Title of Invention

"A PROCESS FOR THE MANUFACTURE OF A NOVEL CERMET ANODE USEFUL FOR ECO-FRIENDLY ELECTROLYTIC EXTRACTION OF METALS FROM FUSED SALTS"

Abstract A PROCESS FOR THE MANUFACTURE OF A NOVEL CERMET ANODE USEFUL FOR ECO-FRIENDLY ELECTROLYTIC EXTRACTION OF METALS FROM FUSED SALT The present invention relates to a process for the manufacture of a novel cermet anode useful for eco-friendly electrolytic extraction of metals, such as aluminum, from fused salts. The process provides a novel cermet anode which consists of compositions of mixed oxides of transition and rare earth metals in combination with metal powders, without any binders, and is amenable to high-pressure compacting and high temperature sintering methods. The novel cermet anode manufactured by the process of the present invention is thermally stable at 1000° C, is chemically inert and non-consumable in a cryolite melt and does not contaminate the cathode product, has low and high anodic over voltages for oxygen and fluorine evolution, respectively, and is dense and resistant to oxidation.
Full Text The present invention relates to a process for the manufacture of a novel cermet
anode useful for eco-friendly electrolytic extraction of metals from fused salts.
Metals, which are less noble than hydrogen in the emf series, have necessarily to
be electro-won from fused salts. Even other reduction processes may not be
economically viable for production such as in the case of metals like aluminium,
titanium, Be, Ca, Mg, Na. Hence, electrolytic route becomes necessary for the
extraction of such metals. Further, an eco-friendly electrolytic extraction of such
metals is definitely needed.
The novel cermet anode of the present invention will be particularly useful for
eco-friendly electrolytic extraction of metals such as aluminum.
The aluminium metal presently is manufactured by the Hall-Heroult process by
the electrolysis of aluminia - cryolite melt between consumable carbon anode
and carbon block cathode at temperatures ranging from 950 to 980° C. During
the electrolysis aluminium metal is pooled to the cathode at the bottom and
carbon dioxide, (COz) is liberated at the carbon anode. The evolution of CO2 - a
green house gas is by the inherent consumption of anode carbon according to
the following reaction:
2 AI203 + 3 C - 4 Al + 3 C02
Theoretically 334 Kg of carbon only is required for one ton of aluminium but in
practice about 500 kg is consumed, liberating 2 tons of C02 to the atmosphere.
The use of carbon as anode for aluminium electrolysis has the following
disadvantages:
1. Liberation of carbon dioxide, a green house gas with harmful effects.
2. The carbon must be very high purity, free from silicon, sulphur, vanadium.
3. Frequent lowering and adjustment of the anode to maintain optimum
anode - cathode distance.
4. Turbulance and unsteady voltage conditions resulting higher voltage and
higher energy consumption.
5. Process is labour intensive and environmentally hazardous.
6. Necessity of a separate anode shop.
Reference may be made to U.S.Patent 3930967 (1976) in which electrodes
made from SnO2, SbaOa and CuO were used for aluminum production. The main
drawback is that very low current density ranging from 0.001 to 0.025 A/cm2 only
has been applied.
Reference may be made to another U.S Patent No.4057480 (1977), wherein
mixed materials of SnO2, Fe20s, CoO, ZnO are used as inert anodes for
aluminium electrolysis. The drawback being the contamination of the cathode
product with excess tin.
In a Japanese patent No.1461155 (1977), oxygen ion conducting anodes are
disclosed in which both spinel and perovskite structures containing ZrOz as major
constituent have been tested. The trial run faced many operational difficulties,,
Electrolysis with anodes fabricated from oxides of Fe, Co, Ni, Zn, Sn, Y and Cu
powder up to 0 - 30% is given in U.S patent 6126799 (2001). The problem
encountered was the contamination and high wear rate of the electrodes.
Work on similar lines with cermet anodes incorporating Ag powders have been
patented in Canada pat 2317596, (2001). The difficulty with the electrolysis
being dissolution of the electrode and contamination of the aluminum metal
produced.
Reference may be made to a paper by T.R.AIcorn etal, "Light metals 1993" (Ed)
Subodh.K.Das Minerals, Metals and Materials Society, Warrendale PA (1993) P.
433-443, in which operational results of a pilot cell test with inert anode has been
published. The drawbacks are the instability of the electrode materials and tested
up to a current density of 0.5 A/cm2 only.
In a paper by J.S.Gregg etal., Light Metals, 1993 (Ed) Suboth.K.Das, Minerals,
Metals and Materials Society, Warrendale P.A. (1993) P.455-464, have
discussed the testing of copper - nickel ferrite / NiO with or without cerium oxide
coating for electrowinning of aluminium. The high energy cost due to low
conductivity of the anode was attributed as the main drawback.
The main object of the present invention is to provide a process for the
manufacture of a novel cermet anode useful for eco-friendly electrolytic
extraction of metals from fused salts.
Another object of the present invention is to provide a process for the
manufacture of a novel cermet anode which consists of compositions without any
binders and is amenable to high-pressure compacting and high temperature
sintering methods.
Yet another object of the present invention is to provide a process for the
manufacture of a novel cermet anode which is thermally stable at 1000° C.
Still another object of the present invention is to provide a process for the
manufacture of a novel cermet anode which is chemically inert and nonconsumable
in a cryolite melt and should not contaminate the cathode product.
Still yet another object of the present invention is to provide a process for the
manufacture of a novel cermet anode which has high electrical conductivity.
A further another object of the present invention is to provide a process for the
manufacture of a novel cermet anode which has low and high anodic over
voltages for oxygen and fluorine evolution, respectively.
A still further object of the present invention is to provide a process for the
manufacture of a novel cermet anode which is dense and resistant to oxidation.
Another object of the present invention is to provide a process for the
manufacture of a novel cermet anode which should be cheap and amenable for
fabrication by the existing techniques.
Still another object of the present invention is to provide a process for the
manufacture of a novel cermet anode which will be particularly useful for ecofriendly
electrolytic extraction of metals such as aluminum from alumina in
molten cryolite.
Yet another object of the present invention is to provide a process for the
manufacture of a novel cermet anode which can substitute the consumable
carbon anodes of the Hall Heroult cell with non-consumable cermet anodes for a
trouble free and environmentally clean production of aluminium from alumina by
electrolysis.
In the present invention there is provided a process for the manufacture of a
novel cermet anode useful for eco-friendly electrolytic extraction of metals, such
as aluminum, from fused salts. The process provides a novel cermet anode
which consists of compositions of mixed oxides of transition and rare earth
metals in combination with metal powders, without any binders, and is amenable
to high-pressure compacting and high temperature sintering methods. The novel
cermet anode manufactured by the process of the present invention is thermally
stable at 1000° C, is chemically inert and non-consumable in a cryolite melt and
does not contaminate the cathode product, has low and high anodic over
voltages for oxygen and fluorine evolution, respectively, and is dense and
resistant to oxidation.
Accordingly, the present invention provides a process for the manufacture of a
novel cermet anode useful for eco-friendly electrolytic extraction of metals from
fused salts, which comprises mixing intimately 80 to 90 wt.% dry powders of
oxides of one or more of the metals selected from Cu, Ni, Co, Fe, Zn, Al, Ti, Cr,
Ce, La, Nb, and 10 to 20 wt. % metal powders selected from Au, Ag, Bi, Sb, Cu,
Ni, Zn, either alone or in combination, to obtain a dry blend of powder
composition, compacting the dry blend to obtain green compacts, sintering the
green compacts at a temperature of up to 1400°C under normal atmospheres,
allowing the sintered compact to cool and fixing current leads to obtain a novel
cermet anode.
In an embodiment of the present invention the intimate mixing to obtain a dry
blend of powder composition of metal oxide powders and meta! powders is
carried out by known methods.
In another embodiment of the present invention the size reduction and size
analysis of metallic oxides and metal powders is effected by known ceramic
technology methods.
In yet another embodiment of the present invention the dry blend of powder
composition optionally consists of binders.
In still another embodiment of the present invention the compacting of the dry
blend is done, in sizes ranging from 5 -12 cm diameter and 5 -12 cm height, in a
hydraulic press to obtain green compacts.
In still yet another embodiment of the present invention the sintering of the green
compacts is carried out in a furnace, such as an electric furnace, at a
temperature of up to 1400°C, with a holding schedule of the order of several
hours at intermediate temperatures.
The novelty of the present invention is that it provides a process for the
manufacture of a novel cermet anode useful for eco-friendly electrolytic
extraction of metals from fused salts. The novel cermet anode of the present
invention consists of compositions without any binders and is amenable to highpressure
compacting and high temperature sintering methods. The novel cermet
anode manufactured by the process of the present invention is thermally stable
at 1000° C, is chemically inert and non-consumable in a cryolite melt and does
not contaminate the cathode product, has low and high anodic over voltages for
oxygen and fluorine evolution, respectively, and is dense and resistant to
oxidation.
The above noted novel features have been made possible due to the nonobvious
inventive steps of the present invention which comprises mixing
intimately 80 to 90 wt.% dry powders of oxides of one or more of the metals
selected from Cu, Ni, Co, Fe, Zn, Al, Ti, Cr, Ce, La, Nb, and 10 to 20 wt. % metal
powders selected from Au, Ag, Bi, Sb, Cu, Ni, Zn, either alone or in combination,
to obtain a dry blend of powder composition, compacting the dry blend to obtain
green compacts, sintering the green compacts at a temperature of up to 1400°C
under normal atmospheres.
The following examples are given by way of illustration and therefore should not
be construed to limit the scope of the present invention.
Example -1
A cermet anode having composition containing 85 wt.% mixture of NiO, Fe203,
Nb2O5 and 15 wt.% combination of metal powders of Cu, Bi was compacted and
used in an eco-friendly electrolyser. The electrolyser was operated with molten
aluminum over carbon block cathodes containing cryolite with excess aluminum
fluoride and 8 wt% of alumina as electrolyte at a constant current density of 0.50
A/cm2. Continuous electrolysis was carried out at 950°C, for 180 hrs at an interelectrode
distance of 3.5cm. Aluminum metal was produced at an energy
consumption of 13.4 kwh/ kg of aluminum.
Example - 2
An electrolytic cell for the production of aluminum metal was operated with
cermet anode of composition 80 wt.% mixture of NiO, Fe2O3, Ce2O3 and 20 wt %
combination of metal powders of Bi plus Cu, in a cryolite electrolyte containing 6
wt % of AI2C«3 maintained at a temperature of 980° C and an inter-electrode
distance of 4 cm at a current density of 0.80 A/cm2. Pure aluminum was
deposited to cathode at a current efficiency of 82%. The purity of the metal
obtained was 99 4 wt % with the impurities of Fe = 0.15 wt %, Ni = 0.04 wt % and
Cu = 0.04 wt %.
Example - 3
An eco-friendly electrolyser consisting of non-consumable cermet anodes made
by ceramic technology containing 90 wt % of mixture of Fe2O3, NiO and La2O3
and 10 wt % of a combination of metal powders of Ni, Cu and Sb, carbon block
cathode, and molten cryolite electrolyte was operated at a current density of 1.0
A/cm2 at a temperature of 960° C for 140 hrs. to obtain primary aluminum at the
cathode and pure oxygen at the anode at a current efficiency of 85%. The metal
so obtained was of 99.2% purity with the impurities Cu 0.05 wt %, Fe 0.20wt %
and Ni 0.05 wt %.
From the above examples it is confirmed that the novel cermet anode
manufactured by the process of the present invention is stable and not
consumed during the electrolysis and can be a suitable substitute for carbon of






We claim:
1. A process for the manufacture of a novel cermet anode useful for eco-friendly
electrolytic extraction of metals from fused salts, which comprises mixing intimately 80
to 90 wt.% dry powders of oxides of one or more of the metals selected from Cu, Ni,
Co, Fe, Zn, Al, Ti, Cr, Ce, La, Nb, and 10 to 20 wt. % metal powders selected from Au,
Ag, Bi, Sb, Cu, Ni, Zn, either alone or in combination, to obtain a dry blend of powder
composition, compacting the dry blend to obtain green compacts, sintering the green
compacts at a temperature of up to 1400°C under normal atmospheres, allowing the
sintered compact to cool and fixing current leads to obtain a novel cermet anode.
2. A process as claimed in claim 1-3, wherein the dry blend of powder composition optionally consists of binders.
3. A process as claimed in claim 1-5, wherein the sintering of the green compacts is carried out in a furnace, such as an electric furnace, at a temperature of up to 1400°C, with a holding schedule of the order of several hours at the temperature ranging between 950°C to 980°C.
4. A process for the manufacture of a novel cermet anode useful for eco-friendly
electrolytic extraction of metals from fused salts, substantially as herein described with
reference to the examples.



Documents:

34-DEL-2003-Abstract-(27-01-2009).pdf

34-del-2003-abstract.pdf

34-DEL-2003-Claims-(27-01-2009).pdf

34-del-2003-claims.pdf

34-DEL-2003-Correspondence-Others-(27-01-2009).pdf

34-del-2003-correspondence-others.pdf

34-del-2003-corresponence-po.pdf

34-del-2003-description (complete).pdf

34-DEL-2003-Form-1-(27-01-2009).pdf

34-del-2003-form-1.pdf

34-DEL-2003-Form-18-(27-01-2009).pdf

34-del-2003-form-18.pdf

34-del-2003-form-2.pdf

34-del-2003-form-3.pdf


Patent Number 228350
Indian Patent Application Number 34/DEL/2003
PG Journal Number 08/2009
Publication Date 20-Feb-2009
Grant Date 02-Feb-2009
Date of Filing 10-Jan-2003
Name of Patentee COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH
Applicant Address RAFI MARG, NEW DELHI-110 001, INDIA.
Inventors:
# Inventor's Name Inventor's Address
1 MEENAKSHI SUNDARAM RAGHAVAN CENTRAL ELECTROCHEMICAL RESEARCH INSTITUTE, KARAIKUDI-630 006, TAMILNADU, INDIA
2 LAWRENCE JOHN BERCHMANS CENTRAL ELECTROCHEMICAL RESEARCH INSTITUTE, KARAIKUDI, TAMILNADU, INDIA
3 CHANASSERY OUSO AUGUSTIN CENTRAL ELECTROCHEMICAL RESEARCH INSTITUTE, KARAIKUDI-630 006, TAMILNADU, INDIA
PCT International Classification Number C25C 1/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA