3,333,924 Recovery of acids

Patent Number/Link:

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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EXTRACTION OF H3P04

WITH AMINE SOLVENT

100 200 300 400 500 600 700

AQUEOUS CONCENTRATION

GM H3P04 PER LITER

STRIPPING OF H3P04

FROM AMINE SOLVENT

WITH .AQUEOUS S02

ADED SOLVENT

GM H3P04 PER LITER

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SOLVENT CONCENTRATION

GM H3P04 PER LITER

INVENTOR.

WAYNE C. HAZEN

ANGUS V HENRICKSON

S~-J~~

ATTORNEYS

Aug. 1, 1967

Filed Jan. 10, 1964

W. C. HAZEN ETAL

RECOVERY OF ACIDS

3,333,924

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20% AMI NE SOLVENT WITH

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100 200 300 400 500

AQUEOUS CONCENTRATION

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FROM AMINE SOLVENT

WITH WATER ALONE

AND WATER AND S02

100 200 300 400 500 600 700

AQUEOUS CONCENTRATION

GM Hl04 PER LITER

INVENTOR.

WAYNE C. HAZEN

ANGUS V. HENRICKSON

S~-J7?~

ATTORNEYS

Aug. 1,1967

Filed Jan; 10, 1964

W. C. HAZEN ETAL

RECOVERY OF ACIDS

3,333,924

4 Sheets-Sheet 3

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STRIPPING OF H3P04

FROM VARIOUS AMINE

SOLVENTS WITH

AQUEOUS S02

100 200 300 400 500 600 700

AQUEOUS CONCENTRATION

GM H3P04 PER LITER

INVENTOR.

WAYNE C. HAZEN

ANGUS V. HENRICKSON

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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H2S04 INORGANIC PHASE (GPL)

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

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-

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

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

Example 2.-Stfipping of HaP04 from tri-caprylyl amine

solvent with aqueous S02

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

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.)

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

tested the most effective temperature is 10° C. and the

least effective is 50° c., indicating that ,at higher temper-

(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

<.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

(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

.__________ 657

504= ---------------_______________________ 106

F- 19.9

R20 S* -------------------- 93.3

Fe 10

3,333,924

'Homologous mixture containing 18-24 carbon atoms-primary amine.

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.

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

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.

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

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.

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.