Selective removal of chromium, nickel, cobalt, copper and lead cations from aqueous effluent solutions

Aqueous effluent solutions containing metal cations may be treated with an extractant comprising an organophosphinic acid, a di-2-ethylhexyl phosphoric acid and/or an aliphatic amine to selectively separate chromium, nickel, cobalt, copper and lead cations from the aqueous solution. Typical extraction techniques include liquid-liquid extraction employing either mixer settlers or columns, liquid membrane extraction and selective supported membrane extraction.

BACKGROUND OF THE INVENTION 
The present invention relates to the recovery of metal cations from aqueous 
effluent solutions, especially aqueous effluent solutions from metal 
finishing plants, by solvent extraction and stripping techniques. 
The removal of copper, nickel and chromium from the aqueous effluent of a 
metal finishing plant is known. In a typical known system, the metals are 
recovered by short bed ion exchange. Periodically, the ion exchangers are 
regenerated to yield a concentrated metal salt solution which is recycled 
to the appropriate plating bath. "Copper, Nickel, and Chrome Recovery in a 
Jobshop to Eliminate Waste Treatment and Sludge Disposal", Michael Dejak 
et al, Hazardous Waste & Hazardous Materials, Vol. 4, No. 3, 1987. See 
U.S. Pat. No. 4,186,174. 
There is still a need, however, for other methods of removing metal cations 
from metal finishing plant effluent which are efficient and 
cost-effective. 
SUMMARY OF THE INVENTION 
The present invention provides a process for the selective removal of metal 
cations (e.g., chromium, nickel, cobalt, copper and lead cations) from 
aqueous effluent solutions, especially aqueous effluent solutions from 
metal finishing plants, by solvent extraction and stripping techniques. 
The extractant comprises an organophosphinic acid, a di-2-ethylhexyl 
phosphoric acid and/or an aliphatic amine.

DETAILED DESCRIPTION OF THE INVENTION 
In carrying out the present invention, extraction techniques compatible 
with an extractant comprising an organophosphinic acid, a di-2-ethylhexyl 
phosphoric acid and/or an aliphatic amine are employed and include, but 
are not limited to, liquid-liquid extraction employing either 
mixer-settlers or columns, such as pulse columns, liquid membrane 
extraction and selective supported membrane extraction. 
An organic-soluble phosphinic acid or salt thereof extractant may be used 
in the extraction of metal cations. The free phosphinic acids and their 
alkali metal or ammonium salts are preferred, but other salts may be 
employed. Although pure extractant can be used, it is generally preferred 
to employ a diluent comprising from about 2 to 99 parts by volume of 
extractant with from about 98 to 1 parts by volume of a water-immiscible 
organic diluent, preferably from about 2 to 70 parts by volume of the 
extractant with from about 98 to 30 parts by volume of diluent. The 
diluent may optionally contain from about 1 to 15 parts by volume of a 
phase modifier to promote the separation of the phases and/or increase the 
solubility of the extracted metal cation in the organic phase. If a phase 
modifier is employed, the amount of organic diluent used should be reduced 
by a corresponding amount. 
Generally, a wide variety of water-immiscible organic liquids may be used 
as the diluent. Suitable diluents include, but are not limited to, carbon 
tetrachloride, toluene, xylene, kerosene, naphtha, tridecanol, 
methylisobutylketone, tributylphosphate, cyclohexane, decane, pyridine, 
dibromoethane, and the like. Preferably, the diluent is an aliphatic or 
aromatic petroleum distillate. Suitable phase modifiers, when employed, 
include: tributylphosphate, trimethylphosphine oxide, tributylphosphine 
oxide, trihexyl phosphine oxide, triootylphosphine oxide, isodecanol, and 
the like. The preferred process employs bis(2,4,4-trimethylpentyl) 
phosphinic acid (e.g., American Cyanamid Company, CYANEX 272) which is 
totally miscible with common aromatic and aliphatic diluents. 
The organic-soluble phosphinic acid or salt thereof is generally 
represented by the following structure: 
##STR1## 
wherein R.sub.1 and R.sub.2 are individually substituted or unsubstituted 
alkyl, cycloalkyl, alkoxyalkyl, alkylcyclo alkyl, aryl, alkylaryl, aralkyl 
or cycloalkylaryl radicals and X is either hydrogen or a salt-forming 
radical. Preferably, the organic-soluble phosphinic acid is 
bis(2,4,4-trimethylpentyl) phosphinic acid. Typical other organophosphinic 
acids which may be employed are listed in U.S. Pat. No. 4,348,367. 
In carrying out the process of the present invention, the aqueous solution 
is contacted either by batch, co-current or counter-current contact, with 
the organic phosphinic extractant. The aqueous solution should have a pH 
of at least 3 depending on the metal to be removed. It is preferred that 
the aqueous solution have a pH of about 4 to 8. Aqueous to organic ratios 
of from about 1:20 to 20:1 are believed to be effective. Phase contact is 
suitably achieved in "mixer-settlers", although many other types of 
devices are also suitable. In the mixer, one phase is dispersed within the 
other by stirring or some other appropriate form of agitation. The 
extractant then forms a complex with the metal(s) in the organic phase of 
the two-phase liquid mixture. The dispersion then flows to the settler 
where phase disengagement occurs under quiescent conditions. Generally, 
extraction is carried out between about 0-80 degrees C., preferably about 
20-70 degrees C. 
The pregnant extractant is stripped by contacting it with a solution of a 
mineral acid at about 0-80 degrees C., preferably about 20-60 degrees C., 
at a pH of approximately 0.5 to 6. The mineral acid preferably has a 
concentration of about 0.001 to 250 g/l. Aqueous to organic ratios of 
about 0.1 to 1.0 are suitable. As a result, the metal cation forms a 
soluble salt of the mineral acid employed. Phase contact may be achieved 
with mixer-settlers, or other suitable devices. Suitable mineral acids 
include sulfuric, hydrochloric, hydrofluoric, nitric, and the like. 
The stripped extractant is recycled to the contactor for treatment of 
incoming aqueous solution. The extractant may be recycled to the contactor 
in the form of the free phosphinic acid. In this case, pH control by the 
addition of a base is required in the contactor. Alternatively, the 
recycled solvent may be pretreated and converted to the alkali metal or 
ammonium salt form before returning to the contactor. In the latter case, 
pH control is not required. 
Depending on the metal cation to be extracted, the extractant may also be 
di-2-ethylhexyl phosphoric acid ("DEPA") or salt thereof. Although pure 
extractant can be used, it is generally preferred to employ a diluent 
comprising from about 1 to 40 parts by volume of extractant with from 
about 60 to 99 parts by volume of a water-immiscible organic diluent, 
preferably from about 5 to 10 parts by volume of the extractant with from 
about 90 to 95 parts by volume of the diluent. The diluent may be 
aliphatic or aromatic and the same type of diluent may be employed as with 
the organophosphinic acid extractant. The extractant solution preferably 
contains a modifier such as discussed herein with respect to the 
organophosphinic acid extractant. 
In carrying out the process of the present invention, the aqueous solution 
is contacted with the DEPA as discussed herein with respect to the 
organophosphinic acid extractant. The aqueous solution should have a pH of 
at least 2 depending on the metal cation to be recovered. It is preferred 
that the aqueous solution have a pH of about 2 to 5. Aqueous to organic 
ratios of from about 0.1 to 20 are believed to be effective. Phase contact 
is achieved in "mixture-settlers" and the like as discussed herein with 
respect to the organophosphinic acid extractant. Generally, extraction is 
carried out between about 10 to 70 degrees C., preferably about 15 to 30 
degrees C. 
The pregnant extractant is stripped by contacting it with a mineral acid at 
about 20 to 80 degrees C., preferably about 30 to 50 degrees C., at a pH 
of approximately 0.5 to 5. The mineral acid preferably has a concentration 
of about 0.001 to 250 g/l. Aqueous to organic ratios of about 0.1 to 10 
are suitable. As a result, the metal anion forms a soluble salt of the 
mineral acid employed. Phase contact may be achieved with mixer-settlers, 
or other suitable devices. Suitable mineral acids are those discussed 
herein for stripping the organophosphinic acid extractant. 
The stripped extractant is recycled to the contactor for treatment of 
incoming aqueous solutions. The extractant may be recycled to the 
contactor in the form of free DEPA or converted to the salt form before 
returning to the contactor. 
Depending on the metal cation to be extracted, the extractant also may be 
an aliphatic amine, preferably an aliphatic quaternary amine. Although 
pure extractant can be used, it is generally preferred to employ a diluent 
comprising from about 1 to 40 parts by volume of extractant with from 
about 60 to 99 parts by volume of a water-immiscible organic diluent, 
preferably from about 5 to 10 parts by volume of the extractant with from 
about 90 to 95 parts by volume of the diluent. The diluent may be 
aliphatic or aromatic and the same type of diluent may be employed as with 
the organophosphinic acid extractant. 
The aliphatic amine may be a primary, secondary or tertiary amine. The 
aliphatic portion of the amine extractant is preferably alkyl such as 
octyl or decyl. Preferably, the aliphatic amine is triootyl methyl 
ammonium hydroxide. A typical other aliphatic amines which may be employed 
is tridecyl methyl ammonium hydroxide. 
In carrying out the process of the present invention, the aqueous solution 
is contacted with the aliphatic amine as discussed herein with respect to 
the organophosphinic acid extractant. The aqueous solution should have a 
pH of at least 2 depending on the acidic anion to be recovered. It is 
preferred that the aqueous solution have a pH of about 3 to 8. Aqueous to 
organic ratios of from about 0.1 to 10 are believed to be effective. Phase 
contact is achieved in "mixture-settlers" and the like as discussed herein 
with respect to the organophosphinic acid extractant. Generally, 
extraction is carried out between about 20 to 45 degrees C., preferably 25 
to 35 degrees C. 
The pregnant extractant is stripped by contacting it with a solution of an 
alkali metal or ammonium salt at about 45 to 80 degrees C., preferably 
about 35 to 65 degrees C., at a pH of approximately 8 to 10. The alkali 
metal or ammonium salt preferably has a concentration of about 50 to 150 
g/l. Aqueous to organic ratios of about 0.1 to 10 are suitable. As a 
result, the acidic anion forms a soluble salt of the alkali metal or 
ammonium salt employed. Phase contact may be achieved with mixer-settlers, 
or other suitable devices. The preferred alkali metal or ammonium salt is 
ammonium hydroxide. The stripped extractant is recycled to the contactor 
for treatment of incoming aqueous solution. 
The process of the present invention is used to treat effluent from metal 
finishing plants and the like to yield water containing less than about 1 
ppm of dissolved metal anions. A typical metal finishing plant is a 
printed circuit board manufacturing plant which requires electroplating, 
etching, and cleaning processes that generate metal-bearing rinse water. 
Metal concentrations are typically between about 1 and 200 ppm, more 
typically between about 1 and 30 ppm. 
Electrolytes in aqueous solution dissociate, to a greater or lesser degree, 
into anions and cations. Typical effluent from a metal finishing plant 
contains one or more of the following electrolytes and resulting cations 
and anions: 
______________________________________ 
Cation Anion 
______________________________________ 
Sulphuric acid H.sub.2 SO.sub.4 
2H++ SO.sub.4 -- 
Nickel Sulphate NiSO.sub.4 
Ni++ SO.sub.4 -- 
Copper Sulphate CuSO.sub.4 
Cu++ SO.sub.4 -- 
Lead Sulfate PbSO.sub.4 
Pb++ SO.sub.4 -- 
Cobalt Sulfate CoSO.sub.4 
Co++ SO.sub.4 -- 
Divalent Chromous Sulphate CrSO.sub.4 
Cr++ SO.sub.4 -- 
Trivalent Chromic Sulphate Cr.sub.2 (SO.sub.4).sub.3 
2Cr+++ 3SO.sub.4 -- 
Hexavalent Chromic Acid H.sub.2 CrO.sub.4 
2H++ CrO.sub.4 -- 
______________________________________ 
To provide a better understanding of the process of the present invention, 
the process will be described in general with reference to the 
accompanying figure. Rinse water from the plating solution in the metal 
finishing plant is fed via line 10 to filter 12. Filter 12 is a 
cartridge-type filter which can remove particles down to 10 microns. From 
filter 12, the rinse water flows via line 14 to carbon tower 16. Carbon 
tower 16 is a conventional carbon filter for removing organics and the 
like. After passing through carbon tower 16, the rinse water passes via 
line 18 to contactor 20. Contactor 20 is a mixer-settler or other 
contactor is described herein. In contactor 20, the rinse water is 
contacted with barren extractant recycled to contactor 20 via line 22. 
After separation, the aqueous phase is fed via line 24 through carbon 
tower 26 to remove any residual organics and is then recycled to the 
plating operation or discharge from the metal finishing plant via line 28. 
After phase separation, the pregnant extractant is fed via line 30 to 
stripping unit 32 which may be a mixer-settler or the like. In stripping 
unit 32, the pregnant extractant is contacted with a stripping solution 
fed to stripping unit 32 via line 34 from stripping solution tank 36. The 
stripping solution may be, for example, sulfuric acid in the case of an 
organophosphinic acid extractant or a DEPA extractant, or ammonium 
hydroxide in the case of an aliphatic amine extractant. After phase 
separation, the barren extractant is recycled to contactor 20 via line 22 
and the metal anion concentrate solution is removed from the stripping 
unit 32 via line 38. If the metal concentrate solution is to be treated in 
a remote refinery, it may be stored in storage tank 40 and removed from 
the metal 
.TM.for further treatment at a remote finishing plant via line 42 for the 
treatment at a remote location. It will be understood that the process 
flow diagram of the accompanying figure will be modified as required to 
accommodate additional extraction, stripping, scrubbing and re-extraction 
steps as will be discussed herein. 
Chromium Recovery 
An aliphatic amine extractant such as trioctyl methyl ammonium hydroxide 
(R.sub.4 NOH) dissolved in kerosene is used to clean up an aqueous 
solution containing traces of sulfuric acid and chromic acid. The aqueous 
solution at pH of about 2 to 8, preferably at pH of about 6 to 8, is first 
extracted with R.sub.4 NOH. 
______________________________________ 
A. Extraction 
Aqueous Phase Extractant Phase 
______________________________________ 
In H.sub.2 SO.sub.4 +H.sub.2 CrO.sub.4 +H.sub.2 O 
R.sub.4 NOH 
Out H.sub.2 O (R.sub.4 N).sub.2 CrO.sub.4 
(R.sub.4 N).sub.2 SO.sub.4 
______________________________________ 
The pregnant extractant is then stripped with ammonium hydroxide (NH.sub.4 
OH). 
______________________________________ 
B. Strip 
Aqueous Phase Extractant Phase 
______________________________________ 
In NH.sub.4 OH+H.sub.2 O 
(R.sub.4 N).sub.2 CrO.sub.4 
(R.sub.4 N).sub.2 SO.sub.4 
Out H.sub.2 O+(NH.sub.4).sub.2 CrO.sub.4 +(NH.sub.4).sub.2 SO.sub.4 
R.sub.4 NOH 
______________________________________ 
The barren extractant (R.sub.4 NOH) is recycled to the extraction stage and 
the aqueous strip solution shipped to a remote refinery. The chromic 
cation is recovered at the remote refinery by re-extracting the aqueous 
strip solution at pH of about 2 to 8, preferably at pH of about 6 to 8, 
with an aliphatic amine. 
______________________________________ 
C. Re-extraction 
Aqueous Phase Extractant Phase 
______________________________________ 
In H.sub.2 0+(NH.sub.4).sub.2 CrO.sub.4 +(NH.sub.4).sub.2 SO.sub.4 
+H.sub.2 SO.sub.4 R.sub.4 NOH 
Out H.sub.2 O+(NH.sub.4).sub.2 SO.sub.4 
(R.sub.4 N).sub.2 CrO.sub.4 
______________________________________ 
The aqueous phase is disposed of to the fertilizer industry, for example, 
and the pregnant extractant stripped with ammonium hydroxide. 
______________________________________ 
D. Strip 
Aqueous Phase Extractant Phase 
______________________________________ 
In NH.sub.4 OH+H.sub.2 O 
(R.sub.4 N).sub.2 CrO.sub.4 
Out (NH.sub.4).sub.2 CrO.sub.4 +H.sub.2 O 
R.sub.4 NOH 
______________________________________ 
The barren extractant (R.sub.4 NOH) is recycled to the reextraction stage, 
and the chromium is recovered from the (NH.sub.4).sub.2 CrO.sub.4 by 
crystallization. 
Selective Recovery of Chromium, Cobalt and Nickel 
An aqueous solution containing traces of chromic acid, nickel sulphate and 
cobalt sulphate having a pH of about 2 to 8, preferably a pH of about 6 to 
8, is extracted with an aliphatic amine (R.sub.4 NOH) as in "Chromium 
Recovery". 
______________________________________ 
A. First Extraction 
Aqueous Phase Extractant Phase 
______________________________________ 
In H.sub.2 CrO.sub.4,NiSO.sub.4,CoSO.sub.4,NaOH+H.sub.2 O 
R.sub.4 NOH 
Out NiSO.sub.4,CoSO.sub.4,NaOH+H.sub.2 O 
(R.sub.4 N).sub.2 CrO.sub.4 
______________________________________ 
The pregnant extractant is stripped and shipped to a remote refinery for 
further processing in an identical manner to that in "Chromium Recovery". 
The aqueous solution at a pH of 5 proceeds to the second extraction and is 
extracted with DEPA dissolved in kerosene with isodecanol as a modifier. 
The extraction results in cobalt and nickel being extracted and alkali 
metal salts (e.g., Na), as well as alkaline earth metal salts (e.g., Ca, 
Mg), being left in the aqueous solution. 
______________________________________ 
B. Second Extraction 
Aqueous Phase Extractant Phase 
______________________________________ 
In NiSO.sub.4,CoSO.sub.4,NaOH + H.sub.2 O 
(RO).sub.2 PO.sub.2 H 
Out H.sub.2 O + Na.sub.2 SO.sub.4 
[(RO).sub.2 PO.sub.2 ].sub.2 Co 
[(RO).sub.2 PO.sub.2 ].sub.2 Ni 
______________________________________ 
The pregnant DEPA extractant is stripped with sulfuric acid (H.sub.2 
SO.sub.4). 
______________________________________ 
C. Strip 
Aqueous Phase Extractant Phase 
______________________________________ 
In H.sub.2 SO.sub.4 + H.sub.2 O 
[(RO).sub.2 PO.sub.2 ].sub.2 Co 
[(RO).sub.2 PO.sub.2 ].sub.2 Ni 
Out NiSO.sub.4,CoSO.sub.4,H.sub.2 SO.sub.4 + H.sub.2 O 
(RO).sub.2 PO.sub.2 H 
______________________________________ 
The barren extractant phase is recycled to the extraction stage and the 
NiSO.sub.4,CoSO.sub.4,H.sub.2 SO.sub.4 aqueous solution is shipped to a 
remote refinery for the recovery of nickel and cobalt. At the refinery, 
the aqueous solution is re-extracted with bis(2,4,4-trimethylpentyl) 
phosphinic acid dissolved in kerosene with isodecanol as a modifier. The 
extraction takes place at pH of about 5 to 6, preferably at pH of about 
5.5, thereby extracting the cobalt and leaving the majority of the nickel 
behind in the aqueous phase. 
______________________________________ 
D. First Re-extraction 
Aqueous Phase Extractant Phase 
______________________________________ 
In NiSO.sub.4,CoSO.sub.4,H.sub.2 SO.sub.4, 
R.sub.2 PO.sub.2 H 
NH.sub.4 OH + H.sub.2 O 
Out NiSO.sub.4,(NH.sub.4).sub.2 SO.sub.4, 
(R.sub.2 PO.sub.2).sub.2 Co 
H.sub.2 SO.sub.4 + H.sub.2 O 
(R.sub.2 PO.sub.2).sub.2 Ni 
R.sub.2 PO.sub.2 NH.sub.4 
______________________________________ 
The aqueous phase proceeds to the second re-extraction stage and the 
pregnant extractant is scrubbed with cobalt sulfate (CoSO.sub.4). 
______________________________________ 
E. Scrub 
Aqueous Phase Extractant Phase 
______________________________________ 
In CoSO.sub.4 + H.sub.2 O 
(R.sub.2 PO.sub.2).sub.2 Co 
(R.sub.2 PO.sub.2).sub.2 Ni 
R.sub.2 PO.sub.2 NH.sub.4 
Out NiSO.sub.4,(NH.sub.4).sub.2 SO.sub.4,H.sub.2 SO.sub.4 
(R.sub.2 PO.sub.2)Co 
+ H.sub.2 O 
______________________________________ 
The aqueous phase proceeds to the second re-extraction stage and the 
pregnant extractant is stripped with sulfuric acid. 
______________________________________ 
F. Strip 
Aqueous Phase 
Extractant Phase 
______________________________________ 
In H.sub.2 SO.sub.4 + H.sub.2 O 
(R.sub.2 PO.sub.2).sub.2 Co 
Out CoSO.sub.4 + H.sub.2 O 
R.sub.2 PO.sub.2 H 
______________________________________ 
The barren extractant phase is recycled to the first reextraction stage and 
the cobalt is either recovered from the CoSO.sub.4 by crystallization or 
the CoSO.sub.4 converted to cobalt metal by electrowinning. The aqueous 
phase from the first re-extraction is extracted with 
bis(2,4,4-trimethylpentyl) phosphinic acid dissolved in kerosene with 
isodecanol as a modifier but the extraction takes place at pH of about 6.5 
to 7.5, preferably pH of about 7. 
______________________________________ 
G. Second Re-extraction 
Aqueous Phase Extractant Phase 
______________________________________ 
In NiSO.sub.4,(NH.sub.4).sub.2 SO.sub.4, 
R.sub.2 PO.sub.2 H 
NH.sub.4 OH,H.sub.2 O 
Out (NH.sub.4).sub.2 SO.sub.4 + H.sub.2 O 
(R.sub.2 PO.sub.2).sub.2 Ni 
R.sub.2 PO.sub.2 NH.sub.4 
______________________________________ 
The aqueous phase is disposed of to the fertilizer industry, for example, 
or used in the electrowinning of nickel metal. The pregnant extractant is 
scrubbed with nickel sulfate (NiSO.sub.4). 
______________________________________ 
H. Scrub 
Aqueous Phase 
Extractant Phase 
______________________________________ 
In NiSO.sub.4 + H.sub.2 O 
(R.sub.2 PO.sub.2).sub.2 Ni 
R.sub.2 PO.sub.2 NH.sub.4 
Out (NH.sub.4).sub.2 SO.sub.4 + H.sub.2 O 
(R.sub.2 PO.sub.2).sub.2 Ni 
______________________________________ 
The aqueous phase is disposed of to the fertilizer industry, for example, 
or used in the electrowinning of nickel metal. The scrubbed extractant is 
stripped with sulfuric acid. 
______________________________________ 
I. Strip 
Aqueous Phase 
Extractant Phase 
______________________________________ 
In H.sub.2 SO.sub.4 + H.sub.2 O 
(R.sub.2 PO.sub.2).sub.2 Ni 
Out NiSO.sub.4 + H.sub.2 O 
R.sub.2 PO.sub.2 H 
______________________________________ 
The extractant phase is recycled to the second re-extraction and the nickel 
is either recovered from the NiSO.sub.4 by crystallization or the 
NiSO.sub.4 is converted to nickel metal by electrowinning. 
Copper Recovery 
An aqueous solution at pH of about 3 to 5, preferably at pH of about 4.5, 
containing traces of copper salt (ca. 30 ppm Cu) is extracted with DEPA 
dissolved in kerosene with isodecanol as a modifier. 
______________________________________ 
A. First Extraction 
Aqueous Phase 
Extractant Phase 
______________________________________ 
In CuSO.sub.4 + H.sub.2 O 
(RO).sub.2 PO.sub.2 H 
Out H.sub.2 SO.sub.4 + H.sub.2 O 
[(RO).sub.2 PO.sub.2 ].sub.2 Cu 
______________________________________ 
The aqueous phase proceeds to the second extraction. The pregnant 
extractant is stripped with sulfuric acid. 
______________________________________ 
B. Strip 
Aqueous Phase Extractant Phase 
______________________________________ 
In H.sub.2 SO.sub.4 + H.sub.2 O 
[(RO).sub.2 PO.sub.2 ].sub.2 Cu 
Out CuSO.sub.4,H.sub.2 SO.sub.4 + H.sub.2 O 
(RO).sub.2 PO.sub.2 H 
______________________________________ 
The extractant phase is recycled to the first extraction and the aqueous 
phase shipped to a remote refinery for the recovery of copper. 
C. Cu Recovery at the Remote Refinery 
The copper in the aqueous phase is either recovered from the CuSO.sub.4 
solution by crystallization and the H.sub.2 SO.sub.4 recycled to the 
second extraction, or the CuSO.sub.4 is converted to copper metal by 
electrowinning. 
The aqueous solution from the first extraction is extracted with an 
aliphatic amine extractant (R.sub.4 NOH) dissolved in kerosene. 
______________________________________ 
D. Second Extraction 
Aqueous Phase 
Extractant Phase 
______________________________________ 
In H.sub.2 O + H.sub.2 SO.sub.4 
R.sub.4 NOH 
Out H.sub.2 O (R.sub.4 N).sub.2 SO.sub.4 
______________________________________ 
The aqueous phase out is either discharged to drain or recycled to the 
process. The pregnant extractant is stripped with ammonium hydroxide. 
______________________________________ 
E. Strip 
Aqueous Phase 
Extractant Phase 
______________________________________ 
In NH.sub.4 OH + H.sub.2 O 
(R.sub.4 N).sub.2 SO.sub.4 
Out (NH.sub.4).sub.2 SO.sub.4 + H.sub.2 O 
R.sub.4 NOH 
______________________________________ 
The aqueous phase is disposed of to the fertilizer industry, for example, 
and the barren extractant recycled to the second extraction. 
Selective Recovery of Copper, Lead and Nickel 
An aqueous solution containing traces of copper, lead and nickel (30 ppm 
each) at pH of about 4 to 5, preferably pH of about 4.5, is extracted with 
DEPA dissolved in kerosene with isodecanol as a modifier. 
______________________________________ 
A. Extraction 
Aqueous Phase Extractant Phase 
______________________________________ 
In CuSO.sub.4, NiSO.sub.4, PbSO.sub.4, 
(RO).sub.2 PO.sub.2 H 
NaOH + H.sub.2 O 
Out Na.sub.2 SO.sub.4 + H.sub.2 O 
[(RO).sub.2 PO.sub.2 ].sub.2 Cu 
[(RO).sub.2 PO.sub.2 ].sub.2 Ni 
[(RO).sub.2 PO.sub.2 ].sub.2 Pb 
______________________________________ 
The pregnant extractant is stripped with nitric acid (HNO.sub.3). 
______________________________________ 
B. Strip 
Aqueous Phase Extractant Phase 
______________________________________ 
In HNO.sub.3 + H.sub.2 O 
[(RO).sub.2 PO.sub.2 ].sub.2 Cu 
[(RO).sub.2 PO.sub.2 ].sub.2 Ni 
[(RO).sub.2 PO.sub.2 ].sub.2 Pb 
Out Cu(NO.sub.3).sub.2, Ni(NO.sub.3).sub.2, 
(RO).sub.2 PO.sub.2 H 
Pb(NO.sub.3).sub.2 + H.sub.2 O 
______________________________________ 
The barren extractant is recycled to extraction and the aqueous phase 
shipped to a remote refinery for metal cation recovery. 
C. Pb Recovery 
The pH of the aqueous solution is raised and maintained at about 6 to 8, 
preferably about 7, while CO.sub.2 is bubbled in to precipitate the lead 
as PbCO.sub.3 according to the equation: 
EQU Cu(NO.sub.3).sub.2, Ni(NO.sub.3).sub.2, Pb(NO.sub.3).sub.2 +H.sub.2 
O+NH.sub.3 +CO.sub.2 .fwdarw.Cu(NO.sub.3).sub.2, Ni(NO.sub.3).sub.2 
+H.sub.2 O+NH.sub.4 NO.sub.3 +PbCO.sub.3 
The PbCO.sub.3 is filtered off and washed and the aqueous solution and wash 
liquor proceed to the re-extraction where they are re-extracted with 
bis(2,4,4-trimethylpentyl) phosphinic acid dissolved in kerosene with 
isodecanol as a modifier. 
______________________________________ 
D. Re-extraction 
Aqueous Phase Extractant Phase 
______________________________________ 
In Cu(NO.sub.3).sub.2,Ni(NO.sub.3).sub.2, 
R.sub.2 PO.sub.2 H 
NH.sub.4 NO.sub.3,NH.sub.4 OH + H.sub.2 O 
Out NH.sub.4 NO.sub.3 + H.sub.2 O 
[R.sub.2 PO.sub.2 ].sub.2 Ni 
pH 8 [R.sub.2 PO.sub.2 ].sub.2 Cu 
______________________________________ 
The aqueous phase is disposed of to the fertilizer industry, for example. 
The pregnant extractant is stripped with nitric acid at pH of about 4 to 
6, preferably at pH of about 5. 
______________________________________ 
E. First Strip 
Aqueous Phase Extractant Phase 
______________________________________ 
In HNO.sub.3 + H.sub.2 O 
(R.sub.2 PO.sub.2).sub.2 Ni 
Out Ni(NO.sub.3).sub.2 + H.sub.2 O (pH 5) 
(R.sub.2 PO.sub.2).sub.2 Cu 
______________________________________ 
The nickel is recovered from the Ni(NO.sub.3).sub.2 by crystallization. The 
copper-bearing extractant is stripped with nitric acid at pH of about 1 to 
3, preferably at pH of about 1. 
______________________________________ 
F. Second Strip 
Aqueous Phase Extractant Phase 
______________________________________ 
In HNO.sub.3 + H.sub.2 O 
(R.sub.2 PO.sub.2).sub.2 Cu 
Out Cu(NO.sub.3).sub.2,HNO.sub.3 + H.sub.2 O 
R.sub.2 PO.sub.2 H 
(pH 1) 
______________________________________ 
The barren extractant is recycled to re-extraction, the copper is recovered 
from the Cu(NO.sub.3).sub.2 by crystallization and the HNO.sub.3 recycled. 
The following non-limiting examples further illustrate the invention. 
EXAMPLE 1 
Two volumes of an aqueous solution of CuSO.sub.4 containing 1000 ppm Cu, 
together with one volume of organic extractant containing 5% w/v 
di-2-ethylhexylphosphoric acid dissolved in kerosene and modified with 4% 
v/v isodecanol were agitated for 5 minutes. The phases were allowed to 
separate, separated and analyzed. Results: 
______________________________________ 
Concentration 
(ppm Cu) pH 
______________________________________ 
Aqueous phase 0.3 7.0 
Extractant phase 2,000 -- 
______________________________________ 
EXAMPLE 2 
Example 1 was repeated using the organic extractant from Example 1 and a 
further 2 volumes of the 1000 ppm Cu, aqueous CuSO.sub.4 solution. 
Results: 
______________________________________ 
Concentration 
(ppm Cu) pH 
______________________________________ 
Aqueous phase 2.5 7.0 
Extractant phase 4,000 -- 
______________________________________ 
EXAMPLE 3 
Example 2 was repeated using the organic extractant from Example 2 and a 
further 2 volumes of the 1000 ppm Cu aqueous CuSO.sub.4 solution. Results: 
______________________________________ 
Concentration 
(ppm Cu) pH 
______________________________________ 
Aqueous phase 1.3 7.0 
Extractant phase 6,000 -- 
______________________________________ 
EXAMPLE 4 
Example 1 was repeated except that the two phases were manually shaken 
together, for 15 seconds, in a stoppered separatory funnel. Results: 
______________________________________ 
Concentration 
(ppm Cu) pH 
______________________________________ 
Aqueous phase 0.9 7.0 
Extractant phase 2,000 -- 
______________________________________ 
EXAMPLE 5 
Example 4 was repeated using the organic extractant from Example 4 and a 
further 2 volumes of the 1000 ppm Cu aqueous CuSO.sub.4 solution. Results: 
______________________________________ 
Concentration 
(ppm Cu) pH 
______________________________________ 
Aqueous phase 0.7 7.0 
Extractant phase 4,000 -- 
______________________________________ 
EXAMPLE 6 
Example 5 was repeated using the organic extractant from Example 5 and a 
further 2 volumes of the 1000 ppm Cu aqueous CuSO.sub.4 solution. Results: 
______________________________________ 
Concentration 
(ppm Cu) pH 
______________________________________ 
Aqueous phase 1.9 7.0 
Extractant phase 6,000 -- 
______________________________________ 
EXAMPLE 7 
Two volumes of the organic extractant used in Example 1 together with one 
volume of an aqueous solution of CuSO.sub.4 containing 27 ppm Cu were 
manually shaken together for 15 seconds in a stoppered separation funnel. 
The phases were allowed to separate, separated and analyzed. Results: 
______________________________________ 
Concentration 
(ppm Cu) pH 
______________________________________ 
Aqueous phase 0.2 4.0 
Extractant phase 13.3 -- 
______________________________________ 
EXAMPLE 8 
Example 7 was repeated using one volume of the organic extractant and two 
volumes of the 27 ppm Cu aqueous CuSO.sub.4 solution. Results: 
______________________________________ 
Concentration 
(ppm Cu) pH 
______________________________________ 
Aqueous phase 0.2 4.0 
Extractant phase 52.9 -- 
______________________________________ 
EXAMPLE 9 
Example 7 was repeated using one volume of the organic extractant and four 
volumes of the 27 ppm Cu aqueous CuSO.sub.4 solution. Results: 
______________________________________ 
Concentration 
(ppm Cu) pH 
______________________________________ 
Aqueous phase 0.4 4.0 
Extractant phase 105 -- 
______________________________________ 
EXAMPLE 10 
Example 7 was repeated using one volume of the organic extractant and six 
volumes of the 27 ppm Cu aqueous CuSO.sub.4 solution. Results: 
______________________________________ 
Concentration 
(ppm Cu) pH 
______________________________________ 
Aqueous phase 0.5 4.0 
Extractant phase 157 -- 
______________________________________ 
EXAMPLE 11 
Example 7 was repeated using one volume of the organic extractant and six 
volumes of an aqueous CuSO.sub.4 solution containing 60 ppm Cu. Results: 
______________________________________ 
Concentration 
(ppm Cu) pH 
______________________________________ 
Aqueous phase 0.8 4.0 
Extractant phase 355 -- 
______________________________________ 
EXAMPLE 12 
Example 7 was repeated using one volume of the organic extractant and six 
volumes of an aqueous CuSO.sub.4 solution containing 90 ppm Cu. Results: 
______________________________________ 
Concentration 
(ppm Cu) pH 
______________________________________ 
Aqueous phase 1.3 4.0 
Extractant phase 532 -- 
______________________________________ 
The following table summarizes the results of additional tests carried out 
on a continuous, countercurrent centrifugal extractor. In all tests, the 
combined flow rates were 1200 milliliters per minute: 
__________________________________________________________________________ 
Aqueous to 
Extractant Concentration (ppm Cu) 
Flow Rates 
Time 
Aqueous 
Aqueous 
Extrac- 
Test 
Ratio (mins.) 
Feed Raffinate 
tant 
pH 
Extractant 
__________________________________________________________________________ 
1 2 5 0.2 59.6 5% w/v DEPA 
10 30 0.2 59.6 
3.5 
dissolved in 
20 0.3 59.4 kerosene and 
modified with 4% 
v/v isodecanol 
2 0.5 5 30 0.48 14.8 
3.0 
same as test 1 
10 0.86 14.6 
2 5 0.31 59.4 
10 0.51 59.0 
15 0.47 59.1 
4 5 0.28 118.9 
10 0.46 118.2 
15 0.45 118.2 
6 5 0.32 178.1 
10 0.40 177.6 
15 0.44 177.4 
8 5 0.31 237.5 
10 0.32 237.4 
__________________________________________________________________________ 
EXAMPLE 13 
Five volumes of an aqueous solution of (NH.sub.4).sub.2 CrO.sub.4 
containing 9 ppm of hexavalent chromium together with one volume of 
organic extractant containing 5% w/v of monomethyl trialkyl (C.sub.8-18) 
quaternary in the hydroxide form dissolved in kerosene and modified with 
4% v/v isodecanol were manually shaken together, for 1 minute, in a 
stoppered separatory funnel. The phases were allowed to separate and 
analyzed. This procedure was repeated using aqueous solutions of varying 
hexavalent chromium content. Results: 
______________________________________ 
Extraction Products 
Feed Solution 
Aqueous Phase Organic Phase 
(ppm Cr.sup.6) 
(ppm Cr.sup.6) 
(pH) (ppm Cr.sup.6) 
______________________________________ 
9 0.16 7.0 45 
23 0.09 7.0 113 
45 0.08 7.0 226 
68 0.48 7.0 338 
______________________________________ 
EXAMPLE 14 
Five volumes of an aqueous solution of Ni(NO.sub.3).sub.2 containing 8 ppm 
of Ni together with one volume of organic extractant containing 5% w/v 
di-2-ethylhexylphosphoric acid dissolved in kerosene and modified with 4% 
v/v isodecanol were manually shaken together for 1 minute in a stoppered 
separatory funnel. The phases were allowed to separate and analyzed. This 
procedure was repeated using aqueous solutions of varying Ni content. 
Results: 
______________________________________ 
Extraction Products 
Feed Solution 
Aqueous Phase Organic Phase 
(ppm Ni) (ppm Ni) (pH) (ppm Ni) 
______________________________________ 
8 0.02 7.0 42 
21 0.33 7.0 103 
42 0.33 7.0 208 
63 5.08 7.0 290 
______________________________________ 
EXAMPLE 15 
Five volumes of an aqueous solution of Pb(NO.sub.3).sub.2 was extracted as 
in Example 14. Results: 
______________________________________ 
Extraction Products 
Feed Solution 
Aqueous Phase Organic Phase 
(ppm Pb) (ppm Pb) (pH) (ppm Pb) 
______________________________________ 
7 0.13 7.0 36 
19 0.25 7.0 91 
37 1.48 7.0 178 
56 12.11 7.0 217 
______________________________________ 
EXAMPLE 16 
Five volumes of an aqueous solution of Co(NO.sub.3).sub.2 were extracted as 
in Example 14. Results: 
______________________________________ 
Extraction Products 
Feed Solution 
Aqueous Phase Organic Phase 
(ppm Co) (ppm Co) (pH) (ppm Co) 
______________________________________ 
25 1.35 7.0 116 
49 2.97 7.0 230 
74 12.05 7.0 307 
______________________________________ 
Whereas the exact scope of the instant invention is set forth in the 
appended claims, the following specific examples illustrate certain 
aspects of the present invention. However, the examples are set forth for 
illustration only and are not to be construed as limitations on the 
present invention except as set forth in the appended claims.