U.S. patent application number 13/575275 was filed with the patent office on 2012-11-29 for method and arrangement for producing metal powder.
This patent application is currently assigned to OUTOTEC OYJ. Invention is credited to Ville Nieminen, Henri Virtanen.
Application Number | 20120298523 13/575275 |
Document ID | / |
Family ID | 41620919 |
Filed Date | 2012-11-29 |
United States Patent
Application |
20120298523 |
Kind Code |
A1 |
Nieminen; Ville ; et
al. |
November 29, 2012 |
METHOD AND ARRANGEMENT FOR PRODUCING METAL POWDER
Abstract
In a method for producing metal powder, the first part of an
acid-containing starting solution is fed on the anode side of an
electrolytic cell as anolyte, to contact the anode and supply
material containing yield metal, and a second part of the
acid-containing starting solution, which also contains intermediary
metal, is fed on the cathode side of the electrolytic cell, to
contact the cathode as catholyte. Yield metal is oxidized and
dissolved in the anolyte by leading electric current in the anode.
The yield metal contained in the second part of the starting
solution is reduced on the cathode side. Anolyte solution and
catholyte solution are fed to a precipitating chamber for mixing
the dissolved, oxidized yield metal and the second part of the
starting solution containing reduced intermediary metal.
Inventors: |
Nieminen; Ville; (Pori,
FI) ; Virtanen; Henri; (Pori, FI) |
Assignee: |
OUTOTEC OYJ
Espoo
FI
|
Family ID: |
41620919 |
Appl. No.: |
13/575275 |
Filed: |
January 25, 2011 |
PCT Filed: |
January 25, 2011 |
PCT NO: |
PCT/FI2011/050056 |
371 Date: |
July 25, 2012 |
Current U.S.
Class: |
205/571 ;
204/263; 204/275.1; 205/560; 205/563; 205/564; 205/572; 205/573;
205/574; 205/587; 205/594; 205/602; 205/610 |
Current CPC
Class: |
C25B 1/00 20130101; B22F
9/24 20130101; C25C 5/02 20130101 |
Class at
Publication: |
205/571 ;
205/560; 205/574; 205/594; 205/587; 205/602; 205/573; 205/610;
205/564; 205/572; 205/563; 204/275.1; 204/263 |
International
Class: |
C25C 1/00 20060101
C25C001/00; C25C 1/08 20060101 C25C001/08; C25C 1/22 20060101
C25C001/22; C25C 1/20 20060101 C25C001/20; C25C 1/10 20060101
C25C001/10; C25C 1/14 20060101 C25C001/14; C25C 1/12 20060101
C25C001/12; C25C 1/16 20060101 C25C001/16 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 29, 2010 |
FI |
20105083 |
Claims
1. A method for manufacturing metal powder, wherein dissolved yield
metal is mixed with a solution containing at least one intermediary
metal for precipitating the dissolved yield metal into yield metal
powder (14), wherein in the method a first part of an
acid-containing starting solution is brought as an anolyte (1) to
the anode side (6) of an electrolytic cell, to be in contact with
the anode (2) and the supply material containing yield metal; and a
second part of the acid-containing starting solution, which also
contains intermediary metal in addition to acid, is brought to the
cathode side (8) of the electrolytic cell, as a catholyte (3) to be
in contact with the cathode (4); the yield metal is oxidized and
dissolved in the anolyte (1) by conducting electric current in the
anode (2); the intermediary metal contained in the second part of
the starting solution is reduced on the cathode side (8); and
anolyte solution and catholyte solution are brought into a
precipitation chamber (12) for mixing the oxidized yield metal
dissolved in the first part of the starting solution and the second
part of the starting solution containing reduced intermediary
metal.
2. A method according to claim 1, wherein the first part of the
starting solution contains intermediary metal for boosting the
dissolution of yield metal on the anode side.
3. A method according to claim 1, wherein the first part of the
circulating solution created as a result of mixing the anolyte
solution and the catholyte solution is returned back to anolyte
(1).
4. A method according to claim 3, wherein the first part of the
starting solution is composed of the first part of the circulating
solution.
5. A method according to claim 3, wherein the second part of the
circulating solution created as a result of mixing the anolyte
solution and the catholyte solution is returned back to catholyte
(3).
6. A method according to claim 5, wherein the second part of the
starting solution is composed of the second part of the circulating
solution.
7. A method according to claim 5, wherein the circulating solution
is conducted essentially completely back to electrolyte, so that
the circulating solution is essentially composed of a first part of
the circulating solution and of a second part of the circulating
solution.
8. A method according to claim 1, wherein the anolyte (1) and the
catholyte (3) are mechanically separated by an electroconductive
diaphragm (7).
9. A method according to claim 1, wherein electroconductive
separator solution (5) is conducted in between the two diaphragms
(7) separating the anolyte (1) and the catholyte (3) in order to
prevent a premature mixing of the anolyte (1) and the catholyte
(3).
10. A method according to claim 1, wherein the yield metal is
copper.
11. A method according to claim 1, wherein the yield metal is
selected among the following group: nickel, cobalt, zinc, silver,
gold, ruthenium, rhodium, palladium, osmium, iridium, platinum,
manganese, zirconium, tin, cadmium and indium.
12. A method according to claim 1, wherein the intermediary metal
is vanadium.
13. A method according to claim 1, wherein the intermediary metal
is selected among the group titanium, chromium and iron.
14. A method according to claim 1, wherein the intermediary metal
is selected among the following group: manganese, zirconium,
molybdenum, technetium, tungsten, quicksilver, germanium, arsenic,
selenium, tin, antimony, tellurium and copper.
15. A method according, to claim 1, wherein the supply material
containing yield metal is located in the anode (2).
16. A method according to claim 1, wherein the yield metal is
selected so that the chosen yield metal is dissolved in the anolyte
(1) as a soluble salt of the acid that is contained in the first
part of the starting solution.
17. A method according to claim 1, wherein the starting solution
contains sulfuric acid.
18. A method according to claim 1, wherein the content of sulfuric
acid in the starting solution is at least 50 g/l and preferably 50
g/l-1500 g/l.
19. A method according to claim 1, wherein the starting solution
contains hydrochloric acid or nitric acid.
20. An arrangement for producing metal powder by precipitating
yield metal powder (14) by mixing dissolved yield metal with a
solution containing at least one intermediary metal, wherein the
arrangement comprises an electrolytic cell for dissolving the yield
metal located on the anode side of the electrolytic cell and for
oxidizing it in the anolyte, and for reducing the dissolved
intermediary metal located on the cathode side (8) of the
electrolytic cell on the cathode side; a precipitating chamber (12)
that is essentially separate from the electrolytic cell; as well as
means for feeding anolyte solution and catholyte solution
respectively from the anode side (6) of the electrolytic cell and
from the cathode side (8) of the electrolytic cell to the
precipitating chamber (12) for mixing the yield metal dissolved in
the anolyte and the catholyte solution containing reduced
intermediary metal, from outside the electrolytic cell.
21. An arrangement according to claim 20, wherein the electrolytic
cell comprises an electroconductive diaphragm (7) in between the
anode side (6) and the cathode side (8) of the electrolytic cell
for mechanically separating the anode side (6) and the cathode side
(8).
22. A method according to claim 20, wherein the electrolytic cell
comprises two electroconductive diaphragms (7) in between the anode
side (6) and cathode side (8) of the electrolytic cell for
mechanically separating the anode side (6) and the cathode side (8)
by means of an electroconductive separator solution (5) provided in
the space left between the two diaphragms (7).
23. A method according to claim 20, wherein the yield metal
supplied on the anode side (6) of the electrolytic cell is located
in the anode (2) of the electrolytic cell.
24. A method according to claim 20, wherein the electrolytic cell
comprises at least one bag, defined by a diaphragm (7), for keeping
the anolyte and/or the catholyte inside the bag.
25. A method according to claim 20, wherein the electrolytic cell
comprises means for conducting a separator solution (5) from the
space left between the two diaphragms (7) to the anode side (6)
and/or to the cathode side (8).
26. A method according to claim 20, wherein the electrolytes are
placed in an oxygen-free environment for preventing the oxidation
of the yield metal and/or intermediary metal contained in the
electrolytes.
Description
FIELD OF THE INVENTION
[0001] The invention relates to the production of finely divided
metal powder. In particular, the invention relates to a
dissolution-precipitation method and arrangement for producing
metal powder.
BACKGROUND OF INVENTION
[0002] Generally the end product in many metal manufacturing
processes is a plate-like object in cathode form. This kind of end
product is obtained for example by means of pyrometallurgical
production routes utilizing electrolysis. In these methods, a metal
anode that is pyrometallurgically made of a concentrate is
electrolytically refined to cathode copper, which can for example
be cast into products with various different forms. These types of
methods can be used for producing copper, nickel or cobalt
products, among others.
[0003] However, in the production of metals, in many cases it would
be advantageous for instance with respect to further processing, if
the metal received as the end product of the manufacturing process
would be obtained in some other form than as a uniform solid
object, such as a cathode plate. Particularly methods where the end
product is obtained as pure metal powder would be extremely
useful.
[0004] In the patent application JP2002327289, there is introduced
a method for producing copper powder in electrolysis. In the
method, an aqueous solution of sulfuric acid, containing, titanium
cathodes, is conducted to an anode chamber, so that the titanium
cathodes reduce the copper dissolved in the anode chamber, thus
precipitating it in the anode chamber into finely divided copper
powder. The problem with this method is that the catholyte solution
is conducted directly to the anode chamber, wherefore it is not
possible to effectively control the mixture ratios of the catholyte
solution and the anolyte solution. Moreover, in the method copper
is precipitated directly into the anode chamber, which makes it
more troublesome to remove the precipitated copper from the
electrolytic arrangement. These problems constitute a risk for the
creation of copper agglomerates, which makes it more difficult to
control the particle size of copper powder.
[0005] The patent publication US2005/0023151 introduces a method
where copper powder is made by electrolytically precipitating
copper from copper sulfate on a cathode. The method makes use of a
ferrous/ferric anode reaction, by which the energy consumption of
the method is reduced. Said publication also describes a
through-flow arrangement where the precipitated copper powder is
recovered from the electrodes by means of an electrolyte flowing
through the electrodes. A drawback with the method and arrangement
illustrated in the publication US2005/0023151 is, among others, an
unreliable recovery of copper from the cathodes, owing for example
to the precipitation of copper in various different locations in
the chamber containing electrodes, and to the attachment of copper
on the cathode. Owing to the above mentioned drawbacks, among
others, it is difficult to control the grain size of copper powder
and of the morphology of copper particles, as well to achieve a
homogeneous quality with separate electrodes. In addition, the
precipitation of copper directly onto the cathode also depends on
the cathode material and on the surface morphology, which in part
increases the unreliability of the method.
[0006] The patent application WO2008/017731 introduces a method for
manufacturing metal powder. In this method, valuable metal powder
is precipitated by reducing the valuable metal dissolved in the
method by means of another metal. In said method, also the
dissolution of precious metal takes place in a reaction with said
other metal, which weakens the control of the process kinetics as
well as the efficiency thereof, and makes the method and the
arrangement used therein fairly complicated.
OBJECT OF INVENTION
[0007] The object of the invention is to eliminate above mentioned
drawbacks of the prior art and to set forth a new method and
arrangement for manufacturing metal powder in a
solution-precipitation method making use of electrolysis.
SUMMARY OF INVENTION
[0008] The method according to the invention is characterized by
what is set forth in the independent claim 1.
[0009] The arrangement according to the invention is characterized
by what is set forth in the independent claim 20.
[0010] In the method according to the invention for manufacturing
metal powder, dissolved yield metal is mixed with a solution
containing at least one intermediary metal for precipitating the
dissolved yield metal into a yield metal powder. In the method, a
first part of an acid-containing starting solution is brought to
the anode side of the electrolytic cell as an anolyte, to be in
contact with the anode and the supply material containing yield
metal, and a second part of the acid-containing starting solution,
which also contains intermediary metal in addition to acid, is
brought to the cathode side of the electrolytic cell, as a
catholyte to be in contact with the cathode; the yield metal is
oxidized and dissolved in the anolyte by conducting electric
current to the anode; the intermediary metal contained in the
second part of the starting solution is reduced on the cathode
side; and anolyte solution and catholyte solution are brought into
a precipitation chamber for mixing the oxidized yield metal
dissolved in the first part of the starting solution and the second
part of the starting solution containing reduced intermediary
metal.
[0011] The arrangement according to the invention is an arrangement
for producing metal powder by precipitating yield metal powder by
mixing dissolved yield metal powder with a solution containing at
least one intermediary metal. The arrangement according to the
invention comprises an electrolytic cell for dissolving the yield
metal located on the anode side of the electrolytic cell and for
oxidizing it in the anolyte, and for reducing, on the cathode side,
the dissolved intermediary metal located on the cathode side of the
electrolytic cell; a precipitation chamber arranged essentially
separately from the electrolytic cell; as well as means for feeding
anolyte solution and cathode solution respectively from the anode
side and the cathode side of the electrolytic cell to the
precipitation chamber for mixing the oxidized yield metal that is
dissolved in the anolyte, and the cathode solution containing
reduced intermediary metal, outside the electrolytic cell.
[0012] Among the advantages of the invention, let us point out for
example good controllability of the particle size of the
precipitating yield metal powder, which is made possible
particularly by the feeding of the anolyte solution and cathode
solution, to be mixed together, in a separate precipitation
chamber, in which case the mixing ratio of said solutions can be
controlled easily and accurately, as well as optimized according to
the process conditions. Moreover, when the precipitation step takes
place in a separate precipitation chamber, away from the vicinity
of the electrodes, the effect of the electrodes in the
precipitation process and in collecting the precipitate can be
minimized, so that the reliability of the process is improved. Also
the recovery of the yield metal precipitate becomes easier and more
reliable. With a correct mixing ratio and an effective precipitate
recovery, the creation of yield metal agglomerates can be prevented
in the precipitation step, and consequently the homogeneity of the
yield metal particles contained in the powder is enabled with
respect to their size. A correct mixing ratio also facilitates a
process with a better efficiency, which can be utilized for
reducing the amount of energy needed in the process for producing a
certain quantity of yield metal mass.
[0013] Unless otherwise stated, in the present document the
expressions "anode side" and "cathode side" refer to those parts of
the electrolytic cell that contain anolyte or catholyte in the
vicinity of the anode or cathode, respectively. The "anode side" or
the "cathode side" need not be a uniform part of the electrolytic
cell, but the "anode side" or the "cathode side" may consist of
several mutually separate elements comprising an anode or a cathode
and anolyte or catholyte, respectively.
[0014] Unless otherwise stated, in the present document the
expression "diaphragm" refers to any suitable film or thin
mechanical obstacle, such as a membrane, an industrial textile or
the like.
[0015] Unless otherwise stated, in the present document the
expression "oxidation state", "oxidation level" or a corresponding
expression refers to a charge level where an atom appears alone or
apparently in a molecule. Thus the expressions "oxidation state",
"oxidation level" or a corresponding expression can also refer to
the apparent charge of an atom.
[0016] In an embodiment of the invention, the first part of the
starting solution contains intermediary metal for boosting the
dissolution of yield metal on the anode side. In an embodiment of
the invention, the first part of the circulating solution created
as a result of mixing the anolyte solution and the catholyte
solution is returned to anolyte. In an embodiment of the invention,
the first part of the starting solution is composed of the first
part of the circulating solution. Further, in an embodiment of the
invention, the second part of the circulating solution created as a
result of mixing the anolyte solution and the catholyte solution is
returned to catholyte. Further, in an embodiment of the invention,
the second part of the starting solution is composed of the second
part of the circulating solution. Moreover, in an embodiment of the
invention, the circulating solution is returned essentially
completely back to electrolyte, in which case the circulating
solution is essentially composed of the first part of the
circulating solution and of the second part of the circulating
solution. When an anolyte solution that is formed of the first part
of the starting solution and a catholyte solution that is formed of
the second part of the starting solution are mixed together, there
is created yield metal powder as the yield metal that was oxidized
and dissolved in the anolyte is reduced, and the intermediary metal
that was reduced in the catholyte is oxidized. The obtained
circulating solution is recirculated in an arrangement to be used
in the process in one of the embodiments of the invention, so that
the circulating solution is partly or completely, after the mixing
step and after the yield metal precipitate is separated from the
solution, returned back to anolyte and/or catholyte. Now the
intermediary metal is again reduced in the catholyte. Thus it is
possible to realize an electrolytic regeneration of the
intermediary metal in the catholyte, which means that in some
embodiments of the invention, it is essentially not necessary to
feed in the process new solution containing intermediary metal. In
addition, when also the anolyte in some embodiments of the
invention contains intermediary metal, said intermediary metal
intensifies the dissolution of the yield metal in such process
conditions, for example with relatively low acid contents, where
dissolution with the combined effect of electric current and acid
solution would not be efficient.
[0017] In an embodiment of the invention, the anolyte and the
catholyte are mechanically separated by an electroconductive
diaphragm. In an embodiment of the invention, the electrolytic cell
comprises an electroconductive diaphragm provided in between the
anode side and the cathode side of the electrolytic cell for
mechanically separating the anode side and the cathode side.
[0018] Further, in an embodiment of the invention, an
electroconductive separator solution is conducted in between the
two diaphragms separating the anolyte and the catholyte in order to
prevent a premature mixing of the anolyte and the catholyte. In an
embodiment of the invention, the electrolytic cell comprises two
electroconductive diaphragms provided in between the anode side and
the cathode side of the electrolytic cell for mechanically
separating the anode side and the cathode side by means of an
electroconductive separator solution placed in the space between
the two diaphragms.
[0019] In order to efficiently separate the precipitation step from
the electrolytic cell and to realize this step in a controlled
fashion and essentially completely in a separate precipitation
chamber, the anolyte and the catholyte can in an embodiment of the
invention be separated by means of an electroconductive diaphragm.
In this document, the term "electroconductive diaphragm" refers to
a diaphragm that is electroconductive to such extent that the
diaphragm facilitates an effective operation of the electrolytic
cell. However, in some embodiments of the invention, the
electroconductivity of the diaphragm may be lower than the
electroconductivity of those solutions that are mechanically
separated by the diaphragm. Consequently, the purpose of the
diaphragm is to mechanically separate the solutions located on
different sides of the diaphragm, i.e. to serve as a mechanical
obstacle, while at the same time being electroconductive to that
extent that the electrolytic cell is capable of functioning
effectively. This diaphragm divides the electrolytic cell to an
anode part (or anode side), where the anolyte is located, and to a
cathode part (or cathode side), where the catholyte is located.
Thus the anolyte and the catholyte cannot be mixed together without
disturbing the anode and cathode reactions, and metal powder cannot
be formed in the vicinity of those electrodes in the electrolytic
cell. For further intensifying the separation of the anode and the
cathode, it is possible to use in between the anode side and the
cathode side two partition diaphragms, and a separator solution can
be fed in between said diaphragms.
[0020] In an embodiment of the invention, the yield metal is
copper. In an embodiment of the invention, the yield metal is
selected among the following group: nickel, cobalt, zinc, silver,
gold, ruthenium, rhodium, palladium, osmium, iridium, platinum,
manganese, zirconium, tin, cadmium and indium.
[0021] In an embodiment of the invention, the intermediary metal is
vanadium. Further, in an embodiment of the invention, the
intermediary metal is selected among the following group: titanium,
chromium and iron. Further, in an embodiment of the invention, the
intermediary metal is selected among the following group:
manganese, zirconium, molybdenum, technetium, tungsten,
quicksilver, germanium, arsenic, selenium, tin, antimony, tellurium
and copper. In the various embodiments of the invention, the yield
metals and intermediary metals can be selected among a group that
depends on various different process parameters, particularly on
the pH value of the electrolyte (i.e. on the oxygen content). On
the basis of this description of the invention, a man skilled in
the art is capable of finding in the above enlisted groups a
suitable intermediary metal for a certain yield metal by means of
routine testing. In particular, it has been found out that for
example copper powder can be efficiently and reliably produced in
an embodiment of the invention, when the selected intermediary
metal is vanadium.
[0022] In an embodiment of the invention, the supply material
containing yield metal is placed in the anode. Further, in an
embodiment of the invention, the yield metal located on the anode
side of the electrolytic cell is placed in the anode of the
electrolytic cell. When the supply material containing yield metal
is placed in the anode, the rate per unit of time of the electric
current passing through the yield metal, and consequently also the
mass of the dissolving yield metal per unit of time, can be
efficiently controlled. The advantage of this embodiment is a
particularly precise control of the dissolving reaction by means of
electricity; yield metal is dissolved accurately according to the
used quantity of electricity in the course of the given time period
according to Faraday's laws. Moreover, the kinetics in the
dissolution step are rapid, as the quantity of yield metal
dissolved in the anolyte is directly proportional to the charge
that has flown through the anode. Thus also the quantity of yield
metal that is dissolved in the anolyte can be efficiently and
accurately controlled, which facilitates a more precise control of
the process dynamics, and an improvement in reliability.
[0023] In an embodiment of the invention, the yield metal is
selected so that the selected yield metal is dissolved in the
anolyte as a soluble salt of the acid that is contained in the
first part of the starting solution.
[0024] In an embodiment of the invention, the electrolytes are
placed in an oxygen-free environment, in order to prevent the
oxidation of the yield metal and/or intermediary metal that is
contained in the electrolytes. This makes it easier to control the
acid content of the electrolytes, which means that the balance of
chemical reactions taking place in the different solutions of the
process and containing for example yield metal and/or intermediary
metal can be adjusted more accurately, which in turn improves the
reliability and efficiency of the process, among others.
[0025] In an embodiment of the invention, the starting solution
contains sulfuric acid. Further, in an embodiment of the invention
the sulfuric acid content in the starting solution is at least 50
g/l and preferably within the range 50 g/l-1,500 g/l. In an
embodiment of the invention, the starting solution contains
hydrochloric acid or nitric acid. Further, in an embodiment of the
invention the hydrochloric acid content in the starting solution is
within the range 15 g/l-500 g/l. Yet in an embodiment of the
invention the starting solution contains, in addition to
hydrochloric acid, also alkaline chloride, the content of which in
the starting solution is within the range 15 g/l-500 g/l. The
suitability of an acid in the starting solution depends, among
others, on the supply material, the yield metal and the
intermediary metal in question. In some embodiments of the
invention, the solutions may also contain more than one acid. On
the basis of this description of the invention, a man skilled in
the art is capable, by routine testing, of finding a suitable acid
for a certain supply material, yield metal and intermediary metal,
and a suitable content for said acid. In particular, it has been
found out that in some embodiments of the invention, a sulfuric
acid content of the starting solution that is at least 50 g/l
provides for an efficient oxidation of a copper anode and its
dissolution in the anode, when the intermediary metal is vanadium.
A suitable acid, and content for said acid, must be chosen so that
the yield metal is dissolved from the supply material to the
anolyte, instead of the oxidation of the intermediary metal.
Therefore the anolyte pH (i.e. oxygen content) must be suitable.
When the employed yield metal is copper, and the intermediary metal
is vanadium, the oxygen content must be as high as possible.
[0026] In an embodiment of the invention, the electrolytic cell
comprises at least one bag defined by a diaphragm in order to
restrict the anolyte and/or catholyte inside the bag. Further, in
an embodiment of the invention the electrolytic cell comprises
means for conducting the separator solution from a space left in
between two diaphragms to the anode side and/or the cathode
side.
[0027] The above described embodiments of the invention can be
freely combined with each other. Several different embodiments can
be combined in order to create a new embodiment. A method or
arrangement that the invention relates to can include one or
several of the above described embodiments of the invention.
DETAILED DESCRIPTION OF INVENTION
[0028] In the specification below, the invention is described with
reference to the appended drawings, where
[0029] FIG. 1 is a flowchart illustrating an embodiment of a method
according to the invention,
[0030] FIG. 2 is a schematical illustration of an embodiment of an
arrangement according to the invention,
[0031] FIG. 3 is a schematical block diagram illustrating an
embodiment of a method according to the invention,
[0032] FIG. 4 is a schematical illustration of an embodiment of the
electrolytic cell in an arrangement according to the invention,
[0033] FIG. 5 shows scanning electron microscope images (SEM
images) of copper powder produced by an embodiment of the
invention.
[0034] For the sake of simplicity, reference numbers referring to
various elements of the invention remain the same in connection
with corresponding repeated elements.
[0035] In the preparation step S1 of an embodiment of the method
according to FIG. 1, there is produced and fed into the
electrolytic cell, both to the anode side and to the cathode side,
acid-bearing starting solution, electrolyte solution, which
contains intermediary metal in its high potential value (i.e. in a
higher oxidation state). In the method it is essential that at
least the second part of the starting solution, which is fed to the
cathode side, contains said intermediary metal in its high
potential value, because in step S2, in the catholyte there is
carried out the reduction of the intermediary metal to its low
potential value (i.e. to a lower oxidation state), i.e. the
regeneration of the intermediary metal. Also the first part of the
starting solution, i.e. the part that is fed as the anolyte, may
contain intermediary metal in its high potential value. In some
embodiments of the invention, the starting solution may contain two
or even several different intermediary metals. In some embodiments
of the invention, the first and second part of the starting
solution are identical in composition. By this procedure, the
possibility that the composition of the electrolytes would be
changed after starting the process is minimized, which means that
the operating point of the process is stabilized more rapidly, and
the controllability of the process is improved.
[0036] The type of intermediary metal suited in the method
essentially depends on the selected yield metal, which should be
dissolved in the anolyte in step S2, and which is later
precipitated into powder in the mixing step S3. The intermediary
metal and the selected yield metal together define the other
features of the starting solution suited in the method,
particularly the acid contained in the solution, and content of
said acid in the solution. For example, the pH value of the
solution must be such that in the prevailing process conditions, on
the anode side there is more advantageously carried out the
oxidation of yield metal and its dissolution in the anolyte than
the oxidation of the intermediary metal in the anolyte. This kind
of process conditions, i.e. functional windows, can be found for
many different pairs of yield metal and intermediary metal. In the
light of the description of the present invention as well as in the
light of the Pourbaix diagrams of various different intermediary
metals and yield metals, the finding of these functional windows
represents routine testing for a man skilled in the art.
[0037] The starting solution can be produced in many different
ways, which depend, among others, on the suitable intermediary
metal. One way is for example to dissolve, in an aqueous solution
of a suitable acid, oxide containing the desired intermediary
metal. When necessary, the acid content of the starting solution
and the oxidation number of the dissolved intermediary metal can
thereafter be adjusted to be suitable with respect to the starting
solution. The adjusting of the oxidation number of the intermediary
metal can be carried out for example electrolytically.
[0038] When the starting solution is formed in step S1, it is fed
as electrolyte in an electrolytic cell, where supply material
containing yield metal is located on the anode side. In a method
according to FIG. 1, after step 1, in step 2 yield metal is
dissolved on the anode side of the electrolytic cell from the
supply material to the anolyte, as the yield metal is at the same
time oxidized, and on the cathode side the intermediary metal of
the starting solution is reduced from a high potential value to a
low potential value. Because of productional considerations, among
others, it is advantageous that the intermediary metal content and
the content of the dissolved yield metal in the solutions is as
high as possible. Thus a certain solution volume gives more
precipitated yield metal powder in the mixing step S3, than in a
situation where the contents of the intermediary metal and/or
dissolved yield metal in the solutions are low.
[0039] The method according to FIG. 1 can be realized by means of
an arrangement illustrated schematically in FIG. 2, where the
employed supply material is present as an anode 2, which provides
for rapid kinetics in the dissolution of yield metal, while the
dissolution of the supply material is directly proportional to the
charge flowing through the anode 2. Now the dissolution reactions
can be controlled particularly accurately by using electricity; in
a given period of time, the mass quantity of yield metal dissolved
and oxidized on the anode is accurately proportional to the
employed quantity of electricity, according to Faraday's laws.
Respectively, an equimolar quantity of the intermediary metal is
regenerated (reduced) on the cathode. The arrangement of FIG. 2
also comprises a cathode 4, an anode side 6 of the electrolytic
cell, a cathode side 8, anolyte filtering equipment 10, a
precipitation chamber 12, separator equipment 16, and cleaning
equipment 18 for the circulating solution. The anolyte 1 and the
catholyte 3 are mechanically separated by means of an
electroconductive separator solution 5 placed in the intermediate
space 11 and by means of two electroconductive diaphragms 7 that
define the intermediate space. The purpose is to ensure that the
yield metal cations created on the anode side and the intermediary
metal that is reduced to a low-potential value on the cathode side
do not get into mutual contact in the electrolytic cell. Thus yield
metal powder cannot be precipitated directly on the anode or
cathode side of the electrolytic cell, which would, in case it
happened, weaken the controllability of the process for example as
regards the particle size of the yield metal powder as well as the
process efficiency, and in addition, the recovery of the yield
metal powder would become more difficult. In order to improve the
separation of the anolyte 1 and the catholyte 3, the separator
solution 5 provided in the intermediate space 11 can also be
maintained at a higher hydrostatic pressure than the anolyte 1 and
the catholyte 3.
[0040] After step S2, in step S3, anolyte solution is conducted
from the anode side of the electrolytic cell and catholyte solution
is conducted from the cathode side thereof, for example by means of
suitable pipes or in some other way, to the precipitation chamber
12, in a suitable ratio away from the vicinity of the electrodes 2,
4. Because anolyte solution and catholyte solution are conducted to
a separate precipitation chamber 12, the mixing ratio of the
solutions can be controlled easily and accurately, and it can be
optimized according to the process conditions. With a correct
mixing ratio and an effective precipitate recovery, the creation of
yield metal agglomerates can be prevented in the precipitation
step, and consequently the homogeneity, with respect to their size,
of the yield metal particles contained in the yield metal powder 14
is ensured. A correct mixing ratio also facilitates a process with
a better efficiency, which results in reducing the amount of energy
needed in the process for producing a certain quantity of yield
metal mass.
[0041] In the precipitation chamber 12, there is mixed, or there
can be continuously mixed the anolyte solution and the catholyte
solution conducted in the chamber 12. Prior to conducting the
anolyte solution into the precipitation chamber 12, it can in some
embodiments of the invention be also purified of metallic
impurities and/or other possible impurities disturbing the yield
metal precipitation process in an anolyte filtering equipment 10
that is suited for this purpose. As a result of the mixing process,
the oxidized yield metal of the anolyte solution is reduced and
precipitated into solid yield metal powder 14, at the same time as
the intermediary metal reduced in the catholyte solution is
oxidized back to its high-potential value. From the obtained
circulating solution, there is separated, in step S4, yield metal
for example by centrifuging the circulating solution in separator
equipment 16 suited for the purpose.
[0042] When the yield metal powder 14 is recovered, the created
circulating solution is recirculated back to the electrolytic cell
in step S5, part of it into anolyte 1 and part into catholyte 3.
Before conducting the circulating solution back to the electrolytic
cell, any dissolved yield metal that is possibly left in the
circulating solution is removed therefrom, as well as yield metal
particles, in cleaning equipment 18 suited for this purpose. The
cleaning operation can be carried out for example electrolytically
by reduction and filtering. A thorough removal of yield metal, both
dissolved and precipitated, from the circulating solution prior to
recirculating the circulating solution back to the electrolytic
cell is useful for the reliability of the process, for improving
process efficiency and the controllability of the particle size of
the yield metal powder.
[0043] In the above described method, the composition of the
circulating solution is essentially identical with the composition
of the starting solution, because in precipitation, the
intermediary metal is oxidized back into its starting solution
value, and the yield metal dissolved in the anolyte 1 on the anode
side is precipitated and separated from the solution. Thus the
circulating solution created in the method can be reused as a
starting solution. If also the recirculating of the circulating
solution back to anolyte and catholyte is carried out with the same
ratio that was applied when a corresponding electrolyte was fed
from the anode side and the cathode side to the precipitation
chamber in step S3, an essentially closed electrolyte circulation
can be used in the process, without a need to separately add/remove
solution to or from the anode side 6 of the electrolytic cell, or
to or from the cathode side 8.
[0044] In practice, the method of FIG. 1 is generally realized as a
continuous electrolyte circulation, as a result of which in the
precipitation chamber 12 there is continuously accumulated yield
metal powder 14 to be separated from the circulating solution and
to be recovered, until the recirculation of the electrolyte
solution (circulating electrolyte) in the arrangement is stopped,
or when the yield metal contained in the supply material (anode 2)
is completely dissolved in the electrolytic cell. When there is no
more need to produce yield metal powder 14, or when the yield metal
of the supply material is finished on the anode side 6 of the
electrolytic cell, the recovered yield metal powder 14 is treated
in a finishing treatment in step S6, and the process is stopped. In
some other preferred embodiments of the invention, the finishing
treatment for the recovered yield metal powder 14 can be carried
out simultaneously with the other steps of the process, in the
course of the process of separating yield metal powder 14 and
feeding it to the finishing treatment equipment (not
illustrated).
[0045] In an example according to FIG. 3, illustrated as a block
diagram, the employed intermediary metal is vanadium, which in its
high-potential value is V.sup.3+ in cations. The employed yield
metal is copper, which is located in the supply material serving as
the anode 2. The starting solution containing the vanadium
intermediary metal in V.sup.3+ cations can be produced for instance
by dissolving vanadium oxide V.sub.2O.sub.3 for instance to an
aqueous solution of sulfuric acid. When the starting solution that
contains V.sup.3+ cations in an aqueous solution, the sulfuric acid
content of said solution being for example within the range 50
g/l-1500 g/l, is formed, its first part is fed to the anode side 6
of the electrolytic cell as the anolyte 1, and the second part is
fed to the cathode side 8 as the catholyte 3. When electric current
flows through the electrolytic cell, the V.sup.3+ cations are
reduced on the cathode side 8 to V.sup.2+ cations in the catholyte
3, and copper is dissolved from the anode 2 to the anolyte 1 as
oxidized Cu.sup.2+ cations. Consequently, the anode reaction is
Cu.sup.0->Cu.sup.2+2e.sup.-, and the cathode reaction is
V.sup.3++e.sup.-->V.sup.2+.
[0046] In the dissolution of copper and its oxidation in the
anolyte 1, the intermediary metal may in some embodiments of the
invention participate in corresponding reactions, thus improving
both dissolution and oxidation, in such process conditions, for
example with fairly low acid contents, where dissolution and
oxidation with the combined effect of a mere electric current and
an acid solution would not be efficient. Now the precise mechanism
how the intermediary metal participates in the dissolution and
oxidation of the yield metal depends on the selected yield metal
and intermediary metal. In the above described example, when the
yield metal is copper and the intermediary metal is vanadium,
vanadium may be oxidized on the anode side 6 into an intermediary
oxidation state V.sup.5+, which is even higher than the V.sup.3+
state, whereafter the V.sup.5+ reacts with copper, thus oxidizing
and dissolving copper. Now the "over-oxidized" vanadium V.sup.5+ is
reduced back to its original high-potential value V.sup.3+. On the
anode side 6, a corresponding "overoxidation" to an intermediate
oxidation state is also possible with other intermediary metals
than vanadium.
[0047] Thereafter anolyte solution and catholyte solution are
conducted and mixed in a suitable ratio, for example in the ratio
1:3, in the precipitation chamber 12, where copper is precipitated
through the reaction 2V.sup.2++Cu.sup.2+->2V.sup.3++Cu.sup.0. On
the basis of this precipitation reaction, anolyte and catholyte are
in theory needed in the mixing ratio 1:2, in order to make all
V.sup.2+ and Cu.sup.2+ cations present in the solutions participate
in the precipitation of copper. An optimal mixing ratio depends on
the reaction state of the anode reactions and on the current
efficiency, as well as on the reaction state and current efficiency
of the cathode reactions.
[0048] As regards the efficiency and reliability of the process, it
is useful to ensure that any remarkable amounts of V.sup.2+ and/or
Cu.sup.2+ cations are not left in the circulating solution. In some
embodiments of the invention, it is for example advantageous to try
and make sure that all Cu.sup.2+ cations are consumed in the
precipitation reaction, in which case the real mixing ratio of
anolyte and catholyte can be 1:N, where N>2. However, the value
of the parameter N also depends on how the circulating solution is
cleaned before feeding it back to the electrolytic cell. On the
basis of the description of the present invention, the finding of a
suitable mixing ratio is obvious routine testing for a man skilled
in the art.
[0049] When copper is precipitated into powder 14 and separated
from the rest of the solution by means of the separator equipment
16, the remaining circulating solution is cleaned in the cleaning
equipment 18 of any copper that is possibly left in the solution in
the separation process, both of solid copper and dissolved,
unprecipitated Cu.sup.2+ cations. The cleaning can be carried out
for example electrolytically by precipitating and filtering. After
said chemical and mechanical cleaning, the remaining circulating
solution is essentially the same in composition as the starting
solution, containing as a result from the precipitation reaction
vanadium cations V.sup.3+ and sulfuric acid in aqueous solution.
This circulating solution is again divided in a suitable ratio into
anolyte 1 on the anode side 6 and into catholyte 3 on the cathode
side 8. After the above described regeneration, the same
circulation electrolyte can again be conducted through the
arrangement and the method for precipitating more/new copper powder
14 to the precipitation chamber 12.
[0050] The solid yield metal powder 14 separated from the solution
is finished (FIG. 1, step S6) in a finish treatment arrangement.
The separation and finish treatment processes can include many
different steps, depending on the desired properties of the end
product. In some embodiments of the invention, the yield metal
powder 14 separated from the circulation electrolyte is washed in
water for minimizing impurities carried along from the solution,
whereafter the yield metal powder 14 is dried and coated with a
passivation layer for preventing an oxidation of the powder, among
others. In order to minimize the redissolution of the precipitated
yield metal powder 14 back into the circulating solution, it is
useful to perform the separation of the yield metal powder 14 from
the circulating electrolyte by the separator equipment 16, and it
is advisable to perform the washing as quickly as possible after
the precipitation reaction.
[0051] In some embodiments of the invention, the yield metal powder
14 is subjected to various separate washing operations. In between
the washing operations, the yield metal powder 14 is separated from
the washing liquid. In an embodiment of the invention, the yield
metal powder 14 that is obtained from the separator equipment 16,
which is separated from the circulating electrolyte by centrifuging
but is still wet, is mixed in water in the mass mixing ratio 1:20
(one part of wet yield metal powder 14 and 20 parts of water) three
times. In between the mixing operations, the yield metal powder 14
is separated from the washing liquid.
[0052] The exact structure and operation of the washing equipment
can vary even to a great extent, and for a man skilled in the art,
the production of such equipment is obvious in the light of the
description of the present invention. In a preferred embodiment of
the invention, the washing equipment for realizing several
successive washing operations can be for example a conveyor-belt
type arrangement, where the wet yield metal powder 14 is poured on
a conveyor belt, which conveys the yield metal powder 14 to the
washing liquid, from which the yield metal powder is poured on the
next conveyor belt, etc. Now the settling of the yield metal powder
14 takes place when it is separated from the washing liquid, i.e.
when the washing liquid containing yield metal powder is poured on
the conveyor belt.
[0053] In addition to the above described example, or instead of
the procedure described therein, the separated yield metal powder
can naturally also be washed by many known methods, for example by
means of a syphon.
[0054] Various different electrolytic cell structures can be
designed for dissolving and oxidizing yield metal on the anode side
of an electrolytic cell, and for reducing intermediary metal on the
cathode side of an electrolytic cell. The electrolytic cell
structure illustrated schematically in FIG. 4 can be used in the
arrangement for producing yield metal powder 14 in a reliable and
efficient way, with a good efficiency.
[0055] In the electrolytic cell of FIG. 4, both the anode side 6
and the cathode side 8 comprise several sections, i.e. diaphragm
bags, defined by a diaphragm 7. Each diaphragm bag respectively
includes an anode 2 or a cathode and anolyte 1 or catholyte 3.
Naturally the anodes 2 and the cathodes 4 are connected to a power
source (not illustrated). In between each diaphragm bag, there is
supplied electroconductive separator solution 5, which in one
embodiment of the invention contains intermediary metal in a
suitable high-potential value, i.e. in an oxidized state; in the
case of the above described example, the separator solution 5 may
contain for example V.sup.3+ ions.
[0056] In addition, the electrolytic cell of FIG. 4 comprises a
feed pipe 9 for feeding separator solution to the intermediate
space 11 left between the diaphragm bags, an overflow channel 13
for the separator solution 4, drain channels 15 for the anolyte
solution and the catholyte solution, as well as a protective film
17. The electrolytic cell of FIG. 4 can be connected to another
arrangement, for example to a precipitation chamber 12 (not
illustrated in FIG. 4), by intermediation of the drain channels 15
and the feed pipe 9.
[0057] In an embodiment of the invention, the separator solution 5
serves as the starting solution, in which case the composition of
the separator solution 5 is identical to that of the starting
solution. Now the starting solution can be fed to the intermediate
space 11 of the electrolytic cell illustrated in FIG. 4 through the
apertures provided in the feed pipe 9. From the intermediate space
11, the separator solution 5 flows to the diaphragm bags as anolyte
1 and catholyte 3 through perforations provided in the diaphragms
7. In addition or instead, the diaphragm can be semi-permeable, so
that the separator solution 5 (starting solution) has access to
flow in a controlled fashion through the diaphragm 7 as anolyte 1
and/or catholyte 3. Anode reactions and cathode reactions take
place in the diaphragm bags in the way described above. The
obtained catholyte solution, containing reduced intermediary metal,
as well as the anolyte solution containing dissolved or oxidized
yield metal, can be conducted to the precipitation chamber 12 for
example through outlets 15. In some embodiments of the invention,
the outlets 15 can serve as overflow channels for removing excess
electrolyte from the arrangement, in which case anolyte solution
and/or catholyte solution can be brought in the precipitation
chamber 12 via another route, for example through suction inlets
provided for this purpose. The circulating solution created in the
precipitation chamber 12 can in turn be recirculated, after
possible cleaning steps, for example via a feed pipe 9 back to the
intermediate space 11 and further to anolyte 1 and/or catholyte
3.
[0058] By adjusting the permeability of the diaphragms 7 in the
cell illustrated in FIG. 4, or the size of the perforations
provided in the diaphragms 7, the quantity of the solution flowing
through the anode side 6 and/or the cathode side 8 per unit of time
can be efficiently controlled. The permeability of the diaphragms 7
can be selected separately for the diaphragms 7 on the anode side 6
and/or for the diaphragms 7 on the cathode side 8. By suitably
controlling the quantity of solution per time unit that has access
to flow in the diaphragm bags on the anode side 6 and/or on the
cathode side 8 through the diaphragms 7, in relation to the
quantity of solution per time unit to be fed in the intermediate
space 11, the hydrostatic pressure of the separator solution 5
placed in the intermediate space 11 can be adjusted to be higher
than the hydrostatic pressure of the electrolytes contained in the
diaphragm bags located in the separator solution 5. Thus it is
possible to prevent an undesired flowing of the electrolyte through
the diaphragm 7 towards the intermediate space 11, away from the
diaphragm bag. By suitably arranging the measures of the overflow
channel 13, for example by arranging it at a suitable height, it is
possible to ensure according to FIG. 4 that the hydrostatic
pressure difference between the intermediate space 11 and the anode
side 6 and/or the cathode side 8 does not rise too high, but any
excess separator solution flows out of the cell through the
overflow channel 13. Respectively, also by arranging the measures
and locations of the outlets 15, it is possible to affect the
formation of said hydrostatic pressure difference. When the
diameter of the perforations possibly provided in the diaphragms 7
is large, said hydrostatic pressure difference, together with the
permeability of the diaphragms 7, essentially defines the quantity
of solution that flows through the anode side 6 and the cathode
side 8 per unit of time. On the basis of the description of the
present invention, the above described design of the measures of
the electrolytic cell, and the placing of the perforations, is
obvious routine testing for a man skilled in the art.
[0059] As was described above, in some embodiments of the invention
it is not necessary to directly feed starting solution and/or
circulating solution to the anode side 6 and/or cathode side 8 of
the electrolytic cell, for example to the diaphragm bags, but
essentially all solution in the arrangement circulates through the
intermediate space 11. In case the diaphragms 7 are selected to be
such that they are completely impermeable to solution, circulating
solution and/or starting solution can be fed to the anode side 6
and/or to the cathode side 8, for example to the diaphragm bags,
directly and not through the intermediate space 11. In some other
embodiments of the invention, instead of the diaphragms 7, there
can be used for example ion-selective membranes that only permeate
ions of a certain type.
[0060] In the electrolytic cell according to FIG. 4, the
electrolytic cell structure is covered by a protective film 17, by
means of which the intermediate space 11 can be pressurized for
example with nitrogen gas or with some other inert gas in order to
prevent a possible oxidation caused by air or the surrounding
environment. Also the diaphragm bags can be closed and pressurized
with nitrogen in order to prevent oxidation.
[0061] The cell structure of FIG. 4 enables a reliable separation
of the anolyte and the catholyte in the electrolytic cell, which
reduces premature oxidation and/or reduction reactions.
Consequently, by using the electrolytic cell structure according to
FIG. 4, there is achieved a good efficiency in the method. In
addition, the risk of a premature precipitation of the yield metal
powder in the electrolytic cell is reduced, which improves the
reliability of the method and makes the maintenance of the
equipment easier.
EXAMPLE
[0062] By applying a method according to the block diagram
illustrated in FIG. 3, there was manufactured, in an arrangement
representing essentially the type illustrated in FIG. 2, copper
powder by employing as the starting solution an aqueous solution of
sulfuric acid, said solution containing V.sup.3+ cations. In this
starting solution, the measured sulfuric acid concentration was
about 500 g/l, and the measured vanadium concentration was about 16
g/l. The employed supply material was Class A cathode copper plate,
which also served as the anode of the electrolytic cell. The
employed cathode was a lead plate, measures 275 mm.times.130 mm. In
test conditions, the solution temperatures were roughly
20-35.degree. C.
[0063] The starting solution was fed to the electrolytic cell,
where copper anode was oxidized and dissolved in the anolyte. The
measured content of the dissolved copper was roughly 4 g/l.
Thereafter anolyte solution was conducted from the anode side, and
catholyte solution was conducted from the cathode side to the
precipitation chamber, which in this example was a glass bottle.
The mixing ratio of the anolyte solution and the catholyte solution
was 1:3. As a result of the mixing operation, copper powder was
formed in the precipitation chamber, according to the description
above. The electron microscope images taken of the obtained copper
powder are illustrated in FIG. 5; from these images it can be
observed, for example, that the size distribution of the copper
particles is fairly homogeneous, large particle agglomerates are
not created, and the average size of the particles is below the
micrometer range.
[0064] Although some examples and embodiments illustrating the
invention are above described as methods for manufacturing copper
powder, a man skilled in the art is on the basis of this
description of the invention easily capable of manufacturing
powders also of other metals than copper when applying the various
embodiments of the invention. Likewise, on the basis of this
description of the invention, a man skilled in the art is easily
capable of using, in the various embodiments of the invention,
other intermediary metals and/or acids than those enlisted in the
above examples. The invention is not restricted to the above
described examples only, but it can be realized in many different
modifications within the scope of the appended claims.
* * * * *