Selective recovery of zinc from metal containing brines

Zinc is extracted from an aqueous zinc containing brine (3) by contacting the brine with an organic reagent (5) consisting essentially of an extracting agent comprising a quaternary amine salt, a phase modifier, and an organic diluent so as to form a zinc amine complex (7) whereby a substantial portion of the zinc ions in the brine is transferred to the organic phase. The quaternary amine salt is a methyl triakyl ammonium chloride herein the alkyl groups contain from 8 to 10 carbon atoms. The zinc amine complex (7) is then contacted with an aqueous strippant (11) comprising a solution of sodium sulfate in water so as to form a sulfated quaternary amine salt whereby a substantial portion of zinc in the zinc amine complex is stripped therefrom and transferred to the aqueous phase as an aqueous zinc chloride solution (13) from which zinc may be recovered by electrowinning or chemical precipitation.

BACKGROUND OF THE INVENTION 
The present invention relates generally to the recovery of zinc from 
solutions of metallic ions and, more particularly, to a process for 
selectively recovering zinc from brines containing from about 20% to about 
25% by weight of dissolved solids including zinc amongst a variety of 
other metallic ions. 
The term "brine" is commonly applied to any aqueous solution that contains 
a substantial quantity of dissolved metallic solids. One very common type 
of brine is a waste stream or byproduct stream of an industrial process. 
Such brines often have substantial quantities of metallic ions which can 
be of commercial value if recovered, such as magnesium, manganese, zinc, 
potassium, boron, lithium, lead, copper and silver among others. Another 
type of brine is that from geothermal sources below the earth's surface. 
With the increasing use of geothermal energy for the production of 
electricity, this source of brine is becoming more readily available. 
Most geothermal reservoirs consist of hot liquid pools which are maintained 
at high pressure beneath the earth's surface. When these liquid pools are 
tapped for geothermal power generation, a fraction of the liquid brine is 
vaporized in a flash-steam power plant to produce the electricity. The 
remainder of the brine, which remains a liquid, is often reinjected into 
the geothermal reservoir. Geothermal brines typically contain numerous 
dissolved metals in addition to zinc, including sodium, calcium, 
potassium, iron, manganese, barium, strothium, magnesium, boron, lithium, 
lead, copper and silver. It would be commercially advantageous to process 
such geothermal brine prior to reinjection to recover the zinc therefrom. 
Various solvent extraction processes are known for recovering zinc from 
solutions containing zinc in the form of the dissolved ion. For example, 
Canadian Pat. No. 1,026,951 discloses a two-cycle solvent extraction 
process for preparing a zinc solution for electrolytic deposition from a 
solution containing zinc and a high concentration of chloride ions. In the 
first cycle, zinc is extracted from the solution by means of an organic 
solution containing an extracting agent selected from an amine or a 
quaternary ammonium compound of minimum solubility in water and an organic 
diluent. The zinc is then re-extracted from the organic phase with an 
aqueous solution to obtain a zinc enriched aqueous solution. A second 
extraction cycle is then performed wherein the zinc enriched aqueous 
solution from the first cycle is reacted with an organic acid admixtured 
with an organic diluent. The zinc is then re-extracted from the organic 
phase using a strong sulphate acid solution. 
Another zinc extraction process is disclosed in U.S. Pat. No. 4,203,964 
wherein a kerosene solution of an organic amine or phosphorous compound is 
used to extract zinc from an acid chloride-bearing aqueous solution. The 
organic extraction solution is contacted with an aqueous solution of 
sulfuric acid to transfer metal ions and chloride ions to the aqueous 
solution. The acidified aqueous solution is then heated to drive off 
hydrogen chloride in water and recover the zinc as zinc sulfate. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a method for 
selectively recovering zinc from an aqueous brine containing a quantity of 
dissolved metallic ions in addition to the zinc ions. 
It is a further object of the present invention to provide such a method 
for selectively recovering zinc at efficiencies of better than 80%. 
In accordance with the present invention, the aqueous zinc containing brine 
is contacted with an organic reagent consisting essentially of an 
extracting agent comprising a quaternary amine salt, a phase modifier, and 
an organic diluent so as to form a zinc amine complex whereby a 
substantial portion of the zinc ions in the brine are selectively 
extracted therefrom and transferred to the organic phase. The quaternary 
amine salt is a methyl triakyl ammonium chloride wherein the alkyl groups 
contain from 8 to 10 carbon atoms. The zinc amine complex is then 
contacted with an aqueous strippant comprising a solution of sodium 
sulfate in water so as to form a sulfated quaternary amine salt whereby a 
substantial portion of zinc in the zinc amine complex is stripped 
therefrom and transferred to the aqueous phase as an aqueous zinc chloride 
solution. The organic phase sulfated quaternary ammonium salt may then be 
separated from the aqueous zinc chloride solution and the zinc recovered 
from the aqueous chloride solution by electrowinning or chemical 
precipitation.

DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring now to the drawing, there is depicted therein a plant for 
recovering zinc from an aqueous solution, termed "brine" which contains a 
substantial quantity of dissolved metal ions including zinc. The raw 
brine, such as but not limited to that derived fom geothermal wells, 
typically contains numerous dissolved metallic ions in addition to zinc, 
including for example: sodium, potassium, calcium, iron, manganese, 
barium, strontium, magnesium, boron, lithium, lead, copper and silver. 
The raw brine 1 is first passed through a filtering apparatus 10, such as a 
media bed filter, wherein the brine is coarse filtered to remove suspended 
solids therefrom to produce a filtered brine containing dissolved solids 
but relatively free of suspended solids thereby avoiding contamination of 
the downstream extracting, stripping and recovering vessels. The filtered 
brine 3 is passed to an extraction unit 0 which, as in the embodiment 
shown in the drawing, may comprise a single mixer/settler vessel of 
conventional type having a mixing chamber 22 and a settling chamber 26. 
The filtered brine 3 enters the mixing chamber 22 of the extraction unit 
20 and is contacted therein with an organic extraction solution 5 supplied 
from preparation tank 50. The mixing chamber 22 is provided with an 
agitator 24 which stirs the contents of the mixing chamber 22 to 
thoroughly mix the aqueous brine 3 and the organic extraction solution 5. 
After mixing, typically for a residence time of about 5 minutes, the 
aqueous brine and organic extraction solution mixture are passed to the 
settling chamber 26 wherein the mixture is allowed to settle, typically 
for a residence time of about 15 minutes, to permit the organic phase and 
aqueous phase to separate from each other with the organic phase 7 
floating atop the liquid phase 9. The liquid phase 9 comprises a zinc 
deficient brine which may be passed to waste or, in the case of geothermal 
wells, reinjected into the well. The organic phase 7 comprises a zinc 
amine compound, having the general formula (R.sub.4 N).sub.2 ZnCl.sub.4 
wherein the zinc chloride complex is in turn complexed with the two 
quaternary amine radicals. 
The organic phase zinc amine solution is passed from the extraction unit 20 
to the stripping unit 30 which, as in the embodiment shown in the drawing, 
may comprise a single mixer/settler vessel of conventional type having a 
mixing chamber 32 and a settling chamber 26. The organic phase zinc amine 
compound 7 enters the mixing chamber 32 of the extraction unit 30 and is 
contacted therein with an aqueous sodium sulphate stripping solution 11. 
The mixing chamber 32 is also provided with an agitator 34 which stirs the 
contents of the mixing chamber to thoroughly mix the organic phase zinc 
amine complex 7 and the sodium sulfate stripping solution 11. After 
mixing, typically for a residence time of about 5 minutes, the mixture of 
organic phase zinc amine complex and sodium sulfate solution is passed to 
the settling chamber 36 of the stripping unit 30. 
In the settling chamber 36, the mixture is allowed to settle for a 
residence time typically of about 15 minutes to permit the organic phase 
and the aqueous phase to separate. In the stripping process, the zinc is 
transferred from the organic phase zinc amine to form an aqueous phase 
sodium and zinc chloride/sulfate solution 13. The organic phase amine is 
complexed with sulfate from the stripping solution to form an amine 
sulfate complex 15. In the settling chamber 36, the organic phase sulfated 
amine separates from the aqueous phase zinc solution 13 with the organic 
phase 15 floating above the aqueous phase 13. The aqueous zinc solution 13 
is passed from the settling chamber 36 of the stripping vessel 30 to a 
zinc recovery unit 60 wherein zinc is removed from the solution by any of 
a number of well known means, preferably electrowinning or chemical 
precipitation. 
The organic phase sulfated amine solution 15 is passed to an amine recovery 
vessel 40 which, as in the embodiment shown in the drawing, may comprise a 
single mixer/settler vessel of conventional type having a mixing chamber 
42 and a settling chamber 46. The organic phase sulfated amine enters the 
mixing chamber 42 of the amine recovery unit 40 and is contacted therein 
with an aqueous solution 17 containing chloride ions, preferably a sodium 
chloride solution. The mixing chamber 42 is provided with an agitator 44 
which stirs the contents of the mixing chamber 42 to thoroughly mix the 
organic phase sulfated amine and the chloride solution so as to permit 
interaction therebetween whereby the sulfated amine complex will be 
transformed back to a quaternary ammonium chloride and the sulfate ions 
transferred to the aqueous phase. After mixing, again typically for a 
residence time of about 5 minutes, the mixture is passed to the settling 
chamber 46 of the recovery unit 40 and allowed to settle therein for a 
residence time of about 15 minutes to permit separation of the organic 
phase quaternary ammonium chloride and the aqueous phase sulfate and 
chloride solution with the organic phase quaternary ammonium chloride 
solution 21 floating on the aqueous sulfate and chloride solution 19. 
Due to an excess of chloride ions the chloride solution 19 is recycled and 
mixed with makeup sodium chloride to form the aqueous chloride solution 17 
which is to be contacted with the sulfated amine in the recovery vessel 
40. A purge stream 23 is drawn of the aqueous sulfate and chloride 
solution 19 prior to recycle in order to maintain the sulfate ion content 
of the chloride solution 17 passed to the recovery vessel 40 at acceptable 
levels. If chemical precipitation is used for zinc recovery, the purge 
stream 23 may be recycled to the stripping vessel 30 and mixed with makeup 
sodium sulfate to form the sodium sulfate stripping solution 11 admitted 
to the stripping vessel 30 for stripping the zinc tetrachloride ions from 
the amine zinc complex, provided the high chloride ion concentration does 
not become excessive. If electrowinning is used for zinc recovery, the 
purge stream 23 is not recycled. 
In order to reduce consumption of chloride and sulfate in carrying out the 
process of the present invention, the aqueous phase zinc solution 13, 
which contains Zn.sup.++, Na.sup.+, SO.sub.4 = and Cl.sup.- ions, may be 
processed, either before or after zinc recovery, to separate the chloride 
and sulfate ions. For example, if electrowinning is used for zinc 
recovery, the aqueous zinc solution 13 from the settling chamber 36 of the 
stripping vessel 30 may be first processed in separator 70 to remove a 
substantial portion of the chloride ions therefrom prior to introduction 
into the zinc recovery unit 60. The high chloride stream 27 separated from 
the aqueous phase zinc solution 13 in separator 70 would be passed to the 
amine recovery unit 40 as part of the aqueous chloride solution 17 thereby 
reducing make-up chloride consumption. The waste stream 61 from the 
electrowinning process would comprise a predominantly sodium sulfate 
solution suitable for passing to the stripping vessel 30 as part of the 
sulfate solution 11 thereby reducing make-up sodium sulfate consumption. 
If chemical precipitation is used, for example, via zinc carbonate 
formation following soda ash addition to the aqueous phase zinc solution 
in the zinc recovery unit 60, the chloride ions may be separated post zinc 
recovery. In such case, the sodium sulfate/chloride solution 25 remaining 
after zinc recovery is passed from the zinc recovery unit 60 to a 
separator 80 wherein the solution 25 is split into a high chloride ion 
stream 29 and a high sulfate ion stream 31. The high chloride ion stream 
29 would be passed to the amine recovery unit 40 as part of the aqueous 
chloride solution 17 thereby reducing make-up chloride consumption, while 
the high sulfate ion stream 31 would be passed to the stripping vessel 30 
as part of the sulfate solution 11 thereby reducing make-up sodium sulfate 
consumption. 
The organic extraction solution 5 contacted with the filtered brine 3 in 
the extraction vessel 20 consists essentially of a mixture of an 
extracting agent comprising a quaternary ammonium chloride salt, a phase 
modifier, and an organic diluent. The organic phase quaternary ammonium 
chloride solution 21 recovered in the recovery vessel 40 is recycled from 
the separating chamber 46 thereof back to the preparation tank 50 so as to 
reduce the addition of makeup chemicals added to the preparation tank 50 
to produce the quaternary ammonium chloride solution 5 to be contacted 
with the filtered brine 3 in the zinc extraction unit 50. The quaternary 
amine salt which has been found to permit the selective recovery of zinc 
from a brine containing a substantial quantity of other metallic ions in 
addition to zinc is a methyl trialkyl ammonium chloride wherein each of 
the trialkyl groups is a hydrocarbon containing from 8 to 10 carbon atoms. 
The use of this particular quaternary ammonium salt in conjunction with 
the sodium sulfate stripping step and the amine recovery step has produced 
a very economical and extremely efficient process wherein at least 80% of 
the zinc in the brine is recovered with only small amounts of additional 
metals being recovered in addition to the zinc. Therefore, a relatively 
pure zinc solution suitable for electrowinning or chemical precipitation 
can be obtained. 
The phase modifier is included in the organic stripping agent to prevent 
the formation of multiple organic phases as the reagent formulation 
becomes enriched with zinc. The preferred phase modifier is a mixture of 
at least two alcohols, each of the alcohols selected from the group 
consisting of straight and branched chain alcohols containing from 9 to 11 
carbon atoms. However, other commercially available chemicals which have 
been commonly used as phase modifiers in commercial systems, such as 
tributyl phosphate, isodecanol, p-nonylphenol, and 2-ethylhexanol, may 
also be used in the process of the invention. 
The organic diluent to be used in this process must have a sufficiently 
high flash point to preclude potential explosion at the temperatures at 
which the process is carried out. Common organic diluents normally used in 
hydrometallurgy processes may have flash points below the elevated 
temperatures of the brines. Therefore, for safety reasons, the organic 
diluents must have a flash point above that at which the process of the 
present invention is practiced. It was found that an organic diluent 
having a low aromatic content, less than about 1%, was the preferred 
diluent for use in conjunction with the preferred 9 to 11 carbon chain 
alcohol phase modifier. This combination resulted in a formation of only 
one organic phase at high metal loading when the organic extraction 
solution of the present invention was contacted with the filtered brine. 
In laboratory tests to evaluate the process of the present invention, a 
number of different extraction agents were tested to evaluate their 
potential for recovering zinc from synthetic brines containing a 
substantial quantity of metal ions in addition to the zinc ions. Included 
among the chemicals tested were napthenic acid, neo-decanoic acid, 
neo-pentanoic acid, dibutyl butyl phosphonate, Kelex 100, a trialkyl 
tertiary amine, and the methyl trialkyl quaternary amine of the present 
invention. Each of these extraction agents was tested in a extracting 
solution comprising 10% by volume of the extraction agent, 10% by volume 
of the Neodol 91, a mixture of 9 to 11 chain alcohol marketed by Shell 
Chemical Company, as a phase modifier, and 80% by volume of Tellura 705, 
an organic diluent marketed by the Exxon Chemical Company. The synthetic 
brine was at a temperature of 75.degree. F. when contacted with the 
various organic reagent solutions at a ratio of organic extracting 
solution to aqueous brine of 1 to 3. The zinc extraction obtained with 
each of these extracting agents is presented in Table I below: 
TABLE I 
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METAL EXTRACTION FROM SYNTHETIC BRINE 
AT 3:1 AQUEOUS/ORGANIC RATIO AND 75.degree. F. 
Equi- 
% Extraction librium 
Extractant (10 v %) 
Na Ca K Mn Zn Sr Li Ba Pb Mg pH 
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Napthenic Acid 0 9.5 1.9 
0 0 10.3 
0 0 0 0 3.97 
Neo-decanoic Acid 
0 5.1 3.1 
0 0 7.8 
0 0 0 0 4.04 
Neo-pentanoic Acid 
2.0 7.9 0 0 0 0 0 0 0 0 2.85 
Tertiary Amine (Adogen 383) 
2.6 7.5 0 5.2 
51.9 
0 5.2 
0 0 0 2.59 
Quarternary Amine (Adogen 464) 
2.4 8.7 1.2 
0 97.6 
0 2.8 
4.6 
8.9 
0 3.85 
DBBP 7.7 6.3 0 8.6 
1.6 
0 0 0 0 0 2.84 
Kelex 100.sup.(1) 
4.8 7.1 9.3 
0 2.1 
2.6 
0 0 0 0 4.33 
Blank 0 4.7 0 0 0 0 0 0 0 0 5.35 
Absolute Precision 
.+-.1% 
.+-.3% 
.+-.1% 
.+-.1% 
.+-.0.5% 
.+-.2% 
.+-.1% 
.+-.4% 
.+-.4% 
.+-.1% 
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.sup.(1) Keloex 100 is a substituted 8hydroxyquinoline marketed by the 
Sherex Chemical Company. 
As can be seen from Table I, only the tertiary amine, which was Adogen 383, 
a product of the Sherex Chemical Company, and the quaternary amine, Adogen 
464, a product of the Sherex Chemical Company, obtained any appreciable 
zinc removal with the quaternary amine substantially out-performing the 
tertiary amine by extracting 97.6% of the zinc whereas the tertiary amine 
extracted only 51.9% of the zinc. 
To verify the effectiveness of the methyl triakly quaternary amine chloride 
of the present invention in extracting zinc from geothermal brines, field 
tests were performed on a geothermal brine from the Imperial Valley of 
California in a mobile test laboratory. The extractant solution comprised 
a mixture of 10% by volume of a methyl trialkyl quaternary ammonium 
chloride with each of the alkyl groups having 8 to 10 carbon atoms, 10% by 
volume of Neodol 91, a mixture of 9 to 11 chain carbon alcohols, as the 
phase modifier, and 80% by volume of a commercially available mineral seal 
type oil, Tellura 705, with a flash point of more than 200 F. The brine 
was at a temperature of 160 F. when contacted with the organic extraction 
solution at a ratio of organic extraction solution to aqueous brine of 1 
to 3. The results of the extraction for various metals in the brine are 
presented in Table II below. 
TABLE II 
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METAL EXTRACTION FROM GEOTHERMAL BRINE 
Aqueous/Organic Ratio = 3.1 
Fresh Brine - 160 F. 
Brine Connection 
Initial % Final % Recovery 
Metal (wppm) err (wppm) err % err 
______________________________________ 
Na 59481 1.7 60794 0.2 -1.8 1.7 
Ca 32608 2.8 33042 1.5 -1.3 3.2 
K 17023 1.7 17501 0.2 -2.8 1.7 
Fe 2324 1.8 2278 1.2 2.0 2.1 
Mn 1705 1.3 1709 0.6 -0.2 1.4 
Zn 714 1.6 101 2.4 85.9 
2.2 
Sr 592 3.3 595 1.1 -0.6 3.5 
Ba 263 5.4 267 4.2 -1.7 6.9 
Li 252 1.3 260 0.3 -3.2 1.3 
Mg 110 2.2 112 0.0 -2.2 2.2 
Pb 157 14.6 147 7.6 6.1 16.3 
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These results demonstrate the effectiveness of the extraction process of 
the present invention for selectively recovering zinc from metal 
containing brines. Zinc recovery was 85.9%. The selectiveness of the 
process is verified by the fact that the only other metals removed during 
the zinc extraction were iron and lead at levels of 2% and 6.1% 
respectively. Therefore, the process of the present invention is capable 
of greater than 80% selective recovery of zinc from high solids brines, 
such as geothermal brine.