Method for separating and recovering selenium and fixing arsenic in copper anode slime by vacuum roasting

Abstract

This invention discloses a method for separating and recovering selenium and fixing arsenic in copper anode mud using vacuum roasting, comprising the following steps: a) crushing and screening the copper anode mud to obtain powder; b) uniformly mixing the obtained powder with an iron-based arsenic fixing agent to obtain mixture A; c) placing mixture A in a roasting furnace, then introducing a mixture of inert carrier gas and oxygen-containing gas, and maintaining the system absolute pressure at 1-20 kPa and oxygen partial pressure at 1%-10%, roasting at 400-750℃ for 0.5-4 hours to obtain roasting residue B with arsenic fixed in the form of ferric arsenate and selenium-containing flue gas C; d) passing the selenium-containing flue gas C into a sodium thiosulfate solution for absorption and reduction, and obtaining elemental selenium product D after filtration, washing, and drying; e) leaching the roasting residue B with dilute sulfuric acid to recover the valuable metals copper and silver therein. The above method has a short process flow, good selenium and arsenic separation effect, and can ensure environmental safety in the subsequent valuable metal recovery process.

Description

Technical Field

[0001] This invention relates to the field of non-ferrous metal metallurgy and comprehensive utilization of secondary resources, and in particular to a method for vacuum roasting to separate and recover selenium and fix arsenic from copper anode mud. Background Technology

[0002] Copper anode slime is a byproduct rich in precious and rare metals produced during copper electrolytic refining. It is a primary raw material for extracting important elements such as selenium, tellurium, gold, and silver. With the rapid development of industries such as electronics, photovoltaics, and glass, the demand for selenium continues to grow. Efficient recovery of selenium from copper anode slime is crucial for ensuring resource supply.

[0003] However, copper anode slime has an extremely complex composition and often contains highly toxic arsenic. In traditional pyrometallurgical processes, especially in oxidative roasting or sulfation roasting, selenium and arsenic, due to their main volatile forms—SeO2 and As2O3—have similar volatility, making them highly susceptible to co-volatilization during roasting. This co-volatilization of selenium and arsenic is a core challenge facing existing technologies: firstly, arsenic severely contaminates selenium products, significantly reducing their purity and economic value; secondly, the treatment of arsenic-containing fumes requires complex and expensive purification systems, which not only significantly increases equipment and operating costs but also generates a large amount of difficult-to-treat arsenic-containing waste, posing serious environmental risks and pressures. Existing technologies mostly focus on complex separation and purification after the co-volatilization of selenium and arsenic, failing to fundamentally solve this bottleneck problem, resulting in poor overall process economy and environmental performance.

[0004] In existing technologies, the mainstream processes for recovering selenium from copper anode slime typically involve oxidative roasting or sulfation roasting, which causes the selenium to volatilize and then recover it through condensation, alkaline absorption, or SO2 reduction. However, these processes face a common core challenge: the difficulty of achieving deep separation between selenium and arsenic. The volatilized arsenic severely pollutes selenium products, reducing their grade and value; simultaneously, the treatment of arsenic-containing fumes requires complex purification systems (such as multi-stage scrubbing, baghouse dust collection, and electrostatic precipitators), which not only increases equipment and operating costs but also generates large amounts of difficult-to-treat arsenic-containing wastewater and waste residue, posing a serious environmental challenge.

[0005] Therefore, developing a short-process, green, and clean new process that can suppress arsenic volatilization at the source and achieve efficient separation of selenium and arsenic is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] The purpose of this invention is to address the above-mentioned issues by providing a method for separating and recovering selenium and fixing arsenic in copper anode mud using vacuum roasting. This method has a short process flow, good selenium and arsenic separation effect, and can ensure environmental safety in the subsequent valuable metal recovery process.

[0007] The specific solution of this invention is: a method for separating and recovering selenium and fixing arsenic in copper anode mud by vacuum roasting, comprising the following steps:

[0008] a. Crush and screen the copper anode mud to obtain powder;

[0009] b. Mix the obtained powder with the iron-based arsenic fixative uniformly to obtain mixture A;

[0010] c. Place the mixture A in a calcining furnace, then introduce a mixture of inert carrier gas and oxygen-containing gas and maintain the system absolute pressure at 1-20 kPa and oxygen partial pressure at 1%-10%, and calcinate at 400-750℃ for 0.5-4 hours to obtain calcining residue B with arsenic fixed in the form of ferric arsenate and selenium-containing flue gas C.

[0011] d. Selenium-containing flue gas C is passed into sodium thiosulfate solution for absorption and reduction. After filtration, washing and drying, elemental selenium product D is obtained.

[0012] e. Leach the roasted slag B with dilute sulfuric acid to recover the valuable metals copper and silver.

[0013] Furthermore, the powder obtained in step a of this invention has a particle size ≥ 100 mesh.

[0014] Furthermore, in step b of this invention, the iron-based arsenic-fixing agent is one or more of the following: iron oxide, ferrous oxide, iron(II) oxide, iron hydroxide, hematite, and magnetite.

[0015] Furthermore, in step b of this invention, the amount of iron-based arsenic fixative added, calculated based on its effective component Fe2O3, is in a molar ratio of n(Fe2O3) / n(As) to arsenic in the copper anode mud of 1.0 to 3.0.

[0016] Furthermore, in step b of this invention, concentrated sulfuric acid may optionally be added to the mixture A, with the amount added being 0% to 30% of the dry weight of the copper anode mud.

[0017] Furthermore, in step c of this invention, the inert carrier gas is nitrogen.

[0018] Furthermore, in step c of this invention, the absolute pressure of calcination is 5–10 kPa, the calcination temperature is 400–750°C, and the calcination time is 0.5–4 hours.

[0019] Furthermore, in step d of this invention, the concentration of the sodium thiosulfate solution is 0.5–3 mol / L, and the absorption temperature is 40–80 °C.

[0020] Furthermore, in step e of this invention, 1-3 mol / L dilute sulfuric acid is used to leach the roasted residue B at 60-90 °C for 1-3 hours.

[0021] The present invention has the following beneficial effects:

[0022] 1. This invention utilizes the excellent stability of ferric arsenate to ensure that arsenic does not leach out during the subsequent acid leaching process, thus solving the environmental bottleneck.

[0023] 2. The raw material cost of this invention is low and economical, and cheap natural iron ore can be used directly as an arsenic fixative.

[0024] 3. Arsenic fixation and selenium volatilization are completed in a single process, and selenium recovery is seamlessly integrated with valuable metal recovery. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0026] This invention relates to a method for separating and recovering selenium and fixing arsenic in copper anode mud using vacuum roasting, comprising the following steps:

[0027] a. Crush and screen the copper anode mud to obtain powder;

[0028] b. Mix the obtained powder with the iron-based arsenic fixative uniformly to obtain mixture A;

[0029] c. Place the mixture A in a calcining furnace, then introduce a mixture of inert carrier gas and oxygen-containing gas and maintain the system absolute pressure at 1-20 kPa and oxygen partial pressure at 1%-10%, and calcinate at 400-750℃ for 0.5-4 hours to obtain calcining residue B with arsenic fixed in the form of ferric arsenate and selenium-containing flue gas C.

[0030] d. Selenium-containing flue gas C is passed into sodium thiosulfate solution for absorption and reduction. After filtration, washing and drying, elemental selenium product D is obtained.

[0031] e. Leach the roasted slag B with dilute sulfuric acid to recover the valuable metals copper and silver.

[0032] Furthermore, the powder obtained in step a of this invention has a particle size ≥ 100 mesh.

[0033] Further, in step b of this invention, the iron-based arsenic-fixing agent is one or more of iron oxide, ferrous oxide, magnetite, ferric oxide, hematite, and magnetite. Further, in step b of this invention, the amount of iron-based arsenic-fixing agent added, based on its effective component Fe2O3, has a molar ratio of n(Fe2O3) / n(As) of 1.0–3.0 with the arsenic element in the copper anode slime. Further, in step b of this invention, concentrated sulfuric acid may optionally be added to the mixture A, with an addition amount of 0%–30% of the dry weight of the copper anode slime. Further, in step c of this invention, the inert carrier gas is nitrogen. Further, in step c of this invention, the absolute roasting pressure is 5–10 kPa, the roasting temperature is 400–750 °C, and the roasting time is 0.5–4 hours. Further, in step d of this invention, the concentration of the sodium thiosulfate solution is 0.5–3 mol / L, and the absorption temperature is 40–80 °C. Furthermore, in step e of this invention, 1-3 mol / L dilute sulfuric acid is used to leach the roasted residue B at 60-90 °C for 1-3 hours.

[0034] The main reaction principle of this invention is as follows: During the negative pressure calcination stage with controllable low oxygen partial pressure, the following key reactions occur:

[0035] Arsenic fixation: Iron-based arsenic fixatives react with arsenic oxides to produce ferric arsenate, which is stable at high temperatures and sparingly soluble in dilute acids.

[0036] As₂O₃ + Fe₂O₃ → 2FeAsO₄

[0037] As₂O₅ + Fe₂O₃ → 2FeAsO₄

[0038] 2As2O3 + 4Fe3O4 + 5O2→ 12FeAsO4

[0039] (When ferric sulfate is used, the Fe2O3 produced by its thermal decomposition also participates in the above reaction.)

[0040] Oxidative volatilization of selenium: Various selenides and elemental selenium in copper anode mud are oxidized by oxygen into volatile SeO2.

[0041] Cu2Se + O2 → 2CuO + SeO2↑ (Oxidation of cuprous selenide)

[0042] 2CuSe + O2 → 2CuO + 2SeO2↑

[0043] Ag₂Se + O₂ → 2Ag + SeO₂↑

[0044] Se + O2 → SeO2↑

[0045] (If sulfuric acid is added arbitrarily, a sulfation reaction will occur, which will enhance oxidation: Cu2Se + 6H2SO4 → 2CuSO4 + SeO2↑ + 4SO2↑ + 6H2O; the generated SO2 can be further oxidized to SO3 and provide an oxidizing environment.)

[0046] Selenium recovery: The volatilized SeO2 gas is reduced to elemental selenium by sodium thiosulfate in the absorbent liquid.

[0047] 3SeO2+2Na2S2O3+2H2O→3Se↓+2Na2SO4+2H2SO4

[0048] The key improvement of this invention lies in the preferred use of iron-based materials as arsenic fixatives. This is because ferric arsenate, formed during the roasting process, has extremely low solubility in weakly acidic to neutral environments, and its stability is far higher than that of calcium arsenate. This characteristic ensures that when copper and silver are leached with dilute sulfuric acid in step e, arsenic can be firmly fixed in the leaching residue, fundamentally avoiding secondary leaching of arsenic and achieving green recycling throughout the entire process.

[0049] Furthermore, the iron-based arsenic-fixing agent is not limited to chemical products but can be extended to natural iron minerals such as hematite (main component Fe2O3) and magnetite (main component Fe3O4). This greatly broadens the source of raw materials, significantly reduces production costs, and provides convenience for industrial applications. The addition of concentrated sulfuric acid is no longer a necessary step but an optional one, used to treat certain extremely difficult-to-oxidize selenides (such as Ag2Se). Under normal circumstances, sufficient oxidation can be achieved simply by controlling the oxygen partial pressure, temperature, and time. The required low-pressure, low-oxygen environment is dynamically maintained by combining vacuum pump extraction with controlled gas intake. The introduced inert carrier gas (such as nitrogen) serves as a transport medium, rapidly carrying away the volatilized SeO2 from the reaction zone, ensuring continuous process operation.

[0050] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto. The main components (mass percentage) of the copper anode mud used in the embodiments are: Se 6.5-9.0%, As 3.5-5.0%, Cu 15-20%, Ag 4-7%, with the balance being Pb, Te, SiO2, etc.

[0051] Example 1:

[0052] Take 500g of copper anode mud (composition: Se 8.5%, As 4.2%) and pre-crush it. After crushing, grind it through a 100-mesh standard sieve to obtain uniform powder.

[0053] Based on the arsenic content, 59.8 g of industrial-grade iron oxide was weighed out according to the molar ratio of n(Fe2O3) / n(As) = 2.0. The weighed iron oxide was then thoroughly mixed with the anode mud powder in a mixer for 30 minutes to ensure uniform mixing, resulting in mixture A. Concentrated sulfuric acid was not added in this example.

[0054] Mixture A was loaded into the corundum crucible of the vacuum calcining furnace. The furnace door was closed, and the vacuum system was started. Nitrogen gas was then introduced into the furnace at a flow rate of 0.5 L / min as a carrier gas, and a suitable amount of air was mixed into the nitrogen flow using a mass flow controller to ensure that the oxygen content of the mixed gas entering the furnace was approximately 5% (v / v). By adjusting the vacuum pump's pumping rate and the air inlet flow rate, the absolute pressure inside the furnace was dynamically balanced at 8 kPa. The furnace was then heated to 520°C at a heating rate of 10°C / min and calcined at this temperature for 1.5 hours. The SeO2-containing flue gas generated during calcination was carried by nitrogen gas and continuously discharged from the furnace.

[0055] Selenium-containing flue gas C was passed into an absorption tower containing 1.5 L of a 1.5 mol / L Na₂S₂O₃ solution. The temperature of the absorbent was maintained at 60 °C using a water bath. After reacting for a period of time, the absorbent was filtered, and the red elemental selenium precipitate was collected. The filter cake was washed three times with deionized water and then dried in a vacuum drying oven at 80 °C for 4 hours to obtain elemental selenium product D. Weighing and chemical analysis showed that the direct recovery rate of selenium was 92.5%, and the purity of the product reached 99.2%.

[0056] The roasted residue B was leached for 2 hours at 80 °C with 2 mol / L dilute sulfuric acid at a liquid-to-solid ratio of 5:1. The filtrate after leaching was tested, and the arsenic concentration in the leaching solution was less than 15 mg / L, the copper leaching rate was over 95%, and silver was enriched in the leaching residue.

[0057] Example 2:

[0058] Take 500g of copper anode mud (composition: Se 7.8%, As 4.8%) and pre-crush it. After crushing, grind it through a 100-mesh standard sieve to obtain uniform powder.

[0059] Weigh out hematite powder, ground to 200 mesh with a Fe2O3 content of 90%, according to a molar ratio of n(Fe2O3) / n(As) = 2.2. Calculations show that 66.3g of hematite powder is required. Thoroughly mix the hematite powder with the anode mud powder to obtain mixture A. Concentrated sulfuric acid is not added in this example.

[0060] Mixture A was loaded into the corundum crucible of the vacuum calcining furnace. The furnace door was closed, and the vacuum system was started. Nitrogen gas was then introduced into the furnace at a flow rate of 0.8 L / min as a carrier gas, and a suitable amount of air was mixed into the nitrogen flow using a mass flow controller to ensure that the oxygen content of the mixed gas entering the furnace was approximately 6% (v / v). By adjusting the vacuum pump's pumping rate and the air inlet flow rate, the absolute pressure inside the furnace was dynamically balanced at 10 kPa. The furnace was then heated to 600 °C at a heating rate of 10 °C / min and calcined at this temperature for 2 hours. The SeO2-containing flue gas generated during calcination was carried by nitrogen gas and continuously discharged from the furnace.

[0061] Selenium-containing flue gas C was passed into an absorption tower containing 1.5 L of a 2.0 mol / L Na₂S₂O₃ solution. The temperature of the absorbent was maintained at 40 °C using a water bath. After reacting for a period of time, the absorbent was filtered, and the red elemental selenium precipitate was collected. The filter cake was washed three times with deionized water and then dried in a vacuum drying oven at 85 °C for 4 hours to obtain elemental selenium product D. Weighing and chemical analysis showed that the direct recovery rate of selenium was 90.1%, and the product selenium purity reached 99.0%.

[0062] Acid leaching experiments were conducted on roasted slag B (under the same conditions as in Example 1). The arsenic concentration in the leachate was below 20 mg / L, demonstrating that natural hematite can effectively fix arsenic, and the product is stable in dilute acid. The copper leaching rate exceeded 94%.

[0063] Example 3:

[0064] Take 500g of high silver copper anode mud (composition: Ag 10.5%, Se 7.5%, As 4.0%) and pre-crush it. After crushing, grind it through a 100-mesh standard sieve to obtain uniform powder.

[0065] 43.2 g of iron oxide powder was weighed according to the molar ratio of n(Fe2O3) / n(As) = 1.8. Meanwhile, to enhance the oxidation of the difficult-to-decompose Ag2Se, 5% (by weight of the copper anode mud) of concentrated sulfuric acid was optionally added, considering the more complex copper anode mud material. The anode mud powder, iron oxide, and concentrated sulfuric acid were carefully mixed evenly in an acid-resistant container to obtain mixture A.

[0066] Mixture A was loaded into the corundum crucible of the vacuum calcining furnace. The furnace door was closed, and the vacuum system was started. Nitrogen gas was then introduced into the furnace at a flow rate of 0.8 L / min as a carrier gas, and a suitable amount of air was mixed into the nitrogen flow using a mass flow controller to ensure that the oxygen content of the mixed gas entering the furnace was approximately 4% (v / v). By adjusting the vacuum pump's pumping rate and the air inlet flow rate, the absolute pressure inside the furnace was dynamically balanced at 6 kPa. The furnace was then heated to 700℃ at a heating rate of 10 ℃ / min and calcined at this temperature for 2 hours. The SeO2-containing flue gas generated during calcination was carried by nitrogen gas and continuously discharged from the furnace.

[0067] Selenium-containing flue gas C was passed into an absorption tower containing 1.5 L of a 1.5 mol / L Na₂S₂O₃ solution. The temperature of the absorption liquid was maintained at 50 °C using a water bath. After reacting for a period of time, the absorption liquid was filtered, and the red elemental selenium precipitate was collected. The filter cake was washed three times with deionized water and finally dried in a vacuum drying oven at 85 °C for 5 hours to obtain elemental selenium product D. Weighing and chemical analysis showed that the direct recovery rate of selenium was 96.1%, and the purity of the product reached 99.4%.

[0068] Acid leaching experiments were conducted on roasted slag B (under the same conditions as in Example 1). The arsenic concentration in the leachate was below 30 mg / L, demonstrating that natural hematite can effectively fix arsenic, and the product is stable in dilute acid. The copper leaching rate exceeded 94%.

[0069] Example 4:

[0070] Take 500g of high silver copper anode mud (composition: Ag 10.5%, Se 7.5%, As 4.0%) and pre-crush it. After crushing, grind it through a 100-mesh standard sieve to obtain uniform powder.

[0071] Weigh 83.4 g of iron oxide powder according to the molar ratio of n(Fe2O3) / n(As) = 2.8. Mix the weighed iron oxide powder and anode mud powder thoroughly in a mixer for 30 minutes to ensure uniform mixing, obtaining mixture A. Concentrated sulfuric acid is not added in this example.

[0072] Mixture A was loaded into the corundum crucible of the vacuum calcining furnace. The furnace door was closed, and the vacuum system was started. Nitrogen gas was then introduced into the furnace at a flow rate of 0.8 L / min as a carrier gas, and a suitable amount of air was mixed into the nitrogen flow using a mass flow controller to ensure that the oxygen content of the mixed gas entering the furnace was approximately 5% (v / v). By adjusting the vacuum pump's pumping rate and the air inlet flow rate, the absolute pressure inside the furnace was dynamically balanced at 15 kPa. The furnace was then heated to 450 °C at a heating rate of 10 °C / min and calcined at this temperature for 3.5 hours. The SeO2-containing flue gas generated during calcination was carried by nitrogen gas and continuously discharged from the furnace.

[0073] Selenium-containing flue gas C was passed into an absorption tower containing 2.0 L of a 1.0 mol / L Na₂S₂O₃ solution. The temperature of the absorbent was maintained at 50 °C using a water bath. After reacting for a period of time, the absorbent was filtered, and the red elemental selenium precipitate was collected. The filter cake was washed three times with deionized water and then dried in a vacuum drying oven at 85 °C for 4 hours to obtain elemental selenium product D. Weighing and chemical analysis showed that the direct selenium recovery rate was 84.0%, and the product selenium purity reached 98.4%.

[0074] Acid leaching experiments were conducted on roasted residue B (under the same conditions as in Example 1). The arsenic concentration in the leachate was below 25 mg / L, demonstrating that natural hematite can effectively fix arsenic, and the product is stable in dilute acid. The copper leaching rate exceeded 92%.

[0075] The above embodiments demonstrate that the method of the present invention, using iron-based arsenic fixatives, especially industrial iron oxide or natural iron minerals (hematite, magnetite), can effectively achieve efficient selenium recovery and stable arsenic fixation under different process conditions. The resulting ferric arsenate exhibits extremely high stability in subsequent dilute acid leaching, fundamentally solving the problem of secondary arsenic pollution and providing a reliable and economical technical solution for the green and efficient treatment of copper anode mud.

Claims

1. A method for separating and recovering selenium and fixing arsenic in copper anode mud by vacuum roasting, characterized in that, Includes the following steps: a. Crush and screen the copper anode mud to obtain powder; b. Mix the obtained powder with the iron-based arsenic fixative uniformly to obtain mixture A; c. Place the mixture A in a calcining furnace, then introduce a mixture of inert carrier gas and oxygen-containing gas and maintain the system absolute pressure at 1-20 kPa and oxygen partial pressure at 1%-10%, and calcinate at 400-750℃ for 0.5-4 hours to obtain calcining residue B with arsenic fixed in the form of ferric arsenate and selenium-containing flue gas C. d. Selenium-containing flue gas C is passed into sodium thiosulfate solution for absorption and reduction. After filtration, washing and drying, elemental selenium product D is obtained. e. Leach the roasted slag B with dilute sulfuric acid to recover the valuable metals copper and silver.

2. The method for vacuum roasting to separate and recover selenium and fix arsenic in copper anode mud according to claim 1, characterized in that, The powder obtained in step a has a particle size ≥ 100 mesh.

3. The method for vacuum roasting to separate and recover selenium and fix arsenic in copper anode mud according to claim 1, characterized in that, In step b, the iron-based arsenic fixative is one or more of the following: iron oxide, ferrous oxide, iron(II) oxide, iron hydroxide, hematite, and magnetite.

4. The method for vacuum roasting to separate and recover selenium and fix arsenic in copper anode mud according to claim 1, characterized in that, The amount of iron-based arsenic fixative added in step b, based on its effective component Fe2O3, is in the molar ratio of arsenic in the copper anode mud n(Fe2O3) / n(As) = 1.0 to 3.

0.

5. The method for vacuum roasting to separate and recover selenium and fix arsenic in copper anode mud according to claim 1, characterized in that, In step b, concentrated sulfuric acid may optionally be added to mixture A, in an amount of 0% to 30% of the dry weight of the copper anode mud.

6. The method for vacuum roasting to separate and recover selenium and fix arsenic in copper anode mud according to claim 1, characterized in that, In step c, the inert carrier gas is nitrogen.

7. The method for vacuum roasting to separate and recover selenium and fix arsenic in copper anode mud according to claim 1, characterized in that, The absolute pressure of calcination in step c is 5–10 kPa, the calcination temperature is 400–750 ℃, and the calcination time is 0.5–4 hours.

8. The method for vacuum roasting to separate and recover selenium and fix arsenic in copper anode mud according to claim 1, characterized in that, The concentration of the sodium thiosulfate solution in step d is 0.5–3 mol / L, and the absorption temperature is 40–80 °C.

9. The method for vacuum roasting to separate and recover selenium and fix arsenic in copper anode mud according to claim 1, characterized in that, In step e, 1–3 mol / L dilute sulfuric acid is used to leach the roasted residue B at 60–90 °C for 1–3 hours.