United States Patent
Baltz et al.
[ 19) [ II]
[45]
4,012,481
Mar. 15, 1977
[54] PROCESS FOR THE SEPARATION OF
PLATINUM GROUP METALS
[56] References Cited
UNITED STATES PATENTS
FOREIGN PATENTS OR APPLICATIONS
2,457,672 6/1975 Germany 423/22
[75] Inventors: John Baltz, Lakewood; Enzo
Coltrinari, Arvada, both of Colo.
[73] Assignee: PGP Industries, Inc., Sante Fe
Springs, Calif.
[22] Filed: Nov. 7, 1975
[21] Appl. No.: 629,879
[52] U.S. CI•............................. 423/22; 75/101 BE;
423/658.5
[51] Int. CI.2 COlG 55/00
[58] Field of Search 423/22, 658.5;
75/101 BE
ABSTRACT
OTHER PUBLICATIONS
Beamish, "Talanta", vol. 14, 1967, pp. 991-1009.
Faye et aI., "Analytical Chemistry", vol. 35, July, 1963,
pp. 985-988.
Primary Examiner-Herbert T. Carter
Attorney, Agent, or Firm-Darby & Darby
13 Claims, No Drawings
[57]
Disclosed herein. is a process for the separation and
recovery of Rhodium values from aqueous mineral acid
solutions also containing Iridium and/or Ruthenium
which comprises contacting the metal bearing aqueous
solution with a water immiscible organic solvent containing
an organically substituted quaternary amine salt
to extract Iridium and Ruthenium into the solvent
phase leaving Rhodium in the aqueous raffinate. The
loaded organic phase is stripped of Iridium and Ruthenium
in two sequential steps by contacting it first with
an alkaline solution then redissolving the resulting precipitate
in an acidified reducing solution.
Ziegler 423/22
Donauma 423/22
MacGregor 423/22
1/1974
7/1974
6/1976
3,787,554
3.823.220
3.960.549
1
4,012,481
2
stripped and recovered from the loaded organic by
sequential contact with predetermined stoichiometric
quantities of an alkaline solution and an acidified reducing
solution.
It is accordingly an object of the present invention to
provide a highly selective process for separating Rhodium
from aqueous solutions containing Iridium, Rhodium
and Ruthenium.
Another aspect of the invention is a method for sepa-
10 rating Rhodium from an aqueous solution also containing
Ruthenium and Iridium by extracting the Iridium
and Ruthenium into an organic phase containing a
substituted quaternary ammonium compound.
A further aspect of the present invention involves the
15 method of stripping and recovering the Iridium and
Ruthenium complex from the loaded amine organic
phase by sequential treatment with predetermined stoichiometric
quantities of an alkaline solution and an
acidified reductant stripping solution.
20 These and other aspects of the present invention are
more completely explained in the following specification
and examples.
According to the present invention, cationic Rhodium
is separated from an aqueous mineral acid solu-
25 tion containing cationic salts of Rhodium as well as
Iridium And Ruthenium in their anionic oxidized state
by solvent extraction with an organically substituted
quaternary ammonium salt. Contacting the aqueous
solution with a solvent containing the quaternary amine
30 leads the Iridium and Ruthenium values to form a complex
with the amine that is preferentially soluble in the
solvent phase, leaving Rhodium in the aqueous raffinate.
As used in the present invention, the term "raffinate"
refers to an aqueous solution (or phase) after
35 solvent extraction, i.e., a solution that has been depleted
of all or part of its valuable metal content by
transfer to an organic phase.
The Rhodium, which must be present in the mineral
acid solution in its cationic state, is not extracted into
40 the amine solvent, and is won from the aqueous raffinate
by conventional processes such as copper cementation.
The Iridium-Ruthenium loaded organic amine
phase is treated with at least the stoichiometric quantity
of an aqueous solution of an alkaline reagent re-
45 quired to breakup the amine complex formed between
Iridium and Ruthenium and produce a precipitate
which is the alkaline salt form of the extracted metal
values. The resulting alkaline/solvent mixture is then
contacted with an acidified reducing agent to solubilize
50 the Iridium and Ruthenium precipitates into an aque.ous
acidic solution from which they may readily be
isolated by known methods.
The aqueous phase from which Iridium and Ruthenium
are extracted in the present invention is ordinarily
55 a mineral acid leach solution of the type normally resulting
from the fusion and leaching of Platinum metal
ore concentrates. The invention will be further described
by reference to separation and recovery of
Rhodium, Iridium and Ruthenium from hydrochloric
60 acid solutions such as generally occur in Platinum
group metal recovery. However, the invention is not
limited as such and may be operated to separate metals
from solutions of other mineral acids which are used in
the recovery or assay of Platinum group metal values,
65 provided the acid does not attack or degrade the organic
extractant and will afford the formation of organic
soluble complexes of the desired metals with the
quaternary amine extractant. In aqueous chloride solu-
PROCESS FOR THE SEPARATION OF PLATINUM
GROUP METALS
This invention relates to a method for separating
dissolved metal salts from aqueous mineral acid solu- 5
tions and more specifically to a scheme for separating
Rhodium from Iridium and/or Ruthenium by solvent
extraction with an organically substituted quaternary
ammonium salt and recovering the Iridium and Ruthenium
values from the loaded organic. Still more specifically,
the invention relates to a method for the organic
solvent extraction of Iridium and/or Ruthenium from
aqueous chloride solutions containing Rhodium, Iridium
and Ruthenium and recovery of the isolated Iridium
and Ruthenium values from the loaded organic
phase.
The separation of Rhodium from Iridium has long
been considered a difficult aspect of Platinum group
metal separation. The traditional methods for separating
Rhodium-Iridium-Ruthenium from one another are
well known in the art, but involve long and tedious
processing operations.
More recently, somewhat faster methods have been
evolved for separating Iridium-Rhodium-Ruthenium
from aqueous solution by ion exchange. There are,
however, several drawbacks and disadvantages involved
in such processes. Ruthenium may be reduced
on ion exchange resins and the IrCl6"2 ion is difficult to
elute. Also, the nature of the Rhodium-containing species
is very sensitive to solution conditions on the resin
column and may change when the metal bearing solution
is on the column to prevent the separation.
Tertipis et al. describe the solvent extraction of Iridium
from hydrochloric acid solutions containing Rhodium
through the use of tributyl phosphate in Analytical
Chemistry 33 (1961), No. 12,pages 1650 through
1652. However, this technique is undesirable since it
involves reaction conditions which significantly restrict
its general usefulness.
The problem of successfully separating Rhodium
from Iridium by solvent extraction with tributyl phosphate
is further complicated when the pregnant aqueous
solution in which the metals are dissolved also
contains Ruthenium. In such instances substantial difficulty
is encountered in obtaining a pure Rhodium product
as the Ruthenium contaminates both the Iridium
and Rhodium thereby frustrating the isolation of a pure
form of either metal.
It has now been unexpectedly discovered that Rhodium
values can be quickly and easily separated from
aqueous mineral acid solutions containing Rhodium,
Iridium and Ruthenium by solvent extraction with an
organic solvent containing an organically substituted
quaternary ammonium compound. It has also been
found that the Iridium-Ruthenium values extracted into
the amine solvent can be stripped and recovered as a
mixture of Iridium and Ruthenium salts by sequentially
contacting the loaded organic with an aq ueous alkaline
solution and an acidified reducing agent. In operation,
a water immiscible organic solvent containing an organically
substituted quaternary ammonium salt is
brought into contact with the aqueous mineral acid
solution and forms a complex with iridium and Ruthenium
which are present in the solution in their anionic
states. The complex is extracted into the solvent phase
leaving Rhodium (present in the acid solution as a
cation) in the aqueous raffinate phase. After phase
separation, Iridium and Ruthenium are simultaneously
Wherein RJ, R2, R3 and R4 are straight or branched
aliphatic alkyl or aromatic hydrocarbon groups. Generally
at least one of R\, R2, R3 and ~ are fatty alkyl
groups. Aliquat 336, methyl tricaprylyl ammonium
chloride, manufactured by General Mills, is an effective
extractant and has the following cation:
4,012,481
3 4
tions, the soluble Rhodium-Iridium-Ruthenium com- wherein Rh R2, anel R3 are hydrocarbon chains havpounds
are generally present as complex chloro salts or ing eight to ten carbOn atoms, with eight carbon atoms
in a form of their corresponding hydrochloric acid prevailing. Also useful as the ainine solvent extractant
complexes. Typically, such leach solutions result from are Adogen 468 methyltri-n-alkylammonium chloride
crude ore processing operations and range between 0.1 5 (average CIO), and Adogen 464 methyltri-n-alkylamto
abOut 5 normal HCI and up to abOut 250 grams per monium chloride (Cs-CIO) (bOth made by Ashland
liter CL- and in some instances higher. In addition to Chemical Co.). The"organically substituted quaternary
the Platinum group metals, the solutions may contain amines which may be used in the present invention
other base metal impurities such as lead, copper, bis- must be sufficiently soluble in at least one of the sollOuth,
nickel, aluminum, silica, silver, and barium. 10 vents referred to below, or mixtures of them to make at
It has been discovered that in order to achieve an least a 1% solution. Finally, the ammonium compound
effective separation of Iridium and Ruthenium from should provide for ready phase disengagement follow-
Rhodium in the preferred hydrochloric acid solutions, ing extraction. The preferred organic extractant in the
it is necessary to have Rhodium present in the form of present invention is Aliqwit-336. Prior to use in the
a cationic chloro complex of Rhodium and for the 15 extraction the amine extractant is usually conditioned
Iridium and Ruthenium to exist as oxidized Iridium and to the form of the acid solution to be contacted. Thus
Ruthenium chloro complexes respectively. This is im- in the preferred "embOdiment in w~ich Iridium and
portant as the oxidized Iridium and Ruthenium chloro Ruthenium are extracted from hydrochloric acid solucomplexes
behave as an anion toward the organic ex- tion, the extractant is conditioned to chloride form by
traction mixture and are extracted, whereas the Rho- 20 treatment with NaCI in IN HC\.
dium chloro complex behaves as a cation and is not The major constituent of the extraction liquid is a
extractable with the organically substituted quaternary water immiscible carrier solvent in which the organic
amine extraction agent. The foregoing differences in amine extractant is dissolved to form the organic phase.
ionic condition are maintained throughout the extrac- Con~enti?nal. organic solvents inclll:ding, for examtionso
that the organic phase containing the amine 25 ~Ie,.ahphatlc hydrocar.bons suc~ as pet~oleum derived
complexing agent does not become fouled with Rho- hqUld hydrocarbOns, eIther straIght cham or branched,
dium chloro complexes which would behave as anionic kerosene, fuel oil, etc., are useful in the invention.
species and be extracted. The aqueous acid solutions Various aromatic solvents or chlorinated aliphatic solfrom
which the aforementioned metals are extracted vents may also be employed such as benzene, toluene,
are preferably substantially free ofgold, iron, Platinum, 30 xylene, c~bOntetrachloride and perchloroethylene.
and Palladium which are removed beforehand by con- TI;te .orgamcsolvents mu~t be .substantially .water imventional
techniques well known in the art. m.lsclble an~ capable of dlssolvmg t~~ organIcally sub-
The extract~on liquid used to separate Iridium and/or stltuted a~mne extractl~.nt. In ad~ltlOn, .the s<;>lvent
Ruthenium from Rhodium consists of three constitu- should be mert and not mterfere WIth the extraction of
ents: an organic extractant, a water immiscible carrier 35 Iridium and Ruthenium metal values from acid solution
solvent and a phase modifier. by the organically s~bstituted amine. Kerosene avail-
In the present invention an aqueous mineral. acid ~ble as AMS~O .175 IS preferably employed because of
solution containing, for example, Iridium, Rhodium Its ready ava~lablhty an~ as a matter of econ~my.
an,d Ruthenium dissolved in a hydrochloric acid solu- The orgamcally s~bstltuted quat~rnary amme comtion
is. contacted with a water immiscibIe organic sol- 40 pone~~ of t~e orgamc extractant ml~ture.must have a
vent containing a quaternary ammonium compound solubIlIty of at least about 1~ by weIght I~ the hydrocapable
offorming complexes with Iridium and Ruthe- ~arbOn s~lvent of the orgamc phase whIch must be
nium that are preferentially soluble in the resultant msoluble m wat~r. . " .
organic phase. The quaternary ammonium compounds A phase modIfier IS also admIxed WIth the carner
capable of performing these functions have the follow- 45 so~vent and ~xtra~ta~t to prevent the formation of a
ing basic structure: ~hlrd phase I~ stnppIng the pre~ant .organic. Water
Insoluble straIght or branched cham alIphatic alcohols
containing at least 6 carbOn atoms are generally used as
phase modifiers. Examples of suitable phase modifiers
50 include isodecanol, 2-ethyl hexanol andtridecano\.
Isodecanol is preferred for use in the present invention.
The organic mixtures of the present invention will
usually contain from about 5 to 15 volume percent (%)
of the organic amine extractant, between abOut 85 and
55 95 volume percent (%) of the carrier solvent, and from
about 1 to abOut 5 volume percent (%) of the phase
modifier. Although the preceding criteria are generally
applicable, the invention is not limited to operation
within these boundaries. Since only a limited amount of
60 the active extracting ingredient is present in the solvent
phase, it can only hold a limited amount of any given
metallic element at saturation. Once the concentration
of metal in the solVent has reached the saturation level,
no additional metal will go into the solvent regardless
65 of its concentration in the aqueous phase. The quantity
of metal which is given solvent extractant will hold is
termed "the maximum loading" and governs the total
quantity of solvent required to do a given amount of
4,012,481
6
(e.g., peroxide) can be employed to accomplish the
same results as sodium hypochlorite.
The iridium-ruthenium extraction and stripping operations
are preferably carried out at about 25° C although
satisfactory performance has been achieved at
temperatures in the range 20°-40° C and up to 50° C
and higher. At temperatures below about 20° C the
phase disengagement is slow, while operation above
40° C is hazardous due to the danger of fire.
Alkaline stripping reagents for use in the present
invention must be water soluble compounds which will
convert the extracted metal values contained in the
organic solvent into reaction products that are readily
soluble when contacted with the acidic reduction solution.
Stripping efficiency (i.e., the ability to remove a
large quantity of metal salt per unit volume of strippant)
is also an important criteria for selection of an
alkaline stripping agent. Suitable alkaline stripping
agents include water soluble alkali and· alkaline earth
20 carbonates, bicarbonates and hydroxides, e.g., sodium
and potassium hydroxide, carbonate or bicarbonate,
although sodium hydroxide is perferably employed.
The amount of alkaline strippant required is at least the
quantity which will neutralize the acid salt (usually the
chloride) form of the quaternary amine organic and
desirably includes in excess of the stoichiometric
amount (preferably about 50-100%) of the alkaline
agent to insure efficient stripping within the shortest
possible contact times. By contacting the loaded or-
30 ganic solvent with the alkaline stripping solution, the
organic soluble Iridium and Ruthenium organic amine
complexes are converted to metal salts and chloride
form of the amine.
Although metallic values can be recovered from the
loaded organic using only the acidified reducing strip
solution and without a prior contact with an alkaline
reagent, it has been unexpectedly discovered that a
consistently higher percentage of the Iridium and Ruthenium
metals present in the organic solvent were
stripped using sequential treatment with alkaline solution
and an acidic reducing agent.
The acidified reductant stripping agents are selected
based upon their capacity to contribute additional
stripping action to the alkaline treated loaded amine
organic as well as for their ability to maintain a reducing
environment in the strip solution. The latter criteria
is most important to prevent inadvertent reextraction
of the Platinum group metal values from the stripsolution.
Also, the strippant should not contribute any foreign
metals to the organic which might cause eventual
fouling or a reduction in loading capacity. Satisfactory
reductant stripping agents include acidic solutions of
hydrazine salts, hydroxylamine salts, S02, and conventional
organic reducing agents (i.e., organic acids such
as oxalic). The reductant stripping solutions are acidified
to between about 0.5-2.5 N (preferably 2.0 N) to
solubilize the Iridium and Ruthenium alkaline salts.
One suitable reducing solution is hydrazine dihydrochloride
(N2H4.2HCI) acidified to 2.0 N HCI.
The quantity of acidified reducing agent utilized is at
least the stoichiometric amount based upon the alkaline
strippant previously added, and desirably includes
in excess of the stoichiometric amount (preferably
about 100-150%) to insure complete dissolution of the
precipitated Iridil;1m.and Ruthenium values in the aqueous
phase. Additionally, some further stripping action
is realized during the contact period with the acidified
reducing strip solution. Although suggested concentra-
5
extraction. Based upon the maximum loading characteristics
of the particular extractant, the metal-bearing
characteristics of the leach liquor that is to be extracted
and the number of extraction stages to be employed,
the concentration of extractant and phase modifier in 5
the solvent may be adjusted, or the Organic/Aqueous
(O/A) ratio for any particular extractant concentration
may be varied to achieve a desired loading. In one
effective version of the extraction process the organic
liquid mixture used to extract Iridium and Ruthenium 10
from an aqueous hydrochloric acid solution comprises
10 volume percent (%) Aliquat-336, 87 volume percent
(%) kerosene and 3 volume percent (%) isodecanol.
As a measure of economy, it is preferred to employ
the lowest organic/aqueous ratio that will provide effi- 15
cient separation of the desired metal values from a
given aqueous mineral acid solution.
The liquid-liquid extraction may be carried out by
continuous countercurrent or batch processing procedures.
Typical apparatus for use in the present invention
could include (without limitation thereto) a multiple
stage countercurrent mixer-settler system in which the
barren organic solvent and a pregnant aqueous stream
are mixed together for a predetermined time period 25
following which they are permitted to separate in a
settling reservoir. The solvent and aqueous then flow in
opposite directions to the next stage of contact.
Briefly summarizing the separation and recovery
process operation, fresh metal bearing aqueous mineral
acid solution is contacted and admixed with the organically
substituted quaternary amine solvent for a predetermined
time period under oxidizing conditions. The
iridium and ruthenium anions in the aqueous solution
form a complex with the amine and are extracted into 35
the solvent phase~ The admixture is permitted to settle
into distinct organic and aqueous phases which are
isolated from one another..Iridium and ruthenium are
simultaneously stripped from the metal loaded organic
phase by sequential treatment with at least the stoichio- 40
metric quantity of alkaline solution which will neutralize
the acid salt of the amine followed by treatment
with an acidic reducing solution. Rhodium is won from
the aqueous raffinate by known methods (e.g., cementation
with copper powder). Iridium and ruthenium 45
may also be isolated from the stripping solution using
conventional techniques known to the art.
An important aspect of the present invention involves
conditioning (oxidizing) the metal bearing acid
solution to an emf or redox potential as measured by 50
means of a platinum-calomel electrode of between
about -500 and -1000 millivolts (otimally about -900
mv) prior to the organic extracting operation in order
to maintain high extraction efficiencies and promote
the production of rhodium solutions essential1y barren 55
of iridium and ruthenium. It should be noted that while
the extraction process will operate at emf values less
than -500 mv, extraction efficiencies become correspondingly
lower. The conditioning treatment is continued
through the extraction to insure that the aque- 60
ous phase is maintained in the oxidized state. The conditioning
operation can be accomplished by the addition
of sodium hypochlorite (NaOCI) solution at a
controlled rate to the aqueous acid solution to be extracted
to maintain the solution in an oxidized condi- 65
tion (indicated byobtaining an emf reading between
-500 and -1000 millivolts, and preferably about -900
mv). Alternatively, chlorine gas (CI2) or other oxidants
4,012,481
7 8
tions of strippant solutions have been described herein, nol, and 87 volume % kerosene (AMSCO 175) and was
those skilled in the art will recognize that these may be conditioned to the chloride form. of the organic by
varied depending upon the organic volumes to be contacting with a solution of 100 gil NaCI in I normal
treated, stripping efficiency of a particular strippant, to HCI folIowed by washing using a solution 20 gil NaCI
adjust the quantity and concentration of strip to yield 5 adjusted to pH 1.5 with HC\.
Table 1
Rh-Ir-Ru Extraction by Aliquat-336 at Various Solution EMF's
Assay gil
Test Contact Aqueous Feed Agueous Raffinate Loaded Organic % Extracted
No. No. EMF. mv Rh Ir Ru Rh Ir Ru Rh Ir Ru Rh Ir Ru
.,.520 4.6 1.25 4.5
I 4.3 0.43 1.8 0.06 0.30 1.4
2 4.1 0.34 1.3 0.08 0.05 0.23
3 3.9 0.31 l.l 0.09 0.03 0.09
4 3.7 0.27 0.8 0.09 0.03 0.08 20 78 82
2 -900 4.6 1.25 4.5
I 4.4 0.02 0.7 0.04 0.54 2.0
2 4.1 0.03 0.1 0.07 0.02 0.27
3 3.9 0.03 0.02 0.08 0.01 0.04
4 3.8 0.03 0.008 0.06 <0.01 0.009 17 97 99
strip solutions containing significant quantities of dis- It wilI be seen from the above results that maintesolved
Iridium and Ruthenium values and to avoid nance of a high oxidation state during extraction results
dilution and handling of weak and/or large volumes of in a more complete separation of Iridium-Ruthenium
solution. . 25 from Rhodium and produces a lower lridium/Ru-
The time required for stripping contact will vary from thenium raffinate for recovery of Rhodium by cemenone
loaded organic to another depending upon the tation.
particular solvent system, the quantity of Iridium and The examples presented in Table 2 were performed
Ruthenium sought to be stripped and the temperature to show the increase in stripping efficiency when using
at which the stripping operation is conducted. In most 30 the combination alkaline plus acidified reducing soluinstances
strip contact times of between I and 10 min- tion strip treatment. For both examples in Table 2 a
utes can be utilized to provide satisfactory results. 10% by volume Aliquat-336 solution in kerosene con-
The invention is further illustrated by the folIowing taining 3% by volume isodecanol was loaded with lridexamples.
. ium and Ruthenium by contacting with an acidic
The examples present in Table 1 were performed to 35 Rhodium-Iridium-Ruthenium chloride solution oxiillustrate
the method of effecting a more complete dized to emf -900 mv by addition of 50 gil NaOCI
separation of Rhodium from Iridium and Ruthenium by solution. A 100 m1 portion of the loaded organic was
maintaining a high oxidation state of the aqueous feed agitated for 10 minutes with 50 gil N2H4.2HCI in 2 N
liquor. It should be noted, however, that the present HCI at an organic to aqueous ratio of 2 to I at room
invention is not limited to operation strictly according 40 temperature. The percentage of Iridium and Rutheto
the instant example. nium stripped was determined by analysis of the sepa-
In Test No. I a predetermined amount of Iridium- rated phases. A second 100 ml portion of the same
Rhodium-Ruthenium aqueous acid solution analyzing loaded solvent was agitated with 8 ml of 200 gil NaOH
4.6 gil Rhodium, 1.25 gil Iridium and 4.5 gil Ruthe- (2X stoichiometric based on the normality of the prenium,
265 g/I CI- at I normal HCI and having a mea- 45 pared amine organic) for 5 minutes at room temperasured
emf of -520 millivolts was contacted four times ture. Following the caustic reaction periOd, 42 ml of 50
in succession with fresh organic extractant at an or- gil N2~.2HCI in 2 N HCI was added (2.IX stoichioganic
to aqueous ratio of 2 to I. Each contact was for metric based on the amount of caustic solution added)
a period of 2 minutes. Following each contact the and the mixture stirred for an additional 10 minutes at
phases were separated and the amount of Iridium and 50 room temperature. The final stripped volumes so ob-
Ruthenium extracted determined by analysis. In Test tained had an organic to aqueous ratio of 2/ I. As in the
No.2 the identical Rhodium-Iridium-Ruthenium solu- first test, the percentage of Iridium and Ruthenium
tion was adjusted to emf -900 millivolts by gaseous CI2 stripped was determined by analysis of the separated
oxidation and then extracted 4 times in succession with phases.
Table 2
% of Iridium-Ruthenium Stripped
Organic Assay gil Assay gil
Test Loaded Stri~rd Strip Solution % Stripped
No. Strippant Rh Ir Ru Rh Ru Rh Ir Ru Rh Ir Ru
N.H., .2HCI 0.030 0.32 0.59 0.020 0.18 0.49 0.020 0.28 0.21 33 44 17
in 2N HCI
2 NaOH plus 0.030 0.32 0.59 0.008 0.04 0.08 0.044 0.56 0.97 73 88 86
N.H•. 2 HCI
in 2N HCI
fresh solvent in a like manner described above. The
extraction organic in both of the above examples contained
10 volume % Aliquat-336, 3 volume % isodeca-
It can be seen from the above table that the alkaline
plus acidified reductant strip system significantly increases
the percentage recovery of Iridium and Ruthe4,012,481
wherein R.. R2, R3 and ~ are hydrocarbon groups for
a predetermined time period to form an organic
extract phase and an aqueous raffinate phase,
maintaining said Iridium and Rhodium containing
aqueous chloride solution at an emf between about
-500 and -1000 millivolts during said contacting
operation,
separating said extract phase from said aqueous
phase,
contacting said separated extract phase with at least
the stoichiometric amount of aqueous sodium hydroxide
solution required to neutralize the chloride
form of said amine and form a metallic hydroxide
precipitate, said contact resulting in formation of a
treated extract phase and a treated aqueous phase,
contacting said treated extract phase and said treated
aqueous phase with at least a stoichiometric
amount based on the stoichiometric value of said
sodium hydroxide solution of an acidified aqueous
reducing agent, said contact resulting in the formation
of a loaded aqueous phase and a stripped organic
phase,
separating said loaded aqueous phase and said
stripped organic phase, and recovering Iridium
from said loaded aqueous phase.
* * * * *
10
7. The process of claim 3 which comprises adding
copper powder to said separated aqueous raffinate
phase to recover Rhodium.
8. The process of claim 2 wherein said alkaline strip-
S ping agent is a water soluble member selected from the
group consisting of the carbonates, bicarbonates and
hydroxides of alkali and alkaline earth metals whereby
said contact results in the formation of an Iridium and
Ruthenium loaded aqueous phase and a stripped or-
10 ganic phase.
9. The process of claim 1 which comprises contacting
said loaded aqueous phase and said stripped organic
phase with a sufficient quantity of said acidified reducing
agent solution to maintain the emf of said loaded
IS aqueous phase below about -600 millivolts.
10. The process of claim 9 wherein said reductant
stripping agent is a member selected from the group
consisting of acidified solutions of hydrazine salts, hydroxyl
amine salts, reduced metalIic salts, S02' and
20 organic dicarboxylic acids.
11. The process of claim 10 wherein said acidified
reductant is hydrazine dihydrochloride of the formula
N2H.t.2HCI.
12. The process of claim 11 which comprises .con-
25 tacting the stripped organic phase with an aqueous
mineral acid following treatment with said acidified
reducing agent to remove entrained metal values and
subsequently reusing the organic phase to extract a
fresh metal containing acidic medium.
3 13. A continuous process for the separation and re-
O covery of Rhodium dissolved in aqueous chloride solutions
with Iridium which comprises:
contacting said aqueous chloride solution with an
organic solvent containing at least 1% by weight of
an organically substituted quaternary ammonium
halide having the following structure:
65
9
nium from the loaded solvent. The beneficial result
obtained from the two-step stripping system is the production
of good barren organic for recycle back to the
extraction stages of the Rhodium separation circuit.
From the foregoing it will be seen that the present
invention combines a rapid technique for separation of
Iridium and/or Ruthenium from Rhodium with an efficient
extraction and stripping system. The separation
and recovery procedure are quite specific and will
function in solutions containing widely varying quantities
of the respective metals. The economy and speed
of operation of the present process make it ideal for
incorporation as part of a continuous processing system
for separation of Rhodium essentially free of tridium
and/or Ruthenium from aqueous acid solutions of such
metals.
What is claimed is:
1. A process for the separation and selective recovery
of Rhodium, and/or Ruthenium and Iridium values
from an aqueous acidic medium which comprises:
contacting the medium with an organic extraction
reagent comprising a water immiscible solvent having
dissolved therein an organically substituted
quaternary ammonium compound having the
structure
wherein RJ, R2, R3 and Rt are hydrocarbon groups,
said compound being sufficiently soluble in said 35
solvent to make a 1%solution and capable offorming
complexes with Iridium and Ruthenium that are
preferentially soluble in said solvent and whereby
said contacting results in the formation of an organic
extract phase and an aqueous raffinate pha<;e, 40
maintaining said medium at an emf between about
-500 and -1000 mv during said contacting operation,
separating said organic extract phase from said aqueous
raffinate phase, 45
contacting said organic extract phase with at least the
stoichiometric quantity of an aqueous alkaline
stripping agent required for neutralization of the
organic extract phase, said contact resulting in the
formation of an aqueous phase loaded with Iridium 50
and Ruthenium and a stripped organic phase, and
contacting said stripped organic phase and said
loaded aqueous phase with a solution consisting of
an acidified reducing agent which is at least the
stoichiometric equivalent of said alkaline agent. 55
2. The process of claim 1 wherein at least one of RJ,
R2, R3 and R4 is a fatty alkyl group.
3. The process according to claim 2 which comprises
introducing an oxidant into said aqueous medium to
maintain said medium at an emf between about -500 60
and about -1000 millivolts during said contacting operation.
4. The process of claim 3 which comprises conducting
said contacting operation at a temperature between
about 20° and 40° C.
5. The process according to claim 3 wherein said
oxidant is sodium hypochlorite.
6. The process of claim 2 wherein said aqueous acidic
medium is hydrochloric acid.