JPH0578879A - Metallic anode for electrolytic acid solution containing fluoride or fluoroaniline complex - Google Patents

Abstract

PURPOSE: To provide a low cost anode having excellent resistance against oxygen, generated at the time of electrolytically recovering a metal from a metallic compound solution containing an anionic fluorocomplex and a free fluoride, with low electrolytic potential small in power consumption as a natural consequence and having excellent catalytic property to the generation of oxygen.

CONSTITUTION: In the anode containing a metallic matrix capable of being passivated, an electrode catalytic compound and at least one of an additive, the electrode catalytic compound is selected from a group containing cobalt, cerium dioxide and tin oxide.

COPYRIGHT: (C)1993,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION Electrolytes containing anionic fluoro complexes are commonly used in the general art of electrolytically recovering metals such as lead, tin and chromium. In the particular case of recovering lead from battery scrap, the scrap is leached with an acidic solution containing tetrafluoroborate BF ₄ ⁻ and hexafluorosilicate SiF ₆ ═. By electrolysis of these solutions, lead is obtained as a solid precipitate, so that the electrolytic cell does not require a diaphragm and has an extremely simple structure. However, this advantage has traditionally been offset by the little resistance of the substrate to the attack of the anionic anionic fluoro complex of the oxygen generating anode. In addition, parasitic reactions can occur with galvanic precipitation of the metal with the formation of lead dioxide which reduces lead, thus reducing the overall efficiency of the system.

[0002]

When the prior art is carefully considered, for example, U.S. Pat. Nos. 3,985,630 and 4,135,9.
No. 97, No. 4,230,545, No. 4,272,
No. 340, No. 4,460, 442, No. 4,83
4,851 and Italian Patent Application No. 67723A /
No. 82 taught. That is, the following can be concluded.

Anodes coated with lead dioxide or made of carbon or graphite alone are known in the art,
It exhibits a rather limited active life in the range of 100 hours due to the oxidizing action of oxygen evolution. It is clear that this adds to the maintenance costs of replacing the anode, as well as the attendant costs associated with the consequential production losses: -Anodes made of titanium coated with lead dioxide, platinum, or platinum group metal oxides. Is far less than carbon or graphite, but is still corroded,
In each case, it is not sufficient to offset the high construction costs, and the anode made of tantalum coated with platinum metal or metal oxide has a much longer life than titanium, but is extremely expensive to manufacture, The parasitic reaction of lead dioxide deposition on any type of anode can be prevented by the addition of suitable inhibitors to the leach solution, such as phosphoric acid, antimonic acid or arsenic acid. However, the required amount may impair the denseness of the lead metal deposit. This problem is overcome by aiding the anode with a coating made of platinum group metals or metal oxides and at least one element from the group of arsenic, antimony, bismuth, tin. In this case, a remarkably small amount of inhibitor is required to prevent the anodic deposition of lead dioxide and the deterioration of the lead deposit formed is eliminated.

[0004]

As described above, the prior art is a feature necessary for a wide range of industrial applications (10).
It is clear that it does not result in an anode that gives a low cost as well as a long life (> 00 hours).

The present invention is of low cost, excellent resistance to the aggressive condition of oxygen evolution in solutions containing even anionic fluorocomplexes and even free fluorides, and a low electrolysis potential which necessarily consumes less energy. It is possible to overcome the drawbacks of the prior art by providing an anode characterized by good catalytic properties for oxygen evolution.

[0006]

The anode of the present invention facilitates oxygen evolution by forming one or more metals or metal alloys that can be passivated by forming a protective layer of oxide or oxyfluoride. It comprises a matrix made of one or more compounds of suitable elements which are capable of being encapsulated in the matrix or applied to the matrix in the form of an outer coating. The anode is suitable for use in electrometallurgical processes to deposit lead, tin, chromium from solutions containing fluorocomplex anions such as tetrafluoroborate and hexafluorosilicate or free fluoride.

The present invention also provides an electrolysis method for recovering metals in a battery provided with an acidic solution containing an anionic fluoro complex such as tetrafluoroborate and hexafluorosilicate and a metal ion, which comprises an anode and a cathode. Included, in which case the anode is of the type described above.

The following discussion considers the particular case of electrolytic recovery of lead for simplicity. In this method, the leach solution to be electrolyzed has the following composition:

-Tetrafluoroboric acid, HBF ₄ , or hexafluorosilicic acid, H ₂ SiF ₆ : 40-240 g
/ L; -Dissolved lead: 40-80 g / l; -Temperature: 15-35 ° C; -Current density (for anode and cathode): 150-2
000 A / m ² .

Electrolysis occurs between the anode and the cathode and involves the following reactions.

[0011] - cathode: Pb ^{++ (complex)} + 2e - ---> Pb (dense metal) - ^{_{anode: H 2 O-2e - ---}} > 2H + +1/2 O 2 ( main reaction) Pb ^{+ + _{(complex) + 2H 2 O-2e -}} ---> PbO 2 + 4H + ( parasitic reactions) suitable anode elements: titanium, niobium, tantalum, tungsten, or alloys thereof, for example - titanium - palladium (Pd 0.2 %),-Titanium-nickel (Ni 0.5-1.5%);-titanium-yttrium-titanium-tantalum (Ta 0.5-5.0%)-titanium-niobium (Nb 0.5-5. 0%)-Titanium-Tungsten (W 0.5-5.0%)-Copper-Tantalum (niobium);-Titanium-Tantalum (niobium); Further, sintering elemental powder or in a suitable mold. By melting and pouring into The resulting nickel-copper alloy is readily passivated on contact with the solution, i.e. when the copper content is in the range 2.5 to 30%, more preferably 5 to 20%. It was surprising that it was found to be coated with a protective layer of oxide or oxyfluoride insoluble fluoride.

The low electrical conductivity of the protective film formed on the above metals results in high potentials and thus high energy consumption in the lead recovery process.

When using tungsten and nickel-copper alloys, dispersing the appropriate elements in the metal matrix significantly reduces the oxygen evolution potential, making energy consumption practically acceptable for lead-producing industrial applications. Is allowed to reach.

Suitable compounds for nickel-copper anodes are Nb ₂ O ₅ (1-5%), NiO (0.5-2).
_{%), Pr 6 O 11 (} 0.5-2%), CuO (0.5-
2%) added cerium oxide (CeO ₂ ) and Sb ₂
O ₃ (0.5-4%) and CuO (0.5-2%) added tin dioxide (SnO ₂ ); while for tungsten-based anodes optionally small amounts of iron and nickel (1- 2%) mixed cobalt (5-35%),
Addition of copper, palladium and cerium makes it more positive.

Similar results have been obtained with the alternative that the metal matrix is provided with a coating exhibiting electrocatalytic performance against oxygen evolution, chemical stability and possibly limited vacancies to ensure that it provides sufficient protection against the metal matrix. It can also be obtained by applying.

In the case of tungsten and nickel-copper alloys, a suitable coating is obtained with cerium oxide and tin oxide as described above as dispersion in a metal matrix. Similarly for other alloys, a suitable coating may be used as an electrocatalyst for oxygen evolution to prevent possible parasitic reactions, such as tungsten or other metals of group VIB (70-99%), cobalt (1%).
-30%) and a suitable additive (0.5-2%) selected from the group consisting of nickel, palladium, cerium and copper, or optionally a mixture of said metals. The test results showed that this must be done.

The following examples illustrate various aspects of the present invention, but do not limit the invention thereto.

[0018]

【Example】

[0019]

EXAMPLE 1 Monostatic side compression method starting with 8 powder rods of 20 mm diameter and 100 mm length made of nickel-copper alloys of different composition starting with elemental powder (1-10 microns). (About 250
kg / cm ² ), and further in an inert atmosphere at 950-1150 ° C. for 6-12 hours (preferably 9
Following the next heat treatment at 80 to 1080 ° C. for 8 to 10 hours), in air at 900 to 1300 ° C. for 100 to 600 hours (970 to 100% if the copper content is more than 10 to 15%).
The second oxidation treatment was performed at 1000 ° C. for 300 to 400 hours). At the same time, three control samples were prepared as follows.

-1 is a 400 type and the other is a K500 type industrial Monel ^(R) , which is oxidized under the conditions used for the sample obtained by sintering, and has a diameter of 20 mm and a length of 10
10 made of technical graphite coated with beta PbO ₂ precipitate obtained by galvanic precipitation from two 0 mm rod-nitrate baths 10
One sheet of × 100 × 1 mm.

Sintered rods and control samples were tested as anodes in electrolysis from fluorobolic solutions, a typical electrolyte used to recover metallic lead from battery scrap.

The operating conditions and test results are shown in Tables 1.1 and 1.2 below.

[0023]

[Table 1.1]

[0024]

[Table 1.2] The following considerations can be derived from the above results.

-Oxygen evolution on beta PbO ₂ is 400
2.07 at a current density of 1000 to 1000 A / m ^2.
It occurs at a potential (PO) that occupies 2.24 volts from volts. Any material with a corrosion potential (PC) lower than these values is characterized by instability (propensity to dissolve). The different potentials indicate the reference standard hydrogen electrode (NHE).

Materials with a copper content of 5 to 20% are stable under oxygen evolution.

Similar materials obtained by molding with cast wax rather than sintering exhibited similar behavior.

[0028]

Example 2 Diameter 20 m made of sintered nickel-copper alloy
Twelve m, 100 mm long rods were prepared by the method described in Example 1, but with the addition of a tin oxide and cerium oxide based preforming powder (pigment). Electrolysis conditions and anode potential, V (NHE) of hydrogen generation at 1000 A / m ² after 300 hours,
The test results, expressed in terms of% cathodic induced current efficiency calculated based on lead, and stability / instability of the material under corrosion are shown in Tables 2.1 and 2.2.

[0029]

[Table 2.1]

[0030]

[Table 2.2] The following conclusions are drawn from the results obtained for the Ni-Cu alloys.

Tin dioxide: -Corrosion on SnO ₂ without additives-When operated with oxygen evolution on SnO ₂ with Sb ₂ O ₃ , there is no visible corrosion after 300 hours of operation. Anodic corrosion on without additive CeO ₂ - - cerium dioxide for CeO ₂ including additives, if to ° operated while generating oxygen, corrosion visible after actuation 3 00 hours is absent - electrocatalytic activity following CeO ₂ <CeO ₂ + Ta ₂ O ₅ <CeO ₂ + Ta ₂ O ₅ + N
iO <CeO ₂ + Ta ₂ O ₅ + NiO + Pr ₆ O ₁₁ Similar results were obtained with a Ni-Cu structure having the same composition as the particles used for the dispersion surrounded by the electrocatalytic coating and surrounded by the matrix. Can be obtained when applied by thermal decomposition of paints containing suitable precursors. It can also be pointed out that the addition of only 2 g / l of phosphoric acid ensures a cathode induced current efficiency of 100%, which means that no lead dioxide is produced at the anode.

[0032]

Example 3 Diameter of 20 mm made of nickel-copper alloy
4 rods 100 mm in length with tin oxide and /
Or cerium oxide powder (diameter 40-60 microns)
It was obtained by pouring the component metals together. The sample was tested as an anode for electrolysis of fluorobolic solutions by the conditions and methods described in Example 2. The results are shown in Table 3.1.

[0033]

[Table 3.1] The samples listed in Table 3.1 were also Cu _{20 (10)} -Ni
_The metallic structure made of _{80 (90)} does not cause any visible corrosion when used as an oxygen generating anode after addition of SnO ₂ or CeO ₂ with additives.

[0034]

EXAMPLE 4 Fifteen industrial tungsten rods containing various contents of cobalt, nickel and iron were used as an anode for oxygen generation in the electrolysis of a fluorobolic solution as shown in Example 2. The test results are shown in Table 4.1.
Shown in.

[0035]

[Table 4.1] The following conclusions are drawn from these results.

-Tungsten is stable when used as an anode in fluorobolic solutions (passivation) -Small amounts of elements like Co, Ni, Fe function electrocatalytically for oxygen evolution- The series show that the electrocatalytic activity increases in the following order: Fe <Ni <Co <Co + Ni + Fe-The limiting concentration threshold for each additive or mixture thereof is the value at which the passivation or corrosion phenomenon occurs. Similar results can be obtained by applying an electrocatalytic coating as shown in Example 2 to the tungsten structures found to exceed.

[0037]

Example 5 A rod 6 having a diameter of 20 mm and a length of 100 mm
The following labels are attached to the individual pieces, and the second embodiment, No. Sample 1 as in Example 6, Example 2, No. Sample 2 as No. 12 Example 3, No. Sample 3 as in Example 3, Example 3, No. Sample 4 as in Example 4, Example 4, No. Sample 5 as in Example 4, Example 4, No. Sample 6 such as 11 was used as an anode for electrolysis of a fluorosilicic solution containing lead ions and phosphoric acid.

The electrolysis conditions are shown in Table 5.1.

[0039]

[Table 5.1] The test results are shown in Table 5.2.

[0040]

[Table 5.2]

[0041]

Example 6 Six anodes having a passivable metal matrix and tungsten and cobalt based coatings were prepared, and four more anodes were also tested as described below. 100 × 10 × of pure titanium for industrial use
1mm sheet-shaped anode is sandblasted,
Samples 1-3 were further chemically pickled in boiling 20% HCl. All samples were then coated with various coatings and tested under the same conditions as given in Example 2. Anode description and test results are given in Table 6.1.
And 6.2.

[0042]

[Table 6.1]

[0043]

[Table 6.2] Conventional coatings on titanium such as valve metals, precious metals (eg P
t) and noble metal oxides stabilized with lead dioxide (beta PbO ₂ ) (eg RuO ₂ and IrO ₂ ) are mechanical (PbO ₂ ) and / or chemical (PbO ₂ ) even after tens of hours.
t, IrO ₂ , RuO ₂ ) is unstable, with the consequent corrosion of the remaining uncoated substrate part. The tungsten-based coating was passivated after a few minutes. The cobalt-based coating corroded after a few hours, but the tungsten-cobalt-based coating with a cobalt content of approximately 10% showed neither corrosion nor passivation. A lower cobalt content does not prevent the passivation effect of tungsten from prevailing over time, whereas a higher cobalt content reveals dissolution which causes mechanical instability of the residual coating.

[0044]

Example 7 Fifteen industrial 10 × 10 × 1 mm sheets of pure titanium were used for corindone (pressure: 7 atm; distance of spray pistol from substrate: 30).
-35 cm; Abrasive particles: irregular shape, acute angle, average particle size about 300 micron), followed by plasma jet or thermospray coating with tungsten and cobalt coatings containing nickel, palladium and copper as doping elements. The sample thus obtained was used as an anode in the electrolysis of a lead tetrafluoroborate solution under the same conditions as shown in Example 2. The characteristics of the anode are shown in Table 7.1 and the relevant results are shown in Table 7.1.
2 shows.

[0045]

[Table 7.1]

[0046]

[Table 7.2] From the test results, it can be said that the lowest amount of nickel, palladium, copper (1-1.5%) in the possible combinations improves the chemical and electrochemical stability of the coating. The optimum concentration for each additive was determined within the range of 1-1.5% corresponding to the best performance. The presence of the above concentrations of nickel, copper and palladium renders the anodic leaching of cobalt no longer occurring or, in any case, significantly reduces it. Complex existence of the above elements, for example 1-
Ni + Pd or Ni + Cu up to 1.5% stabilize the operating potential. This effect is particularly pronounced when the coating is applied by thermospray.

[0047]

Example 8 Seventeen sheets (100 × 10 × 1 mm) made of industrial titanium and titanium alloy were prepared by the method shown in Example 7, and W + Co, W + Co + Ni, W + Co + N were prepared by the plasma or thermospray method.
i + Pd, W + Co + Ni + Cu based precipitates were coated. The sample was tested as an anode in the electrolysis conditions set forth in Example 2, except that the anode current density was doubled (200
0 A / m ² ). The properties of the samples are shown in Table 8.1, while the test results are shown in Table 8.2.

[0048]

[Table 8.1]

[0049]

[Table 8.2] The following considerations are obtained from the results obtained at 2000 A / m ² .

Titanium structures that come into contact with the electrolyte by accident due to chemical or mechanical desorption of the coating are significantly corroded. This negative behavior is less significant in the case of ternary or quaternary precipitates, since these precipitates are more dense, especially when obtained by the thermospray method.

-Titanium-Yttrium (Y 0.35
%) Samples show similar behavior compared to technical titanium samples with identical coatings-titanium-palladium (Pd 0.20%) and titanium-nickel (Ni 1.5%) samples have excellent stability. Indicates. Corrosion is minor as can be seen from the stable anodic potential over time: the actual increase in potential is an indication of passivation of the coating, whereas a decrease in potential indicates corrosion of the substrate.

[0052]

Example 9 Five sheets (100 × 10 × 1 mm) made of titanium, tantalum, niobium, tungsten, and a nickel (90%)-copper (10%) alloy were used as shown in Example 7. After treatment, W (89) + Co (10) + Ni (0.5) + Pd applied by plasma jet
Coated with (0.5) coating. The sample is Example 8.
It was tested as an anode in the electrolysis of a lead tetrafluoroborate solution under the same conditions as shown in. The test results are shown in Table 9. The cathode deposition efficiency of lead was 100%.

[0053]

[Table 9.1] The following conclusions are derived from the test results.

If the substrate is made of tantalum, tungsten or a Ni (90) -Cu (10) alloy, good stability and a constant anodic potential of the coating applied to the substrate are experienced.

The titanium substrate is unstable and the anodic potential of the coating drops rapidly over time.

In the case of niobium substrates, the anode potential drops slightly with time and an intermediate situation is experienced.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Antonio Nidra 20100 Milan, Via Fuarneteti 5 (72) Inventor Carlo Traini Italy 20100 Milan, Via Pisani Dotushi 31 (72) Inventor Urderico Nebosi Italy 20100 Milan, Via Paradani 5

Claims (18)

[Claims] 1. Oxygen is generated from a solution containing a fluoride or anionic fluoro complex such as tetrafluoroborate and hexafluorosilicate,
In an anode comprising a passivable metal matrix and an electrocatalytic compound, containing at least one additive, said electrocatalytic compound being selected in the group comprising cobalt, cerium dioxide or tin oxide. An anode characterized by. 2. The anode according to claim 1, wherein the electrocatalytic compound comprises cobalt and at least one selected from the group of nickel, copper, iron, palladium and cerium. 3. The anode according to claim 1, wherein the electrocatalytic compound comprises cerium dioxide and at least one selected from the group consisting of niobium oxide, nickel oxide, praseodymium oxide and copper oxide. 4. The anode according to claim 1, wherein the electrocatalytic compound comprises at least one selected from the group consisting of tin oxide and antimony oxide or copper oxide. 5. At least the outer metal matrix is tungsten, tantalum, niobium, titanium,
2. The anode according to claim 1, characterized in that it is made of their alloys or alloys thereof with palladium, nickel, yttrium and nickel-copper alloys whose nickel content accounts for 5 to 20%. 6. The anode according to claim 1, wherein the electrocatalytic compound is present as an alloy or dispersion in the metal matrix. 7. The anode of claim 1, wherein the electrocatalytic compound is in the form of a coating applied to the metal matrix. 8. The metal matrix comprises tungsten, and the electrocatalytic compound comprises at least one selected from the group consisting of cobalt and nickel, copper, iron, palladium, cerium. 6
Anode. 9. The anode according to claim 5, wherein the concentration of tungsten in the metal matrix is 70 to 99% by weight. 10. The cobalt concentration is 1 to 30% by weight.
The anode of claim 8, wherein the anode comprises 11. The anode according to claim 8, wherein the concentration of the additive is 0.5 to 2% by weight. 12. The metal matrix is 5 to 2
Comprising a nickel-copper alloy having a copper content of 0% by weight,
And the electrocatalytic compound comprises cerium dioxide doped with at least one oxide selected from niobium oxide, nickel oxide, praseodymium oxide, copper oxide itself or mixtures thereof. anode. 13. The metal matrix comprises a nickel-copper alloy having a tungsten or copper content of 5 to 20% by weight, and the coating comprises, as the electrocatalytic compound, niobium oxide, nickel oxide, praseodymium oxide, 8. The anode of claim 7, comprising cerium dioxide containing at least one additive selected from the group of copper oxides or mixtures thereof. 14. The metal matrix comprises a nickel-copper alloy having a tungsten or copper content of 5 to 20% by weight, and the coating comprises, as the electrocatalytic compound, antimony oxide or copper oxide or a mixture thereof. 8. The anode of claim 7, comprising tin dioxide containing at least one additive selected from the mixture. 15. The metal matrix is 5 to 2
Including a nickel-copper alloy having a copper content of 0% by weight,
And the coating as the electrocatalytic compound,
8. The anode of claim 7, comprising tungsten and cobalt containing at least one additive selected from the group nickel, copper, iron, palladium, cerium. 16. A method for electrolytic recovery of metal carried out in a battery, comprising an anode and a cathode, and supplied with a solution containing a metal ion and a fluoride or anionic fluoro complex, wherein the anode is described in any one of claims 1 to 15. The method is characterized in that it is an anode. 17. The method of claim 16, wherein the metal is lead. 18. The method of claim 17, wherein up to 2 grams of phosphoric acid per liter is added to the solution.