CN119162616A

CN119162616A - A kind of cathode copper with low silver content and preparation method thereof

Info

Publication number: CN119162616A
Application number: CN202411316102.4A
Authority: CN
Inventors: 郑国渠; 高瑜恒; 冯闻宇; 曹华珍; 张惠斌
Original assignee: Zhejiang University of Technology ZJUT
Current assignee: Zhejiang University of Technology ZJUT
Priority date: 2024-09-20
Filing date: 2024-09-20
Publication date: 2024-12-20

Abstract

The invention belongs to the field of electrode materials, and particularly relates to cathode copper with low silver content and a preparation method thereof. The method comprises the steps of 1) preparing a bromine-containing copper electrolyte, 2) taking pyrometallurgy anode copper as an anode, taking an inert material as a cathode, and carrying out electrolytic refining by taking the copper electrolyte obtained in the step 1) as the electrolyte to obtain the cathode copper with low silver content. According to the invention, the original Cl ^‑ additive is replaced by the bromine salt additive, and the concentration of the novel additive is controlled, so that the concentration of free Ag ⁺ in the copper electrolyte is greatly reduced, a long-term stable effect can be formed, the method is suitable for industrial electrolytic copper production, and compared with the conventional process, the silver content in the prepared electrolytic copper can be greatly reduced, and the quality of the electrolytic copper is improved.

Description

Cathode copper with low silver content and preparation method thereof

Technical Field

The invention belongs to the field of electrode materials, and particularly relates to cathode copper with low silver content and a preparation method thereof.

Background

The pyrometallurgical process of copper sulphide ores produces a large part of the world's blister copper. However, because the matte produced in the smelting process and the raw copper obtained after blowing are excellent Ag trapping agents, ag is easy to be dissolved in copper sulfide and copper metal, and a large amount of noble metal Ag is associated in the raw copper produced by pyrometallurgy. The Ag in the blister copper mainly exists in the form of solid solution, during the electrolytic refining process of copper serving as an anode, along with electrochemical dissolution of copper, silver in the blister copper can be dissolved into electrolyte, wherein most of the Ag enters anode mud in the form of complex oxides such as Cu-Ag-Se-Te-Pb-O, and the like, and the small part of the Ag enters the electrolyte in the form of Ag ⁺, and because the reduction potential of Ag ⁺ is far higher than that of Cu ²⁺, the Ag ⁺ is finally discharged and separated out on the surface of cathode copper under the action of an electric field and a flow field, so that the Ag enters cathode copper.

Ag is a noble metal that is hundreds of times more expensive than copper. Silver in the cathode copper cannot participate in pricing, which causes huge economic loss to copper production enterprises. Meanwhile, silver as a noble metal becomes a harmful impurity in cathode copper, so that the silver content is one of important indexes for judging the quality of cathode copper. It is desirable to reduce the silver content of the cathode copper as much as possible during copper electrolysis production. During copper electrolysis, silver in the electrolyte mainly enters cathode copper in the form of free Ag+ reduction and Ag-containing particle mechanical inclusion, and according to FENG W, CAO H, SHEN Y, et al. Migration regularity and control of silver inclusions during copper electrorefiningprocess[J]. Transactions of Nonferrous Metals Societyof China, 2023, 33(9): 2853-2865., more than 60% of the total Ag content in the cathode copper is caused by the reduction of free Ag ⁺. At present, a part of the data report a method for reducing Ag impurity in cathode copper by using specific additives. For example, china patent office published an invention patent application No. CN114150349A on day 3 and 8 of 2022, which discloses a method for reducing silver content in cathode copper. The method is mainly characterized in that the method is characterized in that an electrolyte circulation mode is changed, ag-containing suspended matters in the electrolyte are filtered and separated, and the mechanical adhesion of silver-containing particles in cathode copper is reduced, so that the Ag content is effectively reduced. Obviously, when the process is applied, only the influence of Ag-containing particles on the Ag content of cathode copper can be solved, but the discharge reduction of Ag ⁺ at the cathode is still not obvious.

In order to reduce the concentration of free Ag ⁺ in the electrolyte and to suppress its reduction by cathodic discharge, a method of adding an additive such as Cl ^- is widely used in industry. However, cl ^- is actually used as an additive with low practical utilization, most of Cl ^- is combined with Cu ²⁺, and since AgCl has a large solubility product, a large amount of Cl ^- needs to be added to make the free Ag ⁺ concentration lower than the lowest concentration at which reduction can take place in preference to Cu ²⁺, which is difficult to withstand for copper electrolysis systems.

Among the numerous silver salt precipitates with smaller solubility product, agBr has a solubility product of 4.9x10 ^-13, which is several orders of magnitude .Zhang P, Wei Y, Ou M, et al. Behind the role of bromide ions in the synthesis of ultrathin silver nanowires[J]. Materials Letters, 2018, 213: 23-26. smaller than that of AgCl (1.8x10 ^-10), and it is shown that AgBr complex is more stable in solution than AgCl, which is more difficult to release Ag ⁺. The data on the binding equilibrium constants also show that the stable complexation constant for the reaction of Br ^- with Ag ⁺ to form AgBr is significantly greater than that for the reaction of Cl ^- with Ag ⁺ to form AgCl, in other words, the affinity of Cl ^-,Br^- for Ag ⁺ is greater, the extent of reaction with Ag ⁺ is greater, and the solubility product of the precipitate species formed is smaller. In addition, br and Cl are the same genus elements, and the addition of Br ^- in the copper electrolyte has little influence on the existing copper electrorefining process. Therefore, the invention proposes to use Br ^- to replace Cl ^- as an additive in the copper electrorefining process so as to effectively reduce the Ag content in the cathode copper product.

Disclosure of Invention

In order to solve the problem that the concentration of free Ag ⁺ in the electrolyte is reduced due to limited effect of a Cl ^- additive in the traditional copper electrolysis process, so that the silver content of cathode copper is still too high, the invention provides the cathode copper with low silver content and the preparation method of the cathode copper.

The invention aims at:

1. the content of impurity silver in cathode copper is reduced, and the purity and quality of the cathode copper are improved;

2. the method is suitable for industrial copper electrolysis production, is suitable for the existing electrolysis flow, and has current efficiency reaching more than 95%;

3. the continuous control effect on the Ag content of cathode copper is good under the condition of long-time electrolysis.

In order to achieve the above object, the present invention adopts the following scheme.

A method for preparing cathode copper with low silver content,

The method comprises the following steps:

1) Preparing a bromine-containing copper electrolyte;

2) And (3) carrying out electrolytic refining by taking the pyrometallurgical anode copper as an anode, taking an inert material as a cathode and taking the copper electrolyte obtained in the step (1) as an electrolyte, thus obtaining the cathode copper with low silver content.

As a preferred alternative to this,

The copper electrolyte in the step 1) contains 10-100 mg/L of bromine salt;

and stirring the mixture for 5-10 min at a constant temperature of 50-70 ℃ after adding the bromine salt.

As a preferred alternative to this,

The cations in the bromine salt are alkali metal cations and/or cations with reduction potential less than or equal to the reduction potential of copper ions.

As a preferred alternative to this,

The concentration of Cu ²⁺ ions in the copper electrolyte in the step 1) is 30-60 g/L;

The concentration of sulfuric acid in the copper electrolyte in the step 1) is 150-250 g/L.

As a preferred alternative to this,

Step 2) in the electrolytic refining process:

the current density is controlled to be 150-350 mA/cm ², the pole distance between the cathode and the anode is 6-8 cm, and the electrolytic refining process is carried out at 50-70 ℃.

A cathode copper with low silver content.

For the technical scheme of the invention, the bromine salt additive is adopted to replace the original Cl ^- additive, and the characteristic of stronger complexing ability with Ag ⁺ is utilized, so that free Ag ⁺ in the electrolyte forms AgBr precipitates more, and the concentration of residual free Ag ⁺ in the electrolyte is reduced. According to the Nernst equation, the reduction potential of Ag ⁺ is reduced, and the difficulty of discharge reduction at the cathode is increased, so that the Ag content in the cathode copper is obviously reduced. Meanwhile, due to smaller complex constants of Br ^- and Cu ²⁺, the generation amount of copper-containing complex phases such as CuBr ⁺ is also smaller, and the utilization of additives is more efficient. On the other hand, the periodic electrolyte circulation replenishment and the dissolution of anode copper in the industrial copper electrorefining production process can continuously introduce impurity Ag into the electrolyte. Thus, the continuous production of an effect of an additive is also critical for industrial implementation. The bromine salt additive adopted by the invention has the advantages that due to the smaller complexing constant of Br ^- and Cu ²⁺, the utilization of the additive is more efficient, and under the condition of regular small-quantity supplement, the bromine salt additive in an electrolyte system can be stably kept at the required concentration, and the effect of continuously precipitating Ag is better.

However, it should be noted that the effect of cations in the bromide salt on the technical scheme of the invention is that when the cations have a larger reduction tendency, new impurities are further introduced, while for the scheme of the invention, the preparation of cathode copper with low silver content is mainly realized based on electrochemical reaction, so that the generation of the new impurities can be relatively effectively avoided by selectively controlling the cations in the bromide salt to have a smaller reduction potential.

In addition, the amount of bromine salt additive used also requires strict control. With the addition of Br ^-, according to the law of equilibrium and the law of conservation of mass, free Cu ²⁺ in the electrolyte can also form various complexes with Br ^-, such as CuBr ⁺, etc., and these positively charged ions are easily transferred to the cathode surface under the action of an electric field, which may lead to the inclusion of more Br in the cathode copper.

In addition, the reduction of the silver content of impurities in the cathode copper is realized through the complexation reaction of Ag ⁺ and Br ^-, and the precipitation of AgBr is accompanied, so that the temperature, time and solution state during electrolysis are also obviously influenced. In a temperature range of 55-65 ℃, too low temperature can have a great influence on the solubility of copper sulfate, so that the concentration of Cu ²⁺ in the solution is reduced, concentration polarization is easy to occur, and the current efficiency in the electrolysis process is influenced, and meanwhile, ag ⁺ is more likely to be reduced. And as the temperature rises, the viscosity of the electrolyte is reduced, and AgBr existing in a small amount in the electrolyte is easier to diffuse to the surface of the cathode along with floating anode mud, so that the content of copper Ag in the cathode is increased. The optimal electrolysis temperature is 60 ℃.

Generally, the concentration of free Ag ⁺ in the copper electrolyte after the bromine salt is added is lower than 0.1 mg/L, and the content of Ag in cathode copper can reach 6 ppm at the lowest. The Ag content in the cathode copper is reduced by more than 50% compared with that in the cathode copper which adopts Cl ^- as an additive under the same condition.

After the treatment by the process provided by the invention, free silver in the copper electrolyte is mainly converted into AgBr to be precipitated into anode slime, and compared with the cathode copper silver content (about 12-15 ppm) of the original Cl-additive, the cathode copper silver content obtained by the electrolysis of the copper electrolyte added with the bromine/salt additive is obviously reduced.

Whereas for the electrorefining process, cu ²⁺ reduced at higher current densities, depleted domains of Cu ²⁺ appear more readily on the cathode surface, but the accompanying higher current densities, free Ag ⁺, moves more readily to the cathode surface, which makes the Ag ⁺ discharge-reduced more likely and becomes entrapped in the copper deposit as Cu ²⁺ is deposited. But too low a current density also results in a reduced production efficiency of the copper electrolysis process. It is therefore desirable to control the formation of a relatively optimum current density range to effectively reduce copper ions while minimizing movement of free silver ions to the cathode surface, the optimum current density being 300A/m ².

In addition, in the electrolytic refining process, the solution circulation rate is 1-6L/h.

At high circulation rates, the mass transfer rate of free Ag ⁺ is increased, and discharge reduction occurs more easily to the cathode surface. But simultaneously, for AgBr particles which are mixed on the surface of the cathode, the AgBr particles can be taken away from the surface of the electrode by the electrolyte with a relatively high flow rate, and cannot be mixed in cathode copper. Under the combined action of the two factors, the Ag content in the cathode copper obtained by the two electrolytes is in a tendency of descending and ascending along with the increase of the circulation rate of the electrolytes. The optimal circulation rate is 5L/h.

The silver content in the cathode copper prepared by the method can be lower than 6ppm, the minimum silver content can even be lower than 1 ppm, and the cathode copper has excellent use effect.

The beneficial effects of the invention are as follows:

According to the invention, the original Cl ^- additive is replaced by the bromine salt additive, and the concentration of the novel additive is controlled, so that the concentration of free Ag ⁺ in the copper electrolyte is greatly reduced, a long-term stable effect can be formed, the method is suitable for industrial electrolytic copper production, and compared with the conventional process, the silver content in the prepared electrolytic copper can be greatly reduced, and the quality of the electrolytic copper is improved.

Drawings

FIG. 1 is a schematic view of an electrolytic device according to an embodiment of the present invention;

FIG. 2 is an optical photograph and SEM image of cathode copper obtained by electrolytic preparation of example 1 of the present invention;

FIG. 3 is an XRD pattern of anode mud obtained by electrolysis of the clean electrolyte used in example 1 of the present invention.

Detailed Description

The invention is described in further detail below with reference to specific examples and figures of the specification. Those of ordinary skill in the art will be able to implement the invention based on these descriptions. In addition, the embodiments of the present invention referred to in the following description are typically only some, but not all, embodiments of the present invention. Therefore, all other embodiments, which can be made by one of ordinary skill in the art without undue burden, are intended to be within the scope of the present invention, based on the embodiments of the present invention.

The raw materials used in the examples of the present invention are all commercially available or available to those skilled in the art unless otherwise specified, and the methods used in the examples of the present invention are all known to those skilled in the art.

The implementation of the method according to the embodiments of the present invention is based on the apparatus shown in fig. 1 unless otherwise specified.

If no special description exists, the invention simulates the industrial production environment for the laboratory environment, so that the conventional industrial electrolyte after long-time electrolysis is used as the initial copper electrolyte, and KBr with a certain concentration is added as the bromine salt additive to replace the original Cl ^- additive. The anode blister copper used was all commercially available blister copper of the same batch.

If not specified, the copper ion concentration of the initial copper electrolyte is measured by adopting an iodometry, and characterization results show that the Cu ²⁺ ion concentration is about 42-43 g/L, the sulfuric acid concentration is about 220-228 g/L in terms of sulfate radical, and the copper ion concentration and the sulfuric acid concentration are kept at initial set values by supplementing CuSO ₄·5H₂ O and dilute sulfuric acid.

Example 1

A method of preparing a low silver content cathode copper, the method comprising:

1) KBr (calculated by mass of Br) is added into the initial copper electrolyte according to the solid-to-liquid ratio of 20 mg to 1L, and the solution is stirred at the constant temperature of 60 ℃ for reaction 10 min and fully mixed;

2) And (2) carrying out electrolytic refining on the copper electrolyte obtained in the step (1) by taking blister copper as an anode and stainless steel as a cathode, wherein the temperature is 60 ℃ during electrolytic refining, the current density is 250A/m ², the electrolyte circulation flow rate of the electrolytic tank is 5L/h, the total electrolysis duration is 100 h, and KBr is periodically supplemented to keep Br ^- in the electrolyte at 20 mg/L. And recovering after the electrolysis is completed to obtain electrolytic copper material, namely cathode copper.

The cathode copper prepared in the embodiment is subjected to optical photograph and SEM characterization, the characterization result is shown in figure 2, and the optical photograph shows that the cathode copper prepared by the invention has smooth and flat surface and has no defects such as dendrite nodulation, and the like, which also shows that the use of a bromine salt additive does not have obvious influence on the surface state and quality of the cathode copper.

The distribution of Ag in the copper electrolyte and cathode copper in steps 1) and 2) of this example is shown in the following table.

Group of	Initial copper electrolyte	Bromine salt electrolyte	Cathode copper obtained by electrolysis of initial electrolyte	Cathode copper obtained by electrolysis of bromine salt electrolyte
					Silver content	0.20 mg/L	0.07 mg/L	16 ppm	6.0 ppm

Firstly, the method can effectively reduce the content of free Ag ⁺ in the copper electrolyte and silver in cathode copper. In addition, XRD characterization is performed on the anode slime obtained by filtering the original copper electrolyte and the copper electrolyte added with the bromine salt additive respectively, the characterization results are shown in fig. 3, it is obvious from fig. 3 that free Ag ⁺ in the original copper electrolyte containing the Cl ^- additive mainly becomes precipitate in the form of AgCl and enters the anode slime, and after Br ^- is added, the precipitate is mainly converted into AgBr. Continuously sampling and characterizing the electrolytic copper material in the preparation process. The results of the continuous sampling characterization are shown in the following table.

Sampling time (h)	5 h	10 h	20 h	30 h	50 h	70 h	100 h	Mean value of
									Silver content (ppm)	5.7	5.9	6.0	6.1	6.0	6.2	6.0	6.0

From the long-time electrolysis results, the cathode copper silver content overall tends to fluctuate as the electrolysis proceeds, probably because of the time-period of Br-addition, and the concentration of Br ^- in the electrolyte fluctuates to some extent as the electrolysis proceeds, resulting in a small change in the concentration of free Ag ⁺ in the electrolyte. However, for the technical scheme of the invention, the silver content of the obtained copper material is only increased by about 0.3 ppm compared with that of the copper material obtained by electrolytic refining of 100 h when the silver content is 5. 5 h, which shows that the copper electrolyte with the bromine salt as the additive has good effect of reducing the Ag content in cathode copper for a long time.

Comparative example 1

A method of electrorefining a copper material, the method comprising:

and (3) carrying out electrolytic refining (the concentration of Cl ^- is about 50 mg/L) in an initial copper electrolyte by taking blister copper as an anode and stainless steel as a cathode, wherein the temperature is 60 ℃ during electrolytic refining, the current density is 250A/m ², the electrolyte circulation flow rate of an electrolytic tank is 5L/h, the total electrolysis duration is 200 h, and the electrolytic copper material, namely cathode copper, is recovered after the completion of the electrolytic refining.

And continuously sampling and characterizing the electrolytic copper material in the preparation process. The results of the continuous sampling characterization are shown in the following table.

Sampling time (h)	5 h	10 h	20 h	30 h	50 h	70 h	100 h	Mean value of
									Silver content (ppm)	15.3	15.5	15.5	15.7	15.8	16.0	16.0	15.7

From the above characterization results, it can be seen that the increasing trend of silver content is more remarkable with the progress of the electrolysis process, and the average silver content of the cathode copper is increased by more than one time compared with example 1. It can be seen that the copper electrolyte with Cl ^- as an additive has limited effect on reducing the silver content of the cathode copper. The result of the comparative example also shows that the process of the invention has the effects of keeping the quality of electrolytic copper material stable and realizing the long-term stability of cathode copper with low silver content.

Example 2

1) KBr (calculated by mass of Br) is added into the initial copper electrolyte according to the solid-to-liquid ratio of 10 mg to 1L, and the solution is stirred at the constant temperature of 60 ℃ for reaction 10 min and fully mixed;

2) And (2) carrying out electrolytic refining on the copper electrolyte obtained in the step (1) by taking blister copper as an anode and stainless steel as a cathode, wherein the temperature is 60 ℃ during electrolytic refining, the current density is 250A/m ², the electrolyte circulation flow rate of the electrolytic tank is 5L/h, the total electrolysis duration is 100 h, and KBr is periodically supplemented to keep Br ^- in the electrolyte at 10 mg/L. And recovering after the completion to obtain electrolytic copper material, namely cathode copper.

The distribution of Ag ⁺ in the copper electrolyte and the cathode copper in steps 1) and 2) of this example is shown in the following table.

Group of	Initial copper electrolyte	Bromine salt electrolyte	Cathode copper obtained by electrolysis of initial electrolyte	Cathode copper obtained by electrolysis of bromine salt electrolyte
					Silver content	0.2 mg/L	0.09 mg/L	16 ppm	6.8 ppm

The table shows that the method can effectively reduce the content of free Ag ⁺ in the copper electrolyte and silver in cathode copper. The addition of 10 mg/L Br ^- significantly reduced the copper and silver content of the cathode and the free Ag ⁺ content of the electrolyte compared to comparative example 1. However, in comparative example 1, it was found that when the concentration of Br ^- was lower than 20 mg/L, the amount of added Br ^- could not sufficiently precipitate free Ag ⁺ as AgBr in the electrolyte, resulting in that a still part of free Ag ⁺ was discharged at the cathode, and thus the silver content was slightly higher than that in the cathode copper obtained by electrolysis of the copper electrolyte to which 20 ppm Br ^- was added.

Example 3

A method of reducing silver content in cathode copper, the method comprising:

1) KBr (calculated by mass of Br) is added into the initial copper electrolyte according to the solid-to-liquid ratio of 50 mg to 1L, and the solution is stirred at the constant temperature of 60 ℃ for reaction 10 min and fully mixed;

2) And (2) carrying out electrolytic refining in the copper electrolyte containing the bromine salt additive obtained in the step (1) by taking blister copper as an anode and stainless steel as a cathode, wherein the temperature is 60 ℃ during electrolytic refining, the current density is 250A/m ², the circulation flow rate of the electrolyte in the electrolytic tank is 5L/h, the total electrolysis duration is 100h, and KBr is periodically supplemented to keep Br ^- in the electrolyte at 50 mg/L. And recovering after the completion to obtain electrolytic copper material, namely cathode copper.

The distribution of Ag ⁺ in the copper electrolyte and the cathode copper in step 1) 2) of this example is shown in the following table.

Group of	Initial copper electrolyte	Bromine salt electrolyte	Cathode copper obtained by electrolysis of initial electrolyte	Cathode copper obtained by electrolysis of bromine salt electrolyte
					Silver content	0.20 mg/L	0.06 mg/L	16 ppm	6.5 ppm

It can be seen that the addition of 50 ppm of Br ^- greatly reduced the copper and silver content of the cathode and the free Ag ⁺ content of the electrolyte compared to comparative example 1.

From the above characterization results, it can be seen that the copper electrolyte obtained by adding 50 mg/L of the bromine salt additive in this example is actually worthy of slightly increasing the Ag content in cathode copper compared with example 1. This is because a higher concentration of Br ^- results in a significant increase in AgBr concentration in the electrolyte, and the probability of inclusion of these AgBr particles on the cathode surface is also greatly increased. It can thus also be seen that for the technical solution of the invention, not the more bromine salt additive is used, but the more appropriate amount is used to construct the corresponding stabilizing system in the copper electrolyte.

Continuously sampling and characterizing the electrolytic copper material in the preparation process. The results of the continuous sampling characterization are shown in the following table.

Sampling time (h)	5 h	10 h	20 h	30 h	50 h	70 h	100 h	Mean value of
									Silver content (ppm)	6.1	6.2	5.9	6.1	6.3	6.4	6.5	6.2

From the long-time electrolysis results, the cathode copper silver content overall tends to fluctuate as the electrolysis proceeds, probably because of the time-period of Br-addition, and the concentration of Br ^- in the electrolyte fluctuates to some extent as the electrolysis proceeds, resulting in a small change in the concentration of free Ag ⁺ in the electrolyte. However, for the technical scheme of the invention, the silver content of the obtained copper material is only increased by about 0.4 ppm when being compared with that of the copper material at 5h, which shows that the copper electrolyte taking the bromine salt as the additive has good effect of reducing the Ag content in cathode copper for a long time.

Example 4

A method of reducing silver content in cathode copper, the method comprising:

1) KBr (calculated by mass of Br) is added into the initial copper electrolyte according to the solid-to-liquid ratio of 20 mg to 1L, and stirred at a constant temperature of 56 ℃ for reaction 10 min to be fully mixed;

2) And (2) carrying out electrolytic refining in the copper electrolyte containing the bromine salt additive obtained in the step (1) by taking blister copper as an anode and stainless steel as a cathode, wherein the temperature is 56 ℃ during electrolytic refining, the current density is 250A/m ², the circulation flow rate of the electrolyte in the electrolytic tank is 5L/h, the total electrolysis duration is 100 h, and KBr is periodically supplemented to keep Br ^- in the electrolyte at 20 mg/L. And recovering after the completion to obtain electrolytic copper material, namely cathode copper.

Group of	Initial copper electrolyte	Bromine salt electrolyte	Cathode copper obtained by electrolysis of initial electrolyte	Cathode copper obtained by electrolysis of bromine salt electrolyte
					Silver content	0.20 mg/L	0.07 mg/L	16 ppm	6.2 ppm

The method can greatly reduce the content of copper and silver in the cathode and the content of free Ag ⁺ in the electrolyte. Meanwhile, the Ag content of the cathode copper in this example is slightly higher than that of example 1, because as the temperature increases, the difference between the critical concentration of free Ag ⁺ reduction and the actual concentration thereof is reduced according to the thermodynamic calculation of the nernst equation and species balance, i.e., the reduction amount of free ag+ in the electrolyte is reduced, and thus the Ag content in the cathode copper is reduced.

Sampling time (h)	5 h	10 h	20 h	30 h	50 h	70 h	100 h	Mean value of
									Silver content (ppm)	6.0	5.9	5.8	6.1	6.3	6.3	6.2	6.1

From the long-time electrolysis results, the cathode copper silver content fluctuates slightly as a whole as the electrolysis proceeds, which is probably due to the time-period nature of the addition of Br ^-, and the concentration of Br ^- in the electrolyte fluctuates to some extent as the electrolysis proceeds, resulting in a small change in the concentration of free Ag ⁺ in the electrolyte. However, for the technical scheme of the invention, the silver content of the obtained copper material is only increased by about 0.2 ppm when being compared with that of the copper material at 5h, which shows that the copper electrolyte taking the bromine salt as the additive has good effect of reducing the Ag content in cathode copper for a long time.

Example 5

A method of reducing silver content in cathode copper, the method comprising:

1) KBr (calculated by mass of Br) is added into the initial copper electrolyte according to the solid-to-liquid ratio of 20 mg to 1L, and the mixture is fully mixed after the reaction is stirred at the constant temperature of 64 ℃ for 10 min;

2) And (2) carrying out electrolytic refining on the copper electrolyte obtained in the step (1) by taking blister copper as an anode and stainless steel as a cathode, wherein the temperature is 64 ℃, the current density is 250A/m ², the electrolyte circulation flow rate of the electrolytic tank is 5L/h, the total electrolysis duration is 100 h, and KBr is periodically supplemented to keep Br ^- in the electrolyte at 20 mg/L. And recovering after the completion to obtain electrolytic copper material, namely cathode copper.

Group of	Initial copper electrolyte	Bromine salt electrolyte	Cathode copper obtained by electrolysis of initial electrolyte	Cathode copper obtained by electrolysis of bromine salt electrolyte
					Silver content	0.20 mg/L	0.07 mg/L	16 ppm	6.4 ppm

The method can greatly reduce the content of copper and silver in the cathode and the content of free Ag ⁺ in the electrolyte. Meanwhile, the Ag content of the cathode copper in the example is slightly higher than that of the example 1, because the content of the floating anode slime in the electrolyte is rapidly increased at a higher temperature, and the viscosity of the electrolyte is reduced along with the temperature rise, so that Ag-containing particles such as AgBr and the like are more likely to be mixed in the cathode copper along with the diffusion of the floating anode slime to the surface of the cathode, and the Ag content of the cathode copper is increased.

Sampling time (h)	5 h	10 h	20 h	30 h	50 h	70 h	100 h	Mean value of
									Silver content (ppm)	6.1	6.4	6.1	6.0	6.4	6.3	6.4	6.2

From the long-time electrolysis results, the cathode copper silver content fluctuates slightly as a whole as the electrolysis proceeds, which is probably due to the time-period nature of the addition of Br ^-, and the concentration of Br ^- in the electrolyte fluctuates to some extent as the electrolysis proceeds, resulting in a small change in the concentration of free Ag ⁺ in the electrolyte. However, for the technical scheme of the invention, the silver content of the obtained copper material is only increased by about 0.3 ppm when being compared with that of the copper material at 5h, which shows that the copper electrolyte taking the bromine salt as the additive has good effect of reducing the Ag content in cathode copper for a long time.

Example 6

A method of reducing silver content in cathode copper, the method comprising:

2) And (2) carrying out electrolytic refining on the copper electrolyte obtained in the step (1) by taking blister copper as an anode and stainless steel as a cathode, wherein the temperature is 60 ℃ during electrolytic refining, the current density is 250A/m ², the electrolyte circulation flow rate of the electrolytic tank is 4L/h, the total electrolysis duration is 100 h, and KBr is periodically supplemented to keep Br ^- in the electrolyte at 20 mg/L. And recovering after the completion to obtain electrolytic copper material, namely cathode copper.

Group of	Initial copper electrolyte	Bromine salt electrolyte	Cathode copper obtained by electrolysis of initial electrolyte	Cathode copper obtained by electrolysis of bromine salt electrolyte
					Silver content	0.2 mg/L	0.07 mg/L	16 ppm	6.2 ppm

The method can greatly reduce the content of copper and silver in the cathode and the content of free Ag ⁺ in the electrolyte. Meanwhile, the content of cathode copper Ag in the example is slightly higher than that in the example 1, because the concentration of free Ag ⁺ in the electrolyte is very low due to the addition of Br ^-, namely the inclusion amount of AgBr and Ag-containing colloidal particles plays a key role in the content of cathode copper Ag. According to the analysis of the reason why the circulating flow rate of the electrolyte in the third chapter affects the Ag content of the cathode copper, the increase of the flow rate makes the inclusion of AgBr and Ag-containing colloidal particles difficult, so that the Ag content of the cathode copper prepared by the embodiment is higher than that of the embodiment 1 under the condition of smaller flow rate.

Example 7

A method of reducing silver content in cathode copper, the method comprising:

1) NaBr (calculated by mass of Br) is added into the initial copper electrolyte in a solid-to-liquid ratio of 20 mg to 1L, and stirred at a constant temperature of 60 ℃ for reaction 10 min to be fully mixed;

2) And (2) carrying out electrolytic refining on the copper electrolyte obtained in the step (1) by taking blister copper as an anode and stainless steel as a cathode, wherein the temperature is 60 ℃ during electrolytic refining, the current density is 250A/m ², the electrolyte circulation flow rate of the electrolytic tank is 5L/h, the total electrolysis duration is 100 h, and the NaBr solution is periodically replenished to keep Br ^- in the electrolyte at 20 mg/L. And recovering after the completion to obtain electrolytic copper material, namely cathode copper.

The method can greatly reduce the content of copper and silver in the cathode and the content of free Ag ⁺ in the electrolyte. The control effect of the HBr solution and KBr solid on the Ag content in cathode copper is basically consistent.

Sampling time (h)	5 h	10 h	20 h	30 h	50 h	70 h	100 h	Mean value of
									Silver content (ppm)	6.0	5.9	6.1	6.3	6.1	6.3	6.2	6.1

From the long-time electrolysis results, the cathode copper silver content fluctuates slightly as a whole as the electrolysis proceeds, which is probably due to the time-period nature of the addition of Br ^-, and the concentration of Br ^- in the electrolyte fluctuates to some extent as the electrolysis proceeds, resulting in a small change in the concentration of free Ag ⁺ in the electrolyte. However, for the technical scheme of the invention, the silver content of the obtained copper material is only increased by about 0.2 ppm when compared with that of the copper material at 5h, which shows that the copper electrolyte taking NaBr as an additive also has good effect of reducing the Ag content in cathode copper for a long time.

Claims

1. A method for preparing cathode copper with low silver content, characterized in that:

The method comprises:

1) Prepare bromine-containing copper electrolyte;

2) Using pyrometallurgical anode copper as the anode and inert material as the cathode, and using the copper electrolyte obtained in step 1) as the electrolyte for electrolytic refining, thus obtaining cathode copper with low silver content.

2. The method for preparing cathode copper with low silver content according to claim 1, characterized in that:

Step 1) The copper electrolyte contains 10-100 mg/L of bromine salt;

After the bromine salt is added, the mixture is stirred at a constant temperature of 50 to 70° C. for 5 to 10 minutes.

3. The method for preparing cathode copper with low silver content according to claim 2, characterized in that:

The cations in the bromide salt are alkali metal cations and/or cations with a reduction potential ≤ the reduction potential of copper ions.

4. The method for preparing a low-silver content cathode copper according to claim 1, 2 or 3, characterized in that:

Step 1) The Cu ²⁺ ion concentration in the copper electrolyte is 30 to 60 g/L;

Step 1) The concentration of sulfuric acid in the copper electrolyte is 150-250 g/L.

5. The method for preparing cathode copper with low silver content according to claim 1, characterized in that:

Step 2) During the electrolytic refining process:

The current density is controlled to be 150-350 mA/cm ² , the distance between the cathode and the anode is 6-8 cm, and the electrolytic refining process is carried out at 50-70 ℃.

6. A cathode copper with low silver content obtained by the method according to any one of claims 1 to 5.