Note: Descriptions are shown in the official language in which they were submitted.
3499 FF
ELECTRODE WITH LEAD 8ASE AND M~HOD OF MAKlNG SAME
Technical Field
The present invention relates to dimensionally stable electrodes, and
more particularly to anodes for oxygen evolution :n an acid electrolyte, such
as are used e.g. in processes for electrowinning metals from acid
electrolytes.
.
Backqround Art
Lead or lead alloy anodes have been widely used in processes for
electrowinning metals from sulphate solutions. They nevertheless have
important limitations, such as a high oxygen overvoltage and loss of the
anode material leading to contamination of the electrolyte, as well as the
metal product obtained on the cathode.
Anodes of lead-silver alloy provide a certain decrease of the oxygen
overvoltage and improvement of the current efficiency, but they still have
the said limitations as a whole,
It has been proposed to use dimensionally stable titanium anodes with
a platinum metal oxide coating for anodic evolution of oxygen, but such
anodes are generally subject to more or less rapid passivation and oxidation
of the titanium base.
It hss also been proposed to provide the titanium base with a
protective undercoating compri~ing a platinurn 91 oup metal berleath the
',
36~3L
outer coating, but such coatings do generally not provide sufficient
prDteCtion of the titsniun base to justify the high.cost of using precious
metals.
s Metal electrowinning cells generally require a large anode surface
and operate at a low current density in order to ansure an even
electrodeposition of metal on the cathode, ~o that the cost of u~ing a
titanium base becomes rela~ively important and rnust also be taken into
accour)t.
Dimensionally stable anodes with mixed oxide coating~ comprising
platinum group metals and valve metals are described in U.S. Pat. 3 632 498.
An exampls of this patent relates to the preparation of a fine Ti-Pd mixed
~` oxide powder which is then applied by rolling or hammering into a rod of
soft-quality titanium. However, the amount of precious metal incorporated
in the mixed oxide powder and applied to the electrode in this manner could
be prohibitive for various industrial applications. Thus, when the electrode
surface is to be substantially covered with the mixed oxide powder, and
more particularly when the electrode is intended for operation at a
relatively low current density such as is used in metal electrowinning, the
cost of precious metal thus applied in the form of a mixed oxide may be
especially prohibitive.
.
.
1: isclosure of the Invention
.
An object of the invention is to provide an improved anode for
evolving oxygen in an acid electrolyte.
Another object of the invention i8 to provide an anode with a base of
lead or lead alloy with improved electrochemical p0rformance for anodically
evolving oxygen in an scid electrolyte, 80 as to substantlally a~,Did
10s8 of the snode material and the~r sai~ 1~oitati~ns of can~tianal
lead or leat alloy anodea
A further object of the invention i~ to provids a sirnple method of
making ~uch an electrode wlth Improved perforrnance.
.
, ,
~Z~B~
These objects are essentially met by the invention as set forth in the
claims.
The electrochemical performance of the anode is improved in
accordance with the invention by providing the aoode with titanium parti-
cles which are catalytically activated by means of ruthenium in oxide form
and are partly embedded at the surface uf the anode base of lead or lead
alloy, so that they are firmly anchored and electrically connected to the
base. The remaining, non-embedded part of said catalytic particles thus
projects from said surface of the anode ba~e, and thereby can præsent a
surface for oxyqen evolutiDn which can be considerably larger than the
underlying surface of the anode base of lead or lead alloy.
Said partly embedded catalytic particles are preferably arran~ed
accordin~ to the invention, so that they substantially cover the entire
surface of the lead or lead alloy base, present a maximu~ surface for
oxygen evolution, and thereby more especially provide a substantially
uniform distribution of the anode current density.
The use of ruthenium to catalytically activate titanium particles in
accordance with the inventiDn is parSicularly advantageous since ruthenium
can provide an excellent electro-catalyst for Dxygen evolution at a
relatively low cost with respect to othsr metals of the platinum group.
The catalytic particles applied according to the invention
advantageously consist of titanium sponge and may have a size Iying in the
range between 150 and 1250 micron~, and preferably in the range of about
300-lD00 micron~.
The amount or loading of said catalytic particles applied according to
the invention per unit area of the anode base should generally be adequate
to ~ubstantially cover the anode base.
It has now been found th~t relatively high particle loadings corres-
ponding to more than 400 g/m2 are generally necessary for the manufacture
of electrodes with sati~factory performance. Higher loadings up to
1000 g/m2 or mors have likewlse besn found to be advsntEIgeoua
Th~ catalytic partlcles advantageously comprl~e a~ ~ve1y smal1 ~unt
o~ ruthenium, corresponding to at most 6 % by weight of the tltanium of
said particles, evenly distrlbuted on a very large surfacæ.
The high loading~ of catalytic particle~ indicated above B~9.
~36111~
500-1000 g/m may nevertheless necessitate quite high ruthenium
costs. Consequently, it is particularly important to reduce the
loss of ruthenium during anodic operation as far as possible.
I~ has now been established experimentally that activating
the titanium particles with manyanese as well as ruthenium in
oxide form increases the stability of the catalyst with respect
to ruthenium dioxide alone or in other combinations.
This improved electrocatalytic performance and stability of
the Ru-Mn oxide system under the conditions of oxygen evolution
in acid media constitutes a particularly advantageous feature of
the catalytically activated titanium particles used on a lead
base according to the present in~ention.
It has also been found that the formation of titanium oxide
by thermal decomposition on the activate~ particles provides a
further impro~ement of the stability of the particles.
It has moreover been established that a more efficient use
of the ~uthenium is achieved when larger activated particles are
first pressed into the lead anode base and this is ~ollowed ~y
pressing smaller particles, which may advantageously haYe a
higher proportion of ruthenium than the large~ particles. This
2-step pressing procedure has been found to improve the contact
with ~he lead base as well as the long-term stability of the
catalytically acti~ated particles.
It has moreover been found that an additional pressing step
to apply non-activated particles of a ~alve metal or a valve metal
oxide, more particularly zirconium dioxide, can further increase
the stability of the activated particles. This is especially
important in processes for electrowinning metals from electrolytes
containing Mn2+ ions, where the deposition of poorly conducting
MnO2 can be detrimental for anode performance.
Thus, and in accordance with the present teachings, a
catalytic anode is provided or evolving oxygen in an acid
electrolyte comprising an anode base of lead or lead alloy and
titanium particles catalytically activated with a minor amount
of ruthenium in oxide form, the particles being uniformly dis-
tributed, partly embedded and firmly anchored in the surface o~
r
86~
--4a-
the base so that oxygen can be anodically evolved on the particles
at a reduced potential at which the underlying lead or lead alloy
at the surface of the anode base remains electrochemically inactive,
the activated titanium particles comprising a minor amount of
ruthenium and manganese in oxide form obtained by thermal decomposi-
tion of corresponding compounds, and the cafalytically actiYated
particles comprise more than 400 grams of titanium per square meter
of anode base surface, the particles having a size greater than
300 microns.
In accordance with a further aspect of the present teachings,
a method is provided of making an oxygen evolved anode by the
steps of:
a) catalytically acti~ating titani~m sponge particles having
a size greater than 300 microns by impregnating the particles with
an activating solution containing thermally decomposable ruthenium
and manganese compounds and thermally converting the compounds in
an oxidizing atmosphere into ruthenium and manganese oxide;
b) uniformly distributing the activated particles obtained
by step a) over the surface of the anode base of lead or lead alloy,
pressing, partly embedding and tnereby anchoring the activated
particles in the surface of the anode base so that the amount of
titanium in the catalytically activated, partly embedded particles
correspond to more than 400 grams per square ~eter of the anode
base surface.
The following examples serve to illustrate different modes of
carrying out the present invention.
Example 1
An activating solution was prepared by dissolving 0.57 g
RuC13.aq and 1 33 g Mn(N03~2 aq in 4 ml l-butylalcohol The
solution was then
~¢,
,~
diluted with six times its weight of l-butylalcohol.
3.25 9 of Ti sponge (p~rticle size greater than 630 microns) was
degreased with trichlorethylene, dried and impregnated with the activating
solution. A~ter each impregnation, the titanium sponge was dried at 100C
fDr about 1 h. A heat treatment was then effected at 200C for 10 minutes
and finally at 400C under an external air flow for about 10 minutes. This
activation procedure was carried out 5 times. The Ru and Mn loadings thus
obtained amounted to 28.4 mg Ru/g Ti and 36.0 mg Mn/g Ti.
The same activating solution was used also on 4.9 9 Ti sponge
(particle size 315-630 micronsj. The temperatures for drying and heating as
well as the number of impregnations were identical to those applied to the
larger particles. However, the duration of the heat treatment at 400~C was
12 minutes. The Ru and Mn loadings in this case amounted to ~7 mg Ru/g Ti
sponge and 34 mg Mn/g Ti sponge.
The activated titanium sponge particles were then pressed onto a
lead sheet coupon. The larger particles size ( greater than 630 microns )
were pressed first at 290 kg/cm2 to give Ti, Mn and Ru loadings per unit
lead-sheet area of 322, 11.5 and 9.1 g/m2 respectively. Subsequentlyt
smaller activated titanium particles (315-630 microns) were then pressed at
36û kg/cm2 tG give Ti, Mn and Ru loadings of 40û, 13.7 and 1~.8 g/m2
respectively.
An electrode sample (L 62) was thus obtained with a lead base
uniformly covered with F~u Mn oxide activated titanium sponge particles in
an amount corresponding to 722 g/m2 Ti sponge, 19.9 g/m2 Ru and
25.2 g/m2 Mn.
This electrode sample was tested as an oxygen evolving anode in
H2SO4 (150 gpl). The electrode potential (oxygen half-cell potential) at a
current density of 500 A/m2 amounted to 1.57 V V5. NHE after 68 days, 1.59
V after 194 days, and 1 75 V after 210 days of anodic operation.
For comparison, another anode sample (L 61), which was obtained by
directly pressing smaller particles of activated Ti sponge on lead, wlth
higher Ru and Mn loadings corre~panding to 27.9 and 35.4 g/rn2 respectlvely,
exhibited anode potential of 1.62 V after 69 day~ of operation under
identical conditions, and a potential of 1.63 V when anode operation was
-- 6 --
stopped after 194 days,
A further anode sample (L 76) was prepared like L 62 but the larger
particles were only activated 4 times instead of 5. The overall Ru and Mn
loadings amounted in this case to 22.1 and 28.0 g/m2 respectively, The
anode was tested under identical conditions and showed a potential of 1.5 vs
NHE after 22 days and 1.8 V after 140 days of operation.
Example 2
An anode sample (L 64) was prepared like L 62 of Example 1 but with
higher Ru and Mn loadings of 2~.1 and 29.~ g/m2 respectively. The anode
was tested in a Zn electrowinning solution eontaining Mn2~ as a major
impurity.
Its potential after 60 h and 120 h of operation as an oxygen evolving
anode in this medium, amounted respectively to 1.6a V and 1,73 V vs. NHE.
The current density was 400 A/m2. No deposit of,Mn-oxide occured during
this period.
For comparison, lead samples comprising either only large activated
particles (size greater than 630 microns ) or only smaller ones (size 315 -
630 microns), with overall Rù and Mn loadings corresponding to 19-20 and
24-25 g/m2 respectively, showed a higher anode potential of about 1.72 -
1,75 V vs. NHE after 60 h of operation. A thick anodic deposit of Mn oxide
was observed in both cases.
Example 3
Ti sponge (particle size 315- 630 microns ) was activated like in
Example 1. It was then pressed onto lead at 270 kg/cm2 to give a loading of
Ti, Mn and Ru corresponding to 427, 15.1 and 11.9 g/m2 respectively. Finally
particulate ZrO2 tparticle size 150-500 microns ) was pressed with a
pressure of about 410 kg/cm2 on top of the Ti sponge to give a ZrO2 loading
corresponding to 248 g/m2.
The electrode sample thus obtainsd (L 82) was test~d as an oxygen
evolving anode in H2SO4 (159 gpl). The electrode potential at a current
density of 500 A/m2, amounted to 1.50 V V3 NHE after 150 h of anodic
operation. It amounted to 1.59 V after 293 days, and is still opE~rating. This
~2~
corresponds to a voltage saving of 410 mV with respect to pure, untreated
lead.
Exam~le 4
Ti sponge (particle size 315 - 630 microns ) was activated first with a
Ru and Mn containing solution as described in Example 1.
The activation method was also identical to the one described in Example 1.
Following this activation, a top-coating was applied by impregnation
with a solution containing Ti-butoxide whlch was prepared by dissolving
1.78 9 Ti-butoxide in 3.75 ml l-butylalcohol and 0.25 ml HCl.
The impregnated sponge was dried at 100C for about 1 h. A heat
treatment was then effected at 250C for 12 minutes and finally at 400C
under an external air flow for about 12 minutes.
The resulting activated titanium particles were then pressed on lead
at about 250 kg/cm2. The electrode sample (L B4) was thus obained with a
lead base uniformly covered with Ru^Mn oxide activated titanium sponge
particles "topcoated" with Ti-oxide in amounts corresponding to 13.3 9
Ru/m2, 16.9 9 Mn/m2, 5.8 9 Ti/m2 and 515 9 Ti sponge/m2.
This electrode sample was tested as an oxygen evolving anode in
H2SO4 (150 gpl). Its potential at a current density of 500 A/m2 amGunted to
1.49 V vs NHE after 130 h of anodic operation. This corresponds to a 510 mV
saving over untreated lead. The anode potential amounted to 1.64 V after
128 days, which corresponds to a 360 mV saving over untreated lead.
Example 5
Ti sponge (particle size 315-630 microns) was activated first with a
Ru-containing solution prepared by dissolving 134 9 of RUcl3H2o per liter
of butylalcohol. The Ti sponge was impregnated with the Ru containing
solution, heated at 120C during 20 minutes in order to evaporate the
solvent, heat treated at 250C for 15 min. and finally at 450C for another
15 min. This impregnation, drying and baking was repeated four times. The
ruthenium loading thus obtained amounted to 30 mg/g of Ti sponge.
Following this activation, a top-coating of TiO2 was applied on the
~z~
activated particles by impregnation with a solution obtained by mixing 1.8 9
of titanium butoxide with 3.75 ml of b~ltylalcohol. The drying~ heating and
baking steps were the same as mentioned above for the Ru containing
activating solution. These steps were repeated twice to give a loading of
titanium, applied as TiO2, amounting to 5 mg/g Ti sponge.
The activated titanium particles were then pressed on lead at 250
kg/cm2 onto a lead sheet coupon, with a particle loading of 500 g/m2
corresponding to 15 9/rn2 Ru and 2.5 g/m2 of Ti applied to the particles
uniformally distributed on the lead surface.
This electrode sample was tested as an oxygen evolving anode in
H2S04 (150 gpl) The electrode potential at a current density of 500 A/m2
amounted to 1.66 V vs NHE after 200û hours of anodic operation.
Example 6
TiO2 rutiie particles having a size ranging from 315 to 630 microns
are activated by impregnation with the following solution :0.54 9
RuC13.H20; 1.8 9 butyltitanate; 0.25 ml HCl; and 3.75 ml butylalcohol.
After impregnation, the particles are dried at lOO~C in air and baked
at 440C for lD minutes under air flow. This procedure is repeated 4 times.
The resulting particles are activated with Ruo2-Tio2.
The particles are then pressed onto a lead sheet coupon by applying a
pressure of 250 kg¦cm2. The particle loading amounted to 400 g/m2
corresponding to a Ru and Ti loading of 15 and 16 g/m2 respectively(applied
as RUo2-Tio2).
The obtained activated lead electrode was tested as an anode in an
aqueous solution containing 150 gpl H2S04 at room temperature. The
applied anode current density applied amounted to 500 A/m2. An oxygen
half cell potential of 1.75 V Y8 NHE was obtained after 300 hours of
operation. After 1000 hours, the anode potential reached the same value as
that of an anode of pure, untreated lead.
Example 7
An activating solution was prepared as described in Exarnple 1, but
instead of dlluting it 8iX time~ (exarnple 1), it wa~ dllut~d with only three
- 9-
times its amoun~ of n-butylalcohol.
4.11 9 of Ti sponge (particle size 400-630 microns), was impregnated
with the activating solution After each impregnation, the titanium sponge
was dried at 100C for about 1 hour. A heat treatmlent was then effected at
250C for about 10 minutes and finally at 400C under an external air flow
for about 10 minutes. This activation procedure was carried out 3 times. The
Ru and Mn loadings thus obtained amounted ~o 36.2 mg Ru/g Ti and 45.8 mg
Mn/g Ti.
The activation procedure, described in Example 1 for the Ti sponge
with a particle size larger thant 630 microns, was applied also in this case
for the larger particles (greater than 630 microns). However, the activation
was carried out only 4 times. The Ru and Mn loadings thus obtained
amounted to 2~.5 mg Ru/g Ti and 29.9 mg Mn/g Ti.
The activated titanium sponge particles were then pressed and partly
embedded at the surface of a lead sheet coupon. The larger particles ( size
greater than 63D microns) were pressed first at 240 kg/cm2 to give Ti, Mn
and Ru loadings per unit lead sheet areea of 350, 10.5 and 8.3 g/m2
respectively. An electrode sample (L95) was thus obtained with a lead base
uniforrnly covered with F'cu-Mn oxide activated titanium sponge particles in
an amount corresponding to 760 g/m2 Ti sponge, 23.Z g/m2 Ru and 29.3
g/m2Mn. This electrode s~mple was tested as an oxygen evolving anode in
H25O4 (150 gpl). The electrode potential, at a current density of 500 A/m2,
amounted to 1.65 V vs NHE after 2B7 days of anodic operation.
For comparison, another anode sample (L93), which was obtained by
directly pressing smaller particles of activated Ti sponge at 2B0 kg/cm2 on
lead, with Ru and Mn loadings corresponding to 15.4 and 19.5 g/m2
respectively, was tested under identical conditions. The electrode potential,
after 289 days, was 1.78 V vs NHE.
A further anode sample (L92) was prepared like L95 but the smaller
particles (400-630 microns) were activated like in Example 1 (L62). The
overall Ti, Mn and Ru loadings amounted in this case to 726, 22.5 and 17.7
glm2 respectively. Pressing of the larger particles and smaller particles was
carried out at 290 kg/cm2 and 41D kg/cm2 respectively. The anode has bePn
- 10 -
tested under identical conditions and showed a potential of 1.78 V vs NHE
after 289 days of operation.
Example 8
An activating solution was prepared as dsscribed in Example 7 4.22 9
of larger particles (particle size above 630 microns) was activated twice
under the conditions specified in Exarnple 7 to give 21.5 mg Ru/g Ti and 27.4
mg Mn/g Ti.
Another activating solution was appiied to Ti sponge with a smaller
particle size ranging from 400-630 microns. This activation solution
corresponds to the one described in Example 7 with the difference that it
was diluted with only twice its amount of l-butylalcohol. Two activations
were carried out in accordance with Example 7. The Ru and Mn loadings per
gram Ti amounted to 25.9 and 32.9 mg respectively.
An anode sample (L 12û) was prepared by pressing the larger particles
first at 210 kg/cm2 to give Ti, Mn and Ru loadings of 360~ 9.8 and 7.7 g/m~
respectively. Smaller activated titanium particles (400-63û microns) were
then pressed at 320 kg/cm2 to give Ti, Mn and Ru loadings of 420, 13.9 and
lD.9 g/m2 respectively. The overall Ti, Mn and-Ru loadings thus obtained
amounted to 780, 2}.7 and 18.6 g/m2 respectively.
The electrode sample was tested as an oxygen evolving anode in
H2SO4 (150 gpl). The electrodes potential, at a current density of 500 A/rn2,
amounted to 1.58 V vs NHE after 218 days of anodic operation.
Example 9
Titanium sponge (40~630 microns) was oxidized as ~ollows, prior to
activation with Ru-Mn oxide.
4,7b, 9 of titanium sponge was activated once with the activation
~olution described in Exampl~ 1. The heat treatment was carried out at
400~C for 1~ minutes under an external air flow, after subjecting the Ti
sponge to drying at 100C. The Ru and Mn loadln~s were 5.2 and 6.6 mg/g Ti
Qponge respectively. The sponge wa~ then subjected to heat treatment For 4S
h at 480C undsr an e%ternal air flow to convert it into its respectjve oxide.
3.5 9 of the oxidized Ti sponge thus obtained was then activated as
described in Example 1 wlth the only difference that an intermediate heat
treatment was carried out at 250C instead of 200"C after each activation.
The Mn and Ru loadings per g sponge amounted to 32 8 and 25.~ mg
respectively.
The preoxidized and activated Ti sponge was then pressed in two
steps, first at 230 kg/cm2 and then at 29û kg/cm2 to give Mn and Ru
loadings of 21.1 and 16.6 g/rn2 respectively. The loading of the oxidized Ti
sponge amounted to 643 g/m2. Considering the Mn and Ru loadings in the Ti-
oxide, prior to final activation, the overall Mn and Ru loadings amount to
25.3 and 19.9 g/m2 respectively.
The electrode has been tested in 150 gpl H2504 at 500 A/m2 and its
potential after 275 days of operation amounted to 1.65 V vs NHE.
Example 10
Two activating solutions were prepared with a larger Mn/Ru ratio
than described in Example 1.
Solution A: û.537 9 RuC13.aq and 2.0819 9 Mn ~N03)2.aq in 3.75 ml n-
butylalcohol
Solution B: C.537 9 RuC13.aq and 4.6844 g Ivm(N03)2. aq in 3.75 ml n-
butylalcohol
Both solutions A and B were diluted with 3 times their amount of n-
butylalcohol prior to application. Solution A corresponds to a moiar ratio of
MnO2/RuO2 = 4 and solution B corresponds to a molar ratio of MnO2/RuO2 =
9.
4.27 9 of Ti sponge (particle size 315-63~ microns) was impregnated
with diluted activation solution A. After each impregnation, the titanium
sponge was dried at 100C for about 1 h~ A heat treatment was then
effected at 250C for 14 minutes and finally at 400C under an external air
flow for about 14 minutes. Thia activation procedure was carried out
3 times. The Ru and Mn loadings thus obtained amounted to 29.3 mg Ru/g Ti
and 63.8 mg Mn/g Ti.
4.16 9 of Ti sponge (particle size 315-630 microns) was irnpregnated
with diluted activation solution B. The activatlon was carried out in the
- 12 -
same manner as with activating solution A. The Ru and ~In loadings thus
obtained amounted to 19.9 mg Ru/g Ti and 97.4 rng Mn/g Ti.
The activated Ti sponge particles were then pressed onto a lead sheet
coupon. The larger particles (greater than 630 microns), activated as in
Example 8, were pressed first at 230 kg/cm2 to give Ti, Mn and Ru loadings
per unit lead-sheet area of 449, 12.0 and '3.4 g/m2 respectively.
Subsequently smaller activated (with diluted solution A) Ti particles (315-
630 microns) were pressed at 350 kg/cm2 to give Ti, Mn and Ru loadings of
399, 25.5 and 11.7 g/m2 respectively.
An electrode sample (L 164) was thus obtained with a lead base
uniformly covered with Ru-Mn oxide activated titanium sponge particles in
an amount corresponding to 848 g/rn2 Ti sponge, 20.8 g/m2 Ru and 37.5
glm2 Mn.
This electrode sample was tested as an oxygen evolYing anode in 15û
gpl H2S04. Its po~ential,at a current density of 500 A/m2, amounted to 1.50
V vs NHE after 36 days of anodic operation.
For comparison~ another anode sample (L 161), was obtained by
directly pressing smaller particles of activated Ti sponge (with diluted
solution A) at 32û kg/cm2 on lead, with Ti, Ru and Mn loadings
corresponding to 531, 15.6 and 34.0 g/m2 respectively.
This 01ectrode L 161 has been tested under identical conditions and
showed a potential of 1.60 V vs NHE after 70 days of operation.
In another set of experiments, Ti sponge particles larger than 630
microns, activated as in Example 8, were pressed first at 230 kg/cm2 to give
Ti, Mn and Ru loadings per unit lead-sheet area of 428, 11.5 and 9.0 g/m2
respectively. Smaller activated titanium sponge particles (size 315-630
microns), obtained with activating solution B, were then prassed at 350
kg/cm2 to give Ti, Mn and Ru loadings of 493, 48.0 and 9.8 g/m2
respectively. An electrode sample (L 163) was thus obtained with a lead base
uniformly covered with Ru-Mn oxide activated titanium sponge particles in
an amount corresponding to 921 g/m2 Ti, 59.5 g/m2 Mn and 18.8 g/m2 Ru.
This electrode has been tested as an oxygen evolving anode in 150 gpl
H2S04 at 500 A/m2. Its potential after 33 days of operation amounted to
1.57 V vs NHE.
o~
- 13 -
Example 11
For comparison (with L 163 in Example 10), another anode sample (L
162) was obtained by directly pressing smaller particles (315-630 microns~ of
activated Ti sponge (with diluted solution B~ at 290 kg/cm2 on lead with Ti,
Ru and Mn loadings corresponding to 652,13~0 and 63.6 g/m2 respectively.
The electrode has been tested at 5ûû A/m2 in 150 gpl H25D4 and
shows a potential of 1.74 V vs NHE after 18 days (430 h~ of operation under
these conditions.
Exam~le 12
An activating solution was prepared by dissolving 0.54 9 RuCl3- aq
(38 % Ru) and 0.12 9 PdC12 in 15 ml of butyl-alcohol. Th~ solution was
stirred until all the salts were dissolved and 1.84 9 of buty~titanate was
added.
~ .5 9 of titanium sponge having a particle SiZ8 ranging From 315 to
63~ microns was impregnated with this activated solution, dried at 140~C
for 20 minutes, fired at 250C for 15 minutes and finally fired for another
period of 15 mirutes at 45ûC. All these heating steps were carried out in
air. After cooiing, the impregnating, drying and flring operations were
repeated six times. The Ru and Pd loadings thus obtained on the particles
amounted to ~0 mg Ru/g Ti and 11 mg Pdtg Ti. The activated titanium
sponge particles were pressed onto a lead sheet coupon with a pressure of
250 kg/cm2 in order to get the respective loadings: 5ûû g/m2 Ti sponge, 15
glm2 Ru, 5.5 g/m2 Pd.
This electrode sample was tested as an oxygen evolving anode in
H2504 (151~ gpl) at 500 A/m2. The electrode potential (oxygen half-cell
potential) amounted to 1.78 V vs NHE after 2û8 days of anodic operation.
Example 13
7 g of titanium ~ponge (particle 3ize 315-630 m;crans) wa3
impregnated with 1.4 ml of a solution containing 7 mg/ml of Ir in the form
of IrCI~ aq, di~solved in isopropyl-alcohol. After impregnation, the titanium
sponge was dried at 140C for 15 rnin., fired at 250C during 10 min. and
fired again at 450C for 10 rnin., all of the~e ~tep~ being carried out in air.
- 14-
The activated titanium sponge particles were pressed onto a l~ad
sheet ooupon by applying a pressure of 25D kg/cm2~ The amount of particles
was chosen so as to obtain a titanium and iridium loading of 700 g/m2 and 1
g/m2respectively.
A second activating solution was the applied to the electrDde sample
in the following manner. A solution is prepared by dissolving 5.û g of Mn
(N3)2 4 H20 and 0.32 9 Co ~Na3)2 6 H2û and D.5 ml ethanol. This solution is
applied to the electrode surface, dried for 15 minutes at 140~C and baked at
250~C (10 min.) in air. After cooling, the painting, drying and baking steps
were repeated five times so as to get a final loading of 24û g/m2 Mr~02 and
12 g/m2 cobalt oxide (calculated as Co304).
This electrode sample was tested as an oxygen evolving anode in
H2504 (15û gpl). The electrode potential (oxygen half-cell potential) at a
current density of 500 A/m2 amounted to 1.78 Volts (vs NHE) after seven
months of anodic operation.
Example 14
The electrode sample was prepared as in Example 13, except that
IrCI3 aq was replaced by RuU3 aq (14 mg/ml of Ru) and that the
impregnation step was repeated twice so as to get a ruthenium loading of 4
g/m2 for a titanium sponge loading of 700 g/m2-
When tested under the same conditions as in example 13, the oxygenhalf cell potential amounted to 1.80 V (vs NHE) after 6 1/2 rnonths of
operation.
Example 15
An activating solution was prepared by dissolving 0.44 9 RuC13 aq (~8
weight % Ru), O.û90 9 SnClz.2H20 + 0.52 9 Mn (N03)2.4H20 in four ml of
butyl-alcohol.
Z.5 g of titanium sponge (particle size 315-630 microns) was
impregnated with this activating solutlon in the followlng rnanner: 0.77 ml
of solution wa~ uniformly applied to th~ titanium sponge, drisd at 14ûC
during 15 rnin., baked at 25ûC for 10 min. and at 420C for 10 min., all
drying and baking steps in air. After cooling, the titanium sponge was
12~860~L
- 15 -
activated twice again, each time with 0.5 ml of activating solution, dried
and baked as mentioned above.
The activated titanium particles were pressed onto the surface of a
lead-calcium alloy (0.06 % Ca) coupon at 25û kg/cm2 so as to get the
following respective loadings: Ti 70û g/m2, Ru 20 g/m2, Sn 5.8 g/m2 and Mn
13.7 9/m20
This electrode sample was tested as an oxygen evolving anode in
H2SO4 (15~ gpl) at 500 A/m2. The electrode potential amounted to 1.67 V vs
NHE after 7 months of operation.
As may be seen from the above examples, an anode according to the
invention can be fabricated in a simple manner and be used for prolonged
evolution of oxygen at a potential which is significantly lower than the
anode potential corresponding to oxygen evolution on lead or lead alloy
under otherwise similar operating conditions.
It may be noted, that no loss of lead from the base could be o~served
when testing anode samples according to the invention, as described in the
above examples, whereas a notable lead loss could be observed in the
electrolyte when testing lead or lead alloy reference samples under the
same conditions.
It has moreover been found that simultaneously applying heat and
pressure, when partly embedding the valve metal particles in the lead or
lead alloy at the surface of the anode baæ, can facilitate their fixation,
while preventing the particles from being completely ernbedded in and/or
flattened on the base.
It may also be noted that further improvements may well be expected
with respect to the above examples by determining the best conditions for
providing anodes according to the invention with optimum, stable
el~ctrochemical performance with maximum economy of precious metals.
It is understood that the catalytic particles may be applied and
anchored 'co the lead or lead alloy base of the anode, not only by means of a
pre~s as in the examples described above, but also by any other n-eans such
as pres~ure rollers for example, which rnay be ~ultable for providlng the
essential advantages of the invention.
It has alBO been found that the application of heat (e.g at about
250C) during the pressing step can prornots partial embedmenc of the
~8~
catalytic particles into the lead or lead alloy surface.
The invention provides various advantages of whieh the following may
be mentioned for example:
(a) The anode ac~ording to the im~ntion c~n be operated at a
significantly reduced potential, well b low that oF cDnventional anDdes of
lead or lead alJoy currently uæd in industrial cells for electrowinning metals
from acid solutions. The cell voltage and hence the energy costs for
electrowinning metals may thus be decresæd accordingly.
(b) ~ontamination of the electrDlyte and the cathodic deposit by
materials coming from the anode l~an be substantially avoided, since it has
been experimentally established that oxygen is eYolved on the catalytic
particies at a reduced potential, at which the lead or Jead alloy of the anode
base is effectively protected from corrosion.
(c) Dendrite formation on the cathode which may lead to short
circuits with the anode and can thereby burn holes into the anode, will
nevertheless lead to no serious deterioration of the performance of the
anode according to ~he invention, since it operates with oxygen evolution on
the catalytic particles at a reduced potential, at which any part of the lead
or lead base which is exposed does not undergo noteble eorrosion.
(d) Conventional lead or lead alloy anodes may be readily converted
~nto improved anodes according to the invention and it thus becomes
possible to retrofit industrial cells for electrowinning metals in a
psrticularly simple and inexpensive mannsr to provide improved
performance.
(e) The reduced cell voltage obtained with anodes according to the
invention can be readily monitored SDtllat c~e is ~ible t~ rapidly dç~tect a~y
notable rise which may occur in-the anode potential. The eatalytic particles
on the lead or lead alloy base may thus be readily reactivated or replaced
whenever this should become necessary.
(f) Ruthenium can be used as catalyst in an extremely ecor.omical
manner, by combining it in a very small proportion with titaniurn spDnge
particles applied in a many timea larger amount to the anode base of lead or
lead alloy~ The cost of ruthsnium can thus be Justified by the resulting
improvement in anode performance.
(g) Rutheniurn can thus be used in very restricted smounts and
- 17 -
combined with less expensive stable materials.
(h) Decreased short-circuits could be observed in copper
electrowinning plants equipped with anodes according to the invention. This
resulted in an improved cathodic current efficiency, thereby further
increasing the energy savings already achieved by the reduced cell voltage
due to operation of the anode for the invention at a reduced oxygen half-cell
potential.
INDUSTRIAL APPLICA13ILITY
Anodes according to the invention may be advantageously applied
instead of currently used anodes of lead or lead alloy, in order to reduce the
energy costs required for industrially electrowinning metals such as zinc,
copper, cobalt, and nickel and to imprDve the purity of the metal produced
on the cathode.
Such anodes may be usefully applied to various processes where
oxygen evolution at a reduced overvoltage is required.
