A method for removing tin from a medium-low grade crude lead

Abstract

The application discloses a tin removal method for crude lead with medium-low tin grade, and belongs to the technical field of tin removal of crude lead. The tin removal method comprises the following steps: step 1, melting the crude lead, removing copper by liquation and removing copper by sulfuration, and obtaining a melt with a tin content of 0.05-0.5wt%; step 2, spraying and adding silicon-aluminum alloy powder to carry out reaction under the condition of 500-520 DEG C and with inert gas as a carrier gas; step 3, adding an ammonium-free covering type slagging agent to carry out reaction under the condition of 540-560 DEG C; and step 4, standing and removing slag. The silicon-aluminum alloy powder is composed of 45-55wt% of Si and the balance of Al; and the ammonium-free covering type slagging agent is composed of 50-60wt% of sodium chloride, 25-35wt% of sodium carbonate and the balance of calcium fluoride. The tin removal rate of the tin removal method reaches more than 98%, the lead content of tin slag is less than or equal to 4.5wt%, the direct lead recovery rate reaches 98.5%, and no harmful gas is discharged.

Description

Technical Field

[0001] This invention belongs to the field of detinning technology for crude lead, specifically relating to a method for detinning crude lead with medium to low tin content. Background Technology

[0002] Crude lead typically contains impurities such as tin, copper, arsenic, and antimony. Among these, tin is a harmful element that affects the electrolytic refining of lead and the quality of the final lead product. Excessive tin content not only affects electrolytic stability but also reduces the processing performance of refined lead. Therefore, crude lead usually requires pyrometallurgical refining to remove tin, reducing the tin content to below 0.01 wt%, with high-end lead materials even requiring a tin content no higher than 0.005 wt%.

[0003] Currently, commonly used methods for detinning crude lead mainly include alkaline oxidation and ferrosilicon detinning. Alkaline oxidation involves adding oxidants such as NaOH and NaNO3 to the molten lead to achieve detinning. While it has a certain detinning effect, it easily generates NOx fumes and produces a large amount of difficult-to-treat alkaline tin-containing slag, resulting in high environmental impact and difficult post-treatment. As for ferrosilicon detinning, it is mainly suitable for high-tin crude lead (tin content generally greater than 2 wt%), but its detinning rate is limited for medium- and low-tin crude lead, and it is difficult to achieve deep detinning.

[0004] In recent years, many technologies have attempted to use new methods such as direct oxygen blowing or adding manganese dioxide for detinning. However, since lead itself is easily oxidized, it often leads to increased lead oxidation loss. At the same time, it is difficult to separate lead and tin in the resulting tin slag, making it difficult to obtain refined lead with a tin content of no more than 0.005 wt% at low cost in industrial production.

[0005] In conclusion, there is an urgent need to develop an environmentally friendly, economical deep detinning process suitable for crude lead with medium to low tin content. Summary of the Invention

[0006] The purpose of this invention is to provide a method for removing tin from crude lead of medium to low tin grade, achieving a tin removal rate of over 98%, a lead content in tin slag of ≤4.5wt%, a lead recovery rate of 98.5%, and no harmful gas emissions throughout the process, thus possessing advantages such as clean production and being green.

[0007] A method for detinning crude lead with medium to low tin content includes the following steps: Step 1: After completely melting the crude lead into molten lead, copper is removed by melting and precipitation to obtain melt A. Melt A is then sulfided to remove copper to obtain melt B. Step 2: Heat the melt B and keep it at that temperature. Add silicon-aluminum alloy powder by blowing it with an inert gas as the carrier gas and stir to react, thus obtaining melt C. In this stage, silicon preferentially reacts with tin to form a high-melting-point Sn-Si intermetallic compound. The use of inert gas blowing enhances the mass transfer of low-grade impurities, achieving deep detinning and low lead loss. Step 3: Reheat the melt C, keep it at that temperature, add an ammonium-free covering slag-forming agent, stir and react to obtain melt D; the slag layer melted in this stage can deeply adsorb and dissolve fine tin compounds and capture residual aluminum slag. Step 4: After the melt D has been allowed to stand, remove the surface slag.

[0008] As a preferred technical solution of the present invention, in step 1, the complete melting of crude lead into molten lead refers to the complete melting of crude lead into molten lead at 450-500℃.

[0009] As a preferred embodiment of the present invention, in step 1, the temperature for melting and removing copper is controlled at 340-350°C.

[0010] As a preferred technical solution of the present invention, in step 1, the copper removal by sulfidation refers to adding a sulfide to remove copper at a temperature controlled at 330-340℃; the sulfide is sodium sulfide; the amount of sulfide used is 1.4-1.8 times the theoretical amount; the theoretical amount refers to the required mass of sulfide calculated based on the fact that all the copper in the melt A can undergo the sulfidation reaction.

[0011] As a preferred embodiment of the present invention, in step 1, the copper content of the melt B is less than 0.01 wt% and the tin content is 0.05-0.5 wt%.

[0012] As a preferred embodiment of the present invention, in step 2, the temperature rise is to 500-520℃.

[0013] In a preferred embodiment of the present invention, in step 2, the inert gas is nitrogen.

[0014] As a preferred embodiment of the present invention, in step 2, the silicon-aluminum alloy powder is composed of 45-55 wt% Si and the balance Al; the particle size of the silicon-aluminum alloy powder is 150-200 mesh; and the amount of silicon-aluminum alloy powder used is 6-9 times the mass of tin in the melt B.

[0015] As a preferred embodiment of the present invention, in step 2, the stirring reaction time is 15-20 min.

[0016] As a preferred embodiment of the present invention, in step 3, the temperature rise is to 540-560℃.

[0017] As a preferred embodiment of the present invention, in step 3, the amount of the ammonium-free covering slag-forming agent is 0.1-0.3% of the mass of the melt C; the ammonium-free covering slag-forming agent is composed of 50-60 wt% sodium chloride, 25-35 wt% sodium carbonate and the balance calcium fluoride.

[0018] Preferably, the amount of the ammonium-free covering slagging agent is 0.2-0.3% of the mass of the melt C.

[0019] As a preferred embodiment of the present invention, in step 3, the stirring reaction time is 5-10 minutes.

[0020] As a preferred embodiment of the present invention, in step 4, the settling time is 3-5 minutes.

[0021] The beneficial effects of this invention are: 1. This invention achieves deep removal of tin and precise quantitative consumption of reagents by using pre-alloyed silicon-aluminum powder and stepwise temperature control, allowing highly active silicon to react preferentially with low-concentration tin in the low-temperature stage, and then having aluminum complete the tail-off collection in the high-temperature stage.

[0022] 2. This invention adopts a reverse temperature control concept that deviates from the conventional "low temperature initiation and high temperature slag formation", combined with inert gas blowing, to enhance the mass transfer of low-grade impurities and achieve deep detinning and low lead loss.

[0023] 3. The ammonium-free covering slag-forming agent added in this invention not only eliminates harmful gases, but its specific fluorochlorocarbonate system has a better capture effect on fine tin compound particles than conventional slag-forming agents, forming a synergistic effect with the stepwise reaction and significantly improving the detinning rate.

[0024] 4. The process parameters of this invention are precise, the window is clear, the reagents are readily available, and it can be directly implemented on a general crude lead refining pot. The working environment is completely harmless, and the economic and environmental benefits are significant.

[0025] 5. The detinning method of the present invention achieves a detinning rate of over 98%, a lead content of tin dross of ≤4.5wt%, and a lead recovery rate of 98.5%. Detailed Implementation

[0026] The claims of the present invention will be further described in detail below with reference to specific embodiments, but this does not constitute any limitation on the present invention. Any limited modifications made by any person within the scope of protection of the claims of the present invention are still within the scope of protection of the claims of the present invention.

[0027] Example 1 A method for detinning crude lead with medium to low tin content includes the following steps: Step 1: In a lead melting pot, crude lead is completely melted into molten lead at 450°C, and copper is removed by melting and precipitation. The temperature for copper removal is controlled at 340°C to obtain melt A. Then, the temperature is controlled at 330°C, and sodium sulfide is added to melt A to remove copper by sulfidation. The amount of sodium sulfide used is 1.4 times the theoretical amount. The theoretical amount refers to the mass of sodium sulfide required calculated based on the fact that all the copper in melt A can undergo the sulfidation reaction. Melt B with copper content less than 0.01wt% and tin content of 0.42wt% is obtained. Step 2: Heat the melt B to 500°C and hold it at that temperature. Add silicon-aluminum alloy powder by blowing it in with nitrogen as the carrier gas. The silicon-aluminum alloy powder consists of 45wt% Si and 55wt% Al, with a particle size of 150 mesh. The amount added is 6 times the mass of tin in the melt B. Stir and react for 15 minutes to obtain melt C. Step 3: Reheat the melt C to 540℃, keep it at that temperature, add an ammonium-free covering slagging agent, the amount of which is 0.1% of the mass of the melt C. The ammonium-free covering slagging agent consists of 52wt% sodium chloride, 33wt% sodium carbonate and 15wt% calcium fluoride. Stir and react for 10 minutes to obtain melt D. Step 4: After the melt D has been left to stand for 3 minutes, remove the surface slag.

[0028] Example 2 A method for detinning crude lead with medium to low tin content includes the following steps: Step 1: After completely melting crude lead into molten lead in a lead melting pot at 480°C, copper is removed by melting and precipitation. The temperature for copper removal is controlled at 348°C to obtain melt A. Then, the temperature is controlled at 334°C, and sodium sulfide is added to melt A to remove copper by sulfidation. The amount of sodium sulfide used is 1.6 times the theoretical amount. The theoretical amount refers to the mass of sodium sulfide required calculated based on the fact that all the copper in melt A can undergo the sulfidation reaction. Melt B with copper content less than 0.01 wt% and tin content of 0.29 wt% is obtained. Step 2: Heat the melt B to 510°C and hold it at that temperature. Add silicon-aluminum alloy powder by blowing it in with nitrogen as the carrier gas. The silicon-aluminum alloy powder consists of 52wt% Si and 48wt% Al, with a particle size of 200 mesh. The amount added is 8 times the mass of tin in the melt B. Stir and react for 20 minutes to obtain melt C. Step 3: Reheat the melt C to 560°C, maintain the temperature, add an ammonium-free covering slagging agent, the amount of which is 0.22% of the mass of the melt C. The ammonium-free covering slagging agent consists of 50wt% sodium chloride, 35wt% sodium carbonate and 15wt% calcium fluoride. Stir and react for 5 minutes to obtain melt D. Step 4: After the melt D has been left to stand for 5 minutes, remove the surface slag.

[0029] Example 3 A method for detinning crude lead with medium to low tin content includes the following steps: Step 1: In a lead melting pot, crude lead is completely melted into molten lead at 500°C, and copper is removed by melting and precipitation. The temperature for copper removal is controlled at 350°C to obtain melt A. Then, the temperature is controlled at 340°C, and sodium sulfide is added to melt A to remove copper by sulfidation. The amount of sodium sulfide used is 1.7 times the theoretical amount. The theoretical amount refers to the mass of sodium sulfide required calculated based on the fact that all the copper in melt A can undergo the sulfidation reaction. Melt B with copper content less than 0.01wt% and tin content of 0.35wt% is obtained. Step 2: Heat the melt B to 510°C and hold it at that temperature. Add silicon-aluminum alloy powder by blowing it in with nitrogen as the carrier gas. The silicon-aluminum alloy powder consists of 55wt% Si and 45wt% Al, with a particle size of 200 mesh. The amount added is 9 times the mass of tin in the melt B. Stir and react for 15 minutes to obtain melt C. Step 3: Reheat the melt C to 555℃, keep it at that temperature, add an ammonium-free covering slagging agent, the amount of which is 0.3% of the mass of the melt C. The ammonium-free covering slagging agent consists of 60wt% sodium chloride, 30wt% sodium carbonate and 10wt% calcium fluoride. Stir and react for 5 minutes to obtain melt D. Step 4: After the melt D has been left to stand for 3 minutes, remove the surface slag.

[0030] Example 4 A method for detinning crude lead with medium to low tin content includes the following steps: Step 1: In a lead melting pot, crude lead is completely melted into molten lead at 490°C, and copper is removed by melting and precipitation. The temperature for copper removal is controlled at 350°C to obtain melt A. Then, the temperature is controlled at 340°C, and sodium sulfide is added to melt A for sulfidation to remove copper. The amount of sodium sulfide used is 1.4 times the theoretical amount. The theoretical amount refers to the mass of sodium sulfide required calculated based on the fact that all the copper in melt A can undergo the sulfidation reaction. This results in melt B with a copper content of less than 0.01 wt% and a tin content of 0.13 wt%. Step 2: Heat the melt B to 520°C and hold it at that temperature. Add silicon-aluminum alloy powder by blowing it in with nitrogen as the carrier gas. The silicon-aluminum alloy powder consists of 46wt% Si and 54wt% Al, with a particle size of 150 mesh. The amount added is 6 times the mass of tin in the melt B. Stir and react for 15 minutes to obtain melt C. Step 3: Reheat the melt C to 545℃, keep it at that temperature, add an ammonium-free covering slagging agent, the amount of which is 0.2% of the mass of the melt C. The ammonium-free covering slagging agent consists of 57wt% sodium chloride, 31wt% sodium carbonate and 12wt% calcium fluoride. Stir and react for 10 minutes to obtain melt D. Step 4: After the melt D has been left to stand for 5 minutes, remove the surface slag.

[0031] Example 5 A method for detinning crude lead with medium to low tin content includes the following steps: Step 1: In a lead melting pot, crude lead is completely melted into molten lead at 475°C, and copper is removed by melting and precipitation. The temperature for copper removal is controlled at 350°C to obtain melt A. Then, the temperature is controlled at 335°C, and sodium sulfide is added to melt A to remove copper by sulfidation. The amount of sodium sulfide used is 1.4 times the theoretical amount. The theoretical amount refers to the mass of sodium sulfide required calculated based on the fact that all the copper in melt A can undergo the sulfidation reaction. Melt B with a copper content of less than 0.01 wt% and a tin content of 0.42 wt% is obtained. Step 2: Heat the melt B to 500°C and hold it at that temperature. Add silicon-aluminum alloy powder by blowing it in with nitrogen as the carrier gas. The silicon-aluminum alloy powder consists of 49wt% Si and 51wt% Al, with a particle size of 150 mesh. The amount added is 9 times the mass of tin in the melt B. Stir and react for 15 minutes to obtain melt C. Step 3: Reheat the melt C to 560°C, maintain the temperature, add an ammonium-free covering slagging agent, the amount of which is 0.3% of the mass of the melt C. The ammonium-free covering slagging agent consists of 51wt% sodium chloride, 34wt% sodium carbonate and 15wt% calcium fluoride. Stir and react for 5 minutes to obtain melt D. Step 4: After the melt D has been left to stand for 3 minutes, remove the surface slag.

[0032] Comparative Example 1 Based on Example 4, step 3 is changed to not raising the temperature, and the operation continues at 520°C, while the other settings, parameters and steps remain the same.

[0033] Comparative Example 2 Based on Example 4, step 2 is changed to raising the temperature to 545°C, while the other settings, parameters, and steps remain the same.

[0034] Comparative Example 3 Based on Example 4, calcium fluoride and other similar substances were replaced with sodium chloride and sodium carbonate in a mass ratio of 57:31, while the rest of the settings, parameters, and steps remained the same.

[0035] The detinning rate, lead content in tin slag, and lead recovery rate of the detinning methods in Examples 1-5 and Comparative Examples 1-3 were determined respectively.

[0036] Table 1. Measurement Results This invention provides a detinning method suitable for crude lead with medium to low tin content (0.05-0.5wt%), achieving a detinning rate of over 98%, a lead content in tin slag of ≤4.5wt%, a lead recovery rate of 98.5%, and no harmful gas emissions throughout the process, offering advantages such as clean production and environmental friendliness.

[0037] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, features in the embodiments of the present invention can be combined with each other unless otherwise specified.

Claims

1. A method for detinning crude lead with medium to low tin content, characterized in that: Includes the following steps: Step 1: After completely melting the crude lead into molten lead, copper is removed by melting and precipitation to obtain melt A. The copper in melt A is then removed by sulfidation to obtain melt B. Step 2: Heat the melt B and keep it at that temperature. Add silicon-aluminum alloy powder by blowing it in with an inert gas as the carrier gas, and stir to react, to obtain melt C. Step 3: Reheat the melt C, keep it at that temperature, add an ammonium-free covering slagging agent, stir and react to obtain melt D; Step 4: After the melt D has been allowed to stand, remove the surface slag.

2. The method for detinning crude lead of medium to low tin grade according to claim 1, characterized in that: In step 1, the temperature for copper removal by melting is controlled at 340-350℃.

3. The method for detinning crude lead of medium to low tin grade according to claim 1, characterized in that: In step 1, the copper content of melt B is less than 0.01 wt%, and the tin content is 0.05-0.5 wt%.

4. The method for detinning crude lead of medium to low tin grade according to claim 1, characterized in that: In step 2, the temperature is increased to 500-520℃.

5. The method for detinning crude lead of medium to low tin grade according to claim 1, characterized in that: In step 2, the inert gas is nitrogen.

6. The method for detinning crude lead of medium to low tin grade according to claim 1, characterized in that: In step 2, the silicon-aluminum alloy powder consists of 45-55 wt% Si and the balance Al; the particle size of the silicon-aluminum alloy powder is 150-200 mesh; and the amount of silicon-aluminum alloy powder used is 6-9 times the mass of tin in the melt B.

7. The method for detinning crude lead of medium to low tin grade according to claim 1, characterized in that: In step 2, the stirring reaction takes 15-20 minutes.

8. The method for detinning crude lead of medium to low tin grade according to claim 1, characterized in that: In step 3, the temperature is increased to 540-560℃.

9. The method for detinning crude lead of medium to low tin grade according to claim 1, characterized in that: In step 3, the amount of the ammonium-free covering slag-forming agent is 0.1-0.3% of the mass of the melt C; the ammonium-free covering slag-forming agent is composed of 50-60 wt% sodium chloride, 25-35 wt% sodium carbonate and the balance calcium fluoride.

10. A method for detinning crude lead of medium to low tin grade according to claim 1, characterized in that: In step 3, the stirring reaction takes 5-10 minutes.

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