METAL ELECTROWINNING ANODE AND ELECTROWINNING METHOD

Abstract

An electrowinning system is provided that is capable of suppressing accumulation of a side reaction product on an anode and a rise of an electrolysis voltage caused thereby, and an electrowinning method is provided using the system. To solve this problem, the electrowinning system of the present invention applies predetermined electrolysis current between an anode and a cathode placed in an electrolyte, thereby depositing a desired metal on the cathode, in which the electrolyte is a sulfuric acid-based or chloride-based solution containing ions of the metal, and the anode has a catalytic layer, containing amorphous iridium oxide or amorphous ruthenium oxide, formed on a conductive substrate.

Claims

1. A nickel electrowinning method comprising: contacting an anode with a chloride-based electrolyte containing nickel ions; and extracting nickel from the electrolyte, wherein the anode comprises a conductive substrate and a catalytic layer formed on the conductive substrate, and the catalytic layer is a composite oxide of amorphous ruthenium oxide and amorphous titanium oxide.

2. The nickel electrowinning method according to claim 1, wherein the anode further comprises an intermediate layer made of tantalum or a tantalum alloy, and the intermediate layer is formed between the conductive substrate and the catalytic layer.

3. The nickel electrowinning method according to claim 1, wherein the catalytic layer is a composite oxide of 25 to 35 at. % of amorphous ruthenium oxide in terms of metal and 75 to 65 at. % of amorphous titanium oxide in terms of metal.

4. The nickel electrowinning method according to claim 2, wherein the catalytic layer is a composite oxide of 25 to 35 at. % of amorphous ruthenium oxide in terms of metal and 75 to 65 at. % of amorphous titanium oxide in terms of metal.

5. The nickel electrowinning method according to claim 1, further comprising: forming a cathode along with the anode, wherein the cathode comprises a zinc plate.

6. A nickel electrowinning method comprising: contacting an anode with a chloride-based electrolyte containing nickel ions; and extracting nickel from the electrolyte, wherein the anode comprises a conductive substrate and a catalytic layer formed on the conductive substrate, and the catalytic layer is a composite oxide of completely amorphous ruthenium oxide and completely amorphous titanium oxide.

7. The nickel electrowinning method of claim 6, wherein the catalytic layer consists of only completely amorphous ruthenium oxide and completely amorphous titanium oxide.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] FIG. 1 is a graph for electrolysis voltage where zinc electrowinning is carried out using electrowinning systems according to Example 1, Comparative Example 1, and Comparative Example 2.

MODE FOR CARRYING OUT THE INVENTION

[0048] While the present invention will be described in detail below by way of Examples and Comparative Examples, the present invention is not limited to the following examples.

[Zinc Electrowinning Using Sulfuric Acid-Based Electrolyte]

Example 1

[0049] In Example 1, zinc electrowinning was carried out using an electrowinning system, which included a sulfuric acid-based electrolyte containing zinc ions, an electrowinning anode (hereinafter, simply referred to as an “anode”) having a catalytic layer, containing amorphous iridium oxide, formed on a conductive substrate, and a cathode placed in the electrolyte along with the anode.

[0050] In anode production, initially, a commercially available titanium plate (5 cm long, 1 cm wide, 1 mm thick) was dipped and etched in a 10% oxalic acid solution at 90° C. for 60 minutes, and then washed with water and dried. A coating solution was prepared by adding iridium chloride acid hexahydrate (H.sub.2IrCl.sub.6.6H.sub.2O) and tantalum chloride (TaCl.sub.5) to a butanol (n-C.sub.4H.sub.9OH) solution containing 6 vol. % concentrated hydrochloric acid, such that the molar ratio of iridium to tantalum was 80:20 and a total amount of iridium and tantalum was 70 mg/mL in terms of metal. The coating solution was applied to the dried titanium plate and then dried at 120° C. for 10 minutes before thermal decomposition for 20 minutes in an electric furnace maintained at 360° C. The coating, drying and thermal decomposition was repeated five times in total, thereby producing an anode having a catalytic layer formed on the titanium plate, which acted as a conductive substrate.

[0051] The anode was structurally analyzed by X-ray diffraction, resulting in an X-ray diffraction pattern with no diffraction peak profile corresponding to either IrO.sub.2 or Ta.sub.2O.sub.5. That is, the catalytic layer of the anode was formed of amorphous iridium oxide and amorphous tantalum oxide.

[0052] A zinc plate (2 cm×2 cm) was used as the cathode, and the electrolyte used was a sulfuric acid-based electrolyte obtained by dissolving 0.8 mol/L ZnSO.sub.4 in distilled water and adjusting the pH to −1.1 with sulfuric acid. Moreover, the anode was embedded in a polytetrafluoroethylene holder, so that the electrode area to be contacted with the electrolyte was regulated to 1 cm.sup.2.

[0053] The anode and the cathode were placed in the electrolyte so as to oppose each other at a predetermined inter-electrode distance. Then, an inter-terminal voltage (electrolysis voltage) between the anode and the cathode was measured while carrying out zinc electrowinning in which electrolysis current with current densities of 10 mA/cm.sup.2, 50 mA/cm.sup.2, and 100 mA/cm.sup.2 based on the electrode area of the anode was applied between the anode and the cathode.

Comparative Example 1

[0054] In Comparative Example 1, zinc electrowinning was carried out using the same electrowinning system as in Example 1 under the same conditions as in Example 1 except that the thermal decomposition temperature at which to form the catalytic layer was changed from 360° C. to 470° C.

[0055] The anode according to Comparative Example 1 was structurally analyzed by X-ray diffraction, the result being that a sharp diffraction peak profile corresponding to IrO.sub.2 was recognized but any diffraction peak profile corresponding to Ta.sub.2O.sub.5 was not recognized. That is, the catalytic layer of the anode was made of crystalline iridium oxide and amorphous tantalum oxide.

Comparative Example 2

[0056] In Comparative Example 2, zinc electrowinning was carried out using the same electrowinning system as in Example 1 under the same conditions as in Example 1 except that a commercially available Pb—Sb (5% Sb) alloy electrode was used as the anode.

[0057] Where the electrowinning systems according to Example 1, Comparative Example 1, and Comparative Example 2 were used in zinc electrowinning with the electrolyte temperature at 30° C., the electrolysis voltage was as shown in FIG. 1 for each system. In addition, the electrolysis voltage at three minutes after the start of electrolysis was shown in Table 1.

TABLE-US-00001 TABLE 1 Difference (Improvement) In Electrolytic Electrolysis Voltage Electrolysis Voltage Current Comp. Comp. Comp. Comp. Density Ex. 1 Ex. 1 Ex. 2 Ex. 1-Ex. 1 Ex. 2-Ex. 1 10 mA/cm.sup.2 2.37 V 2.49 V 2.91 V 0.12 V 0.54 V 50 mA/cm.sup.2 2.49 V 2.67 V 3.07 V 0.18 V 0.58 V 100 mA/cm.sup.2 2.62 V 2.82 V 3.20 V 0.20 V 0.58 V

[0058] As shown in Table 1, the electrolysis voltage was 0.12V to 0.20V lower in Example 1, where the catalytic layer containing amorphous iridium oxide was used, than in Comparative Example 1, where the catalytic layer containing crystalline iridium oxide was used. Moreover, the electrolysis voltage was even 0.54V to 0.58V lower in Example 1 than in Comparative Example 2, where the commercially available Pb—Sb alloy electrode was used as the anode. That is, the electrowinning system according to Example 1 of the present invention succeeded in significantly reducing power consumption for electrolysis.

[0059] Furthermore, similar experiments were conducted where the electrolyte temperature was changed to 40° C., 50° C., and 60° C. The results are shown in Table 2 (40° C.), Table 3 (50° C.), and Table 4 (60° C.).

TABLE-US-00002 TABLE 2 Difference (Improvement) Electrolytic Electrolysis Voltage In Electrolysis Voltage Current Comp. Comp. Comp. Comp. Density Ex. 1 Ex. 1 Ex. 2 Ex. 1-Ex. 1 Ex. 2-Ex. 1 10 mA/cm.sup.2 2.34 V 2.46 V 2.86 V 0.12 V 0.52 V 50 mA/cm.sup.2 2.46 V 2.62 V 3.01 V 0.16 V 0.55 V 100 mA/cm.sup.2 2.57 V 2.76 V 3.12 V 0.19 V 0.55 V

TABLE-US-00003 TABLE 3 Difference (Improvement) In Electrolytic Electrolysis Voltage Electrolysis Voltage Current Comp. Comp. Comp. Comp. Density Ex. 1 Ex. 1 Ex. 2 Ex. 1-Ex. 1 Ex. 2-Ex. 1 10 mA/cm.sup.2 2.32 V 2.43 V 2.82 V 0.11 V 0.50 V 50 mA/cm.sup.2 2.43 V 2.58 V 2.96 V 0.15 V 0.53 V 100 mA/cm.sup.2 2.53 V 2.71 V 3.06 V 0.18 V 0.53 V

TABLE-US-00004 TABLE 4 Difference (Improvement) In Electrolytic Electrolysis Voltage Electrolysis Voltage Current Comp. Comp. Comp. Comp. Density Ex. 1 Ex. 1 Ex. 2 Ex. 1-Ex. 1 Ex. 2-Ex. 1 10 mA/cm.sup.2 2.29 V 2.41 V 2.77 V 0.12 V 0.48 V 50 mA/cm.sup.2 2.40 V 2.55 V 2.91 V 0.15 V 0.51 V 100 mA/cm.sup.2 2.49 V 2.66 V 3.03 V 0.17 V 0.54 V

[0060] As shown in Tables 2 to 4, the electrolysis voltage was 0.11V to 0.19V lower in Example 1, where the catalytic layer containing amorphous iridium oxide was used, than in Comparative Example 1, where the catalytic layer, containing crystalline iridium oxide, was used. Moreover, the electrolysis voltage was even 0.48V to 0.55V lower in Example 1 than in Comparative Example 2, where the commercially available Pb—Sb alloy electrode was used as the anode. That is, the electrowinning system according to Example 1 of the present invention succeeded in significantly reducing power consumption for electrolysis as well for the case where the electrolyte temperature was in the range from 40° C. to 60° C.

[Cobalt Electrowinning Using Sulfuric Acid-Based Electrolyte]

Example 2

[0061] In Example 2, cobalt electrowinning was carried out using an electrowinning system, which included a sulfuric acid-based electrolyte containing cobalt ions, an anode having a catalytic layer, containing amorphous iridium oxide, formed on a conductive substrate, and a cathode placed in the electrolyte along with the anode.

[0062] The present example used the same anode as in Example 1, i.e., an anode which had a catalytic layer, containing amorphous iridium oxide, formed on a titanium plate and whose electrode area for acting on electrolysis was regulated to 1 cm.sup.2. Moreover, a cobalt plate (2 cm×2 cm) was used as the cathode, and the electrolyte used was a sulfuric acid-based electrolyte obtained by dissolving 0.3 mol/L CoSO.sub.4 in distilled water and adjusting the pH to 2.9 with sulfuric acid.

Comparative Example 3

[0063] Comparative Example 3 used the same anode as in Comparative Example 1, i.e., an anode which had a catalytic layer, containing crystalline iridium oxide, formed on a titanium plate and whose electrode area for acting on electrolysis was regulated to 1 cm.sup.2. Other than that, the same electrowinning system as in Example 2 was used for cobalt electrowinning.

Comparative Example 4

[0064] In Comparative Example 4, the same electrowinning system as in Example 2 was used for cobalt electrowinning, except that a commercially available Pb—Sb alloy electrode (5% Sb) was used as the anode.

[0065] Where the electrowinning systems according to Example 2, Comparative Example 3, and Comparative Example 4 were used in cobalt electrowinning with electrolysis current having a current density of 10 mA/cm.sup.2 based on the electrode area of the anode and the electrolyte temperature at 40° C., the electrolysis voltage at three minutes after the start of electrolysis was as shown in the following table.

TABLE-US-00005 TABLE 5 Difference (Improvement) In Electrolysis Electrolytic Electrolysis Voltage Voltage Current Comp. Comp. Comp. Comp. Density Ex. 2 Ex. 3 Ex. 4 Ex. 3-Ex. 2 Ex. 4-Ex. 2 10 mA/cm.sup.2 1.91 V 2.01 V 2.08 V 0.10 V 0.17 V

[0066] As shown in Table 5, the electrolysis voltage was 0.10V lower in Example 2, where the catalytic layer containing amorphous iridium oxide was used, than in Comparative Example 3, where the catalytic layer containing crystalline iridium oxide was used, and also 0.17V lower in Example 2 than in Comparative Example 4, where the commercially available Pb—Sb alloy electrode was used as the anode. That is, also in cobalt electrowinning using a sulfuric acid-based electrolyte, the electrowinning system according to Example 2 of the present invention succeeded in significantly reducing power consumption for electrolysis.

[Nickel Electrowinning Using Chloride-Based Electrolyte]

Example 3

[0067] In Example 3, nickel electrowinning was carried out using an electrowinning system, which included a chloride-based electrolyte containing nickel ions, an anode having a catalytic layer, containing amorphous iridium oxide, formed on a conductive substrate, and a cathode placed in the electrolyte along with the anode.

[0068] The present example used the same anode as in Example 1, i.e., an anode which had a catalytic layer, containing amorphous iridium oxide, formed on a titanium plate and whose electrode area for acting on electrolysis was regulated to 1 cm.sup.2. Moreover, a nickel plate (2 cm×2 cm) was used as the cathode, and the electrolyte used was a chloride-based electrolyte obtained by dissolving 0.08 mol/L NiCl.sub.2 in a 0.5 mol/L HCl aqueous solution.

Comparative Example 5

[0069] Comparative Example 5 used the same anode as in Comparative Example 1, i.e., an anode which had a catalytic layer, containing crystalline iridium oxide, formed on a titanium plate and whose electrode area for acting on electrolysis was regulated to 1 cm.sup.2. Other than that, the same electrowinning system as in Example 3 was used for nickel electrowinning.

Comparative Example 6

[0070] In Comparative Example 6, the same electrowinning system as in Example 3 was used for nickel electrowinning, except that a commercially available Pb—Sb alloy electrode (5% Sb) was used as the anode.

[0071] Where the electrowinning systems according to Example 3, Comparative Example 5, and Comparative Example 6 were used in nickel electrowinning with electrolysis current having a current density of 10 mA/cm.sup.2 based on the electrode area of the anode and the electrolyte temperature at 40° C., the electrolysis voltage at three minutes after the start of electrolysis was as shown in the following table.

TABLE-US-00006 TABLE 6 Difference (Improvement) In Electrolysis Electrolytic Electrolysis Voltage Voltage Current Comp. Comp. Comp. Comp. Density Ex. 3 Ex. 5 Ex. 6 Ex. 5-Ex. 3 Ex. 6-Ex. 3 10 mA/cm.sup.2 1.76 V 1.82 V 2.75 V 0.06 V 0.99 V

[0072] As shown in Table 6, the electrolysis voltage was 0.06V lower in Example 3, where the catalytic layer containing amorphous iridium oxide was used, than in Comparative Example 5, where the catalytic layer containing crystalline iridium oxide was used, and also even 0.99V lower in Example 3 than in Comparative Example 6, where the commercially available Pb—Sb alloy electrode was used as the anode. That is, also in nickel electrowinning using a chloride-based electrolyte, the electrowinning system according to Example 3 of the present invention succeeded in significantly reducing power consumption for electrolysis.

[Cobalt Electrowinning Using Chloride-Based Electrolyte]

Example 4

[0073] In Example 4, cobalt electrowinning was carried out using an electrowinning system, which included a chloride-based electrolyte containing cobalt ions, an anode having a catalytic layer, containing amorphous ruthenium oxide, formed on a conductive substrate, and a cathode placed in the electrolyte along with the anode.

[0074] In anode production, initially, a commercially available titanium plate (5 cm long, 1 cm wide, 1 mm thick) was dipped and etched in a 10% oxalic acid solution at 90° C. for 60 minutes, and then washed with water and dried. A coating solution was prepared by adding ruthenium chloride trihydrate (RuCl.sub.3.3H.sub.3O) and titanium n-butoxide (Ti(C.sub.4H.sub.9O).sub.4) to a butanol (n-C.sub.4H.sub.9OH) solution, such that the molar ratio of ruthenium to titanium was 30:70 and a total amount of ruthenium and titanium was 70 mg/mL in terms of metal. The coating solution was applied to the dried titanium plate and then dried at 120° C. for 10 minutes before thermal decomposition for 20 minutes in an electric furnace maintained at 340° C. The coating, drying and thermal decomposition was repeated five times in total, thereby producing an anode having a catalytic layer formed on the titanium plate, which acted as a conductive substrate.

[0075] The anode was structurally analyzed by X-ray diffraction, resulting in an X-ray diffraction pattern with no diffraction peak profile corresponding to RuO.sub.2, but a weak diffraction line in a broadened pattern corresponding to a RuO.sub.2—TiO.sub.2 solid solution was recognized. That is, the catalytic layer of the anode was made of a composite oxide of amorphous ruthenium oxide and titanium oxide.

[0076] A platinum plate (2 cm×2 cm) was used as the cathode, and the electrolyte used was a chloride-based electrolyte obtained by dissolving 0.9 mol/L CoCl.sub.2 in distilled water and adjusting the pH to 1.6 with hydrochloric acid. Moreover, the anode was embedded in a polytetrafluoroethylene holder, so that the electrode area for acting on electrolysis was regulated to 1 cm.sup.2.

[0077] The anode and the cathode were placed in the electrolyte so as to oppose each other at a predetermined inter-electrode distance. Then, cobalt electrowinning was carried out for 40 minutes with electrolysis current having a current density of 10 mA/cm.sup.2 based on the electrode area of the anode and the electrolyte temperature at 60° C.

Comparative Example 7

[0078] In Comparative Example 7, cobalt electrowinning was carried out using the same electrowinning system as in Example 4 except that the thermal decomposition temperature at which to form the catalytic layer was changed from 340° C. to 450° C.

[0079] The anode according to Comparative Example 7 was structurally analyzed by X-ray diffraction, resulting in an X-ray diffraction pattern in which a sharp diffraction peak profile corresponding to a solid solution (composite oxide) of crystalline RuO.sub.2 and TiO.sub.2 was recognized. That is, the catalytic layer of the anode contained crystalline ruthenium oxide but did not contain amorphous ruthenium oxide.

[0080] On the basis of the weight of the anodes before and after electrolysis for cobalt electrowinning with the electrowinning systems according to Example 4 and

[0081] Comparative Example 7, the weight of cobalt oxyhydroxide deposited on the anodes was calculated, and the percentage of the quantity of electrolytic electricity (hereinafter, simply referred to as current efficiency) consumed for generating cobalt oxyhydroxide was calculated. The results are shown in the following table.

TABLE-US-00007 TABLE 7 Electrolytic Current Efficiency Current Comp. Density Ex. 4 Ex. 7 10 mA/cm.sup.2 8.3% 24%

[0082] As shown in Table 7, in Example 4, where the catalytic layer containing amorphous ruthenium oxide was used, the current efficiency was about ⅓ of that in Comparative Example 7, where the catalytic layer containing crystalline ruthenium oxide was used. Specifically, in Example 4, most of the electrolysis current (90% or more) was consumed for chlorine evolution, the main reaction, resulting in a considerable reduction of power required for electrowinning of the same amount of cobalt. Moreover, in Example 4, cobalt oxyhydroxide was kept from being accumulated on the anode, thereby suppressing a rise of the electrolysis voltage while electrowinning was continued for a long period of time.

[Other (Variants)]

[0083] While the electrowinning anode according to the present invention has been described above with respect to preferred embodiments, the present invention is not limited to these configurations, and numerous types of variants are conceivable.

[0084] For example, amorphous tantalum oxide can be omitted from the catalytic layers of the electrowinning anodes according to Examples 1 to 3, so long as amorphous iridium oxide is at least included. However, from the viewpoint of reducing oxygen evolution potential or increasing durability, the catalytic layers preferably include both amorphous iridium oxide and amorphous tantalum oxide.

[0085] Similarly, titanium oxide can be omitted from the catalytic layer of the electrowinning anode according to Example 4, so long as amorphous ruthenium oxide is at least included.

[0086] Furthermore, the catalytic layers of the electrowinning anodes according to Examples 1 to 3 may be formed on protective layers, containing crystalline iridium oxide, formed on the conductive substrates. In the case where a metal such as titanium or tantalum is used as the conductive substrates, the protective layers containing crystalline iridium oxide adhere well to the conductive substrates, and also to the catalytic layers, so that the catalytic layers can be more stably formed on the conductive substrates, resulting in enhanced durability. Particularly suitable for such a protective layer is a mixed oxide layer made of crystalline iridium oxide and amorphous tantalum oxide.

[0087] Similarly, in order to achieve enhanced durability, the catalytic layer of the electrowinning anode according to Example 4 may be formed on a protective layer, containing crystalline ruthenium oxide, formed on the conductive substrate. Particularly suitable for such a protective layer is a composite oxide layer made of crystalline ruthenium oxide and titanium oxide.

[0088] Furthermore, in the case where the current density of the electrolysis current is increased to 0.1 A/cm.sup.2 or more, an intermediate layer made of tantalum or a tantalum alloy is preferably formed between the conductive substrate and the catalytic layer. Forming the intermediate layer makes it possible to prevent the conductive substrate from being oxidized and corroded by an acidic electrolyte penetrating through the catalytic layer, resulting in improved durability of the anode. The intermediate layer can be formed by methods such as sputtering, ion plating, CVD, electroplating, etc.

[0089] Furthermore, zinc, cobalt, and nickel electrowon in the examples are illustrative, and the electrowinning anode and the electrowinning method according to the present invention can electrowin noble metals, rare metals, and other metals.