U.S. patent application number 13/947342 was filed with the patent office on 2015-01-22 for electrowinning cell and process.
This patent application is currently assigned to CASE WESTERN RESERVE UNIVERSITY. The applicant listed for this patent is Rohan Akolkar, Uziel Landau. Invention is credited to Rohan Akolkar, Uziel Landau.
Application Number | 20150021195 13/947342 |
Document ID | / |
Family ID | 51352770 |
Filed Date | 2015-01-22 |
United States Patent
Application |
20150021195 |
Kind Code |
A1 |
Akolkar; Rohan ; et
al. |
January 22, 2015 |
ELECTROWINNING CELL AND PROCESS
Abstract
An electrochemical cell and method for electrowinning a variety
of multivalent metals including titanium is described. In one
aspect, the invention provides an electrochemical cell comprising
an anolyte chamber comprising an anode and configured for
containing an anolyte, a catholyte chamber comprising a cathode and
configured for containing a catholyte comprising a metal to be
electrolytically produced, and a diaphragm separating the anolyte
chamber and the catholyte chamber, the diaphragm configured to
control the potential drop across the diaphragm so that it is below
the potential difference required for inducing bipolarity at the
diaphragm.
Inventors: |
Akolkar; Rohan; (Beachwood,
OH) ; Landau; Uziel; (Shaker Heights, OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Akolkar; Rohan
Landau; Uziel |
Beachwood
Shaker Heights |
OH
OH |
US
US |
|
|
Assignee: |
CASE WESTERN RESERVE
UNIVERSITY
Cleveland
OH
|
Family ID: |
51352770 |
Appl. No.: |
13/947342 |
Filed: |
July 22, 2013 |
Current U.S.
Class: |
205/572 ;
204/252; 205/560; 205/587 |
Current CPC
Class: |
C25C 1/06 20130101; C25C
1/10 20130101; C25C 1/22 20130101; C25C 3/28 20130101; C25C 7/04
20130101 |
Class at
Publication: |
205/572 ;
204/252; 205/560; 205/587 |
International
Class: |
C25C 7/04 20060101
C25C007/04; C25C 1/10 20060101 C25C001/10; C25C 1/06 20060101
C25C001/06; C25C 1/22 20060101 C25C001/22 |
Claims
1. An electrochemical cell comprising: an anolyte chamber
comprising an anode and configured for containing an anolyte; a
catholyte chamber comprising a cathode and configured for
containing a catholyte comprising a metal to be electrolytically
produced; and a diaphragm separating the anolyte chamber and the
catholyte chamber, the diaphragm configured to control the
potential drop across the diaphragm so that it is below the
potential difference for the onset of bipolarity at the
diaphragm.
2. The electrochemical cell of claim 1, wherein the diaphragm has a
thickness lower than a thickness that allows bipolar reactions.
3. The electrochemical cell of claim 2, wherein the diaphragm
comprises a plurality of diaphragms.
4. The electrochemical cell of claim 3, comprising a space between
successive diaphragms of the plurality of diaphragms.
5. The electrochemical cell of claim 3, wherein the space between
successive diaphragms comprises an open space to be filled by
electrolyte or comprises a porous insulating spacer disposed in the
space.
6. The electrochemical cell of claim 3, wherein each diaphragm has
a different thickness.
7. The electrochemical cell of claim 2, wherein the metal to be
electrolytically produced is titanium.
8. The electrochemical cell of claim 2, wherein the diaphragm has a
thickness of about 0.8 cm or less.
9. The electrochemical cell of claim 2, wherein the diaphragm
comprises a plurality of diaphragms, and each diaphragm in the
plurality of diaphragms has a thickness of about 0.8 cm or
less.
10. The electrochemical cell of claim 9, comprising a space
disposed between successive diaphragms.
11. The electrochemical cell of claim 1, wherein the diaphragm has
a porosity that is larger than a porosity that allows for the onset
of bipoloar reactions for a given thickness, electrolyte
conductivity, and current density.
12. The electrochemical cell of claim 11, wherein the diaphragm
comprises a plurality of diaphragms, and each diaphragm has a
porosity that is larger than a porosity that allows for the onset
of bipoloar reactions for a given thickness, electrolyte
conductivity, and current density.
13. The electrochemical cell of claim 12, wherein each diaphragm
has a different porosity.
14. An electrowinning process for deposition of a metal from a
solution comprising: (a) providing an electrochemical cell
comprising: an anolyte chamber comprising an anode and an anolyte
solution dispersed in the anolyte chamber; a catholyte chamber
comprising a cathode and an cathode solution dispersed in the
cathode chamber, the catholyte solution comprising a fluid
containing at least one metal dissolved therein; and a diaphragm
separating the anolyte chamber and the catholyte chamber; and (b)
establishing a predetermined voltage and current across the
electrolytic cell sufficient to effect reduction and deposition of
the at least one metal at the cathode and cause an oxidation
reaction at the anode, wherein the diaphragm is configured to
control the potential drop across the diaphragm so that it is below
the onset potential for bipolarity.
15. The electrowinning process of claim 14, wherein the diaphragm
has a thickness lower than a thickness that allows for the onset of
bipolar reactions.
16. The electrowinning process of claim 14, wherein the diaphragm
comprises a plurality of diaphragms.
17. The electrowinning process of claim 16, comprising a space
separating successive diaphragms in the plurality of
diaphragms.
18. The electrowinning process of claim 16, wherein the diaphragms
each have a thickness lower than a thickness that allows for the
onset of bipolar reactions.
19. The electrowinning process of claim 14, wherein a constant or
time-varying current or potential is applied to the diaphragm.
20. The electrowinning process of claim 14, comprising depositing
titanium, chromium, iron, uranium, a trans-uranium metal, or a
combination of two or more thereof at the cathode.
21. The electrowinning process of claim 14, wherein the catholyte
and anolyte comprise aqueous or non-aqueous solutions.
22. The electrowinning process of claim 14, wherein the diaphragm
has a porosity that is larger than a porosity that allows for the
onset of bipolar reactions for a given thickness, electrolyte
conductivity, and current density.
Description
FIELD
[0001] The present invention relates to electrochemical cells, and
in particular to an electrochemical cell that may be used for
electrowinning processes.
BACKGROUND
[0002] The electrowinning process typically occurs in an
electrochemical cell. In processes where a metal is electrowon from
electrolytes containing metal salts, the metal is deposited at the
cathode while, depending on the electrolyte composition, chlorine
or oxygen may evolve at the anode. The electrowinning process may
be used to extract many different types of metals, including, but
not limited to titanium (Ti).
[0003] A permeable membrane or diaphragm is placed between the
anode and cathode within the electrochemical cell to separate the
electrolyte in the anode compartment (anolyte) from that in the
cathode compartment (catholyte). In electrowinning processes
involving multivalent metals, the diaphragm serves to retard the
migration of metallic ions (cations) with lower oxidation states
from the cathode to the anode. Without the diaphragm, cations with
lower oxidation states will migrate to the anode and get oxidized
at the anode, thereby degrading cell efficiency. In the case of
electrowinning from chloride-containing electrolytes, the diaphragm
also serves the purpose of confining the anodically generated
chlorine to the vicinity of the anode and preventing the chlorine
gas from interfering with processes at the cathode.
[0004] Presently, titanium is extracted from its ore using the
Kroll process where the ore (TiO.sub.2) is first chlorinated to
TiCl.sub.4, and the TiCl.sub.4 is then reduced to titanium using
electrolytically produced magnesium (Mg) as the reducing agent. The
Kroll process is energy intensive (requiring about 100 KWh per kg
of titanium), which is partly due to the need for electrowinning
the reducing agent (such as magnesium) and separating the product
(Ti) from the by-product (MgCl.sub.2). In an alternative route,
titanium can be electrowon directly from a molten salt electrolyte
containing TiCl.sub.4 in NaCl or KCl/LiCl.
[0005] Circumventing the need for electrowinning magnesium and
separating titanium from the byproduct can save about 60 KWh of
energy per kg of Ti. In spite of this advantage, attempts to
commercialize Ti electrowinning (including, for example, attempts
by the U.S. Bureau of Mines in the 1950s, TIMET in the 1970s, and
Dow-Howmet in the 1980s) have failed. Porous ceramic diaphragms,
diaphragms coated with metals, cathodic and anodic biased
diaphragms--all exhibited early failure due to the uncontrollable
deposition of titanium within the diaphragm, which clogged the
diaphragm and halted cell operation.
[0006] At present, titanium cannot be electrowon due to plugging of
the diaphragm used in the cell to separate the anolyte and
catholyte. Titanium deposition within the diaphragm occurs due to
the development of bipolarity at the diaphragm. Bipolarity causes
electrochemical reactions at the diaphragm, including Ti deposition
on the anolyte side of the diaphragm and oxidation of dissolved Ti
ions on the catholyte side of the diaphragm. Bipolarity leads to
cell efficiency loss and early diaphragm and cell failure.
SUMMARY
[0007] The present invention provides an electrochemical cell and
method for electrowinning a variety of multivalent metals including
titanium. In one aspect, the invention provides an electrochemical
cell comprising an anolyte chamber comprising an anode and
configured for containing an anolyte, a catholyte chamber
comprising a cathode and configured for containing a catholyte
comprising a metal to be electrolytically produced, and a diaphragm
separating the anolyte chamber and the catholyte chamber, the
diaphragm configured to control the potential drop across the
diaphragm so that it is below the potential difference for bipolar
reactions at the diaphragm.
[0008] In one embodiment, the diaphragm has a thickness lower than
a thickness that allows the onset of bipolar reactions. In another
embodiment, the diaphragm has a thickness l, such that the
following inequality is satisfied: il/.kappa.<.DELTA.E, where i
is the current density, .kappa. is the effective electrolyte
conductivity of an electrolyte in the cell, and .DELTA.E is the
reduction potential of the bipolar reactions at the diaphragm.
[0009] In one embodiment, the diaphragm may have a thickness of
about 0.8 cm or less. In a different embodiment, the diaphragm may
have a thickness of about 0.3 cm or less.
[0010] In one embodiment, the diaphragm comprises a plurality of
diaphragms. The diaphragms may have the same thicknesses, differing
thicknesses or a combination thereof. There may be a space between
successive diaphragms of the plurality of diaphragms.
[0011] In one embodiment, each of the diaphragms in the plurality
of diaphragms has a thickness lower than a thickness that allows
the onset of bipolar reactions. In another embodiment, each of the
diaphragms have a thickness l and satisfy the following inequality:
il/.kappa.<.DELTA.E, where i is the current density, .kappa. is
the effective electrolyte conductivity of an electrolyte in the
cell, and .DELTA.E is the reduction potential of the bipolar
reaction at the diaphragm. In one embodiment, each diaphragm in the
plurality of diaphragms has a thickness of about 0.8 cm or less. In
one embodiment, the diaphragms each have a thickness l of about 0.3
cm or less. In one embodiment, the electrochemical cell may
comprise 3 or 4 diaphragms each having a thickness of about 0.8 cm.
In one embodiment, the electrochemical cell may comprise 3 or 4
diaphragms each having a thickness of about 0.3 cm.
[0012] In one embodiment, the diaphragm has a porosity that is
larger than a porosity that allows for the onset of bipolar
reactions for the given diaphragm thickness, electrolyte
conductivity, and current density. In one embodiment, each
diaphragm has the same porosity. In another embodiment, each
diaphragm has a different porosity.
[0013] In one embodiment, the metal to be electrolytically produced
is titanium.
[0014] In another aspect, the invention provides an electrowinning
process for deposition of a metal from a solution comprising:
providing an electrochemical cell comprising an anolyte chamber
comprising an anode and an anolyte solution dispersed in the
anolyte chamber, a catholyte chamber comprising a cathode and an
cathode solution dispersed in the cathode chamber, the catholyte
solution comprising a fluid containing at least one metal dissolved
therein, and a diaphragm separating the anolyte chamber and the
catholyte chamber. The process further comprises establishing a
predetermined voltage and current across the electrolytic cell
sufficient to effect reduction and deposition of the at least one
metal at the cathode and cause an oxidation reaction at the anode,
wherein the diaphragm is configured to control the potential drop
across the diaphragm so that it is below the onset potential for
bipolarity.
[0015] In one embodiment, the diaphragm has a thickness lower than
a thickness that allows bipolar reactions. In another embodiment,
the diaphragm l satisfies the following inequality:
il/.kappa.<.DELTA.E, where i is the current density, .kappa. is
the effective electrolyte conductivity of an electrolyte in the
cell, and .DELTA.E is the reduction potential of the bipolar
reaction for the at least one metal.
[0016] In another embodiment, the diaphragm comprises a plurality
of diaphragms. The diaphragms may have the same thicknesses,
differing thicknesses or a combination thereof. In one embodiment,
there is a space separating successive diaphragms in the plurality
of diaphragms. In one embodiment, the diaphragms each have a
thickness l of less than 0.8 cm. In one embodiment, the diaphragms
each have a thickness l of about 0.3 cm or less.
[0017] In one embodiment, the metal being deposited comprises
titanium, chromium, iron, uranium, a trans-uranium metal, or a
combination of two or more thereof.
[0018] In one embodiment, a constant or time-varying current or
potential is applied to the diaphragm. In one embodiment, the
catholyte and anolyte comprise aqueous or non-aqueous solutions. In
another embodiment, the diaphragm is electrically conductive, and
the method comprises applying a current or potential across the
diaphragm to dissolve any metal deposits that form at the
diaphragm. The current or potential applied across the diaphragm is
chosen from a constant or a periodic current or potential. In one
embodiment, the fluid is titanium tetrachloride in NaCl, LiCl--KCl,
LiCl--KCl--NaCl, or LiCl--KCl--CaCl.sub.2.
[0019] These and other aspects and embodiments of the present
invention can be further understood with respect to the drawings
and following description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a schematic illustration of an electrochemical
cell in accordance with an embodiment of the present invention;
and
[0021] FIG. 2 is a schematic illustration of an electrochemical
cell in accordance with another embodiment of the present
invention.
DETAILED DESCRIPTION
[0022] The present invention provides an electrochemical cell
suited for electrowinning of metals such as, for example, titanium.
For the purposes of this application, the apparatus and process may
be discussed with reference to titanium, but it will be appreciated
that the electrochemical cell and process can also be used for the
electrowinning of other metals, including, but not limited to,
chromium, cobalt, niobium, iron, manganese, and others.
[0023] FIG. 1 shows an electrochemical cell 100 suited to
electrowin metal from a fused salt bath, e.g. titanium in a fused
salt bath of compounds of titanium. The electrochemical cell 100
includes a body 102 adapted to hold the electrolytes including a
fused salt bath comprising the metal ion or metal compound to be
electrowon (e.g. titanium from titanium tetrachloride) without
substantial adverse effects to the material of which the body 102
is constructed. Although a number of different materials are
suitable, the body 102 can be, formed of a metal, such as steel,
nickel, hastelloy, or any other suitable material.
[0024] The body 102 is internally divided into at least an anolyte
chamber 104 and a deposition catholyte chamber 106. An anode 108 is
disposed in the anolyte chamber 104 and adapted to be at least
partially immersed in the bath during operation of the
electrochemical cell 100. The material of which the anode 108 is
formed is resistant to the corrosive effects of the bath and also
to the elemental chlorine formed at the positive charged anode 108
during operation of the cell. Suitable anode 108 materials are, for
example, carbon and graphite. However, it is not necessary for the
invention that the anode 108 remains impervious to the electrolyte
or non-reacting during the process. The invention can also be
applied to cells and processes in which the anode 108 reacts and is
consumed during the process, for example a carbon anode 108 that
can react with oxygen to form carbon dioxide. The process can be
used to extract a variety of metals from a solution. In one
embodiment, the metals can be chosen from titanium, chromium, iron,
uranium, a trans-uranium metal, or a combination of two or more
thereof.
[0025] A cathode 110 is suitably disposed within the catholyte
chamber 106 to be at least partially immersed in the bath during
operation of the electrochemical cell 100. The deposition cathode
110 is formed from a material such as carbon or a metal such as,
for example, plain carbon steel, hastelloy, etc. onto which a metal
of interest (e.g., metallic titanium) can be deposited or plated
and subsequently recovered.
[0026] The cathode chamber 106 can also include a means (not shown)
suitable to heat, cool, or otherwise maintain the contents of the
electrochemical cell 100 at a desired temperature, and/or a feed
means adapted to provide a feed material comprising the metal of
interest (e.g., titanium) to the bath during operation of the
electrochemical cell 100.
[0027] The anolyte chamber 104 and the catholyte chamber 106 are
spaced apart from each other by at least one diaphragm 112. A
diaphragm support (not shown) can optionally be combined with the
diaphragm 112 to complement the diaphragm strength during operation
of the electrochemical cell 100.
[0028] The diaphragm 112 may be formed of a metal screen, sheet, or
film with a multiplicity of holes or pores extending through the
thickness of the diaphragm l. The diaphragm 112 substrate can be,
for example, iron such as steel or stainless steel, and a metal,
such as cobalt, nickel or an alloy of two or more. In one
embodiment, the diaphragm 112 substrate comprise, at least about 50
weight percent cobalt or nickel, which is resistant to the
corrosive environment within the body 102 and retains sufficient
strength at predetermined operating temperature to act as a
diaphragm 112. The pores can be formed by, for example, drilling,
punching, weaving, sintering, and the like. The pores in the
diaphragm 112 can be the same or different sizes. In one
embodiment, the pores are of a substantially uniform size. The
diaphragm 112 may have a consistent membrane porosity and
tortuosity, or these factors may vary across the thickness of the
diaphragm 112.
[0029] The diaphragm 112 can comprise a ceramic non-conductive
material on which sufficient metal has been deposited by
electrolytic or electroless procedures. Examples of suitable metals
for coating the ceramic diaphragm 112 include, but are not limited
to, cobalt, nickel, etc.
[0030] In accordance with the present technology, the diaphragm 112
is configured to control the potential drop across the diaphragm
112 so that is below the onset potential for bipolarity. That is,
the diaphragm 112 is configured to prevent oxidation and reduction
reactions, involving the metal of interest, from occurring at the
diaphragm 112. The inventors have found that bipolarity can be
prevented by controlling the potential drop across the diaphragm
112 to a lower value than that of the standard potential for the
bipolar reaction which can take place at the diaphragm 112. It has
been found that the potential drop across the diaphragm can be
limited below the onset potential by keeping the diaphragm
sufficiently thin, keeping the diaphragm sufficiently porous,
keeping the current density across the diaphragm sufficiently low,
or a combination of two or more thereof. In one embodiment, the
electrochemical cell comprises one or more diaphragms, each having
a thickness and porosity such that the ohmic potential drop
(.DELTA..PHI.) across the diaphragm is less than the difference in
the reduction potentials (.DELTA.E) for the bipolar reactions at
the diaphragm. As used herein, the term "bipolar reaction" refers
to the reduction/oxidation reaction at the diaphragm surface and
within its pores that would result in the formation and deposition
of solid species, e.g., metal at or within the diaphragm.
[0031] In one aspect, the diaphragm 112 has a thickness such that
the following inequality is satisfied:
il/.kappa.<.DELTA.E
where i is the current density, l is the thickness of the diaphragm
112, .kappa. is the effective electrolyte conductivity within the
diaphragm 112, and .DELTA.E is the difference between the oxidation
potential and the reduction potential the bipolar reactions at the
diaphragm 112. The value il/.kappa. is equal to the ohmic potential
drop (.DELTA..PHI. across the diaphragm 112. It should be
recognized that .kappa. is the effective electrolyte conductivity
within the diaphragm 112, and as such it is affected not only by
the make-up of the electrolyte, but also by the porosity of the
diaphragm 112 and the tortuosity of the pores. Higher porosity is
achieved by providing more open space within the diaphragm 112, and
lower tortuosity corresponds to having more straight and less
convoluted pores; higher porosity and lower tortuosity correspond
to a higher .kappa. or lower diaphragm resistance, and hence to
lower potential drop across the diaphragm 112. One method of
measuring the diaphragm effective conductivity, .kappa., taking
into account the effects of the porosity and tortuosity, is to (1)
apply a certain measured current, I, across a diaphragm having an
area, A, that is immersed into or soaked with an electrolyte, and
(2) measure the voltage drop, V, across this diaphragm using a
voltmeter. The diaphragm effective conductivity is
.kappa.=I*l/(.DELTA.*V), where l is the thickness of the diaphragm.
This technique eliminates the need to determine independently the
values of diaphragm porosity and tortuosity which can be difficult
to directly measure. This experimentally determined effective
conductivity .kappa. incorporates already the effects of the
porosity and tortuosity.
[0032] It should be further noted that the value of the ohmic drop
across the diaphragm 112 can be controlled to be smaller than
.DELTA.E as indicated by the inequality above, by having a thin
diaphragm 112, i.e., making the thickness, l, small, or having
highly conductive electrolyte with highly porous diaphragm with
minimal tortuosity leading to high effective conductivity .kappa.,
or by maintaining the average current density, i, at the diaphragm
at a small value such that the inequality above is maintained.
[0033] Using titanium as an example, the bipolar reactions at the
diaphragm 112 may be: [0034] Ti.sup.+2+2e.fwdarw.Ti (anolyte side
of the diaphragm); and [0035] 2Ti.sup.+2.fwdarw.2Ti.sup.+3+2e
(catholyte side of the diaphragm).
[0036] More generally, the bipolar reactions at the diaphragm may
be: [0037] M.sup.+n+ne.fwdarw.M (anolyte side of the diaphragm);
and [0038] X.sup.+z.fwdarw.X.sup.+(n+z)+ne (catholyte side of the
diaphragm). In the latter equation, species X can be the metal M or
any other oxidizable species. z is the initial oxidation number of
species X
[0039] When bipolarity develops at the diaphragm 112, the diaphragm
112 can become plugged by deposits of the metal of interest,
leading to efficiency loss and early failure. In accordance with
the present technology, by keeping the voltage drop across the
diaphragm 112 low, by, e.g. keeping the thickness of the diaphragm
l at an appropriate low value, deposition of the metal at or within
the diaphragm 112 can be prevented.
[0040] While one diaphragm 112 may be suitable for use, the
diaphragm can be provided as a plurality of diaphragms 112 in a
single electrochemical cell. In one embodiment, the diaphragm 112
comprises a plurality of diaphragms 112. The diaphragms 122 are
disposed adjacent to one another. In arranging and configuring the
diaphragms 112, the diaphragms 112 must be oriented such there is a
space or gap disposed between successive diaphragms 112 such that
the individual diaphragms 112 in the stack do not touch one
another. However, such gap may be filled or partially filled by an
insulating porous non-conductive spacer. FIG. 2 illustrates an
embodiment of an electrochemical cell 100' comprising a plurality
of diaphragms. The cell 100' is similar to the cell 100 of FIG. 1
except that cell 100' comprises a plurality of diaphragms 112a,
112b, and 112c. The diaphragms 112 are arranged such that there is
a space (e.g., 114, 116) disposed between excessive diaphragms 112.
The space (e.g., 114, 116) is maintained to avoid the individual
diaphragms 112a, 112b and 112c from touching each other, which can
compromise their electrical isolation from one another. The space
(e.g., 114, 116) may comprise of an open space to be filled by an
electrolyte, by a perforated insulating spacer, or a porous
insulator.
[0041] In a cell comprising multiple thin diaphragms 112, the
diaphragms are generally provided such that each diaphragm has a
thickness whereby il/.kappa.<.DELTA.E. In embodiments comprising
a plurality of diaphragms, the thickness of each diaphragm 112 can
be the same, or the diaphragms can have different thicknesses,
providing however, that the inequality above is maintained for each
individual diaphragm in the stack. The number of diaphragms 112,
the thickness of each diaphragm l, and the space (e.g., 114, 116)
between successive diaphragms can be individually chosen to provide
a desired separation effect between the catholyte and the anolyte.
The number of diaphragms is chosen to provide sufficient diffusion
resistance to the migrating titanium ions so that they do not reach
the anode 108 in excessive amounts.
[0042] The thickness of the diaphragms l may also depend on the
metal of interest to be deposited from the solution. In one
embodiment, the diaphragm 112 has a thickness of about 0.8 cm or
less; about 0.6 cm; or less; about 0.4 cm or less; about 0.3 cm or
less; even about 0.1 cm. In one embodiment, the diaphragm 112 has a
thickness of from about 0.1 cm to about 0.8 cm; from about 0.2 cm
to about 0.6 cm; even about 0.3 cm to about 0.4 cm. In still
another embodiment, the diaphragm 112 has a thickness of from about
0.1 cm to about 0.3 cm. Here as elsewhere in the specification and
claims, numerical values can be combined to form new and
non-disclosed ranges. As previously described, when a plurality of
diaphragms 112 are employed, the thickness of the diaphragms 112
can be the same or different, and the space or distance between
successive diaphragms 112 can be the same or different.
[0043] Further, an electrolyte flow may be maintained through the
diaphragm 112 or the stack thereof, such that the flow further
reduces the undesirable transport of species across the diaphragm
112 or diaphragm stack. The electrolyte on the two sides of the
diaphragm or plurality of diaphragms can be maintained at the same
or different levels.
[0044] Further, the diaphragms 112 can be electrically conductive
and connected to a power source (not shown). The power source can
be adjustable to provide a constant or periodic current or
potential waveform to dissolve or remove any undesired bipolar
reaction from accumulating on or within the diaphragms 112.
[0045] The source of the metal to be electrolytically produced and
deposited at the cathode 110 can be chosen as desired. For example,
titanium can be electrowon from materials such as titanium
tetrachloride, titanium tetrabromide, titanium trifluoride,
titanium carbide, titanium dioxide etc.
[0046] The salt may be chosen as desired for the metal of interest
to be extracted. Such salts or mixtures thereof can be, for
example, NaCl, LiCl--KCl, LiCl--KCl--NaCl, and
LiCl--KCl--CaCl.sub.2. When titanium is recovered from titanium
tetrachloride, the fused salt bath desirably contains a mixture of
alkali or alkaline earth metal halides, preferably lithium and
potassium chlorides. A eutectic mixture of the salts employed in
the bath is advantageous because of the low melting temperature of
such mixture. Alternatively, when electrowinning at room
temperature is desired, metal salts dissolved in aqueous medium may
be employed as the electrolyte.
[0047] The electrowinning process is performed by applying a
current across the electrodes to effectuate deposition of the metal
of interest (e.g., titanium) at the cathode 110. In one embodiment,
the method comprises (a) providing an electrochemical cell 100
comprising an anolyte chamber 104 comprising an anode 108; a
catholyte chamber 106 comprising a cathode 110; and a diaphragm
stack separating the anolyte chamber 104 and the catholyte chamber
106; (b) the catholyte solution comprising an fluid containing at
least one metal dissolved therein; and (d) establishing a
predetermined voltage or current across the electrolytic cell
sufficient to effect reduction and deposition of the at least one
metal at the cathode 110 and cause an oxidation reaction at the
anode 108, wherein the diaphragm 112 is configured to prevent
bipolar reactions at the diaphragm 112.
[0048] This written description uses examples to disclose the
invention, including the best mode, and also to enable any person
skilled in the art to practice the invention, including making and
using any devices or systems and performing any incorporated
methods. The patentable scope of the invention is defined by the
claims, and may include other examples that occur to those skilled
in the art. Such other examples are intended to be within the scope
of the claims if they have structural elements that do not differ
from the literal language of the claims, or if they include
equivalent structural elements with insubstantial differences from
the literal languages of the claims.
* * * * *