U.S. patent application number 14/421445 was filed with the patent office on 2015-07-23 for recovery of rare earth metals.
This patent application is currently assigned to JERNKONTORET. The applicant listed for this patent is JERNKONTORET. Invention is credited to Barati Mansoor, Seshadri Seetharaman, Sridhar Seetharaman, Lidong Teng.
Application Number | 20150203979 14/421445 |
Document ID | / |
Family ID | 50685665 |
Filed Date | 2015-07-23 |
United States Patent
Application |
20150203979 |
Kind Code |
A1 |
Seetharaman; Seshadri ; et
al. |
July 23, 2015 |
RECOVERY OF RARE EARTH METALS
Abstract
The invention concerns a process for recovering at least one
rare earth metal (REM) from the group of Sc, Y, La, Ce, Pr, Nd, Pm,
Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. A chloride salt melt is
provided and aluminium chloride is used to chlorinate a
REMcontaining resource. The REM can be recovered by electrolysis,
vaporisation or hydrometallurgical methods.
Inventors: |
Seetharaman; Seshadri;
(Taby, SE) ; Teng; Lidong; (Vasteras, SE) ;
Seetharaman; Sridhar; (Pittsburg, PA) ; Mansoor;
Barati; (Ontario, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
JERNKONTORET |
Stockholm |
|
SE |
|
|
Assignee: |
JERNKONTORET
sTOCKHOLM
SE
|
Family ID: |
50685665 |
Appl. No.: |
14/421445 |
Filed: |
August 14, 2013 |
PCT Filed: |
August 14, 2013 |
PCT NO: |
PCT/SE2013/050970 |
371 Date: |
February 13, 2015 |
Current U.S.
Class: |
205/339 ;
205/368; 75/392 |
Current CPC
Class: |
C25C 3/34 20130101; C22B
7/00 20130101; C22B 59/00 20130101; C25C 7/06 20130101; Y02P 10/20
20151101; Y02P 10/212 20151101 |
International
Class: |
C25C 3/34 20060101
C25C003/34; C22B 59/00 20060101 C22B059/00; C22B 7/00 20060101
C22B007/00; C25C 7/06 20060101 C25C007/06 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 17, 2012 |
SE |
1250932-9 |
Claims
1. A process for recovering at least one rare earth metal (REM)
from the group of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy,
Ho, Er, Tm, Yb, and Lu, said process including the steps of: a)
providing a crucible for supporting a salt melt; b) providing a
salt melt consisting of (in weight %): 60-99 of a chloride salt
composition consisting of at least two metal chlorides selected
from the group consisting of chlorides of Li, Na, K, Rb, Cs, Fr,
Be, Mg, Ca, Sr, Ba, and Ra; 1- 30 of AlCl.sub.3 and, optionally
.ltoreq.10 of halides, additional chlorides, sulphides and/or
oxides; c) providing at least one REM containing resource to the
crucible before or after heating to form the salt melt, said REM
containing resource including at least one rare earth metal from
the group of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er,
Tm, Yb, and Lu; d) reacting the aluminium chloride as a chloride
donor with at least one rare earth metal of the REM containing
resource to form at least one rare earth metal chloride dissolved
in the salt melt; e) maintaining the content of AlCl.sub.3 in the
salt melt by adding AlCl.sub.3 stepwise or continuously as it is
consumed or by in situ formation of AlCl.sub.3 in the salt melt; f)
recovering said at least one REM, preferably by electrolysing the
salt melt and selectively electrodepositing at least one REM.
2. A process as claimed in claim 1, wherein the salt composition
comprises at least two of the salts selected from the group: NaCl,
KCl, LiCl, and CaCl.sub.2, preferably at least three of the salts
selected from the group: NaCl, KCl, LiCl, and CaCl.sub.2.
3. A process as claimed in claim 1, wherein the salt composition
essentially consists of by weight % of the salt composition, 3-20
NaCl, 30-70 KCl, 20-60 LiCl, preferably 5-15 NaCl, 40-60 KCl, 30-50
LiCl, more preferably 7-12 NaCl, 45-55 KCl, 35-45 LiCl.
4. A process as claimed in claim 1, wherein the salt composition
essentially consists of by weight % of the salt composition, 10-50
NaCl, 2-20 KCl, 50-80 CaCl.sub.2 preferably 25-35 NaCl, 3-10 KCl,
60-75 CaCl.sub.2.
5. A process as claimed in claim 1, wherein the salt composition
essentially consists of by weight % of the salt composition, 5-20
NaCl, 20-40 LiCl, 40-70 CaCl.sub.2 preferably 7-15 NaCl, 25-35
LiCl, 50-60 CaCl.sub.2.
6. A process as claimed in claim 1, wherein the salt composition
essentially consists of by weight % of the salt composition, 35-65
KCl, 20-50 LiCl, 5-20 CaCl.sub.2 preferably 45-55 KCl, 30-40 LiCl,
10-15 CaCl.sub.2.
7. A process as claimed in claim 1, wherein the salt composition
has a liquidus temperature below 700.degree. C. preferably below
600.degree. C., more preferably below 500.degree. C.
8. A process as claimed in claim 1, wherein the process includes at
least one of the following: providing the at least one REM
containing resource into said liquid salt melt stepwise or
continuously; maintaining the content of AlCl.sub.3 within .+-.7%,
preferably within .+-.5%.
9. A process as claimed in claim 1, wherein the process includes at
least one of the following: vaporizing metal chlorides from the
melt and condensing them for subsequent recovery of the metals of
the condensed chlorides; leaching metal chlorides from the melt in
water and extracting the metals as hydroxides by a
hydrometallurgical method; recycling the chloride salts of the
melt; recovering a processing residue including Al.sub.2O.sub.3 and
preferably using it for landfill, building construction, or as a
raw material for refractory industry crushing and/or grinding
and/or milling the REM containing resource before adding it to the
crucible.
10. A process as claimed in claim 1, wherein the at least one
REM-resource is at least one of: Permanent magnets, in particular
Nd containing magnets, preferably NdFeB magnets; Batteries,
preferably cathodes containing AB.sub.5, where A is lanthanum,
cerium, neodymium and/or praseodymium, and B is nickel, cobalt,
manganese and/or aluminium; Thin films lightnings and displays ores
rare earth concentrates from ores.
11. A process as claimed in claim 1, wherein the at least one
REM-resource includes at least one rare earth oxide from the group
of: La.sub.2O.sub.3, CeO.sub.2, Pr.sub.6O.sub.11, Nd.sub.2O.sub.3,
Sm.sub.2O.sub.3, Eu.sub.2O.sub.3, Gd.sub.2O.sub.3, Tb.sub.4O.sub.7,
Dy.sub.2O.sub.3,Ho.sub.2O.sub.3, Er.sub.2O.sub.3, Tm.sub.2O.sub.3,
Yb.sub.2O.sub.3, Lu.sub.2O.sub.3, and Y.sub.2O.sub.3.
12. A process as claimed in claim 1, wherein providing at least one
anode and at least one cathode to be in contact with the salt melt,
and wherein recovering of the metals includes electrolyzing the
salt melt to form at least one REM from the group Sc, Y, La, Ce, Pr
Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu on the at least
one cathode, preferably selectively electrodepositing at least one
REM from the group Sc, Y, La, Ce, Pr Nd, Pm, Sm, Eu, Gd, Tb, Dy,
Ho, Er, Tm, Yb, and Lu.
13. A process as claimed in claim 1, wherein the method includes at
least one of the steps of: providing an aluminium melt at the
bottom of the crucible, said aluminium melt forming the anode or a
part of the anode, and providing an initiating chloride donor to
the salt melt for starting the reactions in the salt melt, said
initiating chloride donor being aluminium chloride and/or at least
one metal chloride that can be electrolyzed, preferably the initial
chloride donor is able to form aluminium chloride at the contact
surface between the aluminium melt and the salt melt.
14. A process according to claim 13 wherein the initiating chloride
donor is a metal chloride of the same type as provided in the
chloride salt composition.
15. A process according to claim 13 wherein the initiating chloride
donor includes aluminium chloride added to the mixture before
heating it or to the salt melt, said aluminium chloride being added
up to 20% by weight of the chloride salt mixture, preferably 1-15%
by weight, more preferably 5-10% by weight.
16. A process as claimed in claim 13, wherein the salt melt and the
aluminium melt is held at a temperature above 660 .degree. C.,
preferably between 700.degree. C. and 1000.degree. C., more
preferably below 900.degree. C.
17. A process as claimed in claim 13, wherein step d) and step f)
are preformed simultaneously, preferably for at least 2 hours.
18. A process as claimed in claim 13, wherein the process is partly
or wholly self-supporting during steady state by the aluminum
chloride formed during the electrolyzing.
19. A process as claimed in claim 1, wherein the flux in the form
of aluminium chloride is added to the mixture before heating it to
a salt melt and/or to the salt melt, the aluminium chloride can be
added in a single batch or in several batches as the aluminium
chloride is consumed, preferably 5-30% by weight of the salt
mixture when added in a single batch, more preferably 5-20% by
weight of the mixture, most preferably 7-15 wt %.
20. A process as claimed in claim 19 including at least one of the
following during step e) and g), holding the salt melt at a
temperature of at least 500.degree. C. and at most 900.degree. C.,
preferably holding the salt melt at a temperature in the range of
550-700.degree. C., more preferably 580-650.degree. C.; in step g),
electrolyzing the melt for a time period on the order of 2 to 8
hours, preferably 3-6 hours; collecting chlorine gas evolved during
the electrolysis; in step e), reacting the aluminium chloride for
time period on the order of 2-10 hours, preferably 3-8 hours;
controlling the weight ratio "flux"/"REM in the resource" is in the
range of 0.1-3, preferably 0.2-2.0, more preferably 0.3-1.0, most
preferably 0.4-0.6.
Description
TECHNICAL FIELD
[0001] The invention relates to a process for recovering at least
one rare earth metals (REM) from the group of Sc, Y, La, Ce, Pr,
Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu.
BACKGROUND
[0002] Rare earth metals (i.e. Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu,
Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) are becoming increasingly important
in today's society. It is therefore an increased demand in finding
improved methods of extracting rare earth metals from various
resources such as permanent magnets, in particular Nd containing
magnets such as NdFeB--magnets, batteries such as battery cathodes
containing AB5, where A is lanthanum, cerium, neodymium and/or
praseodymium, and B is nickel, cobalt, manganese and/or aluminium,
thin films, lightings and displays, ores, rare earth concentrates
from ores.
[0003] The rare metals can be present in metallic form but commonly
as oxides, e.g. La.sub.2O.sub.3, CeO.sub.2, Pr.sub.6O.sub.11,
Nd.sub.2O.sub.3, Sm.sub.2O.sub.3, Eu.sub.2O.sub.3, Gd.sub.2O.sub.3,
Tb.sub.4O.sub.7, Dy.sub.2O.sub.3, Ho.sub.2O.sub.3, Er.sub.2O.sub.3,
Tm.sub.2O.sub.3, Yb.sub.2O.sub.3, Lu.sub.2O.sub.3, and
Y.sub.2O.sub.3.
OBJECT OF THE INVENTION
[0004] The object of the invention is to provide a process for
recovering at least one rare earth metal from the group of Sc, Y,
La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu from
a resource containing at least one of these metals.
[0005] Another object of the invention is to recover Nd and/or Dy
from Nd/Dy containing magnets.
DESCRIPTION OF THE INVENTION
[0006] At least one of the objects mentioned above is met by a
process for recovering at least one rare earth metals (REM) from
the group of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er,
Tm, Yb, Lu, said process including the steps of: [0007] a)
providing a crucible for supporting a salt melt; [0008] b)
providing a salt melt consisting of (in weight %): [0009] 60-99 of
a chloride salt composition consisting of at least two metal
chlorides selected from the group consisting of chlorides of Li,
Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, and Ra, [0010] 1-30 of
AlCl.sub.3, and [0011] optionally 0-10 of halides, additional
chlorides, sulphides and/or oxides; [0012] c) providing at least
one REM containing resource to the crucible before or after heating
to form the salt melt, said REM containing resource including at
least one rare earth metal from the group of Sc, Y, La, Ce, Pr, Nd,
Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu; [0013] d) reacting
the aluminium chloride as a chloride donor with at least one rare
earth metal of the REM containing resource to form at least one
rare earth metal chloride dissolved in the salt melt; [0014] e)
optionally maintaining AlCl.sub.3 levels by adding AlCl.sub.3
stepwise or continuously as it is consumed or by in situ formation
of AlCl.sub.3 in the salt melt; [0015] f) recovering said at least
one REM, preferably by electrolysing the salt melt and selectively
electrodepositing at least one REM.
[0016] Thereby at least one rare earth metal from the group of: Sc,
Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu
can be recovered.
[0017] The salt melt is preferably heated under protective
atmosphere, suitably argon. The atmosphere may also be nitrogen.
Furthermore, chlorine gas may be admixed to the nitrogen or argon
atmosphere.
Salt Composition
[0018] For given salt combination of the least two chloride salts,
it is preferred that the contents of the salts are within 10% by
weight from the lowest eutectic point of the salt combination, more
preferably within 5% by weight, most preferably within 1% by
weight. However, other contents may be used as long as the liquidus
temperature of the salt combination is at least 50.degree. C. lower
than the operating temperature during electrolyzing; preferably
100.degree. C. lower than the operating temperature. Preferably the
salt composition comprises at least two of the salts selected from
the group: NaCl, KCl, LiCl, and CaCl.sub.2, preferably at least
three of the salts selected from the group: NaCl, KCl, LiCl, and
CaCl2.
[0019] In preferred embodiment the at least one chloride salt
composition includes by weight % of the at least one chloride salt,
3-20 NaCl, 30-70 KCl, 20-60 LiCl, preferably 5-15 NaCl, 40-60 KCl,
30-50 LiCl, more preferably 7-12 NaCl, 45-55 KCl, 35-45 LiCl.
[0020] In an alternative embodiment the at least one chloride salt
composition includes by weight % of the at least one chloride salt,
10-50 NaCl, 2-20 KCl, 50-80 CaCl.sub.2 preferably 25-35 NaCl, 3-10
KCl, 60-75 CaCl.sub.2.
[0021] In an alternative embodiment the at least one chloride salt
composition includes by weight % of the at least one chloride salt,
5-20 NaCl, 20-40 LiCl, 40-70 CaCl.sub.2 preferably 7-15 NaCl, 25-35
LiCl, 50-60 CaCl.sub.2.
[0022] In an alternative embodiment the at least one chloride salt
composition includes by weight % of the salt composition, 35-65
KCl, 20-50 LiCl, 5-20 CaCl2 preferably 45-55 KCl, 30-40 LiCl, 10-15
CaCl.sub.2.
Flux
[0023] The flux is AlCl.sub.3. The flux can be added before or
after forming the salt melt. It may also be added stepwise as it is
consumed. In one embodiment at least a fraction up to all of the
AlCl.sub.3 is generated in situ by reacting chloride ions in the
salt melt with an aluminium anode, preferably the aluminum anode is
an aluminum melt at the bottom of the crucible.
REM Containing Resource
[0024] The REM containing resource may be crushed and/or ground
and/or milled before being provided to the crucible. The crushed
and/or ground and/or milled may be pelletized before being provided
to the crucible.
[0025] The REM containing resource may e.g. be: [0026] permanent
magnets, in particular Nd and/or Dy containing magnets, preferably
NdFeB--magnets where Nd may be partially replaced by Dy. The
magnets may be coated with metallic zinc, nickel, nickel+nickel,
copper+nickel, nickel+copper+nickel,gold. These coatings may be
selectively electrodeposited during electrolysis. The magnets may
also include other metals such as Nb and Co. These metals may be
selectively electrodeposited during electrolysis. [0027] batteries,
preferably cathodes containing AB5, where A is lanthanum, cerium,
neodymium and/or praseodymium, and B is nickel, cobalt, manganese
and/or aluminium; [0028] thin films; [0029] lightnings and
displays; [0030] ores; [0031] rare earth concentrates from
ores.
[0032] Rare earth oxides are particularly suitable, for instance
rare earth oxides from the group of: La.sub.2O.sub.3, CeO.sub.2,
Pr.sub.6O.sub.11, Nd.sub.2O.sub.3, Sm.sub.2O.sub.3,
Eu.sub.2O.sub.3, Gd.sub.2O.sub.3, Tb.sub.4O.sub.7, Dy.sub.2O.sub.3,
Ho.sub.2O.sub.3, Er.sub.2O.sub.3, Tm.sub.2O.sub.3, Yb.sub.2O.sub.3,
Lu.sub.2O.sub.3, and Y.sub.2O.sub.3. Resources of particular
interest are those containing at least one of Dy, Nd, Pm, Sm, Ho,
Er, Tm, Yb and Lu. At present the most interesting elements to
recover are Dy and Nd since these elements may be present in high
contents in permanent magnets.
[0033] According to a preferred embodiment the ocean floor nodule
ore is excluded as a REM containing resource because said raw
material normally has a very low content of rare earth oxides and
since they contain high amounts of base metals such as Mn, Fe and
Ni.
Dissolving
[0034] The flux AlCl.sub.3 acts as a chloride donor dissolving rare
earth metal oxides and/or rare earth metals to rare earth metal
chlorides in the salt melt. The following chlorides can be formed
depending on which are earth oxides or metals that are present in
the resource to be dissolved: LaCl.sub.3, CeCl.sub.3, PrCl.sub.3,
NdCl.sub.3, SmCl.sub.3, EuCl.sub.3, GdCl.sub.3, TbCl.sub.3,
DyCl.sub.3, HoCl.sub.3, ErCl.sub.3, TmCl.sub.3, YbCl.sub.3,
LuCl.sub.3, and YCl.sub.3.
[0035] When AlCl.sub.3 dissolves rare earth metal oxides, aluminium
will form Al.sub.2O.sub.3. When AlCl.sub.3 dissolves rare earth
metals, Al metal is released which will is highly reactive and is
hence likely to react with other reducible chlorides in the salt
melt.
[0036] In one embodiment the dissolving step d) is performed before
the recovering step d). However they may in different embodiments
partly or fully overlap as will be described below, in particular
in relation to the use of a liquid aluminium anode. To dissolve the
REM-containing resource, the salt melt is kept at high temperature
usually for a time between about 2 and about 10 hours, preferably
3-8 hours, more preferably 4-8 hours. The amount of REM-containing
resource is preferably such that a weight ratio "flux"/"REM in the
resource" is between 0.1-3, preferably 0.2-2.0, more preferably
0.3-1.0, most preferably 0.4-0.6. The temperature should be lower
than 1000.degree. C., more preferably lower than 900.degree. C. For
optimal economy, the temperature is preferably in the range of
550-700.degree. C. during the dissolution, more preferably
580-650.degree. C. To improve viscosity of the salt melt, the
temperature of the salt melt is preferably at least 50.degree. C.
above the liquidus temperature of the salt melt, more preferably at
least 100.degree. C. above the liquidus temperature of the salt
melt.
[0037] When dissolving a neodymium magnet (Nd.sub.2Fe.sub.14B) the
reactions can be: [0038] Nd+AlCl.sub.3=Al+NdCl.sub.3 [0039]
Fe+AlCl.sub.3=Al+FeCl.sub.3 [0040] B+AlCl.sub.3=Al+BCl.sub.3
[0041] The Gibbs energy of neodymium chloride formation is
negative, whereas the Gibbs energy for formation of FeCl.sub.3 and
BCl.sub.3 are positive. Therefore formation of NdCl.sub.3 is more
feasible than that of FeCl.sub.3 and BCl.sub.3. Neodymium can be
recovered from neodymium chloride by electrolysis and/or
vaporization.
[0042] Recovering To recover the REM-resource from the melt various
processes may be used. The salt melt used for extraction may
optionally be recycled. Preferably the at least one rare earth
metal and other metals can be selectively electro-deposited from
the salt melt. However, it is also possible to use vaporization of
the metal chlorides and condensing them, or leach the salt phase in
water and extracting the metals as hydroxides by hydrometallurgy
method. The process can be designed to be continuous by combining
the two steps. Residues after processing, such as Al.sub.2O.sub.3,
may be used for landfill, building construction or as a raw
material for the refractory industry. The salts can be recovered
and reused.
[0043] In a preferred embodiment, the REM is recovered by
electrolysis by having at least one anode and at least one cathode
are connected to the salt melt. In this embodiment the recovering
includes the step of electrolyzing the salt melt to form at least
one rare earth metal at the cathode. Preferably at least one REM
from the group Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho,
Er, Tm, Yb, Lu is selectively electrodeposited on the at least one
cathode.
[0044] In one embodiment the electrolysis is done using
conventional anode/s and cathode/s which is further described under
"Electrolysis using conventional anode/s and cathode/s".
[0045] In the most preferred embodiment, the electrolysis includes
an aluminium anode which facilitates an in situ formation of an
aluminium chloride. This is further described under "Dissolving and
electrolysis using aluminium anode".
Electrolysis Using Conventional Anode/s and Cathode/s
[0046] According to one embodiment a conventional anode and cathode
configuration is used, e.g. at least one cathode and at least one
anode submerged in the salt melt.
[0047] Preferably, two electrodes, e.g. of graphite, are immersed
into the melt and connectable to a DC source. The theoretical
decomposition voltage for MCl.sub.3, where M is a rare earth metal
is around 2.5-3 V. Preferably a voltage in the range of 2.5-5 V is
used for the electrolysis, more preferably 3-4 V. If AlCl.sub.3
remains in the salt melt it may be selectively electrodeposited or
co-deposited with the rare earth metal on the cathode.
[0048] The flux, AlCl.sub.3, can be added in a single batch or in
several batches as the aluminium chloride is consumed, preferably
5-30% by weight of the salt mixture when added in a single batch,
more preferably 5-20% by weight of the mixture, most preferably
7-15 wt %. Since the flux is difficult to recover after the
extraction process, it is desirable that there is no excessive
addition of aluminium chloride.
[0049] Accordingly, it is preferable to have a careful control of
the content of aluminium chloride in the salt melt. Moreover, as
set out under "Dissolving" a sufficient amount of AlCl.sub.3 in the
melt is preferred in order to get a sufficient formation of
REM-chlorides in the salt melt. Accordingly, in a preferred
embodiment the amount of AlCl.sub.3 is maintained at a sufficient
level. This may be done by adding AlCl.sub.3 stepwise or
continuously as it is consumed and/or by in situ formation of
AlCl.sub.3 in the salt melt. In situ formation of AlCl.sub.3 is
discussed under "Dissolving and electrolysis using aluminium
anode". The content of aluminium chloride in the salt melt is
dependent on the material to be treated. For neodymium magnets
(Nd.sub.2Fe.sub.14B) the AlCl.sub.3/Nd-ratio is 2/1 considering the
reaction set out above. In the example 20 wt. % AlCl.sub.3was used.
Preferably, the amount of AlCl.sub.3 is controlled within .+-.7%,
preferably within .+-.5% or within .+-.3%.
[0050] The electrolysis preferably is carried out in the crucible
that holds the salt melt with the dissolved REM containing resource
containing at least one rare earth metal from the group of Sc, Y,
La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.
[0051] During electrolysis chloride ions will be attracted to the
anode. With the use of a conventional anode/s, e.g. a graphite
electrode/s, chlorine gas will form and evaporate from the salt
melt. The chlorine gas is preferably recovered.
[0052] Preferably the batch of melt is electrolyzed for 2 to 8
hours. During the electrolysis, the temperature of the salt melt is
preferably lower than 1000.degree. C., more preferably lower than
900.degree. C. For optimal economy the temperature is preferably in
the range of 550-700 .degree. C., more preferably 580-650.degree.
C. To improve viscosity of the salt melt, the temperature of the
salt melt is preferably at least 50.degree. C. above the liquidus
temperature of the salt melt, more preferably at least 100.degree.
C. above the liquidus temperature of the salt melt.
[0053] The dissolving step and the electrolysis step may be
performed separately or they may fully or partly overlap.
[0054] The at least rare earth metal of the group Sc, Y, La, Ce,
Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and optionally
other dissolved metals, can selectively be electrodeposited on the
cathode. After depositing one metal the cathode can be removed and
the metal deposited on the cathode can be extracted. To avoid
interrupts of the electrolysis, another "clean" electrode can be
submerged. Alternatively, the salt melt may have a plurality of
electrodes which one after the other is activated as a cathode
while the former is deactivated. Thereby, the metals can be
selectively deposited at individual electrodes.
[0055] After recovering the at least one rare earth metal and
possibly other metals, the chloride salts of the salt melt may be
recycled. The residue after processing contains Al.sub.2O.sub.3 and
for instance other stable oxides such as SiO.sub.2, depending on
the contents of the REM containing resource. The residues may for
instance be used for landfill, building construction or as a raw
material for the refractory industry.
Dissolving and Electrolysis Using Aluminium Anode
[0056] In a preferred embodiment the at least one anode includes
aluminium, preferably in the form of an aluminium melt provided at
the bottom of the crucible. The aluminium melt form the anode or a
part of the anode, for instance by immersing an electrode, e.g. a
graphite electrode, in the aluminium melt and connecting it to
positive polarity during electrolysis. Alternatively, the crucible
is at least partly made in a conductive material being in contact
with the aluminium melt, and connecting the crucible positive
polarity during the electrolysis. Thereby, the crucible and the
molten aluminium operate as an anode. Of course at least one
cathode is still required during electrolysis, e.g. one or more
graphite electrode/s submerged in the salt melt.
[0057] When using an aluminium melt at the bottom of the crucible
as the anode or part of the anode, the salt melt and the aluminium
are heated to a temperature where both are in liquid phase. To
improve viscosity of the salt melt, the temperature of the salt
melt is preferably at least 50.degree. C. above the liquidus
temperature of the salt melt, more preferably at least 100.degree.
C. above the liquidus temperature of the salt melt. The temperature
should be at least 660.degree. C. and not more than 1000.degree.
C., preferably the temperature is in the range of 700-900.degree.
C.
[0058] During the electrolysis metals/s from metal chloride/s is
deposited at the cathode. At the contact surface between the salt
melt and the aluminium melt chloride ions are reacting with
aluminium, thereby forming AlCl.sub.3. This means that during
steady state the salt melt can be wholly or partly self-supporting
in regards of the flux, AlCl.sub.3 and also that emission of
chlorine gas is reduced. Lesser amounts of chlorine gas may form
even when using an aluminium melt as the anode or part of the
anode. This gas may be recovered.
[0059] An initiating chloride donor is provided to start the
reactions in the salt melt. The initiating chloride donor may be
aluminium chloride and/or at least one metal chloride that can be
electrolyzed, i.e. so that chloride ions forms AlCl.sub.3 at the
contact surface between the salt melt and the aluminium melt.
[0060] In one embodiment, the initiating chloride donor includes a
metal chloride of the same type as provided in the chloride salt
composition, e.g. at least one metal chloride selected from the
group consisting of chlorides of Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca,
Sr, Ba, and Ra.
[0061] In a preferred embodiment, the initiating chloride donor
includes aluminium chloride added to the mixture before heating it
or to the salt melt, said aluminium chloride being added up to 20%
by weight of the salt mixture, preferably 1-15% by weight, more
preferably 5-10% by weight.
[0062] When using aluminium melt as the anode or part of the anode
the steps dissolving and recovering by electrolysis are expedited
simultaneously, preferably for at least 2 hours.
[0063] As the rare earth metal is deposited, additional REM
containing resource can be stepwise or continuously added to the
salt melt. The electrolysis and dissolving operation can for
instance be performed for 2-8 hours; where after metals deposited
at the cathode/s is collected, and the electrolysis can be
restarted. To avoid interrupts of the electrolysis, another "clean"
electrode can be submerged. Alternatively, the salt melt may have a
plurality of electrodes which one after the other is activated as a
cathode and while the former is deactivated. Thereby the metals can
be selectively deposited at individual electrodes.
[0064] The voltage is suitably within the range of 2.5-5V,
preferably 3-4 V. The rare earth metal may be co-deposited with
aluminum or they may be selectively electrodeposited.
[0065] The residue after processing may contain Al.sub.2O.sub.3 and
for instance other stable oxides such as SiO.sub.2, depending on
the contents of the REM containing resource; in particular if the
REM containing resource contains REM oxides Al.sub.2O.sub.3 may
form when chlorinating the REM oxides. The residues may for
instance be used for landfill, building construction or as a raw
material for the refractory industry
EXAMPLE
[0066] Neodymium refining from neodymium magnet was performed in a
salt bath containing LiCl, KCl and NaCl. Eutectic composition of
the three salts was found from the ternary phase diagram and
desired amounts of sodium chloride, lithium chloride and potassium
chloride powders were mixed together carefully and the mixture was
put in a dryer (T=110.degree. C.) for 24 hours. The Neodymium
magnet (Nd2Fe14B) was crushed and added together with aluminum
chloride as fluxing agent to the mixture. The AlCl3/neodymium ratio
was 2/1 and the AlCl3/salt ratio was 20 wt %. The whole mixture was
weighted before each experiment. The masses of the each material
are shown in the table 1.
TABLE-US-00001 TABLE 1 amounts of different component used in the
bath Material AlCl3 Nd2Fe14B NaCl KCl LiCl Amount [g] 3.69 7.5 1.87
7.8 8.81
[0067] The powders were poured in an alumina crucible and the
crucible was put in the vertical furnace.
[0068] The time to reach the target temperature which was
850.degree. C. was about 6 hours. Then the graphite electrodes were
dipped into the salt bath and the electrolysis was started. The
voltage was first set on 4 but due to the high current it was
decreased to 3.2 in order to avoid constant current condition. The
saturation current of the equipment which was used in this
experiment was 5. By fixing the voltage on 4 the current increased
to 4.99 (saturation current). Hence the voltage was decreased to
3.2 V. The electrolysis was done during 5 hours.
[0069] After the experiment, a thick deposited layer on cathode was
observed. The deposited layer contained over 40% by weight of Nd
and over 20% by weight of Al. The amount of Fe was below 5% by
weight. It should be noted that the essentially all Fe remained in
the salt melt although the theoretical decomposition voltage of
FeCl.sub.3 is below 1 V. From the experiment it can be concluded
that Nd can be recovered from the salt melt by electrolysis.
* * * * *