Method for safe oxidative dissolution of metallic silver

Abstract

Disclosed is a method for safe oxidative dissolution of metallic silver, comprising the following steps: step 1, preparing a silver dissolving solution, the silver dissolving solution being a solution containing an ammonium salt; and step 2, mixing metallic silver, the silver dissolving solution, and hydrogen peroxide, to cause the metal silver to undergo a chemical reaction in the silver dissolving reaction solution containing the silver dissolving solution and the hydrogen peroxide, to generate a silver salt and / or a silver complex product, and, during the reaction process, controlling the pH value of the silver dissolving reaction solution to be pH 0.5-10.5. The present invention achieves safe production during a process of dissolving metallic silver, reduces pollution, and lowers energy consumption.

Description

A method for safely oxidizing and dissolving metallic silver Technical Field

[0001] The invention belongs to the technical field of metal oxidation reactions, and particularly relates to a method for safely oxidizing and dissolving metallic silver. Background Art

[0002] There are two common processes for dissolving metallic silver to produce silver compounds. One is the nitric acid silver dissolution method, and the other is the metallic silver anodic electrolytic silver dissolution method.

[0003] The silver nitrate dissolution method uses nitric acid to react with silver metal to produce water-soluble silver nitrate, which is then further chemically reacted to produce silver compounds. However, silver nitrate is a Class A hazardous chemical and its production must be carried out in a Class A workshop, which has high production conditions and management costs. Furthermore, silver nitrate is highly toxic and corrosive, posing a serious threat to the human body. If it enters the ecological environment, it can pollute water and soil and is highly corrosive to production equipment. Furthermore, the wastewater containing nitrate is difficult to treat, and the silver nitrate dissolution method presents wastewater treatment challenges, making the production cost of other silver compound products made from the silver nitrate intermediate high.

[0004] The silver anodic electrolytic silver dissolution method uses silver as the anode to electrolyze and produce silver oxide or silver ammonia solution. This method produces a large amount of hydrogen during operation, a flammable and explosive gas, posing a safety hazard. Furthermore, when producing silver oxide, the surface of the anode silver is tightly coated with newly formed silver oxide, forming a single anode. The electrolytic silver dissolution process involves the electrolysis of water in the electrolyte, consuming significant amounts of electricity. When ammonia is used as the electrolyte to prepare the silver ammonia solution with the silver oxide (Ag2O) produced on the anode silver, the production process produces ammonia-containing waste gas, requiring environmental treatment. Furthermore, the resulting silver ammonia solution may form explosive precipitates such as silver nitride (Ag3N), silver imide (Ag2NH), and silver azide (AgN3) over time.

[0005] Therefore, improvements to the production process of dissolved metallic silver must not only meet the needs of large-scale production efficiency, but also be considered from the perspective of safe production, so that the production and processing of silver complexes and / or silver salts can be safer, more environmentally friendly and energy-saving. Summary of the Invention

[0006] The present invention provides a method for safely oxidizing and dissolving metallic silver, thereby achieving safe production of the metallic silver dissolving process, reducing pollution and lowering energy consumption.

[0007] The present invention adopts the following technical solutions to achieve the above-mentioned objectives.

[0008] A method for safely oxidizing and dissolving metallic silver comprises the following steps:

[0009] Step 1: preparing a silver-soluble solution, wherein the silver-soluble solution is a solution containing ammonium salt;

[0010] Step 2: Mixing metallic silver, a silver dissolving solution and hydrogen peroxide, allowing the metallic silver to undergo a chemical reaction in a silver dissolving reaction solution containing the silver dissolving solution and hydrogen peroxide to generate a silver salt and / or a silver complex product, and controlling the pH value of the silver dissolving reaction solution to be between pH 0.5 and pH 10.5 during the reaction.

[0011] The method of the present invention can be carried out in an ordinary tank container. Hereinafter, the tank container used for oxidizing and dissolving metallic silver of the present invention is referred to as an oxidation reaction tank.

[0012] In step 1, the ammonium salt is selected from at least one of ammonium sulfate, ammonium bisulfate, ammonium carbonate, and ammonium bicarbonate. Preferably, the silver dissolving solution contains ammonium sulfate and / or ammonium bisulfate. In other words, at least one of the ammonium salts is ammonium sulfate or ammonium bisulfate. More preferably, the silver dissolving solution contains ammonium sulfate. Preferably, the ammonium salt concentration in the silver dissolving solution is 0.1 g / L to 680 g / L.

[0013] The present invention can mix metallic silver, a silver-dissolving solution, and hydrogen peroxide in the following manner: ① adding metallic silver and hydrogen peroxide to the silver-dissolving solution, ② adding metallic silver to the mixture of the silver-dissolving solution and hydrogen peroxide, and ③ adding metallic silver and hydrogen peroxide to the mixture of the silver-dissolving solution and hydrogen peroxide. The hydrogen peroxide content in the silver-dissolving reaction solution is set according to the silver-dissolving solution formula performance and the silver-dissolving speed required by the process. When the silver-dissolving speed is lower than the set value required by the process, the hydrogen peroxide content in the silver-dissolving reaction solution is increased; when the silver-dissolving speed is higher than the set value required by the process, the hydrogen peroxide content in the silver-dissolving reaction solution is reduced. Preferably, the hydrogen peroxide content in the silver-dissolving reaction solution is 0.1 g / L to 100 g / L.

[0014] In step 2, the hydrogen peroxide in the silver dissolving reaction solution reacts chemically with the metallic silver to generate silver oxide Ag2O. The generated silver oxide is affected by the lone electron pair of nitrogen in the ammonia and / or ammonium and / or organic amine in the silver dissolving reaction solution and undergoes a coordination dissolution reaction to generate [Ag(NH3)2]2SO4 and / or [Ag(NH3)2]2CO3 silver complex. + When the ion concentration is low, it will also react with sulfate and / or carbonate in the silver-soluble reaction solution to generate silver sulfate and / or silver carbonate.

[0015] Preferably, to reduce the decomposition of hydrogen peroxide during the reaction, promote the oxidation of metallic silver, and improve the solubility of silver oxide in the reaction solution, the silver dissolving solution further contains additives and / or pH adjusters. These additives are specifically selected from one or more of ethylenediaminetetraacetate, cyclohexylamine, methenamine, and phenacetin. Cyclohexylamine, methenamine, and phenacetin serve as hydrogen peroxide stabilizers. EDTA reacts with silver to form a silver complex, accelerating the dissolution of oxidized silver and increasing the concentration of soluble silver ions in the reaction solution. The EDTA is preferably diammonium EDTA to reduce the precipitation of cations in the silver dissolving reaction solution and / or the resulting significant pH fluctuations that can affect chemical reactions and process control when using other EDTA salts. The pH adjuster is sulfuric acid or aqueous ammonia. Preferably, the concentration of these additives in the silver dissolving reaction solution is ≥ 0.001% by weight.

[0016] As a preferred embodiment of the present invention, during the reaction process, the pH value of the silver dissolving reaction solution is controlled within the process-defined range by adding the aforementioned pH adjuster to the solution. The present invention has found that the higher the pH value of the silver dissolving reaction solution, the more readily the hydrogen peroxide decomposes to produce water and oxygen, and is more likely to cause the solution to release a large amount of ammonia gas. However, for a given hydrogen peroxide concentration, the higher the pH value, the faster the silver dissolving reaction. Furthermore, when the silver dissolving solution contains ammonium bicarbonate, the heat released by the rapid decomposition of hydrogen peroxide can easily cause the ammonium bicarbonate in the solution to decompose, leading to an imbalance in the silver dissolving reaction. Therefore, during production, it is important to comprehensively consider the impact of multiple factors to avoid unilaterally pursuing a high pH value for the silver dissolving reaction solution, which can lead to ammonia odor in the production workshop, polluting the environment, and creating a dangerous source of oxygen enrichment. Preferably, the pH value of the silver dissolving reaction solution is controlled between pH 4 and pH 8.

[0017] The method of the present invention can be implemented in the following two specific embodiments: (1) a production process scheme in which the silver ion concentration of the silver dissolving reaction solution is maintained at the process concentration set value for continuous production; (2) a production process scheme in which the silver ion concentration of the silver dissolving reaction solution rises to the process concentration set value as the operation ends. During the reaction process, the silver ion concentration in the silver dissolving reaction solution can be reflected by the value detected by the hydrometer. When implementing embodiment (1), if metallic silver is present in the silver dissolving reaction solution, the silver ion concentration of the silver dissolving reaction solution is maintained at the process concentration set value by adding a silver dissolving solution and hydrogen peroxide, or a mixture of a silver dissolving solution and hydrogen peroxide, to the silver dissolving reaction solution.

[0018] The method of the present invention can prioritize the production of silver salts or silver ammonia complexes by adjusting the formula ingredients of the silver dissolving solution and / or setting the pH value of the silver dissolving reaction solution. The lower the concentration of ammonia and / or ammonium salt and / or organic amine contained in the silver dissolving reaction solution, and / or the lower the pH value of the silver dissolving reaction solution, the more likely the silver dissolving reaction is to produce a silver salt. Continuous reaction saturates the silver dissolving reaction solution to precipitate a solid silver salt product. Conversely, the higher the concentration of ammonia and / or ammonium salt and / or organic amine contained in the silver dissolving reaction solution, and / or the higher the pH value of the silver dissolving reaction solution, the more likely the silver dissolving reaction is to produce a silver complex, that is, a silver complex solution product is produced in the ammonia-rich silver dissolving reaction solution.

[0019] The present invention can be improved as follows: during the reaction process, the concentration of hydrogen peroxide in the silver dissolving reaction solution is tested, and hydrogen peroxide is added to the silver dissolving reaction solution according to the test result, so that the concentration of hydrogen peroxide in the silver dissolving reaction solution is maintained at the process set value to ensure that the chemical reaction can be carried out safely and efficiently.

[0020] The present invention can also be improved as follows: a thermometer and a hot and cold temperature exchanger are added to control the temperature of the silver dissolving reaction solution for process control, so that the operating temperature of the silver dissolving reaction solution meets the process requirements, ammonia escape is reduced, and thermal decomposition of hydrogen peroxide and ammonium bicarbonate is reduced.

[0021] The present invention can also be improved by utilizing the oxygen and / or ammonia released during the reaction in step 2 for the silver dissolving reaction in the subsequent oxidation reaction tank. Specifically, two or more oxidation reaction tanks are connected in series, and a gas-liquid mixer is installed in the subsequent oxidation reaction tank to draw the oxygen and / or ammonia tail gas released from the previous oxidation reaction tank into the silver dissolving reaction liquid in the subsequent oxidation reaction tank for oxidation reaction. This saves production materials and reduces environmental pollution.

[0022] The present invention can also be improved by providing a mobile hydrogen peroxide mixing and dosing device in combination with the oxidation reaction tank to reduce the decomposition of hydrogen peroxide added to the silver dissolving reaction solution. The mobile hydrogen peroxide mixing and dosing device is designed according to Bernoulli's fluid dynamics principle and includes a main pipeline, a hydrogen peroxide dosing branch pipe connected to the main pipeline, and a pressure dynamic balance pipe, as shown by component 2 in Figures 2, 3, and 4. The main pipeline is connected to the oxidation reaction tank as a circulation pipeline, allowing the silver dissolving reaction solution to flow therein. It is mixed and compressed in the main pipeline with hydrogen peroxide added to the oxidation reaction tank or hydrogen peroxide in the silver dissolving reaction solution within the oxidation reaction tank. This allows the hydrogen peroxide and decomposed oxygen to dissolve in the reaction solution, allowing it to fully contact the surface of the metallic silver and accelerate the oxidation reaction of the metallic silver. Preferably, the silver dissolving reaction solution containing hydrogen peroxide flowing from the main pipeline is used to flush and corrode the metallic silver block, stripping the outer layer of silver oxide and exposing the underlying metallic silver. This accelerates contact with the silver dissolving reaction solution and allows the metallic silver to dissolve rapidly.

[0023] The present invention can also be improved as follows: in order to accelerate the oxidation reaction of metallic silver, two or more flowing hydrogen peroxide mixing and adding devices are arranged in parallel in the oxidation reaction tank to promote the reaction, so as to meet the technical requirements of large-scale oxidation reaction equipment.

[0024] The present invention can also be improved by adding a silver accumulation through-hole groove for accumulating silver metal within the oxidation reaction tank, and using a liquid spraying pipe to directly and centrally spray the silver dissolving reaction liquid onto the silver metal within the through-hole groove to promote the chemical reaction. To reduce the risk of silver metal within the silver accumulation through-hole groove being sprayed away from the silver accumulation through-hole groove during the silver dissolving reaction liquid spraying process, the silver metal within the silver accumulation through-hole groove is preferably silver ingot.

[0025] The present invention can also be improved as follows: during the silver dissolving reaction, ultrasound is applied to the silver dissolving reaction solution. Since hydrogen peroxide in the silver dissolving reaction solution easily decomposes to produce oxygen bubbles, ultrasound is used to break up the oxygen bubbles in the silver dissolving reaction solution, allowing oxygen to more easily dissolve into the reaction solution and exert its oxidizing effect. Simultaneously, ultrasound is used to stir the hydrogen peroxide and disperse it in the silver dissolving reaction solution, thereby increasing the contact surface area between oxygen, hydrogen peroxide, and the metallic silver block, thereby promoting the oxidative dissolution reaction of the metallic silver.

[0026] The present invention can also be improved as follows: solid-liquid separation is performed on the insoluble substances produced in the silver dissolving reaction liquid during the reaction process, thereby reducing the insoluble substances from blocking the contact between the silver dissolving reaction liquid and the metal silver block, so that the silver dissolving reaction proceeds smoothly.

[0027] The present invention can also be improved as follows: the hydrogen peroxide storage container is connected to the mobile hydrogen peroxide mixing and adding device through a hydrogen peroxide adding branch pipe, and a one-way valve is additionally installed on the hydrogen peroxide adding branch pipe to prevent the silver dissolving reaction solution from flowing back into the hydrogen peroxide storage container and causing a dangerous accident.

[0028] The present invention can also be improved as follows: when adding external hydrogen peroxide to the oxidation reaction tank, a metering pump is preferably used as the hydrogen peroxide addition pump, so that the external hydrogen peroxide can be added evenly in a metered manner or evenly added according to the concentration results of on-site testing, thereby ensuring stable oxidation of the metallic silver. The metering pump is specifically installed in the pipe connecting the mobile hydrogen peroxide mixing and adding device and the hydrogen peroxide storage container.

[0029] The present invention can also be improved as follows: additional sensors and an automatic detection and feeding controller are provided, wherein the sensors include an oxidation-reduction potentiometer (ORP meter), a pH meter, a liquid level meter, a thermometer, a hydrometer, a photoelectric colorimeter, a hydrogen peroxide titration concentration detector, and an ammonia concentration detector. The automatic detection and feeding controller and the sensors are used to automate the production process, and production safety is ensured and environmental pollution is controlled by controlling the device.

[0030] The present invention can also be improved as follows: an electrolytic cell is used as an oxidation reaction cell, the metallic silver involved in the reaction is used as a soluble electrolytic anode, and the silver dissolving reaction solution is used as an electrolyte to carry out electrolytic silver dissolving. During the electrolysis operation, the metallic silver anode undergoes an electrochemical oxidation reaction and an oxidation reaction with hydrogen peroxide in the silver dissolving reaction solution simultaneously. The combination of these two oxidation reactions accelerates the conversion of the metallic silver into silver oxide (Ag2O), which then reacts with the silver dissolving reaction solution to form Ag2SO4 and / or Ag2CO3 and / or [Ag(NH3)2]2SO4 and / or [Ag(NH3)2]2CO3. Due to the presence of hydrogen peroxide in the reaction solution, cathode electrolysis can be avoided and the amount of hydrogen released can be reduced. Preferably, a liquid spray pipe directed toward the electrolytic cathode is added to the electrolytic cell to spray the electrolyte containing hydrogen peroxide onto the electrolytic cathode, more effectively preventing electrochemical reactions at the electrolytic cathode from releasing metallic silver and / or hydrogen.

[0031] The present invention can also be improved by adding a liquid circulation agitator to the oxidation reaction tank. This agitator, consisting of a pipeline, a pump, and a nozzle head, causes the silver dissolving reaction liquid to circulate and stir within the oxidation reaction tank. This circulating agitation sprays liquid onto the surface of the silver block, accelerating the silver dissolving chemical reaction. Preferably, a flow-adjustable valve is added to the liquid flow pipeline of the liquid circulation agitator to adjust the spray pressure and flow rate, or a variable frequency pump is used to adjust the spray pressure and flow rate. The liquid circulation agitator also ensures that the concentration and temperature of the reaction liquid are uniform and controllable.

[0032] The present invention can also be improved by adding an exhaust gas treatment tank for environmentally friendly treatment of exhaust gas escaping from the oxidation reaction tank and exhaust gas escaping from other tanks. Preferably, the exhaust gas absorption reaction liquid in the exhaust gas treatment tank is sulfuric acid, and the ammonium sulfate solution obtained by the reaction is reused as a production raw material.

[0033] The present invention can also be improved as follows: the silver dissolving reaction liquid is set to become silver dissolving reaction waste liquid when the silver ion concentration therein reaches a set value or the silver dissolving speed drops to a set value, sulfuric acid and / or carbon dioxide are added to the silver dissolving reaction waste liquid to react with the silver compound dissolved in the silver dissolving reaction waste liquid to generate silver sulfate and / or silver carbonate solids, and the resulting filtrate is recycled as one of the raw materials of the silver dissolving reaction liquid after solid-liquid separation. The filtrate may contain silver ions or not, and the silver dissolving reaction liquid containing the filtrate is called a regenerated silver dissolving reaction liquid. The ammonium salt anion concentration, additive concentration, ammonia and / or ammonium concentration, hydrogen peroxide concentration, and pH value of the regenerated silver dissolving reaction liquid must meet the silver dissolving reaction liquid requirements set by the process. The filtrate can be prepared into a regenerated silver dissolving solution and then added to the silver dissolving reaction liquid as a silver dissolving solution to participate in the reaction. The ammonium salt anion concentration and additive concentration of the regenerated silver dissolving solution meet the silver dissolving solution requirements set by the process.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. Compared with the method of dissolving silver in nitric acid, the present invention has less equipment investment and less environmental pollution, and the silver dissolving speed can meet the requirements of large-scale production efficiency.

[0036] 2. Compared with the silver dissolving method using metallic silver anode electrolysis, the present invention solves the problem of hydrogen evolution during electrolysis and improves production safety. In addition, when the present invention uses an electrolytic cell as an oxidation reaction cell, a silver dissolving reaction solution containing hydrogen peroxide is used as the electrolyte, which can avoid silver evolution at the cathode and reduce the amount of hydrogen evolved at the electrolytic cathode, thereby improving production efficiency, reducing production energy consumption, and ensuring production safety.

[0037] 3. The present invention directly oxidizes the silver salt or silver complex to produce a silver salt or silver complex, or uses it as an intermediate product and then uses other processing methods to produce a silver-containing plating solution or other required silver compound products, which can solve the problems of high manufacturing cost, production safety and waste liquid treatment of silver nitrate intermediate products or silver ammonia solution intermediate products.

[0038] 4. The mixed tail gas of ammonia and oxygen generated during the production process of the present invention is collected and reused, which reduces environmental pollution and saves production materials.

[0039] 5. The waste liquid produced during the production process of the present invention is easy to treat, and the treated waste liquid can be recycled to reduce environmental pollution.

[0040] 6. The present invention is simple to operate, the process reaction parameters are easy to control, the equipment capital investment is small and the economic benefit is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] FIG1 is a process flow chart of the safe oxidation and dissolution of metallic silver according to Example 1 of the present invention and a schematic structural diagram of the device used.

[0042] FIG2 is a process flow chart of the safe oxidation and dissolution of metallic silver according to Example 2 and Example 3 of the present invention and a schematic structural diagram of the device used.

[0043] FIG3 is a process flow chart of the safe oxidation and dissolution of metallic silver according to Example 4 of the present invention and a schematic structural diagram of the device used.

[0044] FIG4 is a process flow chart of the safe oxidation and dissolution of metallic silver according to Example 5 of the present invention and a schematic structural diagram of the device used.

[0045] FIG5 is a process flow chart of the safe oxidation and dissolution of metallic silver according to Example 6 of the present invention and a schematic structural diagram of the device used.

[0046] FIG6 is a process flow chart of the safe oxidation and dissolution of metallic silver according to Example 7 of the present invention and a schematic structural diagram of the device used.

[0047] Figure 7 is a process flow chart for the safe oxidation and dissolution of metallic silver according to Example 8 of the present invention and a schematic structural diagram of the device used, wherein Figures 7-1 and 7-2 are partial enlarged views of Figure 7, and the two constitute a complete process flow chart and a schematic structural diagram of the device used in Example 8.

[0048] Figure 1-oxidation reaction tank, 2-flowing hydrogen peroxide mixing and adding device, 3-hydrogen peroxide storage container, 4-fluid power device, 5-hydrogen peroxide adding pump, 6-mainstream pipeline, 7-mainstream pipeline inlet, 8-mainstream pipeline outlet, 9-air pressure dynamic balance pipe, 10-hydrogen peroxide adding branch pipe, 11-connecting port between main pipeline and hydrogen peroxide adding branch pipe, 12-sensor, 13-automatic detection and feeding device (PLC), 14-solid-liquid separator, 15-oxidation reaction tank sealing cover, 16-metallic silver, 17-hydrogen peroxide, 18-silver-dissolving solution, 19-sulphuric acid, 20-ammonia water, 21-liquid ammonia, 22-silver-dissolving reaction solution, 23-silver compound product, 24-ammonia, 25-oxygen, 26-clean water, 27-ammonium sulfate, 28-additive, 29-cold and hot temperatures Exchanger, 30-liquid circulation agitator, 31-liquid circulation agitator nozzle head, 32-ultrasonic generator, 33-ultrasonic generator auxiliary liquid tank, 34-metal silver accumulation through-hole tank, 35-silver dissolving waste liquid, 36-blower, 37-gas-liquid mixer, 38-exhaust gas treatment tank, 39-temporary storage tank, 40-valve, 41-pump, 42-overflow buffer tank, 43-check valve, 44-electrolytic cell, 45-electrolytic anode, 46-electrolytic cathode, 47-electrolytic power supply, 48-ammonium bisulfate, 49-ammonium carbonate, 50-ammonium bicarbonate, 51-hydrogen peroxide addition pipe, 52-reaction tank, 53-silver sulfate, 54-silver carbonate, 55-carbon dioxide gas, 56-regenerated silver dissolving reaction solution, 57-ammonium bicarbonate, 58-ammonium carbonate, 59-ammonium bisulfate.

[0049] In the drawings and the following embodiments, multiple components of the same component type in the device are represented by "reference numerals." For example, valve 40 - 1 refers to valve 1, and valve 40 - 2 refers to valve 2. DETAILED DESCRIPTION

[0050] The present invention is further illustrated below through specific examples. The process of the present invention overcomes the problems existing in existing silver nitrate and existing methods for producing silver ammonia solutions by electrolysis of soluble metallic silver using anodes by improving the formulation of the silver dissolving solution. The process of the present invention primarily utilizes hydrogen peroxide and an ammonium salt solution, or other additives, to oxidatively dissolve metallic silver. The oxidation reaction of silver by hydrogen peroxide is a crucial step in the silver dissolving reaction, and the stability of hydrogen peroxide in the reaction solution is determined by the pH value of the solution. Therefore, in each of the following examples, the pH value of the silver dissolving reaction solution is used to further illustrate the process reaction.

[0051] In the following examples, the oxidation reaction tank, mobile hydrogen peroxide mixing and dosing device, hydrogen peroxide storage tank, mixer fluid dynamic device, liquid circulation agitator, gas-liquid mixer, tail gas treatment tank, oxidation reaction tank sealing cover, etc., are all manufactured by Yegao Environmental Protection Equipment Manufacturing Co., Ltd. in Foshan, Guangdong, China. The hot and cold temperature exchangers, solid-liquid separators, sensors, automatic detection and feeding controllers, valves, pumps, and chemical raw materials are all commercially available products. In addition to the above, those skilled in the art may also select other products with similar performance to those listed above, and any of these products can achieve the objectives of the present invention.

[0052] Example 1

[0053] As shown in FIG1 , which is a process flow chart of Example 1 of the present invention, the device used in this embodiment includes an oxidation reaction tank 1 , a hydrogen peroxide storage container 3 , a hydrogen peroxide addition pump 5 , a sensor 12 , and a hot and cold temperature exchanger 29 .

[0054] The oxidation reaction tank 1 is an open reaction tank with an effective volume of 10 liters and is equipped with a hot and cold temperature exchanger 29.

[0055] The sensor 12 is a thermometer, which is arranged in the oxidation reaction tank 1 .

[0056] The hydrogen peroxide storage container contains 10% hydrogen peroxide and is connected to the oxidation reaction tank 1 through a hydrogen peroxide adding pipe 51 ; a hydrogen peroxide adding pump 5 is provided on the hydrogen peroxide adding pipe 51 .

[0057] The silver dissolving solution 18 used in this embodiment is a mixture of ammonium sulfate and sulfuric acid at a concentration of 0.1 g / L; the amount of silver mass involved in the reaction is 1.3 g.

[0058] The characteristic of this embodiment is that during the silver dissolving reaction, the pH value of the silver dissolving reaction solution approaches the process set value pH 0.5. The hydrogen peroxide concentration of the silver dissolving reaction solution during the reaction process is 0.1 g / L.

[0059] The steps of safe oxidation and silver dissolution in this embodiment are as follows:

[0060] 1. Add 10 liters of silver solution and 1.3 grams of silver block to the oxidation reaction tank 1 and place them below the nozzle of the hydrogen peroxide addition pipe 51. Turn on the hot and cold temperature exchanger 29 to raise the silver solution to 65°C.

[0061] 2. Start the hydrogen peroxide addition pump 5 to spray hydrogen peroxide onto the silver block. During this process, the silver-dissolving reaction solution containing 0.1 g / L hydrogen peroxide concentration reacts with the metallic silver to generate silver oxide.

[0062] 3. After the silver oxide reacts with the silver-dissolving reaction solution 22, the pH value of the reaction solution gradually rises to near pH 0.5. After 6 hours of reaction, the silver block is completely dissolved, and a mixed solution of silver sulfate and a silver complex [Ag(NH3)2]2SO4 is prepared, with a silver ion concentration of 0.13 g / L.

[0063] The raw materials, process control parameters and quality indicators of the reaction products used in this example are listed in Table 1.

[0064] Example 2

[0065] As shown in FIG2 , which is a process flow chart of Example 2 of the present invention, the device used in this embodiment includes an oxidation reaction tank 1, a mobile hydrogen peroxide mixing and adding device 2, a hydrogen peroxide storage container 3, a fluid power device 4, a hydrogen peroxide adding pump 5, a thermometer 12, and a hot and cold temperature exchanger 29.

[0066] The oxidation reaction tank 1 is an open reaction tank with an effective volume of 10 liters.

[0067] The mobile hydrogen peroxide mixing and adding device 2 consists of a mainstream pipeline 6, a hydrogen peroxide adding branch pipe 10 connected to the mainstream pipeline 6, and an air pressure dynamic balance pipe 9; the inlet of the mainstream pipeline is connected to the oxidation reaction tank 1 through a pipeline equipped with a liquid flow power device 4, and the outlet of the mainstream pipeline is located in the oxidation reaction tank 1.

[0068] The sensor 12 is a thermometer, which is arranged in the oxidation reaction tank 1; the hot and cold temperature exchanger 29 is installed on the oxidation reaction tank 1.

[0069] The hydrogen peroxide storage container 3 contains 35% hydrogen peroxide and is connected to a pipeline provided with a hydrogen peroxide adding pump 5 and a hydrogen peroxide adding branch pipe 10 .

[0070] The silver dissolving solution 18 used in this embodiment is a mixture of sulfuric acid, 680 g / L ammonium sulfate, and 0.001% of an additive, wherein the additive is disodium ethylenediaminetetraacetic acid; and the silver mass involved in the reaction is 52.1 g.

[0071] The characteristic of this embodiment is that during the silver dissolving reaction, the pH value of the silver dissolving reaction solution continuously rises and approaches the process set pH 2. During the reaction process, the concentration of hydrogen peroxide in the silver dissolving reaction solution is 2 g / L.

[0072] The steps of safe oxidation and silver dissolution in this embodiment are as follows:

[0073] 1. Add the silver-soluble solution 18 in the temporary storage tank 39 to the oxidation reaction tank 1, and start the hot and cold temperature exchanger 29 to control the silver-soluble reaction solution at 50°C.

[0074] 2. A 52.1-gram silver nugget is added to the oxidation reaction tank 1 and placed under the outlet of the main pipeline of the mobile hydrogen peroxide mixer 2 to be flushed and corroded by the silver-dissolving reaction solution. The pump in the hydraulic motor 4 and the hydrogen peroxide dosing pump 5 are activated to mix and compress the hydrogen peroxide and silver-dissolving solution in the mobile hydrogen peroxide mixer 2 before spraying the mixed solution onto the silver nugget. During this process, the hydrogen peroxide reacts with the metallic silver to form silver oxide, and some of the hydrogen peroxide decomposes.

[0075] 3. Silver oxide reacts with the silver-dissolving reaction solution 22, causing the pH of the silver-dissolving reaction solution to gradually increase toward pH 2. The metallic silver is gradually and completely dissolved in the silver-dissolving reaction solution, yielding a silver complex solution product having a silver ion concentration of 5.21 g / L [Ag(NH3)2]2SO4.

[0076] The raw materials, process control parameters and quality indicators of the reaction products used in this example are listed in Table 1.

[0077] Example 3

[0078] As shown in FIG2 , the process flow and the apparatus used in Example 3 of the present invention are the same as those in Example 2.

[0079] The hydrogen peroxide storage barrel 3 contains 35% hydrogen peroxide.

[0080] The silver dissolving solution 18 used in this embodiment is a mixture of sulfuric acid, 580 g / L ammonium sulfate, and 20% additives. The additives include 99% cyclohexylamine, 0.5% phenacetin, and 0.5% hexamethylenetetramine.

[0081] The amount of silver involved in the reaction is 106 grams.

[0082] The characteristic of this embodiment is that during the silver dissolving reaction, the pH value of the silver dissolving reaction solution continuously rises and approaches the pH value of 4.8 set in the process. During the reaction process, the concentration of hydrogen peroxide in the silver dissolving reaction solution is maintained at 100g / L.

[0083] The steps of safe oxidation and silver dissolution in this embodiment are as follows:

[0084] 1. Add the silver solution 18 in the temporary storage tank 39 to the oxidation reaction tank 1, and start the hot and cold temperature exchanger 29 to control the reaction solution at 45°C.

[0085] 2. A 106-gram silver block is added to the oxidation reaction tank and placed under the outlet of the main pipeline of the mobile hydrogen peroxide mixer 2 to be flushed and corroded by the silver-dissolving reaction solution. The pump in the hydraulic motor 4 and the hydrogen peroxide dosing pump 5 are activated to mix and compress the hydrogen peroxide and the silver-dissolving solution in the mobile hydrogen peroxide mixer 2 before spraying them onto the silver block. During this process, the hydrogen peroxide reacts with the metallic silver to form silver oxide, and some of the hydrogen peroxide decomposes.

[0086] 3. Silver oxide reacts with the silver-dissolving reaction solution 22, gradually raising the pH of the solution toward pH 4.8. The metallic silver gradually dissolves in the solution. When the silver ion concentration in the solution reaches 10.27 g / L, solid silver salt begins to precipitate. Continued reaction completely dissolves the silver, yielding a silver complex solution product ([Ag(NH3)2]2SO4) and a small amount of solid silver sulfate.

[0087] The raw materials, process control parameters and quality indicators of the reaction products used in this example are listed in Table 1.

[0088] Example 4

[0089] FIG3 is a process flow chart of Example 4 of the present invention. The apparatus used in this embodiment includes an oxidation reaction tank 1, a mobile hydrogen peroxide mixing and adding device 2, a hydrogen peroxide storage container 3, a fluid dynamic device 4, a hydrogen peroxide adding pump 5, a sensor 12, a solid-liquid separator 14, a hot and cold temperature exchanger 29, a temporary storage tank 39, two reaction tanks 52-1 and 52-2, and multiple valves and pumps.

[0090] The oxidation reaction tank 1 has an effective volume of 10 liters, and is equipped with a hot and cold temperature exchanger 29 for heating and regulating the temperature of the reaction liquid, and a sensor 12 for a thermometer.

[0091] The mobile hydrogen peroxide mixing and adding device 2 consists of a main pipeline 6, a hydrogen peroxide adding branch pipe 10 connected to the main pipeline 6, and an air pressure dynamic balance pipe 9; the inlet of the main pipeline is connected to the oxidation reaction tank 1 through a pipeline equipped with a liquid flow power device 4, and the outlet of the main pipeline is located below the liquid level in the oxidation reaction tank 1.

[0092] The hydrogen peroxide storage container 3 contains 27.5% hydrogen peroxide and is connected to a pipeline provided with a hydrogen peroxide adding pump 5 and a hydrogen peroxide adding branch pipe 10 .

[0093] The oxidation reaction tank 1 is also connected to the reaction tank 52-1 via the temporary storage tank 39. The reaction tank 52-1 is used to extract silver salts from the silver-dissolving waste liquid 35. The reaction tank 52-2 is used to prepare the regenerated silver-dissolving reaction liquid and is connected to the reaction tank 52-1 via the solid-liquid separator 14; the solid-liquid separator 14 is a filter.

[0094] The silver dissolving solution 18 used in this embodiment is a mixture of sulfuric acid, 250 g / L ammonium sulfate, and 15% additives, including 99% cyclohexylamine, 0.9% hexamethylenetetramine, and 0.1% phenacetin. A total of 210 g of metallic silver powder is used in the reaction.

[0095] The characteristic of this embodiment is that during the silver dissolution reaction, the concentration of hydrogen peroxide in the silver dissolution reaction liquid is 70g / L, and its pH value continuously rises and approaches the process set value of pH 5.5. The solid-liquid mixture in the oxidation reaction tank after the silver dissolution reaction is completed can be used as the product. Alternatively, the silver dissolution reaction liquid after the reaction is completed can be further processed to extract a solid silver salt product; the method is to add sulfuric acid to the solution after the silver dissolution reaction to react to generate a silver sulfate precipitate, and then perform solid-liquid separation on the reaction liquid to obtain a solid silver sulfate product. The filtrate is then prepared and recycled as a regenerated silver dissolution reaction liquid. This two-step process for producing a solid silver salt product takes advantage of the rapid silver dissolution reaction rate of the intermediate silver complex solution.

[0096] The steps of safe oxidation and silver dissolution in this embodiment are as follows:

[0097] 1. Add silver powder 16 into the oxidation reaction tank 1 and then inject the silver solution 18.

[0098] 2. Start the fluid power device 4, hydrogen peroxide dosing pump 5 and hot and cold temperature exchanger 29. The silver-dissolving reaction liquid carries the silver powder into the mobile hydrogen peroxide mixing and dosing device 2 and is mixed and compressed with the hydrogen peroxide, so that the silver powder reacts with the hydrogen peroxide to generate silver oxide.

[0099] 3. During the reaction process, the concentration of hydrogen peroxide in the silver dissolving reaction solution was manually detected and hydrogen peroxide was intermittently added to the oxidation reaction tank to maintain the hydrogen peroxide concentration of the reaction solution at 70 g / L. At the same time, the temperature of the silver dissolving reaction solution was controlled at 35°C to promote the oxidation reaction of silver. The pH value of the reaction solution gradually approached pH 5.5, and the silver powder was continuously dissolved.

[0100] 4. After a period of reaction, the silver ion concentration of the silver dissolving reaction solution rises to 18.5 g / L and the solution becomes [Ag(NH3)2]2SO4. Solid silver salt begins to precipitate and the silver dissolving rate decreases to 0.051 mg / (cm 2 min), and when the silver powder is completely dissolved, a solid-liquid mixture product containing Ag(NH3)2SO4 and solid silver sulfate is obtained.

[0101] 5. The solid-liquid mixture in the oxidation reaction tank is pumped to the temporary storage tank 39 by pump 41-1 for temporary storage. The solution in the temporary storage tank 39 is pumped to the reaction tank 52-1 by pump 41-2 and sulfuric acid is added to react so that Ag2SO4 precipitates out of the solution.

[0102] 6. Open valve 40-4 and start pump 41-3 to separate the solid-liquid mixture in tank 52-1. The resulting filter residue, silver sulfate product, is retained in the filter. The filtrate is drained into reaction tank 52-2 and ammonia, ammonium sulfate, and additives are added to reconstitute the regenerated silver dissolving reaction solution 56.

[0103] 7. After the regenerated silver dissolving reaction liquid is prepared according to the process requirements and tested to be qualified, it is pumped to the oxidation reaction tank via pump 41-3 for recycling. The silver ion concentration of the regenerated silver dissolving reaction liquid is 11.3 g / L.

[0104] The raw materials, process control parameters and quality indicators of the reaction products used in this example are listed in Table 1.

[0105] Example 5

[0106] As shown in FIG4 , which is a process flow chart of Example 5 of the present invention, the device used in this embodiment includes an oxidation reaction tank 1, a flowing hydrogen peroxide mixer 2, a hydrogen peroxide storage container 3, a fluid power device 4, a hydrogen peroxide dosing pump 5, two sensors 12, a solid-liquid separator 14, a hot and cold temperature exchanger 29, and a valve 40.

[0107] The oxidation reaction tank 1 has an effective volume of 10 liters and houses a mobile hydrogen peroxide mixer 2. The mobile hydrogen peroxide mixer 2 comprises a main flow pipe 6, a hydrogen peroxide dosing branch pipe 10 connected to the main flow pipe 6, and a pressure dynamic balance pipe 9. The main flow pipe inlet is connected to the oxidation reaction tank 1 via a pipe equipped with a fluid dynamic device 4, and the main flow pipe outlet is inserted into the silver dissolving reaction solution 22 within the oxidation reaction tank 1.

[0108] The hydrogen peroxide storage container 3 contains 27.5% hydrogen peroxide and is connected to a hydrogen peroxide addition branch pipe 10 provided with a hydrogen peroxide addition pump 5 and a one-way valve 43 .

[0109] The sensor 12 - 1 is a thermometer, and the sensor 12 - 2 is a hydrogen peroxide titration concentration detector, both of which are arranged in the oxidation reaction tank 1 .

[0110] The oxidation reaction tank 1 is also connected to the reaction tank 52-1 via the temporary storage tank 39; the reaction tank 52-1 is used to extract silver salt from the silver-dissolving waste liquid 35. The reaction tank 52-2 is used to prepare the regenerated silver-dissolving reaction liquid and is connected to the reaction tank 52-1 via the solid-liquid separator 14.

[0111] In this embodiment, the silver dissolving solution 18 is a mixture of sulfuric acid, 100 g / L ammonium bicarbonate, 270 g / L ammonium sulfate, 60 g / L hydrogen peroxide, and 10% additives. The additives include 98% cyclohexylamine, 1.5% diammonium ethylenediaminetetraacetate, 0.05% phenacetin, and 0.95% hexamethylenetetramine. The silver metal mass involved in the reaction weighs a total of 96 grams.

[0112] A characteristic of this embodiment is that during the silver dissolution reaction, the pH of the silver dissolution reaction solution continuously rises toward the process setpoint pH of 6.9. The solution after the silver dissolution reaction can be used as the product, or carbon dioxide gas can be added to the solution after the silver dissolution reaction to extract a solid silver salt product. The solution after the solid silver salt product has been extracted is reconstituted into a regenerated silver dissolution reaction solution for recycling. This two-step process for producing a solid silver salt product takes advantage of the rapid silver dissolution reaction of the intermediate silver complex solution.

[0113] The steps of safe oxidation and silver dissolution in this embodiment are as follows:

[0114] 1. Add a metallic silver block and 10 liters of silver-dissolving solution 18 into an oxidation reaction tank 1. The silver block is placed under the outlet of the main flow pipe of a mobile hydrogen peroxide mixing and adding device 2 so that it is washed and corroded by the silver-dissolving reaction solution.

[0115] 2. Turn on the fluid power device 4 and the hot and cold temperature exchanger 29. The silver dissolving reaction liquid enters the mobile hydrogen peroxide mixing and adding device 2, is mixed with hydrogen peroxide, compressed and sprayed toward the silver block, so that the metallic silver undergoes oxidation and dissolution reaction in the reaction liquid at a temperature of 25°C.

[0116] 3. During the reaction, the concentration of hydrogen peroxide in the reaction solution is detected by an automatic hydrogen peroxide titration detector. Based on the detection result of the detector, the hydrogen peroxide addition pump 5 is controlled to start hydrogen peroxide to add hydrogen peroxide to the silver dissolving reaction solution to maintain a concentration of 60 g / L, and the pH value of the silver dissolving reaction solution tends to pH 6.9. When the silver block is completely dissolved, a mixed solution of [Ag(NH3)2]2SO4 and [Ag(NH3)2]2CO3 with a silver ion concentration of 9.6 g / L is obtained as the silver compound product 23.

[0117] 4. To extract the solid silver salt product, the prepared mixed solution is pumped into a reaction tank 52-1. Carbon dioxide gas is added to the solution in the reaction tank 52-1 to cause a reaction to produce silver carbonate and silver sulfate precipitates. After solid-liquid separation, the filtrates [Ag(NH3)2]2CO3 and [Ag(NH3)2]2SO4 solutions are obtained, respectively. The filter residues are silver sulfate and silver carbonate as the solid silver salt products.

[0118] 5. The filtrate is drawn into the reaction tank 52-2, and hydrogen peroxide, ammonium sulfate, ammonium bicarbonate, and additives are added to prepare the regenerated silver dissolving reaction solution 56 according to the process standards, wherein the silver ion concentration is 7.8 g / L.

[0119] 6. The regenerated silver dissolving reaction solution 56 is returned to the oxidation reaction tank to participate in the reaction again, and the collected filter residue is the solid silver salt product.

[0120] The raw materials, process control parameters and quality indicators of the reaction products used in this example are listed in Table 1.

[0121] Example 6

[0122] FIG5 is a process flow chart of Example 6 of the present invention. The apparatus used in this embodiment includes an electrolytic cell 44, an electrolytic anode 45, an electrolytic cathode 46, an electrolytic power supply 47, a hydrogen peroxide storage container 3, a hydrogen peroxide dosing pump 5, four sensors 12, a hot and cold temperature exchanger 29, a liquid circulation agitator 30, a temporary storage tank 39, an overflow buffer tank 42, a one-way valve 43, a hydrogen peroxide dosing pipe 51, and multiple valves and pumps.

[0123] The electrolytic cell 44 is the oxidation reaction tank used in this embodiment for silver oxidation dissolution. It is a reaction device that combines two oxidation reactions: electrochemical oxidation dissolution using metallic silver as the electrolytic anode and oxidation dissolution of the metallic silver using an oxidizing electrolyte. Electrolytic cell 44 has an effective volume of 100 liters and is equipped with sensors 12-1, 12-2, 12-3, and 12-4, which respectively represent a pH meter, a hydrometer, a hydrogen peroxide titration concentration meter, and a thermometer. Electrolytic cell 44 is also equipped with a hot and cold temperature exchanger 29 and a liquid circulation agitator 30. Liquid circulation agitator 30 comprises piping, a pump, and a liquid circulation agitator nozzle head 31, which is connected to electrolytic cell 44 for liquid circulation. The liquid circulation agitator nozzle head 31 faces the electrolytic anode 45 of the metallic silver, allowing it to be flushed and corroded by the silver dissolution reaction solution (electrolyte).

[0124] The hydrogen peroxide storage container 3 contains 27.5% hydrogen peroxide and is connected to the electrolytic cell 44 via a hydrogen peroxide injection pipe 51 equipped with a hydrogen peroxide injection pump 5. A one-way valve 43 is installed on the hydrogen peroxide injection pipe 51, which serves as a liquid injection pipe. The liquid outlet of the hydrogen peroxide injection pipe 51 is located below the liquid level of the electrolytic cell 44 and faces the electrolytic cathode 46.

[0125] The overflow buffer tank 42 receives the overflow solution from the electrolytic tank 44 and transfers it to the temporary storage tank 39-3 for temporary storage.

[0126] The temporary storage tank 39 - 1 is used to temporarily store ammonia water as a pH adjuster, and the temporary storage tank 39 - 2 is used to temporarily store the silver dissolving solution 18 , and both are connected to the electrolytic tank 44 through pipelines.

[0127] The silver dissolving solution used in this embodiment is a mixture containing 40 g / L hydrogen peroxide, ammonia water, 15 g / L ammonium carbonate, 350 g / L ammonium sulfate, and 4% additives, wherein the additives are 99.5% cyclohexylamine and 0.5% phenacetin. The metallic silver soluble anode participating in the reaction weighs 7 kg.

[0128] The process characteristics of this embodiment are that a pH meter controls pump 41-1 to add ammonia solution to maintain a pH of 8.7 in the silver dissolving reaction solution. A hydrometer controls the addition of silver dissolving solution 18 to the silver dissolving reaction solution 22 in the electrolytic cell to initiate the reaction. A hydrogen peroxide titration meter controls hydrogen peroxide dosing pump 5 to maintain a hydrogen peroxide concentration of 40 g / L in the silver dissolving reaction solution. Through the electrochemical oxidation of metallic silver and the oxidation reaction of hydrogen peroxide, a silver compound product 23 with a silver ion concentration of 26 g / L is prepared.

[0129] The steps of safe oxidation and silver dissolution in this embodiment are as follows:

[0130] 1. Place metallic silver as a soluble electrolytic anode 45 in the electrolytic cell 44, turn on the pump 41-2 to pour the silver solution 18 in the temporary storage tank 39-2 into the electrolytic cell 44 until the liquid level reaches the overflow port.

[0131] 2. Turn on the liquid circulation agitator 30 and the hot and cold temperature exchanger 29 to circulate the electrolyte in the electrolytic cell 44 and control the temperature at 20°C.

[0132] 3. Electrolysis power supply 47 is turned on and electrolysis is performed at a cell voltage of 1.5V. The reaction solution sprays onto the electrolytic anode 45, causing the silver metal to undergo oxidation and dissolution. The silver ion concentration in the electrolyte continuously increases, approaching the process setpoint of 26 g / L. The pH value of the electrolyte decreases, approaching the process setpoint of pH 8.7. To maintain a stable pH of 8.7, a pH meter controls pump 41-1 to add ammonia solution. During this process, a hydrogen peroxide titration meter monitors the hydrogen peroxide concentration online and controls hydrogen peroxide dosing pump 5 to add hydrogen peroxide to the electrolyte, maintaining a constant hydrogen peroxide concentration of 40 g / L. During the reaction, no silver metal or hydrogen gas is deposited at the electrolytic cathode.

[0133] 4. When the silver ion concentration in the electrolyte reaches 26 g / L (specific gravity value 1.198 g / L), the hydrometer controls pump 41-2 to add dissolved silver solution 18 to the electrolytic cell, causing some electrolyte to overflow the cell. The overflow is pumped by pump 41-3 of the overflow buffer tank to the temporary storage tank 39-3 for collection.

[0134] 5. The solution in the temporary storage tank 39-3 is the prepared silver complex product of [Ag(NH3)2]2SO4 and [Ag(NH3)2]2CO3, with a silver ion concentration of 26g / L. After a total of 160 liters of silver complex solution product are produced, the electrolysis operation is completed and the production unit is shut down.

[0135] The raw materials, process control parameters and quality indicators of the reaction products used in this example are listed in Table 1.

[0136] Example 7

[0137] As shown in FIG6 , which is a process flow chart of Example 7 of the present invention, the apparatus used in this embodiment includes an oxidation reaction tank 1, a mobile hydrogen peroxide mixing and adding device 2, a hydrogen peroxide storage container 3, a liquid flow power device 4, a hydrogen peroxide adding pump 5, four sensors 12, a hot and cold temperature exchanger 29, a liquid circulation agitator 30, an ultrasonic generator 32, an auxiliary liquid tank 33, a blower 36, two tail gas treatment tanks 38, two temporary storage tanks 39, an overflow buffer tank 42, a plurality of valves and pumps.

[0138] The oxidation tank 1 has an effective liquid volume of 60 liters and is equipped with a mobile hydrogen peroxide mixing and dosing device 2. The mobile hydrogen peroxide mixing and dosing device 2 is a structural assembly, as shown by reference 2 in Figure 3, consisting of a main pipeline, a hydrogen peroxide dosing branch pipe connected to the main pipeline, and a pressure dynamic balance pipe. The main pipeline inlet is connected to the oxidation tank 1 via a pipeline equipped with a fluid dynamic device 4, and the main pipeline outlet is located in the silver-dissolving reaction solution 22. A liquid circulation agitator 30 is also installed in the oxidation tank 1, and its nozzle head 31 sprays the silver block on the traction pulley. The oxidation tank 1 is also equipped with a hot and cold temperature exchanger 29 and an ultrasonic generator 32. Because the oxidation tank 1 is made of a polymer resin, the installation of the ultrasonic generator 32 requires the use of an ultrasonic generator auxiliary tank 33. The solution in the auxiliary tank transmits ultrasonic waves to the reaction solution in the oxidation tank 1.

[0139] The hydrogen peroxide storage container 3 contains 50% hydrogen peroxide and is connected to a hydrogen peroxide dosing pipe in the mobile hydrogen peroxide mixer 2 via a hydrogen peroxide dosing pump 5. Sensors 12-1, a hydrogen peroxide titration concentration detector, 12-2, a hydrometer, 12-3, a thermometer, and 12-4, a pH meter, are all located within the oxidation reaction tank 1. The pH meter controls the addition of silver dissolving solution 18 into the oxidation reaction tank 1 to participate in the reaction and maintain the pH of the silver dissolving reaction solution at the process-set value of 9.3. The hydrogen peroxide titration concentration detector is used to detect the hydrogen peroxide concentration in the reaction solution and control pump 5 to add hydrogen peroxide to maintain a concentration of 20 g / L. The hydrometer only monitors the silver ion concentration in the silver dissolving reaction solution.

[0140] The tail gas absorption reaction liquid in both tail gas treatment tanks 38-1 and 38-2 is sulfuric acid. Tail gas treatment tank 38-1 is a bubbling gas-liquid mixing tank that receives the escaping gas from the oxidation reaction tank, while tail gas treatment tank 38-2 is a spray tower gas-liquid mixing tank. The two tail gas treatment tanks are connected in series for tail gas treatment.

[0141] The silver dissolving solution 18 used in this embodiment is a mixture of aqueous ammonia, 10 g / L ammonium carbonate, 280 g / L ammonium sulfate, 20 g / L hydrogen peroxide, and 2% additives. The additives are 99.8% diammonium ethylenediaminetetraacetate and 0.2% phenacetin. The mother solution pH is set at 9.3 and the silver ion concentration is 31 g / L. The silver metal flakes involved in the reaction weigh a total of 4000 grams. During the reaction, some silver particles may fall into the silver dissolving solution 22 due to the spraying of the silver dissolving solution and react directly therein.

[0142] The process characteristics of this embodiment are that metallic silver is oxidized using a silver dissolving reaction mother liquor containing silver ions at a concentration of 31 g / L. The hydrogen peroxide concentration of the silver dissolving reaction liquid 22 is 20 g / L, the pH value thereof is maintained stable at pH 9.3, and the specific gravity thereof is within the range of 1.160 to 1.170 g / L.

[0143] The steps of safe oxidation and silver dissolution in this embodiment are as follows:

[0144] 1. Add 60 liters of silver-dissolving reaction mother liquor containing 31 g / L silver ions into the oxidation reaction tank 1, turn on the liquid circulation agitator 30, the liquid flow power device 4, the hot and cold temperature exchanger 29 and the ultrasonic generator 32, and put all sensors into working state.

[0145] 2. Several silver sheets are added to the oxidation reaction tank 1 for oxidation and dissolution reaction. During the process, the oxygen and ammonia escaping from the tank are guided by the blower 36 to the tail gas treatment tank 38-1 and tank 38-2 to react with sulfuric acid to neutralize the waste gas.

[0146] 3. During the reaction process, a hydrogen peroxide titration-type concentration detector directly controls the hydrogen peroxide dosing pump 5 to add hydrogen peroxide to maintain a concentration of 20 g / L. A hydrometer monitors the silver ion concentration in the silver-dissolving reaction solution 22. A thermometer controls the operating state of the hot and cold temperature exchanger 29 to maintain the operating temperature of the reaction solution at 15° C. A pH meter controls the pump 41-1 to add the silver-dissolving solution 18 to the oxidation reaction tank 1 to participate in the reaction and maintain the process-set pH of 9.3.

[0147] 4. As silver blocks, silver dissolving solution, and hydrogen peroxide are continuously added, the silver dissolving reaction solution 22 overflows into the overflow buffer tank 42. The overflowed reaction solution 22 is pressurized and filtered to remove the silver powder via pump 41-2. The filtered filtrate is then drained into a temporary storage tank 39-2 for temporary storage of the silver complex solution product.

[0148] 5. During the process, 60 liters of [Ag(NH3)2]2SO4 and [Ag(NH3)2]2CO3 silver complex solution were prepared, in which the silver ion concentration was 31 g / L.

[0149] 6. The silver-dissolving reaction liquid and undissolved silver blocks and silver powder in the oxidation reaction tank are reserved for next use. After the operation is completed, the production equipment is shut down.

[0150] The raw materials, process control parameters and quality indicators of the reaction products used in this example are listed in Table 1.

[0151] Example 8

[0152] As shown in FIG7 , which is a process flow chart of Example 8 of the present invention, the apparatus used in this embodiment includes oxidation reaction tanks 1-1 and 1-2, two mobile hydrogen peroxide mixing and feeding devices 2-1 and 2-2, a fluid power device 4, a hydrogen peroxide feeding pump 5, fourteen sensors 12, an automatic detection and feeding controller 13, a centrifuge 14-1 and a filter 14-2, two oxidation reaction tank sealing covers 15, an automatic detection and feeding controller 13, two hot and cold temperature exchangers 29-1 and 29-2, three ultrasonic generators 32, three ultrasonic generator auxiliary liquid tanks 33, two metal silver accumulation through-hole tanks 34, a one-way valve 36, a gas-liquid mixer 37, an exhaust gas treatment tank 38, three temporary storage tanks 39, an overflow buffer tank 42, a plurality of valves and pumps.

[0153] The oxidation reaction tank 1-1 has a liquid capacity of 100 liters, while the oxidation reaction tank 1-2 has a capacity of 60 liters. The two are connected by a gas pipeline, with the oxidation reaction tank 1-2 receiving gas escaping from the oxidation reaction tank 1-1. Two mobile hydrogen peroxide mixing and adding devices 2-1 and 2-2, made of a polymer resin, are installed on the oxidation reaction tank 1-1. The main flow pipe inlets of the two devices are connected to the oxidation reaction tank 1 via a pipeline equipped with a fluid dynamic device 4. The main flow pipe outlet of the mobile hydrogen peroxide mixing and adding device 2-1 is inserted into the reaction liquid, and the main flow pipe outlet of the mobile hydrogen peroxide mixing and adding device 2-2 is placed above the liquid surface of the reaction liquid. Both main flow pipe outlets face the silver block, allowing the silver-dissolving reaction liquid to flush and corrode the silver block. Oxidation reaction tank 1-1 is equipped with a silver accumulation through-hole trough 34-1 and a hot / cold temperature exchanger 29-1, as well as sensors 12-3, 12-4, 12-5, 12-6, and 12-7, which correspond to a thermometer, a liquid level gauge, a pH meter, a hydrogen peroxide titration concentration meter, and a hydrometer. Furthermore, oxidation reaction tank 1-2 is equipped with a polymer resin vacuum ejector 37, which houses hot / cold temperature exchanger 29-2 and sensors 12-8, 12-9, 12-10, and 12-11, which correspond to a thermometer, a liquid level gauge, a pH meter, and a hydrometer.

[0154] The ultrasonic generator 32-1 is installed in the ultrasonic generator auxiliary liquid tank 33-1 of the mobile hydrogen peroxide mixer 2-1, the ultrasonic generator 32-2 is installed in the auxiliary liquid tank 33-2 of the mixer 2-2, and the ultrasonic generator 32-3 is installed in the auxiliary liquid tank 33-3 of the vacuum ejector 37. The ultrasonic function promotes the dispersion of the oxidant in the silver dissolving reaction solution.

[0155] A large amount of metallic silver is placed in the two metallic silver accumulation through-hole grooves 34 - 1 and 34 - 2 and immersed in the corresponding oxidation reaction tanks.

[0156] The hydrogen peroxide storage container 3 contains 35% hydrogen peroxide, and is connected to the hydrogen peroxide adding branch pipes of the parallel mobile hydrogen peroxide mixing and adding devices 2-1 and 2-2 through a pipeline provided with a hydrogen peroxide adding pump 5 and a one-way valve 43.

[0157] The sensors 12-1, 12-2 and 12-12 are all level gauges, the sensor 12-13 is a pH meter and the sensor 12-14 is an ammonia concentration detector. The automatic detection and feeding controller 13 is used for process control of the device.

[0158] The solid-liquid separator 14-1 is a centrifuge, and the solid-liquid separator 14-2 is a filter, which is used to separate the silver powder in the silver complex liquid product 23 in the two oxidation reaction tanks. The two solid-liquid separators are installed on the pipes for discharging the silver-dissolving reaction liquid from the two oxidation reaction tanks.

[0159] Temporary storage tank 39-1 is used to temporarily store the silver solution 18 and is connected to the two oxidation reaction tanks via a pump and pipes. Temporary storage tank 39-2 is used to store the silver powder separated by solid-liquid separator 14-1. Temporary storage tank 39-3 is used to temporarily store the silver compound product 23 and is connected to solid-liquid separator 14-2 via pipes.

[0160] The tail gas treatment tank 38 is a vacuum jet tail gas treatment tank, and its air intake is connected to the tail gas escape pipe of each tank. The tail gas absorption reaction liquid is preferably sulfuric acid, which generates ammonium sulfate for reuse after absorbing ammonia.

[0161] The silver dissolving solution and the mother solution for the silver dissolving reaction in the initial stage of the process used in this embodiment are both regenerated silver dissolving reaction solution 56, specifically a mixture of liquid ammonia, 10 g / L ammonium bisulfate, 50 g / L ammonium sulfate, 10 g / L ammonium bicarbonate, 15 g / L ammonium carbonate, 0.5% additives, and a silver compound having a silver ion concentration of 12 g / L. The additives comprise 90% methenamine and 10% phenacetin.

[0162] The weight of the silver flakes and silver balls participating in the reaction in the oxidation reaction tanks 1-1 and 1-2 is 3000 grams, which exceeds the reaction amount required for the dissolution reaction according to the process requirements.

[0163] The process characteristics of this embodiment are that the pH value of the silver dissolving reaction solution is set to pH 10.5 according to the chemical reaction process, and the silver ion concentration of the reaction solution rises to the process setting value of 18g / L during the process. The concentration of hydrogen peroxide in the silver dissolving reaction solution is maintained at 10g / L.

[0164] The steps of safe oxidation and silver dissolution in this embodiment are as follows:

[0165] 1. Turn on the power of the device to enable the automatic detection and feeding controller to process the field data of each sensor and run automatically according to the pre-programmed program.

[0166] 2. The automatic detection feeding controller issues instructions to add excess silver blocks into the metal silver accumulation through-hole grooves 34-1 and 34-2 in the two oxidation reaction tanks, and then adds the start-up silver dissolving reaction mother liquid, i.e., the regenerated silver dissolving reaction liquid 56, into the two oxidation reaction tanks under the control of their respective liquid level meters.

[0167] 3. The automatic detection feeding controller starts the fluid dynamic device 4, pumps 41-4 and 41-6, opens the hot and cold temperature exchangers 29-1 and 29-2, and starts the three ultrasonic generators to make the silver metal 16 and the silver-soluble reaction solution 22 react chemically.

[0168] 4. During the reaction process, the temperature of the silver-dissolving reaction solutions 22-1 and 22-2 in the two oxidation reaction tanks was controlled at 8° C. A hydrogen peroxide titration detector was used to detect the hydrogen peroxide concentration of the silver-dissolving reaction solution 22-1 and to control the hydrogen peroxide addition pump 5 to add hydrogen peroxide on time to maintain a concentration of 10 g / L. The pH meters in the two oxidation reaction tanks monitored the reactions of the silver-dissolving reaction solutions 22-1 and 22-2, respectively. When the values ​​detected by the hydrometers in the two oxidation reaction tanks reached the specific gravity values ​​of 18 g / L of silver ion concentration, pumps 41-1 and 41-2 were controlled to add regenerated silver-dissolving reaction solution 56 to the corresponding oxidation reaction tanks. Scattered silver powder was present in the silver-dissolving reaction solution 22-1. Ammonia and oxygen escaping from the oxidation reaction tank 1-1 were drained into the oxidation reaction tank 1-2 through the gas-liquid mixer 37 to participate in the reaction. The pH values ​​of the silver-dissolving reaction solutions 22-1 and 22-2 were both maintained at pH 10.5.

[0169] 5. As the reaction proceeds, the silver complex solution continuously overflows into the overflow buffer tank 42-1 and is fed into the solid-liquid separators 14-1 and 14-2 via the pump 41-4 for solid-liquid separation. The separated filter residue silver powders 16-3 and 16-4 are fed back into the two oxidation reaction tanks for use. The filtrate is the silver complex solution, i.e., the silver compound product 23, which is temporarily stored in the temporary storage tank 39-3, where the silver ion concentration is 18 g / L.

[0170] 6. The tail gas treatment tank 38 treats the tail gas emitted from each tank, and the produced ammonium sulfate is used as production raw material.

[0171] The raw materials, process control parameters and quality indicators of the reaction products used in this example are listed in Table 1.

[0172] Table 1

Claims

1. A method for safely oxidizing and dissolving metallic silver, characterized in that, It includes the following steps: Step 1: Prepare a silver-dissolving solution, which is a solution containing an ammonium salt; Step 2: Mix metallic silver, the silver-dissolving solution, and hydrogen peroxide, and in an oxidation reaction tank, cause a chemical reaction of metallic silver in a silver-dissolving reaction solution containing the silver-dissolving solution and hydrogen peroxide to generate a silver salt and / or a silver complex product. During the reaction process, control the pH value of the silver-dissolving reaction solution at pH 0.5 to pH 10.

5.

2. The method for safely oxidizing and dissolving metallic silver according to claim 1, wherein, The ammonium salt is selected from at least one of ammonium sulfate, ammonium bisulfate, ammonium carbonate, and ammonium bicarbonate; the concentration of the ammonium salt in the silver-dissolving solution is 0.1 g / L to 720 g / L.

3. The method for safely oxidizing and dissolving metallic silver according to claim 2, characterized in that, The silver-dissolving solution contains ammonium sulfate and / or ammonium bisulfate.

4. The method for safely oxidizing and dissolving metallic silver according to claim 3, characterized in that, The content of hydrogen peroxide in the silver-dissolving reaction solution is 0.1 g / L to 100 g / L; when the silver-dissolving rate is lower than the set value required by the process, increase the content of hydrogen peroxide in the silver-dissolving reaction solution; when the silver-dissolving rate is higher than the set value required by the process, decrease the content of hydrogen peroxide in the silver-dissolving reaction solution.

5. The method for safely oxidizing and dissolving metallic silver according to claim 4, characterized in that, The silver-dissolving solution further contains an additive and / or a pH adjuster; the additive is specifically selected from one or more of ethylenediaminetetraacetate, cyclohexylamine, hexamethylenetetramine, and phenacetin; the pH adjuster is sulfuric acid or ammonia water.

6. The method for safely oxidizing and dissolving metallic silver according to claim 5, characterized in that, Control the pH value of the silver-dissolving reaction solution at pH 4 to pH 8; during the reaction process, control its pH value within the range set in the process by additionally adding the pH adjuster to the silver-dissolving reaction solution.

7. The method for safely oxidizing and dissolving metallic silver according to claim 6, characterized in that, Adopt one of the following two specific production process schemes: (1) Adopt a production process scheme of continuously producing while maintaining the silver ion concentration of the silver-dissolving reaction solution at the set value of the process concentration; (2) Adopt a production process scheme with the silver ion concentration of the silver-dissolving reaction solution rising to the set value of the process concentration as the end mark of the operation.

8. The method for safely oxidizing and dissolving metallic silver according to claim 7, characterized in that, By adjusting the formula components of the silver-dissolving solution and / or setting the pH value of the silver-dissolving reaction solution, choose to preferentially produce a silver salt or a silver ammonia complex.

9. The method for safely oxidizing and dissolving metallic silver according to claim 8, characterized in that, Use the oxygen and / or ammonia gas evolved during the reaction in Step 2 for the silver-dissolving reaction in the subsequent-stage oxidation reaction tank; that is, adopt two or more series-connected oxidation reaction tanks, and by installing a gas-liquid mixer on the subsequent-stage oxidation reaction tank, attract the oxygen and / or ammonia gas tail gas evolved from the previous-stage oxidation reaction tank into the silver-dissolving reaction solution of the subsequent-stage oxidation reaction tank for oxidation reaction utilization.

10. The method for safely oxidizing and dissolving metallic silver according to claim 7, characterized in that, Set up a flow-type hydrogen peroxide mixing and dosing device in combination with the oxidation reaction tank to reduce the decomposition of the externally added hydrogen peroxide into the silver-dissolving reaction solution; The flow-type hydrogen peroxide mixing and dosing device includes a main pipeline, a hydrogen peroxide dosing branch pipe communicating with the main pipeline, and a pneumatic dynamic balance pipe; the main pipeline is connected to the oxidation reaction tank as a circulation pipeline, enabling the silver-dissolving reaction solution to flow therein, and mixing and compressing together with the externally added hydrogen peroxide into the oxidation reaction tank or the hydrogen peroxide in the silver-dissolving reaction solution in the oxidation reaction tank in the main pipeline, so that the hydrogen peroxide and the decomposed oxygen dissolve in the reaction solution and better make full contact with the surface of the metallic silver, accelerating the oxidation reaction of the metallic silver.

11. The method for safely oxidizing and dissolving metallic silver according to claim 10, wherein To accelerate the oxidation reaction of metallic silver, set two or more flow-type hydrogen peroxide mixing and dosing devices in parallel in the oxidation reaction tank to promote the reaction.

12. The method for safely oxidizing and dissolving metallic silver according to claim 10, characterized in that, Use the silver dissolution reaction solution containing hydrogen peroxide flowing out of the mainstream pipeline to wash and corrode the silver metal block, so that the outer layer of silver oxide is stripped off to expose the underlying silver metal, accelerating the contact with the silver dissolution reaction solution to rapidly dissolve the silver metal.

13. The method for safely oxidizing and dissolving metallic silver according to claim 7, characterized in that, Add a silver metal accumulation through-hole groove for accumulating silver metal in the oxidation reaction tank, and use a liquid spraying pipe to directly and centrally spray the silver dissolution reaction solution onto the silver metal in the through-hole groove to promote the chemical reaction.

14. The method for safely oxidizing and dissolving metallic silver according to claim 7, characterized in that, When carrying out the silver dissolution reaction, apply ultrasonic waves to the silver dissolution reaction solution.

15. The method for safely oxidizing and dissolving metallic silver according to claim 7, characterized in that, Use an electrolytic cell as the oxidation reaction tank, use the silver metal participating in the reaction as the soluble electrolytic anode, use the silver dissolution reaction solution as the electrolyte, and carry out electrolytic silver dissolution; and add a liquid spraying pipe facing the electrolytic cathode in the electrolytic cell to spray the electrolyte containing hydrogen peroxide onto the electrolytic cathode.

16. The method for safely oxidizing and dissolving metallic silver according to claim 7, wherein Set that when the silver ion concentration in the silver dissolution reaction solution reaches a set value or the silver dissolution rate drops to a set value, it becomes the waste liquid of the silver dissolution reaction. Add sulfuric acid and / or carbon dioxide to the waste liquid of the silver dissolution reaction to make the silver compound dissolved in the waste liquid of the silver dissolution reaction react to form silver sulfate and / or silver carbonate solids. After solid-liquid separation, use the obtained filtrate as one of the raw materials of the silver dissolution reaction solution for recycling.

17. The method for safely oxidizing and dissolving metallic silver according to claim 7, characterized in that, in Add a liquid flow circulation stirrer to the oxidation reaction tank, which is a component composed of a pipeline, a pump, and a nozzle head, to make the silver dissolution reaction solution perform internal circulation stirring in the oxidation reaction tank and wash the surface of the silver metal block through the circulating stirring and spraying liquid to accelerate the silver dissolution chemical reaction.

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