A method for recovering tellurium from silver electrolytic waste liquid of high-copper-silver nitrate system

Abstract

The application discloses a method for recovering tellurium from silver electrolysis waste liquid of a high-copper-silver nitrate system, and belongs to the technical field of hydrometallurgy. The method takes silver electrolysis refining waste liquid of a high-copper-silver nitrate system as raw material, and sequentially removes suspended solids through pretreatment, differentiates and stepwisely reduces selenium and enriches tellurium through two-stage narrow potential window difference, removes heavy metal impurities through alkali leaching, prepares high-purity TeO2 through acid precipitation, and obtains high-purity tellurium products through liquid phase reduction refining. The application realizes efficient and selective separation of selenium and tellurium by accurately controlling the redox potential of two-stage reduction, removes copper, lead, silver and other impurities through alkali leaching and acid precipitation purification process, the total recovery rate of tellurium is greater than or equal to 98.5%, and the purity of the product is greater than or equal to 99.99%. The application has the advantages of short process flow, low reagent consumption, the liquid after tellurium precipitation can be returned to the electrolysis system for reuse, environmental friendliness, and suitability for industrial large-scale application.

Description

Technical Field

[0001] This invention belongs to the field of non-ferrous metal hydrometallurgical technology, specifically relating to a method for recovering tellurium from silver electrolytic waste liquid in a high-copper-silver nitrate system. Background Technology

[0002] Tellurium is a strategic rare and dispersed metal (semi-metal) with irreplaceable applications in solar photovoltaics, thermoelectric conversion, metallurgical alloys, and electronic semiconductors. In the silver electrolytic refining process of extracting silver from copper-lead anode mud, a silver nitrate-nitric acid electrolyte system is commonly used. Rare and dispersed elements such as tellurium and selenium in the anode continuously accumulate in the electrolyte as silver dissolves. When tellurium and selenium accumulate to a certain concentration, they deteriorate electrolysis conditions, reduce silver current efficiency, affect silver powder quality, and cause the loss of rare and dispersed metal resources. Therefore, efficient recovery of tellurium from silver electrolysis waste liquid is a key step in achieving comprehensive recovery of valuable metals and improving the economic benefits of enterprises.

[0003] Currently, the mainstream industrial methods for recovering tellurium from tellurium-containing acidic solutions include copper powder displacement, SO2 reduction, neutralization precipitation, and solvent extraction. The copper powder displacement method is simple, but the displacement slag contains high levels of impurities such as copper and silver, resulting in a tellurium grade typically below 50%. Subsequent separation and purification processes are lengthy, and the overall tellurium recovery rate is only around 80%. The SO2 reduction method has low operating costs, but it requires strict control over system acidity and potential. Selenium and tellurium easily co-precipitate, resulting in high levels of selenium and copper impurities in the crude tellurium, yielding only a crude tellurium product with 95% purity. Neutralization precipitation generates large amounts of neutralization slag containing heavy metals, placing significant pressure on solid waste treatment, and causing substantial tellurium entrainment losses. While solvent extraction can achieve deep purification, the high cost, easy depletion, and complex regeneration of the extractant limit its industrial application. In summary, existing technologies struggle to balance high tellurium recovery rates with high product purity, often exhibiting problems such as poor impurity separation, lengthy processes, and significant environmental impact. There is an urgent need to develop an efficient, clean, and industrially compatible tellurium recovery process for silver electrolysis waste liquid.

[0004] Chinese invention patent application CN113148963A discloses a "method for separating and recovering tellurium and selenium." This patent processes hydrochloric acid leachate containing high-content tellurium and selenium solids, achieving tellurium and selenium separation using a potential of 450–550 mV in the hydrochloric acid system. However, its raw material is a low-copper, low-silver tellurium and selenium solid hydrochloric acid leachate, relying on a high concentration of Cl... - It complexes silver and copper ions, inhibiting metal hydrolysis and co-reduction. However, it cannot inhibit the reduction of silver and copper ions in a nitric acid system. The reduction process of silver and copper ions consumes the reducing agent, causing the system's ORP to run out of control and premature co-precipitation of tellurium. Ultimately, selenium and tellurium cannot be selectively separated, resulting in a significant decrease in tellurium recovery rate and serious exceedance of product impurities.

[0005] Chinese invention patent application CN102690946A discloses "A method for comprehensively extracting valuable metals from tellurium-containing polymetallic materials." This patent processes a crushed, ball-milled polymetallic solid nitric acid leachate, first removing lead and silver, then precipitating tellurium using sodium sulfite as a single reducing agent. This method has the following main drawbacks: First, the pre-treatment stepwise lead and silver precipitation processes are lengthy and cannot be adapted to online treatment of continuous silver electrolysis wastewater; second, selenium and tellurium are simultaneously precipitated, making selenium-tellurium separation difficult; third, heavy metal hydrolysis and co-precipitation are severe, resulting in crude tellurium purity of less than 70%.

[0006] Chinese invention patent application CN117488079A discloses a "valuable metal separation process for copper anode mud based on oxidation potential control." It primarily involves the sequential leaching of tellurium and selenium through oxidation-reduction. While achieving tellurium-selenium separation, this process is only suitable for sulfuric acid leaching of solid copper anode mud and suffers from the following drawbacks: high reagent costs, lengthy multi-stage solid-liquid separation processes, and the generation of difficult-to-treat sulfur-containing wastewater from silver extraction using thiosulfate. Furthermore, this process relies on high-potential oxidation to dissolve elements, lacking suitable impurity suppression methods for high-copper-silver dissolved wastewater in nitric acid systems. It also lacks multi-stage high-purity purification processes involving alkaline leaching, acid precipitation, and secondary reduction, making it impossible to simultaneously achieve high tellurium recovery rates and high-purity tellurium product preparation, and also preventing the direct recycling of electrolytic wastewater.

[0007] The paper "Separation and Recovery of Selenium and Tellurium from Difficult-to-Treat Precious Metal Acid Sludge" by Chen Zhiyu et al. [Nonferrous Metals (Smelting Section), 2020, No. 2] involves the alkaline leaching separation of tellurium and selenium. The method in this paper is only applicable to solid-phase acid sludge materials and cannot be adapted to the silver nitrate electrolytic waste liquid containing high concentrations of dissolved Cu and Ag described in this invention. This is because the neutralization of nitric acid with large amounts of caustic soda produces a huge amount of sodium salt solid waste, and heavy metal hydroxides co-precipitate with tellurium, completely losing the separation effect; the alkaline leaching tellurium leaching rate is only 77.7%, resulting in significant loss of rare and dispersed metal resources, and the neutralization residue contains high levels of selenium, silver, and lead impurities, producing only low-grade crude tellurium, making it difficult to achieve the goal of preparing high-purity tellurium.

[0008] The paper "Study on the Recovery of Selenium and Tellurium from Gold Precipitation Solution by Hydrochloric Acid Catalyzed SO2 Reduction" (Rare Metals and Hard Alloys, Vol. 54, No. 1), authored by Jia Wenqing et al., discusses the recovery of selenium and tellurium from the gold precipitation solution by SO2 reduction using hydrochloric acid as a catalyst, and involves the effects of sodium sulfite and hydrazine hydrate as reducing agents on the recovery rates of selenium and tellurium in the gold precipitation solution. The process in this paper relies on concentrated hydrochloric acid to provide chloride ions to complex tellurium. If used for chloride-free silver nitrate electrolysis wastewater, chloride ions will react with a large amount of Ag in the system. + The reaction produces silver chloride precipitate, resulting in a significant loss of the precious metal silver. Summary of the Invention

[0009] The technical problem to be solved by this invention is to provide a method for recovering tellurium from silver electrolysis waste liquid of high copper silver nitrate system. This method overcomes the shortcomings of existing technologies, such as inability to adapt to the treatment of silver electrolysis waste liquid of high copper silver nitrate system, difficulty in deep separation of selenium and tellurium, difficulty in removing heavy metal impurities, low tellurium recovery rate and product purity, and inability to recycle waste liquid. This method achieves source separation of selenium and tellurium, deep removal of heavy metals, high recovery rate, and high-purity tellurium preparation. The liquid after tellurium precipitation is directly returned to silver electrolysis, achieving the goal of clean industrial production.

[0010] The technical solution adopted in this invention is as follows: A method for recovering tellurium from silver electrolysis waste liquid in a high-copper-silver nitrate system, wherein the silver electrolysis waste liquid contains Te 0.5-5 g / L, Se 0.2-2 g / L, Ag 0.1-1 g / L, Cu 5-30 g / L, and free HNO3 1-3 mol / L; comprising the following steps performed sequentially: (1) Pretreatment: The silver electrolysis waste liquid is filtered through a 0.45-1μm precision filter to remove solid impurities and obtain a clarified waste liquid; (2) Reduction and selenium removal: The clarified waste liquid is heated to 40-60℃, and then SO2 is introduced into the clarified waste liquid or sodium sulfite solution is added dropwise to control the redox potential of the reaction system to be stable at +400-+500mV relative to the saturated calomel electrode. The reaction is kept at the temperature, and then the selenium residue and the selenium-removed liquid are obtained by filtration. (3) Reduction precipitation of tellurium: Add nitric acid to the selenium-removed solution to adjust the free nitric acid concentration to 2-4 mol / L, and raise the temperature to 60-80℃; then add a reducing agent, control the redox potential of the reaction system to be stable at +200-+300mV, keep the reaction at the temperature, and then filter to obtain coarse tellurium precipitate and tellurium-precipitated solution; the tellurium-precipitated solution is returned to the silver electrolysis system for reuse; (4) Add the crude tellurium precipitate to a sodium hydroxide solution with a concentration of 100-150 g / L at a liquid-to-solid mass ratio of 5-8:1, heat to 70-90℃ and stir to leach; then filter to obtain alkaline leaching residue and purified tellurium solution; return the alkaline leaching residue to the lead-copper smelting system to recover valuable metals; (5) Acid precipitation purification: The purified tellurium solution is heated to 40-50℃, and 1-2 mol / L sulfuric acid solution is slowly added dropwise for neutralization. The pH value is monitored in real time. When the pH of the system reaches 5-6, the acid addition is stopped. The system is kept warm and aged to allow tellurium dioxide to crystallize. The solution is filtered to obtain filtrate and filter residue. The filtrate is sent to the sewage treatment system. The filter residue is washed with deionized water until neutral to obtain tellurium dioxide. (6) Reduction refining: Add tellurium dioxide to 4-6 mol / L hydrochloric acid at a liquid-solid ratio of 4-6:1 and stir at 50-60℃ until completely dissolved; raise the temperature to 70-80℃ and introduce SO2 gas for reduction until the potential is +100-+150mV, and maintain the reaction for a period of time; after the reaction is completed, filter, and wash the filter residue with deionized water and vacuum dry to obtain tellurium powder.

[0011] Preferably, the heat preservation reaction time in step (2) is 1-2 hours; the heat preservation reaction time in step (3) is 2-3 hours; the stirring leaching reaction time in step (4) is 1-2 hours; and the heat preservation aging time in step (5) is 30-60 minutes. The "maintaining a reaction time" mentioned in step (6) refers to maintaining it for 10 to 15 minutes.

[0012] Preferably, the reducing agent in step (3) is a composite reducing agent composed of sodium sulfite and hydrazine hydrate in a mass ratio of 8 to 10:1.

[0013] Compared with the prior art, the present invention has the following beneficial effects.

[0014] First, this invention utilizes the difference in reduction potential between selenium and tellurium, employing a potential-controlled stepwise reduction technique. The first step preferentially and selectively reduces selenium, while the second step precisely reduces tellurium, thus preventing selenium-tellurium co-precipitation from the source. Experiments show that this invention increases the crude tellurium grade to over 85%.

[0015] Secondly, after adjusting the concentration of free HNO3 in the selenium-removed liquid and raising the temperature, the present invention uses a sodium sulfite-hydrazine hydrate composite reducing agent, especially a composite reducing agent with a specific ratio of sodium sulfite and hydrazine hydrate, in conjunction with controlling the system's polarity within a specific range, resulting in a more thorough and faster reduction reaction, with a tellurium precipitation rate of over 99%, while simultaneously reducing the total amount of reducing agent used.

[0016] Third, this invention deeply removes heavy metal impurities such as copper, lead, and silver through an alkaline leaching-acid precipitation process. Combined with subsequent hydrochloric acid dissolution-SO2 reduction refining, the final tellurium product purity can reach over 99.99%.

[0017] Fourth, the nitric acid concentration in the liquid after tellurium precipitation is high, which can be directly returned to the silver electrolysis system for reuse, achieving near-zero wastewater discharge.

[0018] Fifth, this invention has the outstanding advantages of a short process flow, simple operation, conventional equipment, no need for complex automatic control systems, and direct connection to existing silver electrolysis production lines, making it suitable for large-scale industrial production. Detailed Implementation

[0019] The specific embodiments of the present invention will be described in further detail below. The following examples are used to illustrate the present invention.

[0020] Example 1 The silver electrolysis waste liquid used in this embodiment was taken from the silver electrolysis process of a gold smelter. The main components of the waste liquid are: Te 2.3g / L, Se 0.8g / L, Ag 0.5g / L, Cu 18g / L, and free HNO3 2.1mol / L.

[0021] The specific processing steps are as follows: (1) Pretreatment: Take 10L of the above silver electrolysis waste liquid, and remove the suspended anode mud particles by 0.45μm precision filtration to obtain clear waste liquid.

[0022] (2) Reduction and Selenium Removal: The clarified waste liquid is added to a reactor equipped with online ORP monitoring, heated to 50°C, and SO2 gas is slowly introduced while the potential is monitored in real time. When the potential stabilizes at +450mV, the gas supply is stopped, and the reaction is maintained at this temperature for 1.5 hours. Selenium slag and selenium-removed liquid are obtained by filtration. The selenium slag is used for silver recovery, and the selenium-removed liquid is used for step (3).

[0023] The selenium precipitation rate was 98.2%, and the tellurium loss rate was 0.8%.

[0024] Note: The SO2 introduction rate is determined by the set potential. If the SO2 introduction rate is too fast, the local reduction potential will momentarily exceed the set potential, leading to tellurium reduction and reducing the subsequent tellurium recovery rate.

[0025] (3) Reduction of tellurium precipitation: Add 65% concentrated nitric acid to the selenium-removed solution to adjust the free HNO3 concentration to 3 mol / L and heat to 70℃; then add sodium sulfite-hydrazine hydrate composite reducing agent (sodium sulfite-hydrazine hydrate mass ratio 9:1), control the system potential to stabilize at +250mV, react for 2.5h and then filter to obtain crude tellurium precipitate and tellurium precipitation solution; the crude tellurium precipitate is removed from step (4) and the tellurium precipitation solution is returned to the silver electrolysis system for reuse.

[0026] The test results showed that the tellurium precipitation rate was 99.3%.

[0027] Note: The addition rate of the composite reducing agent is determined by the set potential. If the composite reducing agent is added too quickly, the local potential will momentarily exceed +250mV, causing impurity metals to be reduced and incorporated into the crude tellurium, reducing the grade of the crude tellurium and affecting subsequent purification.

[0028] (4) Alkali leaching purification: The crude tellurium precipitate is added to a 120 g / L NaOH solution at a liquid-to-solid ratio of 6:1, and the solution is heated to 80 °C and stirred for 1.5 h. The alkaline leaching residue and the purified tellurium solution are obtained by filtration. The alkaline leaching residue is used to recover silver, and the purified tellurium solution is used in step (5).

[0029] Tests showed that the tellurium leaching rate was 99.1%. The removal rates of copper, lead, and silver were all greater than 99%.

[0030] (5) Acid precipitation purification: The purified tellurium solution is heated to 45℃, and 1.5mol / L sulfuric acid solution is slowly added dropwise to neutralize to pH 5.5. The solution is kept warm and aged for 45min. The solution and filter residue are obtained by filtration. The filtrate is sent to the sewage treatment system, and the filter residue is washed with deionized water until neutral to obtain tellurium dioxide, which is then sent to step (6).

[0031] (6) Reduction refining: Tellurium dioxide was added to 5 mol / L hydrochloric acid at a liquid-to-solid ratio of 5:1 and stirred at 55°C until completely dissolved; the temperature was raised to 75°C, and SO2 was introduced to reduce the solution to a potential of +120 mV, which was maintained for 10 min; the solution and filter residue were obtained by filtration. The filtrate was sent to the wastewater treatment system, and the filter residue was washed with deionized water and dried under vacuum at 60°C to obtain tellurium powder.

[0032] The test results showed that the total tellurium recovery rate in this embodiment was 98.7%, and the tellurium purity of the product was 99.992%.

[0033] Example 2 The composition of the silver electrolytic waste liquid used in this embodiment is: Te 4.5g / L, Se 1.6g / L, Ag 0.8g / L, Cu 25g / L, and free HNO3 1.8mol / L.

[0034] The specific processing steps are as follows: (1) Pretreatment: Same as step (1) in Example 1.

[0035] (2) Reduction and Selenium Removal: The clarified waste liquid is added to a reactor equipped with online ORP monitoring, heated to 55°C, and sodium sulfite solution with a concentration of 200 g / L is added dropwise while monitoring the potential in real time. When the potential stabilizes at +420 mV, the dropwise addition is stopped, and the reaction is maintained at this temperature for 2 hours. The selenium residue and the selenium-removed liquid are obtained by filtration. The selenium residue is used for silver recovery, and the selenium-removed liquid is used for step (3).

[0036] The selenium precipitation rate was tested to be 97.8%.

[0037] (3) Reduction of tellurium precipitation: Add 65% concentrated nitric acid to the selenium-removed solution to adjust the free HNO3 concentration to 3.5 mol / L and heat to 75℃; then add sodium sulfite-hydrazine hydrate composite reducing agent (sodium sulfite-hydrazine hydrate mass ratio 10:1), control the system potential to stabilize at +220mV, filter after reaction for 3h to obtain crude tellurium precipitate and tellurium precipitation solution; the crude tellurium precipitate is removed from step (4), and the tellurium precipitation solution is returned to the silver electrolysis system for reuse.

[0038] The test results showed that the tellurium precipitation rate was 99.1%.

[0039] (4) Alkali leaching purification: The crude tellurium precipitate is added to a 120 g / L NaOH solution at a liquid-to-solid ratio of 7:1, and the solution is heated to 85°C and stirred for 2 hours. The residue is filtered to obtain the alkali leaching residue and the purified tellurium solution. The alkali leaching residue is used to recover silver, and the purified tellurium solution is used in step (5).

[0040] Tests showed that the tellurium leaching rate was 98.9%. The removal rates of copper, lead, and silver were all greater than 99%.

[0041] (5) Acid precipitation purification: The purified tellurium solution is heated to 45℃, and 2mol / L sulfuric acid solution is slowly added dropwise to neutralize to pH 5.2. The solution is kept warm and aged for 60 min. The filtrate and filter residue are obtained by filtration. The filtrate is sent to the sewage treatment system, and the filter residue is washed with deionized water until neutral to obtain tellurium dioxide, which is then sent to step (6).

[0042] (6) Reduction refining: Tellurium dioxide was added to hydrochloric acid with a concentration of 6 mol / L at a liquid-to-solid ratio of 5:1 and stirred at 55°C until completely dissolved; the temperature was raised to 78°C, and SO2 was introduced to reduce the solution to a potential of +110 mV, which was maintained for 10 min; the solution and filter residue were obtained by filtration. The filtrate was sent to the wastewater treatment system, and the filter residue was washed with deionized water and dried under vacuum at 60°C to obtain tellurium powder.

[0043] The test results showed that the total tellurium recovery rate in this embodiment was 98.5%, and the product purity was 99.991%.

[0044] Comparative Example 1 The silver electrolytic waste liquid, which is exactly the same as in Example 1, was treated using the traditional one-step SO2 reduction method: the nitric acid concentration of the waste liquid was adjusted to 3 mol / L, the temperature was raised to 70°C, SO2 was directly introduced until the system potential was +250mV, and after reacting for 3 hours, it was filtered to obtain coarse tellurium.

[0045] The test results showed that the crude tellurium contained 8.7% selenium and 3.2% copper, with a tellurium grade of only 68.3%. After subsequent treatment with the same alkaline leaching-reduction process as in Example 1, the final product purity was 99.2%, and the total tellurium recovery rate was 92.1%. All indicators were significantly lower than those in the embodiments of the present invention.

[0046] Boundary Experiment Example A single-factor controlled experiment on tellurium reduction precipitation was conducted using the selenium-removed liquid produced in step 2 of Example 1 as raw material. Each group only changed three variables: redox potential, the ratio of sodium sulfite-hydrazine hydrate composite reducing agent, and the concentration of free nitric acid. All other process conditions, including operation, temperature, reaction time, and liquid-to-solid ratio, remained consistent with step 3 of Example 1. Specific data are as follows: I. The results of the potential window comparison are shown in Table 1.

[0047] Table 1

[0048] Analysis: Table 1 shows that when the tellurium precipitation potential is too high, the reduction driving force is insufficient, and tetravalent tellurium cannot be fully converted into TeO2 / elemental tellurium, resulting in a decreased tellurium precipitation rate. Conversely, when the potential is too low, the system's reducing power increases, leaving trace amounts of tetravalent selenium and Cu in the solution. 2+ When copper and selenium are simultaneously reduced to elemental form and mixed into the crude tellurium, the copper and selenium impurities in the crude tellurium increase. A narrow window of +200 to +300 mV can achieve a high tellurium precipitation rate. Deviating from the window significantly worsens the situation, specifically manifested in a significant increase in copper impurities and a significant decrease in tellurium precipitation rate in the crude tellurium.

[0049] II. The comparison results of the compound reducing agent ratio are shown in Table 2.

[0050] Table 2

[0051] Analysis: Table 2 shows that an excessively high ratio of sodium sulfite to hydrazine hydrate worsens reduction kinetics, slows tellurium precipitation, and prolongs the reaction cycle; an excessively low ratio results in overly strong reducing power of the composite reducing agent, causing a rapid decrease in the system's ORP even with small amounts added, leading to localized overreduction and a decline in crude tellurium grade. A sodium sulfite to hydrazine hydrate mass ratio of 8–10:1 strikes a balance between reduction efficiency and crude tellurium grade.

[0052] Table 3 shows the comparison results of the acidity of free nitric acid in precipitated tellurium.

[0053] Table 3

[0054] Analysis: Table 3 shows that when the free HNO3 concentration is too low, the tellurium precipitation rate decreases, the crude tellurium copper impurities increase, and the reducing agent consumption increases significantly. When the free HNO3 concentration is too high, the tellurium precipitation rate decreases to some extent, and the crude tellurium copper impurities and reducing agent consumption both increase to some extent.

Claims

1. A method for recovering tellurium from silver electrolytic waste liquid in a high-copper-silver nitrate system, wherein the silver electrolytic waste liquid contains Te 0.5–5 g / L, Se 0.2–2 g / L, Ag 0.1–1 g / L, Cu 5–30 g / L, and free HNO3 1–3 mol / L; characterized in that… This includes the following steps performed sequentially: (1) Pretreatment: The silver electrolysis waste liquid is filtered through a 0.45-1μm precision filter to remove solid impurities and obtain a clarified waste liquid; (2) Reduction and selenium removal: The clarified waste liquid is heated to 40-60℃, and then SO2 is introduced into the clarified waste liquid or sodium sulfite solution is added dropwise to control the redox potential of the reaction system to be stable at +400-+500mV relative to the saturated calomel electrode. The reaction is kept at the temperature, and then the selenium residue and the selenium-removed liquid are obtained by filtration. (3) Reduction precipitation of tellurium: Add nitric acid to the selenium-removed solution to adjust the free nitric acid concentration to 2-4 mol / L, and raise the temperature to 60-80℃; then add a reducing agent, control the redox potential of the reaction system to be stable at +200-+300mV, keep the reaction at the temperature, and then filter to obtain coarse tellurium precipitate and tellurium-precipitated solution; the tellurium-precipitated solution is returned to the silver electrolysis system for reuse; (4) Add the crude tellurium precipitate to a sodium hydroxide solution with a concentration of 100-150 g / L at a liquid-to-solid mass ratio of 5-8:1, heat to 70-90℃ and stir to leach; then filter to obtain alkaline leaching residue and purified tellurium solution; return the alkaline leaching residue to the lead-copper smelting system to recover valuable metals; (5) Acid precipitation purification: Heat the purified tellurium solution to 40-50℃, slowly add 1-2 mol / L sulfuric acid solution for neutralization, monitor the pH value in real time, stop adding acid when the pH of the system reaches 5-6, keep warm and age to allow tellurium dioxide to crystallize; filter to obtain filtrate and filter residue; The filtrate is sent to a wastewater treatment system, where the filter residue is washed with deionized water until neutral to obtain tellurium dioxide. (6) Reduction refining: Add tellurium dioxide to 4-6 mol / L hydrochloric acid at a liquid-solid ratio of 4-6:1 and stir at 50-60℃ until completely dissolved; The temperature is raised to 70-80℃, and SO2 gas is introduced for reduction until the potential is +100-+150mV, and the reaction is maintained for a period of time. After the reaction is completed, the mixture is filtered, and the filter residue is washed with deionized water and vacuum dried to obtain tellurium powder.

2. The method for recovering tellurium from silver electrolytic waste liquid in a high-copper-silver nitrate system according to claim 1, characterized in that: Step (2) The heat preservation reaction time is 1-2 hours; Step (3) The heat preservation reaction time is 2-3 hours; Step (4) The stirring leaching reaction time is 1-2 hours; Step (5) The heat preservation aging time is 30-60 minutes. The "maintaining a reaction time" mentioned in step (6) refers to maintaining it for 10 to 15 minutes.

3. The method for recovering tellurium from silver electrolytic waste liquid in a high-copper-silver nitrate system according to claim 1 or 2, characterized in that: The reducing agent mentioned in step (3) is a composite reducing agent composed of sodium sulfite and hydrazine hydrate in a mass ratio of 8 to 10:1.

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