JP6877007B2 - Operation method of copper electrorefining - Google Patents

Description

The present invention relates to an operation management method for predicting the occurrence of passivation in copper electrorefining.

In industrial electrolytic purification of copper, an anode plate made of blister copper produced in a dry process of copper smelting (hereinafter referred to as an anode) is placed in an electrolytic cell filled with an electrolytic solution containing copper sulfate as a main component. ) And a cathode plate made of copper, stainless steel, titanium, etc. (hereinafter referred to as a cathode) are alternately arranged so as to face each other at regular intervals, and are energized.

By this energization, the copper contained in the anode is eluted as copper ions in the electrolytic solution on the anode side, while the copper ions are electrodeposited on the cathode. At this time, an anode slime in the form of a single substance or a compound is formed on the surface of the anode without elution from the anode like gold, silver or lead, and the thing that peels off from the anode and deposits on the bottom of the tank, such as nickel, from the anode. It takes various forms, such as those that elute but do not precipitate on the cathode, and those that partially elute from the anode and sink to the bottom of the tank, such as antimony and bismuth.

However, on the surface of the above-mentioned anode, a phenomenon called passivation may occur in which a layer called a passivation film is sometimes formed to make it difficult for current to flow. When this passivation occurs, normal electrolytic operation becomes difficult, such as when current does not flow or the voltage rises, and there arises a problem that the productivity of copper is greatly reduced.

The above passivation film is seemingly similar in that it has a blackish color like the anode slime, but the normal anode slime has good electrolyte permeability and peels off from the anode as appropriate, so to speak, it "metabolizes". The difference is that the passivation film "sticks" to the surface of the anode, blocking both the electrolyte and the flow of current.

There are various possible causes for this passivation, but one of the phenomena is that copper sulfate crystals are often deposited on the surface of the copper anode.
Various factors can be considered as factors for forming copper sulfate crystals. For example, the temperature of the electrolyte drops, the diffusion on the anode surface is insufficient due to insufficient convection of the electrolyte in the electrolytic cell, the current density at the anode increases, the copper ion concentration in the electrolyte increases excessively, or in the electrolyte. There is also an increase in the concentration of free sulfate ions in the copper anode, an increase in impurities contained in the copper anode, and a densification of the structure of the anode slime layer adhering to the surface of the copper anode.
It is presumed that these are complexly entangled and the copper eluted from the anode is restricted from diffusing into the electrolytic solution as ions, resulting in supersaturation and precipitation of copper sulfate crystals to form a passivation film.

Various methods have been proposed as measures to prevent passivation. However, the method of relaxing the electrolysis conditions under the condition that passivation is less likely to occur is often the same as the direction in which the productivity decreases, which is not a very preferable method and there are many industrial restrictions.
For example, when the current density is lowered, passivation is less likely to occur, but on the other hand, the productivity is lowered because the amount of copper produced per hour is lowered. Further, if the impurity grade in the copper anode is reduced, passivation is less likely to occur, but on the other hand, even if the impurity grade is reduced, there are restrictions due to the ore situation and economic efficiency of the raw material.
As described above, the measures that can be taken to avoid the influence of passivation at the actual production site are limited, and it has not been easy to completely suppress the occurrence of passivation.

On the other hand, there are also measures to avoid the influence by removing the generated passivation film. For example, the anode can be lifted from the electrolytic cell, the electrolytic solution can be temporarily removed from the electrolytic cell, and water can be sprayed onto the surface of the anode or physically peeled off by brushing, or a large current can be applied at one time to peel off the anode. There are methods and so on. However, the former requires a great deal of labor, and the latter has a problem that the stripped passivation film is caught in the cathode and increases the impurity grade in the electrolytic copper of the product.
Therefore, it has been desired to predict the occurrence of passivation and take measures before the passivation film is formed.

In industrial copper electrorefining, electricity is applied by a constant current density, the so-called constant current method. When passivation occurs, it becomes difficult for current to flow, so it is controlled to apply a large voltage in an attempt to pass the same current. Therefore, it has been practiced to detect the occurrence of a passivation film by measuring the voltage of the electrolytic cell (tank voltage).

However, when passivation occurs, the rise in tank voltage is exponential with respect to elapsed time and rises sharply. Therefore, even if an increase in the tank voltage is detected, the countermeasures cannot catch up and passivation often occurs.
Specifically, one electrolytic refining is usually carried out over a period of about 1 week to 10 days, but an increase in voltage is often confirmed after the 4th day, and from the time when it is confirmed. Since the passivation occurs in earnest in one day or several hours, even if various measures are taken, the passivation occurs before the effect is confirmed.

Therefore, instead of the actual electrolytic cell at the production site, a small beaker-level electrolytic cell is installed separately, and the occurrence of passivation and the characteristics of the generated passivation film are evaluated using an electrochemical method. It has been tried.
For example, in the method as seen in Patent Document 1, a voltage is applied so that the anode potential is 50 mV to 200 mV noble than the immersion potential, and the time during which the current value rapidly increases is measured on the stainless steel surface. This is a method for evaluating the stability of the resulting passivation film.
Using such a method, it is possible to predict the occurrence of anode passivation in copper electrorefining.

When trying to predict the passivation of the anode in copper electrorefining, it is necessary to measure the sharp decrease in the current value due to the formation of the passivation film on the anode surface. However, when using such a method, it is necessary to wait until the time when the passivation actually occurs, which is not much different from the voltage measurement at the production site, and is generated on the copper anode surface during electrolysis. If the anode slime layer is peeled off for some reason, the dissolution of the copper anode will not be hindered, which may cause a discrepancy with the actual production site. At the actual production site, it is uncertain whether or not the anode slime layer will peel off, and it is necessary to take measures assuming that the anode slime layer does not peel off.

Further, for example, in the method as seen in Patent Document 2, the anode potential is swept in a noble direction, a passivation film is formed, and the anode potential is swept in a low direction from a place where the anode potential is raised to a certain potential. By re-doing, this also uses the method of measuring the stability of the passivation film on the stainless steel surface.
In the method of Patent Document 2, when predicting the passivation of the anode in copper electrorefining, each value of the anode polarization curve as shown in FIG. 1 is measured and evaluated.
Specifically, the current density that flows by scanning the potential, that is, the current density is measured, and the current density (hereinafter, also referred to as "critical passivation current density") that starts to form a passivation film and no more current flows. The potential corresponding to the current density (hereinafter also referred to as "passivation potential"), the current density when the current does not flow even if the passivation film is formed and the potential is scanned (hereinafter also referred to as "passivation holding current density"). It can be inferred that the higher the value such as) is, the more difficult it is for the passivation film to be formed.

However, in the measurement of the anode polarization curve as described above, since the measurement is started from the state where the anode slime layer is hardly formed on the surface of the copper anode and the passivation occurs, it has a great influence on the formation of the passivation film. The occurrence of passivation was predicted by excluding the influence of the anode slime layer, which is thought to have an effect, and there were major problems in accuracy and detection time when applied to the management of actual operations.
From these facts, a method that can predict the occurrence of copper anode passivation in a short time while taking into account the influence of the anode slime layer has been desired.

Japanese Patent No. 5830910 Japanese Unexamined Patent Publication No. 7-225217

The present invention predicts the occurrence of short-time copper anode passivation during operation in copper electrorefining, and prevents the passivation to prevent the copper electrorefining operation. ， It provides a smooth and efficient operation method.

In the first invention of the present invention for solving the above problems, blister copper obtained in a copper smelting step is used as an anode and subjected to electrolytic treatment by a constant current method, and an anode slime layer is applied to the surface of the anode. Then, with the anode slime layer attached to the surface of the anode, the anode was subjected to an electrochemical measurement by a potential sweep method using the anode as a working electrode, and the criticality obtained by the electrochemical measurement was performed. The demobilization current density value (Ys) has a relationship of (Ys) <(y) smaller than the current density value (y) calculated in advance by the relational expression shown in the following equation (1). In some cases, it is a method of operating copper electrolytic purification, which is characterized in that immobilization of the anode surface is predicted to occur.

The second invention of the present invention is the case where the anode is electrolyzed by the constant current method so that the thickness of the anode slime layer formed on the surface of the anode in the first invention is in the range of 400 μm or more and 2000 μm or less. It is an operation method of copper electrorefining characterized in that it is the thickness of the anode slime layer to be formed.

In the third invention of the present invention, the anode current density when forming and adhering the anode slime layer on the surface of the anode in the first and second inventions is in the range of ^{300 A / m 2} or more and 1200 A / m ^{2 or less.} It is an operation method of copper electrolytic refining characterized by being present.

According to the fourth aspect of the present invention, electrolysis by the constant current method for forming an anode slime layer on the surface of the anode in the first to third inventions is carried out in a time range of 3 hours or more and 12 hours or less. This is a characteristic copper electrolytic refining operation method.

By using the present invention, it is possible to predict the occurrence of passivation in short-time copper electrorefining, and by utilizing it in actual operations, it will have a remarkable industrial effect.

It is a figure which showed the value of the critical passivation current density, the passivation potential, and the passivation holding current density in the general anodic polarization curve which shows passivation. It is a figure which plotted the value of the dissolution depth and the critical passivation current density of a copper anode under various conditions for setting a threshold value. It is a figure which compared the positional relationship of the formula (straight line) set by the threshold setting, and the critical passivation current density value measured in Example 1 and Comparative Example 1.

When electrolytically purifying copper, the present inventors energize in advance under various electrolytic conditions to electrolyze the anode so that the dissolution depth becomes a constant value, and form an anode slime layer on the anode surface. After adhering, by sweeping the anode potential in the noble direction with the anode slime layer attached to the anode surface, the characteristic items are critical passivation current density, passivation potential, and passivation holding current density. I want to measure either of the above, grasp and set the thresholds of "when passivation occurs" and "when passivation does not occur" on the anode surface, and judge whether or not passivation occurs. By measuring the same characteristic items as the threshold of any of the critical passivation current density, passivation potential, and passivation holding current density under the operating conditions, and comparing the magnitude with the previously set threshold. , It has been found that it is possible to determine whether or not the surface of the anode is passivated under the operating conditions, and the present invention has been completed.

Hereinafter, the specific contents of the present invention will be described in detail.
1. 1. Confirmation of presence / absence of passivation under various electrolysis conditions Under various electrolysis conditions that may be carried out at the actual production site, electrorefining is actually carried out using a small electrolytic cell to passivate. Check if it is.

2. Setting the threshold The electrolytic purification is performed under various electrolytic conditions, and the passivation case and the non-passivation case are classified, and the copper anode surface is electrolyzed so that the dissolution depth of the copper anode becomes a constant value. After forming and adhering an anode slime layer to the body, by sweeping the anode potential in a noble direction, the passivation current density, passivation potential, or passivation holding current density of them can be achieved. By measuring and organizing the values that are closely related to the occurrence, the thresholds for passivation and non-passivation are set.

3. 3. Judgment of prediction of passivation occurrence under the target electrolytic conditions Electrolysis is performed so that the dissolution depth of the copper anode becomes a constant value under the conditions for which it is desired to predict whether or not passivation will occur when electrolytic purification is performed. After forming and adhering an anode slime layer on the surface of the copper anode, the anode potential is swept in the noble direction to passivate the critical passivation current density, passivation potential, and passivation holding current density. By measuring the value that has a great relationship with the occurrence of the above and comparing the magnitude with the threshold obtained in "2. Setting the threshold", passivation occurs when electrolytic purification is actually performed under that condition. Predict whether or not will occur.
In addition to actually predicting, if passivation is expected to occur, take measures to prevent passivation at the production site.

Hereinafter, examples of the present invention will be shown and described in more detail.
[Threshold setting]
First, a copper anode (A, B, C, D, E, F) having six different compositions shown in Table 1 and an electrolytic solution (α, β, γ,) having five different compositions shown in Table 2 are used. δ, ζ) were prepared.

The copper anodes A to F described above are made by cutting electrolytic copper having a purity of 99.99%, placing it in a furnace, heating it to 1150 ° C. to melt it, and using other than oxygen so as to have the composition shown in Table 1. Each impurity was added in the form of metal to form an alloy. The composition of oxygen was adjusted to the composition shown in Table 1 by blowing air into the molten alloy while stirring the alloy.

After heating in a furnace and blowing air in a molten state, the alloy was air-cooled, and the obtained alloy was electrically insulated with masking tape so that the electrode area had a size of 2 × 2 cm. Table 1 shows the copper anode composition.
For the cathode, a thin copper plate having a thickness of about 1 mm was cut and masked with masking tape so that the electrode area was 2 × 2 cm.

The electrolytic solution (α, β, γ, δ, ζ) was prepared by mixing copper sulfate pentahydrate, nickel sulfate hexahydrate, arphoic acid, sulfuric acid having a concentration of 98% by weight, and ion-exchanged water. Table 2 shows the composition of the electrolytic solution.

Combine the anode and electrolyte with the compositions shown in Tables 1 and 2, and perform electrolysis in the same manner as at the actual production site for electrolytic conditions such as electrolytic time, and confirm which combination causes passivation. did.
Specifically, One not a single anode and cathode in a glass beaker 0.5 liters, put the electrode portion is faced to retain the interplanar distance of 20 mm, the temperature of the electrolytic solution 60 ° C. Stirred while maintaining.

^{Electrolysis is performed at a current density of 600 A / m 2} for 12 hours with 12 combinations of anodes A, B, C and D shown in Table 3 and electrolytes α, β and γ to dissolve the copper anode by about 1000 μm in the depth direction. The anode slime layer was formed on the surface of the copper anode.
After that, with the anode slime still attached to the anode surface, an electrochemical measurement was performed in which the anode potential was swept from 0.34 V (vs. NHE) at a sweep rate of 1 mV / sec for 11 minutes in a noble direction, and the criticality was measured. The passivation current density was measured.
The results shown in Table 4 were obtained for the critical passivation current densities measured with the 12 combinations shown in Table 3.

As a result, the occurrence of passivation was observed in the combination with "re" in Table 3, and in the result of the critical immobilization current density in Table 4, the occurrence of passivation occurred in the combination indicated by italicized numbers. Was observed.
In this embodiment, since the anode is dissolved only from a certain direction by coating with an insulating tape, the specific gravity of the anode, which is mostly copper although it contains impurities, is the same as that of pure copper8. Assuming .96, the dissolution depth with respect to the energized amount is calculated as follows when energized for 12 hours at a current density of ^{600 A / m 2 because copper dissolves as divalent ions, and is 952 μm.} Become the depth.
^{600 [A / m 2] ×} 12 [h] /26.8 [A · h / mol] × 63.5 / 2 [g / mol] / (8.96 × 10 6) [g / m 3] = 952 [μm]

Next, using 12 combinations of the electrolytic solution and the anode composition, ^{electrolysis was performed at a current density of 600 A / m 2} for 6 hours to dissolve the copper anode by about 500 μm in the depth direction, and the anode slime layer was formed on the surface of the copper anode. Was generated. After that, the anode potential was set to 0.34 Vvs. The critical immobilization current density was measured by sweeping in the noble direction for 11 minutes at a sweep rate of 1 mV / sec from NHE.
The measurement results are shown in Table 5.

The part in italics in Table 5 is the case where passivation occurs.
Compared with “when the dissolution depth of the copper anode is about 1000 μm” in Table 4, the current density value was higher overall.
From this result, it can be seen that as the thickness of the anode slime layer increases, passivation is likely to occur.

For each current density value in Tables 4 and 5, the presence or absence of passivation is classified, and the horizontal axis of FIG. 2 is the depth of the dissolved copper anode, and the vertical axis is the critical passivation current density. The relationship was plotted.
In FIG. 2, connecting the point where the copper anode was dissolved by about 500 μm but not passivated and the point where the copper anode was dissolved by about 1000 μm but not passivated were connected, “y = −0.47x + 3100”. The relational expression was obtained.

That is, for the condition for determining whether or not passivation occurs, the anode slime layer is formed and adhered to the surface of the copper anode, and then the anode potential is swept in the noble direction to obtain the critical passivation current density. the measured value of the critical passivation current density (Y _S) is, (y) = - compared to the value obtained by substituting the dissolved depth of the anode to 0.47x + 3100, to evaluate its magnitude, the actual It is possible to determine whether or not passivation occurs when electrolytic purification of copper is carried out at the production site of.

When forming an anode slime layer that does not peel off on the surface of the copper anode, if the depth of the copper anode to be dissolved is deepened to a depth of more than 2000 μm, the anode slime layer is likely to peel off. On the other hand, at a depth of less than 400 μm, the anode slime layer is formed only thinly, so that the influence of the anode slime layer cannot be reflected.
That is, the depth needs to be 400 μm or more.

Further, when the anode current density value ^{exceeds 1200 A / m 2} , the anode slime layer is likely to be peeled off. Furthermore, since passivation occurs during the formation of the anode slime layer, the current density of the anode needs to be ^{1200 A / m 2 or less.} On the other hand, if the current density of the anode is ^{too low, less than 300 A / m 2} , it is not efficient because it takes a long time to form the anode slime layer.

Using the copper anode E shown in Table 1 and the electrolytic solution γ shown in Table 2, electrolysis was performed at a ^{current density of 600 A / m 2} for 12 hours to dissolve the copper anode by about 1000 μm in the depth direction, and the anode slime layer was used. Was formed and adhered to the surface of the copper anode.
The anode potential was then swept in the noble direction to measure the critical passivation current density. The critical passivation current density value _was ^{(Y S) = 2930A / m} 2.

Substituting the above-mentioned dissolution depth of 1000 μm into the “formula: (y) = −0.47x + 3100” obtained by the above-mentioned “threshold setting”, (y) became 2630 A / m ² .
Comparing this (y) value with the above-mentioned critical passivation current density (Y _S ) = 2930 A / m ² , the actually obtained (Y _S ) = 2930 A / m 2 was obtained from the equation ^{(Y S) = 2930 A / m 2.} y) = greater than 2630 A / m ^2.
When electrolytic refining was performed at an actual production site using an anode and an electrolytic solution having the same composition as in this example, passivation did not occur and stable operation was possible.
That is, it was confirmed that the passivation did not occur when the value of the critically mobilized current density actually measured was larger than the value (y) of the formula calculated from the "dissolution depth".

(Comparative Example 1)
Using the copper anode F in Table 1 and the electrolyte ζ in Table 2, electrolysis was performed at ^{a current density of 600 A / m 2} for 12 hours to dissolve the copper anode by 1000 μm in the depth direction to form an anode slime layer on the anode surface. It was. Then, the critical mobilization current density was measured by sweeping the anode potential in the noble direction. The critical passivation current density value at this time _was ^{(Y S) = 2350A / m} 2.

Substituting the above dissolution depth into the “formula (y) = −0.47x + 3100” obtained by “threshold setting” in the same manner as in Example 1, (y) = 2630A / m ² .
Comparing this with the critical passivation current density value (Y _S ) = 2350 A / m ² measured above, the actually obtained (Y _S ) = 2350 A / m 2 was obtained from the equation ^{(Y S) = 2350 A / m 2.} y) = a value smaller than ^{2630 A / m 2.}
Therefore, when copper was actually electrorefined, passivation occurred.

Here, FIG. 3 shows the relationship between the “formula (y) = −0.47x + 3100” obtained from the “threshold setting” and the critical passivation current density values measured in Example 1 and Comparative Example 1. It is shown that if the critical passivation current density is located above the threshold straight line, no passivation occurs, while if it is below the threshold line, passivation occurs. It was confirmed that the occurrence of passivation can be predicted by using it.

Claims (4)

The blister copper obtained in the copper smelting process is used as the anode and subjected to electrolytic treatment by the constant current method to form and adhere an anode slime layer to the surface of the anode.
Next, with the anode slime layer adhering to the surface of the anode, the anode is subjected to an electrochemical measurement by a potential sweep method using the anode as a working electrode.
The electrochemical values of the critical passivation current density obtained by the measurement (Ys) is obtained in advance by Aru following (1) the value of the current density calculated from the equation shown in equation (y) smaller than (Ys ) <(Y), it is an operation method of copper electrolytic purification characterized in that the passivation of the anode surface is predicted to occur.

The thickness of the anode slime layer formed on the surface of the anode is the thickness of the anode slime layer formed when the anode is electrolyzed by a constant current method so as to have a depth in the range of 400 μm or more and 2000 μm or less. The method for operating copper electrorefining according to claim 1. The copper electrorefining according to claim 1 or 2, wherein the anode current density at the time of forming and adhering the anode slime layer on the surface of the anode ^{is in the range of 300 A / m 2} or more and 1200 A / m ^{2 or less.} Operation method. The copper according to any one of claims 1 to 3, wherein electrolysis by a constant current method for forming an anode slime layer on the surface of the anode is performed for a time in the range of 3 hours or more and 12 hours or less. Operation method of electrolytic refining.

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