A method for recovering silver from silver-containing waste catalyst

Abstract

The invention discloses a method for recovering silver from silver-containing waste catalysts. The method comprises the following steps: loading the silver-containing waste catalysts into a multi-stage series leaching column, adding a nitric acid solution to the top of the first-stage leaching column for leaching, and flowing out from the bottom of the last-stage leaching column, collecting the flowing silver nitrate leaching solution in sections, returning the silver nitrate leaching solution with a lower concentration to the first-stage leaching column for cyclic leaching, and obtaining metallic silver through precipitation and reduction of the silver nitrate leaching solution with a higher concentration; when the leaching of the silver-containing waste catalyst in the first-stage leaching column is completed, removing the first-stage leaching column and loading a new silver-containing waste catalyst, connecting the first-stage leaching column to the bottom of the last-stage leaching column as a new last-stage leaching column, and the second-stage leaching column as a new first-stage leaching column, and so on. The method has a short silver recovery process for silver-containing waste catalysts, low cost, and a silver recovery rate greater than 99.8%, and a silver ingot purity of ≥99.95%.

Description

Technical Field

[0001] The invention relates to a method for treating a silver-containing waste catalyst, in particular to a method for recovering silver from the silver-containing waste catalyst, and belongs to the technical field of silver-containing waste material recovery. Background Art

[0002] Silver is a precious metal, and its content in the earth's crust is only 0.001 to 0.01 g / t. It has excellent catalytic properties. In the chemical industry, silver can be used as an active component of a variety of oxidation reaction catalysts, especially as a catalyst in the oxidation of ethylene to ethylene oxide, the oxidation of methanol to formaldehyde, and the production of ethylene glycol, and has been industrially used for many years.

[0003] After a period of use, the performance of the silver catalyst will decrease and lose, and it needs to be scrapped to recycle the silver and carrier. Most silver catalysts contain 10% to 30% silver, and a few contain up to 40% silver. The silver catalyst carrier is mainly made of α-aluminum oxide and a small amount of silicon dioxide, which is a small ball or cylinder with a large number of micropores. Silver is distributed on the surface and the inner surface of the micropores. There are also a few catalysts that use natural zeolite as a carrier.

[0004] There are two methods for extracting silver from spent catalysts: wet method and pyrometallurgy. Among them, the wet method includes nitric acid leaching, thiosulfate method and ammonia leaching, and the pyrometallurgy includes soda ash-borax smelting, soda ash-borax-fluorite smelting, plasma smelting iron capture, etc. Waste silver catalysts such as natural zeolite and silica as carriers can be directly smelted. Alumina as a carrier is not suitable for direct smelting by pyrometallurgy because Al 2 O 3 The melting point is very high, and a large amount of flux is consumed during smelting, and Al 2 O 3 The slag-making performance is very poor, the slag viscosity is large, and much silver is lost in the slag, so the wet method is generally used to recover silver. The wet process basically adopts the process of nitric acid dissolution-sodium chloride precipitation of silver chloride-hydrazine hydrate reduction. For example, Chinese patent CN109777959A discloses a method for recovering silver from a silver catalyst, and its process route is as follows: crushing of waste silver catalyst → nitric acid leaching → sodium chloride precipitation of silver → iron plate replacement → molten ingot → metal silver ingot product. This process requires the silver catalyst to be crushed, and it needs to be leached and washed repeatedly to obtain a more ideal leaching rate. At the same time, the mother liquor after silver precipitation with sodium chloride contains a high concentration of NaNO 3 This nitrate wastewater is difficult to treat, and the mother liquor after hydrazine hydrate reduction contains high concentrations of NH 4 -ions, and is also difficult to treat wastewater. Chinese patent CN109536726A discloses a method for recovering silver from a silver catalyst, which uses dilute nitric acid to selectively leach silver from silver-containing waste catalysts, and filters to obtain a silver nitrate solution and a filter residue. Then, a sodium chloride solution is used to precipitate silver chloride and a sodium nitrate filtrate. Finally, hydrogen is used to reduce silver chloride to obtain silver powder, which is then smelted and cast to obtain silver ingots. This technology uses sodium chloride to precipitate silver, and the mother liquor contains a high concentration of Na 2 NO 3 , this nitrate wastewater is difficult to treat. In addition, due to the porosity of the silver catalyst carrier, it has a strong adsorption of silver ions in the leaching solution, which will affect the leaching rate of silver. Therefore, the traditional process requires the silver catalyst to be broken and repeatedly leached and washed to obtain a more ideal leaching rate. The mother liquor after sodium chloride precipitation contains a high concentration of NaNO 3 , this nitrate wastewater is difficult to treat. The mother liquor after hydrazine hydrate reduction contains high concentrations of NH 4 - Ions are also difficult to treat wastewater. Summary of the invention

[0005] In view of the shortcomings of the above-mentioned traditional methods for recovering silver-containing waste catalysts, the purpose of the present invention is to provide a method for recovering silver from silver-containing waste catalysts. The method can not only efficiently leach and recover silver from the silver-containing waste catalysts and obtain high-purity metallic silver products, but also does not require crushing of the silver-containing waste catalysts, has low acid consumption, and does not generate wastewater such as sodium nitrate and ammonium salts. Compared with the existing methods, the method has the characteristics of short process flow, simple equipment, high silver leaching rate and recovery rate, low processing cost, no ammonia nitrogen wastewater discharge, and less wastewater discharge.

[0006] In order to achieve the above technical purpose, the present invention provides a method for recovering silver from silver-containing waste catalysts. The method comprises the following steps: filling the silver-containing waste catalysts in a multi-stage series leaching column, adding a nitric acid solution at the top of a first-stage leaching column of the multi-stage series leaching column, and sequentially passing through each stage of the leaching column to leach the silver-containing waste catalysts, and finally flowing out from the bottom of the last-stage leaching column, collecting the silver nitrate leachate flowing out from the bottom of the last-stage leaching column in sections, returning the low-concentration silver nitrate leachate to the first-stage leaching column for cyclic leaching, and obtaining metallic silver through precipitation and reduction of the high-concentration silver nitrate leachate; when the leaching of the silver-containing waste catalysts in the first-stage leaching column of the multi-stage series leaching column is completed, removing the first-stage leaching column and filling it with a new silver-containing waste catalyst, and then connecting it to the bottom of the last-stage leaching column as a new last-stage leaching column, and the second-stage leaching column as a new first-stage leaching column, and the cycle is repeated.

[0007] In the prior art, the silver-containing waste catalyst adopts the conventional leaching process. Since the silver-containing waste catalyst contains porous carriers such as silicon dioxide and aluminum oxide, these porous carriers have good stability and it is difficult to destroy their porous carrier structure during the nitric acid leaching process. Therefore, the leaching rate of the silver catalyst loaded in the porous carrier is low, so it is necessary to use a strong mechanical force to destroy the porous carrier to achieve efficient dissolution of the silver catalyst loaded thereon. However, the porous carrier has a certain adsorption property for the leached silver ions in the solution system, resulting in a low silver ion leaching rate. In particular, the specific surface of the porous carrier that has been crushed and ground is further increased, and the adsorption capacity is stronger, which is not conducive to the leaching of silver. Repeated washing is required to efficiently recover the silver ions. The key to the technical solution of the present invention is to adopt a multi-stage series leaching method for the silver-containing waste catalyst. The multi-stage series leaching process is a dynamic leaching process, which is essentially different from the conventional leaching process. In the conventional leaching process, on the one hand, due to the influence of changes in acid concentration, leaching equilibrium, etc., the leaching rate of silver in the silver-containing waste catalyst will show a gradient decrease. On the other hand, as the silver and other metals in the silver-containing waste catalyst are leached, the porous carrier has a stronger adsorption effect on the leached silver ions. By adopting the multi-stage series leaching method, there is no need to crush the silver-containing waste catalyst and directly leach and fill the column, which is conducive to improving the flow rate of the leaching agent in the leaching column. The high-concentration silver ion leachate in the leaching process can be transferred to the next-level leaching column in time, thereby promoting the leaching reaction equilibrium to move in the positive direction, and can reduce the adsorption and retention of silver ions by the porous carrier, so the leaching efficiency can be greatly improved. At the same time, the low-concentration silver ion leachate is continuously circulated for leaching, which not only acts as a leachate to further leach the silver catalyst remaining in the porous carrier, but also acts as a washing liquid to elute the silver ions adsorbed and retained by the porous carrier, and enrich it into a high-concentration silver nitrate leachate, which can increase the concentration of the leachate, reduce the generation of waste liquid, and is beneficial to the subsequent precipitation recovery process. Leaching is performed by using a multi-stage series leaching column method, which can realize the cyclic leaching of nitric acid, thereby achieving the maximum utilization of nitric acid, and the column replacement method of the multi-stage series leaching column can ensure that the silver content in the silver-containing waste catalyst from the first-stage leaching column to the last-stage leaching column decreases gradually, thereby achieving preferential leaching of silver in the silver-containing waste catalyst in the first-stage leaching column, which is beneficial to the continuous operation of the entire leaching process, and can ensure that the nitric acid with the highest acid concentration preferentially contacts the silver-containing waste catalyst with a lower silver content, which can ensure that the silver residue in the silver-containing waste catalyst is reduced to the greatest extent.

[0008] As a preferred solution, the multi-stage series leaching column includes 3 to 4 stages of leaching columns. Generally speaking, the more stages of the multi-stage series leaching column, the better the leaching effect on the silver-containing waste catalyst, but after more than 4 stages, the effect is further increased to a limited extent. It has been proved through experiments and practice that 3 to 4 stages of series leaching columns are the best and have the highest cost-effectiveness.

[0009] As a preferred solution, the concentration of the nitric acid solution is 1 mol / L to 2 mol / L. The concentration of nitric acid is preferably controlled within an appropriate concentration range, mainly based on the fact that the use of dilute nitric acid to dissolve the silver in the catalyst releases the least nitrogen oxides and maximizes the utilization rate of nitric acid. The specific reaction is as follows: 3Ag+4HNO 3 (dilute) = 3AgNO 3 +NO 2 ↑+2H 2 O; the reaction equation for dissolving silver using concentrated nitric acid is as follows: 3Ag+6HNO 3 (concentrated) = 3AgNO 3 +3NO 2 ↑+3H 2 O; It is obvious that to dissolve the same mass of silver, the use of concentrated nitric acid increases consumption by 50% compared with dilute nitric acid, and the nitrogen dioxide emissions increase by 2 times, which increases the difficulty of nitrogen oxide tail gas treatment.

[0010] As a preferred solution, during the leaching process, the consumption of nitric acid solution relative to the silver-containing waste catalyst is 2 to 10 L: 1 kg, the initial leaching temperature is room temperature, and the total leaching time is 24 h to 72 h. The leaching process is an exothermic reaction, the initial leaching temperature is room temperature, and the temperature during the leaching process can reach a range of 30 to 60 ° C. Within the preferred range, efficient leaching of silver in the silver-containing waste catalyst can be achieved. The consumption of nitric acid solution relative to the silver-containing waste catalyst is further preferably 2 to 3 L: 1 kg, which has the advantage of low acid consumption.

[0011] As a preferred solution, the concentration of the low-concentration silver nitrate leaching solution is lower than 30 g / L.

[0012] As a preferred solution, the concentration of the high-concentration silver nitrate leachate is above 30 g / L. By using the high-concentration silver nitrate leachate for subsequent precipitation treatment, a high-concentration nitric acid solution can be obtained, which is conducive to acid recycling and reduces waste liquid generation.

[0013] As a preferred solution, hydrochloric acid solution is used as a precipitant during the precipitation process; the amount of the hydrochloric acid solution used is 0.98 to 1.02 times the theoretical molar amount of the hydrochloric acid solution required to convert silver nitrate into silver chloride. Using hydrochloric acid solution as a precipitant can achieve the conversion of silver nitrate into silver chloride precipitation while also achieving the regeneration of nitric acid. The amount of hydrochloric acid solution used is preferably 1:1 with silver nitrate, which can ensure that silver ions are completely precipitated, and there will not be too much hydrochloric acid remaining to affect the recycling of nitric acid.

[0014] As a preferred solution, the precipitation conditions are: temperature of 20°C to 60°C and time of 60min to 120min. Under the preferred conditions, silver nitrate can be efficiently converted into silver chloride precipitation. The preferred temperature is 40 to 60°C.

[0015] As a preferred solution, the nitric acid solution generated during the precipitation process is returned to the leaching process.

[0016] As a preferred solution, an organic aldehyde is used as a reducing agent in the reduction process. The organic aldehyde is generally a small molecule aldehyde, such as formaldehyde. No nitrogen-containing reducing agent is used in the reduction process to avoid the reduction of the mother liquor to produce difficult-to-treat ammonia nitrogen wastewater. The amount of the reducing agent used is 1.2 to 1.5 times the theoretical molar amount of the reducing agent required to convert silver chloride into elemental silver.

[0017] As a preferred solution, the reduction conditions are: pH value of 11-13, temperature of 60°C-95°C, and time of 30min-120min. Under the preferred reduction conditions, silver chloride can be efficiently reduced to elemental silver.

[0018] As a preferred embodiment, the silver-containing spent catalyst comprises an alumina and / or a silica carrier.

[0019] As a preferred solution, metallic silver is melted and cast into high-purity silver ingots.

[0020] The method for recovering silver from silver-containing waste catalyst provided by the present invention comprises the following steps:

[0021] 1) The silver catalyst is kept in its original shape and is not broken. It is loaded into a series of leaching columns. The series of leaching columns is generally 3 to 4 columns in series.

[0022] 2) using a dilute nitric acid solution as a leaching agent, the concentration of the dilute nitric acid is 1 mol / L to 2 mol / L, the consumption of the leaching agent relative to the silver-containing waste catalyst is 2L:1kg to 10L:1kg (ratio of the volume of the leaching agent to the weight of the silver-containing catalyst), the temperature is 30°C to 60°C, without heating, the temperature is the temperature generated by the reaction exotherm, and the reaction time is 24h to 72h; when the leaching of the silver-containing waste catalyst in the first-stage leaching column in the series leaching column is completed, the first-stage leaching column is removed and filled with a new silver-containing waste catalyst, and then connected to the bottom of the last-stage leaching column as a new last-stage leaching column, and the second-stage leaching column is used as a new first-stage leaching column, and the cycle is repeated to achieve continuous operation;

[0023] 3) The silver nitrate leaching solution was collected in sections according to the outflow order and the silver concentration from high to low. 3 Concentration above 30g / L to precipitate AgCl, AgNO 3 The concentration less than 30g / L is returned as silver leaching agent.

[0024] 4) After the qualified silver nitrate leachate is checked and filtered, HCl solution is added to the solution to generate silver chloride precipitation. The amount of HCl is 0.98 to 1.02 times the theoretical amount. The HCl solution is slowly added while stirring. After the chlorine is added, it is allowed to stand for 30 to 600 minutes to age the silver chloride. The reaction temperature is 40°C to 60°C.

[0025] 5) Nitric acid is added to the silver chloride precipitation mother liquor to make the nitric acid concentration 1 mol / L to 2 mol / L, and the nitric acid is returned to be used as a silver leaching agent.

[0026] 6) After filtering and washing the silver chloride, a silver reduction operation is performed, using formaldehyde as a reducing agent, first stirring the silver chloride with a NaOH solution with a pH value of 11 to 13 to make a slurry, then heating to 60° C. to 95° C., slowly adding the reducing agent formaldehyde, without continuously adding the NaOH solution during the process, ensuring that the reduction reaction is carried out at a pH value of 11 to 13, the amount of formaldehyde used is 1.2 to 1.5 times the theoretical amount, and the time is 30 min to 120 min.

[0027] 7) After filtering the silver powder, add 0.1-3 mol / L hydrochloric acid, stir and wash at 20°C-60°C for 30min-200min, filter and wash to nearly neutral, dry and melt the ingot to obtain the product silver ingot, the purity of the silver ingot is greater than 99.95%.

[0028] The reaction equations of the principle and process of the present invention are as follows

[0029] 1. Dissolution of silver: Using dilute nitric acid to dissolve the silver in the catalyst releases the least nitrogen oxides and the utilization rate of nitric acid is the highest. 3 (dilute)=6AgNO 3 +2NO(g)+4H 2 O;

[0030] 2. Silver nitrate is precipitated with hydrochloric acid to prepare silver chloride: AgNO 3 +HCl=AgCl(s)+HNO 3 ;

[0031] The nitric acid generated in the precipitation mother liquor can be returned to continue dissolving silver. Not only does it not need to treat the silver precipitation wastewater, but it can also be returned for use, which greatly saves the amount of nitric acid. - In the case of a slight excess, silver can be completely precipitated. Experiments show that when Cl - When the concentration is 14 mg / L, the Ag in the precipitated mother liquor is 0.51 mg / L, and the residual acid is 1.41 mol / L. It can be returned to be used as a silver leaching agent by adding a small amount of nitric acid.

[0032] 3. Reduction of AgCl - Formaldehyde Reduction Method

[0033] In alkaline solution, silver chloride can be reduced to metallic silver by formaldehyde. Under stirring, adjust the pH of silver chloride slurry to 11-13 with sodium hydroxide, and slowly add formaldehyde. The reduction of silver chloride by formaldehyde is an exothermic reaction with a fast reaction speed.

[0034] 2AgCl+HCHO=2Ag(s)+2HCl+CO(g)

[0035] HCl + NaOH = NaCl + H 2 O

[0036] The reduction mother liquor is a sodium chloride solution, containing less than 5 mg / L of Ag, and the silver reduction recovery rate is greater than 99.99%.

[0037] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0038] 1) The purpose of energy saving, reagent saving and improved silver leaching rate is achieved: the silver catalyst maintains its original shape without crushing, and the reaction process does not need to be heated. A multi-stage series column leaching method is adopted, and low-concentration nitric acid is used to leach the silver in the silver-containing catalyst, thereby eliminating the traditional crushing, heating and filtering processes. Since the reaction process of the series leaching column leaching has a strong driving force, the adsorption and retention of silver ions by the porous carrier can be avoided, and a higher silver leaching rate can be obtained. A high-concentration silver nitrate leaching solution is taken for subsequent precipitation and recovery of silver, and a low-concentration silver nitrate leaching solution is returned for continued leaching, thereby increasing the silver concentration and utilizing the remaining nitric acid.

[0039] 2) Change the precipitation process of silver chloride and the reduction process of silver chloride, so that no ammonia nitrogen wastewater is produced, achieving environmental protection. Silver chloride is precipitated with hydrochloric acid, and the amount of hydrochloric acid added is accurately controlled. The main component of the silver chloride precipitation mother liquor is changed from the original sodium nitrate to nitric acid, which can be returned to leached silver. The reduction process uses formaldehyde instead of the commonly used hydrazine hydrate. The reduction mother liquor does not contain ammonium ions and can be returned for use. It is a green and pollution-free process without ammonia nitrogen wastewater.

[0040] In summary, the technical solution of the present invention has the characteristics of short process flow, simple equipment, high silver leaching rate and recovery rate, low treatment cost, no ammonia nitrogen wastewater discharge, and less wastewater discharge. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0042] According to the operation steps and related parameters disclosed in the present invention, those skilled in the art can achieve the purpose of the present invention according to the operation principle of the present invention, without being limited to the equipment itself and the usage method used in the specific implementation manner. The content of the present invention is described in detail below in conjunction with the embodiments, and the protection scope of the claims of the present invention is not limited by the following embodiments.

[0043] Example 1

[0044] (1) Raw materials and leaching equipment

[0045] Ag-Al containing 24.5% Ag 2 O 3 4kg of waste catalyst, the shape is Φ8×8mm hollow ring, the leaching column is 4 Φ40×1500mm organic glass columns, Ag-Al 2 O 3 The spent catalyst was packed into the column in its original shape, 1000 g of spent catalyst was loaded into each column, and then vibrated. 2.4 L of 2 mol / L nitric acid was prepared, and the water used was purified water.

[0046] (2) Silver leaching - tandem column leaching

[0047] The prepared nitric acid solution enters the leaching column from the top at a flow rate of 50 ml / h, flows out from the bottom, and flows into the next leaching column. The four leaching columns are connected in series in sequence, and flow out from the bottom of the fourth column to obtain AgNO 3 The concentration of silver nitrate in the leaching solution was monitored. 3 Silver nitrate leaching solution with a concentration of more than 30g / L is used to precipitate AgCl, AgNO 3 The silver nitrate leachate with a concentration of less than 30g / L was returned as a silver leaching agent. After 48 hours of operation, 2.4 liters of leachate were collected, with an Ag content of 135g / L. 2 O 3 After the waste catalyst is leached, it is unloaded, ground and mixed, and the remaining Ag content is 0.02% and the Ag leaching rate is 99.92%. The first column is filled with new silver-containing waste catalyst and connected in series to the bottom of the last column as a new last column.

[0048] (3) Silver chloride precipitation

[0049] The obtained AgNO 3 After the leaching solution is checked and filtered, the silver is precipitated by chlorination. Add 500ml of 6mol / L HCl, add slowly while stirring, add it in 30 minutes, continue stirring for 30 minutes, let it stand for 30 minutes, filter it, and wash it with pure water until it is neutral. - The content of Ag is 10mg / L, the content of Ag is 5mg / L, the residual acid is 1.4mol / L, and the Ag precipitation rate is 99.99%.

[0050] (4) The silver chloride precipitation mother liquor is returned to continue leaching silver

[0051] The above silver precipitation mother liquor contains HNO 3 1.4mol / L, add concentrated nitric acid to HNO 3 The concentration was 2 mol / L, and the leaching was carried out in cycles. The collected AgNO 3 The leaching solution continues to precipitate silver chloride with hydrochloric acid, and the silver precipitation mother liquor is added with nitric acid to continue to return to leaching silver, and the leaching is cyclically carried out in this way.

[0052] (5) Reduction of Silver

[0053] The AgNO 3 The leaching solutions are combined, checked and filtered, and then silver is precipitated with hydrochloric acid according to step 3 to obtain AgCl precipitate. The AgCl precipitate is placed in a 5000ml beaker, slurried with 4000ml NaOH solution with pH=12, and heated to 60°C. Then, formaldehyde solution is slowly added to reduce the silver. During the process, sodium hydroxide solution is continuously added to control the pH of the silver chloride slurry to 11-13. After the formaldehyde solution is no longer turbid, stop adding formaldehyde and the reduction reaction is completed. Continue heating and boiling for 30 minutes. After the solution is completely clear, filter and wash to obtain silver powder. The Ag concentration of the reduced mother liquor is 12mg / L, and the silver reduction recovery rate is 99.99%

[0054] The obtained silver powder was cast into ingots by a well-known method. The weight of the obtained silver ingot was 978.1 g, the purity was 99.96%, and the total recovery rate was greater than 99.8%.

[0055] Example 2

[0056] The other conditions are the same as those in Example 1, except that the number of columns in series is changed from 4 leaching columns in series in Example 1 to 2 leaching columns in series.

[0057] First column Ag-Al 2 O 3 After the waste catalyst was leached, it was discharged, ground and mixed evenly, and the residual Ag content in the leached residue was detected to be 0.05%, and the Ag leaching rate was 99.80%. Compared with Example 1, the Ag leaching rate decreased by 0.12%, and the silver grade in the leached residue increased from 0.02% in Example 1 to 0.05%.

[0058] Example 3

[0059] Ag 24.5%Ag-Al 2 O 31kg of waste catalyst was crushed and ground to -200 mesh, and 2.4L of 2mol / L nitric acid was added for leaching. No external heating was performed, and the reaction heat was used for self-heating reaction. The reaction was stirred for 24 hours, filtered, and the leached residue was repeatedly washed with 600ml of pure water. The washing water and the leaching liquid were combined to obtain 3000ml of solution. The solution analysis showed that the Ag concentration was 81.4g / L, the Ag content in the residue was 0.08%, and the silver leaching rate was 99.67%. Compared with Example 1, the silver leaching rate was reduced by 0.25% by adopting the conventional stirring leaching process after crushing and grinding, and the Ag content in the leached residue increased by 600g / t.

Claims

1. A method for recovering silver from a silver-containing waste catalyst, characterized in that: The silver-containing waste catalyst is filled in a multi-stage series leaching column, a nitric acid solution is added to the top of the first-stage leaching column of the multi-stage series leaching column, the nitric acid solution flows through each stage of the leaching column in turn to leach the silver-containing waste catalyst, and finally flows out from the bottom of the last stage leaching column, the silver nitrate leachate flowing out from the bottom of the last stage leaching column is collected in sections, the low-concentration silver nitrate leachate returns to the first-stage leaching column for cyclic leaching, and the high-concentration silver nitrate leachate obtains metallic silver through precipitation and reduction; when the leaching of the silver-containing waste catalyst in the first-stage leaching column of the multi-stage series leaching column is completed, the first-stage leaching column is removed and filled with a new silver-containing waste catalyst, and then connected to the bottom of the last stage leaching column as a new last stage leaching column, and the second stage leaching column is used as a new first stage leaching column, and the cycle is repeated; the silver-containing waste catalyst comprises a porous carrier of silicon dioxide or aluminum oxide; the concentration of the nitric acid solution is 1 mol / L to 2 mol / L; the multi-stage series leaching column comprises 3 to 4 stages of leaching columns.

2. The method for recovering silver from silver-containing waste catalyst according to claim 1, characterized in that: During the leaching process, the consumption of nitric acid solution relative to the silver-containing waste catalyst is 2-10 L:1 kg, the initial leaching temperature is room temperature, and the total leaching time is 24 h to 72 h; The concentration of the low-concentration silver nitrate leaching solution is lower than 30 g / L; The concentration of the high-concentration silver nitrate leaching solution is above 30 g / L.

3. The method for recovering silver from silver-containing waste catalyst according to claim 1, characterized in that: In the precipitation process, hydrochloric acid solution is used as a precipitant; the amount of the hydrochloric acid solution used is 0.98 to 1.02 times the theoretical molar amount of the hydrochloric acid solution required to convert silver nitrate into silver chloride.

4. A method for recovering silver from silver-containing waste catalyst according to claim 1 or 3, characterized in that: The precipitation conditions are as follows: temperature is 20°C to 60°C, and time is 60min to 120min.

5. A method for recovering silver from silver-containing waste catalyst according to claim 1 or 3, characterized in that: The nitric acid solution generated during the precipitation process is returned to the leaching process.

6. The method for recovering silver from silver-containing waste catalyst according to claim 1, characterized in that: In the reduction process, an organic aldehyde is used as a reducing agent; the amount of the reducing agent used is 1.2 to 1.5 times the theoretical molar amount of the reducing agent required to convert silver chloride into elemental silver.

7. A method for recovering silver from silver-containing waste catalyst according to claim 1 or 6, characterized in that: The reduction conditions are as follows: pH value is 11-13, temperature is 60° C.-95° C., and time is 30 min-120 min.

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