JP5804920B2 - Electrolytic extraction of metals - Google Patents

Description

  The present invention relates to a metal electrowinning method.

  In copper electrolytic refining, when a direct current is passed through a pair of electrodes immersed in an electrolytic solution, copper is eluted from the anode side by electrolysis, and copper is deposited on the cathode side. On the other hand, copper is chemically eluted from the anode by sulfuric acid or the like in the electrolytic solution, and the copper concentration in the electrolytic solution gradually increases. For this reason, in order to adjust the copper concentration of the electrolytic solution, electrolytic collection, extraction of copper sulfate crystals, bleed-off, and the like are performed.

Electrolytic sampling uses an electrode that is insoluble in the anode, typically lead alloys (Pb-Sb, Pb-Ca-Sn), and uses the following chemical formula to generate oxygen on the anode side and cathode side during decopperization electrolysis. Then, copper is collect | recovered from electrolyte solution by copper precipitation.
Anode: H ₂ O = 1 / 2O ₂ + 2H ⁺ + 2e ⁻
Cathode: Cu ²⁺ + 2e ⁻ = Cu
(Cathode: CuSO ₄ + 2H ⁺ + 2e ⁻ = Cu + H ₂ SO ₄ )

  In the copper removal electrolysis process, when recovering the copper electrodeposits deposited on the cathode plate, the power supply is switched from the copper removal electrolytic cell to the bypass circuit, the electrolytic cell is in a power failure state, the electrodeposited cathode plate is pulled out, and a new cathode Insert the plate and resume the supply of power into the electrolytic cell.

  Various studies have been made on the problems caused by the operation at the time of power recovery of such copper removal electrolysis. For example, Patent Document 1 discloses electrolysis in electrolytic refining of copper by the permanent cathode method. During a planned blackout at the refinery, the current flowing to the electrolytic cell from the main rectifier permanently installed in the electrolytic refinery is gently dropped, and then the power is cut off at a low current by the auxiliary rectifier attached to the electrolytic refinery. An invention relating to a method for electrolytic purification of copper, which is characterized by energizing until recovery, is disclosed. And according to this, in the permanent cathode (PC) type copper electrolytic refining factory, it is described that the situation where it is difficult to peel off can be avoided as much as possible by thin film electrodeposition of the outer layer of electric copper that can be done after the planned power outage. Yes.

  Also, in Patent Document 2, an electrolytic refinery factory that performs electrolytic purification of copper by the PC method is scheduled for blackout, and after periodic inspection, power is returned to the normal operating value to restore the current flowing through the copper electrolytic purification tank, and electrolytic purification is performed. In the copper electrolytic refining method for restarting the process, an invention relating to a copper electrolytic refining method is disclosed, wherein the power recovery is performed by an operation of increasing the current value in two or more stages. And according to this, it is described that it is possible to avoid a situation in which it is difficult to strip the electrodeposited copper after a planned power outage in a permanent cathode (PC) type copper electrolytic refining factory.

JP 2008-248273 A JP 2009-256742 A

In the conventional electrowinning method, when the current is increased to the value at the time of operation at the time of power recovery after a power failure (310 mA / m ^{2 in} about 1 minute), when a lead alloy is used for the anode, this lead alloy electrode There is a problem that the surface layer mainly composed of lead sulfate formed on the surface layer is peeled off and the life of the lead electrode is reduced. In this regard, the conventional electrowinning method is not a sufficient solution to such a problem.

  Accordingly, an object of the present invention is to realize a long life of an electrode in a metal electrowinning method.

  As a result of intensive studies to solve the above problems, the present inventor has gradually increased the voltage supplied to the electrolytic cell while adjusting the amount of oxygen gas generated on the anode surface from the start of current supply. For example, when the anode is formed of a lead alloy, lead sulfate on the lead alloy electrode surface is gradually changed to lead oxide, and the lead sulfate layer is prevented from peeling into the electrolyte due to a sudden increase in potential. I found out that I can.

The present invention completed based on the above knowledge, in one aspect, gradually increases the voltage supplied to the electrolytic cell while adjusting the amount of oxygen gas generated from the start of current supply to the electrolytic solution in the electrolytic cell. Thus, there is provided a metal electrowinning method including a step of performing electrolysis for electrowinning the metal in the electrolytic solution .

  In one embodiment of the metal electrowinning method according to the present invention, the electrolysis is electrolysis at the start of power recovery after the electrolysis operation is stopped.

  In another embodiment of the metal electrowinning method according to the present invention, the voltage at the start of supply is temporarily held at a potential lower than the electrolysis potential of water, and then the power is restored stepwise.

In still another embodiment of the metal electrowinning method according to the present invention, the electrolytic solution is a sulfuric acid electrolytic solution, and the anode used for electrolysis is a lead alloy .

  According to the present invention, it is possible to extend the life of an electrode in a metal electrowinning method.

The state which arranged the some copper removal electrolysis tank in series is shown. The state which arranged the some copper removal electrolysis tank in series is shown. The state which arranged the some copper removal electrolysis tank in series is shown. Non-Patent Document 1 (J. Urban; Journal of electrochemical society, vol. 106, No. 5, (1959), 369-376) is a conceptual diagram of an anode oxide layer on a lead anode in a sulfuric acid bath. is there. The energization conditions of the copper removal electrolysis of Example 1 are shown. The energization conditions for the copper removal electrolysis of Comparative Example 1 are shown.

  Hereinafter, an embodiment of a metal electrowinning method according to the present invention will be described by taking copper removal electrolysis as an example.

  A general procedure for copper removal electrolysis will be described. An electrolytic solution similar to the electrolytic purification of copper is supplied to the copper removal electrolytic cell. The electrolytic solution is generally sulfuric acid acid, and the copper concentration is, for example, 30 to 60 g / L. A cathode (cathode) plate and an anode (anode) plate are installed in the copper removal electrolytic cell. In general, cathode plates and anodes are alternately arranged in one copper removal electrolytic cell. As shown in FIGS. 1-1 to 1-3, a plurality of copper removal electrolytic cells 11 can be arranged in series. Before the start of copper removal electrolysis, as shown in FIG. 1C, the bypass circuit switch 15 is closed, and the current to the electrodeposition copper electrolysis tank is short-circuited. When the bypass circuit switch 15 was opened and energization to the copper removal electrolytic cell 11 was started, electricity flowed through the copper removal electrolytic cell 11 and dissolved in the electrolytic solution 14 as shown in FIG. The copper component is electrodeposited on the cathode plate 13. When the energization is continued and the electrodeposited copper grows to a predetermined thickness, the supply of current is stopped once, the cathode plate 13 is pulled up from the electrolytic cell 11, the electrodeposited copper is recovered, and is replaced with a new cathode plate 13. When replacing the cathode plate 13, the circuit is short-circuited again before the cathode plate 13 is pulled up to prevent an electric shock, and the state returns to the state shown in FIG. While the cathode plate 13 is replaced, the state shown in FIG. 1-2 is established, and the copper removal electrolytic cell 11 is insulated. A new cathode plate 13 is inserted into the decoppering electrolytic cell 11 to be in the state shown in FIG. 1-3 again, and then energization is repeated. When the arrangement of the new cathode plate 13 is completed, there is a case where the whole power is temporarily cut off in the state shown in FIG.

In the conventional copper removal electrolysis using, for example, a Pb—Sb, Pb—Ca—Sn alloy as the anode and a copper seed plate as the cathode, the following is shown when energized (state shown in FIG. 1-1). Reaction occurs, oxygen is generated by electrolysis of water at the anode, and copper is deposited at the cathode.
Anode: H ₂ O → 1 / 2O ₂ + 2H ⁺ + 2e ⁻
Cathode: CuSO ₄ + 2e ⁻ → Cu + SO ₄ ²⁻
Further, the following reaction occurs before the cathode is pulled up and before energization (the state shown in FIG. 1-3), and a reaction occurs in which copper is eluted from the cathode into the electrolytic solution.
Anode: PbO ₂ + 4H ⁺ + SO ₄ ²⁻ + 2e ⁻ → PbSO ₄ + 2H ₂ O
Cathode: Cu + SO ₄ ²⁻ → CuSO ₄ + 2e ⁻

In such decopperization electrolysis, when energization (recovery) after stopping the operation is increased to the operation voltage at once (for example, 310 mA / m ² , 2.0 V in about 1 minute), the surface of the lead anode There was a problem that the surface layer mainly composed of lead sulfate formed in the layer peeled off and the life of the lead anode was reduced. Here, the present inventor paid attention to the correspondence between the anode oxide layer on the lead anode and the anode potential during electrolysis, thereby solving the above problem. Specifically, Non-Patent Document 1 (J. Urban; Journal of electrochemical society, vol. 106, no. 5, (1959), 369-376) and the lead anode in the sulfuric acid bath described in the document. Attention was paid to the conceptual diagram (FIG. 2) of the anode oxide layer. As shown in FIG. 2, the surface layer is gradually formed on the lead anode from the start of energization, and the form of the surface layer varies depending on the supplied potential. Specifically, the lead anode plate immersed in the electrolytic cell reacts with the sulfuric acid solution to form an insulating layer of lead sulfate on the surface layer. At the start of energization, a thick PbSO ₄ insulator is formed. As the potential increases, the ratio of the insulator gradually decreases as PbO.PbSO ₄ → Pb (OH) ₂ → PbO _t . Here, oxygen gas is always generated from PbO, Pb (OH) ₂ , PbO _t, etc. existing between the lead anode and the insulator layer (PbSO ₄ ) in the surface layer. It was found that when the electric potential was increased at the start of energization, the amount of oxygen gas increased at a stretch, and the insulating layer (PbSO ₄ ), which was the outermost layer, was peeled off, thereby reducing the life of the lead anode. . Therefore, by performing electrolysis by gradually increasing the current supplied to the electrolytic cell while adjusting the amount of oxygen gas generated from the start of current supply to the electrolytic solution in the electrolytic cell, the lead anode It is possible to extend the life of the lead anode by satisfactorily suppressing the peeling of the surface layer.

It is preferable that the voltage at the start of supply is once held at a potential lower than the electrolysis potential of water, and then the power is restored stepwise. As shown in FIG. 2, since the amount of oxygen gas generated increases from a potential equal to or higher than the electrolysis potential of water, it is maintained at a low potential until then and gradually changed from PbSO ₄ → PbO. The surface layer can be favorably suppressed. More specifically, the holding potential at this time is equal to or higher than the potential at which PbSO ₄ changes to PbO and is equal to or lower than the potential at which oxygen is not generated by water splitting. Regarding the numerical value of the holding potential and the holding time, although it depends on the concentration and scale of the electrolytic solution in the electrolytic cell, it is preferably 1.0 to 1.5 V for 10 minutes or more, and 1.5 to 2.0 V to 10 Power is restored step by step in more than minutes

  The oxygen generation amount can be adjusted visually or with an oxygen concentration measuring device. Specifically, it is performed visually. Oxygen generation leads to peeling of the surface layer of the lead anode. Thus, by gradually increasing the supply current while adjusting the amount of oxygen generated from the start of current supply, the peeling of the surface layer can be satisfactorily suppressed. it can.

  Although there is no restriction | limiting in particular as a material of an anode, The alloy containing lead and antimony or the alloy containing lead, calcium, and tin can be used. Lead alloys are preferred because they are inexpensive and readily available and do not contaminate the electrolyte. An insoluble anode (a titanium material coated with iridium oxide) or the like may be used.

  The cathode material is not particularly limited, but titanium or stainless steel is generally used because it is insoluble in the electrolytic solution, and stainless steel is preferably used because of its high potential. The stainless steel is not particularly limited, and any of martensitic stainless steel, ferritic stainless steel, austenitic stainless steel, austenitic / ferrite duplex stainless steel, and precipitation hardened stainless steel may be used.

  Typically, the metal electrowinning method according to the present invention is applied to copper removal electrolysis, but is not limited thereto. For example, in SX-EW, dearsenic electrolysis, production of electrolytic copper powder, and production of electrolytic copper foil. The present invention is applicable to the case of use, and in the present invention, these processes are also included in the concept of electrowinning.

  Next, examples of the present invention will be described. In addition, a present Example is an example to the last, and is not restrict | limited to this example. That is, all aspects or modifications other than the embodiments are included within the scope of the technical idea of the present invention.

(Example 1)
Copper removal electrolysis was performed under the following conditions.
(1) Electrolyte used for copper electrolytic purification Capacity: 7000L
Composition (Cu): 45 g / L (liquid supply side), 35 g / L (drainage side)
Composition (free sulfuric acid): 170 g / L (liquid supply side), 180 to 185 g / L (drainage side)
Liquid temperature: 55-70 degreeC
(2) Decoppering electrolytic cell Three decoppering electrolytic cells were arranged in series. Each electrolytic cell is made of 56 stainless steel (SUS316L) permanent cathode plates (vertical × horizontal × thickness = 1 m × 1 m × 3 mm), and Pb—Ca—Sn alloy (Ca (0.1 mass%), Sn (0%)). .5 mass%)) insoluble anode plates (length × width × thickness = 1 m × 1 m × 10 mm) were alternately charged.
(3) Energization conditions Table 1 and FIG. 3 show the current, current density, voltage, and energization time applied to the electrolytic cell. The amount of oxygen generated during energization at this time was visually adjusted.
(4) Result As a result, by increasing the current value stepwise, the voltage increases stepwise without showing a steep high voltage value (overshoot) due to voltage application to the insulating layer immediately after application. The surface properties of the lead anode were good. Further, the amount of lead stripped from the lead anode was examined by a change in the weight of the lead anode plate before and after use, and the lead stripping from the lead anode surface was reduced to about ½ of the conventional amount.

(Comparative Example 1)
Copper removal electrolysis was performed under the same conditions as in Example 1 except for the energization conditions. As the energization conditions of Comparative Example 1, as shown in FIG. 4, the current density was applied from 80 to 300 A / m ² at a stroke in 2 minutes.
As a result, the voltage after applying the current increased from 2.5 V to 5.5 V at a stretch, and stabilized at 2.1 V over about 30 minutes. This rapid increase in voltage was applied to the insulating layer formed on the lead anode surface at once, the voltage increased rapidly (overshoot), and oxygen gas was suddenly generated from the vicinity of the lead anode surface. As a result, a portion where the thin film was peeled off from the surface of the lead anode was observed.

(Example 2)
57 lead anodes (volume: 1020 mm × 90 mm × 11 mm) in the electrolytic solution were prepared, and copper removal electrolysis was conducted for one year under the conditions of Example 1 to evaluate the use of the lead anode. The lead anode had an initial thickness of 11 mm and a final thickness of 3 mm. As a result of one year of use, the amount of lead in the lead cage was 1162 kg.
As a result, it was confirmed by the following formula that the service life of the lead anode, which was normally about 2 years, was 4.1 years.
Initial lead electrode weight: anode plate volume (1020 mm × 90 mm × 11 mm) × anode plate density (11.34 mg / mm ³ ) × number of anode plates (57) = 6527 kg
Usable amount: initial lead electrode weight (6527 kg) × thickness ((11 mm−3 mm) / 11 mm) = 4747 kg
Life evaluation: Usable amount (4747 kg) / Lead amount in lead pad (1162 kg) = 4.1 years

11 Decopper electrolytic bath 12 Anode plate 13 Cathode plate 14 Electrolyte 15 Bypass circuit switch

Claims (4)

To electrolyze the metal in the electrolytic solution by gradually increasing the voltage supplied to the electrolytic cell while adjusting the amount of oxygen gas generated from the start of current supply to the electrolytic solution in the electrolytic cell electrowinning method of the metal comprising the step of performing electrolysis of.   The method of electrowinning a metal according to claim 1, wherein the electrolysis is electrolysis at the start of power recovery after the electrolysis operation is stopped.   The metal electrowinning method according to claim 2, wherein the voltage at the start of supply is temporarily held at a potential lower than the electrolysis potential of water, and then the power is recovered stepwise. The method for electrowinning a metal according to any one of claims 1 to 3, wherein the electrolytic solution is a sulfuric acid electrolytic solution, and the anode used for electrolysis is a lead alloy.