A method for recovering silver from conductive silver paste

Abstract

This invention belongs to the field of metallurgy and relates to a method for recovering silver from conductive silver paste. The method includes the following steps: S1, spray drying the conductive silver paste to obtain fine silver powder, and ball milling the fine silver powder to obtain a slurry; S2, clarifying and thickening the slurry to obtain a supernatant and a slurry underflow; pressure filtering the supernatant, and returning the filtrate to the ball mill; S3, adding methanesulfonic acid to the slurry underflow for leaching, controlling the time to 10-30 minutes, to obtain a leachate; filtering the leachate, the filter residue being silver powder; returning the filtrate for further leaching, and evaporating and crystallizing the filtrate after the Ag ion concentration in the filtrate reaches saturation to obtain silver methanesulfonate. The method of this invention has selective leaching characteristics for Ag₂O and Ag, and has the advantages of simple process flow, short reaction time, and high product purity, making it highly promising for industrial application.

Description

Technical Field

[0001] This invention belongs to the field of metallurgy and relates to a method for recovering silver from conductive silver paste. Background Technology

[0002] Conductive silver paste is mainly used in thin and thick film conductive circuits, ceramics or solar cells, aerospace, displays and other fields. my country's demand for silver paste reaches thousands of tons every year. If the discarded conductive silver paste is not centrally recycled and disposed of, but is landfilled or incinerated with household waste, the leaching of heavy metals will cause pollution of soil, water and air, thereby endangering human health.

[0003] Silver recovery methods from silver-containing waste are broadly classified into pyrometallurgical and hydrometallurgical processes. Pyrometallurgical processes utilize high temperatures to extract silver and other metals and their compounds from silver-containing waste. However, pyrometallurgical smelting consumes significant amounts of energy, produces gases that severely pollute the air, has low recovery rates, and is complex, requiring high levels of expertise in equipment, temperature control, and operator skill. Hydrometallurgical processes typically utilize the different solubilities of silver and other metals in solvents to extract silver or other impurities. Commonly used leaching chemicals include concentrated sulfuric acid, nitric acid, strong alkalis, and thiourea. After leaching the silver, it is then separated and purified. However, these solvents present problems such as high corrosivity to equipment, low silver recovery rates, and environmentally unfriendly processes.

[0004] Existing technology 201310684293.5 uses hydrochloric acid aqueous solution as the leaching agent in a two-stage countercurrent leaching process to allow valuable metals such as iron, silver, copper, lead, zinc, and arsenic in the slag iron concentrate to enter the leaching solution. The leaching solution is purified using processes such as iron powder replacement, pH control for arsenic precipitation, and sulfide precipitation to separate valuable metals such as copper, silver, lead, zinc, and arsenic. The purified solution is a pure FeCl2 aqueous solution, which is then spray-dried to obtain Fe2O3 powder. The generated HCl gas is absorbed by water and regenerated into hydrochloric acid, which is then returned to the leaching process. This existing technology operates at a temperature range of 400–1000℃, which is relatively high and energy-intensive. Furthermore, since this existing technology uses hydrochloric acid as the leaching agent, and AgCl is a precipitate, it is impossible to leach silver into the solution using hydrochloric acid, thus making it difficult to recover silver from the zinc slag. In addition, the existing technology uses spray pyrolysis, which requires high temperatures and generates a large amount of corrosive HCl gas, which will shorten the service life of the spray pyrolysis equipment and pipelines.

[0005] Existing technology 201010237032.5 involves crushing or spray-drying copper-, lead-, and silver-containing materials, followed by oxidative leaching with hydrogen peroxide in a nitric acid solution. The leaching residue is washed to recover other precious metals. Sodium chloride, sodium sulfate, and sodium carbonate are added sequentially to the leaching solution to recover silver, lead, and copper, respectively. The pH of the solution is adjusted with nitric acid, and then evaporated to crystallize and produce sodium nitrate. Water vapor containing nitrogen oxides generated in each step is absorbed by an aqueous solution containing hydrogen peroxide and returned to the oxidative leaching process, achieving a pollution-free and zero-emission production process. However, this existing technology uses nitric acid as the leaching agent and hydrogen peroxide as the oxidant. Nitric acid and hydrogen peroxide are strong oxidants, and nitric acid is highly corrosive and acidic, severely corroding equipment materials and pipelines. Nitric acid also easily decomposes to generate nitrogen oxides, posing a significant potential environmental risk if not properly disposed of. The silver product obtained by this existing technology is silver chloride precipitate, and the silver purity in this precipitate is low.

[0006] The existing technology (Li Yangxing, Jiang Changyin, Wan Chunrong, et al. Preparation of LiCoO2 ultrafine powder by spray drying [J]. Journal of Inorganic Materials, 1999(04):146-149.DOI:10.3321 / j.issn:1000-324X.1999.04.025.CN103073125) discloses the drying of a mixed solution of lithium acetate and cobalt acetate using an airflow spray dryer, employing a co-flow drying method, using a two-flow nozzle for the atomization device, and using a peristaltic pump to feed the solution at a rate of 12-20 mL / min; the nozzle gas flow rate is controlled by the pressure of compressed air at approximately 0.1 MPa to generate atomization; the air inlet temperature is controlled at 300℃ and the outlet temperature at 100℃; the outlet air is vented after a first-stage vortex separation, and the spray drying yields a mixed powder of polyethylene glycol, lithium acetate, and cobalt acetate. However, this method is used for pure liquid solutions and is not suitable for slurries. Summary of the Invention

[0007] This invention provides a method for recovering silver from conductive silver paste.

[0008] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0009] A method for recovering silver from conductive silver paste includes the following steps:

[0010] S1. Spray dry the conductive silver paste to obtain fine silver powder, and ball mill the fine silver powder to obtain a slurry;

[0011] S2. The slurry is clarified and thickened to obtain supernatant and slurry underflow; the supernatant is pressure filtered, and the filtrate is returned to the ball mill;

[0012] S3. Add methanesulfonic acid to the underflow of the slurry for leaching, controlling the time to 10-30 minutes to obtain the leachate; filter the leachate, and the filter residue is silver powder; return the filtrate to continue leaching, and after the Ag ion concentration in the filtrate reaches saturation, evaporate and crystallize to obtain silver methanesulfonate.

[0013] In one preferred embodiment, the spray drying process in step S1 is as follows: a co-current spray dryer is used for drying; a two-flow nozzle is used for atomization, and a peristaltic pump is used for injection at a rate of 10-20 mL / min; the nozzle gas flow rate is controlled by the pressure of compressed air or nitrogen, and atomization is generated at a pressure of 0.03-0.10 MPa; the inlet temperature of compressed air or nitrogen is controlled at 220-290°C, and the outlet temperature is controlled at 150-220°C.

[0014] In the spray drying process, 1) if the injection speed is too fast, the sample drying intensity will be insufficient and the conductive silver paste at the outlet will still be in paste form; if the injection speed is too slow, the drying efficiency will be too low and energy consumption will be wasted.

[0015] 2) When compressed air is used for pressure control, the presence of oxygen in the air will partially oxidize the silver in the conductive silver paste. The oxidized silver oxide is more likely to react with methanesulfonic acid to form silver methanesulfonate. When nitrogen is used for pressure control, nitrogen is an inert gas. Therefore, the silver in the conductive silver paste is basically not oxidized during the spray drying process. Thus, the reaction of methanesulfonic acid with silver oxide can be controlled to produce silver methanesulfonate, while the remaining silver is a metallic silver powder product.

[0016] 3) If the pressure is too low, the droplet atomization power will be insufficient, the particle size will not be fine enough, and the drying effect will be poor; if the pressure is too high, the spraying will be too fast and the temperature residence time will be too short, which will also result in poor drying effect.

[0017] 4) If the inlet temperature is too low, the drying effect will be incomplete, and the material will still be in a slurry state; if the inlet temperature is too high, the drying efficiency will be too fast, which will easily cause particle coarsening and energy waste.

[0018] 5) If the outlet temperature is too low, the evaporating water mist will easily condense and block the pipe, or fall back onto the material, resulting in incomplete drying of the material; if the outlet temperature is too high, the temperature gradient between the inlet and outlet will be too small, resulting in poor drying effect.

[0019] If the drying effect is poor or incomplete, the silver paste contains a large amount of wet organic matter, which has a certain cementing effect, thus hindering the leaching reaction process and affecting the leaching effect.

[0020] In one preferred embodiment, in step S1, the silver powder is ball-milled using zirconium beads.

[0021] Zirconium beads have high hardness, making them less prone to introducing impurities, and the finely ground material has a more uniform particle size and fewer micro-defects.

[0022] In one preferred embodiment, in step S1, the ball milling time is 20 min to 60 min, and the rotation speed is 500 to 1000 r / min.

[0023] If the ball milling time is too long or the speed is too fast, the silver powder will not be refined further, resulting in energy waste; if the ball milling time is too short or too slow, the silver powder will not be refined sufficiently, which is not conducive to the subsequent leaching process.

[0024] In one preferred embodiment, in step S1, the particle size of the slurry is 600-800 mesh.

[0025] In one preferred embodiment, the slurry clarification time is 20 min to 60 min, and the mass concentration of the underflow is controlled at 30 to 50% during the thickening process.

[0026] In one preferred embodiment, in step S2, the supernatant is pressure filtered to obtain carbon residue.

[0027] In one preferred embodiment, the leaching process with added methanesulfonic acid is as follows: liquid-to-solid ratio 1:1 to 5:1, leaching temperature 20 to 60°C, leaching time 10 to 30 minutes, stirring intensity controlled at 100 to 600 r / min, and the mass ratio of conductive silver paste dry material to methanesulfonic acid 1 to 3:1.

[0028] In the process of methanesulfonic acid leaching, 1) if the liquid-to-solid ratio is too small, less than 1:1, it is difficult to stir, the reaction is incomplete, and the liquid-to-solid separation is not good; if the liquid-to-solid ratio is too large, greater than 5:1, the volume of the reaction vessel will be increased, the unit processing capacity will be weakened, and there will be no significant improvement in the leaching efficiency of Ag.

[0029] 2) If the leaching temperature is too low, the reaction rate will be slowed down, resulting in insufficient Ag2O reaction in the same amount of time, which will affect the silver grade of the obtained silver powder; if the leaching temperature is too high, the reaction rate will be accelerated appropriately, but the improvement is not significant and will also lead to energy waste.

[0030] 3) If the leaching time is too short, the reaction will be incomplete, which will affect the silver grade of the obtained silver powder; if the reaction time is too long, in addition to wasting energy, some of the silver powder will be reacted with methanesulfonic acid to form silver methanesulfonate, which will affect the composition of the product.

[0031] 4) If the stirring intensity is too low, the reaction rate will be weakened, resulting in insufficient Ag2O reaction in the same amount of time, which in turn affects the silver grade of the obtained metallic silver powder; if the stirring speed is too high, the reaction rate will be accelerated appropriately, but the improvement is not significant and will also lead to energy waste.

[0032] 5) If the mass ratio of conductive silver paste dry material to methanesulfonic acid is too small, the amount of methanesulfonic acid will be too large, resulting in insufficient capacity to process conductive silver paste and affecting processing efficiency; if the mass ratio of conductive silver paste dry material to methanesulfonic acid is too large, the amount of methanesulfonic acid will be too small, resulting in insufficient Ag2O reaction and thus affecting the silver grade of the obtained metallic silver powder.

[0033] The present invention will be further explained below:

[0034] This invention directly spray-dries waste conductive silver paste to obtain solid silver powder of a specific particle size. Waste conductive silver paste is in a liquid, gel-like state. Conventional drying processes are difficult to employ with conventional equipment such as rotary kilns, drying drums, disc dryers, and mesh belt dryers. Furthermore, the pre-drying process of this invention aims to remove organic matter and moisture from the waste conductive silver paste and obtain powder of a suitable particle size. These two objectives are difficult to achieve simultaneously with conventional drying equipment. Because the organic solvents in the silver paste evaporate rapidly during spray drying, a small amount of carbon residue remains mixed with the silver powder. Therefore, this invention employs a wet ball milling process to further refine the silver powder obtained from the spray drying process. This carbon residue is then allowed to float on the surface of the water. Additionally, any remaining organic solvents from the previous process can be further removed. The supernatant is then concentrated and filtered to obtain the carbon residue. The underflow from the concentrated solution consists of silver powder and silver oxide. Considering the composition of silver phases and the varying ratios of silver oxide and silver achieved by controlling the spray drying atmosphere, a methanesulfonic acid leaching process is employed. By controlling the conditions, the silver oxide is fully reacted, resulting in two products: a portion of high-purity silver powder and a portion of silver methanesulfonate.

[0035] The water used in wet ball milling mainly comes from the filtrate obtained by filtering the supernatant after thickening. If the thickening and clarification process is not thorough, this part of the filtrate will be returned to the previous wet milling process, which will result in incomplete wet milling of the conductive silver paste dry powder. The organic matter remaining in the returned filtrate will coat and bind the powder, making it difficult for the carbon slag and conductive silver powder to be completely separated in the wet ball milling process. This will affect the purity of the silver powder obtained in the subsequent methanesulfonic acid leaching process and the purity of the silver methanesulfonate product obtained in the subsequent evaporation and crystallization process.

[0036] Silver methanesulfonate has a solubility saturation in aqueous solution. The solubility of Ag in methanesulfonic acid is 713 g / L (23℃). When the concentration exceeds this, precipitation will occur. Therefore, silver methanesulfonate is obtained by reacting a concentrated conductive silver paste underflow with methanesulfonic acid. Since the AgO content varies depending on the spray drying process, the concentration of silver methanesulfonate will also differ. Initially, the Ag ion concentration in the solution is not saturated and can be used as a leaching agent to further leach the conductive silver paste underflow. If the silver methanesulfonate-containing leachate obtained after the reaction of the conductive silver paste underflow with methanesulfonic acid is not reused for leaching, some methanesulfonic acid will be wasted, and the purity of the silver methanesulfonate obtained from evaporation and crystallization will decrease. However, when this concentration approaches the saturation solubility, re-leaching will affect the leaching effect of AgO, thus weakening the effective separation of Ag and AgO, and significantly reducing the purity of the resulting silver powder and silver methanesulfonate products.

[0037] The main chemical reactions involved in this invention include:

[0038] Ag + O₂ = Ag₂O

[0039] Ag2O+CH3SO3H=Ag(CH3SO3)+H2O.

[0040] The beneficial effects of this invention are as follows:

[0041] (1) The spray drying process is used to replace the conventional kiln drying process, so as to achieve rapid volatilization of the conductive silver paste liquid phase and obtain silver powder particles with uniform distribution. The phase transformation degree of silver-containing materials can be selectively controlled by using hot air / nitrogen as carrier through the atomization process, thereby producing different product solutions.

[0042] (2) The carbon slag was refined by wet ball milling, and the carbon slag and silver powder were efficiently separated by thickened supernatant hydraulic filtration, with a carbon slag recovery rate of over 99.95%.

[0043] (3) The leaching agent is methanesulfonic acid, which has selective leaching characteristics for Ag2O and Ag. It has high silver solubility, low equipment corrosion, easy biodegradability, low environmental pressure, simple process flow, short reaction time, realizes the enrichment and separation of silver and silver oxide, and produces two products: metallic silver powder and silver methanesulfonate. The products have high purity, and through process control, the product scheme can also be converted, that is, the output of metallic silver powder and silver methanesulfonate can be appropriately changed according to market demand.

[0044] Therefore, this invention has the advantages of simple process, high silver extraction rate in conductive silver paste, energy saving, environmental friendliness, high safety, and great prospects for industrial application. Attached Figure Description

[0045] Figure 1 This is a process roadmap for the recovery of conductive silver paste. Detailed Implementation

[0046] Example 1

[0047] like Figure 1 As shown, 1000 mL of waste conductive silver paste was measured and dried using a co-flow drying method. The atomization device used a two-flow nozzle, and the feed solution was injected using a peristaltic pump at a rate of 15 mL / min. The nozzle gas flow rate was controlled by the compressed air pressure, and atomization was achieved at 0.10 MPa. The compressed air inlet temperature was controlled at 280℃, and the outlet temperature at 190℃. The outlet air was discharged after passing through a primary vortex separator and tail gas treatment. The silver paste was spray-dried to obtain fine silver powder with a particle size of -200 mesh accounting for 95%.

[0048] The silver powder was produced by zirconium bead ball milling with a ball-to-powder ratio of 8:1, a milling time of 30 minutes, and a rotation speed of 800 r / min to obtain a slurry with a particle size of -800 mesh accounting for 50%.

[0049] After ball milling, the slurry is clarified for 30 minutes, with the concentration controlled at 40% in the underflow. The resulting supernatant contains floating matter; after pressure filtration, carbon residue is obtained, and the filtrate is returned to the ball milling process. The underflow of the slurry is then introduced into a selective leaching process using methanesulfonic acid. This process controls the liquid-to-solid ratio at 3:1, the leaching temperature at 30℃, the leaching time at 20 minutes, and the stirring intensity at 500 rpm. The initial silver powder / methanesulfonic acid mass ratio is 2:1. After leaching, the filtrate is filtered, yielding a silver methanesulfonate solution and silver powder as the residue, with a silver purity of 99.9%. The filtrate, now a silver methanesulfonate solution, is returned for further leaching. After saturation, the filtrate is evaporated and crystallized to obtain silver methanesulfonate product with a purity of 99.99%. At this point, the ratio of silver mass in the silver powder to (silver mass in the silver powder + silver mass in the silver methanesulfonate) is 1:3.

[0050] Comparative Example 1

[0051] 1000 mL of waste conductive silver paste was measured and dried using a co-flow drying method with a two-flow nozzle atomization device. The feed solution was injected using a peristaltic pump at a rate of 15 mL / min. The nozzle gas flow rate was controlled by the compressed air pressure, and atomization was achieved at 0.10 MPa. The compressed air inlet temperature was controlled at 200℃ and the outlet temperature at 190℃. The outlet air was discharged after primary vortex separation and tail gas treatment. No fine silver powder was obtained from the silver paste after spray drying.

[0052] Compared with Example 1, Comparative Example 1 has a lower inlet temperature limit than the gas in the spray drying process, so the liquid silver paste cannot be turned into solid silver powder, and subsequent processes cannot be carried out.

[0053] Comparative Example 2

[0054] 1000 mL of waste conductive silver paste was measured and dried using a co-flow drying method. The atomization device used a two-flow nozzle, and the feed solution was injected by a peristaltic pump at a rate of 15 mL / min. The gas flow rate of the nozzle was controlled by the compressed air pressure, and atomization was achieved at 0.10 MPa. The inlet temperature of the compressed air was controlled at 350℃, and the outlet temperature was controlled at 190℃. The outlet air was discharged after passing through a primary vortex separator and tail gas treatment. The silver paste was spray-dried to obtain fine silver powder with a particle size of -200 mesh accounting for 96%.

[0055] The silver powder was produced by zirconium bead ball milling with a ball-to-powder ratio of 8:1, a milling time of 30 minutes, and a rotation speed of 800 r / min to obtain a slurry with a particle size of -800 mesh accounting for 50%.

[0056] After ball milling, the slurry is clarified for 30 minutes. The resulting supernatant contains floating matter, which is filtered to obtain carbon residue. The filtrate is returned to the ball milling process. The slurry underflow is then fed into a selective leaching process. This process controls the liquid-to-solid ratio at 3:1, the leaching temperature at 30℃, the leaching time at 20 minutes, and the stirring intensity at 500 r / min. The initial silver powder / methanesulfonic acid mass ratio is 2:1. After leaching, the filtrate is filtered, yielding a silver methanesulfonate solution and silver powder as the residue, with a silver content of 99.9%. The filtrate, now a silver methanesulfonate solution, is returned for further leaching. After saturation, the filtrate is evaporated and crystallized to obtain the silver methanesulfonate product. At this point, the ratio of the mass of silver in the silver powder to the mass of silver in the silver powder plus the mass of silver in the silver methanesulfonate is 1:3.5.

[0057] Compared with Example 1, Comparative Example 2 has a higher inlet temperature than the upper limit of the gas in the spray drying process. Liquid silver paste can also be converted into solid silver powder. However, increasing the temperature will increase energy consumption and has no significant impact on the silver content in crude silver. In addition, it also reduces the proportion of silver in silver powder.

[0058] Comparative Example 3

[0059] 1000 mL of waste conductive silver paste was measured and dried using a co-flow drying method. The atomization device used a two-flow nozzle, and the feed solution was injected by a peristaltic pump at a rate of 15 mL / min. The gas flow rate of the nozzle was controlled by the compressed air pressure, and atomization was achieved at 0.10 MPa. The inlet temperature of the compressed air was controlled at 280℃, and the outlet temperature was controlled at 190℃. The outlet air was discharged after passing through a primary vortex separator and tail gas treatment. The silver paste was spray-dried to obtain fine silver powder with a particle size of -200 mesh accounting for 95%.

[0060] The silver powder was produced by zirconium bead ball milling with a ball-to-powder ratio of 8:1, a milling time of 30 minutes, and a rotation speed of 800 r / min to obtain a slurry with a particle size of -800 mesh accounting for 50%.

[0061] After ball milling, the slurry was clarified for 30 minutes. The resulting supernatant contained floating matter, which was then filtered to obtain carbon residue. The filtrate was returned to the ball milling process. The slurry underflow was then fed into a selective leaching process. This process controlled the liquid-to-solid ratio at 3:1, the leaching temperature at 30℃, the leaching time at 20 minutes, and the stirring intensity at 500 r / min. The initial silver powder / sulfuric acid mass ratio was 2:1. After leaching, the filtrate was filtered. The filtrate consisted of sulfuric acid and trace amounts of silver sulfate, while the filter residue was a mixture of silver sulfate and coarse silver powder, with a silver content of only 80.5%.

[0062] Compared with Example 1, Comparative Example 3 uses inorganic acid sulfuric acid as a leaching agent, which cannot achieve efficient separation of silver in conductive silver paste or separate enrichment of products, resulting in products with low silver content.

[0063] Comparative Example 4

[0064] 1000 mL of waste conductive silver paste was measured and dried using a co-flow drying method. The atomization device used a two-flow nozzle, and the feed solution was injected by a peristaltic pump at a rate of 15 mL / min. The gas flow rate of the nozzle was controlled by the compressed air pressure, and atomization was achieved at 0.10 MPa. The inlet temperature of the compressed air was controlled at 280℃, and the outlet temperature was controlled at 190℃. The outlet air was discharged after passing through a primary vortex separator and tail gas treatment. The silver paste was spray-dried to obtain fine silver powder with a particle size of -200 mesh accounting for 95%.

[0065] The silver powder was produced by zirconium bead ball milling with a ball-to-powder ratio of 8:1, a milling time of 30 minutes, and a rotation speed of 800 r / min to obtain a slurry with a particle size of -800 mesh accounting for 50%.

[0066] After ball milling, the slurry was clarified for 30 minutes. The resulting supernatant contained floating matter, which was then filtered to obtain carbon residue. The filtrate was returned to the ball milling process. The slurry underflow was then fed into a selective leaching process. This process controlled the liquid-to-solid ratio at 3:1, the leaching temperature at 30℃, the leaching time at 20 minutes, and the stirring intensity at 500 r / min. The initial silver powder / hydrochloric acid mass ratio was 2:1. After leaching, the filtrate was filtered. The filtrate consisted of hydrochloric acid and trace amounts of silver chloride, while the filter residue was a mixture of silver chloride, silver oxide, and coarse silver powder, with a silver content of only 72.3%.

[0067] Compared with Example 1, Comparative Example 4 uses an inorganic acid salt as the leaching agent, which cannot achieve efficient separation of silver in the conductive silver paste or separate enrichment of the product, resulting in a product with low silver content. Furthermore, Comparative Example 4 uses essentially the same leaching agent as the prior art 201310684293.5, but it still cannot achieve efficient silver recovery and purification.

[0068] Comparison document 5

[0069] 1000 mL of waste conductive silver paste was measured and dried using a co-flow drying method with a two-flow nozzle atomization device. The feed solution was injected by a peristaltic pump at a rate of 30 mL / min. The nozzle gas flow rate was controlled by the compressed air pressure, and atomization was achieved at 0.10 MPa. The compressed air inlet temperature was controlled at 280℃ and the outlet temperature at 190℃. The outlet air was discharged after primary vortex separation and tail gas treatment. After spray drying, the silver paste remained in a silver paste state, and no dry silver powder was obtained.

[0070] Compared with Example 1, Comparative Example 5 had a gas feed rate greater than the upper limit of the spray drying process, which meant that the silver paste was not completely dried and could not be used for subsequent operations.

[0071] Comparative Example 6

[0072] 1000 mL of waste conductive silver paste was measured and dried using a co-flow drying method. The atomization device employed a two-flow nozzle, and the feed solution was injected using a peristaltic pump at a rate of 5 mL / min. The nozzle gas flow rate was controlled by compressed air pressure, with atomization achieved at 0.10 MPa. The inlet temperature of the compressed air was controlled at 280℃, and the outlet temperature at 190℃. The outlet air was discharged after primary vortex separation and tail gas treatment. The silver paste was spray-dried to obtain fine silver powder with a particle size of -200 mesh accounting for 95%.

[0073] The silver powder was produced by zirconium bead ball milling with a ball-to-powder ratio of 8:1, a milling time of 30 minutes, and a rotation speed of 800 r / min to obtain a slurry with a particle size of -800 mesh accounting for 50%.

[0074] After ball milling, the slurry was clarified for 30 minutes. The resulting supernatant contained floating matter, which was filtered to obtain carbon residue. The filtrate was returned to the ball milling process. The slurry underflow was then fed into a selective leaching process. This process controlled the liquid-to-solid ratio at 3:1, the leaching temperature at 30℃, the leaching time at 20 minutes, and the stirring intensity at 500 rpm. The initial silver powder / methanesulfonic acid mass ratio was 2:1. After leaching, the filtrate was filtered, yielding a silver methanesulfonate solution and silver powder as the residue, with a silver content of 99.9%. The filtrate, now a silver methanesulfonate solution, was returned for further leaching. After saturation, the filtrate was evaporated and crystallized to obtain the silver methanesulfonate product. At this point, the ratio of the mass of silver in the silver powder to the mass of silver in the silver powder plus the mass of silver in the silver methanesulfonate was 1:3.

[0075] Compared with Example 1, Comparative Example 6 had a lower feed rate than the lower limit of the gas feed rate in the spray drying process. Although it achieved the basic drying effect and had little impact on the subsequent leaching and separation effect, the reduced material feed rate weakened the processing capacity and was not conducive to production.

[0076] Comparative Example 7

[0077] 1000 mL of waste conductive silver paste was measured and dried using a co-flow drying method. The atomization device used a two-flow nozzle, and the feed solution was injected by a peristaltic pump at a rate of 15 mL / min. The gas flow rate of the nozzle was controlled by the compressed air pressure, and atomization was achieved at 0.01 MPa. The inlet temperature of the compressed air was controlled at 280℃, and the outlet temperature was controlled at 190℃. The outlet air was discharged after passing through a primary vortex separator and tail gas treatment. After spray drying, no dry silver powder was obtained from the silver paste.

[0078] Compared with Example 1, Comparative Example 7 has a pressure control limit lower than that of the spray drying process. Due to the low pressure, the droplet atomization power is insufficient, the particle size is not fine enough, and some parts are not completely dried, remaining as a slurry.

[0079] Comparative Example 8

[0080] 1000 mL of waste conductive silver paste was measured and dried using a co-flow drying method. The atomization device used a two-flow nozzle, and the feed solution was injected by a peristaltic pump at a rate of 15 mL / min. The gas flow rate of the nozzle was controlled by the compressed air pressure, and atomization was achieved at 0.35 MPa. The inlet temperature of the compressed air was controlled at 280℃, and the outlet temperature was controlled at 190℃. The outlet air was discharged after primary vortex separation and tail gas treatment. After spray drying, no dry silver powder was obtained from the silver paste.

[0081] Compared with Example 1, Comparative Example 8 exceeded the upper limit of pressure control in the spray drying process. Excessive pressure caused the silver paste droplets to be sprayed too quickly and the residence time in the high-temperature gas to be too short, resulting in poor liquid phase volatilization and some of the material remaining as a paste.

[0082] Comparative Example 9

[0083] 1000 mL of waste conductive silver paste was measured and dried using a co-flow drying method. The atomization device used a two-flow nozzle, and the feed solution was injected by a peristaltic pump at a rate of 15 mL / min. The gas flow rate of the nozzle was controlled by the compressed air pressure, and atomization was achieved at 0.10 MPa. The inlet temperature of the compressed air was controlled at 280℃, and the outlet temperature was controlled at 190℃. The outlet air was discharged after passing through a primary vortex separator and tail gas treatment. The silver paste was spray-dried to obtain fine silver powder with a particle size of -200 mesh accounting for 95%.

[0084] The silver powder was produced by zirconium bead ball milling with a ball-to-powder ratio of 8:1, a milling time of 30 minutes, and a rotation speed of 800 r / min to obtain a slurry with a particle size of -800 mesh accounting for 50%.

[0085] After ball milling, the slurry was clarified for 30 minutes. The resulting supernatant contained floating matter, which was filtered to obtain carbon residue. The filtrate was returned to the ball milling process. The slurry underflow was then fed into a selective leaching process. This process controlled the liquid-to-solid ratio at 0.5:1, the leaching temperature at 30℃, the leaching time at 20 minutes, and the stirring intensity at 500 r / min. The initial silver powder / methanesulfonic acid mass ratio was 2:1. After leaching, filtration was difficult, and the silver powder and silver methanesulfonate were difficult to separate into liquid and solid components, thus failing to obtain silver methanesulfonate and high-purity silver powder products.

[0086] Compared with Example 1, Comparative Example 9 has a liquid-solid ratio lower than the lower limit of the leaching process. The liquid-solid ratio is too small, which makes it difficult to stir, the reaction is incomplete, and the liquid-solid separation is poor, thus making it impossible to obtain silver mesylate and high-purity silver powder products.

[0087] Comparative Example 10

[0088] 1000 mL of waste conductive silver paste was measured and dried using a co-current drying method. The atomization device used a two-flow nozzle, and the feed solution was injected by a peristaltic pump at a rate of 15 mL / min. The nozzle gas flow rate was controlled by the compressed air pressure, and atomization was achieved at 0.10 MPa. The inlet temperature of the compressed air was controlled at 280℃, and the outlet temperature at 190℃. The outlet air was discharged after passing through a primary vortex separator and tail gas treatment. The silver paste was spray-dried to obtain fine silver powder with a particle size of -200 mesh accounting for 95%.

[0089] The silver powder was produced by zirconium bead ball milling with a ball-to-powder ratio of 8:1, a milling time of 30 minutes, and a rotation speed of 800 r / min to obtain a slurry with a particle size of -800 mesh accounting for 50%.

[0090] After ball milling, the slurry is clarified for 30 minutes. The resulting supernatant contains floating matter, which is filtered to obtain carbon residue. The filtrate is returned to the ball milling process. The slurry underflow is then fed into a selective leaching process. This process controls the liquid-to-solid ratio at 7:1, the leaching temperature at 30℃, the leaching time at 20 minutes, and the stirring intensity at 500 r / min. The initial silver powder / methanesulfonic acid mass ratio is 2:1. After leaching, the filtrate is filtered, yielding a silver methanesulfonate solution and silver powder as the residue, with a silver content of 99.9%. The filtrate, now a silver methanesulfonate solution, is returned for further leaching. After saturation, the filtrate is evaporated and crystallized to obtain the silver methanesulfonate product. At this point, the ratio of silver mass in the silver powder to (silver mass in the silver powder + silver mass in the silver methanesulfonate) is 1:3.

[0091] Compared with Example 1, Comparative Example 10 has a liquid-to-solid ratio greater than the upper limit of the leaching process. An excessive liquid-to-solid ratio will increase the volume of the reaction vessel and will not significantly improve the leaching efficiency of Ag. In addition, it will also lengthen the cycle for saturating silver methanesulfonate and further reduce the processing capacity of silver paste per unit container.

[0092] Comparative Example 11

[0093] 1000 mL of waste conductive silver paste was measured and dried using a co-flow drying method. The atomization device used a two-flow nozzle, and the feed solution was injected by a peristaltic pump at a rate of 15 mL / min. The gas flow rate of the nozzle was controlled by the compressed air pressure, and atomization was achieved at 0.10 MPa. The inlet temperature of the compressed air was controlled at 280℃, and the outlet temperature was controlled at 190℃. The outlet air was discharged after passing through a primary vortex separator and tail gas treatment. The silver paste was spray-dried to obtain fine silver powder with a particle size of -200 mesh accounting for 95%.

[0094] The silver powder was produced by zirconium bead ball milling with a ball-to-powder ratio of 8:1, a milling time of 30 minutes, and a rotation speed of 800 r / min to obtain a slurry with a particle size of -800 mesh accounting for 50%.

[0095] After ball milling, the slurry was clarified for 30 minutes. The resulting supernatant contained floating matter, which was filtered to obtain carbon residue. The filtrate was returned to the ball milling process. The slurry underflow was then fed into a selective leaching process. This process controlled the liquid-to-solid ratio at 3:1, the leaching temperature at 10℃, the leaching time at 20 minutes, and the stirring intensity at 500 r / min. The initial silver powder / methanesulfonic acid mass ratio was 2:1. After leaching, the filtrate was filtered, yielding a silver methanesulfonate solution and silver powder as the residue, with a silver content of 92.4%. The filtrate, now a silver methanesulfonate solution, was returned for further leaching. After saturation, the filtrate was evaporated and crystallized to obtain the silver methanesulfonate product. At this point, the ratio of the mass of silver in the silver powder to the mass of silver in the silver powder plus the mass of silver in the silver methanesulfonate was 1:3.8.

[0096] Compared with Example 1, Comparative Example 11 has a temperature lower than the lower limit of the leaching process. Too low a temperature will weaken the reaction rate, resulting in insufficient Ag2O reaction, which in turn reduces the silver grade of the obtained metallic silver powder.

[0097] Comparative Example 12

[0098] 1000 mL of waste conductive silver paste was measured and dried using a co-flow drying method. The atomization device used a two-flow nozzle, and the feed solution was injected by a peristaltic pump at a rate of 15 mL / min. The gas flow rate of the nozzle was controlled by the compressed air pressure, and atomization was achieved at 0.10 MPa. The inlet temperature of the compressed air was controlled at 280℃, and the outlet temperature was controlled at 190℃. The outlet air was discharged after passing through a primary vortex separator and tail gas treatment. The silver paste was spray-dried to obtain fine silver powder with a particle size of -200 mesh accounting for 95%.

[0099] The silver powder was produced by zirconium bead ball milling with a ball-to-powder ratio of 8:1, a milling time of 30 minutes, and a rotation speed of 800 r / min to obtain a slurry with a particle size of -800 mesh accounting for 50%.

[0100] After ball milling, the slurry is clarified for 30 minutes. The resulting supernatant contains floating matter, which is filtered to obtain carbon residue. The filtrate is returned to the ball milling process. The slurry underflow is then fed into a selective leaching process. This process controls the liquid-to-solid ratio at 3:1, the leaching temperature at 75℃, the leaching time at 20 minutes, and the stirring intensity at 500 rpm. The initial silver powder / methanesulfonic acid mass ratio is 2:1. After leaching, the filtrate is filtered, yielding a silver methanesulfonate solution and silver powder as the residue, with a silver content of 99.9%. The filtrate, now a silver methanesulfonate solution, is returned for further leaching. After saturation, the filtrate is evaporated and crystallized to obtain the silver methanesulfonate product. At this point, the ratio of silver mass in the silver powder to (silver mass in the silver powder + silver mass in the silver methanesulfonate) is 1:3.

[0101] Compared with Example 1, Comparative Example 12 has a temperature greater than the upper limit of the leaching process, which will appropriately accelerate the reaction rate, but the improvement is not significant and will also lead to energy waste.

[0102] Comparative Example 13

[0103] 1000 mL of waste conductive silver paste was measured and dried using a co-flow drying method. The atomization device used a two-flow nozzle, and the feed solution was injected by a peristaltic pump at a rate of 15 mL / min. The gas flow rate of the nozzle was controlled by the compressed air pressure, and atomization was achieved at 0.10 MPa. The inlet temperature of the compressed air was controlled at 280℃, and the outlet temperature was controlled at 190℃. The outlet air was discharged after passing through a primary vortex separator and tail gas treatment. The silver paste was spray-dried to obtain fine silver powder with a particle size of -200 mesh accounting for 95%.

[0104] The silver powder was produced by zirconium bead ball milling with a ball-to-powder ratio of 8:1, a milling time of 30 minutes, and a rotation speed of 800 r / min to obtain a slurry with a particle size of -800 mesh accounting for 50%.

[0105] After ball milling, the slurry was clarified for 30 minutes. The resulting supernatant contained floating matter, which was filtered to obtain carbon residue. The filtrate was returned to the ball milling process. The slurry underflow was then fed into a selective leaching process. This process controlled the liquid-to-solid ratio at 3:1, the leaching temperature at 30℃, the leaching time at 5 minutes, and the stirring intensity at 500 rpm. The initial silver powder / methanesulfonic acid mass ratio was 2:1. After leaching, the filtrate was filtered, yielding a silver methanesulfonate solution and silver powder as the residue, with a silver content of 89.1%. The filtrate, now a silver methanesulfonate solution, was returned for further leaching. After saturation, the filtrate was evaporated and crystallized to obtain the silver methanesulfonate product. At this point, the ratio of the mass of silver in the silver powder to the mass of silver in the silver powder plus the mass of silver in the silver methanesulfonate was 1:4.

[0106] Compared with Example 1, Comparative Example 13 has a leaching time shorter than the lower limit of the leaching process. The leaching time is too short, the reaction is incomplete, and thus the silver grade of the obtained metallic silver powder is affected.

[0107] Comparative Example 14

[0108] 1000 mL of waste conductive silver paste was measured and dried using a co-flow drying method. The atomization device used a two-flow nozzle, and the feed solution was injected by a peristaltic pump at a rate of 15 mL / min. The gas flow rate of the nozzle was controlled by the compressed air pressure, and atomization was achieved at 0.10 MPa. The inlet temperature of the compressed air was controlled at 280℃, and the outlet temperature was controlled at 190℃. The outlet air was discharged after passing through a primary vortex separator and tail gas treatment. The silver paste was spray-dried to obtain fine silver powder with a particle size of -200 mesh accounting for 95%.

[0109] The silver powder was produced by zirconium bead ball milling with a ball-to-powder ratio of 8:1, a milling time of 30 minutes, and a rotation speed of 800 r / min to obtain a slurry with a particle size of -800 mesh accounting for 50%.

[0110] After ball milling, the slurry is clarified for 30 minutes. The resulting supernatant contains floating matter, which is filtered to obtain carbon residue. The filtrate is returned to the ball milling process. The slurry underflow is then fed into a selective leaching process. This process controls the liquid-to-solid ratio at 3:1, the leaching temperature at 30℃, the leaching time at 60 minutes, and the stirring intensity at 500 r / min. The initial silver powder / methanesulfonic acid mass ratio is 2:1. After leaching, the filtrate is filtered, yielding a silver methanesulfonate solution and silver powder as the residue, with a silver content of 99.9%. The filtrate, now a silver methanesulfonate solution, is returned for further leaching. After saturation, the filtrate is evaporated and crystallized to obtain the silver methanesulfonate product. At this point, the ratio of the mass of silver in the silver powder to the mass of silver in the silver powder plus the mass of silver in the silver methanesulfonate is 1:4.5.

[0111] Compared with Example 1, Comparative Example 14 has a longer leaching time than the upper limit of the leaching process. The excessively long reaction time not only leads to energy waste, but also causes some of the metallic silver powder to react with methanesulfonic acid to form silver methanesulfonate, affecting the product composition.

[0112] Comparative Example 15

[0113] 1000 mL of waste conductive silver paste was measured and dried using a co-flow drying method. The atomization device used a two-flow nozzle, and the feed solution was injected by a peristaltic pump at a rate of 15 mL / min. The gas flow rate of the nozzle was controlled by the compressed air pressure, and atomization was achieved at 0.10 MPa. The inlet temperature of the compressed air was controlled at 280℃, and the outlet temperature was controlled at 190℃. The outlet air was discharged after passing through a primary vortex separator and tail gas treatment. The silver paste was spray-dried to obtain fine silver powder with a particle size of -200 mesh accounting for 95%.

[0114] The silver powder was produced by zirconium bead ball milling with a ball-to-powder ratio of 8:1, a milling time of 30 minutes, and a rotation speed of 800 r / min to obtain a slurry with a particle size of -800 mesh accounting for 50%.

[0115] After ball milling, the slurry was clarified for 30 minutes. The resulting supernatant contained floating matter, which was filtered to obtain carbon residue. The filtrate was returned to the ball milling process. The slurry underflow was then fed into a selective leaching process. This process controlled the liquid-to-solid ratio at 3:1, the leaching temperature at 30℃, the leaching time at 20 minutes, and the stirring intensity at 50 r / min. The initial silver powder / methanesulfonic acid mass ratio was 2:1. After leaching, the filtrate was filtered, yielding a silver methanesulfonate solution and silver powder as the residue, with a silver content of 78.9%. The filtrate, now a silver methanesulfonate solution, was returned for further leaching. After saturation, the filtrate was evaporated and crystallized to obtain the silver methanesulfonate product. At this point, the ratio of the mass of silver in the silver powder to the mass of silver in the silver powder plus the mass of silver in the silver methanesulfonate was 1:4.1.

[0116] Compared with Example 1, Comparative Example 15 has a lower limit for stirring intensity during the leaching process. If the stirring intensity is too low, the reaction rate will be weakened, resulting in insufficient Ag2O reaction in the same amount of time, which in turn affects the silver grade of the obtained metallic silver powder.

[0117] Comparative Example 16

[0118] 1000 mL of waste conductive silver paste was measured and dried using a co-flow drying method. The atomization device used a two-flow nozzle, and the feed solution was injected by a peristaltic pump at a rate of 15 mL / min. The gas flow rate of the nozzle was controlled by the compressed air pressure, and atomization was achieved at 0.10 MPa. The inlet temperature of the compressed air was controlled at 280℃, and the outlet temperature was controlled at 190℃. The outlet air was discharged after passing through a primary vortex separator and tail gas treatment. The silver paste was spray-dried to obtain fine silver powder with a particle size of -200 mesh accounting for 95%.

[0119] The silver powder was produced by zirconium bead ball milling with a ball-to-powder ratio of 8:1, a milling time of 30 minutes, and a rotation speed of 800 r / min to obtain a slurry with a particle size of -800 mesh accounting for 50%.

[0120] After ball milling, the slurry was clarified for 30 minutes. The resulting supernatant contained floating matter, which was filtered to obtain carbon residue. The filtrate was returned to the ball milling process. The slurry underflow was then fed into a selective leaching process. This process controlled the liquid-to-solid ratio at 3:1, the leaching temperature at 30℃, the leaching time at 20 minutes, and the stirring intensity at 800 r / min. The initial silver powder / methanesulfonic acid mass ratio was 2:1. After leaching, the filtrate was filtered, yielding a silver methanesulfonate solution and silver powder as the residue, with a silver content of 78.9%. The filtrate, now a silver methanesulfonate solution, was returned for further leaching. After saturation, the filtrate was evaporated and crystallized to obtain the silver methanesulfonate product. At this point, the ratio of silver mass in the silver powder to (silver mass in the silver powder + silver mass in the silver methanesulfonate) was 1:3.

[0121] Compared with Example 1, Comparative Example 16 has a stirring intensity greater than the upper limit of the leaching process. The stirring speed is too high, which will appropriately accelerate the reaction speed, but the improvement is not significant and will also lead to energy waste.

[0122] Comparative Example 17

[0123] 1000 mL of waste conductive silver paste was measured and dried using a co-flow drying method. The atomization device used a two-flow nozzle, and the feed solution was injected by a peristaltic pump at a rate of 15 mL / min. The gas flow rate of the nozzle was controlled by the compressed air pressure, and atomization was achieved at 0.10 MPa. The inlet temperature of the compressed air was controlled at 280℃, and the outlet temperature was controlled at 190℃. The outlet air was discharged after passing through a primary vortex separator and tail gas treatment. The silver paste was spray-dried to obtain fine silver powder with a particle size of -200 mesh accounting for 95%.

[0124] The silver powder was produced by zirconium bead ball milling with a ball-to-powder ratio of 8:1, a milling time of 30 minutes, and a rotation speed of 800 r / min to obtain a slurry with a particle size of -800 mesh accounting for 50%.

[0125] After ball milling, the slurry was clarified for 30 minutes. The resulting supernatant contained floating matter, which was filtered to obtain carbon residue. The filtrate was returned to the ball milling process. The slurry underflow was then fed into a selective leaching process. This process controlled the liquid-to-solid ratio at 3:1, the leaching temperature at 30℃, the leaching time at 20 minutes, and the stirring intensity at 500 r / min. The initial silver powder / methanesulfonic acid mass ratio was 0.5:1. After leaching, the filtrate was filtered, yielding a silver methanesulfonate solution and silver powder as the residue, with a silver content of 99.9%. The filtrate, now a silver methanesulfonate solution, was returned for further leaching. After saturation, the filtrate was evaporated and crystallized to obtain the silver methanesulfonate product. At this point, the ratio of the mass of silver in the silver powder to the mass of silver in the silver powder plus the mass of silver in the silver methanesulfonate was 1:3.5.

[0126] Compared with Example 1, Comparative Example 17 has a lower limit for the initial silver powder / methanesulfonic acid mass ratio in the leaching process, which means that the amount of methanesulfonic acid is too large, the processing capacity is too small, and the processing efficiency is affected.

[0127] Comparative Example 18

[0128] 1000 mL of waste conductive silver paste was measured and dried using a co-flow drying method. The atomization device used a two-flow nozzle, and the feed solution was injected by a peristaltic pump at a rate of 15 mL / min. The gas flow rate of the nozzle was controlled by the compressed air pressure, and atomization was achieved at 0.10 MPa. The inlet temperature of the compressed air was controlled at 280℃, and the outlet temperature was controlled at 190℃. The outlet air was discharged after passing through a primary vortex separator and tail gas treatment. The silver paste was spray-dried to obtain fine silver powder with a particle size of -200 mesh accounting for 95%.

[0129] The silver powder was produced by zirconium bead ball milling with a ball-to-powder ratio of 8:1, a milling time of 30 minutes, and a rotation speed of 800 r / min to obtain a slurry with a particle size of -800 mesh accounting for 50%.

[0130] After ball milling, the slurry was clarified for 30 minutes. The resulting supernatant contained floating matter, which was filtered to obtain carbon residue. The filtrate was returned to the ball milling process. The slurry underflow was then fed into a selective leaching process. This process controlled the liquid-to-solid ratio at 3:1, the leaching temperature at 30℃, the leaching time at 20 minutes, and the stirring intensity at 500 r / min. The initial silver powder / methanesulfonic acid mass ratio was 4:1. After leaching, the filtrate was filtered, yielding a silver methanesulfonate solution and silver powder as the residue, with a silver content of 78.2%. The filtrate, now a silver methanesulfonate solution, was returned for further leaching. After saturation, the filtrate was evaporated and crystallized to obtain the silver methanesulfonate product. At this point, the ratio of the mass of silver in the silver powder to the mass of silver in the silver powder plus the mass of silver in the silver methanesulfonate was 1:2.5.

[0131] Compared with Example 1, Comparative Example 18 has a higher initial silver powder / methanesulfonic acid mass ratio than the upper limit of the leaching process. This means that the amount of methanesulfonic acid is too small, the Ag2O reaction is insufficient, and thus the silver grade of the obtained metallic silver powder is affected.

[0132] Comparative Example 19

[0133] 1000 mL of waste conductive silver paste was measured and dried using a co-flow drying method. The atomization device used a two-flow nozzle, and the feed solution was injected by a peristaltic pump at a rate of 15 mL / min. The gas flow rate of the nozzle was controlled by the compressed air pressure, and atomization was achieved at 0.10 MPa. The inlet temperature of the compressed air was controlled at 280℃, and the outlet temperature was controlled at 190℃. The outlet air was discharged after passing through a primary vortex separator and tail gas treatment. The silver paste was spray-dried to obtain fine silver powder with a particle size of -200 mesh accounting for 95%.

[0134] The silver powder was produced by zirconium bead ball milling with a ball-to-powder ratio of 8:1, a milling time of 10 minutes, and a rotation speed of 800 r / min to obtain a slurry with a particle size of -800 mesh accounting for 20%.

[0135] After ball milling, the slurry was clarified for 30 minutes. The resulting supernatant contained floating matter, which was filtered to obtain carbon residue. However, some carbon residue remained encapsulated within the silver powder and was not completely dissociated. The filtrate was returned to the ball milling process. The slurry underflow was then fed into a selective leaching process. This process controlled the liquid-to-solid ratio at 3:1, the leaching temperature at 30℃, the leaching time at 20 minutes, and the stirring intensity at 500 r / min. The initial silver powder / methanesulfonic acid mass ratio was 2:1. After leaching, the filtrate was filtered, yielding a silver methanesulfonate solution. The filter residue consisted of silver powder and some carbon residue, with a silver content of 85.6%. The filtrate, now a silver methanesulfonate solution, was returned for further leaching. After saturation, the filtrate was evaporated and crystallized to obtain the silver methanesulfonate product. At this point, the ratio of the mass of silver in the silver powder to the mass of silver in the silver powder plus the mass of silver in the silver methanesulfonate was 1:3.6.

[0136] Compared with Example 1, Comparative Example 19 has a ball milling time that is less than the lower limit of the fine grinding process. As a result, the dry silver powder is not finely ground, which is not conducive to the subsequent leaching and purification process. Furthermore, the silver powder obtained is of low grade due to the presence of carbon slag.

[0137] Comparative Example 20

[0138] 1000 mL of waste conductive silver paste was measured and dried using a co-flow drying method. The atomization device used a two-flow nozzle, and the feed solution was injected by a peristaltic pump at a rate of 15 mL / min. The gas flow rate of the nozzle was controlled by the compressed air pressure, and atomization was achieved at 0.10 MPa. The inlet temperature of the compressed air was controlled at 280℃, and the outlet temperature was controlled at 190℃. The outlet air was discharged after passing through a primary vortex separator and tail gas treatment. The silver paste was spray-dried to obtain fine silver powder with a particle size of -200 mesh accounting for 95%.

[0139] The silver powder was produced by zirconium bead ball milling with a ball-to-powder ratio of 8:1, a milling time of 90 minutes, and a rotation speed of 800 r / min to obtain a slurry with a particle size of -800 mesh accounting for 52%.

[0140] After ball milling, the slurry was clarified for 30 minutes. The resulting supernatant contained floating matter, which was filtered to obtain carbon residue. However, some carbon residue remained encapsulated within the silver powder and was not completely dissociated. The filtrate was returned to the ball milling process. The slurry underflow was then fed into a selective leaching process. This process controlled the liquid-to-solid ratio at 3:1, the leaching temperature at 30℃, the leaching time at 20 minutes, and the stirring intensity at 500 rpm. The initial silver powder / methanesulfonic acid mass ratio was 2:1. After leaching, the filtrate was filtered, yielding a silver methanesulfonate solution. The filter residue consisted of silver powder and some carbon residue, with a silver content of 99.9%. The filtrate, now a silver methanesulfonate solution, was returned for further leaching. After saturation, the filtrate was evaporated and crystallized to obtain the silver methanesulfonate product. At this point, the ratio of the mass of silver in the silver powder to the mass of silver in the silver powder plus the mass of silver in the silver methanesulfonate was 1:3.

[0141] Compared with Example 1, Comparative Example 20 has a longer ball milling time than the upper limit of the fine grinding process, and the dry silver powder is not further refined, which also results in energy waste.

[0142] Example 2

[0143] 1000 mL of waste conductive silver paste was measured and dried using a co-flow drying method with a two-flow nozzle atomization device. The feed solution was injected using a peristaltic pump at a rate of 15 mL / min. The nozzle gas flow rate was controlled by the compressed nitrogen pressure, and atomization was achieved at 0.10 MPa. The inlet temperature of the compressed nitrogen was controlled at 300℃, and the outlet temperature at 200℃. The nitrogen gas was discharged after primary vortex separation and tail gas treatment. The silver paste was spray-dried to obtain fine silver powder with a particle size of -240 mesh accounting for 95%.

[0144] The silver powder was produced by zirconium bead ball milling with a ball-to-powder ratio of 10:1, a milling time of 40 minutes, and a rotation speed of 1000 r / min to obtain a slurry with a particle size of -800 mesh accounting for 70%.

[0145] After ball milling, the slurry is clarified for 50 minutes. The resulting supernatant contains floating matter, which is filtered to obtain carbon residue. The filtrate is returned to the ball milling process. The slurry underflow is then fed into a selective leaching process. This process controls the liquid-to-solid ratio at 4:1, the leaching temperature at 60℃, the leaching time at 30 minutes, and the stirring intensity at 500 r / min. The initial silver powder / methanesulfonic acid mass ratio is 3:1. After leaching, the filtrate is filtered, yielding a silver methanesulfonate solution and silver powder as the residue, with a silver content of 99.98%. The filtrate is then returned for further leaching. After saturation, the filtrate is evaporated and crystallized to obtain silver methanesulfonate product with a purity of 99.99%. At this point, the ratio of silver mass in the coarse silver powder to (silver mass in the coarse silver powder + silver mass in the silver methanesulfonate) is 1:6.

[0146] Comparative Example 21

[0147] 1000 mL of waste conductive silver paste was measured and dried using a co-flow drying method. The atomization device used a two-flow nozzle, and the feed solution was injected by a peristaltic pump at a rate of 15 mL / min. The nozzle gas flow rate was controlled by the compressed nitrogen pressure, and atomization was achieved at 0.10 MPa. The inlet temperature of the compressed nitrogen was controlled at 350℃, and the outlet temperature was controlled at 190℃. The nitrogen gas was discharged after primary vortex separation and tail gas treatment. The liquid silver paste could not be converted into solid silver powder.

[0148] Compared with Example 2, Comparative Example 21 has a lower inlet temperature limit than the gas in the spray drying process, so the liquid silver paste cannot be turned into solid silver powder, and subsequent processes cannot be carried out.

[0149] Comparative Example 22

[0150] 1000 mL of waste conductive silver paste was measured and dried using a co-flow drying method. The atomization device used a two-flow nozzle, and the feed solution was injected by a peristaltic pump at a rate of 15 mL / min. The nozzle gas flow rate was controlled by the compressed nitrogen pressure, and atomization was achieved at 0.10 MPa. The inlet temperature of the compressed nitrogen was controlled at 350℃, and the outlet temperature was controlled at 190℃. The nitrogen gas was discharged after primary vortex separation and tail gas treatment. The liquid silver paste could not be converted into solid silver powder, and its particle size of -200 mesh accounted for 96%.

[0151] The silver powder was produced by zirconium bead ball milling with a ball-to-powder ratio of 10:1, a milling time of 40 minutes, and a rotation speed of 1000 r / min to obtain a slurry with a particle size of -800 mesh accounting for 70%.

[0152] After ball milling, the slurry is clarified for 50 minutes. The resulting supernatant contains floating matter, which is filtered to obtain carbon residue. The filtrate is returned to the ball milling process. The slurry underflow is then fed into a selective leaching process. This process controls the liquid-to-solid ratio at 4:1, the leaching temperature at 60℃, the leaching time at 30 minutes, and the stirring intensity at 500 rpm. The initial silver powder / methanesulfonic acid mass ratio is 3:1. After leaching, the filtrate is filtered, yielding a silver methanesulfonate solution and silver powder as the residue, with a silver content of 99.98%. The filtrate, now a silver methanesulfonate solution, is returned for further leaching. After saturation, the filtrate is evaporated and crystallized to obtain the silver methanesulfonate product. At this point, the ratio of silver mass in the crude silver powder to (silver mass in the crude silver powder + silver mass in the silver methanesulfonate) is 1:6.

[0153] Compared with Example 2, Comparative Example 22 has a higher inlet temperature than the upper limit of the gas in the spray drying process. Since nitrogen is used as the carrier gas, the temperature rise will coarsen the particles and increase energy consumption. This will then cause a certain increase in energy consumption in the subsequent wet ball milling process, but will not have a significant impact on product quality and distribution.

Claims

1. A method of recovering silver from a conductive silver paste, characterized by, Includes the following steps: S1. Spray dry the conductive silver paste to obtain fine silver powder, and ball mill the fine silver powder to obtain a slurry; S2. The slurry is clarified and thickened to obtain supernatant and slurry underflow; the supernatant is pressure filtered, and the filtrate is returned to the ball mill; S3. Add methanesulfonic acid to the underflow of slurry for leaching, control the time to 10~30min, and obtain leachate; filter the leachate, the filter residue is silver powder; return the filtrate for leaching, and after the Ag ion concentration in the filtrate reaches saturation, evaporate and crystallize to obtain silver methanesulfonate. The spray drying process in step S1 is as follows: a co-current spray dryer is used for drying; a two-flow nozzle is used for atomization, and a peristaltic pump is used for injection at a rate of 10-20 mL / min; the gas flow rate of the nozzle is controlled by the pressure of compressed air or nitrogen, and atomization is generated at a pressure of 0.03-0.10 MPa; the inlet temperature of compressed air or nitrogen is controlled at 220-290℃, and the outlet temperature is controlled at 150-220℃. The leaching process with added methanesulfonic acid is as follows: liquid-solid ratio 1:1~5:1, leaching temperature 20~60℃, leaching time 10min~30min, stirring intensity controlled at 100r / min~600r / min, and the mass ratio of conductive silver paste dry material to methanesulfonic acid is 1~3:

1.

2. The method of claim 1, wherein, In step S1, the silver powder is milled using zirconium beads.

3. The method of claim 1, wherein, In step S1, the ball milling time is 20 min to 60 min, and the rotation speed is 500 to 1000 r / min.

4. The method of claim 1, wherein, In step S1, the particle size of the slurry is 600-800 mesh.

5. The method of claim 1, wherein, The slurry clarification time is 20-60 minutes, and the mass concentration of the underflow is controlled at 30-50% during the thickening process.

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