JP7271917B2 - Copper electrolytic refining method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a copper electrolytic refining method, and more particularly to a copper electrolytic refining method capable of preventing the occurrence of a passivation phenomenon in an anode.

Copper smelting methods can be broadly divided into dry and wet processes. The former dry process generally comprises a dry smelting process for producing an anode from a copper concentrate as shown in FIG. and an electrolytic refining process to produce electrolytic copper from the anode. Specifically, first, in the pyrometallurgical process, copper concentrate obtained by flotation is melted in a flash furnace and then oxidized in a converter to produce blister copper, which is then processed in a refining furnace. Refined crude copper with a purity of about 99% is obtained. This purified blister copper is poured into a casting machine to cast an anode plate (hereinafter referred to as an anode) for electrolytic copper refining.

Next, in the electrorefining step, a plurality of anodes obtained by the above casting and a plurality of separately prepared cathode plates (hereinafter referred to as cathodes) are placed in an electrolytic bath containing a copper electrolyte solution at regular intervals. alternately one by one. By energizing the anode and cathode, copper ions are eluted from the anode into the electrolytic solution and are electrodeposited on the cathode to produce electrolytic copper having a copper grade of 99.99% or more.

Since the anode contains impurity metals such as Ni, Sn, As, Sb, and Bi, ions of these impurity metals are eluted into the electrolytic solution as well as copper ions as the electrolysis proceeds. do. However, when the grade of impurities in the anode is high, or when the concentration of copper or sulfuric acid in the electrolyte is high, non-conductive copper oxide or copper sulfate crystals are deposited on the surface of the anode. A phenomenon that prevents the elution of metal ions (hereinafter referred to as anode passivation or simply passivation) may occur.

In order to investigate the effect of the impurities in the anode on the passivation of the anode, many studies have been conducted on the types and amounts of the impurities, their coexistence states, and the like. For example, Patent Literature 1 lists Ag, As, Pb, Bi, Sb, Sn, Se, and O as impurities in the anode that affect anode passivation in a copper electrorefining process. A method has been proposed to assess the likelihood of anode passivation occurring based on the impurity grades of .

In addition, in Patent Document 2, when performing electrolytic refining of blister copper at a high current density, even if the copper concentration of the electrolyte is increased, anodic passivation does not easily occur, so that the copper concentration in the electrolyte is A technique is disclosed for adjusting the sulfate group concentration so that the product of the sulfate group concentration and the current density is equal to or less than a predetermined value.

Japanese Patent Application Laid-Open No. 2000-054181 JP 2017-214612 A

Although it is believed that the techniques of Patent Documents 1 and 2 can suppress the occurrence of anode passivation to some extent in the copper electrorefining process, under high-load electrolysis conditions such as electrolysis operation at high current density, Anodic passivation could still occur. The present invention has been made in view of such circumstances, and provides a copper electrolytic refining method capable of suppressing the occurrence of anode passivation even under high load electrolysis conditions such as electrolysis operation at high current density. for the purpose.

The present inventors have extensively studied methods for suppressing the occurrence of anode passivation even under high load electrolysis conditions such as electrolysis operation at a high current density. It was found that not only the grade but also the electrolysis conditions such as the composition of the electrolytic solution affected the electrolysis conditions. For example, if the concentration of copper or sulfuric acid in the electrolyte is high, copper sulfate in the electrolyte reaches saturation solubility due to the eluted copper in the vicinity of the anode, and as a result, copper sulfate crystals precipitate and passivate the anode. is thought to occur.

Therefore, in order to continue stable electrolysis operation under high current density while suppressing the occurrence of anode passivation, it is necessary to adjust both the impurity grade of the anode and the physical properties of the electrolyte. By adjusting the operating conditions for electrolytic refining based on the control index using the passivation inhibition degree P and the electrolyte specific gravity S calculated from The present invention has been completed by finding that it is possible to suppress the

That is, the copper electrolytic refining method according to the present invention includes the passivation suppression degree P calculated from the following formula 1 based on the Cu grade, oxygen grade, Se grade, Ag grade, and As grade in the anode, and The specific gravity S of the electrolytic solution is adjusted so that the passivation occurrence rate Q calculated from the following formula 2 using the specific gravity S as a parameter is 0.005 or less , and the current density is 350 A / m ² or more and 400 A / m ² In the copper electrorefining method operated below, the adjustment of the specific gravity S of the electrolytic solution is performed by adjusting at least one of the copper concentration, sulfuric acid concentration, and nickel concentration of the electrolytic solution, and the copper concentration of the electrolytic solution is within the range of 47 to 51 g/L, the sulfuric acid concentration of the electrolyte within the range of 150 to 210 g/L, and the nickel concentration of the electrolyte within the range of 17 to 23 g/L. and
[Formula 1]
P=([As]−0.5·[Ag] _Free )/([Cu ₂ O]+n·[Cu ₂ Se]+X)
[Formula 2]
Q = S - 0.0025 x P - 1.23
(However, when As/Se is less than 0.2, [Ag] _Free = 0, X = 0.5 · [Ag], n = 0, and when As/Se is 0.2 or more and less than 0.5 , [Ag] _Free = 0, X = 0, n = 0.5, and when As/Se is 0.5 or more and less than 1.0, [Ag] _Free = 0.25, X = 0, n = 0 .5, and when As/Se is 1.0 or more and less than 1.7, [Ag] _Free = ([Ag] - [Se]), X = 0, n = 0.5, and As/Se is 1 .7 or more, [Ag] _Free = ([Ag]-2·[Se]), X = 0, n = 1.0, where [A] is the amount of material A contained in the anode. is the value obtained by dividing the grade by its molecular weight, and As/Se is the value obtained by dividing the As grade by the Se grade in the anode.)

According to the present invention, the occurrence of anode passivation can be suppressed even under high-load electrolysis conditions such as electrolysis operation at high current density, so that stable operation can be continued.

1 is a block flow diagram of a dry copper concentrate process to which the copper electrolytic refining method of the present invention is preferably applied; FIG.

Hereinafter, as an embodiment of the copper electrolytic refining method of the present invention, an electrolytic refining method capable of suppressing the occurrence of anode passivation even under high load electrolysis conditions such as high current density operation will be described. First, the degree of inhibition of passivation P will be explained, and then the degree of occurrence of passivation Q calculated using the degree of inhibition of passivation P and the specific gravity S of the electrolyte as parameters will be explained.

The passivation phenomenon in copper electrorefining occurs because Cu ions become saturated in the electrolytic solution existing in the vicinity of the anode among the electrolytic solutions in the electrolytic bath, and as a result, Cu elution from the anode becomes difficult. . That is, as the copper electrolytic refining progresses, the concentration gradient of Cu ions is generated in the electrolytic solution in the vicinity of the anode due to the Cu ions eluted from the anode. Also, some of the impurities in the anode do not elute and form a slime layer on the surface of the anode. Since this slime layer can prevent Cu ions from diffusing in the electrolyte, the Cu ion concentration in the electrolyte near the anode gradually increases over time.

When the concentration of CuSO ₄ in the electrolyte reaches the saturation concentration due to the increase in the Cu ion concentration, insoluble and non-conductive CuSO ₄ .5H ₂ O crystals are deposited on the anode surface as a passivation layer. , the effective surface area of the anode is reduced. As a result, a substantial increase in current density occurs, causing passivation that appears as phenomena such as an increase in electrolytic cell voltage and an increase in electrode surface temperature. Therefore, in order to prevent the occurrence of the passivation phenomenon, it is sufficient to maintain the condition that Cu ions do not become saturated or supersaturated in the electrolytic solution existing in the vicinity of the anode.

Moreover, it is preferable that the slime layer formed on the surface of the anode has properties that do not hinder the diffusion of Cu ions. Since the properties of this slime layer are affected by components such as As, Ag and oxygen in the anode, the components such as As, Ag and oxygen in the anode indirectly affect the manifestation of the passivation phenomenon. will have an effect. Furthermore, if the slime layer formed on the anode surface contains many Cu particles, the passivation phenomenon is likely to occur. The reason for this is that most of the Cu particles in the slime are generated from monovalent Cu _ions . This is because it becomes easier to reach, and a large amount of CuSO ₄ .5H ₂ O forming a passivation layer is generated.

Therefore, if impurities in the anode that generate monovalent Cu can be eliminated as much as possible, the occurrence of the passivation phenomenon can be suppressed. Among the impurities in the anode, O, Ag, Pb, Sb, Bi, Sn, As, and Se can be cited as those that affect the monovalent Cu ions (Cu ⁺ ). That is, since oxygen (O) present in the anode is partly combined with monovalent Cu ions and exists in the form of Cu ₂ O, the higher the concentration of Cu ₂ O in the anode, the more the above More monovalent Cu ions for the formation of the passivation layer will be supplied.

Ag ⁺ generated by dissolving Ag reacts with Cu ₂ Se and CuAgSe, which are selenides in the anode, to generate monovalent Cu ions. Therefore, if the value obtained by subtracting the mole amount of Se from the mole amount of Ag in the anode, or the value obtained by subtracting the mole amount of Se from the mole amount of Ag, is high, it can be used for forming the passivation layer. the amount of monovalent Cu ions absorbed increases.

Pb, Sb, Bi, and Sn, on the other hand, fix oxygen as oxides in the anode. Therefore, high molar amounts of these impurities in the anode can suppress the amount of monovalent Cu ions supplied for the formation of the passivation layer. That is, the molar amount of Cu ₂ O per unit mass of the anode can be derived from the oxygen balance equation shown below.
[Cu ₂ O]=[O _Anode ]−([PbO]+[SbO]+[BiO]+[SnO])

In this specification, [A] is a value obtained by dividing the grade of substance A such as an impurity element in the anode by its molecular weight. Also, O _Anode means all oxygen in the anode. As shown in the oxygen balance formula above, Pb, Sb, Bi, and Sn are usually present as oxides in the anode. The molar amount of the above oxides can be calculated by dividing the grade of the product by each molecular weight.

As is eluted from the anode and oxidized to the V valence to generate H ⁺ ions, thereby promoting the dissolution of Cu ₂ O. Therefore, when the grade of As in the anode is high, the amount of monovalent Cu ions supplied as the passivation layer can be suppressed. As previously mentioned, Se is present in the anode in the form of Cu ₂ Se or CuAgSe, thus providing monovalent Cu ions. Therefore, a higher molar concentration of Se in the anode increases the amount of monovalent Cu ions supplied as the passivation layer. It should be noted that Ni and Fe present in the anode have little effect on passivation and can be ignored.

As explained above, Cu ₂ O, Cu ₂ Se, CuAgSe and Ag in the anode can be mentioned as sources of monovalent Cu ions responsible for the development of the passivation phenomenon. On the other hand, substances that fix oxygen in the anode, such as Pb, Sb, Bi, and Sn, and As in the anode can be cited as substances that suppress the expression of the passivation phenomenon.

Among the various impurities described above, the fixed form of Ag in the anode is known to change depending on the molar ratio Ag/Se of Ag and Se in the anode. The molar amount of Ag in the form of Ag [Ag] _Free is determined as the molar amount of Ag minus the molar amount of Se in the anode, or the molar amount of Ag minus twice the molar amount of Se. be able to. On the other hand, as described above, selenium is known to exist as selenides such as Cu ₂ Se and CuAgSe. It is related to the amount of generation. Furthermore, it is believed that As dissolves monovalent Cu by oxidizing itself and suppresses the occurrence of passivation.

Therefore, considering the supply or suppression of monovalent Cu ions by each impurity element or compound, the passivation suppression degree P shown in the following formula 1 is introduced as an index representing the difficulty of occurrence of the passivation phenomenon. That is, the grade of the impurity element contained in the anode used for copper electrolytic refining is determined by a quantitative analysis method such as ICP emission spectrometry, and the passivation suppression degree P shown in the following formula 1 calculated from the obtained value is as large as possible. It is preferable to manage the impurity concentration so that
[Formula 1]
P=([As]−0.5·[Ag] _Free )/([Cu ₂ O]+n·[Cu ₂ Se]+X)

However, when As/Se is less than 0.2, [Ag] _Free = 0, X = 0.5 · [Ag], n = 0, and when As/Se is 0.2 or more and less than 0.5, [Ag] _Free = 0, X = 0, n = 0.5, and when As/Se is 0.5 or more and less than 1.0, [Ag] _Free = 0.25, X = 0, n = 0.5. 5, and when As/Se is 1.0 or more and less than 1.7, [Ag] _Free = ([Ag] - [Se]), X = 0, n = 0.5, and As/Se is 1.7. In the case of 7 or more, [Ag] _Free = ([Ag]-2·[Se]), X = 0, n = 1.0. Here, [A] is the value obtained by dividing the grade of substance A contained in the anode by its molecular weight, and As/Se is the value obtained by dividing the As grade by the Se grade in the anode. Further, [Cu ₂ O] can be obtained from the oxygen balance formula described above, and almost all Se in the anode exists as Cu ₂ Se, so the molar concentration of Se can be used as it is as the concentration of Cu ₂ Se. can.

In the copper electrolytic refining method of the embodiment of the present invention, the passivation occurrence rate Q shown in the following equation 2 calculated using the anode passivation inhibition degree P and the specific gravity S of the electrolyte solution obtained above as parameters is adjusted to 0.005 or less. This can suppress the occurrence of the passivation phenomenon.
[Formula 2]
Q = S - 0.0025 x P - 1.23

The specific gravity S of the electrolytic solution can be adjusted, for example, by adjusting at least one of the copper concentration, sulfuric acid concentration, nickel concentration, etc. of the electrolytic solution. , is preferably adjusted within the range of normally set conditions. Specifically, the copper concentration of the electrolytic solution is desirably 47 to 51 g/L for electrolysis at a high current density, which will be described later. The sulfuric acid concentration of the electrolytic solution is preferably as high as possible because the bath resistance of the electrolytic solution is lowered. is desirable. If the nickel concentration of the electrolytic solution is too high, the bath resistance of the electrolytic solution may increase, and nickel sulfate crystals may precipitate, causing problems such as scaling. Since the capacity of the liquid purifier, the target anode grade, the liquid purification cost, etc., differ depending on the electrolysis equipment, the optimum value differs, but generally 17 to 23 g/L is preferable.

The current density employed in the electrolytic refining of copper according to the embodiment of the present invention can be appropriately determined from the number of facilities such as electrolytic cells, the required production volume, and the operating conditions for electrolysis such as operating rate. Industrially, the range of 200 to 400 A/m ² is preferably adopted, but by suppressing the passivation generation rate Q to 0.005 or less, the range of 280 to 400 A/m ² is more preferable. Among them, the occurrence of the passivation phenomenon can be suppressed even at a current density within the more preferable range of 350 A/m ² or more and 400 A/m ² or less.

In general, it is preferable that the temperature of the electrolyte is high, but industrially, considering the heat resistance temperature of the material that can be used for the electrolytic cell, the safety during operation, the energy efficiency to be used, etc., the temperature of the electrolyte is about 60. ~65°C is a practical temperature and there is little practical advantage in doing higher temperatures above 80°C. If the liquid temperature is less than 50° C., the solubility of copper is extremely lowered, and the passivation is remarkably accelerated, which is not preferable.

Twelve types of anode samples 1 to 12 with different impurity grades were prepared, and the impurity grades were determined for each of them using an ICP emission spectrometer. Then, the molar amount of Cu ₂ O per unit mass of each anode was derived from the oxygen balance equation described above, and the passivation inhibition degree P was calculated using Equation 1 described above. Table 1 shows the calculation results.

Next, using each anode, the specific gravity S of the electrolyte is 1.23 to 1.24 g/cm ³ , the current density is 183 to 358 A/m ² , the temperature of the electrolyte is 60 to 66° C., and the composition of the electrolyte is Cu. Copper electrolysis was performed within the range of 41-50 g/L, 150-205 g/L of H ₂ SO ₄ and 0.6-22 g/L of Ni. As a result, in the copper electrolysis using the anode of sample 3, the cell voltage exceeded 500 mV, so it is thought that the passivation phenomenon occurred, but the anodes of samples 1 to 2 and 4 to 12 other than that were used. The cell voltage never exceeded 500 mV in copper electrolysis. The passivation suppression degree P and the electrolyte specific gravity S in the copper electrolysis performed using each of the anodes of these samples 1 to 12 were substituted into Equation 2 to calculate the passivation generation degree Q, together with the electrolysis conditions, in Table 2 below. shown in

As can be seen from the results in Table 2 above, samples 1 to 2 and 4 to 12 did not undergo anodic passivation because the degree of passivation Q was less than 0.005. On the other hand, in sample 3, the passivation occurrence rate Q was greater than 0.005, so anodic passivation occurred. That is, in order to prevent anode passivation under high current density, the passivation occurrence rate Q calculated using the passivation suppression degree P obtained from the impurity grade of the anode and the electrolyte specific gravity S as parameters is It can be seen that by adjusting the electrolysis conditions using , the occurrence of anode passivation can be effectively suppressed even in high current density operation, and stable operation can be continued.

Claims (1)

It was calculated from the following equation 2 using the passivation inhibition degree P calculated from the following equation 1 based on the Cu grade, oxygen grade, Se grade, Ag grade, and As grade in the anode and the specific gravity S of the electrolyte as parameters. A copper electrolytic refining method in which the specific gravity S of the electrolytic solution is adjusted so that the degree of passivation Q is 0.005 or less, and the current density is 350 A/m ² or more and 400 A/m ² or less, The adjustment of the specific gravity S of the electrolytic solution is performed by adjusting at least one of the copper concentration, sulfuric acid concentration, and nickel concentration of the electrolytic solution, and the copper concentration of the electrolytic solution is within the range of 47 to 51 g / L. a sulfuric acid concentration in the range of 150 to 210 g/L, and a nickel concentration in the electrolytic solution in the range of 17 to 23 g/L.
[Formula 1]
P=([As]−0.5·[Ag] _Free )/([Cu ₂ O]+n·[Cu ₂ Se]+X)
[Formula 2]
Q = S - 0.0025 x P - 1.23
(However, when As/Se is less than 0.2, [Ag] _Free = 0, X = 0.5 · [Ag], n = 0, and when As/Se is 0.2 or more and less than 0.5 , [Ag] _Free = 0, X = 0, n = 0.5, and when As/Se is 0.5 or more and less than 1.0, [Ag] _Free = 0.25, X = 0, n = 0 .5, and when As/Se is 1.0 or more and less than 1.7, [Ag] _Free = ([Ag] - [Se]), X = 0, n = 0.5, and As/Se is 1 .7 or more, [Ag] _Free = ([Ag]-2·[Se]), X = 0, n = 1.0, where [A] is the amount of material A contained in the anode. is the value obtained by dividing the grade by its molecular weight, and As/Se is the value obtained by dividing the As grade by the Se grade in the anode.)

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