A two-stage, high-efficiency leaching method for chalcopyrite using reduction and oxidation processes.

Abstract

This invention relates to a high-efficiency two-stage reduction-oxidation leaching method for chalcopyrite based on potential control. The method involves mixing chalcopyrite and / or flotation copper concentrate with copper powder, adding acid to adjust the slurry to obtain slurry A, followed by a first-stage reduction leaching to obtain a leaching solution and reduction slag. The reduction slag is then adjusted to obtain slurry B by adding an oxidant, followed by a second-stage oxidation leaching to obtain a copper leaching solution and leaching slag. During the first-stage reduction leaching, when the potential in the system drops below 0.14V, hydrogen sulfide gas generated during the first-stage reduction leaching is extracted by simultaneously aerating and degassing. During the second-stage oxidation leaching, when the potential in the system drops below 0.55V, an oxidant is added. This invention does not involve high temperature and high pressure, does not introduce impurity ions, has low cost, and is environmentally friendly.

Description

Technical Field

[0001] This invention relates to the fields of hydrometallurgy and mineral processing, specifically to a method for efficient two-stage reduction-oxidation leaching of chalcopyrite. Technical Background

[0002] Chalcopyrite is the most abundant copper-bearing mineral in nature. Currently, the main copper extraction process from chalcopyrite involves crushing and grinding, flotation enrichment, pyrometallurgical smelting, and electrolytic refining. However, with increasing environmental awareness, the pollution problems caused by pyrometallurgical smelting are becoming increasingly apparent. Finding an environmentally friendly and efficient alternative process has become a key focus for the green development of the copper industry.

[0003] The wet leaching of chalcopyrite and chalcopyrite-bearing flotation concentrates involves: dissolving the mineral in a solution system through chemical or microbial oxidation; recovering copper from the leachate after solid-liquid separation through extraction enrichment and electrowinning. Extensive research has been conducted by scholars both domestically and internationally on the oxidation-dissolution mechanism of chalcopyrite. It is generally believed that during the oxidation-dissolution process, intermediate products that hinder further mineral reactions are formed on the surface of chalcopyrite. These include polysulfides (iron-deficient polysulfides), cerium blue, elemental sulfur, iron oxides (iron hydroxides), and insoluble sulfates (potassium jaundice). Recently, some scholars have pointed out that the inherent semiconductor properties of chalcopyrite and the semiconductor properties of the surface products are the reasons for the slow dissolution rate, especially the PN junction formed between chalcopyrite and intermediate products, which slows down the electron transfer rate during the mineral oxidation process.

[0004] Processes for enhancing the hydrometallurgical leaching of chalcopyrite include bioleaching, high-temperature and high-pressure leaching, the Galvanox process, and other variants, most of which utilize iron ions and sulfuric acid. The leaching kinetics of bioleaching are hampered by a "passivation layer"; high-temperature and high-pressure leaching overcomes passivation, but these conditions are often uneconomical in many plants; the Galvanox process is a promising method for improving copper recovery, but its leaching performance is unstable due to significant influence from the type and location of the ore, and therefore it has not been widely adopted industrially.

[0005] Chalcopyrite is reduced to readily leached sulfides (bornite and chalcocite) while releasing hydrogen sulfide and ferrous ions. This kinetic process is relatively rapid and does not exhibit the same passivation as the oxidation process. Thermodynamic calculations of the chalcopyrite-aqueous solution system show that solution pH, redox potential (potential), and temperature are the main factors affecting the reduction of chalcopyrite.

[0006] Reducing agents or direct electrolytic reduction can provide the necessary potential for the reduction of chalcopyrite. In acidic media, metals (aluminum, iron, lead, or zinc) have been used as reducing agents. However, problems such as high reagent consumption, difficulty in recovery, and ion contamination of the system hinder industrial applications. Electro-assisted reduction processes can effectively avoid the problems of reagent consumption and system ion contamination, but in acidic solution systems, the reduction of hydrogen ions to hydrogen gas at the electrode surface is unavoidable, leading to increased power consumption and reduced energy utilization. In all the above reduction processes, a large accumulation of hydrogen sulfide occurs in the solution, causing dissolved ferrous ions to react with it to form iron sulfides such as pyrrhotite on the mineral surface, which inhibits further reduction of chalcopyrite.

[0007] Oxidative leaching of iron-free copper sulfide ores (chalcocite, chalcocite and chalcocite) is much easier than chalcopyrite, requiring only a high potential to leach more than 90% of the copper in a short time (4-6 hours).

[0008] In conclusion, given that the problem of slow oxidation and dissolution of chalcopyrite remains unresolved, the two-stage reduction-oxidation leaching method for chalcopyrite holds promise as an alternative to the direct oxidation leaching process, achieving rapid leaching of chalcopyrite and advancing the overall development of hydrometallurgical processes for chalcopyrite. Summary of the Invention

[0009] In the hydrometallurgical process of chalcopyrite, the slow kinetics of chalcopyrite oxidation and dissolution are a concern. This invention aims to provide a highly efficient two-stage reduction-oxidation leaching method for chalcopyrite. This method uses copper powder obtained from the electrowinning process (electrowinning copper powder) as a primary reducing agent. By employing solution oxidation-reduction potential detection and control technology, the conversion rate and leaching rate of the primary reduction and secondary oxidation stages are ensured, achieving comprehensive recovery of valuable elements from chalcopyrite. This method not only improves the leaching rate and extraction rate of chalcopyrite but also avoids introducing new impurities and is highly adaptable to existing processes.

[0010] The present invention solves the problems of the prior art by adopting the following technical solution:

[0011] This invention discloses a two-stage high-efficiency leaching method for chalcopyrite, comprising mixing chalcopyrite and / or flotation copper concentrate with copper powder, adding acid to adjust the slurry to obtain slurry A, then performing a first-stage reduction leaching to obtain leaching solution and reduction slag, adjusting the reduction slag to obtain slurry B by adding an oxidant, and performing a second-stage oxidation leaching to obtain copper leaching solution and leaching slag.

[0012] During the first-stage reduction leaching process, when the potential in the first-stage reduction leaching system is lower than 0.14V, hydrogen sulfide gas generated during the first-stage reduction leaching process is extracted by simultaneously purging and evacuating the gas.

[0013] During the two-stage oxidative leaching process, when the potential in the two-stage oxidative leaching system is lower than 0.55V, an oxidant is added.

[0014] This invention provides a highly efficient two-stage leaching method for chalcopyrite, involving reduction and oxidation. The inventors discovered that chalcopyrite can be reduced to chalcocite, chalcocite, and chalcocite in acidic solution, while releasing ferrous ions and hydrogen sulfide. This process avoids the problems associated with passivation films. Compared to chalcopyrite, the reduction products, chalcocite and chalcocite, have simpler compositions. In the oxidative leaching process, only cobalt blue is generated as an intermediate product. The adverse effects of cobalt blue on the reaction can be overcome by increasing the temperature and oxidation potential.

[0015] In this invention, copper powder is used as a reducing agent. In a system containing acid and hydrogen sulfide, the electrode potential of metallic copper can drop to -0.35V, thus becoming a reducing agent for the spontaneous reaction of chalcopyrite reduction. The added copper powder is oxidized during the reduction process and then enters the secondary oxidation process with the reduction slag, where it is further oxidized to copper ions. These copper ions can be recovered through electrodeposition. The copper powder possesses the reducing properties required for chalcopyrite reduction without introducing other impurity ions. Furthermore, recycling and regeneration can be achieved using existing processes.

[0016] The inventors discovered that the reduction efficiency is highest when hydrogen sulfide is removed from a reductive leaching system when the potential is below 0.14V. This is because the hydrogen sulfide produced during the reduction of chalcopyrite accumulates in the solution and reacts with simultaneously dissolved ferrous ions and copper ions generated from the oxidation of metallic copper, forming new precipitates such as iron sulfide and copper blue. These new precipitates cover the surface of unreacted particles and hinder further reactions. Timely removal of hydrogen sulfide mitigates the precipitate capping effect and increases the conversion rate. On the other hand, if hydrogen sulfide is completely removed, the system potential will be above 0.14V, causing metallic copper to react with acid and reducing its reaction with chalcopyrite. Therefore, removing hydrogen sulfide when the potential in a reductive leaching system is below 0.14V and maintaining an appropriate amount of hydrogen sulfide can sustain the reducing environment of the system.

[0017] Meanwhile, adding an appropriate amount of oxidant during the second-stage oxidation leaching process is essential to achieve optimal oxidation efficiency. Excessive unreacted oxidant in the slurry will negatively impact subsequent extraction reagents. Insufficient oxidant will lead to incomplete oxidation of the reduction slag, resulting in a decrease in copper recovery.

[0018] Some oxidants, such as hydrogen peroxide, persulfate, oxygen, and ozone, undergo self-decomposition and overflow processes. When the concentration of the oxidant in the system is too high, its self-decomposition and overflow are aggravated, resulting in reduced reagent utilization and increased costs.

[0019] However, by using a real-time slurry potential monitoring device, the addition of oxidant can be precisely controlled through feedback information from the slurry potential. This method provides the oxidizing atmosphere required for the reducing slag without negatively impacting the subsequent extractant, while also ensuring that the oxidant does not decompose or overflow on its own.

[0020] In this invention, the slurry potential is referenced to an Ag / AgCl electrode saturated with KCl (vs. Ag / AgCl).

[0021] In a preferred embodiment, the copper grade of both the chalcopyrite and the flotation copper concentrate is greater than 17%.

[0022] In a preferred embodiment, the particle size of both the chalcopyrite and the flotation copper concentrate is less than 48 mesh.

[0023] In a preferred embodiment, the copper powder is electrowinning copper powder, and the purity of the electrowinning copper powder is >70%.

[0024] In a preferred embodiment, the concentration of slurry A is 2-50%. In this invention, the concentration of slurry A is the mass fraction of chalcopyrite, flotation copper concentrate, and copper powder in slurry A.

[0025] In a preferred embodiment, the acid is sulfuric acid, and the sulfuric acid concentration in slurry A is >5 g / L.

[0026] In a preferred embodiment, nitrogen is purged during the conditioning process of mineral slurry A to remove dissolved oxygen, and the dissolved oxygen concentration in mineral slurry A is <0.5 mg / L.

[0027] The inventors discovered that when slurry A is initially prepared and dissolved oxygen is removed, the slurry potential can quickly drop to below 0.14V within 30 seconds and the reaction can begin. However, if nitrogen is not used to remove dissolved oxygen, it takes 10-20 minutes for the slurry potential to drop to below 0.14V before the reaction can begin.

[0028] In a preferred embodiment, the reduction leaching is carried out in a reactor with a small-diameter opening. Using this specific reactor with a small-diameter opening facilitates the sealing of the reaction system and the removal of gases.

[0029] In actual operation, an inflation / extraction device is used to inflate and expel air simultaneously. The inflation / extraction device causes minimal disturbance to the solution system, and the air inlet and outlet are positioned at high and low positions respectively, allowing for full flow of gas above the page.

[0030] In a preferred embodiment, hydrogen sulfide gas is oxidized to elemental sulfur by a gas washing liquid, and the solid phase obtained by solid-liquid separation of the gas washing liquid is sulfur powder. The gas washing liquid is selected from an oxidizing solution and an alkaline solution filled with an oxidizing gas. The oxidizing solution is selected from at least one of persulfate, hydrogen peroxide, and Fe(III) salt solution, and the alkaline solution is selected from at least one of sodium hydroxide solution and sodium carbonate solution.

[0031] In a preferred embodiment, the temperature of the first-stage reduction leaching is 35–90°C, and the time of the first-stage reduction leaching is 1–4 hours.

[0032] In the preferred embodiment, after the first stage of reduction reaction is completed, the leachate obtained by solid-liquid separation after thickening sedimentation is returned to the pulp for slurry preparation to obtain slurry A.

[0033] Further optimization involves recovering iron by crystallization or precipitation when the ferrous content in the leachate is greater than 180 g / L.

[0034] In a preferred embodiment, the moisture content of the reduction residue is <45%.

[0035] In a preferred embodiment, the oxidant is selected from at least one of hydrogen peroxide, persulfate, oxygen, and ozone.

[0036] In a preferred embodiment, the pH of the slurry B is 1-2, and the slurry concentration is 2-40%.

[0037] In a preferred embodiment, the temperature of the two-stage oxidation leaching is 25-90℃, and the time of the two-stage oxidation leaching is 3-6 hours.

[0038] In a preferred embodiment, the copper-containing leachate is purified, extracted, and electrowinning processes to produce cathode copper, and a portion of the cathode copper is returned as copper powder from the reduction leaching of chalcopyrite and / or flotation copper concentrate.

[0039] In a preferred embodiment, the leaching residue is purified to obtain elemental sulfur.

[0040] The resulting leaching residue is sulfur powder of low purity, which can be purified into elemental sulfur.

[0041] In a preferred embodiment, the potentials in both the first-stage reduction leaching system and the second-stage oxidation leaching system are monitored in real time by an oxidation-reduction potential detection and control system.

[0042] When the potential of the first-stage reduction leaching system is detected to be lower than the set value, the gas filling / exhausting device is turned on to extract the excess hydrogen sulfide gas. When the potential of the second-stage oxidation leaching system is detected to be lower than the set value, the oxidant adding device is turned on to maintain the oxidation atmosphere required for the second-stage oxidation leaching.

[0043] In a further preferred embodiment, the redox potential detection and control system has a signal acquisition cycle of less than 5 seconds, and the control module adopts a PID control strategy.

[0044] Principles and advantages

[0045] Thermodynamic calculations of the Cu-Fe-S-H2O system show that metallic copper can reduce chalcopyrite under acidic conditions. The reduction products are mainly chalcocite and chalcocite. This reaction process is unaffected by a dense passivation layer, exhibiting high conversion rate and fast reaction speed. However, the hydrogen sulfide generated in the reaction accumulates in large quantities within the system, forming precipitates with metal ions in the solution and covering the surface of unreacted particles, thus adversely affecting the reduction reaction. Timely removal of hydrogen sulfide from the reaction system can mitigate its adverse effects.

[0046] When the slurry potential is higher than 0.5V, the reducing slag chalcocite and chalcocite are leached by oxidation. The possible reaction mechanism is: Cu₂S → Cu 31 S 16 →Cu9S5→Cu7S4→Cu 39 S 28 →Cu9S8→CuS→S. Copper blue (CuS) has a dense structure and a slow reaction rate, easily covering the surface of unreacted particles; its oxidation is the rate-limiting step. Increasing the temperature and solution potential can accelerate the oxidation of copper blue, eliminating its adverse effects and thus achieving rapid leaching of the reduction residue.

[0047] Advantages:

[0048] 1. Compared with hot pressing, this method can achieve efficient leaching of chalcopyrite without high temperature and high pressure.

[0049] 2. Compared with bioleaching, this method achieves efficient leaching of chalcopyrite under atmospheric conditions, with a leaching time as short as 6 hours.

[0050] 3. This method is highly compatible with the existing mainstream copper hydrometallurgical process, does not introduce new impurities, and requires minimal modification to the original process.

[0051] 4. The byproducts of this method can be effectively recycled, and there is no discharge of harmful waste gas, wastewater, or waste materials, making it environmentally friendly.

[0052] 5. This method has low requirements for feed quality and can effectively handle harmful elements, which can reduce the pressure of chalcopyrite flotation operations and save beneficiation costs. Attached Figure Description

[0053] Figure 1 These are the potential-pH diagram and component distribution diagram of the Cu-Fe-S-H2O system.

[0054] Figure 2 It is a section on the composition and content of reducing residue.

[0055] Figure 3 This is a process flow diagram of the present invention. Detailed Implementation

[0056] To make the technical means, creative features, objectives, and effects of this invention readily understandable, the invention is further described below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0057] Example 1:

[0058] 20g of chalcopyrite with a copper grade of 34.5% and a particle size of -200 mesh to +400 mesh was mixed with 7g of electrowinning copper powder with a copper content of 99%. Concentrated sulfuric acid and water were added to prepare 1L of slurry A, with a sulfuric acid concentration of 20g / L. During slurry preparation, nitrogen was purged to reduce the dissolved oxygen content of the slurry to 0.5mg / L. The temperature was raised to 50℃. After the reduction reaction began, the slurry potential was maintained below 0V by venting hydrogen sulfide gas. The reduction leaching reaction time was 2 hours. The chalcopyrite reduction conversion rate was 75%. After solid-liquid separation I, 15.4g of reduction residue was obtained. The phase and composition test results are as follows: Figure 2 As shown, the reducing residue was adjusted to obtain slurry B. An oxidant was added to maintain the slurry potential at 0.6V. The leaching temperature was 50℃, and the leaching time was 4 hours. The copper leaching rate was 67%.

[0059] Example 2:

[0060] 100g of chalcopyrite with a copper grade of 34.5% and a particle size of -400 mesh was mixed with 70g of electrowinning copper powder with a copper content of 99%. Concentrated sulfuric acid and water were added to prepare 1L of slurry A, with a sulfuric acid concentration of 20g / L. During slurry preparation, nitrogen was purged to reduce the dissolved oxygen content of the slurry to 0.5mg / L. The temperature was raised to 90℃. After the reduction reaction began, hydrogen sulfide gas was discharged to maintain the slurry potential below 0.14V. The reduction leaching reaction time was 2 hours. The chalcopyrite reduction conversion rate was 99%. After solid-liquid separation I, 69g of reduction residue was obtained. The reduction residue was slurried to obtain slurry B. Hydrogen peroxide was added as an oxidant to maintain the slurry potential at 0.8V. The leaching temperature was 90℃, and leaching was carried out for 2 hours, resulting in a copper leaching rate of 98%.

[0061] Comparative Example 1:

[0062] The other conditions were the same as in Example 1, except that the amount of metallic copper added was 0g, the first-stage reduction conversion rate of chalcopyrite was only 0%, and the second-stage copper oxide leaching rate was 3%.

[0063] Comparative Example 2:

[0064] The other conditions were the same as in Example 1, except that the sulfuric acid concentration in slurry A was 0.5 g / L, the first-stage reduction conversion rate of chalcopyrite was only 7%, and the second-stage copper oxide leaching rate was 10%.

[0065] Comparative Example 3:

[0066] Other conditions were the same as in Example 1, except that the dissolved oxygen concentration in slurry A was 9 mg / L, the first-stage reduction conversion rate of chalcopyrite was only 0%, and the second-stage copper oxide leaching rate was 3%.

[0067] Comparative Example 4:

[0068] The other conditions were the same as in Example 1, except that the slurry potential detection feedback control was not used to extract hydrogen sulfide gas in the first stage of the reduction process. The first stage reduction conversion rate of chalcopyrite was 45%, and the second stage copper oxide leaching rate was 43%.

[0069] Comparative Example 5:

[0070] Other conditions were the same as in Example 1, except that after the first stage of reduction reaction began, the slurry potential was maintained at 0.2V, the first stage reduction conversion rate of chalcopyrite was 50%, and the second stage copper oxide leaching rate was 48%.

[0071] Comparative Example 6:

[0072] The other conditions are the same as in Example 2, except that it is a two-stage oxidation leaching process, maintaining the slurry potential at 0.4V, and the two-stage copper oxidation leaching rate is 50%.

[0073] Comparative Example 7:

[0074] Other conditions were the same as in Example 2, except that the oxidant was added all at once during the preparation of slurry B in the two-stage oxidation leaching process. During the reaction, some hydrogen peroxide decomposed; with the same amount of hydrogen peroxide, the two-stage copper oxide leaching rate was 74%.

Claims

1. A method for efficient two-stage reduction-oxidation leaching of chalcopyrite, characterized in that: Chalcopyrite is mixed with copper powder, and acid is added to adjust the slurry to obtain slurry A. Then, a first-stage reduction leaching is carried out to obtain leaching solution and reduction residue. The reduction residue is adjusted to obtain slurry B by adding an oxidant. A second-stage oxidation leaching is carried out to obtain copper leaching solution and leaching residue. During the first-stage reduction leaching process, when the potential in the first-stage reduction leaching system is lower than 0.14V, hydrogen sulfide gas generated during the first-stage reduction leaching process is extracted by simultaneously purging and evacuating the gas. During the two-stage oxidative leaching process, when the potential in the two-stage oxidative leaching system is lower than 0.55V, an oxidant is added. The acid is sulfuric acid, and the sulfuric acid concentration in slurry A is >5 g / L; During the conditioning process to obtain slurry A by adding acid, nitrogen is purged to remove dissolved oxygen, and the dissolved oxygen concentration in slurry A is <0.5 mg / L; The potential is referenced to an Ag / AgCl electrode saturated with KCl.

2. The method for efficient two-stage reduction-oxidation leaching of chalcopyrite according to claim 1, characterized in that: The copper grade of the chalcopyrite is greater than 17%; The chalcopyrite has a particle size of less than 48 mesh; The copper powder is electrowinning copper powder, and the purity of the electrowinning copper powder is >70%.

3. The method for efficient two-stage reduction-oxidation leaching of chalcopyrite according to claim 1, characterized in that: The concentration of slurry A is 2-50%.

4. The method for efficient two-stage reduction-oxidation leaching of chalcopyrite according to claim 1, characterized in that: The reduction leaching is carried out in a reactor with a small-diameter opening.

5. The method for efficient two-stage reduction-oxidation leaching of chalcopyrite according to claim 1, characterized in that: Hydrogen sulfide gas is oxidized to elemental sulfur by a gas washing liquid. The solid phase obtained by solid-liquid separation of the gas washing liquid is sulfur powder. The gas washing liquid is selected from an oxidizing solution or an alkaline solution filled with an oxidizing gas. The oxidizing solution is selected from at least one of persulfate, hydrogen peroxide, and trivalent Fe salt solution. The alkaline solution is selected from at least one of sodium hydroxide solution and sodium carbonate solution.

6. The method for efficient two-stage reduction-oxidation leaching of chalcopyrite according to claim 1, characterized in that: The temperature of the first-stage reduction leaching is 35~90℃, and the time of the first-stage reduction leaching is 1~4 h; After the first stage of reduction reaction is completed, the leachate obtained by solid-liquid separation after thickening sedimentation is returned to the pulp for slurry preparation to obtain slurry A; When the ferrous content in the leachate is greater than 180 g / L, iron is recovered by crystallization or precipitation. The moisture content of the reducing residue is <45%.

7. The method for efficient two-stage reduction-oxidation leaching of chalcopyrite according to claim 1, characterized in that: The oxidant is selected from at least one of hydrogen peroxide, persulfate, oxygen, and ozone; The pH of the slurry B is 1-2, and the slurry concentration is 2-40%.

8. The method for efficient two-stage reduction-oxidation leaching of chalcopyrite according to claim 1, characterized in that: The temperature of the two-stage oxidation leaching is 25-90℃, and the time of the two-stage oxidation leaching is 3-6 h.

9. The method for efficient two-stage reduction-oxidation leaching of chalcopyrite according to claim 1, characterized in that: The copper leaching solution is purified, extracted, and electrowinning processes to produce cathode copper, and part of the cathode copper is returned as copper powder from the reduction leaching of chalcopyrite. The leaching residue was purified to obtain elemental sulfur.

10. The method for efficient two-stage reduction-oxidation leaching of chalcopyrite according to claim 1, characterized in that: The potentials in both the first-stage reduction leaching system and the second-stage oxidation leaching system are monitored in real time by the oxidation-reduction potential detection and control system. The redox potential detection and control system has a signal acquisition cycle of less than 5 seconds, and the control module adopts a PID control strategy.

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