Method for processing rhenium-rich slags

Abstract

The present application belongs to the technical field of hydrometallurgy of dispersed metals, and particularly relates to a treatment method of rhenium-rich slag, comprising the following steps: (1) slurry; (2) low-potential section oxidative leaching; (3) high-potential section oxidative leaching; (4) solid-liquid separation to obtain a rhenium-containing leaching solution. The above scheme first provides a low-potential condition, As and Bi combine to generate a difficult-to-dissolve bismuth arsenate precipitate, and As and Pb combine to generate a difficult-to-dissolve lead arsenate precipitate, thereby pre-fixing arsenic and bismuth in the slag phase; then a high-potential condition is provided, so that rhenium is fully oxidized into ReO4⁻ and enters the solution. The rhenium-rich slag treatment method of the present application can achieve a rhenium leaching rate of 98% or more, while the arsenic leaching rate can be controlled to be 40% or less, and the bismuth leaching rate can be controlled to be 10% or less, thereby realizing selective separation of rhenium and impurity elements.

Description

Technical Field

[0001] This invention belongs to the field of rare and dispersed metal hydrometallurgical technology, specifically relating to a method for treating rhenium-rich slag, and more particularly to a method for selective leaching of rhenium by segmented control of redox potential. Background Technology

[0002] Rhenium is an important rare and dispersed metal with a high melting point, high strength, and good catalytic properties, and is widely used in aerospace, petrochemical, and electronics industries. During copper smelting, rhenium volatilizes into the flue gas as Re2S7 at high temperatures. After wet washing, it is enriched in the pickling solution and then recovered through precipitation and other methods to obtain rhenium-rich slag.

[0003] Rhenium-rich slag typically contains various elements such as copper, lead, arsenic, bismuth, and selenium. Rhenium mainly exists in multiple forms, including rhenium heptasulfide (Re2S7), rhenium disulfide (ReS2), and rhenium oxide (ReO2). The key to efficiently recovering rhenium from such complex slag lies in achieving selective leaching of rhenium, that is, ensuring a high leaching rate of rhenium while minimizing the leaching of impurities such as arsenic and bismuth.

[0004] In existing technologies, methods for leaching rhenium from rhenium-rich slag mainly include acid leaching, oxidative leaching, and pressure leaching. Among these, oxidative leaching using a sulfuric acid-hydrogen peroxide system is a relatively common method, but this method has poor selectivity, and the leaching rate of arsenic is often as high as 96% or more.

[0005] In recent years, researchers have proposed a potential-controlled oxidation leaching method, which achieves precise control of the leaching process by controlling the oxidation-reduction potential (ORP). Studies have shown that under conditions of an oxidation leaching potential of 700–750 mV, a sulfuric acid concentration of 15%, a leaching temperature of 70℃, and a leaching time of 60 min, the rhenium leaching rate can reach 98.612%, but the leaching rates of other components (including arsenic, copper, etc.) are all higher than 90%. This means that although this method has a high rhenium leaching rate, its selectivity is still insufficient, and a large amount of impurities such as arsenic enters the leachate, increasing the difficulty and cost of subsequent separation and purification.

[0006] Therefore, developing a selective leaching method for rhenium-rich slag that can both ensure a high rhenium leaching rate and effectively suppress the leaching of impurities has significant industrial application value. Summary of the Invention

[0007] The purpose of this invention is to provide a method for treating rhenium-rich slag, which uses a segmented controlled potential oxidation method to suppress the leaching of arsenic, bismuth, and other substances in the rhenium-rich slag and selectively leaches rhenium, thereby achieving efficient separation of rhenium.

[0008] To achieve the aforementioned objectives in Weishi County, the technical solution adopted by this invention is: a method for treating rhenium-rich slag, comprising the following steps:

[0009] (1) Slurry preparation: Rhenium-rich slag is mixed with sulfuric acid solution and stirred evenly to form a slurry;

[0010] (2) Low potential section oxidation leaching: Add oxidant to the slurry, maintain the potential at 400-550 mV under stirring at 50-80℃ for the first stage of oxidation leaching, the leaching time is 69-90 min, and the first stage oxidized slurry is obtained; the oxidant is hydrogen peroxide or ferric sulfate solution;

[0011] (3) High-potential leaching: Continue to add oxidant to the first-stage oxidizing slurry, and maintain the potential at 700-750 mV under stirring conditions at 50-80℃ for the second-stage oxidizing leaching, with a leaching time of 69-90 min;

[0012] (4) Solid-liquid separation: The leachate slurry is filtered to obtain rhenium-containing leachate and leachate residue.

[0013] The above scheme first provides low potential conditions, allowing As(V) to combine with Bi(III) to form insoluble bismuth arsenate (BiAsO4) precipitate and As(V) to combine with Pb(II) to form insoluble lead arsenate (Pb3(AsO4)2) precipitate, thus pre-fixing arsenic and bismuth in the slag phase. Then, high potential conditions are provided to fully oxidize rhenium to ReO4⁻ and allow it to enter the solution. The rhenium-rich slag treatment method of this invention achieves a rhenium leaching rate of over 98%, while the arsenic leaching rate can be controlled below 40% and the bismuth leaching rate below 10%. This achieves selective separation of rhenium from impurity elements, with a simple process, controllable operation, and good selectivity, providing a new approach for the separation and recovery of rare and dispersed metals, especially rhenium. Detailed Implementation

[0014] The technical solution of the present invention will be further described in detail below with reference to the embodiments.

[0015] I. Technical Solution:

[0016] A method for treating rhenium-rich slag includes the following steps:

[0017] (1) Slurrying: Rhenium-rich slag is mixed with sulfuric acid solution and stirred evenly to form a slurry; wherein the mass concentration of sulfuric acid solution is 5%-10%; the liquid-solid ratio is 20:1-50:1, preferably 30:1.

[0018] (2) Low-potential oxidative leaching: An oxidant is added to the slurry, and the first-stage oxidative leaching is carried out under stirring conditions at 50-80℃, maintaining a potential of 400-550 mV (preferably 65℃, 450-500 mV, relative to a saturated calomel electrode), with a leaching time of 69-90 min, to obtain the first-stage oxidized slurry; the oxidant is hydrogen peroxide or ferric sulfate solution. This step is one of the core points of the technical solution of the present invention: under low-potential conditions, As(V) and Bi(III) in the leaching system combine to form insoluble bismuth arsenate (BiAsO4) precipitate, and As(V) and Pb(II) combine to form insoluble lead arsenate (Pb3(AsO4)2) precipitate. Once these precipitates are formed, they are difficult to dissolve again in subsequent acidic solutions. This is equivalent to "locking" arsenic and bismuth in the slag before leaching rhenium. At the same time, the leaching reaction of rhenium under this potential condition has not yet been fully carried out, avoiding excessive consumption of the oxidant.

[0019] (3) High-potential oxidative leaching: Oxidant is added to the first-stage oxidative slurry, and the second-stage oxidative leaching is carried out under stirring conditions at 50-80℃ (preferably 65℃) with a potential maintained at 700-750 mV (relative to a saturated calomel electrode). The leaching time is 69-90 min. This step is the second core point of the technical solution of this invention: Under high potential and strong oxidizing environment, rhenium disulfide (ReS2) and rhenium oxide (ReO2) in the slag are fully oxidized into soluble perrhenate ions (ReO4⁻) and enter the solution. Since most of the arsenic and bismuth have already been fixed in the slag in the form of stable arsenate precipitates in the low-potential section, even if the potential is increased, they are difficult to be released into the solution.

[0020] Once the potential stabilizes within the range of 700-750 mV (relative to a saturated calomel electrode) for 10-30 min, the reaction is considered to have reached its endpoint. The second stage of oxidative leaching is then stopped, and the next step is initiated.

[0021] (4) Solid-liquid separation: The leaching slurry is filtered to obtain rhenium-containing leachate and leaching residue. The rhenium-containing leachate is subjected to deoxidation, ion exchange, and evaporation crystallization to obtain ammonium rheniumate product; the leaching residue mainly contains elements such as copper, lead, and bismuth, which can be sent to subsequent processes to recover valuable metals.

[0022] The oxidant used above is hydrogen peroxide with a mass fraction of 27.5% or ferric sulfate solution with a mass fraction of 10%, which is added to the slurry at a flow rate of 5 L / min. The potential of the mixed slurry is monitored in real time using an oxidation-reduction potentiometer (ORP meter). By controlling the dripping rate of hydrogen peroxide or ferric sulfate solution, the potential of the slurry is maintained at 400-550 mV (relative to a saturated calomel electrode).

[0023] The technical solution of this invention addresses the problem of complex composition and the difficulty in selectively separating rhenium from impurities such as arsenic and bismuth produced in the copper smelting process. It adopts a sulfuric acid-hydrogen peroxide system and uses low-potential and high-potential segments to leach the rhenium-rich slag, controlling different redox potential ranges to achieve selective leaching of rhenium and inhibition of leaching of arsenic, bismuth, etc.

[0024] II. Principle

[0025] 1. Precipitation characteristics of bismuth arsenate (BiAsO4)

[0026] Studies have shown that in acidic leaching systems containing arsenic and bismuth, pentavalent arsenic (As(V)) and trivalent bismuth (Bi(III)) can combine to form a sparingly soluble bismuth arsenate precipitate (BiAsO4). This reaction can be represented as:

[0027] As(V) + Bi(III) → BiAsO4↓

[0028] Bismuth arsenate is theoretically unstable in acidic solutions, but it can form under conditions of reduced local acidity; once formed, it is difficult to dissolve again in acidic solutions.

[0029] 2. Effect of redox potential on bismuth arsenate precipitation

[0030] Studies have shown that redox potential is a key factor affecting the formation of bismuth arsenate precipitate. Specifically, lowering the redox potential of the system can inhibit the formation of bismuth arsenate. Conversely, appropriately low potential conditions are conducive to the formation and stabilization of bismuth arsenate precipitate.

[0031] Further research revealed that when the leaching temperature is below 90℃, As(V) and Bi(III) combine in the reaction system to form crystalline bismuth arsenate (BiAsO4) precipitate, and its thermodynamically dominant region increases with increasing reaction temperature.

[0032] 3. Precipitation characteristics of lead arsenate (Pb3(AsO4)2)

[0033] Similarly, in acidic systems containing arsenic and lead, As(V) and Pb(II) can combine to form a sparingly soluble lead arsenate precipitate (Pb3(AsO4)2). Once formed, this precipitate is also difficult to dissolve again in acidic solutions.

[0034] Based on the above principles, this invention proposes a segmented potential control strategy of "low-potential pretreatment—high-potential leaching": In the low-potential segment (400–550 mV), thermodynamic conditions favorable for the formation of bismuth arsenate and lead arsenate precipitates are created, pre-fixing arsenic and bismuth in the slag as insoluble arsenates in the slag phase, preventing them from being oxidized and leached into the solution in the high-potential segment; in the high-potential segment (700–750 mV), with arsenic and bismuth effectively fixed, the potential is increased to allow for the full oxidative leaching of rhenium, achieving efficient rhenium recovery and selective inhibition of arsenic and bismuth. This design utilizes the chemical characteristic that precipitates such as bismuth arsenate are more easily formed at low potentials and are difficult to dissolve once formed, clearing the way for subsequent high-potential leaching of rhenium.

[0035] III. Relevant Chemical Reaction Equations

[0036] 1. Low potential range – Bismuth arsenate precipitate forms

[0037] As(V) + Bi(III) → BiAsO4↓

[0038] 2. Low potential range – Lead arsenate precipitate forms.

[0039] 2As(V) + 3Pb(II) → Pb3(AsO4)2↓

[0040] 3. High-potential range—oxidative leaching

[0041] Under acidic conditions and with the aid of hydrogen peroxide, rhenium disulfide (ReS2) is oxidized to soluble perrhenic acid (HReO4):

[0042] ReS2 + 4H2O2 → HReO4 + 2SO2↑ + 3H2O,

[0043] ReO2 + 2H2O2 → HReO4 + 2H2O; or:

[0044] ReS2 + 17Fe³⁺ + 12H2O → HReO4 + 2H2SO4 + 17Fe²⁺ + 18H⁺

[0045] ReS2 + 17Fe³⁺ + 12H2O → HReO4 + 2H2SO4 + 17Fe²⁺ + 18H⁺

[0046] IV. Beneficial Effects

[0047] Significantly improved selectivity: By segmented potential control, utilizing the differences in chemical behavior of different metals at different potentials, in the low potential range, As(V) combines with Bi(III) to form insoluble bismuth arsenate (BiAsO4) precipitate, and As(V) combines with Pb(II) to form insoluble lead arsenate (Pb3(AsO4)2) precipitate, thus pre-fixing arsenic and bismuth into the slag phase; in the high potential range, rhenium is leached by concentrated oxidation. Compared with existing single-segment potential control methods (where impurity leaching rates are all >90%), this invention can control the leaching rate of arsenic to below 40% and the leaching rate of bismuth to below 10%.

[0048] Rhenium leaching rate remains high: precise control of the high potential range of 700-750 mV ensures full oxidation of rhenium, and the rhenium leaching rate can reach over 98%.

[0049] The process is precise and controllable: real-time monitoring by the ORP meter and the addition of oxidant enable precise control of the leaching process, avoiding excessive or insufficient addition of oxidant.

[0050] Oxidant consumption optimization: The low potential range avoids excessive consumption of oxidant on highly active impurities, making the oxidant more efficient for rhenium leaching.

[0051] Reduced subsequent processing costs: Since arsenic and bismuth are effectively suppressed during the leaching stage, the impact of arsenic, lead, bismuth and other substances on subsequent ion exchange processes is greatly reduced, thus lowering the processing difficulty and cost.

[0052] V. Specific Implementation

[0053] 1. Equipment Description

[0054] To implement the method of this invention, the segmented potential-controlled oxidation leaching system includes: a leaching reactor with a feed inlet and an oxidant inlet at the top, an internal stirring device, and an external heating jacket; an ORP online monitoring probe and a temperature sensor respectively installed inside the leaching reactor; an automatic hydrogen peroxide dripping system connected to the oxidant inlet via a pipeline; and a PLC controller electrically connected to the ORP online monitoring probe, the temperature sensor, and the automatic hydrogen peroxide dripping system. During the leaching process, the ORP online monitoring probe and the temperature sensor feed back real-time monitoring signals to the PLC controller. The PLC controller outputs control commands to the automatic hydrogen peroxide dripping system according to the set potential value, achieving closed-loop control of the slurry potential. The discharge port of the leaching reactor is connected to a plate and frame filter press via a pipeline.

[0055] Example 1

[0056] Take rhenium-rich slag (containing approximately 3% copper, 15% arsenic, 15% lead, 6% bismuth, 6% selenium, and 6% rhenium), and add sulfuric acid solution (10% sulfuric acid concentration) at a liquid-to-solid ratio of 20:1 to prepare the slurry. Heat the slurry to 65°C and stir at 120 r / min, using an ORP meter to monitor the slurry potential in real time.

[0057] Low potential range: Slowly add 27.5% hydrogen peroxide to control the slurry potential at 450–500 mV and leach for 90 min. Under these conditions, As(V) and Bi(III) in the leaching system combine to form insoluble bismuth arsenate (BiAsO4) precipitate, and As(V) and Pb(II) combine to form insoluble lead arsenate (Pb3(AsO4)2) precipitate. Arsenic and bismuth are fixed in the slag phase.

[0058] High-potential stage: Continue to slowly add hydrogen peroxide to raise the potential of the mixed slurry to 700-750 mV, leach for 90 minutes, and stop the reaction after the potential stabilizes within the set range for 30 minutes. Under these conditions, rhenium disulfide (ReS2) and rhenium oxide (ReO2) are fully oxidized into soluble perrhenate ions (ReO4⁻) that enter the solution.

[0059] After filtration, a rhenium-containing leachate and leachate residue were obtained. Testing showed that the rhenium leaching rate was 98.5%, the arsenic leaching rate was 35.6%, and the bismuth leaching rate was 8.2%.

[0060] Example 2

[0061] Take rhenium-rich slag (composition as in Example 1) and add sulfuric acid solution (8% sulfuric acid concentration) at a liquid-to-solid ratio of 30:1 to prepare the slurry. Heat the slurry to 60°C and stir at 120 r / min.

[0062] Low potential range: Slowly add hydrogen peroxide, control the slurry potential at 400–450 mV, and leach for 80 min. Arsenic and bismuth are fixed in the slag phase as arsenate precipitates.

[0063] High potential section: Continue to add hydrogen peroxide to raise the slurry potential to 720-750 mV, leach for 80 min, and stop the reaction after the potential stabilizes for 20 min.

[0064] After filtration and testing, the leaching rate of rhenium was 98.3%, the leaching rate of arsenic was 38.2%, and the leaching rate of bismuth was 9.5%.

[0065] Example 3

[0066] Take 100 kg of rhenium-rich slag (composition as in Example 1), and add sulfuric acid solution (10% sulfuric acid concentration) to the leaching reactor at a liquid-to-solid ratio of 20:1 to form a slurry. Heat the mixed slurry to 65°C and stir at 120 r / min.

[0067] Low potential range: 27.5% hydrogen peroxide is slowly added through an automatic dripping system, and online ORP meter feedback control is used to maintain the potential of the mixed slurry at 450-500 mV for leaching for 90 min.

[0068] High potential stage: Continue adding hydrogen peroxide to raise the slurry potential to 700-750 mV, leach for 90 min, and stop the reaction after the potential stabilizes for 15 min.

[0069] After filtration, the leachate undergoes ion exchange, ammonia desorption, evaporation and concentration, and cooling crystallization to obtain ammonium perrylate product with a purity of over 99.99%.

[0070] Comparative Example

[0071] The same rhenium-rich slag and leaching conditions (10% sulfuric acid concentration, 30:1 liquid-to-solid ratio, 65℃ temperature, and 180 min leaching time) were used, but without segmented potential control (i.e., raising the potential to 700–750 mV and maintaining it at once). The results showed a rhenium leaching rate of 98.6%, but an arsenic leaching rate as high as 91.2% and a bismuth leaching rate of 85.6%. Literature reports also indicate that under these conditions, "the leaching rates of other components are all higher than 90%."

[0072] As can be seen from the comparison, the present invention, by controlling the potential in segments, significantly inhibits the leaching of arsenic and bismuth while maintaining a high leaching rate of rhenium, thus achieving selective leaching of rhenium.

Claims

1. A method for treating rhenium-rich slag, comprising the following steps: (1) Slurry preparation: Rhenium-rich slag is mixed with sulfuric acid solution and stirred evenly to form a slurry; (2) Low potential section oxidation leaching: Add oxidant to the slurry, maintain the potential at 400-550 mV under stirring at 50-80℃ for the first stage of oxidation leaching, the leaching time is 69-90 min, and the first stage oxidized slurry is obtained; the oxidant is hydrogen peroxide or ferric sulfate solution; (3) High-potential leaching: Continue to add oxidant to the first-stage oxidizing slurry, and maintain the potential at 700-750 mV under stirring conditions at 50-80℃ for the second-stage oxidizing leaching, with a leaching time of 69-90 min; (4) Solid-liquid separation: The leachate slurry is filtered to obtain rhenium-containing leachate and leachate residue.

2. The method for treating rhenium-rich slag according to claim 1, characterized in that: The mass concentration of the sulfuric acid solution in step (1) is 5%-10%.

3. The method for treating rhenium-rich slag according to claim 1, characterized in that: The liquid-solid ratio in step (1) is 20:1-50:

1.

4. The method for treating rhenium-rich slag according to claim 1, characterized in that: The oxidant mentioned in steps (2) and (3) is hydrogen peroxide with a mass fraction of 27.5% or ferric sulfate solution with a mass fraction of 10%, which is added to the slurry at a flow rate of 5 L / min.

5. The method for treating rhenium-rich slag according to claim 1, characterized in that: In step (2), the oxidation leaching potential in the first stage is maintained at 450-500 mV.

6. The method for treating rhenium-rich slag according to claim 1, characterized in that: The potentials mentioned in steps (2) and (3) are relative to a saturated calomel electrode.

7. The method for treating rhenium-rich slag according to claim 1, characterized in that: In step (3), when the potential stabilizes within the range of 700-750mV for 10-30 min, the reaction is considered to be at its endpoint. The second stage of oxidation leaching is then stopped and step (4) is performed.

8. The method for treating rhenium-rich slag according to claim 1, characterized in that: After the rhenium-containing leachate obtained in step (4) is subjected to deoxidation, ion exchange, and evaporation crystallization, ammonium rheniumate product is obtained.