REACTIF SERVANT A ELIMINER LES IONS METALLIQUES D'UNE SOLUTION AQUEUSE PAR UN PROCEDE D'EXTRACTION LIQUIDE/LIQUIDE

METHOD AND A REAGENT MIXTURE FOR REMOVING METAL IONS FROM AN AQUEOUS SOLUTION BY MEANS OF LIQUID-LIQUID EXTRACTION

Abrégé anglais

Abstract: A liquid-liquid extraction process
is disclosed, in which an aqueous
solution, containing metal ions, is
contacted with an organic liquid
substantially insoluble water.
The organic liquid contains two
water-insoluble reagents, viz. a
diester of dithiophosphoric acid
and an organic phosphate, in a pre-
ferred volume ratio of between 1:10
and 2:1. The organic liquid may
also contain a diluent for the
reagents.

Revendications

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A reagent mixture for removing metals from a water solution by means
of liquid extraction, which mixture comprises a dithio phosphoric acid having
the general formula
<IMG>
wherein R1 and R2, independently of each other, represent a hydrophobic group,
R1 and R2 being selected so that the dithiophosphoric acid is insoluble in
water, as well as a water-insoluble phosphate having the general formula
<IMG>
wherein R3 represents a hydrophobic group and R4 and R5, independently of each
other, represent hydrogen or a hydrophobic group, R3, R4 and R5 being selected
so that the phosphate is insoluble in water, in a ratio by volume between the
dithiophosphoric acid and the phosphate of from 1:99 to 9:1.
2. A reagent mixture according to claim 1 wherein the ratio by volume
of dithiophosphoric acid to water-insoluble phosphate is in the range from
1:9 to 2:1.
3. A reagent mixture according to claim 1 or 2, which is diluted with a
diluent in such a quantity that the reagent mixture forms 5 - 80% of the
volume of organic solution.
4. A method of extracting metal ions from an aqueous solution by means
of liquid-liquid extraction which comprises bringing the aqueous solution into
contact with an organic liquid which is insoluble in water and which contains

a reagent mixture including a water-insoluble diester of dithiophosphoric acid
having the general formula
<IMG>
wherein R1 and R2, independently of each other, represent a hydrophobic group,
R1 and R2 being selected so that the dithiophosphoric acid is insoluble in
water, as well as a water-insoluble phosphate having the general formula
<IMG>
wherein R3 represents a hydrophobic group and R4 and R5, independently of each
other, represent hydrogen or a hydrophobic group, R3, R4 and R5 being selected
so that the phosphate is insoluble in water, in a ratio by volume between
the dithiophosphoric acid and the phosphate of from 1:99 to 9:1 whereupon the
metal ions pass to the organic liquid from where said metal ions can be readily
re-extracted and stripped therefrom.
5. A method according to claim 4, wherein the hydrophobic groups R1 and
R2 contain a hydrocarbon residue of 4-24, carbon atoms.
6. A method according to claim 5, wherein R1 and R2, independently of
each other, represent a member selected from the group consisting of a straight
or branched saturated or unsaturated aliphatic group, a cycloaliphatic group,
a phenyl or a mono-, di- or trialkyl-substituted phenyl group, and a group
having the formula R60(A)n-(CH2CH(OH)CH2)m, wherein each A, independently of
the others, represents an oxyalkylene group derived from ethylene oxide, pro-
pylene oxide or butylene oxide, n is a number from 0 - 4, m is 1 or 0, the sum
of n+m being at least 1, and R6 represents a member selected from the group
11

consisting of a straight or branched, saturated or unsaturated aliphatic group,
a phenyl or a mono-, di- or trialkyl-substituted phenyl group, and a cycloali-
phatic group.
7. A method according to claim 4, wherein the hydrophobic groups R3, R4
and R5 contain a hydrocarbon residue of 3 to 24 carbon atoms.
8. A method according to claim 7, wherein the hydrophobic groups R3, R4
and R5, independently of each other, represent a member selected from the
group consisting of a straight or branched, saturated or unsaturated alipha-
tic group, a cycloaliphatic group, a phenyl, a mono-, di- or trialkyl-substituted
phenyl group, and a group having the formula R70(A)n-(CH2CH(OH)CH2)m wherein
each A, independently of the others, represents an oxyalkylene group derived
from ethylene oxide, propylene oxide or butylene oxide, n is a number from
0 - 4, m is 0 or 1, the sum of m+n being at least 1, and R7 represents a mem-
ber selected from the group consisting of a straight or branched, saturated
or unsaturated aliphatic group, a phenyl, a mono-,di- or trialkyl-substituted
phenyl group and a cycloaliphatic group.
9. A method according to claim 4, 5 or 6, wherein R1 and R2, independently
of each other represent a member selected from the group consisting of a
straight or branched, saturated or unsaturated aliphatic group, a cycloalipha-
tic group, a phenyl group and a mono-, di- or trialkyl-substituted phenyl group
with a total of 4-24 carbon atoms in the relevant groups and R3, R4 and R5 rep-
resent independently of each other a member selected from the group consisting
of a straight or branched, saturated or unsaturated aliphatic group, a cyclo-
aliphatic group, a phenyl group and a mono, di- or trialkyl-substituted phenyl
group with a total of 3-24 carbon atoms in said groups.
10. A method according to claim 4, 5 or 6, wherein R1 and R2, independently
of each other represent a member selected from the group consisting of a
12

straight or branched, saturated or unsaturated aliphatic group, a cycloaliphatic
group, a phenyl group and a mono-, di-, or trialkyl-substituted phenyl group
with a total of 6-16 carbon atoms in the relevant groups and R3, R4 and R5
represent independently of each other a member selected from the group con-
sisting of a straight or branched, saturated or unsaturated aliphatic group,
a cycloaliphatic group, a phenyl group and a mono-, di-, or trialkyl-substituted
phenyl group with a total of 3-24 carbon atoms in said groups.
11. A method according to claim 4, 5 or 6, wherein the water solution con-
tains sulphuric acid or hydrochloric acid, in a content of 0.1 - 6.0 mol per
liter.
12. A method according to claim 4, 5 or 6, wherein the ratio by volume of
the dithiophosphoric acid and the phosphate is from 1:10 to 2:1.
13. A method according to claim 4, 5 or 6 wherein the hydrophobic groups
R1 and R2 contain a hydrocarbon residue of 6-16 carbon atoms.
14. A method according to claim 4, 5 or 6 wherein R1 and R2, independently
of each other, represent a member selected from the group consisting of a
straight or branched, saturated or unsaturated aliphatic group, a cyclo-
aliphatic group, a phenyl group and a mono-, di-, or trialkyl-substituted
phenyl group with a total of 6-16 carbon atoms in the relevant groups.
15. A method according to claim 4, 5 or 6 wherein the aqueous solution
contains at least one ion selected from the group consisting of iron, zinc,
copper, nickel, cadmium, chromium, manganese and cobalt.
13

Description

-~ ~L~Z0~4
The invention relates to a method and a reagent mixture for re-
moving metal ions from an aqueous solution by means of liquid-liquid extrac- ~` `
tion.
It is known that an alkyldithiophosphoric acid is a useful reagent
for extraction of nickel ions from an acid aqueous solution with the help
of an organic solution. However, there are certain drawbacks with the known
liquid-liquid extraction process. The washing ~re-extraction) of the nickel
ions out of the organic solution is a very slow process. Furthermore, an
aqueous solution with a high acid contbnt must be used to wash the nickel
ions out of the organic solution.
According to the invention it has now been found that these draw-
backs can be reduced if a diester of dithiophosphoric acid is used in
combination with a phosphate as a reagent mixture for the liquid-liquid
extraction. Furthermore, it has been found possible with extremely good
results to extract, to re-extract and in many cases even to separate metal
ions such as ions of iron, zinc, copper, nickel, cadmium, chromium and
manganese, by using the new reagent mixture. The method according to the
invention is characterized in that the aqueous solution containing metal
ions is brought into contact with an organic liquid containing a water-
insoluble diester of dithiophosphoric acid having the general formula
R1\ Ds '.
p
R20 \ SH
in which Rl and R2, independently of each other, represent a hydrophobic
group, Rl and R2 being selected in such a way that the dithiophosphoric acid
is insoluble in water, and a water-insoluble phosphate having the general
formula R 0
3 \ ~ 0
/ \ " '
R40 5
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in which R3 represen$s a hydrophobic group and R4 and R5, independently
of each other, represent hydrogen or a hydrophobic group, R3, R4 and R5
being selected in such a way that the phosphate is insoluble in water, in
a ratio by volume between the dithiophosphoric acid and the phosphate of
from 1:99 to 9:1, whereupon the metal ions pass to the organic liquid.
The invention also covers the reagent mixture defined above. The
preferred volume ratio of dithiophosphoric acid to phosphate in said reagent
mixture is between 1 to 9 and 2 to 1. The reagent mixture may also contain
a diluent, such as kerosene.
To prevent the dithiophosphoric acid from being noticeably soluble
m water, the hydrophobic groups preferably contains a hydrocarbon residue
of at least 4 carbon atoms, preferably at least 6 carbon atoms. If there
; are more than 24 carbon atoms in the hydrocarbon residue, the extraction
capacity will be reduced. The number of carbon atoms in said hydrocarbon
residue should preferably not be greater than 16. Examples of such hydro-
phobic groups are a straight or branched, saturated or unsaturated aliphatic
groupJ a cycloaliphatic group, a phenyl or a mono-, di- or trialkyl-sub-
stituted phenyl group, or a group having the formula R60(A)n-(CH2CH(OH)CH2)m,
in which each A, independently of the others, represents an oxialkylene
group derived from ethylene oxide, propylene oxide or butylene oxide, n is
a number from 0-4, m is 0 or 1, the sum of m+n being at least 1, and R6
represents a straight or branched, saturated or unsaturated aliphatic group,
a phenyl or a mono-, di- or trialkyl-substituted phenyl group or a cyclo-
aliphatic group. Illustrative examples of Rl, R2 and R6 as aliphatic groups
are butyl, pentyl, hexyl, heptyl, octyl, isoctyl, 2-ethylhexyl, nonyl, isonyl,
decyl, isodecyl, dodecyl, myristyl, palmityl, stearyl, oleyl, ricinoleyl,
arachidyl and behenyl.
If Rl, R2 and R6 represent a cycloaliphatic group, then cyclohexyl,
cyclohexylethyl, cyclohexylbutyl, ethylcyclohexyl, butylcyclohexyl, hexyl-
cyclohexyl and octylcyclohexyl are especially recommended.
If Rl, R2 and R6 represent an aromatic group, useful examples are
,, '
:' :
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phenyl, methylphenyl, dimethylphenyl, propylphenyl, dipropylphenyl, butyl-
phenyl, dibutylphenyl, octylphenyl, dioctylphenyl, nonylphenyl, dinonylphenyl
and dodecylphenyl.
Illustrative examples of group A are oxyethylene, l-oxypropylene,
; 2-oxypropylene, 2-oxy-2,3-butylene and 1-oxy-1,2-butylene.
In order to give the phosphate a low solubility in water, the
hydrophobic group preferably contains a hydrocarbon residue of at least 3
; carbon atoms. There is no upper critical limit for the number of carbon
atoms in said hydrocarbon residue, but the upper limit is suitably not higher
than 24, preferably not higher than 16 carbon atoms. Examples of hydrophobic
groups are a straight or branched, saturated or unsaturated aliphatic group, -
a phenyl or a mono-, di- or trialkyl-substituted phenyl group, or a group
having the formula R70(A)n -~CH2-CH~OH)CH2) , in which each A, independently
of the others, represents an oxyalkylene group derived from ethylene oxide,
i propylene oxide or butylene oxide, n is a number from 0-4, m is 0 or 1, the
sum of n~m being at least 1, and R7 represents a straight or branched, satu-
rated or unsaturated aliphatic group, a phenyl or a mono-, di- or tri- alkyl-
substituted phenyl group, or a cycloaliphatic group.
Illustrative examples of R3, R4, R5 and R7 as aliphatic groups are
-20 propyl, butyl, pentyl, hexyl, heptyl, octyl, isoctyl, 2-ethylhexyl, nonyl,
isonyl, decyl, isodecyl, dodecyl, myristyl, palmityl, stearyl, oleyl, rici- ~ -
' noleyl, arachidyl and behenyl.
~ If R3, R4, R5 and R7 represent a cycloaliphatic group, then cyclo-
! hexyl, cyclohexylethyl, cyclohexylbutyl, ethylcyclohexyl, butylcyclohexyl,
hexylcyclohexyl and octylcyclohexyl are particularly recommended.
If R3, R4, R5 and R7 represent an aromatic group, useful examples
are phenyl, methylphenyl, dimethylphenyl, propylphenyl, dipropylphenyl~
butylphenyl, dibutylphenyl, octylphenyl, dioctylphenyl, nonylphenyl, dinonyl-
, phenyl and docecylphenyl.
Illustrative examples of group A are oxyethylene, l-oxypropylene,
.
' :. ' - " ' : ' ' . : '' , . , ~' ~ :. :' ' ' ' ,

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2-oxypropylene, 2-oxy- 2, 3-butylene and l-oxy-l, 2-butylene.
As ex~raction reagent a mixture of dithiophosphoric acid and
phosphate is preferred in which the groups Rl, R2, R3, R~ and R5, independently
of each other, represent an aliphatic, cycloaliphatic or aromatic group.
If the dithiophosphoric acid or the phosphate or both have suitable
physical properties, the organic liquid may consist only of the phosphate
and the dithiophosphoric acid. However, generally, and particularly if the
reagent mixture consists mainly of dithiophosphoric acid, it is preferred to
dilute the reagent mixture with a diluent, suitably in such proportions that
the reagent mixture constitutes 5 - 80% of the volume of the organic solution.
The diluent should be a good solvent for dithiophosphoric acid and should
also be difficult to dissolve in water. Examples of useful diluents are an
aliphatic or aromatic hydrocarbon of low viscosity at the working temperature,
such as a petroleum fraction with a boiling point interval corresponding to
that of kerosene and having a high flash-point, which is important from the
point of view of safety, or a chlorinated hydrocarbon such as carbon tetra-
chloride, perchloroethylene.
The extraction and also the washing out of the metal ions from the
organic solution can be performed in conventional manner for liquid-liquid
extraction processes. An apparatus of the "mixer-settler" type is preferably
used, having a mixing chamber in which the two liquids are intimately mixed
with the help of a stirrer and a separation chamber in which the two liquids ;
are allowed to separate due to their differing densities. The extraction
and the washing is performed at normal temperature, but it is preferred to use
an increased temperature, for instance 35 - 60C.
The method and the reagent mixture according to the invention can ; ~ ;~
be used for extraction of several metal ions from aqueous solutions, pref-
erably solutions containing free sulphuric acid or hydrochloric acid, suitably -
0.1 - 1.0 mol per liter. Metal ions worth extracting are primarily ions of ~ ~ ~
chromium, manganese,-iron, cobalt, nickel, zinc, cadmium and copper, since ;
_ 5
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these metals often constitute the main proportion of the metal content in
waste solutions, such as drainage water from metal mines, leaching solutions
obtained from leaching dust, ashes, hydroxide deposit, etc. from plants for
pickling metal with acid, from plants for electrolytic coating of metal, or
from other surface-treatment plants. The following examples are intended to
further illustrate the invention.
A water solution containing ions of Cr3 , Mn , Ni , Fe , Co
zn2 , Cd2+ or Cu2+ in a quantity of 0.1 g/l was extracted with a kerosene
solution containing 60 per cent by volume of a reagent mixture consisting of
tributyl phosphate and dioctyldithiophosphoric acid in a ratio of 5:1 by
volume. The distribution of the metals between the water phase and the
organic phase was determined at varying contents of sulphuric acid and hydro-
chloric acid. The result obtained can be seen in the diagrams of Figures 1
and 2, where the abscissa represents the quantity of free sulphuric acid,
or free hydrochloric acid, in the metalliferous water solution, expressed in
mol per liter. The ordinate represents the percentage of extracted metal
(%E), i.e. the quantity of metal, expressed in percentage, which has been
transferred to the organic solution. More spcifically % E is defined in
; the following manner:
D 0 100
% E = -~~~~~~
D is the distribution factor, i.e. the ratio between the concentration
of metal ions in the organic solution and in the water solution. 0 is the
phase ratio, i.e. the volume ratio between the organic solution and the ;
water solution.
. .: .
The usefulness of the invention is exemplified by reference to -
nickel, whicn is of particular interest since the reagent mixture according
to the invention enables the nickel ions to be extracted and, more important,
quickly washed out of an acid aqueous solution.
The diagrams show that the entire nickel content is found in the
organic solution if the content of free acid in the water solution is at
- 6 -

~l05~84
~ . .
most approximately 0.2 mol/l. It is thus possible to almost completely
transfer the nickel ions to the organic solution i the content of free acid
in the aqueous solution does not exceed 0.2 mol/l. It can also be seen
from the diagrams that only 5% of the nickel content is contained in the
organic solution if the content of free acid in the aqueous solution is
approximately 3 mol/l. It is thus possible to substantially completely wash
out the nickel ions from the organic solution with a water solution of
sulphuric acid or hydrochloric acid containing at least 3 mol free acid per
liter. The organic solution washed in this manner can then be used for -~
renewed extraction. Nickel can be recovered from the nickel-containing acid
solution in various ways, such as in the form of metal by means of elec-
trolysis, or as nickel sulphate or nickel chloride by means of crystallization. ;
The diagrams also show that the entire quantity of chromium exists
in the water solution whatever the degree of acidity, and that the chromium
ions cannot be extracted by the method according to the invention. This means
that the invention enables nickel to be effectively separated from chromium
by means of a liquid-liquid extraction.
The diagrams also show that bivalent cadmium and copper ions are
extracted to the organic solution at all degrees of acidity. These metal
ions can easily be removed from acid water solutions by means of the method
according to the invention. On the other hand, they cannot be washed out
of the organic solution with an acid solution, and other methods must
therefore be used, such as direct precipitation of the metal sulphides in
the organic solution, followed by filtration. The most efficient method in
this case lS to blow hydrogen sulphide through the organic solution. Alter-
natively, the organic solution may be washed with an aqueous solution
containing sodium sulphide.
Examples 1-3:
A water solution containing ions of Fe2 , Fe3 ,~ zn2 , Ni2 or Cu2
was extracted at varying contents of sulphuric acid with a kerosene solution

containing 40 per cent by volume of a reagent mixture consisting of dicyclo-
hexyldithiophosphoric acid and tributyl phosphate in a ratio of (1) 1~ 2)
1:5 and (3) 1:10 by volume. From the results shown in the Table, it is clear
that all the metal ions tested can easily be extracted with the reagent
mixture. The higher the content of dithiophosphoric acid the better. It is
also clear that iron ions can be separated from zinc, nickel and copper ions j -~
with the reagent mixture.
Examples 4-6:
A water solution containing ions of Fe , Fe , Zn , Ni or
Cu2 was extracted at varying contents of sulphuric acid with a kerosene
solution containing 40 per cent by volume of a reagent mixture consisting of
(4) di~nonylphenyl-di(oxyethylene~] dithiophosphoric acid and tributyl phos-
phate, (5) dicyclohexyldithiophosphoric acid and tricyclohexyl phosphate,
or (6) di(nonylphenyl)dithiophosphoric acid and tri(nonylphenyl)phosphate in
a ratio of 1:5 by volume for all the reagent mixtures. The results shown in
the Table indicate that all the reagent mixtures are well able to extract one
or more of the metal ions in question.
Examples 7-8:
A water solution containing ions- of Fe2 , Fe3 , zn2 , Ni2 or
Cu2 was extracted at varying contents of sulphuric acid with a kerosene
solution containing (7) 60 and (8~ 3~ per cent hy volume, respectively, of
an extraction mixture consisting of di~ethylhexyll-dithiophosphoric acid and
tributyl phosphate in a ratio of 1:5. The result shown in the Table indicates
that the reagent mixture extracts better at high concentration than at low -
concentration. his is as might te expected.
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