Method for separating silver from high-bismuth silver-lead by vacuum distillation

Abstract

The present application relates to non-ferrous metallurgy technical field, disclose a kind of high bismuth silver lead vacuum distillation separation silver method, comprising the following steps: step 1: high bismuth silver lead is added into iron alloy pot, after adding composite flux, melt and remove surface melting slag after heating, compressed gas is passed into, and composite alkali is added to generate sodium tellurite slag, after removing, chlorine is passed into and is treated to remove impurities, after chlorination, nitrogen is blown, impurity slag is removed again, and the alloy after removing tellurium and impurities is obtained;Step 2: the alloy after removing tellurium and impurities is placed, copper is removed by removing slag spoon, the melt is heated, and the copper dross precipitated is removed, and then the copper-free alloy is vacuum distilled to obtain silver, and bismuth ingot is obtained by refining volatile material chlorine;The composite flux fluxing and mixed gas aeration of the application can avoid melt caking, and the telluride and chloride in the furnace body are eliminated from the source by the composite alkali tellurium removal and segmented impurity removal, and the furnace coking and equipment corrosion are reduced;The purity of crude silver and bismuth ingot is effectively improved by the multiple process synergistic treatment of the application.

Description

Technical Field

[0001] This invention relates to the field of non-ferrous metal metallurgy technology, specifically to a method for separating silver from high-bismuth silver-lead by vacuum distillation. Background Technology

[0002] The high-bismuth silver-lead raw material is a byproduct generated during the production of antimony white powder via low-temperature fumigation after lead-antimony alloys undergo alkali arsenic removal treatment. Its main components include precious and valuable metals such as bismuth (Bi), lead (Pb), gold (Au), and silver (Ag). The tellurium (Te) content in this raw material is 1.5%–3.0%, which does not meet the tellurium content control requirements of the vacuum distillation process. Pre-treatment to remove tellurium is necessary, using an alkali fusion method. However, if the tellurium content in the raw material exceeds the standard (>0.5%), during subsequent vacuum distillation, tellurium easily reacts with impurities such as copper in the raw material to generate a large amount of refractory tellurides (such as cuprous telluride Cu2Te). These compounds continuously deposit and adhere to the inner wall of the distillation furnace, the surface of the crucible, and the electrodes, not only affecting the furnace's heat transfer efficiency but also potentially causing equipment hazards such as poor electrode contact and accelerated crucible wear. The high-bismuth silver-lead raw material after tellurization needs to be further processed by melting to remove copper, reducing the copper grade to below 0.5%. Copper has a strong affinity for tellurium, and the two easily combine at high temperatures to form cuprous telluride (Cu2Te). This compound has high melting and boiling points, making it difficult to remove by vacuum distillation. It easily accumulates in the furnace, forming furnace sludge, which blocks the furnace passages and interferes with the stability of the distillation process, ultimately affecting the separation efficiency and recovery rate of precious metals.

[0003] The invention patent "A Method for Processing High-Antimony, Arsenic, and Precious Lead (ZL202411973651.9)" describes a method that uses vacuum fractionation of high-antimony, arsenic, and precious lead, followed by two-stage condenser plate processing to obtain lead-antimony alloy, crude antimony, crude arsenic, and a high-antimony copper-silver-gold alloy. The high-antimony copper-silver-gold alloy is then smelted to obtain a silver-copper-gold alloy, which is subsequently subjected to vacuum distillation. However, this method easily forms a copper-based low-melting-point eutectic phase, severely compromising the stability of the distillation process and significantly reducing the throughput per batch.

[0004] The invention patent "A method for recovering lead, silver and copper from precious lead as raw material (ZL201410361740.8)" describes separating lead, antimony, bismuth and copper from precious lead through vacuum distillation to produce high-bismuth lead and precious silver. The obtained precious silver is then refined in a converter to produce crude silver. This method is only suitable for precious lead with low tellurium content and has poor raw material adaptability. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for separating silver from high bismuth silver lead by vacuum distillation, so as to solve the problems of the prior art.

[0006] This invention solves the above-mentioned technical problems. The invention provides a method for separating silver from high-bismuth silver-lead using vacuum distillation, comprising the following steps: Step 1: Add high bismuth silver lead to the ferroalloy pot, add composite flux, heat and melt to 500℃~600℃, remove the surface molten slag, introduce compressed gas, and add composite alkali to generate sodium tellurite slag, remove it, then introduce chlorine gas for impurity removal, after chlorination impurity removal, nitrogen gas purging for 2~3 hours, after purging the chloride gas concentration in the furnace ≤0.1ppm, remove the impurity slag again to obtain the tellurium-free and impurity-free alloy; Step 2: After tellurium removal and impurity removal, the alloy is allowed to stand at 350~360℃ for 2-3 hours. Copper is removed with a slag remover. The melt is heated to 400~420℃ and held for 30 minutes. The precipitated copper slag is removed. The copper-free alloy is then vacuum distilled to obtain silver. The volatiles are refined with chlorine gas at 350~500℃ and 0.31~0.5kPa for 5~6 hours to obtain bismuth ingots. The composite flux is composed of steel slag, red mud, and sodium carbonate in a mass ratio of 4:4:1, and the addition amount is 1-3% of the mass of high bismuth silver lead. The steel slag and red mud are crushed and ground (particle size ≤20μm) and dried (moisture content ≤2%). The calcium and silicon compounds in the steel slag and the aluminum and iron oxides in the red mud work synergistically to form a low-temperature eutectic system with sodium carbonate, which improves the fluidity of the melt. At the same time, its molten products can adsorb inert impurities such as iron oxide scale and mud on the surface of the melt and remove them along with the molten slag. It will not introduce new impurities or cause a combustion reaction, thus taking into account both the fluxing and impurity removal effects. The compressed gas flow rate is 800 Nm3 / h, and the introduction time is 12~24h; The compressed gas is air containing 10-20% nitrogen by volume; The composite alkali is caustic soda and potassium hydroxide in a mass ratio of 11-13:1-3.

[0007] The amount of the composite alkali added is 3-8% of the mass of high bismuth silver lead; the impurity removal treatment is to control the temperature inside the pot to be maintained at 500-550℃, the flow rate of chlorine gas is 50-100 Nm³ / h, and the gas flow time is 2-4h; the chlorine gas reacts with trace impurities such as arsenic, antimony, and lead in the alloy to generate soluble chloride slag, which is removed by slag removal and separation. The vacuum distillation process involves transferring the copper-free alloy into a vacuum distillation melting pot, closing the furnace and evacuating it to 0.1~0.3 kPa, heating it to 400~450℃, and distilling it at that temperature for 4~6 hours. The chlorine gas flow rate is 50~100 Nm³ / h. A composite alkali system is used, where KOH lowers the melting point of the alkali fusion system and synergistically enhances the reactivity with tellurium with NaOH, promoting the conversion of high-valence tellurium into easily separable sodium tellurite slag. Mixed compressed gases are used, with nitrogen diluting the air to inhibit excessive oxidation of the main metal, while the air provides the oxygen source for tellurium oxidation. This process breaks the melt boundary layer, allowing the alkali and tellurium to fully contact, thus solving the defects of insufficient tellurium removal reaction and high tellurium residue in traditional static detellurization methods. The beneficial effects of this invention are as follows: By using a composite flux for melting and mixed gas aeration, this invention avoids melt agglomeration; composite alkali detellurization and segmented impurity removal prevent telluride and chloride deposition in the furnace body from the source, reducing furnace slagging and equipment corrosion; this invention, through multi-process synergy, effectively improves the purity of crude silver and bismuth ingots. This method features simple operation, low energy consumption, short process flow, large single-cycle processing capacity, and high silver recovery and direct recovery rates. Detailed Implementation

[0008] The present invention will be further described in detail below through specific implementation examples. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of protection of the present invention. After reading the present invention, any modifications of the present invention in various equivalent forms by those skilled in the art fall within the scope of the appended claims.

[0009] Unless otherwise specified, all raw materials and reagents used in this invention are from the conventional market.

[0010] Example 1 A method for separating silver from high-bismuth silver-lead by vacuum distillation includes the following steps: Step 1: Add high-bismuth silver-lead alloy to a ferroalloy pot, add a composite flux, heat to 550℃ and remove surface slag. Introduce compressed gas and add a composite alkali to generate sodium tellurite slag, remove it, and then introduce chlorine gas for impurity removal. After chlorination, purge with nitrogen for 2 hours. After purging, the chloride gas concentration in the furnace is ≤0.1ppm. Remove impurities again to obtain the tellurium-free and impurity-free alloy. The composite flux is a mixture of steel slag, red mud and sodium carbonate in a mass ratio of 4:4:1, and the amount added is 2% of the mass of high-bismuth silver-lead alloy. The compressed gas flow rate is 800 Nm3 / h, and the introduction time is 18h; The compressed gas is air containing 15% nitrogen by volume; The composite alkali is caustic soda and potassium hydroxide in a mass ratio of 12:2.

[0011] The amount of the composite alkali added is 5% of the mass of the high bismuth silver lead; The impurity removal process involves maintaining the temperature inside the boiler at 520°C, introducing chlorine gas at a flow rate of 80 Nm³ / h, and a gas introduction time of 3 hours. The vacuum distillation process involves transferring the copper-free alloy into a vacuum distillation melting pot, closing the furnace and evacuating it to 0.2 kPa, heating it to 430°C, and distilling it at that temperature for 5 hours. The flow rate of the chlorine gas is 80 Nm³ / h.

[0012] Example 2 A method for separating silver from high-bismuth silver-lead by vacuum distillation includes the following steps: Step 1: Add high-bismuth silver-lead alloy to a ferroalloy pot, add a composite flux, heat to 500℃ and remove surface slag. Introduce compressed gas and add a composite alkali to generate sodium tellurite slag, remove it, and then introduce chlorine gas for impurity removal. After chlorination, purge with nitrogen for 2 hours. After purging, the chloride gas concentration in the furnace is ≤0.1ppm. Remove impurities again to obtain the tellurium-free and impurity-free alloy. The composite flux is a mixture of steel slag, red mud and sodium carbonate in a mass ratio of 4:4:1, and the amount added is 1% of the mass of high-bismuth silver-lead alloy. The compressed gas flow rate is 800 Nm3 / h, and the introduction time is 12h; The compressed gas is air containing 10% nitrogen by volume; The composite alkali is caustic soda flakes and potassium hydroxide in a mass ratio of 11:1.

[0013] The amount of the composite alkali added is 3-8% of the mass of high bismuth silver lead; The impurity removal process involves maintaining the temperature inside the boiler at 500°C, introducing chlorine gas at a flow rate of 50 Nm³ / h, and a gas introduction time of 2 hours. The vacuum distillation process involves transferring the copper-free alloy into a vacuum distillation melting pot, closing the furnace and evacuating it to 0.1 kPa, heating it to 400°C, and distilling it at that temperature for 4 hours. The flow rate of the chlorine gas is 50 Nm³ / h.

[0014] Example 3 A method for separating silver from high-bismuth silver-lead by vacuum distillation includes the following steps: Step 1: Add high-bismuth silver-lead alloy to a ferroalloy pot, add a composite flux, heat to 600℃ and remove surface slag. Introduce compressed gas and add a composite alkali to generate sodium tellurite slag, remove it, and then introduce chlorine gas for impurity removal. After chlorination, purge with nitrogen for 3 hours. After purging, the chloride gas concentration in the furnace is ≤0.1ppm. Remove impurities again to obtain the tellurium-free and impurity-free alloy. The composite flux is a mixture of steel slag, red mud and sodium carbonate in a mass ratio of 4:4:1, and the amount added is 3% of the mass of high-bismuth silver-lead alloy. The compressed gas flow rate is 800 Nm3 / h, and the introduction time is 24h; The compressed gas is air containing 20% ​​nitrogen by volume; The composite alkali is caustic soda and potassium hydroxide in a mass ratio of 13:3.

[0015] The amount of the composite alkali added is 8% of the mass of the high bismuth silver lead; The impurity removal process involves maintaining the temperature inside the boiler at 550°C, introducing chlorine gas at a flow rate of 100 Nm³ / h, and a gas introduction time of 4 hours. The vacuum distillation process involves transferring the copper-free alloy into a vacuum distillation melting pot, closing the furnace and evacuating it to 0.3 kPa, heating it to 450°C, and distilling it at that temperature for 6 hours. The flow rate of the chlorine gas is 100 Nm³ / h.

[0016] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 uses an equal amount of caustic soda flakes instead of compound caustic soda, while everything else remains the same.

[0017] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that Comparative Example 2 does not add a composite flux, while everything else remains the same.

[0018] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the compressed gas in Comparative Example 3 is compressed air, while everything else remains the same.

[0019] High-bismuth silver-lead alloy, as a residue after antimony blowing in lead-antimony alloys, mainly consists of precious metals such as Bi, Pb, and Ag, as well as a small amount of residual antimony. The test results are shown in Table 1.

[0020] Table 1. Main components of high-bismuth silver-lead materials Bi / % Pb / % Sb / % Cu / % Te / % Ag / (g / t) other / % #1 High Bismuth Silver Lead 42.01 41.47 7.78 2.59 2.26 32566 0.63 2# High Bismuth Silver Lead 41.16 41.22 8.93 2.73 2.64 26910 0.63 3# High Bismuth Silver Lead 41.41 41.52 8.33 2.24 2.97 29194 0.61 II. Removing tellurium by adding alkali The test results of high bismuth silver-lead after tellurium removal in the examples and comparative examples are shown in Table 2.

[0021] Table 2 Main components of high bismuth silver-lead excluding tellurium As shown in Table 2, compared with the comparative example, the embodiment has higher tellurium removal efficiency, higher main metal retention rate, and lower impurity content.

[0022] III. Copper Removal by Melting The copper removal effects of the examples and comparative examples are shown in Table 3.

[0023] Table 3 Main components of high-bismuth silver-lead (excluding copper) As shown in Table 3, the composite flux in the examples optimized the interfacial tension of the melt, and the composite alkali + nitrogen-air mixture ensured the detellurization effect, creating a clean system for subsequent low-temperature melting and copper removal, and the Cu residue was stably reduced to below 0.4%.

[0024] IV. Vacuum Distillation Based on the different saturated vapor pressures of various impurity metals in copper-free high-bismuth silver-lead, vacuum distillation was performed on copper-free high-bismuth silver-lead. The higher the saturated vapor pressure, the easier it is to volatilize into the volatiles, and the lower the saturated vapor pressure, the less likely it is to volatilize. Precious metals such as gold and silver also enter the residue. The main components of the vacuum distillation residues obtained in the examples and comparative examples are shown in Table 4.

[0025] Table 4. Main components of vacuum distillation residues (excluding copper, high bismuth, silver, and lead). As shown in Table 4, the tellurium removal and copper removal processes in the embodiments of the present invention are thorough, there is no large amount of Cu2Te furnace spore interference during vacuum distillation, volatile metals such as Bi and Pb are fully volatilized, and Ag is efficiently enriched in the residue.

[0026] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for separating silver from high-bismuth silver-lead using vacuum distillation, characterized in that, Includes the following steps: Step 1: Add high bismuth silver lead to the ferroalloy pot, add composite flux, heat and melt to 500℃~600℃, remove the surface molten slag, introduce compressed gas, and add composite alkali to generate sodium tellurite slag, remove it, then introduce chlorine gas for impurity removal, after chlorination impurity removal, nitrogen gas purging for 2~3 hours, after purging the chloride gas concentration in the furnace ≤0.1ppm, remove the impurity slag again to obtain the tellurium-free and impurity-free alloy; Step 2: After tellurium removal and impurity removal, the alloy is allowed to stand at 350~360℃ for 2-3 hours. Copper is removed using a slag remover. The melt is heated to 400~420℃ and held for 30 minutes. The precipitated copper slag is removed. The copper-free alloy is then vacuum distilled to obtain silver. The volatiles are refined by passing chlorine gas through the slag at 350~500℃ and 0.31~0.5kPa for 5~6 hours to obtain bismuth ingots.

2. The method for separating silver from high-bismuth silver-lead by vacuum distillation according to claim 1, characterized in that, The composite flux is composed of steel slag, red mud and sodium carbonate in a mass ratio of 4:4:1, and the amount added is 1 to 3% of the mass of high bismuth silver lead.

3. The method for separating silver from high-bismuth silver-lead by vacuum distillation according to claim 1, characterized in that, The compressed gas flow rate is 800 Nm3 / h, and the introduction time is 12~24h.

4. The method for separating silver from high-bismuth silver-lead by vacuum distillation according to claim 1, characterized in that, The compressed gas is air containing 10-20% nitrogen by volume.

5. The method for separating silver from high-bismuth silver-lead by vacuum distillation according to claim 1, characterized in that, The composite alkali is caustic soda and potassium hydroxide in a mass ratio of 11-13:1-3.

6. The method for separating silver from high-bismuth silver-lead by vacuum distillation according to claim 1, characterized in that, The amount of the composite alkali added is 3-8% of the mass of high bismuth silver lead.

7. The method for separating silver from high-bismuth silver-lead by vacuum distillation according to claim 1, characterized in that, The impurity removal process involves controlling the temperature inside the pot to be maintained at 500~550℃, introducing chlorine gas at a flow rate of 50~100 Nm³ / h, and a gas introduction time of 2~4h. The chlorine gas reacts with trace amounts of impurities such as arsenic, antimony, and lead in the alloy to generate soluble chloride slag, which is then removed by slag removal and separation.

8. The method for separating silver from high-bismuth silver-lead by vacuum distillation according to claim 1, characterized in that, The vacuum distillation process involves transferring the copper-free alloy into a vacuum distillation melting pot, closing the furnace and evacuating it to 0.1~0.3 kPa, heating it to 400~450℃, and distilling it at that temperature for 4~6 hours.

9. The method for separating silver from high-bismuth silver-lead by vacuum distillation according to claim 1, characterized in that, The flow rate of chlorine gas in step 2 is 50~100 Nm³ / h.

Images