Process for the purification of bismuth

Abstract

A bismuth purification method for recovering bismuth from a liquid obtained after recovering precious metals from copper electrolytic mud comprises six steps: 1) a neutralization process, in which an alkali is added to an acidic solution to adjust the pH to a range of 2.0 or higher and 3.0 or lower, followed by solid-liquid separation to obtain a neutralized filtrate and a neutralized precipitate; 2) an alkali leaching process, in which an alkali is added to the neutralized precipitate obtained from the neutralization process to separate it into an alkali leaching solution and an alkali leaching residue; 3) a sulfuric acid leaching process, in which sulfuric acid is added to the alkali leaching residue to separate it into a sulfuric acid leaching solution and a sulfuric acid leaching residue; 4) a cooling process, in which the sulfuric acid leaching solution obtained from the sulfuric acid leaching process is cooled to obtain bismuth sulfate crystals; 5) a bismuth oxidation process, in which an alkali is added to the bismuth sulfate crystals obtained from the cooling process to obtain bismuth oxide; 6) an electrolysis process, in which an acid solution is added to the bismuth oxide obtained from the bismuth oxidation process to dissolve the bismuth oxide, and the resulting solution is electrolyzed to extract metallic bismuth.

Description

[0001] This application is a divisional application of the application filed on January 30, 2017, with application number 201780037819.7 and invention title "Method for Purifying Bismuth". Technical Field

[0002] This invention relates to a method for purifying (refining) bismuth. More specifically, it relates to a method for recovering bismuth as a valuable metal from copper electrolysis slime generated in a copper electrolysis refining process. Background Technology

[0003] The general method for recovering copper from copper-bearing ore is as follows: the copper-bearing ore is beneficiated to obtain copper concentrate, which is then melted in a furnace at high temperature. This dry smelting process yields crude copper. The crude copper is then used as an anode and immersed in a sulfuric acid solution. Current flows between the anode and a cathode, which is impregnated with a stainless steel plate and a copper plate facing each other. Copper dissolved from the anode is selectively electrolyzed onto the cathode. This electrolytic purification process yields high-purity electrolytic copper.

[0004] In the aforementioned copper-bearing ores, besides the target copper, they often contain a variety of other components, including precious metals such as gold and silver, valuable substances such as bismuth, arsenic, antimony, selenium, lead, iron, and tellurium, as well as impurities. These components are separated as slag in the aforementioned dry smelting process, or as copper electrolytic mud deposited at the bottom of the electrolytic cell along with precious metals during electrolytic purification, thus separating from the copper.

[0005] Because the aforementioned copper electrolytic sludge contains a variety of components, it is necessary to purify the sludge to recover valuable substances.

[0006] There are many known methods for purifying mud. One method is to add sulfuric acid to copper electrolytic mud to dissolve and remove the copper mixed in the mud, which is called copper removal. Then, the copper-removed mud is loaded into a furnace and heated to a high temperature to volatilize and separate selenium and antimony. Next, oxidation is carried out to separate lead in the form of oxides. Finally, precious metals and bismuth are separated.

[0007] While the above method is suitable for processing large quantities of materials, it also faces challenges such as increased processing efficiency due to the need for large-scale equipment, high energy costs, and the fact that the step of recovering precious metals is located in the latter half of the process.

[0008] In light of this, the application of new processing technologies centered on wet methods has gradually been promoted in recent years. These wet processing technologies use wet reduction or roasting methods for selenium separation, and can be broadly classified into the following two methods.

[0009] The first method is the method shown in Non-Patent Document 1, Patent Document 1, or Patent Document 2.

[0010] In these methods, sulfuric acid and oxygen are added to copper electrolytic mud, and a portion of tellurium and copper are leached under high temperature and high pressure conditions. Then, hydrochloric acid and hydrogen peroxide or chlorine are added to the leaching residue to leach gold, platinum group elements, selenium, and tellurium.

[0011] Then, bis(2-butoxyethyl) ether (hereinafter referred to as DBC) is mixed into the leachate as an organic extractant to extract gold into the extractant. The raffinate is then reduced with sulfur dioxide to recover selenium, tellurium, and platinum group elements. Selenium is separated from tellurium and platinum group elements by distillation of the mixture of selenium, tellurium, and platinum group elements in the metallic state. For the chlorine leaching residue, silver is leached out by treatment with ammonia water, and then recovered from the leachate in powder form.

[0012] The second method is shown in Non-Patent Document 2. That is, up to the step of removing copper and tellurium through pressure leaching with sulfuric acid, the process is the same as the first method described above, but the residue is then mixed with sulfuric acid and roasted to volatilize and separate the selenium, while simultaneously converting the silver in the residue into silver sulfate. Then, for the sulfuric acid roasting residue, the silver is first leached with an aqueous solution of calcium nitrate, and then the leaching solution is electrolyzed to recover the silver metal.

[0013] Gold, platinum group elements, selenium, and residual tellurium are leached from the residue after silver leaching using hydrochloric acid and chlorine. DBC is then mixed into the leachate to extract gold, following the same principle as the first method. Furthermore, the platinum group elements and tellurium are recovered as metal powder by hydrazine reduction of the raffinate.

[0014] Furthermore, as a method for recovering silver from sulfuric acid roasting residue in the second method described above, a method using ammonia and a method using sodium sulfite, similar to the first method described above, have been proposed.

[0015] However, in both of the methods described above, the separation of several valuable substances and impurities, such as bismuth, does not disclose the recovery of bismuth in the wet process. For bismuth, the traditionally implemented dry process is used to melt it and recover it from the slag. However, this method has drawbacks, including increased investment in furnaces, energy consumption, and other costs associated with implementing the dry process, making it less than ideal.

[0016] Existing technical documents

[0017] Patent documents

[0018] Patent Document 1: Japanese Patent Application Publication No. 9-316559;

[0019] Patent document 2: Japanese Patent Application Publication No. 9-316561.

[0020] Non-patent literature

[0021] Non-patent literature 1: KESutliff et al, JOM, August (1996), pp42-44; JEHoffman et al, Proceedings of COPPER 95-COBRE 95 International Conference Volume III (1995), The Metallurgical Society of CIM, pp41-57;

[0022] Non-patent document 2: JEHoffmann et al, HY DROMETALLURGY'94, the Institution of Mining and Metallurgy and the Society of Chemical Industry, CHAPMAN&HALL (1994), pp69-105. Summary of the Invention

[0023] The purpose of this invention is to provide a method for efficiently recovering and purifying bismuth from the liquid obtained after recovering precious metals from copper electrolytic mud, using mainly wet processes and minimizing the use of furnaces, etc.

[0024] The first invention is a method for purifying bismuth, characterized in that, in the process of recovering copper by electrolytic purification of crude copper obtained from smelting minerals containing copper, precious metals, bismuth and impurities, and then recovering precious metals from the electrolytic mud generated by electrolytic purification by a wet method, the acidic solution generated after the recovery of precious metals is subjected to the following process, wherein the impurities are one or more of iron, lead, arsenic and tellurium.

[0025] 1) Neutralization process: Add alkali to the aforementioned acidic solution to adjust the pH to the range of 2.0 to 3.0, distribute impurities containing iron and antimony to the neutralization filtrate and remove them, and distribute bismuth, which is to be recovered, and a portion of the impurities to the neutralization precipitate.

[0026] 2) In the alkaline leaching process, 1-5 mol / L sodium hydroxide solution is added to the neutralized precipitate to make the slurry concentration 10-100 g / L, the reaction temperature is set to about 60°C, and impurities containing arsenic and chloride ions are distributed to the leaching solution for removal, so that the proportion of iron, lead and arsenic distributed to the alkaline leaching residue is less than 50%, the molar ratio of arsenic to bismuth in the alkaline leaching residue is less than 0.1, and the chloride ion content is less than 0.1%.

[0027] 3) Washing process: Water is added to the alkaline leaching residue to form a slurry, and the mixture is washed until the pH value is 2.5 to 3.5.

[0028] 4) In the sulfuric acid leaching process, sulfuric acid is added to the washed alkaline leaching residue to separate it into a sulfuric acid leaching solution in which the copper distribution rate in the sulfuric acid leaching solution reaches more than 50%, and a sulfuric acid leaching residue with reduced impurities.

[0029] The sulfuric acid leaching process consists of two stages: primary treatment and secondary treatment.

[0030] The primary treatment involves contacting the washed alkaline leaching residue with sulfuric acid of a weak acid concentration (pH 0–3.5) to leach the residue, separating it into a primary leachate and a primary leaching residue.

[0031] The secondary treatment involves contacting the primary leaching residue with sulfuric acid of a strong acid concentration (pH less than 0) to separate it into a secondary leaching solution and a secondary leaching residue.

[0032] 5) Cooling process: The secondary leachate obtained in the sulfuric acid leaching process is cooled to obtain bismuth sulfate crystals;

[0033] 6) Bismuth oxidation process: An alkali is added to the crystallization of bismuth sulfate to obtain bismuth oxide;

[0034] 7) Electrolysis process: An acid solution is added to the bismuth oxide to dissolve the bismuth oxide, and the resulting solution is electrolyzed to extract metallic bismuth.

[0035] The second invention is a method for purifying bismuth, characterized in that the acid solution used in the aforementioned electrolysis process of the first invention is a solution containing hexafluorosilicic acid.

[0036] According to the first invention, high-purity metallic bismuth can be obtained from an acidic solution generated during copper smelting by sequentially performing the following steps.

[0037] (1) In the neutralization process, bismuth can be separated at a high concentration by setting the pH to 2.0 to 3.0.

[0038] (2) In the alkaline leaching process, an alkaline leaching residue containing bismuth and an alkaline leaching solution containing arsenic impurities are separated. The alkali used is a 1–5 mol / L sodium hydroxide solution, the slurry concentration is 10–100 g / L, and the reaction temperature is approximately 60°C. This allows for rapid reaction, removal of arsenic, and suppression of bismuth loss. Furthermore, by setting the molar ratio of arsenic to bismuth in the alkaline leaching residue to 0.1 or less, the bismuth recovery rate in the subsequent sulfuric acid leaching process can be improved. Moreover, by setting the chloride ion content in the alkaline leaching residue to 0.1% or less, bismuth loss in the subsequent cooling process can be reduced.

[0039] (3) In the washing process, by adding water to the alkali leaching residue, the dispersibility of bismuth is improved. Therefore, in the sulfuric acid leaching process, which is the subsequent process, bismuth can be easily leached in sulfuric acid.

[0040] (4) In the sulfuric acid leaching process, copper and iron are leached in the primary treatment using sulfuric acid with a weak acid concentration. Therefore, in the secondary treatment using sulfuric acid with a strong acid concentration, the solubility of bismuth increases, which can improve the distribution rate of copper in the sulfuric acid leaching solution. Thus, it can avoid the adverse effects on the copper grade in the bismuth product caused by insufficient copper removal.

[0041] (5) After the above processes, bismuth sulfate crystals are obtained in the cooling process, bismuth oxide is obtained in the bismuth oxidation process, and metallic bismuth is obtained in the electrolysis process.

[0042] (6) As long as the above-mentioned processes are implemented, the bismuth contained in the raw solution can be recovered with a high recovery rate, and high-purity metallic bismuth can be obtained.

[0043] According to the second invention, since an electrolyte containing bismuth fluoride is used, high-purity metallic bismuth with impurities sufficiently separated can be obtained. Attached Figure Description

[0044] Figure 1 This is a process diagram of the bismuth purification method of the present invention.

[0045] Figure 2 Is Figure 1 An illustrative diagram illustrating the products obtained in each step of the bismuth purification process.

[0046] The annotations in the attached figures are explained as follows:

[0047] 1. Neutralization process;

[0048] 2. Alkali leaching process;

[0049] 3. Sulfuric acid leaching process;

[0050] 4. Cooling process;

[0051] 5. Bismuth oxidation process;

[0052] 6. Electrolysis process. Detailed Implementation

[0053] The following describes a wet bismuth purification method using the present invention.

[0054] The present invention is characterized in that, in the process of recovering copper by electrolytic purification of crude copper obtained from smelting minerals containing copper, precious metals, bismuth and impurities, and then recovering precious metals from the electrolytic sludge generated by electrolytic purification by wet method, the acidic solution generated after the recovery of precious metals is subjected to the following steps.

[0055] Figure 1 The process of bismuth purification is shown. Figure 2 Is Figure 1 Explanatory diagrams of the products obtained in each process are shown. The symbols 1) to 6) below are consistent with those in the attached figures.

[0056] 1) Neutralization process

[0057] An alkali is added to the acidic solution generated after the recovery of precious metals to adjust the pH to a range of 2.0 or higher and 3.0 or lower. Then, solid-liquid separation is performed to obtain a neutralized filtrate and a neutralized precipitate.

[0058] 2) Alkali leaching process

[0059] Add alkali to the neutralized precipitate obtained from the aforementioned neutralization process to separate it into alkali leachate and alkali leachate residue.

[0060] 3) Sulfuric acid leaching process

[0061] Sulfuric acid is added to the alkali leaching residue obtained from the aforementioned alkali leaching process to separate it into sulfuric acid leaching solution and sulfuric acid leaching residue.

[0062] 4) Cooling process

[0063] The sulfuric acid leaching solution obtained in the aforementioned sulfuric acid leaching process is cooled to obtain bismuth sulfate crystals.

[0064] 5) Bismuth oxidation process

[0065] Adding an alkali to the bismuth sulfate crystals obtained from the aforementioned cooling process yields bismuth oxide.

[0066] 6) Electrolysis process

[0067] An acid solution is added to the bismuth oxide obtained by the aforementioned bismuth oxidation process to dissolve the bismuth oxide, and the resulting solution is electrolytically extracted to obtain metallic bismuth.

[0068] In the minerals to which this invention applies, the impurities consist of one or more of iron, lead, arsenic, and tellurium. Because these impurities behave differently from bismuth during neutralization, electrolytic purification, etc., they can be efficiently separated using the method of this invention, thereby concentrating bismuth. Therefore, this does not hinder bismuth recovery. On the other hand, if the minerals contain high concentrations of impurities other than those mentioned above, such as antimony, their behavior is similar to that of bismuth, resulting in difficulty in effectively concentrating them.

[0069] The following describes in detail each step of the present invention.

[0070] 1) Neutralization process

[0071] An alkali is added to the acidic solution after recovering precious metals from electrolytic mud using the aforementioned wet method to neutralize the acidic solution.

[0072] After neutralization, based on the relationship between solubility product and pH, substances that form neutralized precipitates such as hydroxides are separated for each element, while the neutralized filtrate continues to dissolve without forming a precipitate. Therefore, by finely adjusting the pH, it is possible to separate the neutralized filtrate and the neutralized precipitate.

[0073] In the alkaline leaching and sulfuric acid leaching processes, which are subsequent steps in this invention, it is difficult to effectively separate antimony and iron, which are present as impurities, from bismuth. Therefore, it is important to fully separate antimony and iron in advance during the neutralization process.

[0074] In this neutralization process, for acidic solutions containing impurities such as iron, lead, arsenic, tellurium, antimony, and nickel ions in addition to copper, precious metals, and bismuth, the pH is first adjusted to a range of 2.0–3.0 using alkali. Then, solid-liquid separation is performed to obtain a neutralized filtrate and a neutralized precipitate. If the pH is less than 2.0, the separation efficiency of bismuth is weak; if the pH exceeds 3.0, copper, antimony, arsenic, nickel, etc., begin to precipitate simultaneously with bismuth, leading to a decrease in the grade of bismuth obtained, which is therefore not preferred. When the pH is in the range of 2.0–3.0, bismuth can be separated at a higher concentration.

[0075] For impurities such as iron and antimony, the most suitable separation method at the operational level is in the form of hydroxides. By controlling the pH to be above 2.0 and below 3.0, and preferably above 2.4 and below 2.8, the bismuth concentration can be maximized.

[0076] In solid-liquid separation, known methods such as Nutsche filters and filter flasks, centrifuges, filter presses, and Denver filters can be used to separate the filtrate and precipitate into a neutral state.

[0077] 2) Alkali leaching process

[0078] Elements that can dissolve in both acidic and alkaline conditions are separated into an alkaline leachate and an alkaline leachate residue by adding an alkali. When an alkali is added to the neutralized precipitate, elements such as arsenic, which are amphoteric compounds and also soluble under alkaline conditions, dissolve, allowing the product to be separated into an alkaline leachate and an alkaline leachate residue.

[0079] If we consider studies on leaching using sulfuric acid in subsequent processes, the proportions of iron, lead, and arsenic generated in the above neutralization process and distributed to the residue need to be suppressed to below 50%.

[0080] The added alkali can be slaked lime or sodium hydroxide. The addition method can be by mixing slaked lime with water to form a slurry, or by adding sodium hydroxide in water to obtain a solution, using a metering pump. When slaked lime is used, calcium sulfate (gypsum) is generated, which becomes an impurity for bismuth recovery. Therefore, it is preferable to use water-soluble sodium hydroxide as the neutralized product.

[0081] In one example of the alkaline leaching process, arsenic contained in the neutralized precipitate is leached into an alkaline leachate using sodium hydroxide. The leached arsenic can be separated by a boiling process, in which the alkaline leachate is heated to above 90°C and then cooled to obtain arsenic-containing crystals. That is, the arsenic crystal structure changes under high temperature conditions, thereby selectively separating the arsenic. This boiling process provides the advantage of easy reuse of arsenic.

[0082] To remove more arsenic, a sodium hydroxide solution is added to the aforementioned neutralized precipitate to form a slurry, allowing the reaction to occur. The concentration of sodium hydroxide and the initial slurry concentration are adjusted according to the amount of arsenic contained in the neutralized precipitate.

[0083] Specifically, it is preferable to use a sodium hydroxide solution with a concentration of 1 to 5 mol / L to add the slurry in a manner that makes the concentration 10 to 100 g / L. Furthermore, it is even more preferable to set the sodium hydroxide concentration to approximately 2 mol / L.

[0084] Furthermore, the optimal reaction temperature is around 60°C; below 60°C, the reaction slows down. On the other hand, even above 60°C, the reaction is not significantly accelerated, resulting in excessive energy consumption, and is therefore not preferred.

[0085] When the concentration of sodium hydroxide is below 1 mol / L, there is a risk that arsenic may not be completely removed and some may remain in the neutralization precipitate.

[0086] Furthermore, when the concentration of sodium hydroxide exceeds 5 mol / L excessively, impurities such as antimony and iron, other than arsenic, are also leached out. While this situation has the advantage of increased bismuth purity remaining in the alkaline leaching residue, it also presents problems such as increased costs due to the increased use of sodium hydroxide, and even some bismuth being leached into the alkaline leaching solution, leading to increased losses. Therefore, this approach is not preferred.

[0087] When the slurry concentration is below 10 g / L, the amount of precipitate neutralized relative to the alkaline solution is insufficient, resulting in increased loss of bismuth due to the relatively increased amount of dissolved bismuth. Conversely, when the slurry concentration is above 100 g / L, the amount of precipitate neutralized relative to the alkaline solution is excessive, thus failing to adequately dissolve and remove arsenic, leading to a decrease in arsenic removal efficiency. In contrast, a slurry concentration between 10 g / L and 100 g / L offers the advantage of efficiently removing arsenic while suppressing bismuth loss.

[0088] Furthermore, for example, when the neutralized precipitate contains chloride (Cl) ions from the raw materials or their processing steps, bismuth exists in the form of a compound such as bismuth oxychloride (BiClO), which has a relatively high solubility in sulfuric acid, and may sometimes hinder the precipitation of bismuth sulfate in the cooling process described later. However, by using the alkaline leaching of the present invention, the chloride ion content in the alkaline leaching residue can be suppressed to below 0.1%, resulting in a reduction in bismuth loss in the cooling process described later.

[0089] When the arsenic concentration in the alkaline leaching solution is too high, sodium dihydrogen arsenate crystals may sometimes form in the leaching solution. As crystals form, the filterability will deteriorate, or the washing load required to dissolve and remove the crystals will increase, so this is not preferred.

[0090] Furthermore, leaching is carried out in such a way that the molar ratio (As / Bi) of arsenic to bismuth in the residue obtained in the alkaline leaching process is 0.1 or less. By leaching in this manner, more than 90% of the bismuth can be recovered in the sulfuric acid leaching process described later.

[0091] 3) Sulfuric acid leaching process

[0092] Sulfuric acid is added to the alkali leaching residue obtained from the above-mentioned alkali leaching process, and the difference in solubility caused by the concentration of sulfuric acid is used to separate it into sulfuric acid leachate and sulfuric acid leaching residue.

[0093] It should be noted that, in cases where chloride ions are present as described above, a washing process (pH adjustment process) can be performed between the aforementioned alkaline leaching process and the sulfuric acid leaching process to further reduce the residual chloride content. In the washing process, water is added to the alkaline leaching residue to form a slurry, and washing is performed until the pH reaches 2.5–3.5, preferably around 3. This improves the dispersibility of the bismuth component in the neutralized precipitate, making it easier to leach into sulfuric acid.

[0094] In the sulfuric acid leaching process, it is preferable to perform a two-stage leaching treatment by varying the sulfuric acid concentration. That is, a primary treatment is first performed, in which a low-concentration sulfuric acid is applied to the leaching residue to separate it into a primary leachate and a primary leaching residue. Then, a secondary treatment is performed, in which a high-concentration sulfuric acid is applied to the aforementioned secondary leaching residue to separate it into a secondary leachate and a secondary leaching residue.

[0095] Furthermore, it is preferable to supply the aforementioned secondary leachate to the cooling process. By performing such a two-stage leaching process, the solubility of bismuth increases, making concentration easier.

[0096] In this invention, low-concentration sulfuric acid refers to a weakly acidic sulfuric acid solution with a pH range of 0 to 3.5, preferably around pH 3. High-concentration sulfuric acid refers to a strongly acidic sulfuric acid solution with a pH less than 0, specifically a concentration of 7 mol / L or higher, preferably around 10 mol / L. When using the above-mentioned high-concentration sulfuric acid for leaching, the temperature of the slurry can be set in the range of 30 to 90°C.

[0097] Specifically, sulfuric acid is added to the aforementioned alkaline leaching residue to prepare a slurry with a pH adjusted to the range of 0 to 3.5, from which copper and iron are leached. For the sulfuric acid leaching process with a pH of 0 to 1, the copper (leaching rate) allocated to the sulfuric acid leaching solution from the copper contained in the alkaline leaching residue is preferably 50% or more. If the allocation is less than 50%, the copper removal will be insufficient, which will adversely affect the copper grade in the bismuth product.

[0098] Furthermore, the bismuth distribution (leaching rate) from the alkaline leaching residue to the sulfuric acid leaching solution should be set to less than 2%. If the distribution exceeds 2%, the loss of bismuth in the entire process cannot be ignored.

[0099] 4) Cooling process

[0100] The sulfuric acid leachate obtained in the aforementioned sulfuric acid leaching process is cooled to induce crystallization and obtain bismuth sulfate crystals. This cooling process utilizes the difference in solubility; generally, solubility decreases as temperature decreases, and therefore, it gradually becomes impossible to completely dissolve in the liquid. Thus, bismuth sulfate crystals can be obtained through cooling.

[0101] Cooling can be achieved by, for example, installing a jacket around the reaction tank (cooling tank) filled with the sulfuric acid leaching solution, or installing a coiled pipe inside the reaction tank, allowing cooling media such as water to flow through the jacket or coiled pipe while stirring inside the reaction tank. Alternatively, pre-obtained bismuth sulfate crystals can be added to the leaching solution as seed crystals during cooling.

[0102] While it's possible to cool to a lower temperature, considering the cost and efficiency of cooling, cooling to room temperature below 30°C is sufficient. Furthermore, the cooling time should be set at approximately one hour.

[0103] 5) Bismuth oxidation process

[0104] An alkali is added to the bismuth sulfate crystals obtained from the aforementioned cooling process. When the alkali is added, bismuth oxide is obtained because the elements other than bismuth are dissolved.

[0105] Specifically, for example, mixing a sodium hydroxide solution with a concentration of about 1 to 2 mol / L with the above-mentioned bismuth sulfate crystals to make the slurry concentration about 25 g / L, and stirring for about 1 hour while maintaining the temperature at about 60°C, can yield bismuth hydroxide (Bi(OH)3). If it is dried, bismuth oxide (Bi2O3) can be obtained.

[0106] 6) Electrolysis process

[0107] An acid solution is added to the bismuth oxide obtained by the aforementioned bismuth oxidation process to dissolve the bismuth oxide. When an acid solution is added in this way, the bismuth dissolves into ions. However, if the resulting solution is electrolytically extracted, that is, if an electrode is placed in the solution and an electric current is applied, the bismuth ions accept electrons and are electrodeposited at the cathode as monomeric metallic bismuth.

[0108] Hydrochloric acid and similar acids can be used in the acid solution used in electrolysis, but a fluorinated silicate solution is preferred in order to ensure a sufficiently high solubility of bismuth to guarantee a suitable bismuth concentration for electrolysis and to achieve high separation from coexisting impurities. By using an electrolytic bath containing a fluorinated silicate solution, metallic bismuth with impurities fully separated from the electrolyte existing in the form of bismuth fluoride can be obtained.

[0109] For example, specific electrolytic conditions for obtaining metallic bismuth are as follows: bismuth oxide is dissolved in a fluorosilicic acid solution with a concentration of 300–350 g / L to obtain an initial electrolyte solution with a bismuth concentration of 80–100 g / L. This initial electrolyte solution is then supplied to an electrolytic cell using Hastelloy cathode and carbon anode, and the solution temperature is maintained at 40–50°C, preferably below 50°C, while simultaneously operating at an A / m pressure of 80–120 A. 2A cathode current density is applied, allowing metallic bismuth to be electrodeposited onto the cathode. If the current density exceeds 200 A / m... 2 If the electrodeposition surface is cracked, it is easy to produce particulate precipitates and be entrained by the electrolyte, so it is not preferred.

[0110] If the end time of electrolysis is set, for example, when the bismuth concentration in the electrolyte drops to about 20-30 g / L, the surface deterioration of the deposited bismuth can be suppressed, and a smooth bismuth metal with no influence from electrolyte entry can be obtained, which is therefore preferred.

[0111] Furthermore, adding bismuth metal to the initial electrolyte and impregnating it to precipitate silver ions from the initial electrolyte onto the bismuth metal, and then electrolyzing the liquid after such a displacement reaction, can reduce the silver content in the bismuth metal, which is therefore preferable. The addition of bismuth metal to perform the displacement reaction can be achieved by reducing the redox potential (ORP) of the initial electrolyte, expressed as a silver / silver chloride electrode as a reference electrode, to a range of 400–518 mV or lower.

[0112] Furthermore, after electrolysis, the cathode is lifted up to strip the electrodeposited bismuth, which is then washed with water and placed in a furnace to be melted in an inactive environment at a temperature of around 300°C, slightly above the melting point of bismuth (271°C). This removes impurities and oxides, yielding bismuth metal in ingots or similar shapes.

[0113] Example

[0114] (Example 1)

[0115] Copper concentrate is placed in a furnace and melted at high temperature to separate impurities. The anode obtained by casting crude copper in this way is immersed in an electrolytic cell filled with an acidic sulfuric acid solution. Electricity is passed between the anode and a cathode made of copper or stainless steel placed face to face. Using a known method of copper electrolytic purification, which electrodeposits electrolytic copper on the cathode surface, copper electrolytic mud containing precious metals such as gold and silver is obtained. Using a known method, an oxidizing agent such as chlorine is applied to the copper electrolytic mud to prepare an acidic solution containing precious metals leached from the copper electrolytic mud.

[0116] Then, sodium hydroxide was added to the acidic solution at room temperature to obtain a slurry with a pH adjusted to 2.6. Subsequently, using a Nutsche filter and filter flask, and 5C filter paper, the slurry was solid-liquid separated into a neutralized precipitate and a neutralized filtrate (neutralization process). The proportions of bismuth, iron, lead, and arsenic in the original solution distributed to the neutralized precipitate were determined, resulting in bismuth: 90%, iron: 40%, lead: 40%, and arsenic: 40%, effectively separating more than half of the components other than bismuth.

[0117] (Example 2)

[0118] Similar to Example 1 above, an acidic solution obtained by leaching precious metals from copper electrolytic mud containing precious metals was used. Sodium hydroxide solution was added to adjust the pH to 2.6, and neutralized precipitate and neutralized filtrate (neutralization treatment process) were obtained in the same manner as in Example 1.

[0119] Then, sodium hydroxide at a concentration of 2 mol / L is added to the neutralized precipitate for leaching to obtain alkaline leaching residue (alkaline leaching process). Further, a low concentration of sulfuric acid is added to the obtained alkaline leaching residue to adjust the slurry concentration to 100 g / L, and the mixture is stirred for 1 hour to obtain sulfuric acid leachate (sulfuric acid leaching process). The pH of the slurry after adding sulfuric acid is adjusted to 0.8.

[0120] The leaching rate of copper to sulfuric acid leaching solution was 53%. On the other hand, the leaching of bismuth was suppressed to 0.7%, achieving the target.

[0121] Add 10 mol / L sulfuric acid to the obtained residue to make a slurry, and maintain the temperature at 60°C to leach Bi from the residue.

[0122] After separating the residue, the leachate was cooled to room temperature to obtain bismuth sulfate crystals (cooling process). The obtained crystals were added to a caustic soda solution at pH 14 and stirred to obtain bismuth oxide crystals. The obtained crystals were dissolved in a 336 g / L fluorosilicic acid solution and adjusted to a bismuth concentration of 100 g / L. Separately prepared bismuth metal was then impregnated in this solution, and a displacement reaction was used to remove silver, reducing the silver concentration of the solution from 13 mg / L to below the analytical limit of 5 mg / L. The desilvered liquid was used as the initial electrolyte (bismuth oxidation process).

[0123] The initial electrolyte solution was then loaded into the electrolytic cell, and the liquid temperature was maintained at 45–50°C. A Hastelloy alloy cathode and a carbon anode were arranged in the electrolytic cell with a 50 mm interplanar distance. The electrolyte was then circulated by pumping it back into the electrolytic cell, while maintaining a cathode current density of 100 A / m. 2 The process involves applying electricity (electrolysis). The bismuth concentration in the electrolyte discharged from the electrolytic cell is analyzed, and the electricity is stopped when the bismuth concentration drops below 25 g / L.

[0124] Then, pull the cathode upwards, peel off the electrodeposited bismuth metal from the cathode, wash the bismuth metal with water, and dry it.

[0125] Dividing the amount of bismuth metal obtained by the theoretical electrodeposition amount calculated based on the current flow rate yields a current efficiency of 99.6%.

[0126] The obtained bismuth metal was then analyzed using GDMS (glow discharge mass spectrometry). The results showed that silver, the main impurity, was around 70 ppm, which was significantly reduced compared to 1300 ppm without the substitution reaction, resulting in bismuth metal with a high purity of 99.993%.

[0127] In addition, the leachate and washing liquid obtained in the alkaline leaching process were boiled to a temperature of 90°C, resulting in the crystallization of sodium dihydrogen arsenate. After filtration, arsenic could be separated and recovered in solid form.

[0128] (Example 3)

[0129] Using the same acidic solution as in Examples 1 and 2 above, sodium hydroxide was added to the acidic solution at room temperature to obtain a slurry with a pH adjusted to 2.6. Subsequently, solid-liquid separation was performed using the same method as in Examples 1 and 2 to obtain a neutralized precipitate and a neutralized filtrate (neutralization treatment step). The neutralized precipitate contained 19% wt% bismuth and 11% wt% chloride ions.

[0130] Then, a 2 mol / L sodium hydroxide solution was added to the neutralized precipitate to bring the slurry concentration to 100 g / L. The slurry was stirred for 1 hour while maintaining the temperature at 60°C (alkali leaching process). The slurry after stirring was then subjected to solid-liquid separation. The resulting alkali leaching residue was washed with water, and the washed residue after further solid-liquid separation was analyzed. The results showed a bismuth content of 28.1% by weight, compared to a chloride ion content of 0.01% by weight, representing a significant reduction in chloride content.

[0131] Then, the alkaline leaching residue after washing was treated in the same way as in Example 2 above, and leached with sulfuric acid of 10 mol / L to obtain a leaching solution with a bismuth concentration of 3.7 g / L. The leaching solution was cooled from 60°C to room temperature (25°C) and solid-liquid separation was performed to obtain a filtrate with a bismuth concentration of 1.0 g / L, and 73% of the bismuth contained in the leaching solution was recovered.

[0132] (Example 4)

[0133] An alkaline leaching residue was obtained using the same method as in Example 3 above. Sulfuric acid with a concentration of 8 mol / L was added to this residue to obtain a leaching solution containing bismuth. The leaching solution was then cooled using the same method as in Example 3, and 80% of the bismuth contained in the leaching solution was recovered.

[0134] (Example 5)

[0135] Alkali leaching residue was obtained using the same method as in Example 2 above. Sulfuric acid and water were added to this residue to achieve a slurry concentration of 100 g / L, and the pH was adjusted to 3.0. Stirring was continued for 1 hour. After solid-liquid separation, 10 mol / L sulfuric acid and water were added to the obtained residue to prepare a slurry. Leaching was performed for 2 hours while maintaining a temperature of 60°C. The resulting leachate had a bismuth concentration of 3.0 g / L, confirming that leaching had been sufficient.

[0136] (Comparative Example 1)

[0137] Except for adjusting the pH to 3.8, neutralization was performed using the same apparatus and the same acidic solution as in Example 1 above, and in the same manner. Regarding the proportions allocated to the neutralized precipitate, although 95% bismuth was good, 80% iron, 60% lead, and 40% arsenic only yielded bismuth metal with a bismuth grade of about 52%.

[0138] (Comparative Example 2)

[0139] A neutralized precipitate was prepared in the same manner as in Example 2 above. Instead of alkaline leaching, it was leached with sulfuric acid under the same conditions as in Example 1, resulting in a bismuth leaching rate of 60%. The bismuth concentration in the leachate was 4.0 g / L. However, although the residue was leached with sulfuric acid again under the same conditions, almost no bismuth was leached. Furthermore, even after cooling the leachate, almost no bismuth sulfate crystals were obtained.

[0140] (Comparative Example 3)

[0141] A neutralized precipitate was prepared in the same manner as in Example 2 above. This precipitate was then subjected to alkaline leaching with sodium hydroxide to adjust the pH to 3.5. The aforementioned sulfuric acid solution was added to adjust the pH to 1.2. Otherwise, the treatment was carried out using the same method as in Example 2 above. Although the bismuth fraction in the solution was 1.5%, which is within a suitable range, the copper fraction (leaching rate) was insufficient, at 45%.

[0142] (Comparative Example 4)

[0143] A neutralized precipitate was prepared in the same manner as in Example 2 above. This precipitate was then subjected to alkaline leaching with sodium hydroxide to adjust the pH to 3.5. Subsequently, it was treated with a high concentration of sulfuric acid with a pH less than 0, but otherwise, the treatment was carried out using the same method as in Example 2. The result was a satisfactory leaching rate of 55% of copper into the liquid; however, 3% of bismuth was also leached, which could not be suppressed at the target bismuth leaching rate.

[0144] (Refer to Example 1)

[0145] An alkaline leaching residue was obtained using the same method as in Example 4 above. Sulfuric acid with a concentration of 6 mol / L was added to this residue to obtain a leaching solution containing bismuth. Then, after cooling the obtained leaching solution using the same method as in Example 4, only 45% of the bismuth contained in the leaching solution could be recovered.

[0146] (See Example 2 for reference)

[0147] Alkali leaching residue was obtained using the same method as in Example 5 above. Without pH adjustment, sulfuric acid and water at a concentration of 10 mol / L were directly added to the residue to form a slurry. Leaching was then performed for 2 hours while maintaining the temperature at 60°C. The resulting leachate had a bismuth concentration of 1.2 g / L, indicating only incomplete leaching.

[0148] (Refer to Example 3)

[0149] Alkali leaching residue was obtained using the same method as in Example 5 above. Sulfuric acid and water were added to this residue to achieve a slurry concentration of 100 g / L, and the pH was adjusted to 5. Stirring was continued for 1 hour. After solid-liquid separation, 10 mol / L sulfuric acid and water were added to the obtained residue to prepare a slurry. Leaching was carried out for 2 hours while maintaining a temperature of 60°C. The resulting leachate had a bismuth concentration of 2.5 g / L, indicating that leaching had stopped at the incomplete leaching stage.

[0150] (Refer to Example 4)

[0151] Alkali leaching residue was obtained using the same method as in Example 5 above. Sulfuric acid and water were added to this residue to achieve a slurry concentration of 100 g / L, the pH was adjusted to 0, and stirring was continued for 1 hour. After solid-liquid separation, 10 mol / L sulfuric acid and water were added to the obtained residue to prepare a slurry. Leaching was carried out for 2 hours while maintaining a temperature of 60°C. The resulting leachate had a bismuth concentration of 2.5 g / L, indicating that leaching had stopped at the incomplete leaching stage.

Claims

1. A method for purifying bismuth, characterized in that, In a process of recovering copper by electrolytic purification of crude copper obtained from smelting minerals containing copper, precious metals, bismuth, and impurities, and then recovering precious metals from the electrolytic sludge generated during electrolytic purification using a wet method, the acidic solution generated after the recovery of precious metals undergoes the following process: the impurities are one or more of iron, lead, arsenic, and tellurium. 1) Neutralization process: alkali is added to the acidic solution to adjust the pH to the range of 2.0 to 3.

0. Impurities containing iron and antimony are distributed to the neutralization filtrate and removed. Bismuth and some impurities, which are to be recovered, are distributed to the neutralization precipitate. 2) In the alkaline leaching process, 1-5 mol / L sodium hydroxide solution is added to the neutralized precipitate to make the slurry concentration 10-100 g / L, the reaction temperature is set to about 60°C, and impurities containing arsenic and chloride ions are distributed to the leaching solution for removal, so that the proportion of iron, lead and arsenic distributed to the alkaline leaching residue is less than 50%, the molar ratio of arsenic to bismuth in the alkaline leaching residue is less than 0.1, and the chloride ion content is less than 0.1%. 3) Washing process: Water is added to the alkaline leaching residue to form a slurry, and the mixture is washed until the pH value is 2.5 to 3.

5. 4) In the sulfuric acid leaching process, sulfuric acid is added to the washed alkaline leaching residue to separate it into a sulfuric acid leaching solution in which the copper distribution rate in the sulfuric acid leaching solution reaches more than 50%, and a sulfuric acid leaching residue with reduced impurities. The sulfuric acid leaching process consists of two stages: primary treatment and secondary treatment. The primary treatment involves contacting the washed alkaline leaching residue with sulfuric acid of a weak acid concentration (pH 0–3.5) to leach the residue, separating it into a primary leachate and a primary leaching residue. The secondary treatment involves contacting the primary leaching residue with sulfuric acid of a strong acid concentration (pH less than 0) to separate it into a secondary leaching solution and a secondary leaching residue. 5) Cooling process: The secondary leachate obtained in the sulfuric acid leaching process is cooled to obtain bismuth sulfate crystals; 6) Bismuth oxidation process: An alkali is added to the crystallization of bismuth sulfate to obtain bismuth oxide; 7) Electrolysis process: An acid solution is added to the bismuth oxide to dissolve the bismuth oxide, and the resulting solution is electrolyzed to extract metallic bismuth.

2. The bismuth purification method as described in claim 1, characterized in that, The acid solution used in the electrolysis process is a solution containing fluorosilicic acid.

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