CA2030788A1 - Anode substrate coated with rare earth oxycompounds - Google Patents
Anode substrate coated with rare earth oxycompoundsInfo
- Publication number
- CA2030788A1 CA2030788A1 CA002030788A CA2030788A CA2030788A1 CA 2030788 A1 CA2030788 A1 CA 2030788A1 CA 002030788 A CA002030788 A CA 002030788A CA 2030788 A CA2030788 A CA 2030788A CA 2030788 A1 CA2030788 A1 CA 2030788A1
- Authority
- CA
- Canada
- Prior art keywords
- anode
- oxide
- substrate
- mol
- surface coating
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
- 239000000758 substrate Substances 0.000 title claims abstract description 43
- 229910052761 rare earth metal Inorganic materials 0.000 title claims abstract description 12
- 150000002910 rare earth metals Chemical class 0.000 title claims abstract description 9
- 238000000576 coating method Methods 0.000 claims abstract description 28
- 239000011248 coating agent Substances 0.000 claims abstract description 24
- 229910052751 metal Inorganic materials 0.000 claims abstract description 19
- 239000002184 metal Substances 0.000 claims abstract description 19
- QPLDLSVMHZLSFG-UHFFFAOYSA-N Copper oxide Chemical compound [Cu]=O QPLDLSVMHZLSFG-UHFFFAOYSA-N 0.000 claims abstract description 15
- 239000005751 Copper oxide Substances 0.000 claims abstract description 12
- 229910000431 copper oxide Inorganic materials 0.000 claims abstract description 12
- 239000006104 solid solution Substances 0.000 claims abstract description 12
- 239000003792 electrolyte Substances 0.000 claims abstract description 10
- 229910000480 nickel oxide Inorganic materials 0.000 claims abstract description 10
- GNRSAWUEBMWBQH-UHFFFAOYSA-N oxonickel Chemical compound [Ni]=O GNRSAWUEBMWBQH-UHFFFAOYSA-N 0.000 claims abstract description 10
- 238000005363 electrowinning Methods 0.000 claims abstract description 9
- FUJCRWPEOMXPAD-UHFFFAOYSA-N lithium oxide Chemical compound [Li+].[Li+].[O-2] FUJCRWPEOMXPAD-UHFFFAOYSA-N 0.000 claims abstract description 6
- 229910001947 lithium oxide Inorganic materials 0.000 claims abstract description 6
- 150000003839 salts Chemical class 0.000 claims abstract description 4
- IZVNQBSGTUVWKV-UHFFFAOYSA-N [O-2].[Li+].[Cu+2].[Ni+2] Chemical compound [O-2].[Li+].[Cu+2].[Ni+2] IZVNQBSGTUVWKV-UHFFFAOYSA-N 0.000 claims abstract description 3
- 229910052782 aluminium Inorganic materials 0.000 claims description 15
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 15
- 238000000034 method Methods 0.000 claims description 14
- XVVDIUTUQBXOGG-UHFFFAOYSA-N [Ce].FOF Chemical compound [Ce].FOF XVVDIUTUQBXOGG-UHFFFAOYSA-N 0.000 claims description 13
- 229910052684 Cerium Inorganic materials 0.000 claims description 11
- GWXLDORMOJMVQZ-UHFFFAOYSA-N cerium Chemical compound [Ce] GWXLDORMOJMVQZ-UHFFFAOYSA-N 0.000 claims description 11
- 229910001610 cryolite Inorganic materials 0.000 claims description 10
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims description 8
- 229910052744 lithium Inorganic materials 0.000 claims description 8
- 150000001875 compounds Chemical class 0.000 claims description 6
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 claims description 5
- 239000000843 powder Substances 0.000 claims description 5
- 238000001816 cooling Methods 0.000 claims description 4
- 229910052727 yttrium Inorganic materials 0.000 claims description 4
- VWQVUPCCIRVNHF-UHFFFAOYSA-N yttrium atom Chemical compound [Y] VWQVUPCCIRVNHF-UHFFFAOYSA-N 0.000 claims description 4
- 238000005868 electrolysis reaction Methods 0.000 claims description 3
- 238000010304 firing Methods 0.000 claims description 3
- 229910052746 lanthanum Inorganic materials 0.000 claims description 3
- FZLIPJUXYLNCLC-UHFFFAOYSA-N lanthanum atom Chemical compound [La] FZLIPJUXYLNCLC-UHFFFAOYSA-N 0.000 claims description 3
- 238000002156 mixing Methods 0.000 claims description 3
- 229910052758 niobium Inorganic materials 0.000 claims description 3
- 239000010955 niobium Substances 0.000 claims description 3
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 claims description 3
- 238000005245 sintering Methods 0.000 claims description 3
- 229910052715 tantalum Inorganic materials 0.000 claims description 3
- GUVRBAGPIYLISA-UHFFFAOYSA-N tantalum atom Chemical compound [Ta] GUVRBAGPIYLISA-UHFFFAOYSA-N 0.000 claims description 3
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 2
- 238000000227 grinding Methods 0.000 claims description 2
- 229910052760 oxygen Inorganic materials 0.000 claims description 2
- 239000001301 oxygen Substances 0.000 claims description 2
- 238000003825 pressing Methods 0.000 claims description 2
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 27
- 229910052759 nickel Inorganic materials 0.000 description 14
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 11
- 229910052802 copper Inorganic materials 0.000 description 11
- 239000010949 copper Substances 0.000 description 11
- 239000000463 material Substances 0.000 description 11
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 8
- 239000000956 alloy Substances 0.000 description 7
- 229910045601 alloy Inorganic materials 0.000 description 7
- 239000010410 layer Substances 0.000 description 7
- 239000000203 mixture Substances 0.000 description 7
- 239000000919 ceramic Substances 0.000 description 6
- 150000002739 metals Chemical class 0.000 description 5
- 238000004458 analytical method Methods 0.000 description 4
- 238000005260 corrosion Methods 0.000 description 4
- 230000007797 corrosion Effects 0.000 description 4
- 229910052742 iron Inorganic materials 0.000 description 4
- 230000001681 protective effect Effects 0.000 description 4
- XOLBLPGZBRYERU-UHFFFAOYSA-N tin dioxide Chemical compound O=[Sn]=O XOLBLPGZBRYERU-UHFFFAOYSA-N 0.000 description 4
- 229910018054 Ni-Cu Inorganic materials 0.000 description 3
- 229910018481 Ni—Cu Inorganic materials 0.000 description 3
- 239000011195 cermet Substances 0.000 description 3
- 229910017052 cobalt Inorganic materials 0.000 description 3
- 239000010941 cobalt Substances 0.000 description 3
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 239000000155 melt Substances 0.000 description 3
- 229910020187 CeF3 Inorganic materials 0.000 description 2
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 2
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 2
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 2
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 2
- 239000002131 composite material Substances 0.000 description 2
- 238000000151 deposition Methods 0.000 description 2
- 230000008021 deposition Effects 0.000 description 2
- 239000002019 doping agent Substances 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 229910052749 magnesium Inorganic materials 0.000 description 2
- 239000011777 magnesium Substances 0.000 description 2
- 229910052748 manganese Inorganic materials 0.000 description 2
- 239000011572 manganese Substances 0.000 description 2
- WPBNNNQJVZRUHP-UHFFFAOYSA-L manganese(2+);methyl n-[[2-(methoxycarbonylcarbamothioylamino)phenyl]carbamothioyl]carbamate;n-[2-(sulfidocarbothioylamino)ethyl]carbamodithioate Chemical compound [Mn+2].[S-]C(=S)NCCNC([S-])=S.COC(=O)NC(=S)NC1=CC=CC=C1NC(=S)NC(=O)OC WPBNNNQJVZRUHP-UHFFFAOYSA-L 0.000 description 2
- 150000002736 metal compounds Chemical class 0.000 description 2
- 230000007935 neutral effect Effects 0.000 description 2
- NQNBVCBUOCNRFZ-UHFFFAOYSA-N nickel ferrite Chemical compound [Ni]=O.O=[Fe]O[Fe]=O NQNBVCBUOCNRFZ-UHFFFAOYSA-N 0.000 description 2
- 230000003647 oxidation Effects 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- 239000011253 protective coating Substances 0.000 description 2
- 229910001404 rare earth metal oxide Inorganic materials 0.000 description 2
- 229910052725 zinc Inorganic materials 0.000 description 2
- 239000011701 zinc Substances 0.000 description 2
- 229910000599 Cr alloy Inorganic materials 0.000 description 1
- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical compound [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 description 1
- 229910004380 Li(NO3) Inorganic materials 0.000 description 1
- WGLPBDUCMAPZCE-UHFFFAOYSA-N Trioxochromium Chemical compound O=[Cr](=O)=O WGLPBDUCMAPZCE-UHFFFAOYSA-N 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000001464 adherent effect Effects 0.000 description 1
- 150000001768 cations Chemical class 0.000 description 1
- 229910010293 ceramic material Inorganic materials 0.000 description 1
- 229910000423 chromium oxide Inorganic materials 0.000 description 1
- 238000005253 cladding Methods 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 238000009713 electroplating Methods 0.000 description 1
- 238000002149 energy-dispersive X-ray emission spectroscopy Methods 0.000 description 1
- 239000011737 fluorine Substances 0.000 description 1
- 229910052731 fluorine Inorganic materials 0.000 description 1
- 238000007731 hot pressing Methods 0.000 description 1
- 238000011065 in-situ storage Methods 0.000 description 1
- 229910000765 intermetallic Inorganic materials 0.000 description 1
- OVMJVEMNBCGDGM-UHFFFAOYSA-N iron silver Chemical compound [Fe].[Ag] OVMJVEMNBCGDGM-UHFFFAOYSA-N 0.000 description 1
- XGZVUEUWXADBQD-UHFFFAOYSA-L lithium carbonate Chemical compound [Li+].[Li+].[O-]C([O-])=O XGZVUEUWXADBQD-UHFFFAOYSA-L 0.000 description 1
- 229910052808 lithium carbonate Inorganic materials 0.000 description 1
- 238000003754 machining Methods 0.000 description 1
- 239000002905 metal composite material Substances 0.000 description 1
- 229910000510 noble metal Inorganic materials 0.000 description 1
- 238000007750 plasma spraying Methods 0.000 description 1
- 238000004663 powder metallurgy Methods 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 238000000550 scanning electron microscopy energy dispersive X-ray spectroscopy Methods 0.000 description 1
- 238000005204 segregation Methods 0.000 description 1
- 238000007493 shaping process Methods 0.000 description 1
- 238000010583 slow cooling Methods 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 229910052566 spinel group Inorganic materials 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 239000002344 surface layer Substances 0.000 description 1
- PBCFLUZVCVVTBY-UHFFFAOYSA-N tantalum pentoxide Inorganic materials O=[Ta](=O)O[Ta](=O)=O PBCFLUZVCVVTBY-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
- C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
- C25C3/06—Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
- C25C3/08—Cell construction, e.g. bottoms, walls, cathodes
- C25C3/12—Anodes
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
- C25C7/00—Constructional parts, or assemblies thereof, of cells; Servicing or operating of cells
- C25C7/02—Electrodes; Connections thereof
- C25C7/025—Electrodes; Connections thereof used in cells for the electrolysis of melts
Landscapes
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Engineering & Computer Science (AREA)
- Electrolytic Production Of Metals (AREA)
- Battery Electrode And Active Subsutance (AREA)
- Solid Thermionic Cathode (AREA)
- Secondary Cells (AREA)
- Manufacture And Refinement Of Metals (AREA)
- Superconductors And Manufacturing Methods Therefor (AREA)
- Inorganic Compounds Of Heavy Metals (AREA)
Abstract
An anode for electrowinning a metal from a molten salt electrolyte comprises an electroconductive oxycompound substrate which in use carries a surface coating comprising at least one rare earth oxycompound. The substrate comprises a sintered body composed of a nickel-copper-lithium oxide solid solution, wherein the solid solution preferably contains 70-90 mol % nickel oxide, 5-29 mol %
copper oxide and 1-10 mol % lithium oxide.
copper oxide and 1-10 mol % lithium oxide.
Description
WO90/10735 1 _ 2 0 3 0 7 8 8 PCT/EPgo/003~
.
AN ANODE SUBSTRATE COATED WITH
RARE EARTH OXYCOMPOUNDS
The invention relates to anodes for electrowinning metals such as aluminum fro~ molten salt electrolytes, of the type comprising a substrate made of an electroconductive oxycompound which in use is coated with a surface coating comprising at least one rare earth oxycompound, typically including cerium oxyfluoride. The invention also relates to electrowinning processes using such anodes.
.
BACKGROUND ART ~ :
Materials used as non-consumable anodes in molten electrolytes must have a good stability in an oxidisin~
atmosphere, good mechanical properties, good electrical conductivity and be able to operate for prolonged periods of time under polarising conditions. It is well known that ceramic materials have better resistance to chemical corrosion. However, their low electrical conductivity and difficulties of making mechanical and electrical contact as well as difficulties in shaping and machining these materials seriously limit their use.
US Patent 4 6lq 569 describes a method of electrowinning metals by electrolysis of a melt containing a dissolved species of the metal to be won usinq an anode immersed in the melt wherein the anode has a metal, alloy or cermet substrate and an operative anode surface which ~:: . . :
WO 9U/10735 ~ 7 ~ ~ PCT/EP~0/0~3~4 is a protective surface coating containin~ a compound of a ~etal less noble than the metal to be electrowon, the protective coating being preserved by maintaining in the melt a suitable concentration of a species of this less noble metal. Usually the protective anode coating comprises a fluorine-containing oxycompound of cerium (referred to as "cerium oxyfluoride") alone or in combination with additives such as compounds of tantalum, niobium, yttrium, lanthanum, praesodymium and other rare earth elements, this coating being maintained by the addition of cerium and possibly other elements to the electrolyte. The electrolyte can be molten cryolite containing dissolved alumina, i.e. for the production of aluminum.
This electrowinning method potentially has very significant advantages. To date, however, there remain problems with the anode substrate. When the substrate ls a metal, alloy or cermet, it may be subject to oxidation leadin~ to a reduced life of the anode, despite the excellent protective effect of the cerium oxyfluoride coating which protects the substrate from direct attack by corrosive electrolyte. When the substrate is a ceramic oxycompound, conductivity and corrosion are major problems.
A promising solution to these problems has been the use of a ceramic/metal composite material of at least one ceramic phase and at least one metallic phase, comprising mixed o~ides of cerium with aluminum, nickel, iron and/or copper in the form of a skeleton interwoven with a continuous metallic network of an alloy or intermetallic compound of cerium with aluminum, nickel, iron and/or copper, as described in EP-A-0 257 708. When used as electrode substrates, these materials have promise, particularly those based on cerium and aluminum because - ~
W090/10735 2 0 3 ~ 7 8-8 PCT/EP90/003~
f:
~ ,. . .
....
even if they corrode, this does not lead to corrosion p~oducts that contaminate the electrowon aluminum.
Nevertheless corrosion of the substrate remains a problem.
US Patent 4 374 050 discloses inert electrodes for aluminum production fabricated from at least two metals or metal compounds to provide a combination metal compound.
For example, an alloy of two or more metals can be surface oxidised to form an oxycompound of the metals at the surface on an unoxidised alloy substrate. US Patent 4 374 761 discloses similar compositions further comprisin~ a dispersed metal powder in compositions which may be applied as a preformed o~ide composition on a metal substrate by cladding or plasma spraying, Such application techniques, however, are known to involve many drawbacks and the adhesion is particularly poor. US Patent 4 620 905 describes an oxidised alloy electrode based on tin or copper with nickel, iron silver, zinc, magnesium, aluminum and yttrium, either as a cermet or partially oxidised at its surface. Such partially oxidised alloys suffer serious disadvantages in that the oxide layers formed are far too porous to o~ygen, and not sufficiently stable in corrosive environments. In addition, at high temperatures the partially oxidised structures continue to oxidize and this uncontrolled oxidation causes subsequent segregation of the metal and/or oxide layer. Adherence at the ceramic-metal interfaces is particularly difficult to achieve and this very problem has hampered use of such simple composites. Finally, none of these matesials has proven satisfactory as substrate for cerium oxyfluoride coatings of the type discussed.
Improved metal-based substrates are described in European Patent Applications 88201957.3, 88201851.8, 88201852.6, 88201a53.4 and 882018S4.2 all as yet ...... ., ... . , , ................................ j, ,... . .. . :,., ........ , . - , . .. , ~;.- . .
WO90/10735 2 0 ~ ~ 7 8 8 PCT/EP90/003~
,s unpublished. These typically include a substrate made of an alloy of chromium with nickel, cobalt and/or iron. On the surface of the substrate is a chromium oxide film on top o~ which is a layer of copper oxide in solid solution with nickel or manganese, o~tained by oxidising a layer of nickel/copper or manganese/copper which is applied eg by electroplating. It was also mentioned that the nickel oxide in the surface layer may have its electrical conductivity improved by doping with lithium.
Such composite layers nevertheless remain difficult to prepare and although they have demonstrated superior performance over previous anodes, considerable development is still required to optimize their lifetime and reduce the production cost.
The aforementioned European Patent Application 88201854.2, mentions further embodiments of ceramic intermediate layers which in use serve as anchorage for the in-situ maintained protective coating of cerium oxyfluoride to the metal substrate, these intermediate layers including: nickel ferrite; copper oxide and nickel ferrite; doped, non-stoichiometric and partially substituted ceramic oxide spinels containing combinations of divalent nickel, cobalt, magnesium, manganese, copper and zinc with divalent/trivalent nickel, cobalt, manganese and/or iron, and optionally dopants selected from Ti4+, z 4+ Sn4+ Fe4+ Hf4+, Mn4+, Fe , Ni C 3+ Mn3+ A13+ Cr3+, Fe2+, Ni , Co M92+, Mn2+, Cu2~, zn2 and Li (see US patent No. 4 552 630); as well as coatings based on rare earth oxides and oxyfluorides, in particular pre-applied cerium oxyfluoride alone or in combination with other components.
To date, very little progress has been made with .. . .
.
WO90/10735 2 ~ 3 0 7 8 8 PCTtEP9OfO03~
~"~,, .
anode substrates made of ceramic electroconductive oxycompounds. The most widely tested materials in this category on account of their acceptable conductivity have been based on tin dioxide. However, it has not yet been possible to make an adequate electrode substrate based on tin dioxide despite expedients devised to reduce the amount of substrate material dissolved in the electrolyte.
See for example EP-A-O 257 709 (E00208) which proposed doping the oxyfluoride coating with tantalum to render it more impervious and thereby reduce contamination of the electrolyte and the electrowon aluminum with tin from the substrate.
SUMMARY OF THE INvENTION
An object of the invention is to provide electrode substrates based on electroconductive oxycompounds which can be produced easily, have excellent conductivity and perform well as anode substrates when coated with an oxyfluoride-type coating.
The invention is based on the realization that sintered copper-n~ckel oxide suitably doped with lithium oxide to enhance conductivity fulfills the sought-after requirements of a material for the anode substrate.
According to the invention, an anode for electrowinning a metal from a molten salt electrolyte, comprising an electroconductive oxycompound substrate which in use carries a surface coating comprising at least one rare earth oxycompound, is characterized in that the substrate comprises a sintered body composed of a nickel-copper-lithium oxide solid solution.
., . ~
.: .. : : , :
WO90/10735 2 0 3 0 7 8 8 PC~/EP90/00364 Preferably, the nickel oxide is present in the solid solution in an amcunt of at least 70 mol%, the copper oxide is present in an amount of at most 29 mol% and the iithium oxide is present in an amount of at most 10mol%.
Preferably still, the solid solution contains 70-90 mol%
nickel oxide, 5-29 mol% copper oxide and 1-10 mol% lithium oxide. The concentration the lithium dopant preferably ranges from 1 to 10 atom % with an optimum value at about 5 atom %, this usually in combination with about 70-80 mol~ nickel oxide and about 20-25 mol% copper oxide.
It has been shown that a concentration of 1 to 5 atom% lithium increases the conductivity of the (Ni-Cu)O
solid solution by two orders of magnitude, up to about 200(ohm cm) 1 at 1000C. This makes the material an attractive substrate material for cerium oxyfluoride coatings for aluminum electrowinning.
A method of preparing an anode substrate according to the invention comprises mixing powders of nickel oxide, copper oxide and a compound of lithium, firing at 900~1100C, cooling, grinding, cold pressing and sintering at 1000-1300C for 30-40 hours. Shapes of lithium doped (Ni-Cu)O solid solution can thus conveniently be prepared by mixing powders of Li(,~O3), Li2CO3 or LioH; CuO;
and NiO in the right proportions and firing for example at 900-1050C in air for about 24 hours at a heating rate of about 100C/hour. After cooling, the material is ground, cold pressed (eg at 10 tons/cm2) and sintered at 1000-1300C e.g. 1100-1150C for 30-40 hours. The resulting sintered material shows a density of at least 70% theoretical density, typically 80%, and an electrical conductivity of about 150 (ohm cm) 1 at 980C compared to 1 (ohm cm) 1 for the undoped (Ni-Cu)o. A sintered .. ., ~- . . ..
b WO90/10735 - 7 -- PCT/EP9~00364 ~ t,' '.,", ~ ' specimen of such composition was tested as an anode substrate in a neutral cryolite containing l.5% CeF3 and l.S Ta2O5. A very den~e tantalum-doped cerium oxyfluoride coating was obtained. No noticeable change in the substrate composition near the interface was observed.
The process may be optimized to improve dens~f;cation by hot pressing and/or the addition of sintering aids.
The anode substrate according to the invention can be used as a massive body supporting the rare earth oxycompound coating. But it can, if desired, incorporate a metal or other current collector to assist the supply of electric current and facilitate connection to the power supp ly .
It has been observed that using the anode substrate according to the invention in a cryolite melt containing dissolved alumina and cerium species produces very dense, adherent and homogeneous cerium-oxyfluoride coatings. This is believed to be related to the presence of copper oxide in the substrate surface and to the surface porosity of the sintered material. The rare earth oxide coating may be cerium o~yfluoride alone or preferably may be cerium oxyfluoride together with at least one compound of tatalum, niobium, yttrium, lanthanum, praesodymium and other rare earth elements.
The invention also provides a method of eletrowinning aluminum from molten cryolite containing alumina wherein an anode is immersed, the anode having an eletroconductive oxycompound substrate carying a surface coating comprising at least one rare earth oxycompound, the surface coating being maintained by the presence of cerium species in the molten cryolite, the method comprising passing electrolysis current between the anode and a cathode to evolve oxygen and to maintain the surface coating at the anode and to produce aluminum at the cathode.
The invention will be further illustrated by the following Example.
.
.
::, `: ~ - . ' ', ' W090/10735 2 0 3 0 7 8 ~ PCT/FP90/0036~
ExamPle A Li.o5Ni.70Cu.25O sample was prepared using powder metallurgy techniques: Li(NO3), CuO and NiO
powders were mixed in the right proportions and fired at 1000C in air for 24 hours. The heating rate was 100C/hour. After cooling the specimen was powdered, cold pressed at 10 tons/cm2 and sintered for 35 hours at llS0C. The microstructure of the resulting sample showed a porosity of nearly 20% and CuO precipitates at the grain boundaries due to the slow cooling rate. A typical SEM-EDX
analysis over a window of about 0.25 mm2 gave nickel 71.0 atom% and copper 28.6 atom~, whereas for individual grains the composition was: nickel 76.6 atom% and copper 23.2 atom%. This analytical method is not suitable for detecting the lithium.
An ingot with a surface area of 7.~ cm was prepared from this sample and exposed for 5 hours in a neutral cryolitic bath of 900g containing 1.5% of Ta2O; and 6g (i.e. about 0.7%) CeF3. Using a current density of 200 mA/cm , a dense tantalum-doped cerium oxyfluoride coating was formed on the substrate at a rate ranging from 0.15 to 0.16 g/cm per hour. EDX analysis revealed that the concentration of nickel and copper did not significantly change during the cerium oxyfluoride deposition: 70 and 30 atom% for nickel and copper respectively for a window analysis; 76 atom% nickel and 23 atom~ copper for a grain analysis. This stability of the composition of the sample is an indication of the protective role of the deposit for the cryolite in the previously mentioned conditions. The relative stability of the potential during the deposition may be related to the conductivity of the substrate which is strongly dependant on the lithium concentration.
- . ~ . : -:. . . . , : - :
-- . , .
.
AN ANODE SUBSTRATE COATED WITH
RARE EARTH OXYCOMPOUNDS
The invention relates to anodes for electrowinning metals such as aluminum fro~ molten salt electrolytes, of the type comprising a substrate made of an electroconductive oxycompound which in use is coated with a surface coating comprising at least one rare earth oxycompound, typically including cerium oxyfluoride. The invention also relates to electrowinning processes using such anodes.
.
BACKGROUND ART ~ :
Materials used as non-consumable anodes in molten electrolytes must have a good stability in an oxidisin~
atmosphere, good mechanical properties, good electrical conductivity and be able to operate for prolonged periods of time under polarising conditions. It is well known that ceramic materials have better resistance to chemical corrosion. However, their low electrical conductivity and difficulties of making mechanical and electrical contact as well as difficulties in shaping and machining these materials seriously limit their use.
US Patent 4 6lq 569 describes a method of electrowinning metals by electrolysis of a melt containing a dissolved species of the metal to be won usinq an anode immersed in the melt wherein the anode has a metal, alloy or cermet substrate and an operative anode surface which ~:: . . :
WO 9U/10735 ~ 7 ~ ~ PCT/EP~0/0~3~4 is a protective surface coating containin~ a compound of a ~etal less noble than the metal to be electrowon, the protective coating being preserved by maintaining in the melt a suitable concentration of a species of this less noble metal. Usually the protective anode coating comprises a fluorine-containing oxycompound of cerium (referred to as "cerium oxyfluoride") alone or in combination with additives such as compounds of tantalum, niobium, yttrium, lanthanum, praesodymium and other rare earth elements, this coating being maintained by the addition of cerium and possibly other elements to the electrolyte. The electrolyte can be molten cryolite containing dissolved alumina, i.e. for the production of aluminum.
This electrowinning method potentially has very significant advantages. To date, however, there remain problems with the anode substrate. When the substrate ls a metal, alloy or cermet, it may be subject to oxidation leadin~ to a reduced life of the anode, despite the excellent protective effect of the cerium oxyfluoride coating which protects the substrate from direct attack by corrosive electrolyte. When the substrate is a ceramic oxycompound, conductivity and corrosion are major problems.
A promising solution to these problems has been the use of a ceramic/metal composite material of at least one ceramic phase and at least one metallic phase, comprising mixed o~ides of cerium with aluminum, nickel, iron and/or copper in the form of a skeleton interwoven with a continuous metallic network of an alloy or intermetallic compound of cerium with aluminum, nickel, iron and/or copper, as described in EP-A-0 257 708. When used as electrode substrates, these materials have promise, particularly those based on cerium and aluminum because - ~
W090/10735 2 0 3 ~ 7 8-8 PCT/EP90/003~
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even if they corrode, this does not lead to corrosion p~oducts that contaminate the electrowon aluminum.
Nevertheless corrosion of the substrate remains a problem.
US Patent 4 374 050 discloses inert electrodes for aluminum production fabricated from at least two metals or metal compounds to provide a combination metal compound.
For example, an alloy of two or more metals can be surface oxidised to form an oxycompound of the metals at the surface on an unoxidised alloy substrate. US Patent 4 374 761 discloses similar compositions further comprisin~ a dispersed metal powder in compositions which may be applied as a preformed o~ide composition on a metal substrate by cladding or plasma spraying, Such application techniques, however, are known to involve many drawbacks and the adhesion is particularly poor. US Patent 4 620 905 describes an oxidised alloy electrode based on tin or copper with nickel, iron silver, zinc, magnesium, aluminum and yttrium, either as a cermet or partially oxidised at its surface. Such partially oxidised alloys suffer serious disadvantages in that the oxide layers formed are far too porous to o~ygen, and not sufficiently stable in corrosive environments. In addition, at high temperatures the partially oxidised structures continue to oxidize and this uncontrolled oxidation causes subsequent segregation of the metal and/or oxide layer. Adherence at the ceramic-metal interfaces is particularly difficult to achieve and this very problem has hampered use of such simple composites. Finally, none of these matesials has proven satisfactory as substrate for cerium oxyfluoride coatings of the type discussed.
Improved metal-based substrates are described in European Patent Applications 88201957.3, 88201851.8, 88201852.6, 88201a53.4 and 882018S4.2 all as yet ...... ., ... . , , ................................ j, ,... . .. . :,., ........ , . - , . .. , ~;.- . .
WO90/10735 2 0 ~ ~ 7 8 8 PCT/EP90/003~
,s unpublished. These typically include a substrate made of an alloy of chromium with nickel, cobalt and/or iron. On the surface of the substrate is a chromium oxide film on top o~ which is a layer of copper oxide in solid solution with nickel or manganese, o~tained by oxidising a layer of nickel/copper or manganese/copper which is applied eg by electroplating. It was also mentioned that the nickel oxide in the surface layer may have its electrical conductivity improved by doping with lithium.
Such composite layers nevertheless remain difficult to prepare and although they have demonstrated superior performance over previous anodes, considerable development is still required to optimize their lifetime and reduce the production cost.
The aforementioned European Patent Application 88201854.2, mentions further embodiments of ceramic intermediate layers which in use serve as anchorage for the in-situ maintained protective coating of cerium oxyfluoride to the metal substrate, these intermediate layers including: nickel ferrite; copper oxide and nickel ferrite; doped, non-stoichiometric and partially substituted ceramic oxide spinels containing combinations of divalent nickel, cobalt, magnesium, manganese, copper and zinc with divalent/trivalent nickel, cobalt, manganese and/or iron, and optionally dopants selected from Ti4+, z 4+ Sn4+ Fe4+ Hf4+, Mn4+, Fe , Ni C 3+ Mn3+ A13+ Cr3+, Fe2+, Ni , Co M92+, Mn2+, Cu2~, zn2 and Li (see US patent No. 4 552 630); as well as coatings based on rare earth oxides and oxyfluorides, in particular pre-applied cerium oxyfluoride alone or in combination with other components.
To date, very little progress has been made with .. . .
.
WO90/10735 2 ~ 3 0 7 8 8 PCTtEP9OfO03~
~"~,, .
anode substrates made of ceramic electroconductive oxycompounds. The most widely tested materials in this category on account of their acceptable conductivity have been based on tin dioxide. However, it has not yet been possible to make an adequate electrode substrate based on tin dioxide despite expedients devised to reduce the amount of substrate material dissolved in the electrolyte.
See for example EP-A-O 257 709 (E00208) which proposed doping the oxyfluoride coating with tantalum to render it more impervious and thereby reduce contamination of the electrolyte and the electrowon aluminum with tin from the substrate.
SUMMARY OF THE INvENTION
An object of the invention is to provide electrode substrates based on electroconductive oxycompounds which can be produced easily, have excellent conductivity and perform well as anode substrates when coated with an oxyfluoride-type coating.
The invention is based on the realization that sintered copper-n~ckel oxide suitably doped with lithium oxide to enhance conductivity fulfills the sought-after requirements of a material for the anode substrate.
According to the invention, an anode for electrowinning a metal from a molten salt electrolyte, comprising an electroconductive oxycompound substrate which in use carries a surface coating comprising at least one rare earth oxycompound, is characterized in that the substrate comprises a sintered body composed of a nickel-copper-lithium oxide solid solution.
., . ~
.: .. : : , :
WO90/10735 2 0 3 0 7 8 8 PC~/EP90/00364 Preferably, the nickel oxide is present in the solid solution in an amcunt of at least 70 mol%, the copper oxide is present in an amount of at most 29 mol% and the iithium oxide is present in an amount of at most 10mol%.
Preferably still, the solid solution contains 70-90 mol%
nickel oxide, 5-29 mol% copper oxide and 1-10 mol% lithium oxide. The concentration the lithium dopant preferably ranges from 1 to 10 atom % with an optimum value at about 5 atom %, this usually in combination with about 70-80 mol~ nickel oxide and about 20-25 mol% copper oxide.
It has been shown that a concentration of 1 to 5 atom% lithium increases the conductivity of the (Ni-Cu)O
solid solution by two orders of magnitude, up to about 200(ohm cm) 1 at 1000C. This makes the material an attractive substrate material for cerium oxyfluoride coatings for aluminum electrowinning.
A method of preparing an anode substrate according to the invention comprises mixing powders of nickel oxide, copper oxide and a compound of lithium, firing at 900~1100C, cooling, grinding, cold pressing and sintering at 1000-1300C for 30-40 hours. Shapes of lithium doped (Ni-Cu)O solid solution can thus conveniently be prepared by mixing powders of Li(,~O3), Li2CO3 or LioH; CuO;
and NiO in the right proportions and firing for example at 900-1050C in air for about 24 hours at a heating rate of about 100C/hour. After cooling, the material is ground, cold pressed (eg at 10 tons/cm2) and sintered at 1000-1300C e.g. 1100-1150C for 30-40 hours. The resulting sintered material shows a density of at least 70% theoretical density, typically 80%, and an electrical conductivity of about 150 (ohm cm) 1 at 980C compared to 1 (ohm cm) 1 for the undoped (Ni-Cu)o. A sintered .. ., ~- . . ..
b WO90/10735 - 7 -- PCT/EP9~00364 ~ t,' '.,", ~ ' specimen of such composition was tested as an anode substrate in a neutral cryolite containing l.5% CeF3 and l.S Ta2O5. A very den~e tantalum-doped cerium oxyfluoride coating was obtained. No noticeable change in the substrate composition near the interface was observed.
The process may be optimized to improve dens~f;cation by hot pressing and/or the addition of sintering aids.
The anode substrate according to the invention can be used as a massive body supporting the rare earth oxycompound coating. But it can, if desired, incorporate a metal or other current collector to assist the supply of electric current and facilitate connection to the power supp ly .
It has been observed that using the anode substrate according to the invention in a cryolite melt containing dissolved alumina and cerium species produces very dense, adherent and homogeneous cerium-oxyfluoride coatings. This is believed to be related to the presence of copper oxide in the substrate surface and to the surface porosity of the sintered material. The rare earth oxide coating may be cerium o~yfluoride alone or preferably may be cerium oxyfluoride together with at least one compound of tatalum, niobium, yttrium, lanthanum, praesodymium and other rare earth elements.
The invention also provides a method of eletrowinning aluminum from molten cryolite containing alumina wherein an anode is immersed, the anode having an eletroconductive oxycompound substrate carying a surface coating comprising at least one rare earth oxycompound, the surface coating being maintained by the presence of cerium species in the molten cryolite, the method comprising passing electrolysis current between the anode and a cathode to evolve oxygen and to maintain the surface coating at the anode and to produce aluminum at the cathode.
The invention will be further illustrated by the following Example.
.
.
::, `: ~ - . ' ', ' W090/10735 2 0 3 0 7 8 ~ PCT/FP90/0036~
ExamPle A Li.o5Ni.70Cu.25O sample was prepared using powder metallurgy techniques: Li(NO3), CuO and NiO
powders were mixed in the right proportions and fired at 1000C in air for 24 hours. The heating rate was 100C/hour. After cooling the specimen was powdered, cold pressed at 10 tons/cm2 and sintered for 35 hours at llS0C. The microstructure of the resulting sample showed a porosity of nearly 20% and CuO precipitates at the grain boundaries due to the slow cooling rate. A typical SEM-EDX
analysis over a window of about 0.25 mm2 gave nickel 71.0 atom% and copper 28.6 atom~, whereas for individual grains the composition was: nickel 76.6 atom% and copper 23.2 atom%. This analytical method is not suitable for detecting the lithium.
An ingot with a surface area of 7.~ cm was prepared from this sample and exposed for 5 hours in a neutral cryolitic bath of 900g containing 1.5% of Ta2O; and 6g (i.e. about 0.7%) CeF3. Using a current density of 200 mA/cm , a dense tantalum-doped cerium oxyfluoride coating was formed on the substrate at a rate ranging from 0.15 to 0.16 g/cm per hour. EDX analysis revealed that the concentration of nickel and copper did not significantly change during the cerium oxyfluoride deposition: 70 and 30 atom% for nickel and copper respectively for a window analysis; 76 atom% nickel and 23 atom~ copper for a grain analysis. This stability of the composition of the sample is an indication of the protective role of the deposit for the cryolite in the previously mentioned conditions. The relative stability of the potential during the deposition may be related to the conductivity of the substrate which is strongly dependant on the lithium concentration.
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-- . , .
Claims (10)
1. An anode for electrowinning a metal from a molten salt electrolyte, comprising an electroconductive oxycompound substrate which in use carries a surface coating comprising at least one rare earth oxycompound, characterized in that the substrate comprises a sintered body composed of a nickel-copper-lithium oxide solid solution.
2. The anode of claim 1, wherein the nickel oxide is present in the solid solution in an amount of at least 70mol%, the copper oxide is present in an amount of at most 29mol% and the lithium oxide is present in an amount of at most 10mol%.
3. The anode of claim 2, wherein the solid solution contains 70-90 mol% nickel oxide, 5-29 mol% copper oxide and 1-10 mol% lithium oxide.
4. The coating of claim 3, wherein the solid solution contains about 70-80 mol% nickel oxide, about 20-25 mol%
copper oxide and about 5 mol% lithium oxide.
copper oxide and about 5 mol% lithium oxide.
5. The anode of any preceding claim, wherein the substrate is coated with a surface coating comprising cerium oxyfluoride.
6. The anode of claim 5, wherein the surface coating further comprises at least one compound of tantalum, niobium, yttrium, lanthanum, praesodymium and other rare earth elements.
7. A method of preparing the anode substrate of an anode according to any preceding claim, comprising mixing powders of nickel oxide, copper oxide and a compound of lithium, firing at 900-1100°C, cooling, grinding, cold pressing, and sintering at 1000-1300°C for 30-40 hours.
8. A method of electrowinning aluminum from molten cryolite containing alumina, characterized by using an anode as claimed in any one of claims 1-7.
9. The method of claim 8, wherein a surface coating comprising cerium oxyfluoride is maintained on the anode by the presence of cerium species in the molten cryolite.
10. A method of eletrowinning aluminum from molten cryolite containing alumina wherein an anode is immersed, the anode having an eletroconductive oxycompound substrate carying a surface coating comprising at least one rare earth oxycompound, the surface coating being maintained by the presence of cerium species in the molten cryolite, the method comprising passing electrolysis current between the anode and a cathode to evolve oxygen and to maintain the surface coating at the anode and to produce aluminum at the cathode.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| EP89810175.3 | 1989-03-07 | ||
| EP89810175 | 1989-03-07 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2030788A1 true CA2030788A1 (en) | 1990-09-08 |
Family
ID=8203133
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002030788A Abandoned CA2030788A1 (en) | 1989-03-07 | 1990-03-06 | Anode substrate coated with rare earth oxycompounds |
Country Status (8)
| Country | Link |
|---|---|
| EP (1) | EP0422142B1 (en) |
| AT (1) | ATE123079T1 (en) |
| AU (1) | AU622000B2 (en) |
| CA (1) | CA2030788A1 (en) |
| DE (1) | DE69019664T2 (en) |
| ES (1) | ES2072427T3 (en) |
| NO (1) | NO910306D0 (en) |
| WO (1) | WO1990010735A1 (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1994024321A1 (en) * | 1993-04-19 | 1994-10-27 | Moltech Invent S.A. | Micropyretically-produced components of aluminium production cells |
| JPH10158017A (en) * | 1996-11-29 | 1998-06-16 | Sharp Corp | Lithium-nickel-multiple oxide, its production and its use |
| CN101915073B (en) * | 2010-08-03 | 2012-08-15 | 江西稀有金属钨业控股集团有限公司 | In situ leaching injection process |
| CN109811368B (en) * | 2019-03-20 | 2021-03-16 | 武汉大学 | Lithium ion enhanced inert anode for molten salt electrolysis system and preparation method thereof |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB8301001D0 (en) * | 1983-01-14 | 1983-02-16 | Eltech Syst Ltd | Molten salt electrowinning method |
| DE3685760T2 (en) * | 1985-02-18 | 1993-05-19 | Moltech Invent Sa | METHOD FOR PRODUCING ALUMINUM, CELL FOR PRODUCING ALUMINUM AND ANODE FOR ELECTROLYSIS OF ALUMINUM. |
| EP0203884B1 (en) * | 1985-05-17 | 1989-12-06 | MOLTECH Invent S.A. | Dimensionally stable anode for molten salt electrowinning and method of electrolysis |
| JPS62284095A (en) * | 1986-06-02 | 1987-12-09 | Permelec Electrode Ltd | Durable electrolytic electrode and its production |
| WO1989001991A1 (en) * | 1987-09-02 | 1989-03-09 | Moltech Invent S.A. | A ceramic/metal composite material |
-
1990
- 1990-03-06 WO PCT/EP1990/000364 patent/WO1990010735A1/en active IP Right Grant
- 1990-03-06 EP EP90904311A patent/EP0422142B1/en not_active Expired - Lifetime
- 1990-03-06 DE DE69019664T patent/DE69019664T2/en not_active Expired - Fee Related
- 1990-03-06 ES ES90904311T patent/ES2072427T3/en not_active Expired - Lifetime
- 1990-03-06 AU AU51803/90A patent/AU622000B2/en not_active Ceased
- 1990-03-06 CA CA002030788A patent/CA2030788A1/en not_active Abandoned
- 1990-03-06 AT AT90904311T patent/ATE123079T1/en active
-
1991
- 1991-01-25 NO NO910306A patent/NO910306D0/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| EP0422142B1 (en) | 1995-05-24 |
| AU622000B2 (en) | 1992-03-26 |
| DE69019664D1 (en) | 1995-06-29 |
| NO910306L (en) | 1991-01-25 |
| AU5180390A (en) | 1990-10-09 |
| NO910306D0 (en) | 1991-01-25 |
| ATE123079T1 (en) | 1995-06-15 |
| WO1990010735A1 (en) | 1990-09-20 |
| ES2072427T3 (en) | 1995-07-16 |
| DE69019664T2 (en) | 1995-09-21 |
| EP0422142A1 (en) | 1991-04-17 |
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