A method for separating lead and bismuth in a lead smelting process

Abstract

The application discloses a lead-bismuth separation method in a lead smelting process and belongs to the technical field of lead smelting pyrogenic refining. The method comprises five steps of lead liquid pretreatment, step-by-step reaction bismuth removal, medium-temperature standing enrichment, original coal reduction slagging and deep purification ingot casting in sequence. First, bismuth-containing refined lead is melted and temperature is adjusted to 480-520 DEG C, step-by-step addition of lead-calcium-tin low-melting-point alloy bismuth removal agent A and chlorosalt composite complex bismuth removal agent B is carried out, and bismuth is made to float up in bismuth-containing dross; then, temperature is lowered to 420-460 DEG C and standing is carried out, bismuth elements are adsorbed and separated in situ by using the surface bismuth-containing dross layer; subsequently, original coal reduction slagging is carried out and slag is salvaged; finally, after removal of antimony and tin impurities by sodium hydroxide, an ingot is cast. The application breaks through the traditional intermetallic compound bismuth removal mechanism, is suitable for high-bismuth crude lead raw materials, has high effective utilization rate of bismuth removal agent, low slag rate, smooth temperature connection in the whole process, high production efficiency, low comprehensive cost, and is suitable for industrialized continuous production.

Description

Technical Field

[0001] This invention belongs to the field of pyrometallurgical refining technology for lead smelting, and specifically relates to a method for separating lead and bismuth during lead smelting. Background Technology

[0002] Lead refining is mainly divided into pyrometallurgical refining and electrolytic refining. Bismuth is one of the most difficult impurity elements to remove in pyrometallurgical lead refining. The traditional calcium-magnesium method for removing bismuth utilizes the formation of high-melting-point intermetallic compounds between bismuth and calcium and magnesium to achieve separation, but the slag rate is as high as 10%-20%, the reagent cost is high, and the bismuth removal depth is limited.

[0003] Chinese patent application CN114410982A discloses a deep bismuth removal method for lead pyrometallurgical refining. It uses elemental calcium or high-calcium lead as a bismuth removal agent, combined with a multi-component composite slag-reducing agent, to achieve deep bismuth removal during the cooling process. The bismuth content can be reduced to below 0.005%, and the slag rate can be controlled within 7%.

[0004] However, this method is not very adaptable to raw materials. It cannot effectively remove bismuth from refined lead with a bismuth content of ≥0.02%. Increasing the amount of bismuth removal agent will significantly increase the calcium content in the lead solution, which may lead to excessive calcium content in subsequent alloy production. Additional dilution treatment is required, which presents a technical problem that significantly increases costs. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for separating lead and bismuth in the lead smelting process, which solves the technical problems of the existing process, such as a single bismuth removal mechanism, poor adaptability to high-bismuth crude lead, low effective utilization rate of bismuth removal agent, high slag rate, high energy consumption of process flow, and complex reagent system.

[0006] To address the above technical problems, the following technical solution is adopted: A method for separating lead and bismuth during lead smelting, comprising the following steps: S1. Lead liquid pretreatment: After melting the bismuth-containing refined lead, remove the slag and adjust the temperature of the lead liquid to 480-520℃. The bismuth-containing refined lead is crude lead after preliminary refining of recycled lead by fire, with a bismuth mass fraction of 0.015%-0.030%, and can also be adapted to crude lead raw materials with higher bismuth content.

[0007] S2. Stepwise bismuth removal reaction: First, add bismuth removal agent A evenly to the lead liquid and start medium-speed stirring for 5-10 minutes to allow the low-melting-point bismuth removal agent A to quickly melt and disperse in the lead liquid, releasing the active calcium component; then add bismuth removal agent B and switch to slow stirring for 25-50 minutes to allow the effective components of bismuth removal agents A and B to fully contact the bismuth in the lead liquid, generating a bismuth-containing solid phase product through intermetallic combination and complexation synergistic reaction; the product density is lower than that of the lead liquid, and it gradually floats to the surface of the lead liquid in the form of slag phase.

[0008] Preferably, the bismuth remover A is a lead-calcium-tin low-melting-point alloy, with a calcium mass fraction of 15%-25%, a lead mass fraction of 65%-75%, and the balance being low-melting-point metals such as tin and aluminum.

[0009] Preferably, the measured melting point range of the lead-calcium-tin low-melting-point alloy is 360-460℃.

[0010] Among them, the melting point of the bismuth remover is significantly reduced by alloying lead, tin, aluminum and calcium, and the calcium element is protected by strong reducing metals such as tin and aluminum, which reduces the oxidation loss of calcium element at high temperature and improves the utilization rate of effective components. It can be fully melted and dispersed at 480℃.

[0011] Preferably, the bismuth remover B is a chloride-based complex bismuth remover B, which is a mixture of magnesium chloride and ammonium chloride in a mass ratio of 3-5:1.

[0012] Preferably, chloride ions can form stable AB2[Bi]2³ with bismuth and calcium. - The complex structure promotes the migration of bismuth to the slag phase, which is different from the bismuth removal mechanism of traditional intermetallic compounds.

[0013] Where AB2[Bi]2³ - In the complex structure, A is a metal cation such as calcium or magnesium, and B is a chloride ligand. The chloride ion coordinates with bismuth, calcium, and magnesium to form a stable AB2[Bi]2³. - Type complex anion structure.

[0014] The specific mechanism of the bismuth removal reaction is as follows: In the molten lead refining system, ammonium chloride, as an activating agent, decomposes upon heating, releasing HCl and forming an activating atmosphere. On the one hand, it disperses scum particles and enhances interfacial mass transfer; on the other hand, it inhibits the oxidation loss of calcium and magnesium elements. Combined with the reducing properties of tin and aluminum in bismuth removal agent A, it further reduces the oxidation loss of calcium and magnesium and improves the effective utilization rate of the agent.

[0015] In situ, metallic calcium reduces magnesium chloride to generate highly reactive metallic magnesium. Ca and newly formed Mg react synergistically with bismuth in the molten lead to form a high-melting-point ternary intermetallic compound, CaMg₂Bi₃, in solid crystal form. Simultaneously, the chloride salt component forms a stable AB₂[Bi]₂³ with bismuth and calcium. - The complexed anions drive the migration of bismuth into the slag phase. Calcium chloride, a reduction byproduct, acts as a binder in the slag phase, promoting slag aggregation and flotation, ultimately achieving efficient separation of bismuth and lead.

[0016] The overall reaction equation is: 2MgCl2 + 4NH4Cl + O2 + 3Bi + 5Ca = CaMg2Bi3 + 4CaCl2 + 4NH3 + 2H2O.

[0017] As a preferred option, based on the mass of the lead solution, the amount of bismuth removal agent A added is 0.06%-0.14%, and the amount of bismuth removal agent B added is 0.2%-0.25%.

[0018] Preferably, in step S2, the speed of medium-speed stirring is 1200-1500 r / min, and the speed of slow-speed stirring is 600-1200 r / min.

[0019] Preferably, the preparation method of the bismuth removal agent A is as follows: Calculate the weight of each raw material based on the required weight and element content of bismuth remover A. The raw materials include electrolytic lead, calcium-aluminum alloy, and tin ingots. Weigh the corresponding weight of electrolytic lead into a lead melting pot, heat it to 560-620℃, add the corresponding weight of calcium-aluminum alloy, stir at medium speed for 5-10 minutes, then add the corresponding weight of tin ingots, stir at medium speed for 5-10 minutes, take a sample for analysis and testing. If the element requirements are met, control the temperature at 450-480℃ to cast the ingot. If the element requirements are not met, repeat the above element addition process until the elements are qualified.

[0020] S3. Medium-temperature standing enrichment: Stop stirring and cool the lead liquid to 420-460℃ and let it stand for 10-20 minutes. After the temperature decreases, the solubility of bismuth in the lead liquid decreases, and the unreacted bismuth elements gradually precipitate out and are adsorbed and enriched in situ by the bismuth-containing slag layer that has been formed on the surface, so as to achieve deep removal of bismuth. This process does not require the addition of new reagents, and uses the existing slag layer as an adsorption carrier, avoiding the need to add slag-reducing agents after cooling in existing technologies; at the same time, the temperature range matches the subsequent impurity removal process, eliminating the need for significant cooling and then heating, thus significantly reducing energy consumption.

[0021] S4. Raw coal reduction and slag formation: Maintain 420-460℃, restart medium-speed stirring, and evenly add raw coal for reduction and slag formation. After reacting for 15-20 minutes, remove the scum from the surface of the lead liquid and weigh it.

[0022] The slag-forming mechanism of raw coal: The fixed carbon in the raw coal reduces components such as calcium oxide and lead oxide in the slag, recovering metallic lead and metallic calcium; the carbon skeleton formed by the pyrolysis of raw coal combines with the slag, providing a solidification carrier for bismuth; a small amount of silica in the raw coal reacts with CaMg2Bi3 in the slag phase to generate components such as bismuth silicate and magnesium silicate, which, together with the bonding effect of calcium chloride in the slag and the carbon skeleton, stabilize and solidify bismuth in the slag phase, producing low-viscosity solid powder slag and reducing lead entrainment.

[0023] As a preferred option, the amount of raw coal added is 0.08%-0.12% based on the mass of lead liquid. The preferred raw coal has a particle size of 20-40 mesh, a fixed carbon content of 40-50%, a moisture content of 10-18%, an ash content of ≤18%, and a volatile matter content of 20-28%.

[0024] Among them, raw coal is used as the single slag-forming agent, eliminating the need for compounding sodium salts, borax and other multi-component agents. The raw materials are readily available and inexpensive, making it suitable for the slag-forming needs of bismuth-containing slag systems.

[0025] S5. Deep purification casting: Maintain the temperature of the lead liquid at 420-460℃, add sodium hydroxide to it, and the sodium hydroxide reacts with the residual antimony, tin and other impurities in the lead liquid and oxygen in the air to generate a mixed slag of sodium stannate and sodium antimonite; continue stirring until the lead liquid turns bright white, and after confirming that the impurities have been removed, remove the slag and cast the lead liquid into an ingot to obtain bismuth-free refined lead.

[0026] As another preferred option, the amount of sodium hydroxide added is 0.08%-0.12% based on the mass of the lead solution.

[0027] The beneficial effects of this invention are: (1) This invention abandons the conventional method of using elemental calcium or high-calcium lead in the prior art, and pioneers the use of a lead-calcium-tin low-melting-point alloy as the active carrier for bismuth removal. By alloying tin, aluminum and calcium, the melting point of the reagent is reduced to 360-460℃, so that it can be completely melted and dispersed at 480℃. At the same time, with the reducing protective effect of tin and aluminum, the high-temperature burn-off rate of calcium is reduced from 35% to 15%, and the effective utilization rate is greatly improved. It overcomes the conventional technical prejudice in the field of avoiding the introduction of tin impurities into lead liquid. The introduced trace amount of tin can be removed simultaneously in the subsequent sodium hydroxide alkaline washing process without affecting the quality of the final product. It achieves a significant optimization of bismuth removal efficiency and reagent cost with extremely low impurity introduction cost.

[0028] (2) This invention generates highly active magnesium in situ by reducing magnesium chloride with calcium, synergistically forming a high-melting-point intermetallic compound CaMg2Bi3; on the other hand, it enables bismuth to form AB2[Bi]2³ through chloride salt complexation. - The migration of complex anions into the slag phase demonstrates a significantly stronger dual-reaction driving force than a single mechanism. This design can stably process high-bismuth crude lead with a bismuth content of 0.03%, and its raw material compatibility range is significantly wider than existing processes. It solves the industry pain points of insufficient bismuth removal depth and easy exceedance of calcium content in high-bismuth raw materials in existing technologies.

[0029] (3) The present invention sets up a medium-temperature static enrichment process, using the surface slag layer formed by the reaction as an adsorption carrier to adsorb the bismuth element precipitated by cooling in situ, achieving deep bismuth removal without the need for additional reagents. The temperature of the entire process is controlled in the range of 420-520℃, which is seamlessly connected with the temperature of the subsequent sodium hydroxide impurity removal process, avoiding energy loss caused by repeated heating and cooling; the bismuth removal cycle of a single batch is short, and the production efficiency is more than doubled compared with the existing process, which is suitable for the needs of continuous industrial production.

[0030] (4) This invention uses a single component of raw coal adapted to a bismuth-containing slag system for slag formation, while also having multiple functions such as reducing and recovering valuable metals, constructing a carbon skeleton to solidify bismuth, and reducing viscosity and lead entrainment by silicates. Raw coal is readily available and does not require pre-preparation, which greatly reduces procurement and management costs; the slag ratio is stable after slag formation, and the lead entrainment is low. Under the premise of ensuring that the bismuth removal effect is comparable to that of existing composite agents, the agent cost is low, and the overall economic benefits are significant.

[0031] In summary, this invention utilizes a pyrometallurgical process throughout, eliminating the fluorine pollution and acid mist issues associated with electrolytic systems. It also eliminates the need for strong oxidizing agents such as sodium nitrate, making it particularly suitable for the pyrometallurgical refining technology of lead smelting and meeting the development requirements of clean production and green smelting. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below.

[0033] Example 1 A method for separating lead and bismuth during lead smelting includes: 5.12 tons of refined lead were prepared for processing. Preliminary analysis of the composition showed: Ca 0.0003%, Sn 0.0011%, Cu 0.0004%, As 0.0009%, Ag 0.00008%, Sb 0.0022%, Bi 0.024%, with the remainder being lead.

[0034] The refined lead was transferred to a 5t refining pot for heating and melting. Surface slag was removed, and the temperature was raised and stabilized at 520℃.

[0035] Add 7 kg of bismuth removal agent A, which is a lead-calcium-tin alloy with a calcium content of 20 wt% and a measured melting point of approximately 380 °C. Stir at medium speed for 5 min. Then add 10 kg of bismuth removal agent B, with a magnesium chloride:ammonium chloride ratio of 4:1. Stir at slow speed for 40 min. Take a sample and analyze the composition of the lead solution: Ca 0.0235%, Sn 0.0012%, Cu 0.0004%, As 0.0008%, Ag 0.00008%, Sb 0.0020%, Bi 0.013%.

[0036] Stop stirring, allow to cool naturally to 460℃, let stand for 15 minutes, and take samples for testing: Ca 0.0233%, Sn 0.0012%, Cu 0.0004%, As 0.0009%, Ag 0.00008%, Sb 0.0020%, Bi 0.009%.

[0037] Maintaining the temperature at 460℃, add 5kg of raw coal (30 mesh, 45% fixed carbon) with medium-speed stirring. Reduce and slag for 15 minutes. Take samples for testing: Ca 0.0233%, Sn 0.0012%, Cu 0.0004%, As 0.0009%, Ag 0.00008%, Sb 0.0021%, Bi 0.0092%. Remove the slag and weigh it. The slag weight is 289kg, and the slag rate is 5.64%.

[0038] Maintain 450℃, add 5kg of sodium hydroxide, stir until the lead liquid is bright white, remove antimony and tin impurities, and cast ingots to obtain finished refined lead.

[0039] In this embodiment, the total bismuth removal rate was 61.67%, and the total processing time was approximately 85 minutes.

[0040] Example 2 4.92 tons of refined lead were prepared for processing. Preliminary analysis of the composition showed: Ca 0.00105%, Sn 0.0008%, Cu 0.0007%, As 0.0007%, Ag 0.00021%, Sb 0.0052%, Bi 0.015%, with the remainder being lead.

[0041] The refined lead was transferred to a 5t refining pot for heating and melting. Surface slag was removed, and the temperature was raised and stabilized at 480℃.

[0042] Add 5 kg of bismuth removal agent A, which is a lead-calcium-tin alloy with a calcium content of 20 wt%, and stir at medium speed for 7 min; then add 10 kg of bismuth removal agent B, with a magnesium chloride:ammonium chloride ratio of 4:1, and stir at slow speed for 25 min. Take a sample and test the composition of the lead solution: Ca 0.0183%, Sn 0.0008%, Cu 0.0007%, As 0.0007%, Ag 0.00021%, Sb 0.0050%, Bi 0.0095%.

[0043] Stop stirring, allow to cool naturally to 420℃, let stand for 15 minutes, and take samples for testing: Ca 0.0183%, Sn 0.0009%, Cu 0.0007%, As 0.0007%, Ag 0.00021%, Sb 0.0052%, Bi 0.0034%.

[0044] Maintaining the temperature at 420℃, add 4kg of raw coal (30 mesh, 45% fixed carbon) with medium-speed stirring. Reduce and slag form for 20 minutes. Sampling and testing: Ca 0.0180%, Sn 0.0008%, Cu 0.0007%, As 0.0007%, Ag 0.00021%, Sb 0.0052%, Bi 0.0032%. The slag was removed and weighed, with a slag weight of 259kg and a slag rate of 5.26%.

[0045] Maintain 420℃, add 5kg of sodium hydroxide, stir until the lead liquid is bright white, remove antimony and tin impurities, and cast ingots to obtain finished refined lead.

[0046] In this embodiment, the total bismuth removal rate was 78.67%, and the total processing time was approximately 75 minutes.

[0047] Example 3 4.5 tons of refined lead were prepared for processing. Preliminary analysis of the composition showed: Ca 0.0008%, Sn 0.0018%, Cu 0.0006%, As 0.0007%, Ag 0.00012%, Sb 0.0006%, Bi 0.021%, with the remainder being lead.

[0048] The refined lead is transferred to a 5t refining pot for heating and melting. Surface slag is removed, and the temperature is raised and stabilized at 500℃.

[0049] Add 3 kg of bismuth removal agent A, which is a lead-calcium-tin alloy with a calcium content of 20 wt%, and stir at medium speed for 10 min; then add 10 kg of bismuth removal agent B, with a magnesium chloride:ammonium chloride ratio of 4:1, and stir at slow speed for 50 min. Take a sample and test the composition of the lead solution: Ca 0.0115%, Sn 0.0016%, Cu 0.0006%, As 0.0007%, Ag 0.00012%, Sb 0.0006%, Bi 0.015%.

[0050] Stop stirring, allow to cool naturally to 450℃, let stand for 15 minutes, and take samples for testing: Ca 0.0115%, Sn 0.0018%, Cu 0.0007%, As 0.0007%, Ag 0.00012%, Sb 0.0007%, Bi 0.0085%.

[0051] Maintaining the temperature at 450℃, add 4kg of raw coal (30 mesh) with 45% fixed carbon under medium-speed stirring. Reduce and slag form for 20 minutes. Sampling and testing: Ca 0.0113%, Sn 0.0015%, Cu 0.0007%, As 0.0007%, Ag 0.00012%, Sb 0.0007%, Bi 0.0083%. The slag was skimmed off and weighed, with a slag weight of 140kg and a slag rate of 3.11%.

[0052] Cool to 445℃, add 4kg of sodium hydroxide, stir until the lead liquid is bright white, remove antimony and tin impurities, and cast into ingots to obtain finished refined lead.

[0053] In this embodiment, the total bismuth removal rate was 60.48%, and the total processing time was approximately 95 minutes.

[0054] Example 4 5.5 tons of refined lead were prepared for processing. Preliminary analysis of the composition showed: Ca 0.0012%, Sn 0.0020%, Cu 0.00065%, As 0.0003%, Ag 0.00022%, Sb 0.0007%, Bi 0.030%, with the remainder being lead.

[0055] The refined lead was transferred to a 5t refining pot and heated to melt. Surface slag was removed, and the temperature was raised and stabilized at 520℃. 8 kg of bismuth removal agent A, a lead-calcium-tin alloy with a calcium content of 20 wt%, was added, and the mixture was stirred at medium speed for 10 min. Then, 10 kg of bismuth removal agent B, containing magnesium chloride to ammonium chloride in a 4:1 ratio, was added, and the mixture was stirred slowly for 50 min. A sample of the lead solution was taken for analysis, revealing the following composition: Ca 0.0256%, Sn 0.0024%, Cu 0.00065%, As 0.00032%, Ag 0.00022%, Sb 0.00068%, and Bi 0.017%.

[0056] Stop stirring, allow to cool naturally to 450℃, let stand for 15 minutes, and take samples for testing: Ca 0.0254%, Sn 0.0023%, Cu 0.00065%, As 0.0003%, Ag 0.00022%, Sb 0.00069%, Bi 0.011%.

[0057] Maintaining the temperature at 450℃, add 5kg of raw coal (30 mesh, 45% fixed carbon) with medium-speed stirring. Reduce and slag form for 20 minutes. Sampling and testing: Ca 0.0253%, Sn 0.0024%, Cu 0.00065%, As 0.0003%, Ag 0.00022%, Sb 0.0007%, Bi 0.0091%. The slag was removed and weighed, with a slag weight of 320kg and a slag rate of 5.82%.

[0058] Cool to 440℃, add 5kg of sodium hydroxide, stir until the lead liquid is bright white, remove antimony and tin impurities, and cast into ingots to obtain finished refined lead.

[0059] In this embodiment, the total bismuth removal rate was 69.67%, and the total processing time was approximately 95 minutes.

[0060] Comparative Example 1 Parallel experiments were conducted using the same batch of bismuth-containing refined lead as in Example 1, with Bi content of 0.024%, according to the optimal process parameters specified in CN114410982A: The lead solution was heated to 500°C, and 7.2 g / kg of elemental calcium was added, which is equivalent to the molar amount of calcium in Example 1. After stirring for 10 minutes, the temperature was lowered to 350°C. Add 20g / kg of No. 1 composite slag reducing agent, which is a compound of 7 components including carbon powder, sodium hydroxide, sodium carbonate, and borax. Stir for 10 minutes, then cool to 330℃ and let stand for 20 minutes to remove slag. Reheat to 450℃, add sodium hydroxide to remove antimony and tin impurities, and then cast ingots.

[0061] Results: The final lead solution contained 0.019% bismuth, with a bismuth removal rate of 20.83%; the slag weight was 341 kg, with a slag rate of 6.66%; the total processing time was approximately 180 min; the energy consumption for heating and cooling was approximately 1.8 times that of the present invention; and the overall cost per ton of lead accounted for 280%.

[0062] Comparative Example 2 The process parameters and reagent dosages were exactly the same as in Example 1, except that bismuth removal agent A was replaced with an equal molar amount of elemental calcium.

[0063] Results: The bismuth content in the lead solution after the reaction was 0.017%, and the final bismuth removal rate was 45.83%; the calcium burn-off rate was about 35%, which is much higher than the 15% burn-off rate of the lead-calcium-tin alloy.

[0064] Comparative Example 3 The same raw materials, reagent dosages and process parameters as in Example 1 were used, the only difference being that bismuth removal agent A and bismuth removal agent B were added to the lead liquid at the same time and stirred for 45 minutes.

[0065] Results: The final bismuth removal rate was only 50%, which was significantly lower than that of the stepwise addition process in the same time period. The slag rate was 5.8%, and the processing time for a single batch was about 85 minutes.

[0066] Comparative Example 4 Using the exact same raw materials, reagent dosages, and process parameters as in Example 1, the only difference is that the cooling and settling process is omitted, and raw coal is directly added at 520°C for reduction and slag formation after the bismuth removal reaction is completed.

[0067] Results: The final bismuth removal rate was 47.92%, the bismuth removal depth decreased significantly, the slag rate was 5.7%, and the processing time for a single batch was approximately 70 minutes.

[0068] Comparative Example 5 The same raw materials and process parameters as in Example 1 were used, the only difference being that the raw coal was replaced with an equal mass of the No. 1 composite slag reducing agent in Comparative Example 1.

[0069] Results: The final bismuth removal rate was 62.1%, which was basically the same as that of raw coal, but the reagent cost was 2-3 times that of raw coal.

[0070] Effect Comparison and Analysis The core performance indicators of each embodiment and comparative example are summarized as follows:

[0071] The following conclusions can be drawn from the above data: 1. Compared with Comparative Example 1, under the same initial bismuth content, Example 1 of the present invention increases the bismuth removal rate from 20.83% to 61.67%, significantly improving the bismuth removal depth; the slag rate decreases from 6.66% to 5.64%, reducing lead entrainment loss; the single batch processing time is shortened from 180 min to 85 min, more than doubling the production efficiency; and the comprehensive cost per ton of lead is only about 36% of that of the existing process, demonstrating significant economic advantages.

[0072] 2. Comparing Example 1 and Comparative Example 2, it can be seen that replacing elemental calcium with a lead-calcium-tin low-melting-point alloy can reduce the calcium burn-off rate from 35% to 15% and increase the bismuth removal rate by 15.84 percentage points, proving that alloying design can significantly improve the effective utilization rate of calcium and the bismuth removal effect.

[0073] 3. Comparing Example 1 and Comparative Example 3, it can be seen that the bismuth removal rate is increased by 11.67 percentage points compared with the one-step addition process, which proves that the step-by-step addition can optimize the dispersibility and reaction efficiency of the active ingredients.

[0074] 4. Comparing Example 1 and Comparative Example 4, it can be seen that the medium-temperature static enrichment process can increase the bismuth removal rate by 13.75 percentage points, proving that in-situ adsorption in the slag layer is a key step in achieving deep bismuth removal.

[0075] 5. Comparing Example 1 and Comparative Example 5, it can be seen that the bismuth removal effect of raw coal slag can be comparable to that of composite slag reducing agent, but the cost of the agent is only 1 / 2 to 1 / 3 of the latter, which greatly reduces the production and operation costs.

[0077] Of course, those skilled in the art should understand that the term "a" should be understood as "at least one" or "one or more". That is, in one embodiment, the number of an element can be one, while in another embodiment, the number of the element can be multiple. The term "a" should not be understood as a limitation on the number.

[0078] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art under the technical guidance of the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for separating lead and bismuth during lead smelting, characterized in that, Includes the following steps: S1. Lead liquid pretreatment: After melting the bismuth-containing refined lead, remove the slag and adjust the temperature of the lead liquid to 480-520℃. S2. Stepwise reaction to remove bismuth: First, add lead-calcium-tin low-melting-point alloy bismuth remover A to the lead liquid and stir at medium speed for 5-10 minutes; then add chloride salt complex bismuth remover B and stir at slow speed for 25-50 minutes to allow the bismuth remover to react with the bismuth in the lead liquid and generate bismuth-containing slag that floats on the surface of the lead liquid. S3. Medium-temperature static enrichment: Stop stirring, cool the lead liquid to 420-460℃ and let it stand for 10-20 minutes. Utilize the bismuth-containing slag layer that has been formed on the surface to adsorb the bismuth element that precipitates during cooling, thereby achieving in-situ enrichment of bismuth. S4. Raw coal reduction and slag formation: Maintain 420-460℃ and add raw coal to the lead liquid under medium speed stirring to carry out reduction and slag formation. After reacting for 15-20 minutes, remove the surface slag. S5. Deep purification ingot casting: Sodium hydroxide is added to the lead liquid after slag removal to remove antimony and tin impurities before casting ingots to obtain bismuth-free refined lead.

2. The lead-bismuth separation method according to claim 1, characterized in that: The bismuth removal agent A contains 15%-25% calcium by mass, 65%-75% lead by mass, and the balance is one or two low-melting-point metals selected from tin and aluminum; the measured melting point range of the bismuth removal agent A is 360-460℃.

3. The lead-bismuth separation method according to claim 1, characterized in that: The bismuth removal agent B is composed of magnesium chloride and ammonium chloride mixed in a mass ratio of 3-5:

1.

4. The lead-bismuth separation method according to claim 1, characterized in that: The amount of bismuth removal agent A added is 0.06%-0.14% and the amount of bismuth removal agent B added is 0.2%-0.25% based on the mass of the lead solution.

5. The lead-bismuth separation method according to claim 3, characterized in that: The reaction process in step S2 is as follows: After the bismuth remover A is melted and dispersed, it releases the active calcium component. The active calcium reduces the magnesium chloride in the bismuth remover B to generate active metallic magnesium in situ. The ammonium chloride in the bismuth remover B decomposes upon heating, forming a protective atmosphere to inhibit the oxidation and burn-off of calcium and magnesium. Calcium and the magnesium generated in situ react synergistically with the bismuth in the lead liquid to generate a high-melting-point ternary intermetallic compound CaMg2Bi3 solid crystal. At the same time, the chloride component reacts with bismuth to form AB2[Bi]2³. - Type complex anion; the intermetallic compound and the complex product float together to form a bismuth-containing scum; The calcium chloride produced as a byproduct of the reaction acts as a binder for the slag phase, promoting the agglomeration and formation of the slag phase and achieving efficient separation of bismuth and lead liquid.

6. The lead-bismuth separation method according to claim 1, characterized in that: In step S2, the speed of medium-speed stirring is 1200-1500 r / min, and the speed of slow-speed stirring is 600-1200 r / min.

7. The lead-bismuth separation method according to claim 1, characterized in that: The amount of raw coal added, based on the mass of the lead liquid, is 0.08%-0.12%, the particle size of the raw coal is 20-40 mesh, the fixed carbon content is 40-50%, the moisture content is 10-18%, the ash content is ≤18%, and the volatile matter is 20-28%.

8. The lead-bismuth separation method according to claim 1, characterized in that: The amount of sodium hydroxide added is 0.08%-0.12% based on the mass of the lead solution.

9. The lead-bismuth separation method according to claim 1, characterized in that: The mass fraction of bismuth in the bismuth-containing refined lead is 0.015%-0.030%.

10. The lead-bismuth separation method according to claim 1, characterized in that: In step S4, the fixed carbon in the raw coal reduces the calcium oxide and lead oxide in the slag to metallic calcium and metallic lead; the carbon skeleton formed by the pyrolysis of the raw coal combines with the slag, so that the bismuth element is stably solidified in the slag phase; the silica in the raw coal reacts with the slag phase components to generate silicate substances, which, together with calcium chloride, bind the carbon skeleton, reduce the viscosity of the slag phase, and reduce the amount of lead entrainment.

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