United States Patent [I1J 3,615,170
23/22 X
23/23
23/312 ME
3,259,472
3,302,993
3,387,944
7/1966 Rice .
2/1967 Bray .
6/1968 Sheerington et al. .
OTHER REFERENCES
Elgin et al. " Chemical Engineers Handbook," Sec. 2,
1950,pp.713-718.
Jamrack, " Rare Metal Extraction by Chemical Engineering
Techniques," Vol. 2, MacMillan Co., N.Y. 1963, pp. 181184.
Wayne C. Hazen
Wheat Ridge;
Pablo Hadzeriga, Arvada; Paul R. Kruesi,
Golden, all of Colo.
881,654
Dec. 3, 1969
Oct. 26,1971
Molybdenum Corporation of America
New York, N.Y.
[21] Appl.No.
[22] Filed
[45] Patented
[73] Assignee
[72] Inventors
[54] PROCESS FOR SEPARATING METALS USING
DOUBLE SOLVENT EXTRACTION WITH
BRIDGING SOLVENT MEDIUM
14 Claims, 5 Drawing Figs.
[52] U.S. CI........................................................ 23/22,
23/23,23/24,23/312,
[51] Int. CI•........................................................ C22b 59/00
[50] Field of Search 23/15-20,
22-24,310-312 ME
[56]
3,110,556
3,167,402
3,193,381
References Cited
UNITED STATES PATENTS
11/1963 Peppard et al... .
1/1965 Samuelson et at .
7/1965 George et at .
23/23
23/312 ME
23/20UX
Primary Examiner-Herbert T. Carter
Attorney-Morgan, Finnegan, Durham and Pine
ABSTRACT: Solutions of metal values are fractionated by a
double solvent liquid-liquid extraction process wherein the
solution is contacted with one extractant to selectively remove
at least one metal value, then the solution is contacted with a
second extractant to selectively remove another metal value,
and the solution depleted of both metal values is recycled in a
bridge between the two extractants. The process permits
separation in aqueous and nonaqueous media; and it improves
separation efficiency by allowing equilibration of metal values
between the unmixed extractants and by permitting countercurrent
flows. The process is especially useful to fractionate
rare earth metal values and yttrium.
PATENTED OCT 26 1971
Barren
Organic
.R-a..f.f.i.n-a--te-
3,615,170
SHEET 10F 2
,Aqueous
,Feed
I Solution
Aqueous Reflux
- -Solution - -
2 3 4 5 6
Barren
Organic
A
Raffinate
..----
2
Barren
Organic
B
3
FIG. I
Aqueous
I Feed
I Solution
4 5 6
Aqueous Reflux
--------
Solution
FIG.2
Extract Extract
A B
INVENTORS
WAYNE C. HAZEN
PABLO HADZERIGA
BY PAUL R. kRUESI
1JJ--/~9t:.L$L "21"""'; ATTORNEYS
PATENTED OCT 26 1971 3,615,170
SHEET 2 OF 2
Barren
Organic
B
INVENTORS
WAYNE C. HAZEN
PABLO HADIERIGA
PAUL R.KRUESI
G.3
BY
Extract
B
Aqueous Feed
FIG.5
.. t Barren
00
Organic B
III
• FI
"x x."
~ ?5< (
-
2
g
:-----1
Feed J
prepar~tion Aqueous
,Feed
I
II
L_,
II
,.----,
Aqueous Feed I
Preparation:
f I
I
lI
I
II
I
JII
I
I I
I.. _1_
-T-'
It
Samplin
00
Extract
A
Barren
Organic A
Barren
Organic
A
3 4 5 6
FIG.4 Extract
Extract A
B
Scrubbed Extract
Organic A
A
_._._-
3,615,170
2
DESCRIPTION OF THE INVENTION
BACKGROUNDOF THE INVENTION
1
PROCESS FOR SEPARATING METALS USING DOUBLE
SOLVENT EXTRACTION WITH BRIDGING SOLVENT
MEDIUM
This invention relates to the purification, separation and
recovery of metal values from solutions. In particular, it concerns
improved liquid-liquid solvent extraction methods
which provide unexpectedly more efficient fractionation of
difficult to separate metals than do prior art processes;
the values to be extracted and/or separated are split into two
streams, a depleted aqueous medium, which is designated the
raffinate, and an extract.
A substantial advance in the art ofseparating metal values is
5 provided by use of a two-solvent liquid-liquid extraction
system to separate the rare earth elements, and this is
described in copending U.S. Pat. application Ser. No.
657,580, filed Aug. I, 1967 and now abandoned. In that
system two solvents flow countercurrently to an aqueous solulOtion
and the values to be separated or extracted from the
aqueous feed solution are split into three streams, two extracts
The metals primarily contemplated to be separated by this and one raffinate. It is found in such a system that by proper
invention reside fairly closely and often adjacently to one selection of the organic solvents and the conditions for the exanother.
in the Periodic System. Such difficulty separable ele- 15 traction, the desired separation of the values contained in the
ments include, for example, those of the lanthanide series, and aqueous feed solution can be obtained. The primary adyttrium.
Such metals and their salts, i.e., generically, metal vantage of the system described in the copending application
values, are often together in solution, for example, in aqueous is that it provides SUbstantially improved separations with a
solutions, such as leach liquors resulting from the processing greatly. reduced number· of stages than would be required
of ores and commercial residues, or in organic solutions, such 20 using the same solvent singly. Although such a double solvent
as those obtained by commercial solvent extraction opera- extraction system of the type described in the copending aptions.
It is conventional in various mineral and metallurgical plication is very efficient for the separation of difficult to
processes to seek to separate and recover one desired metal separate metal values, especially the rare earths, it is a requirevalue
free from the other metals in the initial aqueous or or- ment ofthe system that both organic solvents flow cocurrently
ganic solution. The pure rare earth elements and their salts are 25 against the aqueous solution. Because of the cocurrent or
valuable, some ofthem having neutron moderating properties, countercurrent flow of the solvents with one solvent flowing
and the salts of the various rare earths are suitable as pig- cocurrently with the aqueous, in the copending application,
menu, for example, because oftheir different colors. Yttrium, maximum efficiency cannot be increased. Thus, there would
a metal which can be separated by the present process is valu- be a substantial improvement in separation ifa double solvent
able also, for example, as a "getter" in vacuum tubes and in 30 extraction system could be provided which would separate
the production ofyttrium hydride, a neutron moderator. metal values in organic as well as aqueous media; which per-
Closely related elements of the above-mentioned type have mits transfer of values between the solvents until equilibrium
been separated in the past by tedious fractional precipitation is established; and in which the flows can be countercurrent.
methods. More recently, particularly for the separation of ele- Such an improved double solvent extraction process·is proments
in the lanthanide and actinide series and yttrium, in- 3S vided by this invention. It has now been found that if a double
troduction of ion exchange processes marked a notable ad- extraction system is used, in which the extractants are allowed
vance in separation procedures. Still more recently there have to reach equilibrium among themselves using a bridging solbecome
available liquid-liquid extraction procedures for the vent between the two, extraction and separation of dissolved
separat!on. of mixtures. of closely. re~ated metals and t~ese are 40 metal values using two extractants can be carried out in a
of specilli unportance 10 the separation of rare earth mixtures. more efficient manner than heretofore.
Such procedures are based .upo? the.selective extractio~ of It is a primary object of this invention therefore to provide
~etal values from the solu~~ I~ W~IC~ the~ are contaJ.ned an improved double liquid-liquid extraction process to
mto a solvent-extrac~t whlc~ IS Immiscible With the solution. separate difficult to separate metal values.
Merely by way of dl~stratlOn, when ~are earths are to be 4S A further object of the invention is to provide a solvent-solseparated
by such techmques, the selective ~Ivent extractant vent extraction and separation process which can operate on
emplo~ed ~xtracts the rare earth ~aluesand It wou~d generally metal values in aqueous or nonaqueous solutions.
co~~nse, If ~ metal values are 10 aqueous solutio?, such as Still another object of the invention is to provide a process
acidIC leach liquors, at ~east seve~al percent by weight of :m to separate difficult to separate metal values using a double
extrac~t such ~ a ~uI~ble amme or alkyl phosphate ~IS- 50 solvent extraction system in which the flows of the two solsolved
10 a water-.unmlSClble solvent, kerosene generally bemg vents are countercurrent to one another.
used for economl~ reasons. I~ the metal values, on the ?th~r A further object of the invention is to provide an improved
hand, are present 10 ~ organl~ ~Ivent, then th~ separatlo.n IS process to separate the lanthanide rare earths and yttrium, one
called a back ex~tion, stnppmg o~ scrubbm~ operat~on, from the other.
because the separation from the organic solvent IS made mto SS
an aqueous, acidic solution, but in some cases basic or neutral
solutions are used. With respect to solvent extraction, as has
been mentioned, means are now available to achieve a separa- The above valuable objects and additional objects apparent
tion within the rare earth series. For example, if the rare earths to those skilled in the art from a consideration of the descripare
in aqueous solution, liquid-liquid extraction with an im- 60 tion herein are easily achieved by the practice of the present
miscible solvent comprising an amine, will extract the lighter invention which is in essence:
rare earth elements generally beginning with lanthanum and A process for separating metal values dissolved in a solution
proceeding through samarium according to atomic number. containing at least two ofsaid metal values which comprises:
The heavier elements, beginning generally with europium and a. contacting and mixing said solution with a first immiscible
ending with lutetium and including yttrium will not be ex- 65 extractant solvent medium, which extractant solvent
tracted with the amine system. Then if the same aqueous feed, medium exhibits selectivity for at least one of said metal
but depleted in lighter metal values, is subjected to further values to produce a first extract comprising the first selecliquid-
liquid extraction with a phosphate ester extractant in an tively extractable metal values dissolved in said first imimmiscible
solvent there occurs more separation by a selective miscible extractant solvent medium and separating said
extraction of the heavier rare earth elements according to 70 solution depleted in said first metal values from said first
atomic number, beginning generally with europium and end- extract;
ing with lutetium and including yttrium. These techniques are b. contacting and mixing the solution produced in step (a)
employed in the prior art using one solvent system, in the most with a second immiscible extractant solvent medium,
efficient of which the organic extractants flow countercur- which extractant solvent medium exhibits selectivity for
rently to the aqueous feed solution. In all single stage systems 75 at least one of said metal values to produce a second ex3
3,615,170
4
metal values is to be accomplished with the greatest efficiency.
A preferred process will be one wherein the solution is an
aqueous solution; and wherein the first and second immiscible
solvent media are organic solvent media. This defines a "water
bridge" embodiment.
Another preferred process according to this invention will
be one wherein the solution is an organic solvent solution and
wherein the first and second immiscible solvent media are
aqueous media. This defines a nonaqueous "solvent bridge"
embodiment.
It is to be understood that the present process broadly is applicable
to extractions from aqueous solutions into organic
solvents, and to extraction from nonaqueous solutions into
aqueous solutions. In the water bridge embodiment, the extraction
is made from aqueous solutions, for example, in the
case of rare earth and yttrium values from aqueous acid solutions
according to manipulations and in equipment such as
20 described in U.S. Pat. Nos. 2,955,913 and 3,110,556. Such extractions
with a first and second immiscible organic solvent
are described in the said copending application Ser. No.
657,580, now abandoned, filed Aug. I, 1967.
The solvent bridge embodiment is versatile. As in the water
bridge embodiment, it can be used for separation of metal
values. This will be better understood by reference to FIG. 5 in
the drawings. The system illustrated comprises three stages,
each consisting of two mixers and two settlers, with the
nonaqueous phase circulating between. The values to be
separated are present in the organic phase fed in the central
stage. This organic phase enters in contact with two aqueous
solutions, each having a different composition thereby extracting
from the organic feed different values. Aqueous solution
A moves to the right solvent bridge and aqueous solution
8 moves to the left solvent bridge in the flowsheet in a countercurrent
fashion. It will be understood that in the two side
solvent bridges, both solvents are not necessarily the same.
And neither is necessarily the same as the solvent fed into the
central solvent bridge. Thus, in its broadcast aspects, there
can be three or two different solvents or one solvent doing the
three stage solvent bridge system, which permits wide latitude
in selection for separation and purification purposes.
In addition, the values to be separated in either the solvent
bridge or water bridge systems do not necessarily have to be
present in the organic (or aqueous) feed in the central stage.
Referring again to FIG. S, the system illustrated may be used
to purify aqueous solution A whereby the impurities (or metal
values) in A can be efficiently transferred to aqueous solution
8 by use of the solvent bridge. In conventional solvent extraction
processes, if purification or separation has to be made of
values present in aqueous solution A, this solution is countercurrently
contacted with one solvent, then the solvent is
stripped Whereby the impurities or values are transferred to
another aqueous (for instance aqueous solution D). In the solvent
bridge system of the present invention this can be accomplished
more efficiently using appropriate solvents and
directly produced aqueous solution 8.
It is also obvious that the aqueous bridge embodiment provides
the same versatility. It is seen from the drawings, FIG. 4,
that it is not essential for the aqueous feed to contain the
values to be separated. Instead, they may be present either in
"barren" organic Aor Dand the values (or impurities) may be
transferred from one organic to another, entirely analogously
with the solvent bridge process.
A feature of this invention, therefore is a multistage process
wherein the metal values are fed into the system dissolved in
the aqueous or nonaqueous extractant media used in the last
phase of the process. This system can separate metal values
and impurities introduced centrally and terminally.
Another feature of this invention is a multistage process
wherein the metal values or impurities are not fed into the first
stage. This system permits transfer of values or impurities
between terminal stages. The solvent bridge emt:iodiment is
applicable in conventional stripping and scrubbing operations
tract comprising the second selectively extractable metal
values dissolved in said second immiscible extractant solvent
medium and separating said solution depleted in said
fint and second metal values from said second extract;
c. continuously recycling said solution from step (b) 5
between the said first and second media; and
d. recovering said metal values from said first and second
extracts.
This invention also contemplates a number of specific embodiments.
10
In one such process the solution contains at least two selectively
extractable metal values and at least one third metal
value which is not selectively extractable either by the first or
by the second of said immiscible solvents, and the process in- 15
cludes the step of recovering the third metal values from the
solution depleted in said first and second metal values. In this
embodiment a particular element which is desired to be extracted,
such as one particular rare earth element, may be
concentrated in the aqueous solution of a water (or solvent)
bridge. i.e., the solution of step (c) above. If this is the case,
this process may be carried out in such a manner as to continuously
withdraw the particular phase from the selected
bridge and to replace the withdrawn volume with enough
makeup solution to maintain a constant phase relationship. 25
The desired metal is recovered then from the withdrawn
phase.
Another preferred process includes additional stages for
further enhancing the separation of the first and second metal
values. If the extractant in step (a) is designated A and the ex- 30
tractant used in step (b) is designated D, then this preferred
proceu comprises:
I. contacting and mixing extract A with a bridging solvent
medium immiscible with both A and 8 extractant media
to become. in equilibrium with the metal values of the 35
bridging solvent medium; separating the bridging solvent
medium; contacting and mixing the bridging solvent
medium with fresh extractant 8 to produce an extract of
the metal values; continuously recycling the bridging solvent
between extractants A and 8; obtaining a final ex- 40
tract A; and using extract 8 in step (b) of the central
stage; and
II. contacting the mixing extract D with a bridging solvent
medium immiscible with both A and D extractant media
to become in equilibrium with the metal values of the 45
bridging solvent medium; separating the bridging solvent
medium; contacting and mixing the bridging solvent
medium with fresh extractant A to produce an extract of
the metal values; continuously recycling the bridging sol- 50
vent between extractants A and D; obtaining a final extract
8; and using extract A in step (a) of the central
stage. This embodiment provides substantially enhanced
separation efficiency as compared to the broad process
first-above defined. In such an embodiment, in each 55
stage, consisting of a pair of mixer settlers, for example,
the bridging solvent medium circulates between the two
extractants serving as a novel means to transfer the extractable,
difficult to separate metal values causing them
to move from one extractant to the other. Ift1).e bridging 60
solution is an aqueous solution, it may be adjusted in
composition of in pH to perform which ever separation is
most efficient.
An especial1y preferred process'is a continuous countercurrent
multistage process using in each subsequent stage the 65
respective extracts containing the metal values as the extractants,
pairing them through a bridging solvent medium with
extractants to produce subsequent extracts of the metal
vaiues; continuously recycling each bridging solvent between
the extracts; and using the extracts as extractants in the 70
preceding respective stages. There is no substantial upper
limitation on the number of stages which can be employed in
this. embodiment, for example, three, five and seven stages,
and even more can be used, the higher number of stages being
beneficial when the separation of very difficulty separable 75
5
3,615,170
6
in which organic extracts containing the metal values are
treated with immiscible aqueous solutions, such as aqueous
mineral acid solutions, e.g. sulfuric, nitric or hydrochloric
acids, to recover the metal values from the organic extracts.
Such processes are described in U.S. Pat. Nos. 3,077,378 in 5
3,167,402. Illustrative of the aqueous solutions contemplated
for use as feeds in the water bridge embodiment are aqueous
solutions of a plurality of rare earth salts and of yttrium, of
copper and iron, of nickel and cobalt. These solutions are ob- 10
tained by leaching ores, preparing commercial residues for
recovery operations, back extracting organic solvents
pregnant with mixed metal values, and so forth. The organic
solvent solutions employed as feeds in the solvent bridge embodiments
can be obtained by contacting leach liquors from IS
ore processing operations, or liquors from processing of scrap
metals, other types of waste liquors, byproduct streams such
as those produced in phosphate processing and so forth.
Another process of this invention is one in which the metal
values are selected from the group consisting of rare earth and 20
yttrium values. Although the present process broadly is applicable
to the separation of all difficulty separable, extractable
metal values, it is of very substantial importance in
separating the rare earths and yttrium.
The invention also provides a·process in which the feed is an 25
aqueous solution of praseodymium and neodymium values,
the first immiscible extractant solvent medium comprises a
phosphate ester, e.g. diethylhexylphosphoric acid, in a solvent-
diluent, e.g., a hydrocarbon solvent fraction, such as
kerosene; the second immiscible extractant solvent medium 30
comprises an amine, e.g., an aliphatic quaternary amine, in a
solvent-diluent, e.g., kerosene; the first selectively extractable
metal value is neodymium and the second selectively extractable
metal value is praseodymium. 35
Another process ofthis invention is one in which the feed is
an aqueous solution containing the lanthanide series of rare
earths, i.e., lanthanum, cerium, praseodymium, neodymium,
samarium, europium, gadolinium, terbium, dysprosium, holmium,
erbium, thulium, ytterbium and lutetium and yttrium, 40
the first immiscible extractant solvent comprises a phosphate
ester, e.g., diethylhexyl phosphoric acid in a solvent-diluent,
e.g., kerosene; the second immiscible extractant solvent comprises
an amine, e.g., a mixture ofalkyl primary amine isomers
having 18-20 carbon atoms, in a solvent-diluent, e.g., 45
kerosene; the first selectively extractable metal values are the
"heavy" rare earths of atom number from about 63 to the 71,
i.e., europium, gadolinium, terbium, dysprosium, holmium, erbium,
thulium, ytterbium and lutetium, and yttrium, atomic
number 39; and the second selectively extractable metal 50
values are the "light" rare earths ofatomic number of from 58
to about 62, i.e., lanthanum, cerium, praseOdymium,
neodymium, and samarium.
A preferred process according to this invention is a threestage
continuous countercurrent process in which the feed is 55
an aqueous solution containing about 100 grams/liter of rare
earth values which solution is 4 molar in ammonium nitrate,
the metals comprising the lanthanide series, i.e., lanthanum,
cerium, praseodymium, neodymium, samarium, europium, 60
gadolinium, terbium, dysprosium, holmium, erbium, thulium,
ytterbium and lutetium, and yttrium; the first immiscible extractant
solvent medium is 50 percent diethylhexyl phosphoric
acid in an aromatic hydrocarbon solvent (SacoSoI ISO); the
second immiscible extractant solvent medium is 25 percent 65
quaternary aliphatic amines (tricaprylyl methyl ammonium
chloride) in an aromatic hydrocarbon solvent (SacoSol ISO);
the first selectively extractable metals are the "heavy" rare
earths of atomic number of from about 63 to 71, i.e., europium,
gadolinium, terbium, dysprosium, holmium, erbium, thu- 70
Iium, ytterbium and lutetium and yttrium, atomic number 39;
and said second selectively extractable metals are the "light"
rare earths of atomic number of from 58 to about 62, i.e.,
lanthanum, cerium, praseodymium, neodymium and samarium.
75
Another process according to the invention is one in which
the feed is an aqueous solution which is a lanthanum concentrate
containing lanthanum, praseodymium and neodymium
which solution is 4 molar in ammonium nitrate; the first immiscible
extractant solvent medium is 43 percent diethylhexyl
phosphoric acid and 7 percent ammonium diethylhexyl
phosphate in an aromatic hydrocarbon (SacoSol 150); the
second immiscible extractant solvent medium is IS percent
quaternary aliphatic amines (tricaprylyl methyl ammonium
chloride) in an aromatic hydrocarbon (SacoSol 150); the first
extractable metal values are praseodymium and neodymium
and the second extractable metal value is lanthanum.
Still another preferred feature of this invention is a fivestage
process in which the feed is an aqueous lanthanum concentrate
comprising lanthanum, praseodymium and neodymium;
the first immiscible extractant solvent medium is 30 percent
diethylhexyl phosphoric acid in kerosene; the second immiscible
extractant solvent medium is 15 percent alkyl primary
amines having 18-21 carbon atoms is kerosene; the
bridging solvents in stages I to 5, respectively, are aqueous
mineral acids having pH values of 1.4, 1.5,5.7,2.2, and 2.0;
the first extractable metal values are praseodymium and
neodymium and the second metal value is lanthanum.
As will be shown hereinafter, these latter systems provide
substantially enhanced efficiency in the separation of these
difficulty separable, extractable metals. Greater separation
factors are achieved than can be obtained by prior art
methods using either immiscible extractant solvent alone.
When used herein and in the appended claims, the expression
"contacting and mixing" contemplates any suitable
means of bringing together the immisicible fluid phases. In any
case the metal value is separated from the feed material in
processing equipment which is conventional in the art. Such
systems may be adapted to simple phase equilibrations, e.g.,
separatory funnels, continuous countercurrent extraction
using mixer-settler systems, which are preferred; but other
systems amenable to efficient contact and separation of immiscible
fluid phases also can be used. Phase ratios in the
range of about I :20 to 20: I, nonaqueous to aqueous, are
usually satisfactory, and it will be appreciated that concentrations
of the amines and alkyl phosphate, phosphonate or
phosphoric acid ester extractant in the organic solventdiluent,
and, in the water or solvent bridge systems, the pH
and ionic strength of the aqueous solution, are interrelated
and that the particular choice for these variables will depend
on a variety offactors including solubilities of relevant materials,
losses, recovery and purity level desired, and the like. In
the present invention, of course, the organic solvents should
be insoluble in aqueous solutions and they should also have a
selectivity for extraction of the metal values. "Organic immiscible
extractant solvent" media are contemplated to comprise
a solvent-diluent and an extractant, which is an amine or
phosphoric acid ester or mixtures thereof of the character to
be described hereinafter. Paraffins, such as kerosene, other
petroleum fractions, xylene, toluene and the like are excellent
solvent-diluents for the preparation of organic extractant
phases. Especially preferred are kerosene and an aromatic
hydrocarbon mixture sold under the trade name "SacoSol
150". However, many other materials are satisfactory including
aliphatic hydrocarbons, halogenated hydrocarbons and
the like. Selection is usually made on an economic basis and
operational factors. Concentrations of the extractant in the
solvent-diluent can range from about 0.05 percent to pure extractant.
One class of extractants comprises organic soluble
primary, secondary, tertiary and quaternary amines. illustrative
of amines which exhibit selectivity for metal values are
trioctylamine, dodecylamine, heptadecylamine, mixed C12-C.
4 primary aliphatic amines with highly branched chains (sold
by Rohm & Haas Co. under the trade name "Primene 81-R"),
mixed C18-C.1 primary alkyl amines having highly branched
chains (sold by Rohm & Haas Co. under the trade name "Primene
JM-T"), N-benzylheptadecylamine, and the like.
Preferred extractants of this class are the above-described
3,615,170
DESCRIPTION OF THE DRAWINGS
~-
dissolved in aqueous extractant media, they can be recovered
either through boiling off volatile acids, HCI and HF (in appropriate
cases) and subsequent volume reduction through
evaporation; or they can be precipitated by the addition of appropriate
reagents, such as anhydrous ammonia or caustic
soda. Also, ion exchange columns can be used for the intermediate
treatment of the aqueous solutions containing the
metal values by well known techniques in order to recover
said values.
A more complete understanding of the present process and
of the advantages obtained therewith will be understood from
the following discussion with reference to the drawings in
which:
FIG. I., is a flow diagram illustrating a conventional single
solvent extraction process using the solvent countercurrently
in four extraction and two reflux stages, to provide an extract
of the metal values and an aqueous raffinate.
FIG. 2., is a flow diagram illustrating a double solvent extraction
process using both organic solvents cocurrently to advance
countercurrently in two extraction and one reflux stage,
to provide two extracts and an aqueous raffinate. This is a
preferred embodiment of the said copending U.S. Pat. application
Ser. No. 657,580, filed Aug. I, 1967.
FIG. 3., is a flow diagram illustrating a single-stilge aqueous
solvent (water) bridge process using two organic solvents and
a continuously circulating bridging solvent to provide two extracts,
according to this invention.
FIG. 4., is a flow diagram illustrating a three-stage double
extraction water bridge process according to this invention
using two organic extractants, each of which is subjected to a
subsequent stage extraction using paired bridging aqueous
solutions to provide two organic extracts.
FIG. 5., is a flow diagram illustrating a three-stage double
extraction solvent bridge process according to this invention
using two aqueous extractants, each of which is subjected to a
40 subsequent stage extraction using paired bridging organic solvents
to provide two aqueous extracts. This system has been
explained above.
While the legends placed on the drawings make them virtually
self-explanatory, with reference to FIG. I, six stages are
shown, each of which comprise one mixer (top) and one settler
(bottom). The organic extractant flows in countercurrently
to the aqueous feed. In the figure the arrangement
shown comprises four stages ofextraction, 1-4, and two stages
of reflux, 5-6. In the reflux stage, the organic extractant conventionally
is contacted with an aqueous reflux solution to improve
the purity of the extract. Such a reflux step can be
added to any of the systems described for the present invention
without departing from the spirit or scope thereof. With
this prior art system, the metal values to be separated are
recovered from two products, a raffinate from stage 1 and an
extract from stage 6.
FIG. 2 illustrates a double solvent extraction system, which
gives substantially improved separation compared to the single
solvent extraction process of FIG. 1. In this system, two
solvents, A and B, flow in cocurrent to each other, but countercurrently
to the aqueous solution of metal values. In the arrangement
shown, each organic solvent extracts through two
stages and is refluxed in one stage. Recovery of the metal
values from this system are achieved by treating two extracts,
A and B, from stage 5 and 6 respectively, and one raffinate
from stage I may contain unextractable metal values. If the organic
solvents are properly selected, a highly efficient separation
of the values contained in the aqueous feed solution can
be attained. Although the process illustrated in FIG. 2 is
powerful, both organic solvents flow cocurrently against the
aqueous solution and maximum efficiency is limited by this
factor.
In FIG. 3 there is shown a flow path according to the present
invention which will provide improved recovery and purity of
branched chain primary amines or N-benzylheptadecylamine
diluted with kerosene, or SacoSol ISO. Especially preferred
because of high extraction efficiency and because it does not
become water soluble when dilute sulfuric acid is added, is the
product Primene JM-T. Quaternary amines, as have been 5
mentioned, also are of substantial use and are preferred members
of this class of extractants. Special mention is made of the
product (sold by General Mills, Inc. under the trade name
"Aliquat 336") which is described as tricaprylyl methyl ammonium
chloride. A preferred concentration level either for 10
Primine JM-T or Aliquat 336 in the solvent diluent would be
from about 5 percent to about 50 percent weight, illustrative
levels being, for example, 10 percent, 15 percent and 25 percent
by weight.
Another important class of extractants comprises substan- IS
tially water-immiscible alkyl phosphonates or alkyl
orthophosphates, wherein the alkyl groups each contain from
about four to about 20 carbon atoms in straight or branched
chains; Illustrative of these compounds which exhibit selectivi- 20
ty for certain metal values are tributyl phosphate, trioctyl
phosphate, dodecyl phosphoric acid, di-n-butyl
orthophosphate, di-2-ethylhexylorthophosphoric acid (HDEHP)
and the like. Especially preferred in this class is
HDEHP because it has a low solubility in water and a lesser 25
tendency to hydrolyze; it is commercially available. The solvent-
diluent used with this class of extractants are generally
tbesame as those to illustrated for the other class above, e.g.,
toluene, xylene, kerosene, SacoSol ISO and the like. The concentration
of the phosphonates or orthophosphates in the 30
diluent can be varied widely, a concentration between 5 percent
and 75 percent being the preferred range. Also it is useful
sometimes to have present a proportion of an organic-Soluble
salt of an alkyl phosphoric acid, e.g., ammonium diethylhexyl
phosphate to this type of extractant, a preferred composition 35
being, for example, a 50 percent HDEHP in SacoSol ISO
which has been treated with ammonia to the desired extent to
obtain a solvent containing different ratio of the di-2-ethylhexylorthophosphoric
acid and the ammonium di-2-ethylhexylorthophosphate
salt.
While the appended claims and this specification contemplate
"first" and "second" immiscible extractant solvent
media, it is to be understood that this is for convenience in depicting
and explaining the process. There is no intention so to
label either the amine extractant or the alkyl phosphate ex- 45
tractant as defined above. Either can be employed in the first
step ofthe process. Moreover, in carrying out any particular
separation in accordance with this invention, it is not necessary
to use one alkyl phosphate extractant solvent medium with
one amine extractant solvent medium since two amine extrac- 50
tant solvent media or two alkyl phosphate extractant solvent
media can be used provided only that the media selected show
the necessary degree of selectivity for at least one of the metal
values in solution relative to at least one other metal value in 55
the solution. In the organic solvent bridge systems wherein
aqueous media are employed as the first and second immiscible
solvent, such relative selectively is achieved by varying the
pH and ionic strength, and the like, between aqueous media.
These concepts are familiar to those skilled in the art. 60
"Recovering" the metal values can be the valuable out in
any art-recognized manner. For example, in the water bridge
embodiments wherein the extracted metal values are dissolved
in organic extractant media they can be recovered by
precipitation, by evaporation, by re-extraction with an aque- 65
ous phase or by stripping the solvent with an appropriate
aqueous stripping solution, e.g., an aqueous strong mineral
acid, or an alkali metal carbonate, and the stripped solvent
returned to the process. The separated metal values can be
concentrated, for example, merely by evaporating the 70
stripping solution or by proper chemical treatment. Solid
residues can be calcined or subjected to further well-known
treatments and purifications to yield the valuable commercial
products mentioned hereinabove. In the organic solvent
bridge embodiments wherein the extracted metal values are 75
9
3,615,170
10
TABLE I
EXAMPLE 1
Comparison of Separation of
DESCRIPTION OF THE PREFERRED EMBODIMENTS
To further illustrate the present invention with respect to
the separation of extractable but difficulty separable metal
values, especially rare earth values, from solutions thereof, the
following specific examples are presented. An amine solvent
which preferentially extracts the light rare earth values is used
as one of the solvents and a phosphate solvent which
preferentially extracts the heavy rare earth values is used as
the other solvent. The examples are merely illustrative since,
as has been mentioned hereinabove, the first and second extractant
solvents can comprise amines or phosphates or mixtures
of the two, or any other pair of solvents selected to perform
the desired separation.
system of FIG. 1. Assuming this, it becomes possible to compare
the efficiency of the two systems in terms of distribution
coefficients and separation factors. AS will be seen from the
exal"ples, hereinafter, the present process provides separation
5 factors very substantially greater than those of the conventional
single solvent extraction process and substantially
better also than those of the double stage process described in
copending application Ser. No. 657,580, now abandoned,
filed Aug. I, 1967.
10 Because temperatures do not seem to be particularly critical
to the practice of the present invention, they may be varied
over the operating ranges usually employed in solvent extraction
procedures. It has been found, however, that beneficial
results are sometimes obtained if the stages are warmed up in
15 order to improve phase separation in the settlers. Depending
on the diluent used, temperatures of up to 45° C. can be employed.
This moderate elevation in temperature has a favorable
effect on the rate at which the mixed aqueous and organic
20 disengage once transferred from the mixer to the settler. This
is especially true in cases where amines, e.g., Primene 1M-T,
are used as one of the solvents.
60
A pair of mixer-settlers were provided and arranged as
shown in FIG. 3. This system is a single stage water bridge according
to this invention. An aqueous solution was prepared,
containing 75 g./1. of praseodymium-neodymium oxides in
the nitrate form (33 percent Pr-67 percent Nd). One of the
immiscible extractants comprised 50 percent by weight of
diethylhexyl phosphoric acid (HDEHP) dissolved in kerosene.
The other immiscible extractant comprised 25 percent by
weight of a long chain alkyl quaternary amine, tricaprylyl
methyl ammonium chloride Aliquat 336), dissolved in an aromatic
hydrocarbon mixture (SacoSol 150). At phase ratio
0/A of 2.0 for Aliquat and 1.0 for HDEHP, the system was allowed
to reach equilibrium by circulating at a rate of 100
ml./min. for each aqueous and HDEHP and 200 ml./min. for
Aliquat 336. Each organic phase was analyzed for
55 praseodymium and neodymium. The distribution coefficient
(K) for each metal value in each solvent was calculated as
described hereinabove and the separation factor (S) for
praseodymium and neodymium between HDEHP and Aliquat
336 was calculated, also as described hereinabove.
To compare the results of this process with a conventional
single stage single solvent extraction system, an aqueous solution
of praseodymium and neodymium nitrate of the same
composition was extracted with a solution of HDEHP in
kerosene under the same conditions. Another portion was ex-
65 tracted with Aliquat 336 in SacoSol 150 under the same conditions.
The organic and aqueous phases were separated and
analyzed and K and S for the two elements with respect to
each of the two solvents were calculated.
The results of the three processes are summarized in table I:
the extracted elements over the said double solvent extraction
process. In the process of FIG. 3, one extractant solvent is fed
into each end of the double solvent extraction stage and each
is separately mixed with an aqueous solution continuously circulating
between each mixer-settler. Aqueous feed may be introduced
into the system at any point of the system shown by
the broken lines (- - -), by taking some of the circulating
water between the two stages and dissolving metal values, for
example, oxides or carbonates, therein. Once enough acid,
e.g., sulfuric, nitric, hydrochloric and the like, is added to obtain
the desired pH, the aqueous is re-introduced into the
bridge. In this manner, two solvent extracts are obtained. To
analyze the efficiency of the separation, a sample can be taken
from the bridge circuit, e.g., where indicated, and the distribution
coefficients (K) and separation factors (S) can be determined,
as will be described hereinafter.
FIG. 4 illustrates one preferred system of this invention,
which contains three stages of water bridges and has two solvents
flowing countercurrently against each other. This provides
for the use of two organic extractants (each of which
usually are mutually soluble) avoiding mixing of the two. The
feed solution containing the metal values may be introduced
into this system by a number of methods. As is shown in FIG.
4, for example, this feed is introduced into the middle water 25
bridge and what would ordinarily be the raffinate in a single or
double solvent extraction system (FIGS. 1 and 2) is used to
prepare more of the feed. As is mentioned above, however,
the values can also be introduced elsewhere. Each settler and
mixer pair includes an aqueous bridging solution which, as will 30
be shown hereinafter, may be adjusted in pH, ionic strength,
etc., as may be desirable.
FIG. 5 illustrates the solvent bridge solvent extraction
system according to this invention. The feed solution usually
will be an organic solvent (Extract A) containing the metal 35
values desired to be separated. Analogously to the system
shown in FIG. 4, aqueous reflux solutions A and B are introduced
at opposite ends and flow countercurrently against
one another. Corresponding to the raffinate in prior art
systems, will be a scrubbed organic (A). As mentioned above, 40
the metal values can also be fed in aqueous A or B. In each
stage comprising a pair of mixer-settlers there is continuously
circulating an organic bridging solvent (solid line) which
prevents the aqueous refluxes from mixing, while permitting 45
the exchange of metal values between them.
The efficiency of the present process can be measured and
compared with the liquid-liquid extraction processes of the
prior art by obtaining analytical data to calculate distribution
coefficients (K) and separation factors (S). The distribution 50
coefficient is defined as the ratio of concentration of the extractable
species between two immiscible solvent phases - in
the present case, between organic and aqueous solutions:
concentration in organic phase
K concentration in aqueous phase
The separation factor between two elements is defined as the
ratio of the distribution coefficient obtained from above. Thus
the separation factor for two difficult to separate species, A
and B, may be expressed as follows:
KA distribution coefficient for A
s= K B distribution coefficient for B
Those skilled in the art will understand that because two organic
solvents are used in the double solvent process shown in
FIG. 2 and in the double solvent, water bridge and solvent
bridge, processes shown in FIGS. 3-5, it is somewhat difficult
to compare the efficiency of these systems with straight conventional
countercurrent single solvent extraction as shown in
FIG. 1. However, it is reasonable to assume that since one sol- 70
vent is working against the other, one of them is playing the
part of the aqueous in the single solyent system. In other
words, FIG. 1 shows one extractant and one raffinate being
produced and one can assume that extract B in FIG. 3 is. a raffinate,
while extract A is comparable to the extract In the 75
3,615,170
11
Pr_odymiuID and Neodymium in I.Stale
Waler Iridp SYltem with Strailht
Solvent Extraction
Telt
No. SYltem Type Element K S (Nd/Pr)
5
HDEHp· lialle Pr 0.42 1.19
Aq""OUI IOhrent Nd 0.50
2 Aliquat336 oiap Pr 0.76
Aq- eoIvcnt Nd 0.46 1.77
HOEHp· _I>.. Pr 1.01
Aliqut 336) Solvent Nd 2.25 2.23 10
Ir.
It is c¥ident that a arcater Kplration factor WII obtained
with the water bridle according to this invention, test 3, than
could be achieved with either of the conventional single solvent
extraction systems, tests 1 and 2.
12
from heavy rare earths and yttrium. The solvents used were 50
percent HDEHP in an aromatic hydrocarbon solvent mixture
(SacoSoI150), which entered in mixer I (water bridge No.1)
at a rate of 100 ml./hr., and 25 percent Aliquat 336 in SacoSol
ISO entering in mixer 6 (water bridge No.3) at a rate of 1,000
ml./hr. Aqueous feed comprised a rare earth and yttrium mixture
at 100 g. rare earth oxide per liter concentration plus 4
molar NH~NOa, and this was introduced into mixer 4 (water
bridge No.2). Through water bridge No. I there was circulated
aqueous 2 MNH~NOa as the bridging solvent, pH 1.0; in
water bridge No.2, there was circulated the feed, 4M in
NH~NO" pH 1.0; and in water bridge No.3 there was circu·
lated aqueous 4M NH~NOa and 1.5 normal HNOa. After ex·
15 traction, the rare earth feed composition and the extracts were
analyzed and the relevant K values were determined. The
analyses are summarized in table 3:
TABLE 3
EXAMPLE 2 20 _
2.1
4.6
5.5
3'.5
50.1
0.4
'.0
0.1
Aliquat
336.%
0.1
13.4
0.5
36.6
6.2
12.1
1.0
2.7
0.5
1.1
0.3
24.4
Metal Values Extracted
HDEHP• .,
TABLE 4
EXAMPLE 4
1.9
4.1
4.9
27.3
46.8
0.4
9.3
0.7
1.3
0.2
0.3
0.05
0.1
0.04
2.6
Rare Earth at Yttrium
Feed Composition. %
La
Ce
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
Y
Separation of Rare Earths and
Yttrium in a 3~Stage.Water·Bridle
System
Sialic Slale Water Bridp Separation
of Lanthanum from Praseodymium and
Neodymium
Telt
No.
From these data, using the methods described above, separation
factors S were calculated. They are Sm/Nd, 107; Gd/Sm,
23; and Tb/Gd, 8.1. These were substantially greater than
those obtained in the single.stage water bridge system, which
in turn was much more efficient than the single solvent system.
35
40
50 A single-stage water bridge process according to this invention
was used to separate lanthanum from praseodymium and
neodymium. The system is described in FIG. 3. One extractant
comprised HDEHP partially neutralized with ammonia
55 (43percent HDEHP plus 7percent NH~HDEHP) in SacoSoI
150 and the other comprised 15percent Aliquat 336 in
SacoSol 150. The feed solution comprised aqueous La·Pr-Nd
concentrate, 75 g./1. (as REzOa) in the form of nitrate salts,
which solution was 4 molar in NH~NOa. After extraction the
60 extracts were analyzed for rare earth content and the results
are summarized on table 4:
The single-stage water bridge procedure of example I was
used to separate light from heavy rare earths and yttrium. The
47 employed were 15 percent diethylhexyl phosphoric acid
(HDEHP) in kerosene and 15 percent of a primary amine hav- 25
ing 18-21 carbon atoms (Primene-JM-T, Rohm & Haas Co.)
in kerosene. In the aqueous bridge there was placed a rare
earth and yttrium mixture at 27 g./I. concentration (as R~Oa)
and as the sulfates at pH 4. After reaching equilibrium, the organic
and aqueous phases were analyzed and the relevant K 30
values were determined. Table 2 presents the analysis of the
aqueous feed and the extracts obtained; also, the calculated K
values as a ratio ofconcentration of a particular element in the
HDEHP extract and its concentration in the JM-T extract.
From these data the ratios ofK values, i.e., the separation fac·
tors S were calculated as described above. They were Sm/Nd,
9.7; EulSm, 4.8; Gd/Eu, 3.3; and Tb/Gd, 3.7. In contrast, all
amine and phosphate extractant solvents in the literature in
single solvent extractions provided separation factors between
consecutive rare earths on the order of 1.0 to 2.5 at best,
averaging in general about 1.5. Thus the separation factors
with the present process between the middle rare earths
(which are the only ones possible to calculate because the 65
others are not present in one or the other solvent) are substantially
higher than those expected from reported data on the
same solvents acting alone.
TABLE 2
Separation or Rare Earths and Yttrium in aI-StageWater Bridge System
Rare earth and Metal values extracted
yttrium feed
Test compoe1t1on, HDEHP JM-T (HDEHP)
No. percent percent percent K JMT
._•• __ •••••• La,1.8__ ••••••••_••• _._ ••_.. 4. 2 •••••••••••_•••••_
Ce,2.6_ •••••_•••••• _........ Ii. 8 ••_•••_••••••••• _.
PrI 2.1•• •••••••• __ ••••••• 4. 7 ••••••••••••• _••••
No, 11.7••__ ••..• 0.9 25.4 0.043
Bm,33.3__••••••• 17.6 63.3 0.42 45
Eu,l.0.......... 1.1 0.7 2.0
Gd,l8.0......... 28. 0 6.6 6.6
Tb,306._••••••_. 6.9 0.3 23. 8
Ii~"""i"~ I!~":~~:":ii"i~~,~i~~~i~;~~~~~~i
Composition of E..tracls
HDEHP• ., Aliquat
336, .,
Rare Earth Feed
Composition, ,.
Telt
70 No.
EXAMPLE 3
The use of a multistage extraction process according to this
invention multiplies substantially the separation factors obtained
with a single-stage water bridge. A three-stage system 6 La 74.0 41.1 II.'
comprisin" three pairs of mixer-settlers was provided, ar- Pr 7.5 14.7 4.'
ranged asDshown in FIG. 4. This was used to separate light 75 Nd 18.5 44.1 _7.4
3,615,170
14
39.7 \5.8 4\ 3.7 1.0
27.6 47.2 317 6.6 8.0
9.9 25.7 1,729 23.9 43.7
33.3 1.1 12 \3.3 0.3
4.5 3.0 988 54.0 25.0
76 81.2 1.9
2.0 0.\ 135 93.8 3.4
47 100.0 1.2
5.4 0.1 29 78.4 0.7
4 0.1
11.1 0.1 \8 66.6 0.5
2 0.1
0.7 0.\ 547 98.2 \3.7
3,957
4
2.787
441
1,317
718
29
82
Aqueous 1.0 N HN03
mg.1I Distr % Purity
La 206 58.3 2.1
Ce 100 63.0 1.0
Pr 629 56.6 6.5
Nd 3.\47 65.8 32.4
Sm 4.776 66.2 49.2
Eu 47 53.3 0.5
Gd 759 41.5 7.8
Tb 18 \8.8 0.2
Dy 6 4.2 0.\
Ho
Er 6 16.2 0.\
Tm
Yb 22.2 0.\
Lu
Y 6 1.1 0.\
Total 9.706
Pr
Nd
Sm
Eu
Gd
5 Tb
Dy
Ho
Er
Tm
Yb
Lu
10 Y
Total
HDEHP, Aliquat 336,
percent percent
3.3 5.5
36.9 02.4
13.8 2.2 49.3 5.4 30
EXAMPLES
With this system it was possible to increase the lanthanum
content from 74 percent in the feed to 88 percent in the
Aliquat extract and to recover 81.7 percent. Recovery of
Pr-Nd in the HDEHP extract was 81.7 percent.
A lanthanum-praseodymium-neodymium concentrate was
separated in a five-stage water bridge system according to this
invention. The arrangement is very similar to that depicted in
FIG. 4, except that one extra stage was used at each end. The
solvents used were 30percent HDEHP in kerosene entering
Mixer I (water bridge No. I) at at a rate of 300 m!./hr. and
15percent Primene JM-T (defined above) in kerosene entering
Mixer 10 (Water bridge No.5) at a rate of 300 m!. per IS
hour. The aqueous feed was a rare earth sulfate solution (10 - .....----------------------
g./l. as RE.oa) which circulated through water bridge No.3.
(mixer pairs 5 and 6). The pH of the aqueous bridging solvents
were respectively water bridge No. I, 1.4; No.2, 1.5; No.3,
5.7; No.4, 2.2; and No.5, 2.0. After extraction the extracts 20
were analyzed for rare earth content and the results are'summarized
in table 5.
TABLE 5.-FrVE-STAGE WATER BRIDGE SEPARATION OF
LANTHANUM FROM PRASEODYMIUM AND NEODYlIUUM
Metal values extracted 25
13
Rare earth
Test feed composi-
No. tion, percent
7 G./l. RE,03
La 74.0
Pr 7.5
Nd 18.5
EXAMPLE 6
Table 6
Single-Stage Solvent Bridge Separation of Rare Earths and
Yttrium
It was demonstrated that the purity of lanthanum can be increased
up to 92.4 percent in the primary amine (1M-T extract
with a recovery of 82.3 percent.
It can be seen that with only one stage using the system according
to this invention, it was possible to upgrade the yttrium
in the solvent from 3.3 percent to 13.7 percent with 98.2
35 percent recovery. It is also seen that two valuable aqueous
solutions were produced containing the "light" rare earths,
one being richer in the pair Pr-Nd and the other richer in SmGd.
It will be obvious to those skilled in the art that if sufficient
40 stages are provided and the metal values are properly selected,
one element, e.g., a rare earth, which it is desired to separate,
may concentrate in the aqueous bridging solvent. In this case,
the system readily may be modified continuously to withdraw
that particular aqueous from the water bridge and replace the
45 volume with more barren aqueous solution.
Furthermore, since the water bridge system permits two organics
of different qualities to extract from each other the
desired elements, an obvious extension of the basic invention
will comprise the use of three organic extractants, each work-
50 ing against the other two. As has been mentioned, there are
some organic solvents which preferentially extract the light
rare earth elements and others which preferentially extract the
heavy rare earths. However, there are some solvents, such as,
for example, trioctyl phosphine oxide, which preferentially ex-
55 tract the middle rare earths. Means thus now are available to
employ a system using three organic solvents to split, in a few
stages, the rare earths into three different and valuable fractions.
The above invention is not to be limited by the above
60 description or examples which are given merely as illustrative.
The scope of the invention is to be interpreted by the appended
claims.
We claim:
I, A process for separating metal values selected from the
65 group consisting of rare earth and yttrium values dissolved in a
solution containing at least two of said metal values which
comprises:
a. contacting and mixing said solution with a first immiscible
elltractant solvent medium, which extractant solvent
70 medium exhibits selectivity for at least one of said metal
values to produce a first extract comprising the first selectively
extractable metal values dissolved in said first immiscible
extractant solvent medium and separating said
solution depleted in said first metal values from said first
extract;
b. continuously circulating the solution from step (a) in a
bridge between the first immiscible extractant solvent
Aqueous 0.5 N HN03 Final Organic
mg./I. % Distr % Purity mg./1. % Distr %
Purity
75
141 40.0 5.1 6 1.7 0.1
47 29.6 1.7 \2 7.4 0.3
mg. REI!. RE purity. %
La 353 2.\
Ce 159 1.0
Pr 1,112 6.8
Nd 4.782 29.1
Sm 7,224 43.9
Eu 88 0.5
Gd 1,829 11.1
Tb 94 0.6
Dy 147 0.9
Ho 47 0.3
Er 4\ 0.2
Tm Trace
Yb 29 0.2
Lu Trace
Y 547 3.3
Total 16,452
A 50 percent by volume solution of diethylhexyl phosphoric
acid solution in SacoSol150 was loaded with 16.45 g. ofrare
earth elements per liter. The composition of this loaded organic
solution was as follows:
At a phase ratio of 1.0, a one-stage solvent bridge extraction
system was simulated. The loaded organic solution was
equilibrated alternatively and continuously between two aqueous
immiscible nitric acid solutions, at 0.5 and 1.0 N, respectively.
Then the final aqueous and organic solutions were
analyzed for rare earths by X-ray fluorescence techniques.
The results are summarized in table 6:
La
Ce
15
3,615,170
16
medium and a second immiscible extractant solvent
medium;
c. contacting and mixing the solution circulated in step (b)
with the second immiscible extractant solvent medium,
which extractant solvent medium exhibits selectivity for 5
at least one of said metal values to produce a second extract
comprising the second selectively extractable metal
values dissolved in said second immiscible extractant solvent
medium and separating said solution depleted in said
first and second metal values from said second extract; 10
d. continuously circulating the solution from step (c) in a
bridge between the second immiscible extractant solvent
medium and the first immiscible extractant solvent medium,
whereby the bridge circuit obtained by the combination
of steps (b) and (d) provides equilibration of metal 15
values between the first immiscible extractant solvent
medium and the second immiscible extractant solvent
medium; and
e. recovering said metal values from said first and second
extracts. 20
2. A process as defined in claim 1 wherein said solution contains
at least two selectively extractable metal values and at
least one third metal value which is not selectively extractable
either by the first or by the second of said immiscible solvents, 25
including the step of recovering the third metal values from
the solution depleted in said first and second metal values.
3. A process as defined in claim 1 including additional
stages, wherein, if the extractant in step (a) is designated A
and the extractant used in step (c) is designated B, the steps 30
comprise:
t. contacting and mixing extract A with a bridging solvent
medium immiscible with both A and B extractant media
to become in equilibrium with the metal values of the
bridging solvent medium; separating the bridging solvent 35
medium; contacting and mixing the bridging solvent
medium with fresh extractant B to produce an extract of
the metal values; continuously recycling the bridging solvent
between extractants A and B; obtaining a final extract
A; and using extract B in step (c) of the central 40
stage; and
II. contacting and mixing extract B with a bridging solvent
medium immiscible with both A and B extractant media
to become in equilibrium with the metal values of the
bridging solvent medium; separating the bridging solvent 45
medium; contacting and mixing the bridging solvent
medium with fresh extractant A to produce an extract of
the metal values; continuously recycling the bridging solvent
between extractants A and B; obtaining a final extract
B; and using extract A in step (a) of the central 50
stage.
. 4. A multistage process as defined in claim 3 including a
third stage extraction and separation of the metal values using
extracts from the second stage as extractants.
S. A continuous countercurrent multistage process accord- 55
ing to claim 1 using in each subsequent stage the respective
extracts containing the metal values as the extractants, pairing
them through a bridging solvent medium with extractants to
produce subsequent extracts of the metal values; continuously
recycling each bridging solvent between the extracts; and 60
using the extractant solvent media in the preceeding respective
stages.
6. A process as defined in claim 1 wherein said solution is an
65
70
75
aqueous solution and wherein said first and second immiscible
solvent media are organic solvent media.
7. A process as defined in claim 1 wherein said solution is an
organic solvent solution and wherein said first and second immiscible
solvent media are aqueous media.
8. A process according to claim 5 wherein said metal values
are fed into the system dissolved in the extractant media used
in the last stage of said process.
9. A process according to claim 8 wherein said metal values
are not fed into the first stage of said process.
10. A process as defined in claim I wherein said solution is
an aqueous solution containing praseodymium and neodymium,
Said first immiscible extractant solvent medium comprises
an alkyl ester of phosphoric acid in kerosene; said second immiscible
extractant solvent medium comprises an aliphatic
quaternary amine in kerosene; the first selectively extractable
metal value is neodymium and the second selectively extractable
metal value is praseodymium.
11. A process as defined in claim 1 wherein said solution is
an aqueous solution comprising lanthanide series rare earth
values and yttrium values; said first immiscible extractant solvent
comprises diethylhexyl phosphoric acid in kerosene; said
second immiscible extractant solvent comprises a mixture of
tertiary alkyl primary amine isomers having 18-20 carbon
atoms, in kerosene, said first selectively extractable metal
values are heavy rare earth metals and yttrium; and said
second selectively extractable metal values are light rare earth
metals.
12. A three-stage continuous countercurrent separation
process as defined in claim 4, wherein said solution is an aqueous
solution containing about 100 gramslliter of rare earth
values which is 4 molar in ammonium nitrate, said metals
comprising lanthanide series rare earth values and yttrium
values; said first immiscible extractant solvent medium is 50
percent diethylhexyl phosphoric acid in an aromatiC hydrocarbon
solvent; said second immiscible extractant solvent medium
is 25 percent quaternary aliphatic amines in an aromatic
hydrocarbon solvent; said first selectively extractable metal
values are heavy rare earth metals and yttrium; and said
second selectively extractable metals are light rare earth
metals.
13. A process as defined in claim 1 wherein said solution is
an aqueous solution comprising lanthanum, praseodymium
and neodymium which is 4 molar in ammonium nitrate; and
first immiscible extractant solvent medium is 50 percent
diethylhexyl phosphoric acid in an aromatic hydrocarbon solvent
which has been treated with ammonia; said second immiscible
extractant solvent medium is 15 percent quaternary
aliphatic amines in an aromatic hydrocarbon solvent; said first
extractable metal values are praseodymium and neodymium
and said second extractable metal value is lanthanum.
14. A five-stage process as defined in claim 5 wherein said
solution is an aqueous solution comprising lanthanum,
praseodymium and neodymium; said first immiscible extractant
solvent medium is 30 percent diethylhexyl phosphoric
acid in kerosene; said second immiscible extractant solvent
medium is 15 percent ll-Ikyl primary amines having 18-21 carbon
atoms in kerosene; the bridging solvents in stages 1 to 5
respectively, are aqueous mineral acids having pH values of
1.4, 1.5,5.7,2.2 and 2.0; the first extractable metal values are
praseodymium and neodymium and the second metal value is
lanthanum.
* * * * *