United States Patent [19]
Hazen et a1.
[11] 3,857,919
[45] Dec. 31, 1974
Primary Examiner-Leland A. Sebastian
Attorney, Agent, or Firm-Morgan, Finnegan, Durham
& Pine
Double solvent extraction process wherein an aqueous
solution of difficult to separate metals is alternately
contacted with two different solvents and at least one
metal is preferentially extracted by the one solvent
and at least one other metal is preferentially extracted
by the other solvent.
8 Claims, 4 Drawing Figures
OTHER PUBLICATIONS
Jamrack, Rare Metal Extraction by Chemical Engineering
Techniques, Vol. 2, MacMillan Co., N.Y.,
1963, pp. 181 to 184.
Elginet aI., Chemical Engineers Handbook, John H.
Perry, 1950, Section II, Solvent Extraction, pp. 713to
718.
Rice et aI., Amines in Liquid-Liquid Extraction of
Rare Earth Elements, Bureau of Mines Report of Investigations,
5923, 1962, pp. 1 to 14.
[54] SEPARATING METAL VALUES BY
SELECTIVE EXTRACTION
[75] Inventors: Wayne C. Hazen, Denver; Pablo
Hadzeriga, Arvada, both of Colo.
[73] Assignee: Molybdenum Corporation of
America, New York; N.Y.
[22] Filed: June 18, 1969
[21] Appl. No.: 855,792
Related U.S. Application Data
[63] Continuation of Ser. No. 657,580, Aug. 1, 1967,
abandoned.
[52] U.S. CI. 423/9,423/8,423/10,
423/21, 423/23, 423/54, 423/63, 423/73,
423/99,423/139,423/263,75/101 BE
[51] Int. CI. BOld 11/04
[58] Field of Search 23/339,340,341,309,
23/310,311,312;423/8,9,10,21,23,54,
63,73,99, 139
[56] References Cited
UNITED STATES PATENTS
3,110,556 11/1963 Peppard et al... 23/312
AMINE
II/)EHP-~
AMINE
I?AFFINATE
70 ANALYSIS
[57] ABSTRACT
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-<- OIAiKYL PIIO.1PIIAr£ SOLVENT
3,857,919
AqUEOUS
3,857,919
2
(2 )
r = KzIKz+ t = 1.5
. . b ~ Each of the above formulae (l) and (2) may e employed
to calculate a value for the distribution coefficient
Kfor any element KZ+l if a value is determined fOr
the first element Kz•
In accordance with the present invention, for example,
when an aqueous solution of mixed rare earth
metal values is alternately subjected to extraction with
an organic alkyl phosphate solvent and with a primary
1
SEPARATING METAL VALUES BY SELECTIVE aliphatic amine solvent, the overall result is that the
EXTRACTION phosphate will extr<j.ct preferentially the heavy ele-
This application isa continuation of copending appli- ments, the amine solvents will preferentially extract the
cation Ser. No. 657,580, filed on Aug. I, 1967, and light elements with the middle weight elements being
now abandoned. 5 left behind in the aqueous raffinate.
The present invention relates to a process for the se- The separation factor rt for the solvent chosen to be
lective solvent extraction, separation and recovery of selective for a particular metal relative to at least one
metal values in an aqueous feed solution which com- other metal in the solution must be at least greater than
prises alternately contacting an aqueous feed solution I.
with two different solvents each of which selectively ex- 10 The separation factor r2 for the solvent chosen to be
tracts different metals in the aqueous feed solution. selective for a second' metal relative to the first metal
The present invention relates to a double solvent ex- in the solution must be at least 1and preferably greater
traction process adapted to the treatment of an aque- than I.
ous solution containing therein values of difficult to The separation of at least two difficult to separate
separate metals. The present invention is specifically 15 metals can be carried out in an aqueous system in acadapted
to separation and recovery of the rare earth cordance with the present invention using two solvents
metal values from an aqueous solution thereof. where the separation factor of one of the solvents for
Considerable efforts have. been expended by the art the selected metal is more than I and the separation
on the employment of solvent extraction techniques to factor for the second solvent for the other metal is one
separate and recover metal values from aqueous solu- 20 or more than one. The higher the separation factors for
tions. A large portion of the effort has been directed to- the respeCtive solvents and the respective selectively
ward improving solvent selectivity, and in conse- extracted metals, the better the separation.
quence, a considerable body ofbackground knowledge In accordance with the presentinvention an aqueous
exists on the inanysolvents which have been suggested feed solution containing difficult to separate metals can
for this purpose. Thusdistributioncoefficients under 25 betreated to effect the desired separation of the metals
varying conditions are known for many aqueous mixed .by a process which comprises contacting and mixing
metal solutions with numerous solvents. the aqueous feed solution with a first immiscible sol-
The separation factor for different metals deviates vent which .exhibits a degree of selectivity for at least
significantly one from tne Other in different solvent so- one of the metals in the feed solution allowing the mixlutions.
The separation factor may be defined as the 30 ture to separate into a solvent phase and an aqueous
ratio of the distribution coefficients (K) between the phase, si\id aqueous phase being depleted in the semetals
in the aqueous solution. Thus as applied to rare lected metal and. said solvent phase being enriched in
earth separation it has been found (Peppard et aI., J. the selected metal, withdrawing the aqueous phase and
Inorg. Nucl.Chem 4,334, 1957) that Di-2-ethyi hexyl contacting and mixing said aqueous phase with a secphosphoric
acid (HDEHP ) preferentially extracts the 35 ond immiscible solvent which is selective for at least
compounds of the higher atomic number (heavy) ele- one of the other metals in said aqueous feed solution
ments in the rare earth series. Throughout the lantha- allowing said mixture to settle into an aqueous and solnide
series, the separation factor (r) is equal to approx- venfphase, said aqueous phase being depleted in said
imately 2.5. This may be expressed according to the selected metal and said solvent phase being enriched in
following formula: 40 said selected metal and subsequently alternately contacting
said aqueous feed solution with the first solvent
r = Kz+ IIKz= 2.5 and the second solvent until the desired degree of separation
of the metals in the aqueous feed solution has
been accomplished.
wherer equals separation factor; K equals distribution 45 Each of the solvents enriched ill the selected metal is
coefficient (concentration of given element in the or- called an extract phase and the aqueous solution reganic
phase divided by its concentration in the aqueous maining after the desired degree of extraction is carried
phase); z is equal to the atomic number of one metal out is called the raffinate phase. Each solvent phase is
and 2+ I is equal to the atomic number of the other 5 concentrated in the metal for which it is selective and
metal. 0 the.aqueous raffinate phase in a proper case is concen-
Elsewhere it has been reported that primary amine trated in the metals for which neither solvent shows a
solvents extract the compounds of the fight (lower high degree of selectivity.
atomic num ber) rare earths more strongly than heavy The extracted metals in each of the solvents can be
ones with average separation factor for the lanthanide 55 recovered by stipping the solvents with an appropriate
series ofl.5 ,i.e.: aqueous stripping solution and the stripped solvents returned
to the process. The separated metals can be
concentrated for example, by merely evaporating the
stripping solution.
The process of the present invention provides substantially
improved separations with a greatly reduced
number of required extraction stages than would be required
using a single solvent.The important feature of
the present invention is the high degree of separation
65 obtained with relatively few extraction stages, the overall
recovery or yield of a specific metal in an aqueous
feed solution being treated is of secondary importance
and can be increased if desire.d by merely recycling the
3
3,857,919
4
For example, a suitable alkyl phosphate solvent could
comprise a 10rc by volume solution of the selected
alkyl phosphate in xylene.
In carrying out a particular separation, in accordance
5 with this invention, it is not necessary to use an alkyl
phosphate solvent and an amine solvent since two
amine solvents or two alkyl phosphate solvents can be
used providing that the solvents selected show a relative
degree of selectivity for at least one of the metals
in the solution relative to at least one other metal in the
solution.
The number of stages of extraction used can, for example,
be 3 to 12 alternating first with one solvent and
then withthe other solvent. Depending on the particular
aqueous feed solution being treated and the desired
degree of separation, 4 to 10 stages of separation can
be used. It is noted, however, that more than 12 stages
of extraction can be used, for example, if it is desired
to obtain a substantially pure SIngle rare earth element
in either or both of the solvents and/or in the aqueous
raffinate.
In one embodiment of the present invention, two solvent
extraction circuits are used in parallel with one
solvent in one circuit and a second solvent in another.
Fresh solvent can be used in each extraction stage in
each circuit or the same portion of solvent can be used
in each circuit and contacted counter-currently with
the feed in each circuit. The aqueous solution containing
the metal values therein will crisscross so to speak
between the two solvents thereby being subjected to
alternate extraction by the solvents. As applied in a
preferred embodiment to separation of rare earths employing
amine solvents and alkyl phosphates solvents
there will result an amine solvent rich in the light rare
earth elements and a phosphate solvent rich in the
heavier rare earth elements and, frequently, an aqueous
raffinate which may contain a single middle weight
rare earth.
In accordance with a preferred embodiment the two
solvent extraction circuits are operated in parallel with
an amine containing solvent advancing countercurrently
to the aqueous feed in one circuit and the alkyl
phosphate solvent advancing countercurrently in the
aqueous feed in the other circuit. The aqueous solution
containing the rare earths or other metal compounds
passes in a countercurrent flow pattern back and forth
between the two circuits being subjected to extraction
alternately by the amine solvent and phosphate solvent,
thereby producing ultimately the amine solvent rich in
light rare earths and the phosphate solvent rich in the
heavy rare earths. By suitable adjustment of operating
conditions it is possible to obtain in the aqueous raffinate
a concentrated solution of a particular rare earth.
For further understanding of the present invention
reference is now made to the attached drawings
wherein;
FIG. 1 is aflow sheet showing an eIementary form of
double extraction using two solvents and two extraction
stages for each solvent, combining the extracts obtained
by the respective solvents and stripping the combined
extracts to recover the extracted metals.
FIG. 2 is a flow sheet showing a conventional multiple
single solvent extraction employed for comparative
purposes using fresh solvent in each stage and followed
by stripping of the extract to recover the extracted
metal values.
aq ueous raffinate solution to the feed solution. In a
proper process three products can be recovered: one
concentrated in the first solvent, the second concentrated
in the second solvent and the third product concen
tra ted in the aq ueous raffinate.
Many of the modern mining and metallurgical procedures
can be carried out to produce suitable aqueous
metal feed solutions for the present process. The present
invention as has been previously pointed out, has
application to the separation of difficult to separate 10
metals. The process of the present invention has specific
application to the separation of rare earth metal
values from an aqueous solution of rare earth metals.
this process can be used to obtain a first solvent frac- 15
tion concentrated in light rare earth values, a second
solvent fraction concentrated in heavy rare earth values,
and an aqueous raffinate fraction concentrated in
the middle weight rare earth values. In a similar manner
by adjusting the extraction conditions, separations of 20
relatively pure single rare earth metals can be obtained.
Further, the process also has specific and advantageous
application to the separation of other difficult to
separate metals in aqueous solutions of the metal. For
example, certain mixtures of difficult to separate met- 25
als commonly occur in conventional mining and metallurgical
processes. Aqueous solutions of metals containing
significant amounts of mixtures of the following
pairs of metals are suitable feed solutions for the present
process to separate the metals from each other: va- 30
nadium and uranium; hafnium and zirconium; molybdenum
and tungsten; zinc and copper; cobalt and
nickel; and columbium and tantalum.
The solvents to be used must be immiscible or substantially
im miscible with the aqueous metal solution to 35
be treated. This avoids loss of solvent to the raffinate
and also avoids contamination of the solvent stripping
solution by the aqueous feed solution. The solvents
must show a degree of selectivity for the metal it is 40
chosen to selectively separate from the other metals in
the aqueous feed solution.
There are two broad classes of solvents which under
prescribed conditions have exhibited the desired degree
of selectivity necessary to separate certain metals 45
from other metals in aq ueous solutions containing the
metals.
The first class of solvents comprises primary, secondary,
tertiary and quaternary amines which exhibit selectivity
for certain metals. Specific amines that are 50
useful are trioctylamine, dodecylamine, and Primene
JM-T (Rohm & Haas) which is described as mixture of
tertiary alkyl primary amine isomers having 18-21 carbon
atoms, and the like.
The second class of solvents comprises alkyl phos- 55
phates, i.e., organic esters of phosphoric acids which
exhibit a degree of selectivity for certain metals dissolved
in an aqueous mixture of metals. Specific alkyl
phosphates which can be used are tributyl phosphate,
dodecyl phosphoric acid, trion-butyl orthophosphate, 60
and di-2-ethyl hexyl-orthophosphoric acid (HDEHP),
and the like.
The solvents can be used alone or with suitable inert
diluents which diluents' are also immiscible with the 65
aqueous feed solution undergoing treatment. The solvents
are commonly used with hydrocarbon diluents
such as xylene, toluene and kerosene.
3,857,919
mg/l
390
2620
7490
2430
370
340
13.640
Element
Pr
Nd
Sm
Gd
Dy
Y
6
ment per liter of the main constituents was as follows:
5
EXAMPLE I
An aq ueous solution of rare earth and yttrium sulfate
was used in these tests. The composition in mg of ele-
FIG. 3is a flow sheet showing one preferred double
extraction arrangement, using two solvents and countercurrent
flow of the solvents and aqueous feed with
reflux of the alkyl phosphate solvent extract.
FIG. 4 is a flow sheet showing a second preferred 5
double extraction arrangement using two solvents
wherein the aqueous feed is split into two portions and
alternately counter-currently contacted with each of
the solvents.
While legends placed on the drawings make them vir- 10
tually self-explanatory, it may be noted from FIG. 1 -------~------,---------'--
that the basic procedure for double extractive separation
of mixed metal values in an aqueous solution comprises
a flow pattern wherein the aqueous solution This aqueous feed solution was adjusted to pH 1.5
passes successively in alternating contact with a first 15 using sulfuric acid.
solvent, then a second solvent, then· the first solvent. The amine solvent selected comprised a mixture of
Usually a repeated contact with the second solvent is isomers of tertiary alkyl primary amines having ·18-21
carried out. If desired, the .entire sequence may be re- carbons (Primene JMT, from Rohm and Haas Compeated.
According to the mode of FIG. 1, fresh solvent pany). A solution of 10% by volume of this amine was
may be employed in each extraction contact stage 20 prepared using kerosine as diluent. This solution Was
whereas in FIGS. 3 and 4 the same solvent is used. in equilibrated to pH 1.5 using aqueous sulfuric acid,
each extraction stage in each circuit. thereby converting the free amine to its sulfate salt.
Preferably, a countercurrent flow pattern isem.- The alkyl.phosphate solvent was a IO%by volume soployed
wherein the aqueolis solution e,g., FIGS. 3 and 25 lution of di-2-ethyl hexyl-orthophosphoric acid
4, passes in a countercurrent flow pattern, successively (HDEHP) In xylene.
alternating with a first solvent and then with a second In orderto compare the efficiency of using these two
solvent, so thatthe fresh first solvent becomes succes- solvents in a crosscurrent manner in. accordance with
sively enriched in some of the metal values as it passes the present invention as opposed to using only one solthrough
the system, and the second solvent becomes 30 vent, three tests were run using a standard separatory
successively enriched in other of the metal values as it funnel. Mixing time' of aqueous feed and solvent was
passes through. Also as mentioned above with respect about 1.5 minutes and phase ratio was maintained at
to FIG. 3, an aqueous reflux may be employed on one 1.0 throughout these tests, i.e., equal volumes of aqueor
both solvent streams to improve the degree of selec- ous feed and solvent were used in each extraction
tivity. 35 stage.
FIG. 4 illustrates what may be termed a "shoe lace" Test I
pattern wherein the aqueous feed stream is split, then Four crosscurrent stages were used following the procrisscrosses
in alternating passage from the first solvent cedure generally illustrated in FIG. 2 of the drawings:
to the second solvent. . 50 ml. of aqueous feed solution was contacted succes-
To further illustrate the present invention, with re- 40 sively with four equal volumes of the amine solution.
spect to the separation of rare earth values from an The final aqueous phase constituted the raffinate. The
aqueous solution thereof, the following specific exam- four amine extracts were combined and stripped four
pies are presented. A primary aliphatic amine solvent times with 50 ml. of 6 N hydrochloric acid. Raffinate
which preferentially extracts the light rare earth values and re-extract were processed and analyzed using an
is used as one of the solvents and an alkyl phosphate 45 X-ray flourescence technique.
solvent which preferentially extracts the heavy rare Test 2
earth values is used as the other solvent. This test was similar to Test I, but the alkyl phos-
It is difficult to compare the conventional solvent ex- phate solvent was used instead of amine.
traction systems which use only one solvent with the Test 3
present invention. In the former, one organic solvent 50 Following the procedure generally illustrated in FIG.
and one aqueous solution are used and it yields only 1 of the drawings, 50ml. of aqueous feed solution was
two products: im organic extract· and the aqueous raffi- contacted with two stages of amine and two stages of
nate. In the present invention the use of two solvents HDEHP extraction used alternatively in a crosscurrent
results in three products, i.e., two solvent extracts and manner. The two amine extracts as in Test 1 were coman
aqueous raffinate. 55 bined and stripped. The same was done with the two
HDEHP extracts.
The results obtained in these three tests were expressed
as variations of the weight ratios of the main
elements and are shown in Table I.
Table I
Weight Ratio in Extracts
Sm/Gd Sm/Dy Gd/Dy
Test I:
Test 2:
Test 3:
Feed Solution
4 Stages Amine alone
4 Stages HDEHP alone
Alternatively 2 Amine Stages)Amine Ext.
and 2 HDEHP Stages)HDEHP Ext.
3.08
3.28
UO
5.31
0.85
20.2
24.0
6.97
70.6
2.19
6.57
7.32
5.37
13.3
2.56
7
3,857,919
8
rare earth values from an aqueous feed solution to recover
desired middle rare earth values such as Gd in
the aqueous raffinate.
The process of the present invention has distinct and
5 advantageous uses ih obtaining a high degree of separation
of difficult to separate metals in aqueous solutions.
The important characteristic of the process of the invention
is the ability of the process by using two solvents
each immiscible with the feed solution and each
10 sel.ective for a particular metal to obtain in a relatively
few stages of extraction a higher degree of separation
of the metals than can be obtained using either solvent
separately and using substantially more stages of extraction.
The invention has many obvious applications in the
mining industry and the metallurgy industry to separate
metals which can be put in aqueous solution and torecover
heretofore difficult to separate metals economically
and in commercially useful amounts.
The invention is not to be limited by the above description
or examples which are given merely as illustrative.
the scope of the invention is to be interpreted
by the appended claims.
We claim:
1. A process for separating rare earth metal values in
EXAMPLE 2
With this 4-stage crosscurrent extraction, the advantage
of using two solvents over a single solvent for the
separation of rare earth elements can be seen. For example,
in the pair Gd/Dy, it is evident that in extracting
with anyone solvent alone, little or nothing is gained
in only four stages. With two solvent~ used alternatively,
the concentration ratio is almost double in the
amine extract, while it is less than one-half as great in
the HDEHP extract as compared with the aqueous
feed.
This example illustrates how an improved separation
can be obtained using the process of the present invention
as compared with using a single solvent and how 15
a particular rare earth metal value can be concentrated
in the aqueous raffinate.
Using as in Example 1 50 ml. of the same aqueous
feed and the same solvents and a similar procedure to
that used in Example I, two tests were run. In one test, 20
three stages of crosscurrent extraction with amine solvent
were made on the same aqueous solution. In the
other, two stages of amine with an intervening stage of
alkyl phosphate were performed. The analyses of the
several extracts and raffinates obtained are summa- 25
rized in Table 2.
Table 2
Three Stage Crosscurrent Solven.t Exfraction
Single Solvent
Aqueous Feed Amine Extract Raffinate
mg. 'i( Purity mg. 'i( Purity mg. 'i( Purity
Double Solvent
Amine Extract HDEHP Extract
mg. 'i( Purity mg, .'i( Purity
Raffinate
mg 'i( Purity
Pr 390 2.9 275 3.1 115 2.5 280 3.4 2 0.2 108 2.7
Nd 2620 19,2 1600 17,7 1020 22,1 1930 23.4 36 2.6 654 16.3
Sm 7490 54,9 5230 58.0 2260 48.8 5020 60.8 320 23.4 2150 53.4
Gd 2430 17.8 1540 17.1 890 19.2 940 11.4 500 36.5 990 24.6
Dy 370 2.7 230 2.5 140 3.0 55 0,7 300 21.9 15 0,4
Y 340 2.5 140 1.6 200 4,3 25 0.3 210 15.4 105 2.6
It can be seen from the data in Table 2 that with,a single
stage of HDEHP between two amine stages, the
double solvent system has improved 'the purity in both
extremes of the series as compared with using three
stages of amine: better purity of Pr, Nd and Sm in the
amine extract and better purity of Gd, Dy and Y in the
HDEHP fraction. The corresponding recoveries may
be calculated from the values given in table 2. This
shows that the recovery of Pr, Nd and Sm in the amine
fraction is about equal in the single and the double solvent
systems. However, there is a considerable drop in
the recovery of Gd, Dy and Y in the two amine 'stages
for the double solvent system.
An important fact worth noting is that the total Gd
extracted in three amine stages is 63.4l7r, while with the
double solvent system the total Gd extracted is 59.3%(
38.7lk by the two amine fractions plus 20.6lk by the
HDEHP fraction). Though the above system shows a
substantial increase in the concentration of the Gd in
the raffinate as compared with the aqueous feed solu e
tion, it is evident that in the proper system, and with
enough stages, the double solvent system will show a
substantially greater concentration of Gd in the raffinate
than shown in this example.
The process of the present invention can thus be used
to advantage to selectively separate light and heavy
an aqueous solution containing said metalS which comprises
contacting and mixing said aqueous solution with
a first immiscible organic solvent which selectively ex-
45 tracts at least a first rare earth metal from the metals
in the aqueous solution, allowing the mixture t,o settle
into an aqueous phase depleted in the first rare earth
inetal and a solvent phase enriched in said first rare
earth metal, separating the aqueous phase from the sol-
50 vent phase and then contacting said separated aqueous
phase with a second immiscible organic solvent which
selectively extracts at least a second rare earth metal
from said aqueous phase, allowing the mixture to settle
into an aqueous phase depleted is said second rare
55 earth metal and a solvent phase enriched in said second
rare earth metal, separating said aqueous phase and
then contacting and mixing said separated aqueous
phase with said first organic solvent which selectively
extracts an' additional amount of said first rare earth
60 metal, allowing the mixture to separate into an aqueous
phase depleted in said first rare earth metal and a solvent
phase enriched in said first rare earth metal, separately
stripping said first and second solvents to recover
65 a first stripping solution concentrated in said first rare
earth metal and a second rare earth metal, and separating
a last aqueous phase depleted in both of said first
and second rare earth metals.
3,857,919
9
2. A process for separating rare earth metal values in
an aqueous feedsolution containing said rare earth values
which comprises contacting and mixing said feed
solution with a first immiscible organicami.ne solvent
which exhibits a selectivity for at least one of said rare 5
earth metals, separating a solvent phase and an aqueous
phase, contacting and mixing separated aqueous
phase with a second immiscible organic phosphate solvent
which exhibits a selectivity for at least one other
of said rare earth metals, separating an aqueous phase 10
and a solvent phase, alternately contacting said aqueous
phase with said first solvent and with said second
solvent. to selectively extract into the respective solvents
the metal values for which said solvents are selective
and to thereby separate said rare earth values in 15
said feed solution into said respective solvents, separating
said metals from said solvents and recovering said
metals.
3. A double solvent extraction process for the separation
of rare earth metal values from an aqueous solu- 20
tion containing said rare earth metals which comprises:
I. contacting the aqueous solution with a first immiscible
organic amine solvent which has a separation
factor of about 1.5 for the lower atomic number
metal .values, separating an aqueous phase and a 25
solvent phase, and
2. thereafter contacting the aqueous phase with a
second immiscible organiC phosphate solvent
which has a separation factor of about 2.5 for the
higher atomic number metal values, separating an 30
aqueous phase and a solvent phase,
3. then again contacting the aqueous phase with said
first immiscible organic amine solvent, whereby
said rare earth metal values are extracted from said
aqueous solution preferentially into the two sol- 35
vents, separating said metals from said solvents and
recovering said metals.
4. The process of claim 3 wherein the alkyl amine solvent
comprises a mixture of tertiary alkyl primary
amines having 18 to 21 carbon atoms and the alkyl 40
phosphate solvent comprises di-2-ethyl hexyl phosphoric
acid.
5. A. procedure for the solvent extraction of rare
earth values present in an aqueous solution comprising
successively contacting the aqueous solution with a 45
firstimmiscihle organic solvent containing an alkyl
amine and subsequently contacting the aqueous solution
with a second immiscible organic solvent containing
an alkyl phosphate, then contacting the aqueous solution
with said amine containing solvent whereby after 50
each contact an aqueous phase and·a solvent phase are
separated and whereby the lower atomic number rare
earth values are preferentially extracted into the alkyl
amine solvent and the higheratomic number rare earth
values are preferentially extracted into the alkyl phos- 55
phate solvent and the middle atomic number rare earth
60
65
10
values selectively remain in the aqueous raffinate solution,
separating the rare earth metals from said solvents
and raffinate solution and. recovering said metals.
6. A process for separating rare earth metal values in .
an aqueous feed solution containing Pr, Nd, Sm, Gd
and Dy, and yttrium. which comprises contacting and
mixing s,jid feed solution with a first immiscible organic
amine solvent which exhibits a selectivity for the lower
atomic number rare earth metals. separating a solvent
phase and an aqueous phase, contacting and mixing
said separated <iqueous phase with a second immiscible
organic phosphate solvent which exhibits a selectivity
for the higher atomic number rare earth metals and yttrium,
separating an aqueous phase and a solvent
phase, alternately contacting said aqueous phase with
said first solvent and with said second solvent to selectively
extract into the respective solvents the metal values
for which said solvents are selective and to thereby
separate said rare earth values and yttrium in said feed
solution into said respective solvents. separating said
metals from said solvents and recovering said metals.
7. The process of claim 6 wherein the rare earth metals
Pr, Nd and Sm are concentrated in the amine solvent,
the rare earth metal Dy, and the metal yttrium are
concentrated in the organic phosphate solvent and the
rare earth metal Gd is concentrated in the remaining
aqueous phase.
8. A process for separating metals in an aqueous solution
selected from the group consisting of solutions of
vanadium and .uranium; hafnium and zirconium; molybdenum
and tungsten; zinc and copper; cobalt and
nickel; and columbium and tantalum, said process
comprising contacting and mixing said. aqueous solution
with a first immiscible solvent which selectively extracts
at least a first metal from the metals inthe aqueous
solution, allowing the mixture to settle into an
aqueous phase depleted in the first metal and a solvent
phase enriched in said first metal, separating the aqueous
phase from the solvent phase and then contacting
said separated aqueous phase with a second immiscible
solvent which selectively extracts at least a second of
the metals in said aqueous solution, allowing the mixture
to settle into an aqueous phase depleted in said
second metal and a solvent phase enriched in said secondmetal,
separating said aqueous phase and then contacting
and mixing said separated aqueous phase with
said first solvent which selectively extracts an additional
amount of said first extracted metal. allowing the
mixture to separate into an aqueous phase depleted in
said first·metaland a solvent phase enriched in said first
metal, separately stripping said first and second solvents
to recover a first stripping solution concentrated
in said first metal and a second stripping solution concentrated
in said second metal and a last aque()us phase
depleted in both of said first and second metals.
* * * * *
on�-�~ol��0�d-align:none;text-autospace:none'>75-101 R; 423-3,27,29,31,53,68
625,564
866,625
1,483,567
3,183,058
2,964,380
2,896,930
3,441,316
366,103
References Cited
UNITED STATES PATENTS
5/1899 Kendall 423-29
9/1907 Conedera 423-27
2/1924 i\njow 423-53
5/1965 Peter 23-321 X
1211960 Kolodney et al. 23=320
7/1959 Menke 23-320 X
4/1969 Hannifan et al. 75-101 X
7/1887 Hofmann 75-101
10
10
OTHER REFERENCES
De Andrade et al.: "Chemical Treatment of Uranium
Ores at the Mines in a Semi-Mobile Plant," 3rd Conf. on
Peaceful Uses, vol. 12, 1965, pp. 187-193.
Galkin et al.: Technology of Uranium, 1966, p. 103,
(AEC-tr-6638).
Application of Heap-Leaching to the Processing of Argentine
Ores, Cecchetto et aI., 3rd Conf. on Peaceful
Uses, vol. 12, 1965, p. 212.
Arden: Extraction and Refining of the Rarer Metals,
1957, pp. 130-1.
botto�(�01��0�eight: normal;mso-pagination:none;mso-layout-grid-align:none;text-autospace:none'>After the off-gas has been scrubbed of its loading of
30 dust and fume, it consists mainly of sulfur dioxide and
oxygen. The gas may be dried and compressed to liquefy
the sulfur dioxide. The oxygen remains in the gaseous
form and is recycled to the flash roaster.
Table 3 shows the results from re-roasting a number
of calcines:
After re-roasting of the calcine, portions of the copper,
the remaining rhenium not collected in the scrubbers,
and a portion of the sulfur are soluble in mineral
50 acid solutions. Since the process produces a dilute mineral
acid -sulfurous acid- in the scrubbers, it is used
to leach the copper and the remaining rhenium from
the calcine (Table 4).
55 TABLE 4.-REMOYAL OF COPPER AND RESIDUAL RHENIUM
AND SULFUR FROM RE-ROASTED CALCINES
Molybdenum balance BY LEACHING WITH SULFUROUS ACID
(percent distribution)
88 94 6
84 94 6
76 ..
95 .
125
140
218
40
Rhenium balance
567
707
736
736
TABLE I.-ROASTING TEST RESULTS
Preheat temperatures: 650-750'C. range
Hearth temperature: 550-650'C. range
Percent stoichiometric oxygen: 170-240
the latter being the only other gaseous component in
the exhaust stream· pertinent to this control feature.
The sulfur dioxide-oxygen ratio in the exhaust stream
can be partially controlled to provide the optimum
value, if necessary, by the introduction of sulfur dioxide 5
gas with the oxygen. The ratios reflected by 30-35%
volume of sulfur dioxide are by no means critical, but
its use to provide favorable reaction zone conditions
illustrates the effectiveness of this method of control.
There are three other principal parameters affecting
the temperature control and/or the oxidationvolatilization
process, one or all of which may be used
to control these factors in varying degrees. These parameters
are: (1) preheat temperature, (2) the height
ofthe reactor column, and (3) heat dissipation from 15
the column. The first of these, like the oxygen-sulfur
dioxide ratio, is applied during the operation of the process..
The latter two are built-in to the construction of
the apparatus.
The preheat temperature is readily controlled by ad- 20
justing the heat input to the indirect-fired preheat furnace.
The height of the reactor column determines the
dwell time of the sulfide particles in the reaction zone
for complete oxidation and for formation and volatil- 25
ization of rhenium oxide. The optimum height for a
given operation is developed by calculations and measurements
derived from pilot plant operation. For example,
in a continuous pilot plant operation excellent
results were obtained using a vertical column 44 inches
in height and 6 inches in diameter with a rotating
hearth 3 feet in diameter. These dimensional relationships
are not critical and would change with change in
other variables, such as, concentrate characteristics,
composition of feed gases, rate of gas injection, etc. 35
The heat dissipated from the vertical column is controlled
by design, and construction materials used. The
construction can be varied from highly insulated construction
to high conductivity construction with a cooling
media. The radiation and convection loss of heat 40
generated for a metal conducting material and a given
feed rate can be readily calculated. Additional heat
may be removed from the column by water cooling or
other heat exchange media.
The results given below are illustrative of those obc 45
tained by application of the above-described process in
conjunction with the apparatus described.
Table 1 shows some material balances obtained in
roasting tests performed on molybdenite concentrate.
1.. ..
2 ..
3 ..
4 .
Rhenium Product Yolatil- Dust and
T_es_t ___--f,e-ed_--,(p-p_m)--,iz-ed_(_%)__P_ro_du_ct__sc_ru_bb_er 60 Spiaem-
----------------------
The data in Table 1 shows the variability of the rhenium
content of the product produced at somewhat
65 About 7 percent of the molybdenum contained in
the calcines is also solubilized in the sulfurous acid
leach.
3,770,414
JlO
zone,
c. controlling the temperature in the first oxidation
zone durin~ the introduction thereto of said preheated
particles and thereafter to maintain a temperature
therein above the volatilization temperature
of rhenium oxide and below the volatilization
temperature of molybdic oxide to form rhenium
oxide, sulfur dioxide and molybdic oxide, which
latter oxide along with other solids passes to a second
oxidation zone where any unoxidized molybdenite
is completely oxidized, said second oxidation
zone being hec;ted by exothermic heat of the
reactions occurring therein,
d. passing oxygen through said second oxidation zone
to oxidize molybdenite contained therein,
e. passing at least some of the oxygen travelling to
said first oxidation zone through said second oxida,
tion zone to heat the oxygen before it reaches the
first oxidation zone,
20 f. recovering rhenium oxide by collecting it in a recovery
zone outside the first oxidation zone and
dissolving it in water,
g. recovering rhenium from the water solution of rhenium
oxide, and
25 h. recovering insoluble molybdic oxide from the second
oxidation zone.
2. The process of claim 1 in whi'ch said concentrate
is preheated to about 500°C.
30 3. The process of claim 1 in which molybdenum values
are recovered.
4. The process in claim 1 in which rhenium values are
recovered.
5. The method of claim 1I in which the temperature
of the first oxidation zone resulting from exothermic
heat of reaction is controlled by controlling the reaction
rate of the oxidation reactions occurring therein.
6. The method of claim 5 in which said reaction rate
is controlled by adjusting the relative feed rate of oxy40
gen and molybdenite concentrate to the first oxidation
zone to control the stoichiometric ratio of oxygen to
metal sulfides introduced therein.
7. The method of claim 6 in which said stoichiometric
ratio is at least one.
S. The method of claim If) in which said stoichiometric
ratio is at least 120%.
9. The method of claim 6 in which sulfur dioxide is
introduced to the first oxidation zone.
10. The method of claim 6 in which the sulfur diox50
ide-oxygen ratio in the exhaust gases from the first oxidation
zone is used to determine the relative rate of addition
of oxygen and concentrate.
1I1. The method of claim 1 in which the exhaust gas
contains up to about 50% by volume of sulfur diOldde.
55 12. The method of claim 1 in which the dwell time of
concentrate particles in the first oxidation zone is controlled
by varying the diameter and height of said zone.
1I3. The process of claim 1I in which oxygen in the exhaust
gases is recycled for reuse in the method.
60 14. The process of claim 1 in which sulfur dioxide in
the exhaust gases is dissolved in water to form sulfurous
acid and the sulfurous acid used to leach impurities
from the molybdic oxide calcine recovered from the
second oxidation zone.
* >I< >I< * *
About 7% of the molybdenum contained in the calcines
is also solubilized in the sulfurous acid leach.
The leached residue is separated from the leach solution
by filtration and after drying is ready for packaging 5
for sale. The leach solution joins the solutions from the
scrubbers on the flash roaster and re-roaster.
The effectiveness of the above-described process is
graphically illustrated by the high recovery of rhenium
and molybdenum achieved. it provides for the recovery 10
of up to 95% of rhenium and high recovery ofmolybdenum
in molybdenite with a minimum of process time
and a minimum of oxygen and added heat. The economic
advantages of these features are apparent. The
process is adaptable to either a batch or continuous op- is
eration.
It is an attractive side advantage of the. process that
a small volume of exhaust gas containing a high percentage
by volume of sulfur dioxide is produced. The
process is normally operated with an exhaust gas volume
discharge rate of 1,350 cubic feet per minute
(CFM) with up to 220% excess oxygen and 30-50% by
volume of sulfur dioxide in the exhaust gas. This high
volume percentage of sulfur dioxide makes its recovery
economically feasible for various commercial uses. In
contrast, present-day processes utilizing air for cooling
and for supplying oxygen are of necessity operated with
an exhaust volume discharge rate of 40,000 CFM, 16
volume percent excess oxygen and 1-2 volume percent
of sulfur dioxide. This volume percentage of sulfur dioxide
in the exhaust gas is so low that its recovery is not
economically feasible because it involves processing
such large volumes of gas. As a result the sulfur dioxide
is exhausted to the atmosphere creating a serious pollution
problem in heavily populated areas. The process of 35
this invention eliminates this problem.
The reduced volume of exhaust gas also results in a
much higher concentration of rhenium oxide in the exhaust
gas than is obtained in conventional processes.
As a result, recovery of substantially all of the rhenium
is far more feasible and economical than in present processes
using air with resultant large volumes of exhaust
gas to be processed for recovery of the rhenium oxide.
Reduction of the volume of gas processed through
the system by a factor of about 30resultsin a dr1!§jic: 45
reduction in the size of equipment require-d~ith~jgnificant
savings in equipment cost and floor space.
What is claimed is:
n. A method for recovering rhenium and molybdic
mdde from molybdenite concentrate which comprises:
a. pre-heating particles of said concentrate in an oxygen-
free atmosphere to a temperature not in excess
of about 750"C to raise the temperature of the particles
to promote flash oxidation of the molybdenite
when the particles are introduced into a flash
oxidation zone,
b. causing said pre-heated particles to fall through a
first oxidizing zone of heated oxygen with said particles
and heated oxygen moving countercurrent to
each other to disperse said pre-heated molybdenite
particles in said heated oxygen to provide maximum
particle surface contact with heated oxygen
for effective oxidation, said first oxidation zone
being heated substantially by the exothermic heat
of the reactions occurring in said first oxidation 65