Method for recovering valuable metals from copper electrolytic slime

Abstract

To provide a method for collecting valuable metal from copper electrolytic slime, capable of improving a gold reduction rate so as to be equal to or greater than the rate in a conventional method without adding urea in reduction processing for reduction of gold.SOLUTION: There is provided a method for collecting valuable metal from copper electrolytic slime, the method comprising: (a) a step for exuding slurry of the copper electrolytic slime with chlorine, for exuding gold, platinum group metal, selenium, and tellurium; (b) a step for performing solvent extraction processing to the acquired chlorine exudate for extracting the gold to an organic phase, then after washing the organic phase with a hydrochloric acid, reducing the organic phase with an oxalic acid, for collecting the gold as a simple substance. In step (b), in washing the organic phase with the hydrochloric acid, water is added to the organic phase for dilution.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for recovering valuable metals from copper electrolytic slime.

Background Art

[0002] In the copper electrolysis process in the copper smelting process, electrolytic copper is obtained as the main product, and copper electrolytic slime is obtained as an intermediate product.

[0003] The valuable metals such as gold, silver, platinum group, selenium, and tellurium contained in the copper concentrate are concentrated in the intermediate product copper electrolytic slime, and they can be separated and recovered by a process that combines treatments such as chlorine leaching and solvent extraction (hereinafter sometimes referred to as the "valuable metal recovery process").

[0004] In the valuable metal recovery process, it is common to design to reduce the interest burden by shortening the period during which the noble metals stay in the system by recovering the noble metals at an early stage.

[0005] For example, Patent Document 1 describes a method for recovering valuable metals from copper electrolytic slime. Specifically, in Patent Document 1, when recovering noble metals, first, the copper electrolytic slime is treated with chlorine to obtain a leachate in which gold, platinum group elements, selenium, and tellurium are leached, and then gold is extracted into the organic phase by solvent extraction. After washing the organic phase with hydrochloric acid, gold is recovered as a single substance by reduction with oxalic acid. Thereafter, a technique for sequentially recovering platinum group elements, selenium, tellurium, etc. from the raffinate after gold extraction is disclosed.

[0006] Note that FIG. 1 is a diagram showing the overall flow for recovering valuable metals from copper electrolytic slime.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

[0008] The technology disclosed in Patent Document 1 mentioned above is a useful technology that allows for the selective and high-yield recovery of gold, platinum group elements, selenium, and tellurium from copper electrolytic slime by simple wet operations alone.

[0009] However, in conventional techniques, urea is added as a pH adjuster in the process of reducing and recovering gold with oxalic acid. While this improves the reduction rate of gold, it increases the total nitrogen concentration in the reduced solution, requiring wastewater treatment to remove the nitrogen.

[0010] Furthermore, as shown in Figure 2, the wastewater treatment is carried out in the wastewater treatment process (PGM wastewater treatment process) of the process for recovering platinum group elements. Since the wastewater sediment leaching residue generated through this process contains gold derived from the reduced liquid mentioned above, it was necessary to repeat the process of chlorine leaching copper electrolytic slime to minimize gold recovery loss. As a result, there was a problem in that the overall recovery efficiency of platinum group elements decreased.

[0011] This invention was proposed in view of the conventional situation, and aims to provide a method for recovering valuable metals from copper electrolytic slime that can improve the reduction rate of gold to the same level as or higher than conventional methods without adding urea in the reduction treatment for reducing gold. [Means for solving the problem]

[0012] The inventors conducted extensive research. As a result, they discovered that by solvent extraction of the chlorine leachate obtained by chlorine leaching of copper electrolytic slime, and then washing the resulting extract (organic phase) with chlorine, adding water to dilute the chlorine and increase the proportion of the aqueous phase, the reduction rate of gold can be increased without adding urea in the subsequent reduction treatment. This led to the completion of the present invention.

[0013] (1) The first aspect of the present invention is a method for recovering valuable metals from copper electrolytic slime, comprising: [a] leaching gold, platinum group elements, selenium, and tellurium from the slurry of the copper electrolytic slime with chlorine; and [b] subjecting the obtained chlorine leachate to solvent extraction to extract gold into an organic phase, washing the organic phase with hydrochloric acid, and then reducing it with oxalic acid to recover the gold as an element, wherein in step [b], when washing the organic phase with hydrochloric acid, the organic phase is diluted by adding water.

[0014] (2) The second invention of the present invention is a method for recovering valuable metals in which, in step [b] of the first invention, water is added to the organic phase when washing the organic phase with hydrochloric acid, thereby making the ratio of the organic phase to the aqueous phase of the solution after washing 100:55 to 100:85.

[0015] (3) The third invention of the present invention is a method for recovering valuable metals in which, in the first or second invention, urea is not added as a pH adjuster when oxalic acid is added to the organic phase after washing to reduce gold in step [b].

[0016] (4) The fourth invention of the present invention is a method for recovering valuable metals, wherein in any of the first to third inventions, in step [b], gold is extracted into the organic phase by mixing bis(2-butoxyethyl) ether with the chlorine leachate and performing the solvent extraction treatment. [Effects of the Invention]

[0017] According to the present invention, in a method for recovering valuable metals from copper electrolytic slime, the reduction rate of gold can be improved to the same level as or better than conventional methods without adding urea in the reduction treatment for reducing gold. [Brief explanation of the drawing]

[0018] [Figure 1] This diagram shows the overall flow of a method for recovering valuable metals from copper electrolytic slime. [Figure 2]A flowchart related to the process for recovering platinum group elements after the conventional method. [Figure 3] A flowchart related to the process for recovering platinum group elements after the method according to this embodiment.

Embodiments for Carrying Out the Invention

[0019] Hereinafter, specific embodiments of the present invention (hereinafter referred to as "this embodiment") will be described in detail. Note that the present invention is not limited to the following embodiments, and various modifications are possible without changing the gist of the present invention.

[0020] ≪1. Method for Recovering Valuable Metals from Copper Electrolytic Slime≫ The method according to this embodiment is a method for recovering valuable metals from copper electrolytic slime obtained through the copper electrolysis process in the copper electrolysis process. As described above, valuable metals such as gold, silver, platinum group, selenium, and tellurium are concentrated in the copper electrolytic slime. By subjecting such copper electrolytic slime to treatment such as chlorine leaching treatment or solvent extraction treatment, these valuable metals can be effectively recovered.

[0021] Specifically, this method includes [a] a step of leaching gold, platinum group elements, selenium, and tellurium by leaching a slurry of copper electrolytic slime with chlorine (hereinafter also referred to as the "[a] step"), and [b] a step of subjecting the obtained chlorine leachate to solvent extraction treatment to extract gold into the organic phase, washing the organic phase with hydrochloric acid, and then reducing it with oxalic acid to recover gold as a single substance (hereinafter also referred to as the "[b] step").

[0022] And particularly, in the method according to this embodiment, in the [b] step, when washing the organic phase with hydrochloric acid, it is characterized in that the organic phase is diluted by adding water thereto.

[0023] According to such a method, by adding water to the organic phase to increase the water phase ratio in the solution after washing, the subsequent reduction of gold with oxalic acid can be efficiently carried out.

[0024] Furthermore, conventionally, when reducing gold using oxalic acid, urea was added as a pH adjuster to promote the reduction of gold and to suppress the coprecipitation of impurities. In contrast, by washing by adding water to the organic phase to increase the water-phase ratio, as described above, an equivalent or better gold reduction rate can be achieved without adding urea during the gold reduction process. Moreover, since there is no need to add urea in this way, the generation of ammonium chloride based on the reaction of urea in the solution can be prevented, and the total nitrogen (TN) concentration in the wastewater after the reduction treatment can be suppressed, thereby effectively reducing the nitrogen load in the wastewater discharged outside the system.

[0025] In the technology disclosed in Patent Document 1, the reduction of gold can be accelerated by using urea as a pH adjuster in the step of reducing gold (paragraph

[0027] of Patent Document 1). Specifically, by using urea, the chlorine produced as a by-product in the reduction reaction of gold can be neutralized as shown in the following reaction equation, thereby accelerating the reduction reaction. (Equation 1) Reduction by oxalic acid :2HAuCl4+3H2C2O4⇒ 2Au+6CO2+8HCl (Equation 2) Neutralization of hydrochloric acid with urea :8HCl+4(NH2)2CO+4H2O ⇒ 8NH4Cl+4CO2

[0026] Conventional methods like this required wastewater treatment to discharge the wastewater containing the generated ammonium chloride from the system. Specifically, as shown in the flow in Figure 2, for example, the wastewater was treated in a wastewater treatment process (PGM wastewater treatment process) together with the wastewater generated in the process of recovering platinum group elements (PGM purification wastewater). However, at this time, the generated wastewater sediment leaching residue had to be repeated in a process of chlorinating copper electrolytic slime ([a] process), which resulted in a problem in that the overall efficiency of platinum group element recovery decreased in the treatment flow.

[0027] The reason why the wastewater sediment leachate residue is repeatedly treated in the chlorine leaching process is that it contains gold, and in order to recover the remaining gold, it is necessary to repeat the treatment in the initial chlorine leaching process. The reason why the wastewater sediment leachate residue contains gold is, as mentioned above, because the solution after the gold reduction treatment (gold reduction solution) is introduced into the PGM wastewater treatment process for wastewater treatment. In the gold reduction reaction, ammonium chloride is produced by the reaction of urea added as a pH adjuster (buffer), so if it is treated as is, the total nitrogen concentration in the wastewater will increase. As a countermeasure, the ammonium chloride is decomposed in the PGM wastewater treatment process, volatilized as ammonia, collected in the abatement tower, and the circulating liquid is discharged out of the system as an ammonium sulfate solution.

[0028] The inventors conducted basic tests on the role of urea in the gold reduction process and confirmed the consumption rate of added urea. The results showed that approximately 10% of the added urea is consumed by the gold reduction reaction according to the above reaction equation (Equation 2). Therefore, in order to confirm the gold reduction rate and the quality of the reduced gold when the amount of added urea is reduced, tests were conducted in actual operation. The results showed that the gold reduction rate did not change even when the amount of added urea was reduced, and that even without the addition of urea, the gold reduction rate could be made equal to or better than that of the conventional method by increasing the water phase ratio.

[0029] Furthermore, reducing the amount of urea added lowered the total nitrogen concentration in the gold reduction solution, but there was no significant difference in the ammonia nitrogen (NH4-N) concentration. Therefore, it was concluded that the current amount of urea added is excessive, even in actual operation. Unsurprisingly, when no urea was added, both the total nitrogen concentration and the ammonia nitrogen concentration in the gold reduction solution were very low.

[0030] Based on the above, in the method according to this embodiment, in the step of reducing and recovering gold (step [b]), instead of adding urea as a pH adjuster as in the conventional method, when washing the organic phase obtained after solvent extraction with chlorine, water is added to dilute it and increase the water phase ratio in the solution after washing. As a result, a gold reduction rate equal to or higher than that of the conventional method can be achieved.

[0031] Furthermore, the method according to this embodiment can suppress the total nitrogen (TN) concentration in the wastewater after reduction treatment, thereby effectively reducing the nitrogen load in the wastewater discharged outside the system. As a result, as shown in the flow diagram of Figure 3, in the process of recovering platinum group elements, it is no longer necessary to repeat the wastewater sediment leaching residue generated in the wastewater treatment process (PGM wastewater treatment process) into the process of chlorinating copper electrolytic slime ([a] process), and the overall treatment flow can suppress a decrease in the recovery efficiency of platinum group elements (see also the flow diagram of Figure 4 regarding the platinum group element recovery process after the conventional method).

[0032] ≪2. About Each Process≫ The following describes in more detail each step of the method for recovering valuable metals. As described above, the method according to this embodiment includes: [a] a step of leaching a copper electrolytic slime slurry with chlorine; and [b] a step of subjecting the chlorine leachate to solvent extraction to extract gold into an organic phase, washing the organic phase with hydrochloric acid, and then recovering the gold as an element by reduction with oxalic acid.

[0033] [Process of chlorine leaching of copper electrolytic slime ([a] process)] [a] In step [a], gold, platinum group elements, selenium, and tellurium are leached from the copper electrolytic slime slurry with chlorine.

[0034] The copper electrolytic slime to be treated with chlorine leaching is not particularly limited; the slime that accumulates at the bottom of the electrolytic cell during normal copper electrolytic refining can be used as is. Water is added to this copper electrolytic slime so that the slurry concentration, which can be calculated from the selenium and copper content in the slime, is approximately 150 g / L to 300 g / L, and the mixture is stirred to form a slurry.

[0035] The chlorine leaching process is carried out by blowing chlorine gas into the copper electrolytic slime slurry. As a result, copper, selenium, silver, etc. in the copper electrolytic slime are leached out by reacting with the blown-in chlorine gas to form chlorides, as shown in equations 3 and 4 below. (Equation 3) Cu + Cl2 ⇒ CuCl2 (Formula 4)Ag2Se+3Cl2+3H2O ⇒ 2AgCl+H2SeO3+4HCl

[0036] Here, the copper and selenium content in the copper electrolytic slime varies greatly depending on the mineral composition of the raw materials and the pretreatment method, and even if the initial hydrochloric acid and chloride concentrations are kept constant, the chloride concentration in the final chlorine leachate changes significantly. Antimony, which is particularly harmful in subsequent processes, increases rapidly with increasing chloride concentration, so it is important to control the chloride concentration in the chlorine leachate obtained through step [a]. Specifically, since the antimony concentration increases when the chloride concentration exceeds 130 g / L, it is preferable to maintain the chloride concentration in the chlorine leachate at 130 g / L or less, and more preferably at 110 g / L or less. The chloride concentration in the chlorine leachate can be calculated from the selenium grade and metallic copper grade in the raw materials. Alternatively, it can be adjusted by monitoring the chloride concentration of the mother liquor of the chlorine leachate slurry and adding water to adjust the concentration if it exceeds the target concentration.

[0037] Alternatively, before leaching with chlorine gas, an oxidation treatment may be performed by blowing air or oxygen into the copper electrolytic slime slurry to oxidize the copper in the slurry and convert it into copper oxide. The copper oxide produced by the oxidation treatment consumes the hydrochloric acid produced by chlorine leaching (see formula 4 above), so that copper is leached out as copper chloride, and at the same time, the concentration of hydrochloric acid in the chlorine leaching solution decreases. By performing chlorine leaching after this oxidation treatment, the oxidized copper has already been leached out, so the corresponding amount of chlorine gas can be saved. In addition, the concentrations of dissolved chlorine and free hydrochloric acid in the chlorine leaching solution can be controlled, and consequently the chloride concentration can be controlled, so even if the composition of the copper electrolytic slime changes due to a change in the raw material composition of copper smelting, the chloride concentration in the chlorine leaching solution can be stably maintained within the desired range.

[0038] [Process for extracting and recovering gold from chlorine leachate ([b] process)] In step [b], the chlorine leachate obtained in step [a] is subjected to solvent extraction to extract gold into an organic phase. After washing the organic phase with hydrochloric acid, the gold is recovered as elemental gold by reduction with oxalic acid.

[0039] (extraction stage) The extraction treatment of the chlorine leachate is preferably carried out using bis(2-butoxyethyl) ether, which is a gold extraction solvent. By mixing bis(2-butoxyethyl) ether with the chlorine extract, gold is extracted into the organic phase.

[0040] (Washing stage) Next, hydrochloric acid is added to the organic phase, which is the extract from which the gold was extracted, and the mixture is washed. This washes away any impurities that were extracted along with the gold.

[0041] In this embodiment, hydrochloric acid is added to the organic phase, and water is added to dilute it. That is, the hydrochloric acid is diluted by adding water. This increases the proportion of the aqueous phase in the post-wash solution.

[0042] Specifically, the amount of water used for dilution is not particularly limited, but the ratio of the organic phase to the aqueous phase of the solution after washing is preferably in the range of 100:55 to 100:85, and more preferably in the range of 100:60 to 100:80.

[0043] Conventionally, this washing process only involved adding hydrochloric acid to the organic phase, resulting in an organic-to-aqueous phase ratio of approximately 100:50 in the post-wash solution. In contrast, by adding water to the organic phase to dilute the hydrochloric acid, the pH can be adjusted to an appropriate range. In other words, the added water acts as a pH adjuster.

[0044] As mentioned above, in conventional methods, urea was added to the organic phase as a pH adjuster during the reduction treatment with oxalic acid, which will be described later. This was done because, in the reduction of gold with oxalic acid (see Equation 1 above), hydrochloric acid is generated as the reduction reaction progresses. The purpose of neutralizing the generated hydrochloric acid with urea was to accelerate the reduction reaction in order to improve the gold recovery rate (reduction rate).

[0045] In contrast, the method according to this embodiment is characterized by not adding urea in the reduction treatment, but instead adding water to the organic phase in the preceding washing stage to increase the proportion of the aqueous phase, thereby adjusting the pH to a desired range in the subsequent reduction treatment and suppressing the decrease in pH caused by the hydrochloric acid produced.

[0046] This method, using the simple and efficient method of adding water, can improve the gold reduction rate to the same level as or better than conventional methods, enabling high gold recovery. In addition, since urea addition is not required in the reduction treatment, the total nitrogen (TN) concentration in the wastewater after the reduction treatment can be suppressed, effectively reducing the nitrogen load in the wastewater discharged outside the system. As a result, as shown in the flow in Figure 3, in the process of recovering platinum group elements, it is no longer necessary to repeat the wastewater sediment leaching residue generated in the wastewater treatment process (PGM wastewater treatment process) into the process of chlorinating copper electrolytic slime ([a] process), thus suppressing the decrease in the overall treatment flow efficiency of platinum group element recovery.

[0047] Figure 2 is a flowchart of the platinum group element recovery process after going through the conventional method, and Figure 3 is a flowchart of the platinum group element recovery process after going through the method according to this embodiment.

[0048] In this embodiment, as described above, by adding water to the organic phase in the washing step to increase the proportion of the aqueous phase, the reduction rate of gold can be improved, and gold can be recovered with a high recovery rate. Specifically, the reduction rate of gold can be 61.0% or higher. On the other hand, while a higher reduction rate of gold is naturally preferable as it improves the gold recovery rate, impurity elements (e.g., selenium, tellurium, etc.) are also reduced along with the gold during the reduction process, which can lead to a higher concentration of impurities. Therefore, although there is no particular upper limit to the reduction rate of gold, it is preferable to have it at around 68.5% or lower.

[0049] In this context, "gold reduction rate" is expressed as the percentage difference between the gold concentration in the organic phase before and after gold reduction treatment, relative to the gold concentration in the organic phase before gold reduction treatment.

[0050] (Back extraction stage and reduction process) Next, an oxalic acid aqueous solution is added to the solution after the washing treatment (post-washing solution) and heated to back-extract gold from the organic phase and reduce the gold to its elemental state.

[0051] Specifically, in reduction with oxalic acid, gold is back-extracted by the reaction shown in Formula 1 above, and elemental gold is generated and recovered. In this embodiment, urea is not added to the organic phase.

[0052] As described above, in the method according to this embodiment, water is added to the organic phase during the washing process (washing stage), thereby diluting the hydrochloric acid used as the washing solution. This allows for appropriate adjustment of the pH conditions in the subsequent reduction process, improving the reduction rate of gold and enabling effective gold recovery. Furthermore, since the addition of urea is not required in the reduction process, the total nitrogen (TN) concentration in the wastewater after the reduction process can be suppressed, effectively reducing the nitrogen load in the wastewater discharged outside the system. [Examples]

[0053] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way to the following examples.

[0054] ≪Test 1≫ (Preparation of copper electrolytic slime slurry) Water was added to copper electrolytic slime with the composition shown in Table 1 below and mixed to prepare a slurry with a solid content ratio of approximately 30% by mass (approximately 300 g / L).

[0055] [Table 1]

[0056] (Chlorine leaching: [a] process) The prepared slurry was subjected to a chlorine leaching treatment by blowing chlorine gas into the liquid phase until it was saturated with chlorine, under conditions of a reaction time of 4 hours and a reaction temperature of 85°C. Subsequently, the leaching residue was separated using a centrifuge, and the mixture was washed until the washing solution became colorless to obtain a chlorine leachate (including the residue washing solution). Table 2 below shows the composition of the chlorine leachate and the leaching rates of each element.

[0057] [Table 2]

[0058] (Gold recovery: [b] process) Next, the obtained chlorine leachate was subjected to solvent extraction. First, in the extraction stage, the chlorine leachate was mixed and contacted with bis(2-butoxyethyl) ether (hereinafter referred to as "DBC"), and then the organic phase and aqueous phase were separated. An extract in which gold was distributed to the organic phase and a residual extract in which the rest was distributed to the aqueous phase were obtained. The processing volume was set so that the amount of organic phase obtained was 4000 L or more.

[0059] Next, in the washing stage, hydrochloric acid was added to the extract (organic phase) to wash it, and a post-washing solution was obtained consisting of post-washing organic, in which gold remained in the organic phase, and post-washing water, in which the other components remained in the aqueous phase.

[0060] In Example 1, water was added to the extract to dilute the hydrochloric acid, so that the ratio of the organic phase to the aqueous phase in the post-wash solution was 100:70.

[0061] On the other hand, in Comparative Examples 1-3, washing with hydrochloric acid was performed without adding water. The ratio of organic phase to aqueous phase in the solution after washing was 100:50. Therefore, it can be seen that in Example 1, water was added so that the amount of aqueous phase was 1.4 times that of Comparative Examples 1-3.

[0062] Next, an aqueous oxalic acid solution was added to the washed organic material, and the temperature was raised to 90°C to back-extract the gold from the washed organic material. At the same time, the gold was reduced to elemental gold as shown in Equation 5 below to obtain the reduced solution. (Equation 5) Reduction by oxalic acid :2HAuCl4+3H2C2O4⇒ 2Au+6CO2+8HCl

[0063] As can be seen from the reduction reaction equation above, hydrochloric acid is produced as the reduction of gold progresses, and the pH decreases. Therefore, in order to improve the gold recovery rate, it is necessary to facilitate the reduction reaction, and it has been found that it is sufficient to adjust the pH to a level of around -1.5.

[0064] Therefore, in Comparative Examples 1 to 3, an excess amount of urea, greater than the amount equivalent to the reduction, was added to the organic material after washing to neutralize the hydrochloric acid produced as shown in Formula 6 below. The amount of urea added is shown in Table 3 below, and is expressed as a relative amount when the amount added in Comparative Example 1 under normal operation is set to "1.00". (Equation 6) Neutralization of hydrochloric acid with urea :8HCl+4(NH2)2CO+4H2O ⇒ 8NH4Cl+4CO2

[0065] In contrast, in Example 1, where water was added to the extract during the washing stage, the reduction treatment was performed without adding urea.

[0066] Table 3 below shows the treatment conditions for Example 1 and Comparative Examples 1-3. From Table 3 below, it can be seen that in Example 1 as well, the pH range was adjusted to -1.50 ± 0.01.

[0067] [Table 3]

[0068] Table 4 below shows the results of measuring the gold reduction rate, calculated from the gold concentration in the gold-reduced organic solution, and the total nitrogen (TN) concentration remaining in the post-reduction solution (for further treatment) immediately after the gold reduction treatment. In evaluating the gold reduction rate, a reduction rate of 62.0% to 68.5% was marked with "○", and any reduction rate outside this range was marked with "×".

[0069] [Table 4]

[0070] As shown in the results in Table 4, in Example 1, where water was added to the extract for washing and urea was not added in the subsequent reduction treatment, gold could be reduced to almost the same extent as in Comparative Examples 1 and 2. Furthermore, in Example 1, because urea was not added, the total nitrogen concentration in the post-reduction solution was at an extremely low level, making nitrogen removal treatment (N treatment) unnecessary.

[0071] On the other hand, in Comparative Examples 1 and 2, although gold was effectively reduced, the addition of urea increased the nitrogen concentration in the post-reduction solution, necessitating further treatment (N treatment) of the post-reduction solution in the subsequent wastewater treatment process (PGM wastewater treatment process) for recovering platinum group elements. In this case, as shown in the flow diagram in Figure 2, the wastewater sediment leaching residue generated in the wastewater treatment process had to be repeated in the "chlorine leaching process of copper electrolytic slime ([a] process)," raising concerns that the overall recovery efficiency of platinum group elements would decrease.

[0072] Furthermore, in Comparative Example 3, although the total nitrogen concentration in the reduced solution was low and therefore nitrogen removal treatment was unnecessary, the gold reduction rate decreased, and gold could not be recovered effectively.

[0073] ≪Test 2≫ In Experiment 2, the copper electrolytic slime slurry prepared using the same procedure as in Example 1 of Experiment 1 was subjected to chlorine leaching to obtain a chlorine leaching solution with a gold concentration of 32 g / L in the organic phase before gold reduction. Solvent extraction was then performed using this chlorine leaching solution. During the washing stage of the solvent extraction, the ratio of the organic phase to the aqueous phase was changed by adding a predetermined amount of water to the extract (organic phase). Other conditions were the same as in Example 1, and urea was not added during the reduction treatment.

[0074] Table 5 below shows the conditions for the organic phase / aqueous phase ratio in the washing stage and the results for each test example. In evaluating the gold reduction rate, a reduction rate of 62.0% to 68.5% was marked with "○", and any reduction rate outside this range was marked with "×". It should be noted that if the gold reduction rate exceeds 68.5%, impurity elements may also be reduced, potentially leading to a higher impurity concentration.

[0075] [Table 5]

[0076] As shown in the results in Table 5, it was found that gold could be effectively reduced by adding water to the extract during the washing stage of the solvent extraction process, thereby adjusting the organic phase:aqueous phase ratio to a range of 100:55 to 100:85. Furthermore, because urea was not added, the total nitrogen concentration in the post-reduction solution was low, eliminating the need for nitrogen removal treatment (N treatment).

Claims

1. A method for recovering valuable metals from copper electrolytic slime, [a] A step of leaching gold, platinum group elements, selenium, and tellurium from the copper electrolytic slime slurry with chlorine, [b] A step of extracting gold into an organic phase by solvent extraction treatment of the obtained chlorine leachate, washing the organic phase with hydrochloric acid, and then reducing it with oxalic acid to recover the gold as elemental material, Includes, In step [b] above, when washing the organic phase with hydrochloric acid, the organic phase is diluted by adding water. In step [b] above, when oxalic acid is added to the organic phase after washing to reduce the gold, urea is not added as a pH adjuster. Methods for recovering valuable metals.

2. In step [b] above, when washing the organic phase with hydrochloric acid, water is added to the organic phase to make the ratio of the organic phase to the aqueous phase of the solution after washing 100:55 to 100:

85. A method for recovering valuable metals according to claim 1.

3. In step [b] above, gold is extracted into the organic phase by mixing bis(2-butoxyethyl) ether with the chlorine leachate and performing the solvent extraction treatment. A method for recovering valuable metals according to claim 1 or 2.

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