A method for improving the qualified rate of silver ingot by removing impurities in electrolytic silver powder

Abstract

The application discloses a method for improving the qualified rate of silver ingot by removing impurities in electrolytic silver powder. The method is suitable for electrolytic silver powder with excessive copper, lead, iron, tellurium and other impurities in the process of silver electrolytic refining. The method comprises the following steps: preparing a mixed solution of a certain concentration of hydrochloric acid and sodium chlorate (oxidizing agent) to remove copper, lead, iron and other impurities in the silver powder through pre-impregnation, then adding the silver powder into pure alkali and potassium nitrate to remove tellurium impurities through oxidation slagging and smelting, thereby improving the qualified rate of electrolytic silver ingot (in line with the GB / T 4135-2016 standard IC-Ag99.99 national standard 1 # (standard IC-Ag99.99 national standard 1 # ), avoiding the repeated process of secondary electrolytic refining of the electrolytic silver powder due to excessive copper, lead, iron, tellurium and other impurities, and especially developing a new impurity removal technology for the tellurium impurities which are difficult to remove by conventional technology. The method shortens the production cycle of silver electrolytic refining, reduces the backlog of silver, saves the production cost, and reduces the labor intensity of employees.

Description

Technical Field

[0001] This invention belongs to the field of silver electrolytic refining technology and relates to a method for improving the yield of silver ingots. Background Technology

[0002] Silver, as a precious metal, is typically refined through electrolytic processes using raw materials such as silver-rich cyanide gold mud, copper anode mud, and lead anode mud to obtain an alloy containing a total gold and silver content of over 97% (with gold content not exceeding 30%). After electrolytic refining, impurities such as copper, lead, and iron enter the electrolyte. Silver is deposited at the cathode to produce qualified silver powder, while gold remains undissolved and enters the anode bag, thus achieving gold-silver separation and silver purification. As the electrolytic refining process continues, impurities such as copper, lead, iron, and tellurium in the anode plate continuously dissolve into the electrolyte and accumulate. When a certain impurity element accumulates to a certain level in the electrolyte, or if the electrolytic refining conditions are not properly controlled, the electrolytically produced silver powder may contain excessive levels of impurities such as copper, lead, iron, and tellurium, failing to meet the national standard GB / T4135-2016 IC-Ag99.99. # Silver regulations stipulate that if the electrolyte contains excessive levels of impurities such as copper, lead, iron, and tellurium, it needs to be replaced with a new electrolyte. If the silver electrolytic refining operation conditions are not properly controlled, the electrolytic control conditions need to be adjusted promptly. However, the excessive silver powder produced in these situations requires remelting the anode plates and returning the product for re-electrolytic refining. Returning the product for re-electrolytic refining not only increases electrolytic production costs and the labor intensity of employees but also prolongs the silver electrolytic refining production cycle, resulting in silver stockpiling.

[0003] To address the above problems, Chinese invention patent application CN105132706A discloses a "method for removing impurities from electrolytic silver powder." The technology in this patent application involves removing impurities from electrolytic silver powder. The process includes: "soaking the electrolytic silver powder in a room-temperature dilute nitric acid solution with a mass of 18-22 g / L, followed by a first wash with hot water at 60-80°C for 30 minutes; then soaking it in a room-temperature dilute hydrochloric acid solution with a mass fraction of 8-10%, followed by a second wash with hot water at 60-80°C for 30 minutes; and finally drying it with a hot air blower." This process effectively removes impurities such as Cu, Pb, Bi, and Sb from the electrolytic silver powder. The electrolytic silver powder prepared by this invention conforms to GB / T 4135-2002 standard. # According to the regulations for silver, silver ingots that meet the requirements can be produced by melting and casting. The method for removing impurities from electrolytic silver powder is designed to involve two solution soakings, two filtrations, and two washings. This involves many steps, high labor intensity, long impurity removal cycle, and high production cost. In particular, it cannot effectively remove tellurium (Te) impurities. At the same time, the reaction between copper and dilute nitric acid at room temperature is relatively slow. If the electrolytic silver powder contains excessive tellurium (Te) or relatively high copper impurities, this method will be limited.

[0004] Chinese invention patent application CN114410981A discloses a "method for refining gold and silver," which uses sodium chlorate as an oxidant and claims that the resulting silver ingots contain very low levels of impurities such as copper, lead, iron, and tellurium. In this patent application, the oxidant sodium chlorate is mainly used to oxidize and dissolve crude gold in a hydrochloric acid system. The silver in the crude gold is oxidized into solid silver chloride, while most of the impurities such as copper, lead, iron, and tellurium are oxidized and enter the solution. After filtration, the silver chloride is separated from the relatively pure solid silver chloride. The silver chloride is then reduced and replaced to form crude silver ingots, which can be electrolyzed to obtain qualified silver ingots. However, as electrolysis proceeds, the levels of impurity ions such as copper, lead, iron, and tellurium in the silver electrolyte continuously increase, potentially resulting in silver powder containing excessive levels of impurities such as copper, lead, iron, and tellurium.

[0005] Chinese patent CN100360419C discloses a "method for separating and purifying high-purity silver chloride and a method for manufacturing high-purity silver using the high-purity silver chloride". The patent mentions that in an acidic aqueous solution, an oxidizing agent is added to oxidize silver chloride, eluting and separating impurity elements (including copper, lead, iron, and tellurium). It involves separating a soluble compound from a refining intermediate of a sparingly soluble silver compound and impurity elements, then converting it into silver chloride containing certain impurities such as copper, lead, iron, and tellurium. At this point, the silver has already been oxidized to silver chloride. Then, an oxidizing agent such as hydrogen peroxide or chlorate is used to control a higher potential to oxidize and dissolve the impurities such as copper, lead, iron, and tellurium. After filtration and washing, the solid silver chloride is separated from the impurities such as copper, lead, iron, and tellurium, thus obtaining high-purity silver chloride. The high-purity silver chloride is then reduced to obtain high-purity silver. The key advantage of this invention is that it does not require strict control of the concentration of oxidants such as hydrogen peroxide or chlorate in the solution, and the oxidant must be added in excess to completely oxidize and dissolve copper, lead, iron, tellurium, etc. Silver remains in a combined state as silver chloride throughout the oxidation process. Its main disadvantages are that high-purity silver is produced from refining intermediates of insoluble silver compounds and impurity elements, the raw material composition is complex and contains many impurities, there are many purification and washing processes, the process is complex, the production cost is high, the product color is unstable, and it is easy for high-purity silver to contain excessive impurities such as copper, lead, iron, and tellurium. At present, this method is rarely used.

[0006] Chinese invention patent CN113201650A discloses a processing technology for high-silver tellurium gold sludge. This invention involves using borax, soda ash, and potassium nitrate to smelt crude silver powder before silver electrolytic refining to remove most impurities such as copper, lead, and iron through a primary smelting process. A secondary smelting process using soda ash and potassium nitrate is then used to oxidize and remove most tellurium. However, even after oxidation and slag formation, the crude silver still contains less than 0.002% tellurium. As silver electrolytic refining continues, impurities such as copper, lead, and tellurium accumulate in the silver electrolyte. When these impurities reach a certain concentration, they precipitate at the cathode along with silver ions, causing one or more of these impurities to exceed the standard in the electrolytic silver powder. Therefore, the silver powder produced by this invention can only consistently meet the GB / T 4135-2016 standard IC-Ag99.95, and the product belongs to the national standard 2. # Silver Standard.

[0007] Chinese invention patent application CN113481371A discloses a method for efficiently recovering antimony, bismuth, copper, and silver from silver-separated slag in lead anode mud. This method involves reacting lead anode mud in a hydrochloric acid system using oxidants such as sodium chlorate, sodium perchlorate, hydrogen peroxide, ozone, chlorine, oxygen, air, and Fe. 3+ Any one or combination of these methods involves oxidative pre-leaching of pulverized lead anode mud containing silver, thereby oxidizing all silver, copper, lead, bismuth, antimony, and other impurities. Copper, bismuth, antimony, and some lead enter the solution, while silver is converted into solid silver chloride, and the remaining lead is converted into solid lead chloride, which mixes with the silver chloride. The filtered pre-leaching solution is then used to utilize the different pH values ​​of bismuth and antimony hydrolysis in the solution to form their respective precipitates, which are then filtered separately to obtain bismuth and antimony concentrates. The filtered pre-leaching solution is then replaced with iron powder to obtain copper concentrate. The mixture of pre-leached solid silver chloride and lead chloride is pre-leached with sodium sulfite solution, where silver forms a silver complex with sodium sulfite, dissolves, and is filtered, achieving separation of silver from other impurities. The filtrate is then reduced with hydrazine hydrate to obtain crude silver. The key feature of this invention is that it does not require strict control of the oxidants sodium chlorate, sodium perchlorate, hydrogen peroxide, ozone, chlorine, oxygen, air, and Fe in the pre-leaching solution. 3+ Concentration is crucial, and an excess of oxidant must be added to completely oxidize and dissolve copper, bismuth, antimony, etc., converting lead into lead chloride. Silver, during oxidation, must be completely converted into combined silver chloride, not in its elemental state; otherwise, it will affect the separation of silver from other solid impurities in the subsequent sodium sulfite solution pre-leaching. Its main disadvantages include multiple pre-leaching and filtration processes, a complex process flow, and the resulting crude silver, not the GB / T 4135-2016 standard IC-Ag99.99. # silver. Summary of the Invention

[0008] The technical problem to be solved by this invention is to provide a method for improving the yield of silver ingots by removing impurities from electrolytic silver powder, overcoming the defect of existing technology that requires remelting substandard silver powder into anode plates for re-electrolytic refining; and the impurity removal process is simpler, the cost is lower, the cycle is shorter, and the labor intensity is lower; secondly, it solves the problem that existing technology has difficulty in removing impurities such as copper and tellurium.

[0009] The technical solution adopted in this invention is as follows:

[0010] A method for improving the yield of silver ingots by removing impurities from electrolytic silver powder. When all four elements (copper, lead, iron, and tellurium) in the electrolytic silver powder exceed the standard, the following first scheme is adopted; when only copper, lead, and iron elements exceed the standard, the following second scheme is adopted; and when only tellurium elements exceed the standard, the following third scheme is adopted.

[0011] Option 1:

[0012] Step 1: Prepare a mixed solution of hydrochloric acid and sodium chlorate; add the substandard silver powder into the mixed solution for pre-soaking and stirring; then heat to 50-70℃, keep warm and stir, and filter; then wash the silver powder with hot water at 60-80℃, filter and dry the resulting silver powder.

[0013] The mixed solution contains 1.5-3% hydrochloric acid by mass and 0.1-0.3% sodium chlorate by mass, with the remainder being water;

[0014] The second step involves adding soda ash and potassium nitrate to the obtained silver powder, stirring it evenly, and then carrying out oxidation slag formation and smelting; finally, removing the molten slag; and casting it to obtain silver ingots.

[0015] The added soda ash and potassium nitrate account for 1.5–2% and 0.5–1% of the mass of the silver powder obtained after filtration and drying, respectively.

[0016] Option 2:

[0017] Prepare a mixed solution of hydrochloric acid and sodium chlorate; add substandard silver powder to the mixed solution for pre-soaking and stirring; then heat to 50-70℃, keep warm and stir, and filter; then wash the silver powder with hot water at 60-80℃, filter and dry the obtained silver powder; melt and cast to obtain silver ingots.

[0018] The mixed solution contains 1.5-3% hydrochloric acid by mass and 0.1-0.3% sodium chlorate by mass, with the remainder being water;

[0019] Option 3:

[0020] Substandard silver powder is mixed with soda ash and potassium nitrate, stirred evenly, and then subjected to oxidation slag formation and smelting; finally, the molten slag is removed; and silver ingots are cast.

[0021] The added soda ash and potassium nitrate were added at 1.5-2% and 0.5-1% of the mass of the substandard silver powder, respectively.

[0022] Preferably, the liquid-to-solid ratio of the substandard silver powder to the mixed solution is (2.5-3):1.

[0023] Preferably, the heat preservation and stirring time is 40 to 60 minutes.

[0024] Preferably, the washing time for the silver powder is 10 to 15 minutes.

[0025] Preferably, the second step of the first scheme includes the following steps:

[0026] Mix the silver powder, soda ash, and potassium nitrate obtained in the first step until they are evenly stirred, and add them to half the volume of the crucible. Turn on the medium-frequency furnace to 1 / 2 to 2 / 3 of the rated power required for slow heating. Add more silver powder each time the material at the bottom of the crucible just melts and sinks. Stop adding material when the liquid level reaches 2 / 3 of the crucible volume after melting. Maintain the furnace temperature at 1000 to 1100°C after melting. Stir every 2 to 3 minutes. The slag formation time is 10 to 20 minutes. Pay attention to the gas splashing and boiling phenomenon of the melt generated by the decomposition of flux when adding material to the crucible and stirring. Then adjust the rated power and heat to 1100 to 1200°C. Remove the molten slag and cast the silver ingots.

[0027] Preferably, the third solution includes the following steps:

[0028] Mix the substandard silver powder, soda ash, and potassium nitrate thoroughly and add them to half the volume of the crucible. Turn on the medium-frequency furnace to 1 / 2 to 2 / 3 of its rated power and slowly heat up. Add more silver powder each time the material at the bottom of the crucible just melts and sinks. Stop adding material when the liquid level reaches 2 / 3 of the crucible volume after melting. Maintain the furnace temperature at 1000 to 1100°C after melting. Stir every 2 to 3 minutes. The slag formation time is 10 to 20 minutes. Pay attention to the gas splashing and boiling of the melt caused by flux decomposition during crucible addition and stirring. Then adjust the power to the rated power and heat up to 1100 to 1200°C. Remove the molten slag and cast the silver ingots.

[0029] The present invention has the following positive effects:

[0030] According to the method of this invention, the electrolytic silver powder has a large specific surface area, and the content of certain impurities such as copper, lead, iron, and tellurium in the silver powder is higher than that of the national standard IC-Ag99.99 in GB / T 4135-2016. #Silver is present, but the content of impurities is relatively low. Hydrochloric acid, which does not react with silver powder, is chosen as a co-solvent for pre-immersion. Under normal conditions, copper impurities do not react with hydrochloric acid and require an oxidizing agent to dissolve. Heating accelerates dissolution. Sodium chlorate is chosen as the oxidizing agent, and its concentration is controlled to prevent silver from oxidizing to silver chloride. This pre-immersion solution effectively removes almost all copper after oxidation and dissolution, while silver remains unoxidized and in its elemental state. Meanwhile, lead readily reacts with hydrochloric acid to form slightly water-soluble lead chloride, whose solubility increases with increasing chloride ion concentration. The solubility of lead in the electrolyzed substandard silver powder after reaction under appropriate conditions is sufficient to ensure that the lead impurities in the silver powder meet the GB / T 4135-2016 standard IC-Ag99.99 national standard 1. # The silver specifications require that iron reacts rapidly with hydrochloric acid under these conditions and dissolves completely, thus effectively removing iron from the electrolytic silver powder. After pre-soaking, the electrolytic silver powder is mixed with 1.5–2% soda ash and 0.5–1% potassium nitrate, stirred evenly, and then subjected to oxidation slag smelting. This effectively removes tellurium impurities from the silver powder. The molten slag is then removed before casting to obtain the product conforming to GB / T 4135-2016 standard IC-Ag99.99 (national standard 1). # Standard silver ingots.

[0031] This method combines silver powder pre-immersion impurity removal with oxidation slag smelting, avoiding the need to remelt substandard silver powder into anode plates for re-electrolytic refining. It quickly and effectively removes impurities such as copper, lead, and iron from electrolytic silver powder, as well as tellurium impurities that are difficult to remove using conventional techniques, ensuring compliance with GB / T 4135-2016 standard IC-Ag99.99. # The silver powder has a simpler impurity removal process, lower impurity removal cost, shorter removal cycle, lower labor intensity, and wider adaptability to impurities such as copper and tellurium.

[0032] Compared with the Chinese patent CN100360419C entitled "Separation and Refining Method of High-Purity Silver Chloride and Method for Manufacturing High-Purity Silver Using High-Purity Silver Chloride", this invention ensures that silver remains in its elemental state and that impurities such as copper, lead, and iron are effectively removed during the oxidative pre-leaching process of electrolytic silver powder. This process requires strict control of the concentration ratio of hydrochloric acid and sodium chlorate. If the amount of sodium chlorate added is too high, elemental silver will be converted into silver chloride, causing silver chloride to enter the slag. This significantly reduces the direct silver recovery rate after melting and casting, and increases the amount of recycled components. On the other hand, if the amount of sodium chlorate added is insufficient, impurities such as copper and lead contained in the substandard silver powder cannot be effectively removed.

[0033] Compared with Chinese invention patent CN113201650A, "A Process for Treating High-Silver Tellurium Gold Sludge," the tellurium removal process in CN113201650A involves adding soda ash and potassium nitrate to the surface of molten crude silver at least three times for oxidation and smelting to achieve a tellurium content of less than 0.002% in the silver anode plate. Because the crude silver has a relatively high tellurium content, this method has a significant oxidation effect. However, it requires a large dosage of reagents, resulting in a vigorous reaction. Therefore, the method of adding reagents to the surface of molten silver is used. But for materials with low tellurium content, the contact area between this reagent addition method and the tellurium impurities in the molten silver is limited, resulting in an insignificant tellurium removal effect. In contrast, this invention… The process involves pre-soaking silver powder, produced by silver electrolysis and containing excessive levels of copper, lead, iron, and tellurium, in a hydrochloric acid system with sodium chlorate. By strictly controlling the concentration of sodium chlorate, impurities such as copper, lead, and iron are effectively removed, while the silver remains essentially in its elemental state. After filtration, washing, and drying, appropriate amounts of soda ash and potassium nitrate are uniformly added to the silver powder for low-temperature oxidation smelting at 1000–1100℃. This ensures adequate reaction of the reagents and significantly increases the contact area between the reagents and the silver powder, improving the oxidation and slagging effect on the relatively trace tellurium impurities in the substandard electrolytic silver powder. This rapidly and effectively removes the small amount of tellurium from the pre-soaked silver powder, resulting in silver ingots produced by casting that meet GB / T 4135-2016 standard IC-Ag99.99. The product belongs to the national standard 1. # The silver standard, and the method of repeatedly adding soda ash and potassium nitrate to the surface of molten silver, can easily cause severe oxidation and corrosion of the crucible near the silver surface. Iron-containing substances in the refractory material of the crucible can enter the molten silver. This has no effect on the smelting of crude silver in CN113201650A, but it can cause the iron content of the finished silver ingot to exceed the standard again for electrolytic finished silver powder.

[0034] This is similar to the Chinese invention patent application CN113481371A, which describes an efficient method for recovering antimony from silver slag in lead anode mud.

[0035] Compared to methods using bismuth, copper, and silver, the raw material of this invention is substandard electrolytic silver powder, with relatively low levels of impurities such as copper, lead, and iron. The pre-impregnation process is simple, and the product conforms to GB / T 4135-2016 standard IC-Ag99.99 national standard 1. # The standard silver ingot, but the Chinese invention patent application CN113481371A, a method for efficiently recovering antimony, bismuth, copper and silver from silver slag separated from lead anode mud, has the problem of pre-leaching to remove impurities, which is complicated and produces crude silver. Detailed Implementation

[0036] The present invention will be further described below with reference to the embodiments.

[0037] The electrolytic silver powder conforms to GB / T 4135-2016 standard IC-Ag99.99 national standard 1. #The elemental requirements for silver analysis are: Cu≤0.0025%, Pb≤0.001%, Fe≤0.001%, Te≤0.0008%, Bi≤0.00008%, Sb≤0.001%, Pd≤0.001%, Se≤0.0005%. Different impurity elements in the raw materials for silver electrolysis result in different levels of impurities exceeding the standards in the produced electrolytic silver powder. Excessive levels of one, several, or all elements constitute unqualified silver powder. Copper, lead, iron, and tellurium are commonly found to exceed the standards. This invention's method is applicable to electrolytic silver powder where all four elements (copper, lead, iron, and tellurium) exceed the standards. Alternatively, depending on the specific circumstances, only a pre-immersion process for electrolytic silver powder may be used if only copper, lead, or iron exceeds the standards, while only an oxidation and slag-forming process may be used if only tellurium exceeds the standards.

[0038] Example 1 (corresponding to the first scheme)

[0039] This invention provides a method for improving the yield of silver ingots by removing impurities from electrolytic silver powder. It is applicable to the electrolytic refining and purification of silver and includes steps S1 to S8.

[0040] S1: First, the substandard silver powder was tested and analyzed. The results are shown in Table 1. All four elements, copper, lead, iron and tellurium, exceeded the standard.

[0041] S2: Add approximately 600L of water and 30L of hydrochloric acid (HCl concentration approximately 31%, hydrochloric acid accounts for 1.75% of the mass of the mixed solution) to a 1500L titanium reactor and start stirring. Add 3L of sodium chlorate solution with a concentration of approximately 18% (sodium chlorate accounts for 0.11% of the mass of the mixed solution) and stir until homogeneous.

[0042] S3: 230 kg of substandard silver powder was added to the titanium reactor (the impurity element content of the substandard silver powder is shown in Table 1. Three batches of silver powder with different levels of element exceedance were selected under the same pre-impregnation conditions. If any one of the eight impurity elements exceeds the standard, it is considered substandard silver powder), with a liquid-to-solid mass ratio of 2.77:1.

[0043] S4: Stir and heat to about 60°C, keep warm and stir for about 50 minutes, then discharge and filter.

[0044] S5: Wash with hot water at approximately 70°C for 12 minutes, then filter and dry.

[0045] S6: After pre-soaking each batch of silver powder, add 3.5 kg of soda ash (approximately 1.53% of the silver powder mass) and 1.2 kg of potassium nitrate (approximately 0.53% of the silver powder mass) to 230 kg of silver powder and stir evenly. Soda ash acts as a slagging agent, decomposing at high temperatures to produce nitrogen dioxide; potassium nitrate acts as an oxidizing agent, decomposing at high temperatures to produce oxygen.

[0046] S7: Add the silver powder ingredient to 80 #With the crucible filled to 1 / 2 capacity, turn on the medium-frequency furnace at 60 kW (rated power 100 kW) to heat up for melting, oxidation, and slag formation. Add materials as needed when the silver powder at the bottom of the crucible begins to sink and melt, until the crucible is filled to 2 / 3 capacity as expected. When adding materials to the crucible and after melting, pay special attention to the boiling and splashing of the molten gas. The furnace temperature should not be too high during the oxidation and slag formation process. Maintain the furnace temperature at approximately 1000-1100℃ after melting. Stir the molten silver liquid vigorously with a wooden stick five or six times every 2-3 minutes to ensure sufficient oxidation and slag formation. The slag formation time is approximately 12 minutes.

[0047] S8: Remove slag from the surface of the molten metal in the crucible, adjust the furnace power to 100 kW, heat to approximately 1200℃, and pour to obtain IC-Ag99.99 conforming to GB / T 4135-2016 standard. # Standard silver ingots.

[0048] Table 1. Comparison of the results of elemental analysis of various impurities before and after the electrolytic silver powder pre-leaching and oxidation slag-forming processes.

[0049]

[0050] As can be seen from the above embodiments and the data in Table 1, the present invention can quickly and effectively remove excessive impurities such as copper, lead, iron, and tellurium from electrolytic silver powder, producing a product that meets the national standard IC-Ag99.99 of GB / T 4135-2016. # The silver ingot achieved the intended objective of this invention.

[0051] Example 2 (corresponding to the second scheme)

[0052] This invention provides a method for improving the yield of silver ingots by removing impurities from electrolytic silver powder. It is applicable to the electrolytic refining and purification of silver and includes steps S1 to S6.

[0053] S1: First, the substandard silver powder was tested and analyzed. The results are shown in Table 2. Only copper, lead and iron exceeded the standard.

[0054] S2: Add approximately 600L of water and 30L of hydrochloric acid (HCl concentration approximately 31%, hydrochloric acid accounts for 1.75% of the mass of the mixed solution) to a 1500L titanium reactor and start stirring. Add 3L of sodium chlorate solution with a concentration of approximately 18% (sodium chlorate accounts for 0.11% of the mass of the mixed solution) and stir until homogeneous.

[0055] S3: 230 kg of substandard silver powder was added to the titanium reactor (the impurity element content of the substandard silver powder is shown in Table 2. Three batches of silver powder with different levels of element exceedance were selected under the same pre-impregnation conditions. If any one of the eight impurity elements exceeds the standard, it is considered substandard silver powder), with a liquid-to-solid ratio of 2.77:1.

[0056] S4: Stir and heat to about 60°C, keep warm and stir for about 50 minutes, then discharge and filter.

[0057] S5: Wash with hot water at approximately 70°C for about 12 minutes, then filter and dry.

[0058] S6: Melting and casting in an induction furnace yields IC-Ag99.99 conforming to GB / T 4135-2016 standard. # Standard silver ingots.

[0059] Table 2. Comparison of the results of elemental analysis of impurities before and after pre-immersion of electrolytic silver powder.

[0060]

[0061] As can be seen from the above embodiments and the data in Table 2, the present invention can quickly and effectively remove excessive copper, lead, and iron impurities from electrolytic silver powder, producing a product that meets the national standard IC-Ag99.99 of GB / T 4135-2016. # The silver ingot achieved the intended objective of this invention.

[0062] Example 3 (corresponding to the third scheme)

[0063] This invention provides a method for improving the yield of silver ingots by removing impurities from electrolytic silver powder. It is applicable to the electrolytic refining and purification of silver and includes steps S1 to S4.

[0064] S1: First, the substandard silver powder was tested and analyzed. The results are shown in Table 3. Only the tellurium element exceeded the standard.

[0065] S2: Take 200kg of substandard silver powder and mix it with 3.2kg of soda ash (approximately 1.60% of the silver powder mass) and 1.2kg of potassium nitrate (approximately 0.60% of the silver powder mass) and stir evenly. Soda ash is a slag-forming agent that decomposes at high temperature to produce nitrogen dioxide; potassium nitrate is an oxidizing agent that decomposes at high temperature to produce oxygen.

[0066] S3: Add the silver powder ingredient to 80 # With the crucible filled to 1 / 2 capacity, turn on the medium-frequency furnace at 60 kW (rated power 100 kW) to heat up for melting, oxidation, and slag formation. Add materials as needed when the silver powder at the bottom of the crucible begins to sink and melt, until the crucible is filled to 2 / 3 capacity as expected. When adding materials to the crucible and after melting, pay special attention to the boiling and splashing of the molten gas. The furnace temperature should not be too high during the oxidation and slag formation process. Maintain the furnace temperature at approximately 1000-1100℃ after melting. Stir the molten silver liquid vigorously with a wooden stick five or six times every 2-3 minutes to ensure sufficient oxidation and slag formation. The slag formation time is approximately 12 minutes.

[0067] S4: Remove slag from the surface of the molten metal in the crucible, adjust the furnace power to 100 kW, heat to approximately 1200℃, and pour to obtain IC-Ag99.99 conforming to GB / T 4135-2016 standard. # Standard silver ingots.

[0068] Table 3. Comparison of the results of elemental analysis of various impurities before and after oxidation and slag formation of electrolytic silver powder.

[0069]

[0070] As can be seen from the above embodiments and the data in Table 3, the present invention can quickly and effectively remove tellurium-containing impurities from electrolytic silver powder, producing a product that meets the national standard IC-Ag99.99 of GB / T 4135-2016. # The silver ingot achieved the intended objective of this invention.

Claims

1. A method for improving the yield of silver ingots by removing impurities from electrolytic silver powder, characterized in that... Based on the national standard GB / T4135-2016 IC-Ag99.99 grade, when all four elements (copper, lead, iron, and tellurium) in the electrolytic silver powder exceed the standard, the following first scheme shall be adopted; when only copper, lead, and iron elements in the electrolytic silver powder exceed the standard, the following second scheme shall be adopted; when only tellurium elements in the electrolytic silver powder exceed the standard, the following third scheme shall be adopted. Option 1: Step 1: Prepare a mixed solution of hydrochloric acid and sodium chlorate; add the substandard silver powder into the mixed solution for pre-soaking and stirring; then heat to 50-70℃, keep warm and stir, and filter; then wash the silver powder with hot water at 60-80℃, filter and dry the resulting silver powder. The mixed solution contains 1.5-3% hydrochloric acid by mass and 0.1-0.3% sodium chlorate by mass, with the remainder being water; The second step involves adding soda ash and potassium nitrate to the obtained silver powder, stirring it evenly, and then carrying out oxidation slag formation and smelting; finally, removing the molten slag; and casting it to obtain silver ingots. The added soda ash and potassium nitrate account for 1.5–2% and 0.5–1% of the mass of the silver powder obtained after filtration and drying, respectively. Option 2: Prepare a mixed solution of hydrochloric acid and sodium chlorate; add substandard silver powder to the mixed solution for pre-soaking and stirring; then heat to 50-70℃, keep warm and stir, and filter; then wash the silver powder with hot water at 60-80℃, filter and dry the obtained silver powder; melt and cast to obtain silver ingots. The mixed solution contains 1.5-3% hydrochloric acid by mass and 0.1-0.3% sodium chlorate by mass, with the remainder being water; Option 3: Substandard silver powder is mixed with soda ash and potassium nitrate, stirred evenly, and then subjected to oxidation slag formation and smelting; finally, the molten slag is removed; and silver ingots are cast. The added soda ash and potassium nitrate were added at 1.5-2% and 0.5-1% of the mass of the substandard silver powder, respectively.

2. The method for improving the yield of silver ingots by removing impurities from electrolytic silver powder as described in claim 1, characterized in that: The liquid-to-solid ratio of the substandard silver powder to the mixed solution is (2.5-3):

1.

3. The method for improving the yield of silver ingots by removing impurities from electrolytic silver powder as described in claim 1, characterized in that: The time for heat preservation and stirring is 40 to 60 minutes.

4. The method for improving the yield of silver ingots by removing impurities from electrolytic silver powder as described in claim 1, characterized in that: The washing time for silver powder is 10 to 15 minutes.

5. The method for improving the yield of silver ingots by removing impurities from electrolytic silver powder as described in claim 1, characterized in that... The second step of the first plan includes the following steps: Mix the silver powder, soda ash, and potassium nitrate obtained in the first step until they are evenly stirred, and add them to half the volume of the crucible. Turn on the medium-frequency furnace to 1 / 2 to 2 / 3 of the rated power required for slow heating. Add more silver powder each time the material at the bottom of the crucible just melts and sinks. Stop adding material when the liquid level reaches 2 / 3 of the crucible volume after melting. Maintain the furnace temperature at 1000 to 1100°C after melting. Stir every 2 to 3 minutes. The slag formation time is 10 to 20 minutes. Pay attention to the gas splashing and boiling phenomenon of the melt generated by the decomposition of flux when adding material to the crucible and stirring. Then adjust the rated power and heat to 1100 to 1200°C. Remove the molten slag and cast the silver ingots.

6. The method for improving the yield of silver ingots by removing impurities from electrolytic silver powder as described in claim 1, characterized in that... The third option includes the following steps: Mix the substandard silver powder, soda ash, and potassium nitrate thoroughly and add them to half the volume of the crucible. Turn on the medium-frequency furnace to 1 / 2 to 2 / 3 of its rated power and slowly heat up. Add more silver powder each time the material at the bottom of the crucible just melts and sinks. Stop adding material when the liquid level reaches 2 / 3 of the crucible volume after melting. Maintain the furnace temperature at 1000 to 1100°C after melting. Stir every 2 to 3 minutes. The slag formation time is 10 to 20 minutes. Pay attention to the gas splashing and boiling of the melt caused by flux decomposition during crucible addition and stirring. Then adjust the power to the rated power and heat up to 1100 to 1200°C. Remove the molten slag and cast the silver ingots.

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