as fertilizer. This is the wet process pliosphoric
acid which is not usable for detergent, food or
chemical manufacture because of the impurities such as
iron, alumina, arsenic, vanadium, fluoride, etc.
High purity phosphoric acid for industrial and food
uses is made by the electric furnace process and costs
approximately forty dollars per ton (P20 S) more than the 45
fertilizer acid made by the wet method. This emphasizes
the importance of the availability of an economical process
for the recovery and purification of this acid made
by the wet process.
Methods for purification of wet process phosphoric
acid by solvent extraction techniques have been proposed
utilizing alcohols, esters, amines and other organic waterimmiscible
solvents.
In the case of acids other than phosphoric acid, such
as sulfuric acid and hydrochloric acid, there are no economical
processes for recovery and purification although
many efforts have been made to develop such a process.
One of the chief difficulties in the use of solvent extraction
processes for the recovery of acids is that of
stripping the acid from the solvent. Present stripping
techniques using water alone result in very dilute acid
solution or an inefficient recovery of the acid. The dilute
solutions require further concentration by evaporation.
This is particularly true of the amine type solvents. These
3,333,924
592
453
349
214
580
Aqneous phase
45.0
35.2
31. 6
26.5
15.9
Concentration of H3PO, (gm,fl.)
Organic phase
Stage
(1.1) Solvent Composition:
The ,results of the eX!ample are plotted in the graph of
FIG. 1. They show, for example, that for an aqueous concentration
of about 600 grams per liter of H3P04 a solvent
concentration of about 44 grams of H3P04 per liter results.
This i:11ustrates that the solvent is highly effective for extracting
,phosphoric acid. In fact it shows that in a four
stage counter current system ,approximately 99% of the
phosphoric acid would be extracted into the solvent.
Example 2 is included for the purpose of illustrating
the effectiveness of aqueous sulfur dioxide as a stripping
agent for stripping phosphoric acid from tri-caprylyl
amine.
Percent (v.lv.)
Tri-caprylyl amine 10
Isodecanol 10
Kerosene 80
(1.2) Test procedure.-100 ml. of the solvent was contacted
with 30 ml. 50% (w.lw.) H3P04 by vigorous shaking
in a separatory funnel at 25° C. The phases were then
allowed to separate. 5 ml. of the aqueous phase was removed
for H3P04 analysis. The entire solvent phase was
stripped with an equal volume of 5% Na2C03 solution.
This strip solution was separated for P04'" analysis and
the solvent was washed twice with water and recontacted
with the remaining 25 m!. of H3P04 solution from the
first contact. This procedure was repeated through four
stages of extraction.
One separate contact was made between 100 ml. solvent
and 2 volumes of 50 ml. 50% (w.lw.) H3P04 to determine
the distribution at higher solvent loading.
(1.3) Data.-The analysis of each of the aqueous and
solvent phases are given in Table 1.
L._ _
2 • .. _•• _. _.. _.. .
3__ .. • _. ..... . _
4. . _.. ." ..• _. _
60 5 .... ...... .._.. __ .
50 TABLE l.-EXTRACTION OF H3PO, WITH 10% (V.IV.) TRI~~:
YLYL AMINE, 10% (V.IV.) ISODECANOL, IN KERO-
4
and it follows that the sulfur dioxide and water stripping
should be effective with these solvents as well as with
amines.
While the temperature at which the acid may be stripped
5 from the solvent with sulfur dioxide and water is not
critical, it has been found that a temperature of about 25°
C. or below is preferable. It is preferred that sulfur dioxide
be used to the saturation point. The method of removing
sulfur dioxide from the acid and solvent is not
10 critical. Direct heat and vacuum distillation are acceptable
for secondary and tertiary amines and other solvents while
the lime treatment described above is acceptable in the
case of primary amines and other solvents of the type
mentioned herein.
The following examples are included to illustrate the
invention but they are in no way limiting thereof.
The extraction and stripping procedures used in the eXamples
simulate conventional commercial procedures.
The examples illustrate that the process is adaptable to
20 such procedures.
Example 1 was performed to illustrate the effectiveness
of a typical amine for solvent extraction of phosphoric
acid.
Example i.-Extraction of H3P04 with tri-caprylyl
amine solvent
3
easy removal from the acid by heat or vacuum distillation.
While the invention is not limited in its application to
any particular solvent extractant, it is illustrated by examples
in which amines are used as solvent extractants.
When these amines are used they are ordinarily dissolved
in an inert water immiscible diluent, such as, kerosene.
While the secondary and tertiary amine solvent extractants
can be regenerated after the stripping step by direct heat
or vacuum distillation to remove sulfur dioxide, the primary
amines cannot be effectively regenerated in this
manner, apparently because they are too basic in reaction.
However, they can be just as effectively regenerated
by treating them with lime after the stripping step to remove
the sulfur dioxide in the form of a precipitate of 15
calcium sulfite which is removed and heated to regenerate
both sulfur dioxide and lime, the entire procedure resulting
in the regeneration of all three reagents. This procedure
can, of course, be used for other extractants. Among
other equivalent solvent extractants well known in the
art are the lower alkyl phosphate esters, such as butyl,
octyl, tri-butyl and tri-octyl phosphates and others disclosed
as solvents in U.S. Patent 2,955,918, lower aliphatic
alcohols and ketones as disclosed in the combination
of U.S. Patents 1,929,441; 1,929,452; 1,981,145 and 25
2,880,063, and others well known in the art.
When amines are used as solvent extractants, those
preferred are the alkyl substituted amines in which the
alkyl substituents have six or more carbon atoms in the
chain, including branched chain alkyl radicals. Examples 30
are tri-Iauryl amine which is a tertiary C12 straight chain
amine, tri-caprylyl amine, a tertiary amine, di-Iauryl
amine, a secondary straight chain amine, do-decenyl-tri
alkyl methyl amine, a homologous mixture containing 24-
27 carbon atoms, a secondary amine, and tri-alkyl meth- 35
yl amine, a homologous mixture containing 18-24 carbon
atoms, a primary amine.
The preferred stripping agent is water and sulfur dioxide.
This combination, of course, forms sulfurous acid.
The surprising discovery has been made that this gas in 40
the presence of water will strip acids, such as, sulphuric
and phosphoric, from solvents, and meets other requirements
for the stripping agent, including that of being unreactive
with the acid and the solvent. It can be separated
from the acid and a majority of solvent extractants by di- 45
rect heat or vacuum distillation. Sulfur dioxide is a volatile
acid anhydride gas which is compatible and unreactive
with strong acids and solvents used for solvent
extraction of acids.
While the reason for the surprising and unexpected
effectiveness of sulfur dioxide in the presence of water
for stripping acids from solvents has not been determined
with certainty, it may be postulated that the effectiveness
of sulfur dioxide or the sulfurous acid formed for stripping
acids from solvent is due to the competitive effect 55
produced on the solvent-acid bond. In such cases where
the acid is bonded to the solvent through some mechanism
such as hydrogen bonding, then the sulfurous acid (sulfur
dioxide plus water) will compete with the extracted
acid for the solvent bond. This, therefore, would effectively
loosen the attachment of the extracted acid to the
solvent and permit the ready removal in a concentrated
form by water stripping. If the vapor pressure of the sulfurous
acid remaining on the solvent after removal of the
extracted acid is high enough to permit its removal by 65
heat or vacuum, then the solvent can be regenerated for
reuse. This extends the usefulness of the sulfur dioxide
stripping technique, therefore, to classes of solvents which
extract acids where the attachment may be through some
mechanism such as hydrogen bonding. Examples of these 70
solvents are lower alkyl phosphate esters such as butyl
and octyl phosphate tri-butyl and tri-octyl phosphate
lower aliphatic alcohols such as butyl and amyl alcohol:
ketone and other conventional solvent extractants for
acids. Such solvents are known to extract phosphoric acid 75
3,333,924
5
Example 2.-Stfipping of HaP04 from tri-caprylyl amine
solvent with aqueous S02
6
TABLE 3.-STRIPPING OF H3PO, FROM 10% (V.fV.) TRI-CAPRYLYL
AMINE, 10% (V.fV.) ISODECANOL IN KEROSENE
WITH WATER AT 250 C.
Concentration of HaPO, (gm.jl.)
Organic phase Aqueous phase
22.8 274
16.8 109
14.1 52
12.5 32
Concentration of H3PO, (gm.jl.)
100 C. 250 C. 500 C.
Organic Aqueous Organic Aqueous Organic IAqueous
20.0 611 25.9 618 33.6 579
7.6 502 9.1 441 11.1 353
2.0 248 0.60 206 6.1 210
<.03 6.0
TABLE 4.-EFFECT OF TEMPERATURE ON STRIPPING OF
H3PO, WITH AQUEOUS SO, FROM 10% (V./V.) TRI-CAPRYLYL
AMINE, 10% (V./V.) ISODECANOL IN KEROSENE
(4.2) Test procedure.-l00 ml. solvent was contacted
twice with 50% HaP04 by vigorous shaking in a separatory
funnel at 25% C. The aqueous phases were separated
,and the residual HaP04 removed after the second contact
by centrifuging so tlIata clear solvent was obtained.
5 ml. water was then added to the solvent and the mixture
heated or cooled to the desked temperature by placing
in a controlled temperature water bath. 502 was bubbled
through the mixture until both the water and the solvent
were saturated. The mixture was agitated intermittently
to as'sure equilibrium between the phases. At saturation
the phases were separated and analyzed for HaP04• This
stripping procedure was repeated three times.
(4.3) Data.-The ,analysis of the aqueous strips and
the corresponding solvents are given in Table 4. The st,ripping
isotherms are given in FIG. 4.
The results of Example 4 are plotted on the graph of
75 FIG. 4. The graph illustratestlI,at of the temperatures
5
55
The results of Example 3 ,are plotted in FIG. 3 along
with the plot of FIG. 2 for comparative purposes. The
effectiveness of aqueous S02 over water alone ,as a stripping
agent is illustrated by the fact that with the use of
aqueous S02 an aqueous concentration of more than 600
grams of phosphoric acid per liter was obtained whereas
without the S02 the maxinlum concentration obtained was
275 grams of phosphoric acid per liter. In addition, with
water alone more than 10 grams of phosphoric acid per
liter remained in the solvent after stripping whereas with
aqueous S02 the stripping of .phosphoric acid from the
25 solvent was 'Substantially complete. This graphioally illustrates
the effectiveness of aqueous sulfur dioxide as a stripping
agent.
Example 4 records the results of experiments made to
determine the effect of temperature on stripping phos30
phoric acid from tri-caprylyl amine 'Solvent with aqueous
sulfur dioxide.
Example 4.-EfJect of temperature on the stripping of
HaP04 from 10% (v./v.) tri-caprylyl amine, 10%
35 (v.lv.) isodecanol in kerosene with aqueous S02
(4.1) Solvent composition:
Percent (v.lv.)
Tri-caprylyl amine ...: 10
40 Isodecanol 10
J(erosene 80
Percent (v./v.)
10
10
80
60
Concentration of H3PO, (gm.jl.)
Organic phase Aqueous phase
25.9 618
9.1 441
0.60 206
<.03 6.0
Nil 0.81
(3.1) Solvent composition:
(3.2) Test procedure.-l00 ml.of the solvent was
loaded with HaP04 by shaking twice with 50% (w.lw.)
HaP04 solution at 25 0 C. in a separatory funnel. Residual
HaP04 was removed after the second contact by centrifug- 65
ing so that a clear solvent was obtained.
The HaP04 was then stripped by adding 5 m!. water
and shaking vigorously in a separatory funnel. The phases
were then separated and analyzed for HaP04• Four consecutive
strips were made in this manner. 70
(3.3) Data.-The analysis of the aqueous strips and
the corresponding solvents are given in Table 3. The stripping
isotherm is given in FIG. 3. The stripping isotherm
for aqueous S02 is included in FIG. 3 for ease of comparison.
Tri-caprylyl ,amine _
Isodecanol ~--
J(erosene ~ __ ~ _
Example 3.-Stripping of HaP04 from tri-caprylyl amine
solvent with water
The results are plotted in the graph of FIG. 2. The
graph shows, for example, that 'a 'strip solution containing
more than 600 grams of phosphoric ,acid per liter in the
aqueous phase can be obtained by the use of the sulfur
dioxide-water stripping process. In ,addition, it shows that 45
the solvent can be ,completely stripped of its extracted
phosphoric acid by three stages of counter current operation.
Example 3 is a control showing the ineffectiveness of
water alone for stripping phosphoric acid from tricaprylyl 50
amine solvent.
TABLE 2.-STRIPPING OF H3PO, WITH S02 AND WATER
FROM 10% (V.fV.) TRI-CAPRYLYL AMINE, 10% ISODECANOL
IN KEROSENE
(2.2) Test procedure.-l00 ml. of the solvent was 10
loaded with HaP04 by contacting twice with 50 ml. samples
of 50% (w.lw.) HaP04 at 25 0 C. in a separatory funnel.
Residual phosphoric acid was removed after the second
contact by centrifuging so that a clear loaded solvent
was obtained. The HaP04 was stripped from the solvent by 15
,adding 5 ml. distilled water and then saturating the aqueous
acid solvent with S02 at 25 0 C. The mixture was
agitated intermittently to assure equilibrium between the
phases. Phases were then permitted to separate and were
analyzed for H aP04• This stripping procedure was re- 20
peated five times. to determine the distribution in a range
of HaP04 concentrations.
(2.3) .Data.-The analysis of the aqueous H2SOa strips
and the corresponding solvents' are given in Table 2. The
stripping isotherm is given in FIG. 2.
(2.1) Solvent composition:
Percent (v./v.)
Tri-caprylyl amine 10
Isodecanol 10
J(erosene ~------ 80
3,333,924
7
tested the most effective temperature is 10° C. and the
least effective is 50° c., indicating that ,at higher temper-
8
(5.4) Data.-The analyses of the l'affinates and strip
solutions are given in Tables 5 and 5.1.
TABLE 5.-EXTRACTION OF H,PO, FROM SYNTHETIC WET PROCESS
ACID WITH 10% (V.{V.) TRI·CAPRYLYL AMINE, 10% (V.{V.) ISODECANOL
IN KEROSENE, STRIPPING WITH AQUEOUS SO, AT 25° C. DISTRIBUTION
OF H,PO,. 804=, F- AND R,O,
Concentration (gm. I.)
SO, F- Fe
·_-------1---------------
Head Solution (50 ml.} •••• _•••• __ •• _
Raffinate No.1 (50 mI.) _
Raffinate No.2 (50 ml.} .• __ ....•.
Strip No.1 (25 ml.} •••••••....•..•..
Strip No.2 (25 ml) .••••........••..•
Strip No.3 (25 m!.) .. _.. __ ._ .. __ ... _.
Strip No.4 (25 ml.) ••. __ •...• ..•..
657
608
652
103
28
4
<.05
106 19.9 93.3 10.0
53 20.0 100.6 10.6
96 20.1 93.3 10.3
51 <.05 Trace
30 Trace
18 N.D.
35 N.D.
TABLE 5.1-EXTRACTION OF H,PO, WITH 10% (V.{V.) TRI·CAPRYLYL
AMINE, 90% SOLVENT (NO ISODECANOL) FROM SYNTHETIC WET
PROCESS ACID. STRIPPING WITH AQUEOUS 80, AT 25° C. DISTRIBUTION
OF H,PO" SO,=, F-, AND R,O,
Concentration (gm./l.)
SO,= F- Fe
----------1---------------
Head Solution..._.. _................ 657
Raffinate No. 1.._ _._ _ 635
Raffinate No.2...................... 648
Strip No. L _.. _ _. _ 81
Strip No. 2 _ _ _._. .. __ .. _ 6
Strip No.3 _. 0.94
Strip No.4 (NaOH)._.__ _.. 0.09
106 19.9 93.3 10.0
51. 2 91. 0 10.4
92.6 84.4 9.93
41.2 6.8
20.8 N.D.
13.6 N.D.
16.0 N.D.
Example 6.-Regeneration of solvent by heat or steam
distillation after aqueous 502 stripping
55
45
(6.1) General procedure.-Two general procedures
50 were used to regenerate tri-caprylyl solvent which had
been saturated with 502 :
(a) Heating on a steam bath to 75° C. for one-half
hour with a gentle stream of air bubbling through the
solvent. No water present.
(b) Heating on a steam bath at 15-20" vacuum with
an equal volume of water with a gentle stream of air
passing through the water·solvent mixture. Heating continues
until approximately one·half the water had been
distilled off.
Both procedures were effective in removing the 502
and regenerating the solvent to 80% free amine.
Effectiveness of the regeneration was checked by two
methods:
(a) Stripping a portion of the solvent with NaOH and
65 titrating the acidified strip for S02 with standard iodine
solution.
(b) Titrating a sample of the solvent directly with
standard sodium hydroxide solution to the phenolphthalein
end point and titrating a similar sample after acidifying
70 and washing. The degree of regenemtion can then be calculated
from the difference between the two titres.
(6.2) Data.-Regeneration tests by steam distillation
were made on a variety of amine solvents. The degree of
regeneration was determined by titmtion. These results
75 are given in Table 6.
The example shows that the only impurity picked up
in appreciable amounts by the solvent and by the sulfur
40 dioxide is the sulphate and that the amounts carried over
in each are not prohibitive.
Example 6 was performed to illustrate the effectiveness
of regeneration of various amine solvents saturated with
502 by heating under vacuum or by steam distillation.
* So'mbol indicates hydroxides of Fe, AI, Cr.
Percent (v.lv.)
Tri·caprylyl amine 10
Isodecanol 10
](erosene 80
Solvent (b):
Tri·caprylyl,amine 10
Aromatic petroleum fr'actions 90
(5.2) Synthetic wet process acid:
atures the process is less effective. Of course, the temperature
must always be maintained below that at which
sulfur dioxide boils off.
Example 5 was performed on a synthetic wet process
phosphoric acid to which had been 'added certain impurities
ordinarily encountered in the wet process for the
recovery of phosphoric acid. These impurities are set forth
in the example.
Example 5.-Extraction of HSP04 from Synthetic Wet
Process Phosphoric Acid, Distribution of 504=, F- and
R20 S
(5.1) Solvent (a):
(5.3) Test procedul'e.-200 mI. solvent was contacted
twice with 50 ml. synthetic wet process acid by shaking
in a separatory funnel. The loaded organic was centrifuged
to remove entrained phosphoric 'acid and then
stripped three times with 25 ml. water and saturation
with 502 at 25 ° C.
Raffinates 1 and 2 and the three strip solutions were
analyzed for HSP04, S04=, F-, and R20 S'
H gm.ll. 60
S
P0
4
.__________ 657
504= ---------------_______________________ 106
F- 19.9
R20 S* -------------------- 93.3
Fe 10
9
3,333,924
10
'Homologous mixture containing 18-24 carbon atoms-primary amine.
15
The results illustmte that SOz can be effectively removed
from the secondary and tertiary amines by· direct
heat or vacuum distillation. This is a decided advantage
of the process when these amines and many other solvents
are used as extractants in that it provides a purified sol- 20
vent and permits reuse of the sulfur d10xide.
Example 7 was performed to show the effectiveness of
aqueous sulfur dioxide in stripping -phosphoric acid from
various amine solvents. The amines used were primary,
secondary and tertiaryamines. 25
Example 7.-Extraction of HSP04 and stripping with
.aqueous SOz (tests made on various amines)
TABLE 6.-REGENERATION OF SO, SATURATED
SOLVENTS BY STEAM DISTILLATION
Calculated Normality
Solvent
Regen- Percent
erated Acid Regen-
Solvent eration
10% tri-caprylyl amine____________ 0.04 0.20 80
10% tri-Iauryl amine______________ 0.03 0.20 85
10% di-lauryl amine______________ 0.03 0.08 62
10% do-decenyl-tri-alkyl methyl
amine__________________________ 0.03 0.18 83
10% tri-alkyl methyl amine'______ 0.22 0.24 0
o Tri-caprylyl amine
il Tri-lauryl amine
D Di-lauryl amine + Do-decenyl-tri alkyl methyl amine
5 Tri-alkyl methyl amine, homologous mixture 18-24
carbon atoms, primary amine
The results show that phosphoric acid cannot be as
effectively stripped from a primary amine solvent as it
10 can be from the secondary and tertiary amine solvents.
Example 8 is similar to Example 2 except that 20 percent
of the amine was used in the solvent.
Example 8.-Stripping of HSP04 from 20% (v./v.)tricaprylyl
amine, 20% (v./v.) isodecanol with aqueous
SOz
(8.1) Procedure.-100 ml. solvent was loaded with
HSP04 by contacting twice with 50% HSP04 by vigorous
shaking in a separatory funnel at 25° C. After separation
of phases the solvent was stripped by four stages of contact
with 5 ml. water and saturated with SOz. A final
strip was made with NaOH to determine residual HSP04
in the solvent.
(8.2) Data.-The concentration of HSP04 in each of
the aqueous and organic phases is given in Table 8. The
stripping isotherm is plotted in FIGURE 6.
TABLE 8.-STRIPPING OF H,P04 FROM 20% (v.N.) TRI30
~:tJfl:~:li501:~INE, 20% (v.IV.) ISODECANOL IN KEROIt
will be seen from the results of Example 8 as plotted
in the graph of FIG. 6 that acid can be effectively stripped
from 20 percent amine by the process.
59
33
17
7
566
402
270
186
Stage
L _
2 _
3 _
4 _
(7.1) General procedure.-In each test a sample of
the solvent was loaded with HSP04 by contacting 100 ml.
of the solvent twice with 50% (w./w.) HSP04• The
HSP04 was then stripped at 25° C. by adding water and
saturating with SOz. Three or more strips were made in Aqueous Solvent
this manner and finally the solvent was stripped with 35 I ~I ~__
sodium hydroxide to determine the residual HSP04 remaining
in the solvent. Each aqueous strip was analyzed
for HSP04•
(7.2) Data.-Table 7 gives the concentration of
HSP04 found in the aqueous and organic phases in each 40
of the tests. Stripping isotherms for each of the solvents
are given In FIG. 5. Data previously given in section 2
for the tri-caprylyl amine is repeated for easier comparisons.
TABLE 7.-EXTRACTION OF H,P04 AND STRIPPING WITH AQUEOUS SO,
AT 25° C. COMPARISON OF TERTIARY, SECONDARY AND PRIMARY
AMlNES. (AMINE CONCENTRATIONS EXPRESSED IN VOLUME PERCENT.
ALL SOLVENTS MODIFIED WITH AN EQUAL VOLUME PERCENT
OF ISODECANOL)
Gm.H,P04/!.
Solvent Stage Organic
Solvent
Aqueous Loading
(gm.!!.)
Tri-caprylyl amine 10%____________________ 1 25.9 618 ----------6 2 9.1 441
3 0.60 206 ------------
4 <.03 6.0 36
Tri-Iauryl amine 10%_______________________ 1 15.7 58.9 ------------
2 2.8 235 L>.
3 0.5 42 ------------
Di-Iauryl amine____________________________ 1 4.2 275 0
2 1.8 47 ------------
3 .005 26 25
Do-decenyl-tri-alkyl methyl amine 10% ____ 1 11.5 476 ----------+ 2 1.2 187
3 0.2 22 49
Tri-alkyl methyl amine 10%_______________ 1 102 510 ------------
2 68 413 ------------
3 39 328 ---------136 4 19 245
The results of Example 7 are plotted in the graph of
FIG. 5. The key to the symbols used on the graph are
as follows:
Example 9 was performed to test the effectiveness of
aqueous sulfur dioxide for stripping sulfuric acid from
75 amine solvents.
3,333,924
References Cited
UNITED STATES PATENTS
10/1933 Milligon 23-165
10/1957 Seaborg 23-102 X
7/1958 Schornstein et a1. 23~87 X
(Other references on following page)
1,929,442
2,811,415
2,842,424
70
12
tially water immiscible organic extractant medium,
and stripping said acid from said extractant with a
stripping agent;
the improvement in which said stripping comprises:
using a stripping agent comprising water containing
sulfur dioxide in at least an amount substantially
approaching that required to saturate the water
at about 50° C.
2. The process of claim 1 in which an inorganic base
10 capable of forming an insoluble sulfite is added to the
organic extractant after stripping to recover sulfur dioxide
as a sulfite and said sulfite is heated to regenerate sulfur
dioxide.
3. The process of claim 2 in which the base is lime.
4. The process of claim 1 in which the sulfur dioxide
is recovered from the stripped organic extractant by heat.
S. The process of claim 4 in which the organic extractant
is selected from the group consisting of secondary and
20 tertiary amines.
6. The process of claim 1 in which the organic extractant
is selected from the group consisting of amines, lower
aliphatic alcohols, lower aliphatic ketones, and lower aliphatic
phosphate esters.
7. The process of claim 6 in which the organic extractant
is an amine having more than five carbon atoms in the
chain.
S. The process of claim 7 in which an inorganic base
30 capable of forming an insoluble sulfite is added to the
organic extractant after stripping to recover sulfur dioxide
as a sulfite and said sulfite is heated to regenerate sulfur
dioxide.
9. The process of claim 8 in which the base is lime.
10. The process of claim 6 in which the organic extractant
is selected from the group consisting of secondary and
tertiary amines.
11. In a process for the recovery of an acid selected
from the group consisting of sulfuric and phosphoric acids
40 from solutions thereof which comprises the steps of:
extracting the acid from a solution with a substantially
water immiscible organic extractant medium and
stripping said acid from said extractant with a stripping
agent;
the improvement comprising:
using a stripping agent comprising water containing
sulfur dioxide in at least an amount
substantially approaching that required to
saturate the water at about 50° C.;
recovering the sulfur dioxide from the
stripped acid and the extractant; and recycling
the regenerated extractant and the sulfur
dioxide for reuse in the process.
12. The process of claim 11 wherein sulfur dioxide is recovered
from the extractant by adding an inorganic base
capable of forming an insoluble sulfite to the extractant
to recover sulfur dioxide as a sulfite and heating' said
sulfite to regenerate sulfur dioxide.
13. The pmcess of claim 11 wherein said extractant is
selected from the group consisting of secondary and tertiary
amines and the sulfur dioxide is recovered by heating
the extractant.
65 . 14. The process of claim 11 in which the sulfur dioxide
IS recovered from the stripped organic extractant by heating
the extractant.
11
Example 9.-Extraction with tri-caprylyl amine and subsequent
stripping of sulfuric acid with water alone and
with water and sulfur dioxide
A solution of sulfuric acid containing 100 grams of 5
sulfuric acid per liter of solution was agitated with ten
times its volume of a solvent composed of 10 volume
percent tri-caprylyl amine dissolved in kerosene. This
mixture was agitated for three minutes, after which the
phases were allowed to separate. Analysis of the aqueous
phase showed that 98 percent of the sulfuric acid had
been extracted by the solvent.
This solvent was divided into two portions. One portion
was agitated with successive batches of water alone. The
aqueous and organic layers were analyzed with the re- 15
suIts shown in the graph of FIG. 7. The other portion
was agitated with successive batches of water, and sulfur
dioxide bubbled through the mixture while it was
agitated for five minutes. After each agitation the phases
were separated, the excess sulfur dioxide driven from
each phase by boiling, and the solutions analyzed for
sulfuric acid.
The results are shown in the graph of FIG. 7 which
clearly demonstrates the enhanced stripping obtained with
the sulfur dioxide and water. It can be seen that with 25
water alone stripping of the solvent was very inefficient,
whereas with the sulfur dioxide and water not only was
the aqueous strip liquor much more concentrated, but the
solvent was virtually completely stripped of sulfuric acid
content.
The flow diagram of FIG. 8 illustrates how the process
is adaptable to a continous circuit. Acid in the loaded
solvent from the extraction step is stripped with S02'
The solvent is heated to remove S02 and returned to the 35
extraction circuit and the S02 returned to the stripping
circuit. The stripped acid is heated to remove S02 in the
final recovery step and the S02 returned to the stripping
circuit.
The stripping feature of the invention is not particularly
,dependent upon the solvent extractant used as it resides
in the stripping of acid from an acid loaded solvent
extractant with sulfur dioxide and water, thus being
adaptable to any solvent which will extract the acid.
It is seen from the above examples that sulfur dioxide 45
and water are highly effective for stripping acids from
solvent extractants, that sulfur dioxide can be regenerated
from solvents and from the acid after stripping so effectively
that both it and the solvent can be reused, that its use is 50
not dependent upon critical temperature limitations, that
it can be recovered from the solvents by steam or vacuum
distillation or other methods, and that it is effective with
water in the presence of impurities ordinarily present with
the acids. These advantages illustrate that the process is 55
sufficiently economical for commercial adaptation.
A distinct advantage of the process resides in its economic
attractiveness. It makes available for use as a stripping
agent the relatively inexpensive compound, sulfur dioxide.
A further contribution to the economy of the process is 60
the fact that sulfur dioxide can be recovered so effectively
after stripping of the acid that it and the solvent can be
reused in a continuous process.
Although the invention has been illustrated and described
with reference to the preferred embodiments thereof,
it is to be understood that it is in no way limited to
the details of such embodiments, but is capable of numerous
modifications within the scope of the appended
claims.
What is claimed is:
1. In a process for the recovery of an acid selected from
the group consisting of sulfuric and phosphoric acids from
solutions thereof comprising the steps of:
extracting said acid from said solution with a substan- 75
3,333,924
13
2,885,265 5/1959 Cunningham 23-165
2,955,019 10/1960 Dickert et al. 23-102 X
3,072,461 1/1963 Long et al. 23-165
OTHER REFERENCES
Coleman et aI., Proceedings of International Conference
on Eeaceful Uses of Atomic Energy, vol. 28, 1958,
pages 278-288.
5
14
Moore, Analytical Chemistry, vol. 29, No. 11, November
1957, pages 1660---1662.66
Smith et aI., Journal of the Society of Chemical Industry,
vol. 67, No.2, February 1948, pages 48-51.
OSCAR R. VERTIZ, Primary Examiner.
H. T. CARTER, Assistant Examiner.
UNITED STATES PATENT OFFICE
CERTIFICATE OF CORRECTION
Patent No. 3,333,924 August 1, 1967
Wayne C. Hazen et a1.
It is hereby certified that error appears in the above numbered patent
requiring correction and that the said Letters Patent should read as
corrected below.
Column 1, line 19, for "organic" read -- inorganic
Signed and sealed this 25th day of June 1968.
(SEAL)
Attest:
Edward M. Fletcher, Jr.
Attesting Officer .
EDWARD J. BRENNER
Commissioner of Patents
s=MsoN� �ls��0�gin-bottom:0in;margin-bottom:.0001pt;line-height: normal;mso-pagination:none;mso-layout-grid-align:none;text-autospace:none'>leaching reagents and procedures peculiar to the metal 15
being recovered. This feature is illustrated by the per-
·centageyields oCzirconium and molybdenum recovered
in the leach liquors even though the leaching was directed
to the recovery of uranium.
Although the invention has been illustrated and described
with reference to the preferred embodiments thereof,
it is to be understood that it is in no way limited to the
details of such embodiments, but is capable of numerous
modifications with the scope of the appended claims.
What is claimed is:
1. The process for the recovery of metals selected from
the group consisting of uranium, zirconium and molybdenum
from ores of said metals contained in carbonaceous
material which comprises: agglomerating the ore-containing
material to form porous nodules; forming a percolation
leach bed of the nodules; leaching the metal from
the nodules by percolation leaching with a leaching agent;
and recovering the metal from the leach liquor.
2. The process of claim 1 in which a portion of the
leaching agent is added to the are during agglomeration.
3. The process of claim 1 in which the nodules are
cured without drying under high relative humidity conditions.
4. The process of claim 2 in which the nodules are
cured without drying under high relative humidity conditions.
5. The process of claim 1 in which an agglomeration
agent is added to the ore during the agglomeration step.
6. The process of claim 5 in which the agglomeration
agentis a wetting agent.
7. The process of claim 5 in which the agglomeration
agent is a flocculating agent.
S. The process for the recovery of metals selected from
the group consisting of uranium, zirconium and molybdenum
from ores of said metals contained in carbonaceous
material which comprises: forming porous stable nodules
of rthe ore-containing carbonaceous material; forming
a percolation leach bed of the nodules; and percolation
leaching the metal from the nodules with acid leaching
solution.
9. The process of claim 8 in which the acid is sulfuric
acid.
10. The process of claim 9 in which the uranium is recovered
from the leach liquor by solvent extraction. 60
11. The process of claim 8 in which the leaching step
is performed at a pH of less than about two.
12. The process of recovering metals selected from the
group consisting of uranium, zirconium and molybdenum
from ores of said metals contained in carbonaceous mate- 65
rial which comprises: forming the ore-containing carbonaceous
material into stable, porous nodules; forming a
percolation leach bed of the nodules; percolation leaching
the metal from the nodules with an alkaline leaching solution;
and recovering the metal from the leach liquor.
13. The process of claim 12 in which a portion of the
leaching agent is added during forming of the nodules and
the nodules are cured without drying under high relative
humidity conditions.