METHOD AND APPARATUS FOR PREPARING SILVER COMPOUND FROM METALLIC SILVER

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of PCT application No. PCT/CN2024/090129 filed on Apr. 26, 2024, which claims priority to Chinese Patent Application Nos. 202310479503.0, filed on Apr. 28, 2023, and 202310543388.9, filed on May 15, 2023. The contents of all of the aforementioned applications are incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present disclosure belongs to the technical field of processing of silver compounds, and specifically relates to a method and apparatus for preparing a silver compound from metallic silver.

BACKGROUND

There are only a handful of soluble salts of silver, among which silver nitrate is easily produced. Therefore, the existing processes of preparing a silver compound from metallic silver typically involve the use of nitric acid for bridging. Specifically, silver reacts with nitric acid to produce silver nitrate, and silver nitrate then reacts with an alkaline substance to produce silver hydroxide and/or silver oxide, or silver nitrate then reacts with other acids and/or salts to produce other silver salts. Silver powder, which is extensively used in photovoltaic and electronics industries, is produced through a chemical reaction of diaminesilver hydroxide (Ag[NH₃]₂OH). The diaminesilver hydroxide is typically produced through a reaction of silver hydroxide and/or silver oxide with ammonia water. Thus, silver nitrate serves as an intermediate bridging product for the preparation of other silver salts, diaminesilver hydroxide, and silver oxide. Silver nitrate is commonly referred to as an intermediate for silver compound products.

However, silver nitrate is classified as an explosive hazardous chemical with high toxicity, imposing stringent requirements on the production management and the subsequent treatment for environmental protection. Silver nitrate demonstrates very strong toxic and side effects, and can directly cause burns and damage to the human skin and the mucous membrane of the digestive tract. In severe cases, silver nitrate may be life-threatening. Further, nitric acid needs to be used in the production of silver nitrate. Since nitric acid is a highly-corrosive acid, the use of nitric acid introduces significant safety hazards throughout the production process of silver compounds.

Additionally, the production of silver nitrate leads to the generation of large amounts of nitrogen oxide waste gases and ammonia-nitrogen waste liquids. As a result, there are high treatment costs for the “three wastes” (waste gas, waste water, and waste residues) generated throughout the production process of silver compounds. Ammonia-nitrogen waste gases can cause environmental issues such as acid rain, soil acidification, and water eutrophication, and may also jeopardize the respiratory and digestive systems of the human body. The discharge of ammonia-nitrogen waste liquids into water bodies can lead to eutrophication. The eutrophication causes the excessive proliferation of algae and other microorganisms and the reduced dissolved oxygen levels in the water bodies, which results in the death of fish and even the drying up of lakes. Moreover, the discharge of ammonia-nitrogen waste liquids may impair drinking water with unpleasant odors and induce methemoglobinemia in infants, posing direct threats to human health. Therefore, both ammonia-nitrogen waste gases and ammonia-nitrogen waste liquids must be treated to meet the corresponding standards before being discharged.

In terms of production safety, pollution reduction, and cost cutting, it is both necessary and urgent to improve the existing technologies for preparing a silver compound from metallic silver.

SUMMARY

A first objective of the present disclosure is to provide a method for preparing a silver compound from metallic silver, which is intended to address the major issues of safety, pollution, and cost in the existing production technologies for silver compounds. A second objective of the present disclosure is to provide an apparatus for preparing a silver compound from metallic silver, which is intended to achieve the preparation of a silver compound from metallic silver in the present disclosure.

The first objective of the present disclosure can be achieved through the following technical solutions:

A method for preparing a silver compound from metallic silver is provided, including the following steps:

• • (1) arranging at least one electrolytic cell with the metallic silver as an anode and an insoluble electrical conductor as a cathode; and connecting the anode to a positive terminal of an electrolytic power supply, and connecting the cathode to a negative terminal of the electrolytic power supply;
  • (2) feeding an alkaline electrolyte into the at least one electrolytic cell to be in contact with the anode; and
  • (3) starting the electrolytic power supply to conduct electrolysis, such that the metallic silver undergoes a dissolution reaction at the anode and a silver ion resulting from the dissolution reaction reacts with the alkaline electrolyte to produce a solid silver compound and/or a soluble silver complex.

In the step (1), the anode is the metallic silver and the cathode is an electrically-conductive material. Preferably, a material of the cathode is at least one selected from the group consisting of gold, platinum, silver, copper, titanium, iron, an alloy including at least one of the aforementioned metals, stainless steel, and conductive graphite.

In the step (2), the alkaline electrolyte includes an alkaline substance, and the alkaline substance is specifically at least one selected from the group consisting of sodium hydroxide, potassium hydroxide, ammonium carbonate, sodium carbonate, potassium carbonate, ammonium bicarbonate, sodium bicarbonate, potassium bicarbonate, ammonia water, and a silver-ammine complex.

In the step (3), the dissolution reaction of the metallic silver primarily occurs at the anode, which may be accompanied by an electrochemical reaction of oxygen evolution, and an electrochemical reaction of hydrogen evolution and/or an electrochemical reduction reaction of a high-valence metal ion primarily occurs at the cathode. When an electrolyte in contact with the cathode includes a soluble silver complex or a soluble silver salt or when the cathode comes into contact with the generated solid silver compound, the metallic silver may be electrodeposited at the cathode. The solid silver compound includes at least one selected from the group consisting of silver oxide, silver hydroxide, and silver carbonate. The soluble silver complex is a silver-ammine complex and/or a silver ion-hydroxide ion complex. The silver-ammine complex refers to a compound including a silver ammine complex ion [Ag(NH₃)₂]⁺, and the silver ion-hydroxide ion complex refers to a compound including a silver hydroxide complex ion [Ag(OH)₂]⁻.

In the method of the present disclosure, metallic silver is converted into water-insoluble silver oxide and/or silver hydroxide using an alkaline electrolyte, or with the silver oxide and/or the silver hydroxide as an intermediate, other solid silver compounds and/or soluble silver complexes are generated in the alkaline electrolyte. The solid silver compound and/or the soluble silver complex has a wide range of applications and can be easily converted into other silver compounds through simple chemical reactions. Thus, the method can be used in various industries.

During the electrolysis, electrochemical reactions occurring at the electrodes and chemical reactions occurring in the electrolyte are as follows:

A major electrochemical reaction at the anode is as follows: Ag-e⁻→Ag⁺.

A side electrochemical reaction at the anode is as follows: 4[OH]-4e⁻→2H₂O+O₂↑.

A major electrochemical reaction at the cathode is as follows: 2H⁺⁺2e⁻→H₂↑.

Alternatively, the following reaction also occurs at the cathode:

The silver ion resulting from the dissolution reaction of the metallic silver at the anode is combined with a hydroxide ion in the alkaline electrolyte to produce silver hydroxide. In the electrolyte, the silver hydroxide may further undergo the following chemical reactions:

The equilibrium of a complexation reaction between the silver oxide and the hydroxide ion depends on a concentration of the hydroxide ion in the electrolyte. When the concentration of the hydroxide ion in the electrolyte is high, it is prone to generating the silver hydroxide complex ion [Ag(OH)₂]—, which exists in a solution. Therefore, when a product does not meet the process requirements, a concentration of a hydroxide ion in the alkaline electrolyte can be adjusted to control a product or a ratio of silver oxide to a silver ion-hydroxide ion complex.

Additionally, the metallic silver anode reacts with oxygen to produce silver oxide. The silver oxide generated in this way has a relatively-loose structure and easily falls off into the electrolyte:

When the electrolyte includes a carbonate ion CO₃²⁻, silver hydroxide also undergoes the following chemical reaction in the electrolyte:

When the electrolyte includes ammonia water and/or an ammonium salt, silver hydroxide or silver oxide reacts with the ammonia water and/or the ammonium salt in the electrolyte to produce a soluble silver-ammine complex. The corresponding chemical reactions are as follows:

When a solid silver compound is generated at the anode due to the dissolution of metallic silver during electrolysis, the solid silver compound produced in the alkaline electrolyte needs to be collected through solid-liquid separation. A main component of a collected solid silver compound filter residue is at least one selected from the group consisting of silver oxide, silver carbonate, and silver hydroxide.

During the electrolysis in the step (3), if the electrolyte includes ammonia and/or an ammonium ion, a silver-ammine complex will be generated. Alternatively, if a concentration of hydroxide ions in the electrolyte is relatively high, a silver hydroxide complex ion [Ag(OH)₂]⁻ will be generated. When the silver ammine complex ion and/or the silver hydroxide complex ion is in contact with the cathode, silver is electrodeposited at the cathode, which affects the production efficiency of a target silver compound. If concentrations of ammonia, ammonium ions, and hydroxide ions in the electrolyte are relatively low, silver ions resulting from the dissolution of the anode react totally or mostly to produce solid silver compound particles. The oxygen or hydrogen evolved agitates the electrolyte when released, such that the solid silver compound particles float toward the cathode and are in contact with the cathode to produce metallic silver. When the process requirements are not met due to the electrodeposition of metallic silver from the generated solid silver compound floating toward and adhering to the electrolytic cathode, a distance between the electrolytic anode and the electrolytic cathode can be increased to reduce the contact of the solid silver compound with the cathode. In addition to the aforementioned drawback, there is a production safety risk of explosion due to the mixing of oxygen and hydrogen evolved when the at least one electrolytic cell is a separator-free electrolytic cell.

To address the problems mentioned above, the present disclosure adopts the following preferred solution: An electrolytic cell provided with an electrolytic cell separator to divide the electrolytic cell into an anode compartment and a cathode compartment is provided; and the alkaline electrolyte is adopted as an anode electrolyte, and an electrolyte-containing aqueous solution is adopted as a cathode electrolyte. The cathode electrolyte is selected based on characteristics of the electrolytic cell separator. An electrolyte solution with the same or different composition as the anode electrolyte is adopted as the cathode electrolyte, as long as the generation of the target silver compound in the anode compartment is not affected.

The electrolytic cell separator is at least one selected from the group consisting of a filter cloth, a filter plate, an anion exchange membrane, a cation exchange membrane, a bipolar membrane, a reverse osmosis membrane, and a non-ion-selective diaphragm. The electrolytic cell separator is arranged in the electrolytic cell to divide the electrolytic cell into the anode compartment and the cathode compartment. The filter plate commonly includes a polyethylene (PE) microporous filter plate (namely, a PE filter plate) and a ceramic filter plate. The non-ion-selective diaphragm is a material with through holes that allow at least some ions or molecules to pass through, but demonstrate no selectivity for cations and anions. The non-ion-selective diaphragm commonly includes an asbestos diaphragm, a polymer diaphragm, etc. Functions of the electrolytic cell separator: (1) During the electrolysis, the electrolytic cell separator can block the migration of silver ammine complex ions [Ag(NH₃)₂]⁺ and/or silver hydroxide complex ions [Ag(OH)₂]⁻ between the two compartments during the electrolysis, and/or prevent the solid silver compound particles in the anode electrolyte from drifting into the cathode compartment. (2) The electrolytic cell separator can prevent hydrogen bubbles in the cathode electrolyte from drifting into the anode compartment to avoid a safety hazard and facilitate the collection of hydrogen.

Preferably, when the electrolytic cell separator is at least one selected from the group consisting of the filter cloth, the filter plate, the anion exchange membrane, and the non-ion-selective diaphragm, the cathode electrolyte does not include anions that will react with the solid silver compound and/or the soluble silver complex to produce a compound other than the target product, or anions that will contaminate the target product to make the target product fail to meet the process requirements. When the electrolytic cell separator is at least one selected from the group consisting of the filter cloth, the filter plate, the cation exchange membrane, and the non-ion-selective diaphragm, the cathode electrolyte does not include cations that will react with the solid silver compound and/or the soluble silver complex to produce a compound other than the target product, or cations that will contaminate the target product to make the target product fail to meet the process requirements. More preferably, the cathode electrolyte does not include ions that will react with the solid silver compound and/or the soluble silver complex to produce a compound other than the target product, or ions that will contaminate the target product to make the target product fail to meet the process requirements.

If the anode electrolyte includes ammonia and/or an ammonium ion, a silver ammine complex ion will be generated during the electrolysis. In this case, the electrolytic cell separator is at least one selected from the group consisting of the anion exchange membrane, the bipolar membrane, and the reverse osmosis membrane. During the electrolysis, silver ammine complex ions in the electrolyte migrate toward the cathode under an action of an electric field and are converted into metallic silver at the cathode. Therefore, to improve a yield of a silver compound, the electrolytic cell separator is adopted to block the migration of silver ammine complex ions in the anode electrolyte to the cathode compartment of the electrolytic cell. As a result, a silver compound product such as diaminesilver hydroxide solution and/or a silver ammine carbonate complex solution and/or other silver-ammine complex solutions can be produced in the anode electrolyte according to process requirements.

When an alkaline electrolyte without ammonia and/or an ammonium ion is adopted as the anode electrolyte for electrolysis, any one selected from the group consisting of the aforementioned electrolytic cell separators may be employed. Although silver oxide and/or silver hydroxide can react with hydroxide ions to produce silver hydroxide complex ions, these silver hydroxide complex ions demonstrate electronegativity and are thus attracted to a vicinity of the anode due to the electropositivity of the anode. A generation rate of silver hydroxide complex ions is lower than a generation rate of silver ammine complex ions. A proportion of silver hydroxide complex ions generated is significantly influenced by a concentration of hydroxide ions in the alkaline electrolyte. When a large amount of silver oxide is generated in the anode electrolyte, the floating silver oxide particles may adhere to the electrolytic cell separator. Since silver oxide is electrically conductive, silver oxide can become a secondary electrode under an action of an electric field, which easily damages the electrolytic cell separator. In this case, the selection of a cost-effective and durable filter cloth and/or filter plate as the electrolytic cell separator can effectively reduce the production equipment cost.

In the present disclosure, when an electrolytic cell provided with an electrolytic cell separator is adopted, the material of the cathode is preferably at least one selected from the group consisting of gold, platinum, silver, copper, titanium, iron, an alloy including at least one of the aforementioned metals, stainless steel, and conductive graphite. Preferably, the material of the cathode is metallic silver to minimize the contamination of the silver compound product by other metal components.

The present disclosure can be improved as follows: After the solid silver compound is generated from the metallic silver of the anode through the electrolysis of the present disclosure, a silver compound filter residue produced after solid-liquid separation is further allowed to undergo a chemical reaction to produce other desired silver compounds, and the chemical reaction is at least one selected from the group consisting of the following:

• • (1) when the silver compound filter residue includes silver carbonate, heating is conducted to make the silver carbonate decompose into silver oxide and carbon dioxide;
  • (2) the silver compound filter residue and/or a silver compound filter residue left after the reaction (1) is allowed to react with an acid and/or a salt to produce other silver salts; and
  • (3) the silver compound filter residue or the silver compound filter residue left after the reaction (1) is allowed to react with ammonia water and/or sodium hydroxide and/or potassium hydroxide to produce at least one selected from the group consisting of a silver ammine hydroxide complex Ag[NH₃]₂OH, a silver ammine carbonate complex [Ag(NH₃)₂]₂CO₃, silver fulminate Ag₂C₂N₂O₂, and a silver ion-hydroxide ion complex. The silver fulminate Ag₂C₂N₂O₂ can be produced through a reaction of silver carbonate with ammonia water. Preferably, when the silver compound filter residue is treated to produce the silver ion-hydroxide ion complex, a concentration of the sodium hydroxide and/or the potassium hydroxide in a reaction solution is not less than 7%.

The present disclosure can be improved as follows: To enable the efficient electrolytic production of a silver compound, a total concentration of the alkaline substance in the alkaline electrolyte is preferably 0.05 mol/L to 21 mol/L. When a total molar concentration of the alkaline substance in the alkaline electrolyte is too high, an elevated viscosity of the electrolyte impedes the ion mobility in the electrolyte, such that a working voltage of the electrolytic cell increases, resulting in large energy consumption. When the total concentration of the alkaline substance in the alkaline electrolyte is too low, an ion concentration is low, resulting in low electrical efficiency. More preferably, the total concentration of the alkaline substance in the alkaline electrolyte is 0.2 mol/L to 16 mol/L. Further more preferably, the total concentration of the alkaline substance in the alkaline electrolyte is 0.5 mol/L to 6.5 mol/L.

The present disclosure can also be improved as follows: A temperature of an electrolyte is raised to enhance an electrochemical reaction.

The present disclosure can also be improved as follows: The alkaline electrolyte is preferably a sodium hydroxide solution and/or a potassium hydroxide solution and/or ammonia water. More preferably, to ensure that silver oxide is primarily produced from the metallic silver during the electrolysis, a sodium hydroxide and/or potassium hydroxide solution is adopted as the alkaline electrolyte, and the filter cloth or the filter plate is adopted as the electrolytic cell separator, which is intended to reduce the production equipment cost. More preferably, to produce diaminesilver hydroxide from the metallic silver during the electrolysis, the ammonia water or a mixture of the ammonia water and the diaminesilver hydroxide is adopted as the alkaline electrolyte and at least one selected from the group consisting of the anion exchange membrane, the bipolar membrane, and the reverse osmosis membrane is adopted as the electrolytic cell separator, which enables the direct and efficient production of the diaminesilver hydroxide meeting product requirements through the electrolysis while simplifying the process.

The second objective of the present disclosure is to provide an apparatus for preparing a silver compound from metallic silver. The apparatus can achieve the first objective of the present disclosure.

The apparatus for preparing a silver compound from metallic silver includes: at least one electrolytic cell, at least one soluble metallic silver anode, at least one electrolytic cathode, and at least one electrolytic power supply,

• • where when a solid silver compound product needs to be prepared, at least one solid-liquid separator is further provided, and the at least one electrolytic cell is connected to the at least one solid-liquid separator through a pump and a pipeline; and
  • when a liquid silver compound product needs to be prepared, a storage tank configured to store the liquid silver compound product is further provided or the storage tank and a solid-liquid separator that are connected through a pipeline are further provided, and the at least one electrolytic cell is connected to the storage tank either through a pipeline or through the solid-liquid separator and the pipeline.

In the at least one electrolytic cell, an anode is metallic silver connected to a positive terminal of the at least one electrolytic power supply, and a cathode is an insoluble electrical conductor connected to a negative terminal of the at least one electrolytic power supply.

The insoluble electrical conductor is at least one selected from the group consisting of gold, platinum, silver, copper, titanium, iron, an alloy including at least one of the aforementioned metals, stainless steel, and conductive graphite.

Preferably, a material of the cathode is metallic silver to minimize the contamination of the silver compound product by other metals.

The solid-liquid separator is configured to collect solid silver compound particles and a silver powder suspended in an electrolyte through solid-liquid separation.

The solid-liquid separator is selected from the group consisting of a press filter, a filter, and a centrifuge, all of which can achieve the solid-liquid separation.

The present disclosure can be improved as follows: The at least one electrolytic cell is provided with an electrolytic cell separator to divide the at least one electrolytic cell into an anode compartment and a cathode compartment, which can reduce the floating and adhesion of solid silver compound particles in an electrolyte to the cathode for electrodeposition of a silver powder, and can also mitigate the electrodeposition of a silver powder from a soluble silver compound in an electrolyte to improve the production efficiency. Additionally, the electrolytic cell separator can prevent hydrogen from migrating to the anode compartment, thereby avoiding the interference with the electrolysis. The electrolytic cell separator is at least one selected from the group consisting of an anion exchange membrane, a cation exchange membrane, a bipolar membrane, a reverse osmosis membrane, a non-ion-selective diaphragm, a filter cloth, a microporous membrane, and a filter plate. Preferably, the filter cloth and/or the filter plate is adopted. More preferably, the anode is wrapped with an anode filter cloth bag to collect and intercept silver compound particles generated from the anode. When an electrolyte includes ammonia and/or an ammonium ion, the electrolytic cell separator is at least one selected from the group consisting of the anion exchange membrane, the bipolar membrane, and the reverse osmosis membrane.

The present disclosure can be improved as follows: A titanium basket is provided to hold the metallic silver as the anode for an electrochemical reaction. This improvement can prevent metallic silver fragments from scattering and guarantee the effective participation of the metallic silver fragments in an electrolytic reaction to produce a silver compound. The titanium basket is a titanium basket-shaped structure electrically connected to the positive terminal of the at least one electrolytic power supply and is arranged in the at least one electrolytic cell. The titanium basket can load a metallic silver block or a silver powder particle and allows the loaded metallic silver to be energized for an electrochemical reaction. A common structure of the titanium basket is shown in FIG. 1.

The present disclosure can also be improved as follows: A suction and discharge pipe is provided in the titanium basket, and during or after electrolysis, the solid silver compound in the titanium basket is taken out of the at least one electrolytic cell and collected.

The present disclosure can also be improved as follows: A solid feeder is further provided to feed the metallic silver into the titanium basket to enable an electrolytic reaction, which can reduce the labor intensity.

The present disclosure can also be improved as follows: A liquid jet pipe with a liquid outlet facing toward the anode is provided in the at least one electrolytic cell, and the liquid jet pipe is configured to enable a solution from the at least one electrolytic cell to flush the anode. Specifically, an electrolyte is circulated to flush the metallic silver anode, such that silver oxide and/or silver carbonate adhering to the anode detaches from the anode. This design increases an electrochemical reaction area of the metallic silver anode to improve the production efficiency.

The present disclosure can also be improved as follows: The at least one electrolytic cell is further provided with a pump-tube liquid-flow circulating stirrer to stir an electrolyte, ensuring the smooth proceed of an electrochemical reaction. Preferably, a liquid outlet pipe of the pump-tube liquid-flow circulating stirrer is the liquid jet pipe with the liquid outlet facing toward the anode to enable flushing of the anode. With this design, a solution can be thoroughly stirred, and the liquid jet pipe of the stirrer can also serve as a flushing device.

The present disclosure can also be improved as follows: The at least one electrolytic cell is further provided with a heat exchanger to make a reaction temperature of an electrolyte meet a process requirement, which ensures both the safe production and the enhanced chemical reaction efficiency.

The present disclosure can also be improved as follows: The at least one electrolytic cell is further provided with a gas drainage collector, and the gas drainage collector is connected to a hydrogen eliminator for a safe treatment of hydrogen evolved. The gas drainage collector is a spray tower or a vacuum ejector.

The present disclosure can also be improved as follows: A temporary storage tank is further provided to temporarily store a chemical or hold a prepared silver compound solution product or to serve as a chemical reaction tank. Preferably, the temporary storage tank is connected to the at least one electrolytic cell and/or the solid-liquid separator through a liquid pipeline and/or a gas pipeline, or is arranged below a liquid outlet of the at least one electrolytic cell and/or the solid-liquid separator to receive an overflowing liquid.

The present disclosure can also be improved as follows: An electrothermal furnace is further provided to heat silver carbonate produced after electrolysis to produce silver oxide.

The present disclosure can also be improved as follows: A sensor and an automatic program controller are further provided, such that the apparatus of the present disclosure undergoes automated production according to a preset program. The sensor is at least one selected from the group consisting of a pH meter, a liquid level meter, a gravimeter, a thermometer, a weightometer, and a hydrogen concentration detector.

The present disclosure can also be improved as follows: A water-washing tank is further provided for washing to remove soluble impurities from the solid silver compound.

The present disclosure can also be improved as follows: An impeller stirrer is further provided to enable thorough stirring of reactants.

The present disclosure can also be improved as follows: An overflow buffer tank is further provided, and the overflow buffer tank is connected to at least one selected from the group consisting of the at least one electrolytic cell, the solid-liquid separator, and the temporary storage tank. This design can ensure a smooth liquid flow between components of the apparatus.

Compared with the prior art, the present disclosure has the following beneficial effects:

1. The present disclosure utilizes a simple electrolysis process to achieve the single-step preparation of a solid silver compound and/or a soluble silver complex, including silver oxide and/or diaminesilver hydroxide. The present disclosure omits the intermediate procedure of producing silver nitrate, and remarkably reduces the raw material cost.

2. The preparation of silver oxide or diaminesilver hydroxide in the present disclosure does not involve the intermediate procedure of producing silver nitrate, which reduces the environmental pollution.

3. The production process employed in the present disclosure avoids the strong corrosiveness of nitric acid and the toxicity of silver nitrate as an intermediate product, which reduces the production safety risks and guarantees the occupational health and safety for operators.

4. The production process of the present disclosure does not involve the use of nitric acid. Thus, the present disclosure avoids the corrosion of nitric acid to production equipment and lowers the maintenance cost for production equipment.

5. By omitting the intermediate procedure of producing silver nitrate, the present disclosure reduces the process steps and the production energy consumption, thereby achieving the eco-friendly production with reduced energy consumption and reduced emissions.

6. The solid silver compound and/or the soluble silver complex produced by the present disclosure can be further converted into various silver compounds through simple chemical reactions, offering a wide range of applications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a structure diagram of a titanium basket;

FIG. 2 is a schematic diagram of an apparatus and process flow for preparing a silver compound from metallic silver in Example 1 of the present disclosure;

FIG. 3 is a schematic diagram of an apparatus and process flow for preparing a silver compound from metallic silver in Example 2 of the present disclosure;

FIG. 4 is a schematic diagram of an apparatus and process flow for preparing a silver compound from metallic silver in Example 3 of the present disclosure;

FIG. 5 is a schematic diagram of an apparatus and process flow for preparing a silver compound from metallic silver in Example 4 of the present disclosure;

FIG. 6 is a schematic diagram of an apparatus and process flow for preparing a silver compound from metallic silver in Example 5 of the present disclosure;

FIG. 7 is a schematic diagram of an apparatus and process flow for preparing a silver compound from metallic silver in Example 6 of the present disclosure;

FIG. 8 is a schematic diagram of an apparatus and process flow for preparing a silver compound from metallic silver in Example 7 of the present disclosure; and

FIG. 9 shows a part A of FIG. 8, FIG. 10 shows a part B of FIG. 8, and FIG. 9 and FIG. 10 constitute a complete schematic diagram of an apparatus and process flow for preparing a silver compound from metallic silver in Example 7.

REFERENCE NUMERALS

1—electrolytic cell, 2—anode, 3—cathode, 4—electrolytic power supply, 5—electrolytic cell separator, 6—titanium basket, 7—electrothermal furnace, 8—pump-tube liquid-flow circulating stirrer, 9—impeller stirrer, 10—solid-liquid separator, 11—heat exchanger, 12—gas drainage collector, 13—hydrogen eliminator, 14—temporary storage tank, 15—suction and discharge pipe, 16—solid feeder, 17—nitric acid, 18—ammonia water, 19—silver oxide, 20—silver nitrate, 21—sensor, 22—automatic program controller, 23—water-washing tank, 24—alkaline electrolyte, 25—silver compound, 26—metallic silver, 27—spray tower, 28—vacuum ejector, 29—clear water, 30—silver salt, 31—carbon dioxide, 32—valve, 33—pump, 34—diaminesilver hydroxide, 35—silver ammine carbonate complex solution, 36—anode filter cloth bag, 37—sulfuric acid solution, 38—liquid jet pipe, 39—overflow buffer tank, and 40—silver sulfate.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present disclosure will be further described below through specific embodiments.

An electrolytic cell, a titanium basket, a temporary storage tank, a hydrogen eliminator, a heat exchanger, a stirrer, a gas drainage collector, and a water-washing tank used in the embodiments of the present disclosure are all products manufactured by Yegao Environmental Protection Equipment Manufacturing Co., Ltd. in Foshan City, Guangdong Province, China. A sensor, an automatic program controller, a solid-liquid separator, an electrothermal furnace, chemical raw materials, and metallic silver are all commercially available products. Other products with similar properties to the products listed above in the present disclosure may also be adopted by those skilled in the art according to conventional selection, which all can achieve the objectives of the present disclosure.

Example 1

As shown in FIG. 2, an apparatus for preparing a silver compound from metallic silver is provided in Example 1, including an electrolytic cell 1 and a solid-liquid separator 10.

The electrolytic cell 1 is a separator-free electrolytic cell. A material of an anode 2 is metallic silver and connected to a positive terminal of an electrolytic power supply 4. A material of a cathode 3 is metallic silver and connected to a negative terminal of the electrolytic power supply 4. An alkaline electrolyte 24 is primarily a mixed solution of sodium hydroxide, potassium hydroxide, and sodium bicarbonate, with a total alkaline substance concentration of 0.05 mol/L.

The solid-liquid separator 10 is a common filter. The solid-liquid separator is connected to the electrolytic cell 1 through a pipeline. The solid-liquid separator is configured to separate a solid mixture including silver oxide 25-1, silver carbonate 25-2, and a silver powder 26 from the alkaline electrolyte.

A method for preparing a silver compound from metallic silver is provided, including the following steps:

1. The alkaline electrolyte 24 was fed into the electrolytic cell 1 until the anode 2 and the cathode 3 were immersed in the alkaline electrolyte.

2. The electrolytic power supply 4 was started to initiate electrolysis. At the anode, oxygen was evolved, and metallic silver was dissolved and reacted to produce solid silver compounds, namely, silver oxide 25-1 and silver carbonate 25-2. At the cathode, hydrogen was evolved, and a trace amount of metallic silver 26 was electrodeposited.

3. After the electrolysis was completed, the pump 33 was turned on to enable solid-liquid separation for a solid-liquid mixture in the electrolytic cell 1 by the solid-liquid separator 10 to produce a filter residue, which was a mixture of silver oxide, silver carbonate, and a silver powder.

With the apparatus shown in FIG. 2, the method for preparing a silver compound from metallic silver was implemented through the above steps to produce the silver oxide and the silver carbonate as the main products.

Example 2

As shown in FIG. 3, an apparatus for preparing a silver compound from metallic silver is provided in Example 2, including an electrolytic cell 1, a solid-liquid separator 10, a temporary storage tank 14, a valve, and a pump.

The electrolytic cell 1 is a separator-free electrolytic cell. A material of an anode 2 is metallic silver and connected to a positive terminal of an electrolytic power supply 4. A material of a cathode 3 is metallic iron and connected to a negative terminal of the electrolytic power supply 4.

The electrolytic cell 1 is connected to the solid-liquid separator 10 and the temporary storage tank 14 successively.

An alkaline electrolyte 24 is primarily a mixed solution of ammonia water and ammonium carbonate, with a total alkaline substance concentration of 2 mol/L.

The solid-liquid separator 10 is a common filter. The solid-liquid separator is configured to separate a silver powder 26 from the alkaline electrolyte.

A method for preparing a silver compound from metallic silver is provided, including the following steps:

1. The alkaline electrolyte 24 was fed into the electrolytic cell 1 until the anode 2 and the cathode 3 were immersed in the alkaline electrolyte.

2. The electrolytic power supply 4 was started to initiate electrolysis. At the anode, oxygen was evolved, and metallic silver was dissolved and reacted to produce diaminesilver hydroxide and silver ammine carbonate complex. At the cathode, a large amount of hydrogen was evolved, and then a trace amount of metallic silver 26-2 was gradually electrodeposited.

3. The electrodeposition of silver at the cathode indicated the completion of the electrolysis. In this case, the pump 33 was turned on to enable solid-liquid separation for a solid-liquid mixture in the electrolytic cell 1 by the solid-liquid separator 10 to produce a filtrate and a filter residue. The filtrate was a mixed solution of diaminesilver hydroxide and silver ammine carbonate complex. The filtrate was delivered to the temporary storage tank 14 for temporary storage. The filter residue in the solid-liquid separator 10 was then collected to produce a small amount of a silver powder 26-2.

With the apparatus shown in FIG. 3, the method for preparing a silver compound from metallic silver was implemented through the above steps to produce the mixed solution of diaminesilver hydroxide and silver ammine carbonate complex as the main products.

Example 3

As shown in FIG. 4, an apparatus for preparing a silver compound from metallic silver is provided in Example 3, including an electrolytic cell 1, a solid-liquid separator 10, two temporary storage tanks 14, a liquid jet pipe 38, a valve, and pumps.

An electrolytic cell separator 5 is provided in the electrolytic cell 1 to divide the electrolytic cell into an anode compartment and a cathode compartment. A material of an anode 2 is metallic silver and connected to a positive terminal of an electrolytic power supply 4. A material of a cathode 3 is stainless steel and connected to a negative terminal of the electrolytic power supply 4. The anode and the cathode are arranged in the anode compartment and the cathode compartment, respectively. The electrolytic cell separator 5 is a cation exchange membrane.

An anode electrolyte is an alkaline electrolyte 24, which is a sodium hydroxide solution with a total alkaline substance concentration of 0.2 mol/L. A cathode electrolyte is a 4% sulfuric acid solution 37.

The anode compartment of the electrolytic cell 1 is connected to the solid-liquid separator 10 and a temporary storage tank 14-1 successively. The temporary storage tank 14-1 is connected to the liquid jet pipe 38. A liquid outlet of the liquid jet pipe faces toward the anode in the anode compartment. The liquid jet pipe is configured to eject the anode electrolyte onto the metallic silver at the anode.

The solid-liquid separator 10 is a centrifuge equipped with a scraper. The solid-liquid separator is configured to enable solid-liquid separation for a solid-liquid mixture in the anode electrolyte. A separated solid silver compound 25 is silver oxide. A filtrate is returned to the anode compartment through the temporary storage tank 14-1 and the liquid jet pipe 38 to flush the metallic silver at the anode.

A method for preparing a silver compound from metallic silver is provided, including the following steps:

1. The alkaline electrolyte 24 was fed into the anode compartment of the electrolytic cell 1, and the sulfuric acid solution 37 was fed into the cathode compartment, such that the anode 2 and the cathode 3 were immersed in solutions in the anode and cathode compartments, respectively.

2. The electrolytic power supply 4 was started to initiate electrolysis. At the anode, oxygen was evolved, and metallic silver was dissolved and reacted to produce a solid silver compound 25 as a main product. At the cathode, hydrogen was evolved.

3. During the electrolysis, pumps 33-1 and 33-2 were turned on to draw the anode electrolyte into the solid-liquid separator 10 for solid-liquid separation to produce a filter residue and a filtrate. The filter residue was a silver compound 25. The filtrate was delivered through the temporary storage tank 14-1 to the liquid jet pipe 38, such that the returned anode electrolyte could flush the anode through the liquid jet pipe 38.

With the apparatus shown in FIG. 4, the method for preparing a silver compound from metallic silver was implemented through the above steps to produce the silver compound 25 as a silver oxide product.

Example 4

As shown in FIG. 5, an apparatus for preparing a silver compound from metallic silver is provided in Example 4, including an electrolytic cell 1, a solid-liquid separator 10, a heat exchanger 11, an anode filter cloth bag 36, a liquid jet pipe 38, a valve, and a pump.

The electrolytic cell 1 is a separator-free electrolytic cell. A material of an anode 2 is metallic silver and connected to a positive terminal of an electrolytic power supply 4. A material of a cathode 3 is metallic platinum and connected to a negative terminal of the electrolytic power supply 4. The anode filter cloth bag 36 is arranged to wrap a metallic silver block as the anode, and is configured to collect a silver compound 25 produced.

The electrolytic cell 1 is provided with the heat exchanger 11. The heat exchanger 11 is configured to adjust a working temperature of an electrolyte according to a process requirement to promote a chemical reaction.

An alkaline electrolyte 24 is a sodium hydroxide and potassium hydroxide solution with a total alkaline substance concentration of 0.5 mol/L.

The solid-liquid separator 10 is a common filter. The solid-liquid separator is configured to separate a small amount of a silver powder electrodeposited at the cathode from the alkaline electrolyte. The solid-liquid separator is connected to the electrolytic cell 1 through a pipeline. The solid-liquid separator 10 is also connected to the liquid jet pipe 38. A liquid outlet of the liquid jet pipe faces toward the anode in the anode compartment, such that a filtrate could be returned to the electrolytic cell and flush the metallic silver at the anode.

A method for preparing a silver compound from metallic silver is provided, including the following steps:

1. The alkaline electrolyte 24 was fed into the electrolytic cell 1 until the anode 2 and the cathode 3 were immersed in the alkaline electrolyte. The anode 2 was wrapped in the anode filter cloth bag 36.

2. The electrolytic power supply 4 was started to initiate electrolysis. At the anode, oxygen was evolved, and the metallic silver was dissolved and reacted to produce silver oxide. The silver oxide fell into the anode filter cloth bag. At the cathode, hydrogen was evolved, and simultaneously, a small amount of metallic silver 26-2 was electrodeposited. During the electrolysis, a temperature of the electrolyte was adjusted according to a process requirement. Moreover, the pump 33 was turned on to continuously draw the electrolyte to flush the anode. Small amounts of a silver oxide powder and a silver powder 26-2 suspended in the electrolyte were retained in the solid-liquid separator 10 during filtration.

3. After the electrolysis was completed, the anode filter cloth bag 36 was taken out from the electrolytic cell, and the silver compound 25, namely, silver oxide, in the anode filter cloth bag was collected.

With the apparatus shown in FIG. 5, the method for preparing a silver compound from metallic silver was implemented through the above steps to produce the silver compound 25 as a silver oxide product.

Example 5

As shown in FIG. 6, an apparatus for preparing a silver compound from metallic silver is provided in Example 5, including an electrolytic cell 1, an electrothermal furnace 7, solid-liquid separators 10-1 and 10-2, pump-tube liquid-flow circulating stirrers 8-1 and 8-2, an impeller stirrer 9, temporary storage tanks 14-1 to 14-5, a liquid jet pipe 38, valves, and pumps.

An electrolytic cell separator 5 is provided in the electrolytic cell 1 to divide the electrolytic cell into an anode compartment and a cathode compartment. A material of an anode 2 is metallic silver and connected to a positive terminal of an electrolytic power supply. A material of a cathode 3 is conductive graphite and connected to a negative terminal of the electrolytic power supply. The anode and the cathode are arranged in the anode compartment and the cathode compartment, respectively. The electrolytic cell separator 5 is an anion exchange membrane.

A pump-tube liquid-flow circulating stirrer 8-3 including a pipeline, a pump 33-1, and a valve 32-1 is provided in the anode compartment. A liquid outlet pipe of the pump-tube liquid-flow circulating stirrer includes two liquid jet pipes 38 with liquid outlets facing toward the anode 2, such that an anode electrolyte can be ejected onto the metallic silver at the anode.

The anode electrolyte is an alkaline electrolyte 24-1, which is a sodium carbonate and sodium bicarbonate solution with a total alkaline substance concentration of 6.5 mol/L. A cathode electrolyte is an alkaline electrolyte 24-2, which is a sodium hydroxide solution with a hydroxide ion [OH]⁻ concentration of 3 mol/L.

The anode compartment of the electrolytic cell 1 is connected to the solid-liquid separator 10-1 and the temporary storage tank 14-1 successively.

A water-washing tank 23 is connected to the solid-liquid separator 10-2 and the temporary storage tank 14-3 successively. The water-washing tank 23 is configured to wash a solid silver compound 25-2 with water to remove soluble impurities in the solid silver compound.

The solid-liquid separator 10-1 is a centrifuge, and is configured to separate a solid silver compound 25-1 from the anode electrolyte. The solid-liquid separator 10-2 is a press filter, and is configured to separate a solid-liquid mixture in the water-washing tank to produce a solid silver compound 25-3.

The solid silver compounds 25-1, 25-2, and 25-3 are each a solid mixture of silver carbonate and silver oxide.

The electrothermal furnace 7 is configured to heat the solid silver compound 25-3, such that the solid silver compound 25-3 decomposes to produce pure silver oxide 19. A sensor 21 in the electrothermal furnace 7 is a thermometer.

The temporary storage tanks 14-4 and 14-5 serve as chemical reaction tanks, and are provided with the pump-tube liquid-flow circulating stirrers 8-1 and 8-2, respectively. The temporary storage tank 14-4 is configured to enable a reaction of the solid silver compound 25-3 with a sulfuric acid solution 37 to prepare silver sulfate. The temporary storage tank 14-5 is configured to enable a reaction of the silver oxide 19 with ammonia water 18 to prepare a solution of diaminesilver hydroxide 34.

A method for preparing a silver compound from metallic silver is provided, including the following steps:

1. The anode electrolyte was fed into the anode compartment of the electrolytic cell 1, and the cathode electrolyte was fed into the cathode compartment, such that the anode 2 and cathode 3 were immersed in the respective electrolytes.

2. The electrolytic power supply 4 was started to initiate electrolysis. A pump 33-1 was turned on. At the anode, oxygen was evolved, and metallic silver was dissolved and reacted to produce silver hydroxide. A part of the silver hydroxide immediately reacted with a carbonate ion CO₃²⁻ in the anode electrolyte to synthesize silver carbonate. Thus, a resulting silver compound 25-1 was a mixture of silver carbonate and silver oxide. At the cathode, hydrogen was evolved. Moreover, the anode electrolyte could flush the anode 2.

3. After the electrolysis was completed, the pump 33-1 and the electrolytic power supply 4 were turned off. A pump 33-2 was turned on to pump a solid-liquid mixture from the anode electrolyte to the solid-liquid separator 10-1 for solid-liquid separation to produce a filter residue as a silver compound 25-2, which was a solid mixture of silver carbonate and silver oxide.

4. The silver compound 25-2 was washed with water in the water-washing tank 23 to remove soluble impurities. A filter residue produced after solid-liquid separation by the solid-liquid separator 10-2 was a silver compound 25-3, which was a solid mixture of silver carbonate and silver oxide.

5. The silver compound 25-3 was fed into the temporary storage tank 14-4 to react with a sulfuric acid solution 37 to produce silver sulfate, and was also fed into the electrothermal furnace 7 for heating to produce silver oxide 19. Then, a part of the silver oxide 19 was taken out from the electrothermal furnace 7 and fed into the temporary storage tank 14-5 to react with ammonia water to produce the solution of diaminesilver hydroxide 34.

With the apparatus shown in FIG. 6, the method for preparing a silver compound from metallic silver was implemented through the above five steps to produce the silver oxide, the silver sulfate, and the solution of diaminesilver hydroxide as products.

Example 6

As shown in FIG. 7, an apparatus for preparing a silver compound from metallic silver is provided in Example 6, including an electrolytic cell 1, a titanium basket 6, a solid-liquid separator 10, a pump-tube liquid-flow circulating stirrer 8, temporary storage tanks 14-1 and 14-2, a hydrogen eliminator 13, gas drainage collectors 12-1 and 12-2, sensors 21-1 to 21-4, an automatic program controller 22, a suction and discharge pipe 15, a solid feeder 16, a vacuum ejector 28, valves, and pumps.

An electrolytic cell separator 5 is provided in the electrolytic cell 1 to divide the electrolytic cell into an anode compartment and a cathode compartment. The electrolytic cell separator 5 is a bipolar membrane. Liquid level meters are provided in the anode compartment, which are specifically sensors 21-2 and 21-3. An anode 2 is fragmented metallic silver, which is loaded in the titanium basket 6 with a sealed bottom. A suction and discharge pipe 15 is provided in the titanium basket. The titanium basket 6 is suspended by a weightometer (namely, a sensor 21-4). The titanium basket 6 is connected to a positive terminal of an electrolytic power supply 4. A cathode 3 is made of titanium, and is connected to a negative terminal of the electrolytic power supply 4.

The suction and discharge pipe 15 is connected to the solid-liquid separator 10, and is circularly connected to the anode compartment through the temporary storage tank 14-1.

An anode electrolyte is an alkaline electrolyte 24-1, which is a potassium hydroxide solution with a total alkaline substance concentration of 16 mol/L. A cathode electrolyte is an alkaline electrolyte 24-2, which is a sodium hydroxide solution with a hydroxide ion [OH]-concentration of 14 mol/L.

The solid-liquid separator 10 is a press filter, and is configured to allow pressure filtration for a solid-liquid mixture in the titanium basket.

The pump-tube liquid-flow circulating stirrer 8 includes a pipeline, a pump, and a valve. The pump-tube liquid-flow circulating stirrer is arranged in the cathode compartment of the electrolytic cell 1. The pump-tube liquid-flow circulating stirrer is configured to thoroughly stir the cathode electrolyte such that hydrogen evolved can be promptly released to avoid accumulation.

The hydrogen eliminator 13 and the vacuum ejector 28 constitute a hydrogen eliminating system. The vacuum ejector 28 is configured to direct hydrogen released from the cathode compartment into the hydrogen eliminator for a reaction, thereby achieving a safe treatment for hydrogen.

A sensing signal input terminal of the automatic program controller 22 is connected to sensing signal output terminals of the sensors. A control signal output terminal of the automatic program controller is connected to control signal input terminals of the electrolytic power supply 4, the solid feeder 16, and the pumps. As a result, the apparatus of this example could operate automatically according to a set program.

The solid feeder 16 is loaded with fragmented metallic silver, and is configured to feed the fragmented metallic silver as a soluble anode into the titanium basket. A feeding amount of the solid feeder 16 is controlled by the weightometer suspending the titanium basket. When the weightometer reaches a preset maximum value, the solid feeder 16 is shut down. Additionally, based on a preset minimum value of the weightometer, the automatic program controller 22 controls the start of the feeding of the solid feeder 16.

The suction and discharge pipe 15 is configured to suck and discharge a solid-liquid mixture in the titanium basket to the press filter for solid-liquid separation according to process-set timing after the electrolysis is completed. This suction and discharge process is controlled by the sensor 21-2.

A method for preparing a silver compound from metallic silver is provided, including the following steps:

1. A power supply of the apparatus was turned on to make the automatic program controller 22 enter a working state.

2. The pumping of the anode electrolyte from the temporary storage tank 14-1 into the anode compartment of the electrolytic cell by the pump 33-1 was controlled by a liquid level meter in the anode compartment. The feeding of the cathode electrolyte into the cathode compartment was controlled by a liquid level meter in the cathode compartment. As a result, the titanium basket and the cathode were immersed in the respective electrolytes. The titanium basket was suspended by the weightometer. The titanium basket was electrically connected to the positive terminal of the electrolytic power supply 4, and the cathode was electrically connected to the negative terminal of the electrolytic power supply 4.

3. Fragmented metallic silver in the solid feeder 16 was fed into the titanium basket under the control of the weightometer. When the weightometer reached a process-preset weight value, the solid feeder was shut down.

4. The electrolytic power supply 4 was started to initiate electrolysis. The pump-tube liquid-flow circulating stirrer 8 was turned on. At the anode, oxygen was evolved, and the fragmented metallic silver was dissolved and reacted to produce a solid silver compound 25-1.

At the cathode, hydrogen was evolved.

5. During the electrolysis, oxygen evolved in the anode compartment was collected and discharged externally by the gas drainage collector 12-1. Hydrogen evolved in the cathode compartment was collected by the gas drainage collector 12-2 and directed by the vacuum ejector 28 into the hydrogen eliminator 13 for a reaction, thereby achieving a safe treatment of hydrogen.

6. The electrolysis was controlled by adjusting an electrolysis time with an electrolysis current constant. After the electrolysis was completed, the electrolytic power supply 4 and the pump-tube liquid-flow circulating stirrer 8 were turned off, and the pump 33-2 was turned on to pump a solid-liquid mixture from the titanium basket into the solid-liquid separator 10 for solid-liquid separation to produce a filter residue as a silver compound 25-2, which was silver oxide.

7. When the liquid level meter in the cathode compartment reached a set value, the pump 33-2 was turned off under the control of the automatic program controller 22, and the pump 33-1 was turned on once again to feed the anode electrolyte into the anode compartment once again. Once a specified liquid level was reached, the pump 33-1 was turned off, and the electrolytic power supply was restarted.

8. During the operation, when the weightometer reached the preset minimum value, the solid feeder 16 was restarted to feed fragmented metallic silver into the titanium basket once again. Once the preset maximum value condition was met, the automatic program controller 22 shut down the solid feeder 16, ensuring normal production.

With the apparatus shown in FIG. 7, the silver oxide product could be continuously produced according to the above steps.

Example 7

As shown in FIG. 8, FIG. 9 and FIG. 10, an apparatus for preparing a silver compound from metallic silver is provided in Example 7, including two electrolytic cells 1-1 and 1-2, three pump-tube liquid-flow circulating stirrers 8, four solid-liquid separators 10, seven temporary storage tanks 14, seven sensors 21, a water-washing tank 23, an overflow buffer tank 39, and a plurality of valves and pumps.

The two electrolytic cells 1-1 and 1-2 are each provided with an electrolytic cell separator to divide an electrolytic cell into an anode compartment and a cathode compartment. A top of each compartment is provided with a gas drainage collector. An electrolytic cell separator 5-1 is a reverse osmosis membrane, and an electrolytic cell separator 5-2 is a filter cloth. Two metallic silver anodes 2-1 and 2-2 are connected to positive terminals of electrolytic power supplies 4-1 and 4-2, respectively. Two metallic silver cathodes 3-1 and 3-2 are connected to negative terminals of the electrolytic power supplies 4-1 and 4-2, respectively. The two electrolytic cells have identical structures, and are merely provided with different electrolytic cell separators. The electrolytic cell 1-1 has a relatively-high working voltage and thus involves high power consumption, but can directly produce diaminesilver hydroxide.

For the electrolytic cell 1-1, an anode electrolyte is a mixed solution of a soluble silver-ammine complex and ammonia water with a total alkaline substance concentration of 8 mol/L, and a cathode electrolyte is a sodium hydroxide solution. For the electrolytic cell 1-2, an anode electrolyte and a cathode electrolyte are each a sodium hydroxide solution 24 with a total alkaline substance concentration of 10 mol/L.

A temporary storage tank 14-1 is configured to store ammonia water 18, and is connected to anode compartments of the electrolytic cells 1-1 and a temporary storage tank 14-3 successively. A temporary storage tank 14-2 is connected to the anode compartments of the electrolytic cells 1-1 and the temporary storage tank 14-3 successively, and is configured to store a product, namely, the solution of diaminesilver hydroxide 34. The temporary storage tank 14-3 is configured to prepare the solution of diaminesilver hydroxide, and is provided with sensors 21-4 and 21-5, which are a liquid level meter and a gravimeter, respectively.

Both an anode compartment and a cathode compartment of the electrolytic cell 1-1 are provided with pump-tube liquid-flow circulating stirrers. A pump-tube liquid-flow circulating stirrer including a pipeline and a pump 33-6 is provided in an anode compartment of the electrolytic cell 1-2. A liquid outlet pipe of the pump-tube liquid-flow circulating stirrer is a liquid jet pipe 38 with a liquid outlet facing toward the anode 2-2.

The anode compartment of the electrolytic cell 1-2 is connected to the solid-liquid separators 10-2 and 10-1 successively, and is circularly connected to a temporary storage tank 14-5 through these two solid-liquid separators. The temporary storage tank 14-5 is also connected to cathode compartments of the electrolytic cells 1-1 and 1-2.

The anode compartment of the electrolytic cell 1-1 is provided with sensors 21-1 and 21-2, which are a gravimeter and a pH meter, respectively. The cathode compartment of the electrolytic cell 1-1 is provided with a sensor 21-3, which is a liquid level meter. The anode compartment of the electrolytic cell 1-2 is provided with a sensor 21-6, which is a liquid level meter.

The water-washing tank 23 is configured to wash silver oxide 25-1, and is provided with a sensor 21-7, which is a liquid level meter. The water-washing tank 23 is connected to a solid-liquid separator 10-4, a solid-liquid separator 10-3, and a temporary storage tank 14-6 successively.

A method for preparing a silver compound from metallic silver is provided, including the following steps:

1. Ammonia water and diaminesilver hydroxide were fed into the anode compartment of the electrolytic cell 1-1, and a sodium hydroxide solution 24 was fed into the cathode compartment of the electrolytic cell 1-1. The sodium hydroxide solution 24 was fed into both the anode compartment and the cathode compartment of the electrolytic cell 1-2. As a result, each electrode was immersed in a respective solution in each compartment.

2. The electrolytic power supplies 4-1 and 4-2 were started to initiate electrolysis. At the anode of the electrolytic cell 1-1, oxygen was evolved, and metallic silver was dissolved and reacted to produce diaminesilver hydroxide. At the cathode of the electrolytic cell 1-1, hydrogen was evolved. At the anode of the electrolytic cell 1-2, oxygen was evolved, and the anode was dissolved and reacted to produce silver oxide. At the cathode of the electrolytic cell 1-2, hydrogen was evolved.

3. During electrolysis of the electrolytic cell 1-1, the sensor 21-1 as a gravimeter controlled the pump 33-1 to feed ammonia water from the temporary storage tank 14-1 into the anode compartment. The solution containing diaminesilver hydroxide overflowing from the anode compartment was pumped by the pump 33-3 through the overflow buffer tank 39 into the temporary storage tank 14-2 for temporary storage. The sensor 21-2 as a pH meter achieved the safety process monitoring. The sensor 21-3 as a liquid level meter controlled the supplementary feeding of the sodium hydroxide solution from the temporary storage tank 14-5 into the cathode compartment. The pump-tube liquid-flow circulating stirrers 8-1 and 8-2 were started to ensure uniform reactions in the anode and cathode electrolytes. With the continuous electrolytic dissolution of metallic silver, the solution of diaminesilver hydroxide was produced.

4. During electrolysis of the electrolytic cell 1-2, silver oxide was produced in the anode compartment. Moreover, the anode electrolyte was ejected onto the anode 2-2 through the liquid jet pipe 38 to detach silver oxide adhering to the anode 2-2. A solid-liquid mixture in the anode compartment was subjected to two-stage solid-liquid separation to produce silver oxide 25-1.

5. The silver oxide 25-1 was washed in the water-washing tank 23, and subjected to two-stage solid-liquid separation to produce purified silver oxide 25-2. Washing wastewater was discharged into the temporary storage tank 14-6 for temporary storage.

6. The silver oxide 25-2 was fed into the temporary storage tank 14-3 to react with ammonia water to produce the solution of diaminesilver hydroxide. The prepared solution of diaminesilver hydroxide was then pumped into the temporary storage tank 14-2 for temporary storage.

With the apparatus shown in FIG. 8, the method for preparing a silver compound from metallic silver was implemented through the above steps to produce the solution of diaminesilver hydroxide product.

Example 8

The apparatus shown in FIG. 3 is used to repeat the method in Example 2, except that:

The alkaline electrolyte 24 is primarily a sodium hydroxide solution with a total alkaline substance concentration of 21 mol/L.

The solid-liquid separator 10 is a common filter. The solid-liquid separator is configured to separate a silver powder 26 from the alkaline electrolyte.

A method for preparing a silver compound from metallic silver is provided, including the following steps:

1. The alkaline electrolyte 24 was fed into the electrolytic cell 1 until the anode 2 and the cathode 3 were immersed in the alkaline electrolyte.

2. The electrolytic power supply 4 was started to initiate electrolysis. At the anode, oxygen was evolved, and metallic silver was dissolved and reacted to produce a silver hydroxide complex ion. At the cathode, a large amount of hydrogen was evolved, and then a trace amount of metallic silver 26-2 was gradually electrodeposited.

3. The electrodeposition of silver at the cathode indicated the completion of the electrolysis. In this case, the pump 33 was turned on to enable solid-liquid separation for a solid-liquid mixture in the electrolytic cell 1 by the solid-liquid separator 10 to produce a filtrate and a filter residue. The filtrate was a silver ion-hydroxide ion complex solution. The filtrate was delivered to the temporary storage tank 14 for temporary storage. The filter residue in the solid-liquid separator 10 was then collected to produce a small amount of a silver powder 26-2.

Because the electrolyte was a strongly-alkaline concentrated solution, a soluble [Ag(OH)₂]— complex was generated in the electrolyte, resulting in the electrodeposition of metallic silver at the cathode. With the apparatus shown in FIG. 3, the method for preparing a silver compound from metallic silver was implemented through the above steps to produce the silver ion-hydroxide ion complex solution as a main product.