Method for recovering gold and silver from silver nitrate filter element

Abstract

The invention provides a method for recovering gold and silver from a silver nitrate filter element. The method comprises the following steps: firstly, disassembling a silver nitrate filter element to obtain filter cotton containing gold and silver; secondly, organic matter and other impurities in the filter cotton can be removed through incineration, and the incinerated matter is changed into incinerated matter powder through crushing treatment; then, mixing and heating the incinerated material powder and a concentrated nitric acid solution, carrying out solid-liquid separation, and carrying out evaporative crystallization on first filtrate to obtain silver nitrate crystals; mixing, stirring and heating the first filter residue and aqua regia; and finally, nitrate ions in the second filtrate are removed through nitrate removal, meanwhile, gold is reduced out of the solution through reduction treatment, and low-purity sponge gold is obtained through solid-liquid separation. According to the method, gold and silver are enriched through a pyrogenic process, then gold and silver in the silver nitrate filter element are extracted through a wet process of silver separation through nitric acid and gold separation through aqua regia, recycling of precious metal resources is effectively achieved, and great waste of the precious metal resources is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of precious metal recovery, and in particular to a method for recovering gold and silver in a silver nitrate filter element. Background Art

[0002] Gold is very valuable because of its rarity, easy preservation and wide range of uses. In recent years, the commodity, currency and investment attributes of gold have made it more and more valuable. With the booming development of the photovoltaic and electronics industries, silver nitrate, as the core raw material of the industry, requires a huge amount of silver ingots. Gold, as one of the impurities, is intercepted by the silver nitrate filter element and gradually accumulates, and has a certain recovery value.

[0003] Usually, there is a large amount of silver nitrate residue inside the silver nitrate filter. Since the raw material used in the production of silver nitrate is silver ingot, the silver ingots circulating in the market are usually purified and processed by mines. In mines, silver is associated with precious metals such as gold, platinum, palladium, and rhodium. The content of various associated metals ranges from 0.1g / t to 2g / t. These associated precious metals are insoluble in concentrated nitric acid. Therefore, in the production process of silver nitrate, the silver nitrate filter can intercept these precious metals. It can be inferred that although the content of precious metals in the raw material silver ingot is very low, after being intercepted by the silver nitrate filter, a large amount of precious metals are intercepted on the silver nitrate filter, which plays an enrichment role. Therefore, it is of great significance to extract gold and silver from the silver nitrate filter.

[0004] Therefore, a method for recovering gold and silver in a silver nitrate filter element is urgently needed to solve the above technical problems. Summary of the invention

[0005] The purpose of the present invention is to solve the technical problem that the existing silver nitrate filter element is difficult to recycle due to the enrichment of a large amount of precious metals.

[0006] In order to solve the above technical problems, the present invention provides a method for recovering gold and silver in a silver nitrate filter element, comprising: S10, disassembling the silver nitrate filter element to obtain filter cotton containing gold and silver; S20, burning and crushing the filter cotton containing gold and silver to obtain a burnt material powder; S30, mixing the incineration material powder with a concentrated nitric acid solution and performing a heating treatment, obtaining a first filtrate and a first filter residue after solid-liquid separation, and obtaining silver nitrate crystals after evaporation and crystallization of the first filtrate; S40, mixing the first filter residue with aqua regia, stirring and heating, and collecting a second filtrate after solid-liquid separation; S50, the second filtrate is subjected to a nitrate removal and reduction treatment, and a third filtrate and low-purity sponge gold are obtained after solid-liquid separation.

[0007] Preferably, step S10 specifically includes: using a cutting machine or a saw to disassemble the silver nitrate filter element.

[0008] Preferably, step S20 specifically includes: S201, using a carbonization furnace to incinerate the filter cotton containing gold and silver to obtain an incineration product; S202, using a pulverizer to crush the incineration material to obtain incineration material powder.

[0009] Preferably, in step S30: the mass fraction of concentrated nitric acid in the concentrated nitric acid solution is 65% to 68%; the heating temperature of the heating treatment is 70° C. to 80° C., and the heating time of the heating treatment is 2 h to 3 h.

[0010] Preferably, before evaporating and crystallizing the first filtrate in step S30, the process further includes: mixing the first filtrate with silver oxide and then performing impurity removal treatment.

[0011] Preferably, step S40 specifically includes: mixing the first filter residue with aqua regia, heating to 40°C-60°C and reacting for 1 hour, then heating to 95°C-98°C and continuing to react for 2 hours to 3 hours, and collecting the second filtrate after solid-liquid separation.

[0012] Preferably, in step S40: the ratio of adding aqua regia is 900 ml to 1200 ml of aqua regia per kilogram of the first filter residue, and the mixing and stirring speed is 100 r / min to 200 r / min.

[0013] Preferably, step S50 specifically includes: S501, adding concentrated hydrochloric acid dropwise to the second filtrate and then heating it until no reddish brown gas is generated, and the volume of the second filtrate after removing the nitrate is 1 / 3 of the original volume; S502, subjecting the second filtrate treated with nitrate removal to a reduction reaction with anhydrous sodium sulfite at room temperature until the resulting gold-containing slurry is completely turbid and dark earthy gray, and finally obtaining a third filtrate and low-purity sponge gold after solid-liquid separation.

[0014] Preferably, after step S50 is completed, the following steps are further included: Add 50% diluted sulfuric acid to the low-purity sponge gold and boil it for 20 to 30 minutes. After washing with pure water and drying, high-purity sponge gold with a purity of more than 99.5% is obtained. Mix high-purity sponge gold and borax and place them in a gold melting bowl. Heat to above 1200℃ to fully melt the high-purity sponge gold. After cooling for 5s to 10s, use tweezers to pick up the gold ingot and place it in pure water to cool and shape it.

[0015] Preferably, the pH value of the mixture of low-purity sponge gold and sulfuric acid after washing with pure water is neutral.

[0016] The beneficial effects of the present invention are as follows: Different from the prior art, the present invention provides a method for recovering gold and silver in a silver nitrate filter element. The above method first obtains filter cotton containing gold and silver by disassembling the silver nitrate filter element; secondly, impurities such as organic matter in the filter cotton can be removed by incineration, so that the gold and silver components are relatively enriched, and the incinerated material is turned into powder by crushing treatment, which increases its contact area with subsequent chemical reagents and is conducive to the chemical reaction; then, the incineration powder is mixed and heated with a concentrated nitric acid solution, and nitric acid can react with metals such as silver to generate silver nitrate and enter the solution. After solid-liquid separation, the first filtrate can obtain silver nitrate crystals by evaporation and crystallization to achieve preliminary recovery of silver; then, after the first filter residue is mixed, stirred and heated with aqua regia, gold will dissolve into the solution to form a second filtrate, and this step is prepared for the subsequent recovery of gold; finally, the nitrate ions in the second filtrate are removed by driving out nitrate, and gold is reduced from the solution by reduction treatment, and low-purity sponge gold is obtained by solid-liquid separation, and finally the separation and partial recovery of gold and silver are achieved. The method enriches gold and silver by pyrometallurgy, and then extracts gold and silver from the silver nitrate filter element by a wet process of separating silver with nitrate and separating gold with aqua regia, thereby effectively realizing the recycling of precious metal resources and avoiding a huge waste of precious metal resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A flow chart of a method for recovering gold and silver in a silver nitrate filter element provided by an embodiment of the present invention; Figure 2 The waste silver nitrate filter element provided in Comparative Example 1 of the present invention; Figure 3 The state of the waste silver nitrate filter element provided in Comparative Example 1 of the present invention after incineration; Figure 4 The waste silver nitrate filter element provided in Comparative Example 1 of the present invention is disassembled, incinerated, pulverized and crushed to powder; Figure 5 This is the state of the high-purity sponge gold after drying provided in Comparative Example 1 of the present invention; Figure 6 The gold ingot shape after the high-purity sponge gold ingot is cast provided in Comparative Example 1 of the present invention; Figure 7 The state of borax in the gold melting bowl after the high-purity sponge gold ingot is cast as provided in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0018] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] In view of the technical problem that the existing silver nitrate filter element is difficult to recycle due to the enrichment of a large amount of precious metals, the present invention provides a method for recovering gold and silver from a silver nitrate filter element. The present invention adopts pyrometallurgical enrichment of disassembled filter cotton, and the incineration powder obtained by the pyrometallurgical treatment is first treated with nitric acid to extract silver, and then the filter residue is treated with aqua regia to dissolve gold, and the nitrate is driven out. After the nitrate is driven out, the gold ions in the aqua regia are reduced using anhydrous sodium sulfite to obtain sponge gold powder.

[0020] In order to achieve the above technical objectives, this application adopts the following technical solutions: See also Figure 1 , Figure 1 A flow chart of a method for recovering gold and silver in a silver nitrate filter element provided in an embodiment of the present invention; wherein the method specifically comprises: S10, disassembling the silver nitrate filter element to obtain filter cotton containing gold and silver.

[0021] Specifically, step S10 also includes: The silver nitrate filter element is disassembled using cutting machines, saws and other sharp knives to obtain filter cotton containing gold and silver. During the use of the silver nitrate filter element, precious metals such as gold and silver may be enriched on the filter cotton through adsorption, chemical reaction, etc. By disassembling the silver nitrate filter element, the filter cotton containing precious metals can be separated to provide raw materials for subsequent gold and silver recovery processing.

[0022] Optionally, if the disassembled plastic shell contains a large amount of silver, the silver in the plastic shell can be extracted by soaking in dilute nitric acid, while reducing environmental pollution.

[0023] S20, burning and crushing the filter cotton containing gold and silver to obtain incineration powder.

[0024] Specifically, step S20 also includes: S201, using a carbonization furnace to incinerate the filter cotton containing gold and silver to obtain an incineration product; S202, using a pulverizer to crush the incineration material to obtain incineration material powder.

[0025] Furthermore, in step S201, the organic matter in the filter cotton containing gold and silver is incinerated by a carbonization furnace, and the residual incineration is collected after incineration, and the purpose of pyrometallurgical enrichment is achieved through this step. In step S202, a powdering machine is used to pulverize and crush the incineration powder to improve the sufficiency of the reaction between the incineration powder and aqua regia in the following steps. The carbonization furnace should generate open flames for full combustion, and be equipped with a secondary combustion chamber to avoid the occurrence of incompletely burned substances.

[0026] S30, mixing the incineration powder with concentrated nitric acid solution and performing a heating treatment, obtaining a first filtrate and a first filter residue after solid-liquid separation, and obtaining silver nitrate crystals after evaporation and crystallization of the first filtrate.

[0027] Specifically, step S30 also includes: Silver nitrate separation: Cover the powdered incineration material with pure water, slowly add concentrated nitric acid with a mass fraction of 65% to 68%, heat to react for 2h to 3h, perform solid-liquid separation and filtration, collect the first filter residue, and obtain silver nitrate crystals after evaporation and crystallization of the first filtrate; wherein, through the above heating reaction, silver is oxidized to silver nitrate and enters the first filtrate.

[0028] Furthermore, for separating silver nitrate, 65% to 68% concentrated nitric acid needs to be slowly added in batches, and the heating temperature is 70 to 80°C. The collected first filtrate is evaporated and crystallized to obtain silver nitrate crystals. If necessary, silver oxide is added to remove impurities from the first filtrate (silver nitrate mother liquor). The first filter residue must be washed clean several times to avoid silver residue remaining in the filter residue.

[0029] S40, mixing the first filter residue with aqua regia, stirring and heating, and collecting a second filtrate after solid-liquid separation.

[0030] Specifically, step S40 also includes: Aqua regia metallization: Mix the first filter residue with aqua regia in a certain proportion and heat it, react at a temperature between 40 and 60°C for 1 hour, heat it to 95°C to 98°C and continue to react for 2 to 3 hours, perform solid-liquid separation and filtration, collect the second filtrate and the second filter residue; this step plays a role in further separating and extracting precious metals in the entire recovery process. Through the reaction with aqua regia, the precious metals in the first filter residue are dissolved into the solution to form the second filtrate, which provides raw materials containing precious metals for subsequent treatment steps such as driving out nitrate and reduction, thereby achieving efficient recovery of precious metals.

[0031] Furthermore, the reaction is first carried out at a temperature between 40°C and 60°C for 1 hour. This stage may be to start the reaction so that some substances that are more easily reactive react with aqua regia first. Then the temperature is raised to 95°C to 98°C and the reaction is continued for 2h to 3h. High temperature can increase the reaction rate and make the reaction more complete. In this process, the strong oxidizing and corrosive properties of aqua regia can dissolve precious metals in the first filter residue, such as gold.

[0032] Furthermore, in step 4, the gold-containing aqua regia needs to be added in stages, and the ratio of aqua regia added is 900m~1200ml aqua regia per kilogram of incineration material; since the inorganic matter adhesion phenomenon in the incineration powder hinders the discharge of the reaction gas, the gold-containing solution after the first filter residue and aqua regia are mixed and stirred is easy to overflow, so the automatic stirring speed is controlled to 100r / min~200r / min.

[0033] S50, the second filtrate is subjected to a nitrate removal and reduction treatment, and a third filtrate and low-purity sponge gold are obtained after solid-liquid separation.

[0034] Specifically, step S50 also includes: S501, add concentrated hydrochloric acid to the second filtrate and heat it until no red-brown gas is generated. The volume of the second filtrate after removing the nitrate is 1 / 3 of the original volume. At this time, the chloroauric acid solution in the second filtrate after removing the nitrate is dark yellowish brown.

[0035] Furthermore, the heat treatment after adding concentrated hydrochloric acid to the second filtrate is mainly for driving away nitrate. Aqua regia contains nitric acid. In the previous step, nitric acid dissolves the precious metal to form a second filtrate containing nitrate ions. During the heating process, concentrated hydrochloric acid and nitric acid react to produce nitrosyl chloride and chlorine. Chlorine is a yellow-green gas. Substances such as nitrosyl chloride may also decompose to produce reddish-brown nitrogen dioxide gas under certain conditions. When no reddish-brown gas is produced, it means that the nitric acid in the second filtrate is basically reacted, that is, the process of driving away nitrate is basically over.

[0036] Furthermore, the volume of the second filtrate after the removal of nitrate is 1 / 3 of the original volume, which indicates that a large amount of substances (including generated gases and other substances that may volatilize) escape from the solution during the removal of nitrate, causing the volume of the solution to decrease significantly. At the same time, the decrease in volume also means that the concentration of substances such as nitrate ions in the solution has changed, which is conducive to the subsequent further treatment of precious metals.

[0037] S502, subjecting the second filtrate treated with nitrate removal to a reduction reaction with anhydrous sodium sulfite at room temperature until the resulting gold-containing slurry is completely turbid and dark earthy gray, and finally obtaining a third filtrate and low-purity sponge gold after solid-liquid separation.

[0038] Furthermore, at room temperature, the second filtrate treated with nitrate removal is subjected to a reduction reaction with anhydrous sodium sulfite. Anhydrous sodium sulfite is used as a reducing agent to reduce the precious metal ions in the second filtrate to metal elements. For gold ions, the sulfur element in sodium sulfite has a certain reducing property, which can reduce gold ions to gold elements. In the reaction process, sodium sulfite loses electrons, and gold ions gain electrons and are reduced to gold elements.

[0039] Furthermore, when the gold-containing slurry is completely turbid and presents a dull earthy gray color, it indicates that the reduction reaction is basically completed. This turbidity is caused by the generated gold element particles and other insoluble substances that may exist. As the reaction proceeds, gold ions are continuously reduced, and gold element gradually aggregates to form particles, causing the appearance of the slurry to change. Finally, solid-liquid separation is performed to obtain a third filtrate and low-purity sponge gold. Solid-liquid separation can be performed by filtering and other methods to separate the third filtrate containing unreacted substances and other impurities from the gold element. Low-purity sponge gold is a loose and porous form of gold element. Since it is obtained through a reduction reaction, it may contain a small amount of impurities, so it is called low-purity sponge gold.

[0040] Furthermore, this step is one of the key links in the entire precious metal recovery process, which realizes the reduction and separation of gold. Through the reduction reaction with anhydrous sodium sulfite, the gold ions in the second filtrate are converted into gold element, thereby completing the process of recovering gold from precious metal-containing materials such as silver nitrate filter elements. At the same time, it provides a raw material basis for the subsequent further purification of low-purity sponge gold.

[0041] Furthermore, after step S50 is completed, the following steps are further included: First, add 50% diluted sulfuric acid to the low-purity sponge gold and boil it for 20-30 minutes. After washing with pure water and drying, high-purity sponge gold with a purity of more than 99.5% is obtained. At this time, hydrochloric acid can also be used in the pickling process of sponge gold. The pH value of the mixture of low-purity sponge gold and sulfuric acid after pure water washing is neutral to avoid residual acidic solution. Afterwards, mix the high-purity sponge gold with borax and place it in a gold melting bowl, heat it to above 1200°C to fully melt the high-purity sponge gold, cool it for 5s to 10s, use tweezers to pick up the gold ingot and place it in pure water to cool and shape it.

[0042] Specifically, high-purity sponge gold is mixed with borax and placed in a gold melting bowl. Borax acts as a flux in this process, which can lower the melting point of gold and allow the gold to fully melt at a relatively low temperature. When heated to above 1200°C, high-purity sponge gold changes from solid to liquid at high temperature, forming molten gold liquid.

[0043] Furthermore, the molten gold can be cast into a mold, and after the mold is preheated, the molten gold is poured into the mold to be cast into a desired shape of gold ingot.

[0044] Specifically, after cooling for 5s to 10s, use tweezers to pick up the gold ingot and place it in pure water to cool and shape it. Rapid cooling can make the gold liquid solidify quickly to form a solid gold ingot. Cooling in pure water can quickly cool the gold ingot while avoiding excessive reaction with oxygen and other substances in the air, thereby ensuring the purity and quality of the gold ingot.

[0045] The technical solution of the present invention is now further described in conjunction with specific embodiments.

[0046] Comparative Example 1: Comparative Example 1 provides a method for recovering gold and silver in a silver nitrate filter element, the method comprising the following steps: (1) Disassembly of silver nitrate filter element: First, provide 3 used silver nitrate filter elements, such as Figure 2 Afterwards, a medium-sized cutting machine was used to dismantle the gold and silver filter cotton from the three old silver nitrate filter elements; (2) Incineration and crushing of filter cotton: First, use a carbonization furnace to incinerate the organic matter in the filter cotton containing gold and silver to obtain incineration products, such as Figure 3 As shown; after that, the residual incineration material is crushed by a powdering machine to obtain the incineration material powder, such as Figure 4 As shown; (3) Separation of silver with nitrate: Add pure water to the powdered incineration material, slowly add 65% to 68% concentrated nitric acid in batches, react at 70°C to 75°C for 2 to 3 hours, perform solid-liquid separation and filtration, collect the first filtrate and the first filter residue, and evaporate and crystallize the first filtrate to obtain silver nitrate crystals; (4) Aqua regia metallurgy: add 900 ml to 1200 ml of aqua regia per kilogram of incineration powder, react at a temperature between 40°C and 60°C for 1 hour, raise the temperature to 95°C to 98°C and continue to react for 2 to 3 hours, perform solid-liquid separation and filtration, and collect the second filtrate and the second filter residue; (5) Removal of nitrate and reduction treatment: First, concentrated hydrochloric acid is added dropwise to the second filtrate and then heated until no red-brown gas is generated. The volume of the second filtrate after the removal of nitrate is 1 / 3 of the original volume. At this time, the chloroauric acid solution in the second filtrate after the removal of nitrate is dark yellowish brown. Then, the second filtrate after the removal of nitrate is reduced with anhydrous sodium sulfite at room temperature until the gold-containing slurry is completely turbid and dark grayish brown. (6) Purification of low-purity sponge gold: First, the gold-containing slurry is subjected to solid-liquid separation and filtration, and the resulting filter residue is low-purity sponge gold and the resulting filtrate is the third filtrate; then, sulfuric acid with a diluted concentration of 50% is added to the low-purity sponge gold and boiled for 20 minutes to 30 minutes, washed with pure water until neutral, and then dried to obtain high-purity sponge gold with a purity of more than 99.5%, such as Figure 5 shown.

[0047] (7) Casting of high-purity sponge gold ingots: Mix high-purity sponge gold with borax and place in a gold melting bowl. Heat to above 1200°C to fully melt the high-purity sponge gold. After cooling for 5s to 10s, use tweezers to pick up the gold ingot and place in pure water to cool and shape it. Figure 6 as well as Figure 7 shown.

[0048] Embodiment 1: Embodiment 1 of the present invention provides a method for recovering gold and silver in a silver nitrate filter element, which is substantially the same as the method for recovering gold and silver in a silver nitrate filter element provided in Comparative Example 1, except that in step (2), the incinerated material after incineration in the carbonization furnace is not subjected to powdering and crushing treatment.

[0049] Embodiment 2: Embodiment 2 of the present invention provides a method for recovering gold and silver in a silver nitrate filter element, which is substantially the same as the method for recovering gold and silver in a silver nitrate filter element provided in Comparative Example 1, except that: in step (1), the waste silver nitrate filter element is not disassembled, and the waste silver nitrate filter element is directly incinerated in a carbonization furnace in step (2) to obtain an incineration material, and then the residual incineration material is pulverized and crushed by a pulverizer to obtain an incineration material powder.

[0050] Embodiment 3: Embodiment 3 of the present invention provides a method for recovering gold and silver in a silver nitrate filter element, which is substantially the same as the method for recovering gold and silver in a silver nitrate filter element provided in Comparative Example 1, except that: in step (1), the waste silver nitrate filter element is not disassembled, and the waste silver nitrate filter element is directly incinerated in a carbonization furnace in step (2) to obtain an incineration material, and the incineration material after incineration in the carbonization furnace is not subjected to a powdering and crushing treatment.

[0051] Comparative Example 2: Comparative Example 2 provides a method for recovering gold and silver in a silver nitrate filter element, the method comprising the following steps: (1) Disassembly of silver nitrate filter elements: First, provide 100 used silver nitrate filter elements; then, use a medium-sized cutting machine to disassemble the gold and silver filter cotton from the 100 used silver nitrate filter elements; (2) Incineration and crushing of filter cotton: First, the organic matter in the filter cotton containing gold and silver is incinerated in a carbonization furnace to obtain an incineration product; then, the remaining incineration product is crushed by a powder grinder to obtain an incineration product powder; (3) Separation of silver by nitric acid: weigh 1000 g of the powder of the incinerated material after pulverization, cover the powder with pure water, slowly add 1 L of 65% to 68% concentrated nitric acid in batches, react at a temperature of 70°C to 75°C for 2 to 3 hours, perform solid-liquid separation and filtration, collect the first filtrate and the first filter residue, and obtain silver nitrate crystals after evaporation and crystallization of the first filtrate; (4) Aqua regia metallurgy: add 900 ml to 1200 ml of aqua regia per kilogram of incineration powder, react at a temperature between 40°C and 60°C for 1 hour, raise the temperature to 95°C to 98°C and continue to react for 2 hours to 3 hours, perform solid-liquid separation and filtration, and collect the second filtrate and the second filter residue; (5) Removal of nitrate and reduction treatment: First, concentrated hydrochloric acid is added dropwise to the second filtrate and then heated until no red-brown gas is generated. The volume of the second filtrate after the removal of nitrate is 1 / 3 of the original volume. At this time, the chloroauric acid solution in the second filtrate after the removal of nitrate is dark yellowish brown. Then, the second filtrate after the removal of nitrate is reduced with anhydrous sodium sulfite at room temperature until the gold-containing slurry is completely turbid and dark grayish brown. (6) Purification of low-purity sponge gold: First, the gold-containing slurry is filtered for solid-liquid separation. The resulting filter residue is low-purity sponge gold, and the resulting filtrate is the third filtrate. Then, sulfuric acid with a diluted concentration of 50% is added to the low-purity sponge gold and boiled for 20 minutes to 30 minutes. After washing with pure water until neutral, it is dried to obtain high-purity sponge gold with a purity of more than 99.5%.

[0052] (7) Casting of high-purity sponge gold ingots: Mix high-purity sponge gold and borax and place in a gold melting bowl. Heat to above 1200°C to fully melt the high-purity sponge gold. After cooling for 5s to 10s, use tweezers to pick up the gold ingot and place it in pure water to cool and shape it.

[0053] Embodiment 4: Embodiment 4 of the present invention provides a method for recovering gold and silver in a silver nitrate filter element, which is substantially the same as the method for recovering gold and silver in a silver nitrate filter element provided in Comparative Example 2, except that: Step (3) silver nitrate separation: 1000 g of the powder of the incineration material after pulverization is weighed, pure water is added to cover the powder of the incineration material after pulverization, 1 L of 65% to 68% concentrated nitric acid is slowly added in batches, the reaction is carried out at a temperature of 60° C. for 2 to 3 h, solid-liquid separation and filtration are performed, a first filtrate and a first filter residue are collected, and the first filtrate is evaporated and crystallized to obtain silver nitrate crystals.

[0054] Embodiment 5: Example 5 of the present invention provides a method for recovering gold and silver in a silver nitrate filter element, which is substantially the same as the method for recovering gold and silver in a silver nitrate filter element provided in Comparative Example 2, except that: Step (3) silver nitrate separation: 1000 g of the powder of the incineration material after pulverization is weighed, pure water is added to cover the powder of the incineration material after pulverization, 1 L of 65% to 68% concentrated nitric acid is slowly added in batches, the reaction is carried out at a temperature of 80° C. for 2 to 3 h, solid-liquid separation and filtration are performed, a first filtrate and a first filter residue are collected, and the first filtrate is evaporated and crystallized to obtain silver nitrate crystals.

[0055] Embodiment 6: Example 6 of the present invention provides a method for recovering gold and silver in a silver nitrate filter element, which is substantially the same as the method for recovering gold and silver in a silver nitrate filter element provided in Comparative Example 2, except that: Step (4) gold recovery by aqua regia: 900 ml to 1200 ml aqua regia is added per kilogram of incineration powder, reacted at a temperature between 40° C. and 60° C. for 3 h to 4 h, solid-liquid separation and filtration are performed, and a second filtrate is collected.

[0056] Embodiment 7: Example 7 of the present invention provides a method for recovering gold and silver in a silver nitrate filter element, which is substantially the same as the method for recovering gold and silver in a silver nitrate filter element provided in Comparative Example 2, except that: Step (5) nitrate removal and reduction treatment: first, concentrated hydrochloric acid is added dropwise to the second filtrate, followed by heating until no reddish-brown gas is generated, and the volume of the second filtrate after nitrate removal is 1 / 3 of the original volume. At this time, the chloroauric acid solution in the second filtrate treated with nitrate removal is dark yellowish earth; then, the second filtrate treated with nitrate removal is subjected to a reduction reaction with sodium bisulfite at room temperature until the gold-containing slurry obtained is completely turbid and dark grayish earth.

[0057] Embodiment 8: Example 8 of the present invention provides a method for recovering gold and silver in a silver nitrate filter element, which is substantially the same as the method for recovering gold and silver in a silver nitrate filter element provided in Comparative Example 2, except that: Step (5) nitrate removal and reduction treatment: first, concentrated hydrochloric acid is added dropwise to the second filtrate, followed by heating until no reddish-brown gas is generated, and the volume of the second filtrate after nitrate removal is 1 / 3 of the original volume. At this time, the chloroauric acid solution in the second filtrate treated with nitrate removal presents a dull earthy yellow color; thereafter, the second filtrate treated with nitrate removal is subjected to a reduction reaction with hydrazine hydrate having a mass content of 25% at room temperature until the gold-containing slurry obtained is completely turbid and presents a dull earthy gray color.

[0058] Embodiment 9: Example 9 of the present invention provides a method for recovering gold and silver in a silver nitrate filter element, which is substantially the same as the method for recovering gold and silver in a silver nitrate filter element provided in Comparative Example 2, except that: Step (6) purification of low-purity sponge gold: first, the gold-containing slurry is subjected to solid-liquid separation and filtration, and the resulting filter residue is low-purity sponge gold; then, hydrochloric acid having a dilution concentration of 36% to 38% is added to the low-purity sponge gold and boiled for 20 min to 30 min, and then washed with pure water until neutral and then dried to obtain high-purity sponge gold with a purity of more than 99.5%.

[0059] Embodiment 10: Embodiment 10 of the present invention provides a method for recovering gold and silver in a silver nitrate filter element, which is substantially the same as the method for recovering gold and silver in a silver nitrate filter element provided in Comparative Example 2, except that: Step (6) purification of low-purity sponge gold: first, the gold-containing slurry is subjected to solid-liquid separation and filtration, and the resulting filter residue is low-purity sponge gold; then, nitric acid having a diluted concentration of 65% to 68% is added to the low-purity sponge gold and boiled for 20 min to 30 min, and then washed with pure water until neutral and then dried to obtain high-purity sponge gold with a purity of more than 99.5%.

[0060] Specifically, the results of the incineration weight, the boiling phenomenon of gold in aqua regia, and the detection of gold content in high-purity sponge gold in the methods provided in the above Examples 1 to 3 and Comparative Example 1 are shown in Table 1 below: Table 1

[0061] Furthermore, by comparing Comparative Example 1 with Examples 1 to 3, it can be seen that the weight of the incineration material obtained from the disassembled silver nitrate filter element is small, and the amount of auxiliary raw materials consumed is small; the waste silver nitrate filter element is powdered after incineration, the metal is wrapped by inorganic matter, resulting in reduced incomplete silver nitrate separation reaction, and the gold boiling phenomenon of aqua regia is eliminated, and the obtained high-purity sponge gold has higher purity.

[0062] Specifically, 100 waste silver nitrate filter cartridges were disassembled, incinerated, and pulverized, and the elemental composition of the incinerated powder was analyzed, as shown in Figure 2: Table 2

[0063] Specifically, the weight of the incineration powder, the temperature of silver nitrate separation, the reaction phenomenon of silver nitrate separation, and the gold content of the high-purity sponge gold in the methods provided in Examples 4 to 5 and Comparative Example 2 are shown in Table 3 below: Table 3

[0064] Furthermore, by comparing Comparative Example 2 with Examples 4 to 5, it can be seen that for the incineration powder of waste silver nitrate filter elements with a high silver content, the temperature for silver nitrate separation is too low, the reaction of silver and base metals is incomplete, and the purity of sponge gold is not high; when the temperature for silver nitrate separation is too high, the reaction is violent and the solution overflows, the recovered liquid contains too many impurities or the reaction is insufficient, and the purity of sponge gold is low; the optimal temperature for silver nitrate separation is 70°C to 75°C.

[0065] Specifically, the results of the weight of the incinerated powder, the aqua regia gold metallization process, the weight of the high-purity sponge gold, and the gold content of the second filter residue in the methods provided in the above Example 6 and Comparative Example 2 are shown in Table 4 below: Table 4

[0066] Furthermore, by comparing Comparative Example 2 with Example 6, it can be seen that the aqua regia gold dissolution requires a high-temperature water bath at a temperature of 95°C to 98°C to activate the activity of aqua regia and fully react with gold, otherwise the gold element will not be fully dissolved and will remain in the second filter residue.

[0067] Specifically, the weight of the incineration powder, the chloroauric acid reduction reagent, the weight of the high-purity sponge gold, the purity of the high-purity sponge gold, the gold content of the second filter residue, and the gold content of the third filtrate in the methods provided in Examples 7 to 8 and Comparative Example 2 are shown in Table 5 below: Table 5

[0068] Furthermore, by comparing Comparative Example 2 with Examples 7 to 8, it can be seen that chloroauric acid has the same effect when using reducing agents such as anhydrous sodium sulfite, ammonium bisulfite, and hydrazine hydrate, but anhydrous sodium sulfite is cheap and pollution-free, making it the best choice.

[0069] Specifically, the results of the weight of the incinerated powder, the pickling reagent, the gold content of the pickling water, and the weight of the high-purity sponge gold in the methods provided in Examples 9 to 10 and Comparative Example 2 are shown in Table 6 below: Table 6

[0070] Furthermore, by comparing Comparative Example 2 with Examples 9 to 10, it can be seen that during the pickling process to remove the base metals in the low-purity sponge gold, the selected reagent nitric acid will react with the residual hydrochloric acid in the low-purity sponge gold to form aqua regia to dissolve the reduced low-purity sponge gold again, ultimately causing the loss of high-purity sponge gold; the selected reagents sulfuric acid and hydrochloric acid will slightly dissolve a small amount of low-purity sponge gold, but the purification effect is better, the borax in the melting bowl of the high-purity sponge gold ingot has no different color, and the high-purity sponge gold ingot contains few impurities.

[0071] In summary, different from the prior art, the present invention provides a method for recovering gold and silver in a silver nitrate filter element. The above method first disassembles the silver nitrate filter element to obtain filter cotton containing gold and silver; secondly, impurities such as organic matter in the filter cotton can be removed by incineration, so that the gold and silver components are relatively enriched, and the incinerated material is turned into powder by crushing treatment, which increases its contact area with subsequent chemical reagents and is conducive to the chemical reaction; then, the incineration powder is mixed and heated with a concentrated nitric acid solution, and nitric acid can react with metals such as silver to generate silver nitrate and enter the solution. After solid-liquid separation, the first filtrate can be evaporated and crystallized to obtain silver nitrate crystals to achieve preliminary recovery of silver; then, after the first filter residue is mixed, stirred and heated with aqua regia, gold will dissolve into the solution to form a second filtrate, which is a step to prepare for the subsequent recovery of gold; finally, the nitrate ions in the second filtrate are removed by driving out nitrate, and the gold is reduced from the solution by reduction treatment, and low-purity sponge gold is obtained after solid-liquid separation, and finally the separation and partial recovery of gold and silver are achieved. The method enriches gold and silver by pyrometallurgy, and then extracts gold and silver from the silver nitrate filter element by a wet process of separating silver with nitrate and separating gold with aqua regia, thereby effectively realizing the recycling of precious metal resources and avoiding a huge waste of precious metal resources.

[0072] It should be noted that the above embodiments all belong to the same inventive concept, and the description of each embodiment has its own focus. For matters that are not described in detail in some embodiments, reference may be made to the description in other embodiments.

[0073] The above embodiments only express the implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for those of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for recovering gold and silver in a silver nitrate filter element, characterized in that: include: S10, disassembling the silver nitrate filter element to obtain filter cotton containing gold and silver; S20, burning and crushing the filter cotton containing gold and silver to obtain an incineration powder; S30, mixing the incineration material powder with a concentrated nitric acid solution and performing a heating treatment, obtaining a first filtrate and a first filter residue after solid-liquid separation, and obtaining silver nitrate crystals after evaporation and crystallization of the first filtrate; S40, mixing the first filter residue with aqua regia, stirring the mixture, and then heating the mixture, and collecting a second filtrate after solid-liquid separation; S50, performing a nitrate removal and reduction treatment on the second filtrate, and obtaining a third filtrate and low-purity sponge gold after solid-liquid separation.

2. The method for recovering gold and silver in a silver nitrate filter element according to claim 1, characterized in that: The step S10 specifically includes: using a cutting machine or a saw to disassemble the silver nitrate filter element.

3. The method for recovering gold and silver in a silver nitrate filter element according to claim 1, characterized in that: The step S20 specifically includes: S201, using a carbonization furnace to incinerate the filter cotton containing gold and silver to obtain an incineration product; S202, using a powder grinder to crush the incinerated material to obtain the incinerated material powder.

4. The method for recovering gold and silver in a silver nitrate filter element according to claim 1, characterized in that: In the step S30, the mass fraction of concentrated nitric acid in the concentrated nitric acid solution is 65% to 68%; the heating temperature of the heating treatment is 70° C. to 80° C., and the heating time of the heating treatment is 2 h to 3 h.

5. The method for recovering gold and silver in a silver nitrate filter element according to claim 4, characterized in that: Before evaporating and crystallizing the first filtrate in the step S30, the method further includes: mixing the first filtrate with silver oxide and then performing an impurity removal treatment.

6. The method for recovering gold and silver in a silver nitrate filter element according to claim 1, characterized in that: The step S40 specifically includes: mixing the first filter residue with aqua regia, heating to 40°C-60°C and reacting for 1 hour, then heating to 95°C-98°C and continuing to react for 2 hours-3 hours, and collecting the second filtrate after solid-liquid separation.

7. The method for recovering gold and silver in a silver nitrate filter element according to claim 6, characterized in that: In the step S40, the ratio of adding aqua regia is 900 ml to 1200 ml of aqua regia per kilogram of the first filter residue, and the mixing and stirring speed is 100 r / min to 200 r / min.

8. The method for recovering gold and silver in a silver nitrate filter element according to claim 1, characterized in that: The step S50 specifically includes: S501, adding concentrated hydrochloric acid dropwise to the second filtrate and then heating it until no reddish brown gas is generated, and the volume of the second filtrate after removing the nitrate is 1 / 3 of the original volume; S502, subjecting the second filtrate that has been treated with nitrate removal to a reduction reaction with anhydrous sodium sulfite at room temperature until the gold-containing slurry obtained is completely turbid and presents a dull earthy gray color, and finally obtaining the third filtrate and the low-purity sponge gold after solid-liquid separation.

9. The method for recovering gold and silver in a silver nitrate filter element according to claim 1, characterized in that: After the step S50 is completed, the following steps are also included: Add sulfuric acid with a dilution concentration of 50% to the low-purity sponge gold and boil for 20-30 minutes, and then wash with pure water and dry to obtain high-purity sponge gold with a purity of more than 99.5%; The high-purity sponge gold is mixed with borax and placed in a gold melting bowl, heated to above 1200° C. to fully melt the high-purity sponge gold, cooled for 5s to 10s, and then the gold ingot is clamped with tweezers and placed in pure water to cool and shape.

10. The method for recovering gold and silver in a silver nitrate filter element according to claim 1, characterized in that: The pH value of the mixed solution of the low-purity sponge gold and sulfuric acid after being washed with pure water is neutral.

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