A combined purification method for removing impurities from silver nitrate

Abstract

The application discloses a combined purification method for removing impurities in silver nitrate, and comprises the following steps: S1, a silver dissolving process, wherein pure water and silver raw materials are added into a reaction kettle, heating is performed until the temperature reaches 50-70 DEG C, and nitric acid is slowly added, and after reaction, silver nitrate solution is obtained; S2, nanofiltration membrane separation, wherein the silver nitrate solution obtained in the step S1 is pumped into a nanofiltration system, sodium ions in the silver nitrate solution pass through a nanofiltration membrane of the nanofiltration system into a permeate along with part of water molecules, and silver nitrate is intercepted into a concentrated solution; S3, layer type integral crystallization, wherein the concentrated solution obtained in the step S2 is pumped into a layer type crystallization device, and the following operations are sequentially performed: cooling crystallization, draining, heating and residual liquid discharge, cleaning and dissolving material discharge, and high-purity silver nitrate crystals are obtained; and S4, drying and packaging, wherein the high-purity silver nitrate crystals obtained in the step S3 are subjected to centrifugal separation, washing and drying, and low-sodium high-purity silver nitrate products are obtained.

Description

Technical Field

[0001] This invention relates to the technical field of high-purity silver nitrate preparation methods, and particularly to a combined purification method for removing impurities from silver nitrate. Background Technology

[0002] Silver nitrate is an important product in the deep processing of silver and a key raw material for many electronic components, high-end silver halide materials, and photosensitive materials. With the increasing demands for material purity from industries such as electronics and precision chemicals, stricter requirements have been placed on the content of impurity elements in silver nitrate, especially sodium.

[0003] The presence of sodium impurities in silver nitrate products can severely affect their application performance. In the manufacture of electronic components, sodium ions can lead to increased leakage current and decreased reliability. In high-end silver salt materials, sodium impurities can affect the photosensitivity and stability of the silver salts. Therefore, effectively removing sodium impurities from silver nitrate has become a key technical challenge in the preparation of high-purity silver nitrate.

[0004] Currently, the main methods for preparing high-purity silver nitrate include chemical precipitation, crystallization, and electrolysis. Chemical precipitation removes impurities by adding a precipitant, but it easily introduces new impurities and has limited effectiveness in removing sodium ions because sodium ions are difficult to form insoluble precipitates. Crystallization utilizes differences in solubility for separation, but sodium ions and silver ions are prone to co-crystallization during the crystallization process, resulting in unsatisfactory separation. Electrolysis can be used for the purification of silver, but it has low efficiency in removing metallic impurities with low isoelectric potentials, such as sodium.

[0005] Patent CN102560536A discloses a method for purifying silver electrolyte. This method uses a nanofiltration membrane to treat the silver electrolyte, allowing silver nitrate and nitric acid to permeate through the membrane into the permeate, while bismuth, antimony, lead, copper, palladium, and other impurities are retained, thus separating silver from these elements. This method shows good removal efficiency for high-valence metal impurities, but it does not describe the selective separation effect on monovalent ions such as sodium.

[0006] Patent CN116216767A discloses a method for preparing silver nitrate, which involves adding nitric acid in a sealed oxygen-containing atmosphere to achieve complete utilization of the nitrogen element in the nitric acid, thus achieving green production. This method focuses on the environmental friendliness of the production process, but it does not address the control of sodium content in the product.

[0007] Sodium and silver ions are both monovalent cations with similar chemical properties and ionic radii (Na⁺: 1.02 Å, Ag⁺: 1.15 Å), making effective separation difficult with traditional chemical precipitation and ion exchange methods. Therefore, developing a purification process capable of efficiently and deeply removing sodium impurities from silver nitrate has become a pressing technical problem in this field. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention provides a combined purification method for removing impurities from silver nitrate.

[0009] To achieve the above objectives, the technical solution of the present invention is as follows: A combined purification method for removing impurities from silver nitrate includes the following steps: S1. Silver dissolving process: Add pure water and silver raw material to the reaction vessel. The mass ratio of silver raw material to pure water volume is 1:(0.5-1). Heat to 50-70℃ and slowly add nitric acid. The volume ratio of nitric acid to silver raw material mass is (0.8-1.2):1. After the reaction is completed, silver nitrate solution is obtained. S2. Nanofiltration membrane separation: The silver nitrate solution obtained in step S1 is pumped into the nanofiltration system. Taking advantage of the selective separation characteristics of the nanofiltration membrane for monovalent ions, the sodium ions in the silver nitrate solution pass through the nanofiltration membrane of the nanofiltration system along with some water molecules and enter the permeate, while the silver nitrate is retained and enters the concentrate. S3, Layered integral crystallization: The concentrated liquid obtained in step S2 is pumped into the layered crystallization device, and the cooling crystallization, draining, heating and residual liquid discharge, washing and dissolving material discharge operations are carried out in sequence. The temperature is controlled at 55-95℃ during the heating and residual liquid discharge stage to discharge the sodium-containing mother liquor trapped in the crystals and obtain high-purity silver nitrate crystals. S4. Drying and Packaging: The high-purity silver nitrate crystals obtained in step S3 are centrifuged, washed and dried to obtain a low-sodium, high-purity silver nitrate product.

[0010] In step S2, the nanofiltration membrane of the nanofiltration system is a polyamide composite membrane with a molecular weight cutoff of 200-300 Da, an operating pressure of 1.0-2.5 MPa, a silver nitrate rejection rate of ≥95%, and a sodium ion rejection rate of ≤20%.

[0011] In step S2, the addition of a nanofiltration pretreatment agent, wherein the pretreatment agent is an aluminum salt, and the amount added is 0.01%-0.05% of the mass of silver nitrate.

[0012] The aluminum salt is aluminum nitrate, which is added to adjust the pH of the solution to 5.0-6.0.

[0013] In step S3, the cooling rate of layer crystallization is 0.5-5℃ / min, and the final crystallization temperature is 10-25℃.

[0014] In step S3, the heating rate for raising the temperature and draining the residual liquid is 1-10℃ / min, and the final temperature is 70-90℃.

[0015] In step S3, the cleaning process uses high-purity water or a high-purity silver nitrate saturated solution with a sodium content of less than 0.1 ppm.

[0016] The nanofiltration membrane separation in step S2 and the layered integral crystallization in step S3 can be carried out in two or more stages in series.

[0017] The beneficial effects of this invention are: 1. This invention uses a precipitating agent to precipitate impurities, followed by solid-liquid separation to remove them. A three-stage precision filtration system then chemically reacts with and physically separates the impurity metals and other impurities, ensuring a low impurity content in the resulting silver nitrate solution. Simultaneously, standardized filtration parameters effectively remove impurities while preventing the introduction of other ions, thus guaranteeing the purity of the silver nitrate. This not only improves production efficiency and reduces the risk of secondary pollution but also enhances product quality, shortens the production cycle, allows for large batch processing volumes, achieves high product yields, and reduces labor and manpower requirements.

[0018] 2. This invention achieves deep removal of sodium ions through a combination of nanofiltration membrane separation and layered integral crystallization. The nanofiltration membrane utilizes pore size sieving and the Donnan effect to achieve selective separation of silver and sodium ions. Silver ions, due to their larger hydration radius, are retained by the nanofiltration membrane, while sodium ions, with their smaller hydration radius, can permeate through the membrane with the solvent, thus achieving initial separation.

[0019] 3. In this invention, aluminum salt is added as a pretreatment agent before nanofiltration. Aluminum ions hydrolyze to generate hydroxyl complexes, which can adsorb sodium ions or change the form of sodium ions, thereby enhancing the removal effect of sodium ions by the nanofiltration membrane.

[0020] 4. This invention employs layered integral crystallization technology. By heating and draining residual liquid, the solubility of silver nitrate increases dramatically with temperature (its solubility at 100°C is about 7 times that at 0°C). This allows the sodium-containing mother liquor trapped inside and between crystals to dissolve and drain through the gaps after covering a small amount of crystals under heating conditions. This process is similar to the "sweating" process of melting and crystallization, effectively removing sodium impurities trapped inside the crystals.

[0021] 5. The sodium content in the silver nitrate product produced by this invention can be reduced to below 1 ppm, and the purity reaches above 99.995%, which meets the strict requirements for sodium content in high-end electronic materials and silver salt materials.

[0022] 6. The process of this invention is simple to operate, low in cost, and highly efficient, making it suitable for large-scale industrial production. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concepts of the invention.

[0024] Example 1 A combined purification process for removing impurities from silver nitrate includes the following steps: (1) Silver dissolving process: Add 100kg silver ingot (silver content 99.95%) and 80L pure water to the reaction vessel, heat to 60℃, slowly add 100L nitric acid (concentration 65%), control the reaction rate, and obtain silver nitrate solution; (2) Nanofiltration membrane separation: The silver nitrate solution is pumped into the nanofiltration system. The nanofiltration membrane is a polyamide composite membrane with a molecular weight cutoff of 200 Da and an operating pressure of 2.0 MPa. The silver nitrate rejection rate is 96% and the sodium ion permeability rate is 85%. (3) Layer-by-layer integral crystallization: The nanofiltration concentrate is pumped into the layer-by-layer crystallization device and crystallized to 15°C at a cooling rate of 2°C / min. After standing and draining for 2 hours, the residual liquid is discharged at a heating rate of 3°C / min and the crystals are washed with high-purity water with a sodium content of less than 0.1ppm. (4) Drying and packaging: The crystallized silver nitrate crystals are centrifuged, washed and dried at 80°C to obtain a low-sodium, high-purity silver nitrate product.

[0025] Example 2 A combined purification process for removing impurities from silver nitrate includes the following steps: (1) Silver dissolution process: Add 200kg of electrolytic silver powder (silver content 99.90%) and 160L of pure water to the reaction vessel, heat to 55℃, slowly add 180L of nitric acid (concentration 68%), control the reaction rate, and obtain silver nitrate solution; (2) Nanofiltration pretreatment: Add aluminum nitrate to the silver nitrate solution at a concentration of 0.03% of the mass of silver nitrate, and adjust the pH of the solution to 5.5; (3) Nanofiltration membrane separation: The treated silver nitrate solution is pumped into the nanofiltration system. The nanofiltration membrane is a polyamide composite membrane with a molecular weight cutoff of 250 Da and an operating pressure of 1.8 MPa. Two-stage nanofiltration is used in series. (4) Layer-by-layer integral crystallization: The nanofiltration concentrate is pumped into the layer-by-layer crystallization device and crystallized to 20°C at a cooling rate of 1°C / min. After standing and draining for 1.5 hours, the residual liquid is discharged at a heating rate of 5°C / min and the crystals are washed with a high-purity silver nitrate saturated solution. (5) Drying and packaging: The crystallized silver nitrate crystals are centrifuged, washed and dried at 90°C to obtain a low-sodium, high-purity silver nitrate product.

[0026] Example 3 A combined purification process for removing impurities from silver nitrate includes the following steps: (1) Silver dissolving process: Add 500kg silver ingot (silver content 99.97%) and 300L pure water to the reaction vessel, heat to 65℃, slowly add 550L nitric acid (concentration 70%), control the reaction rate, and obtain silver nitrate solution; (2) Nanofiltration pretreatment: Add aluminum nitrate to the silver nitrate solution at a concentration of 0.05% of the mass of silver nitrate, and adjust the pH of the solution to 5.8; (3) Nanofiltration membrane separation: The treated silver nitrate solution is pumped into the nanofiltration system. The nanofiltration membrane is a polyamide composite membrane with a molecular weight cutoff of 300 Da and an operating pressure of 2.2 MPa. A three-stage nanofiltration system is used in series. (4) Layer-by-layer integral crystallization: The nanofiltration concentrate is pumped into the layer-by-layer crystallization device and crystallized to 10°C at a cooling rate of 3°C / min. After standing and draining for 2.5 hours, the residual liquid is discharged at a heating rate of 2°C / min and the crystals are washed with high-purity water with a sodium content of less than 0.1ppm. (5) Drying and packaging: The crystallized silver nitrate crystals are centrifuged, washed and dried at 85°C to obtain a low-sodium, high-purity silver nitrate product.

[0027] The low-sodium, high-purity silver nitrate prepared through the above embodiments has a sodium content of less than 1 ppm, and other impurity indicators meet or exceed the standards for superior-grade silver nitrate, fully satisfying the stringent requirements for sodium content in high-end electronic materials and silver salt materials.

[0028] Example 4 A combined purification method for removing impurities from silver nitrate includes the following steps: S1. Silver dissolving process: Add pure water and silver raw material to the reaction vessel. The mass ratio of silver raw material to pure water volume is 1:0.5. Heat to 50°C and slowly add nitric acid. The volume ratio of nitric acid to silver raw material mass is 0.8:1. After the reaction is completed, silver nitrate solution is obtained. S2. Nanofiltration membrane separation: The silver nitrate solution obtained in step S1 is pumped into the nanofiltration system. Taking advantage of the selective separation characteristics of the nanofiltration membrane for monovalent ions, the sodium ions in the silver nitrate solution pass through the nanofiltration membrane of the nanofiltration system along with some water molecules and enter the permeate, while the silver nitrate is retained and enters the concentrate. S3, Layered integral crystallization: The concentrated liquid obtained in step S2 is pumped into the layered crystallization device, and the cooling crystallization, draining, heating and residual liquid discharge, washing and dissolving material discharge operations are carried out in sequence. The temperature is controlled at 55°C during the heating and residual liquid discharge stage to discharge the sodium-containing mother liquor trapped in the crystals and obtain high-purity silver nitrate crystals. S4. Drying and Packaging: The high-purity silver nitrate crystals obtained in step S3 are centrifuged, washed and dried to obtain a low-sodium, high-purity silver nitrate product.

[0029] In step S2, the nanofiltration membrane of the nanofiltration system is a polyamide composite membrane with a molecular weight cutoff of 200 Da, an operating pressure of 1.0 MPa, a silver nitrate rejection rate of ≥95%, and a sodium ion rejection rate of ≤20%.

[0030] In step S2, the addition of a nanofiltration pretreatment agent, wherein the pretreatment agent is an aluminum salt, and the amount added is 0.01% of the mass of silver nitrate.

[0031] The aluminum salt is aluminum nitrate, which is added to adjust the pH of the solution to 5.0.

[0032] In step S3, the cooling rate of layer crystallization is 0.5℃ / min, and the final crystallization temperature is 10℃.

[0033] In step S3, the heating rate for heating and draining residual liquid is 1℃ / min, and the final temperature is 70℃.

[0034] In step S3, the cleaning process uses high-purity water or a high-purity silver nitrate saturated solution with a sodium content of less than 0.1 ppm.

[0035] In this process, nanofiltration membrane separation in step S2 and layered monolithic crystallization in step S3 can be performed in a two-stage series operation.

[0036] Example 5 A combined purification method for removing impurities from silver nitrate includes the following steps: S1. Silver dissolving process: Add pure water and silver raw material to the reaction vessel. The mass ratio of silver raw material to pure water volume is 1:1. Heat to 70°C and slowly add nitric acid. The volume ratio of nitric acid to silver raw material mass is 1.2:1. After the reaction is completed, silver nitrate solution is obtained. S2. Nanofiltration membrane separation: The silver nitrate solution obtained in step S1 is pumped into the nanofiltration system. Taking advantage of the selective separation characteristics of the nanofiltration membrane for monovalent ions, the sodium ions in the silver nitrate solution pass through the nanofiltration membrane of the nanofiltration system along with some water molecules and enter the permeate, while the silver nitrate is retained and enters the concentrate. S3, Layered integral crystallization: The concentrated liquid obtained in step S2 is pumped into the layered crystallization device, and the cooling crystallization, draining, heating and residual liquid discharge, washing and dissolving material discharge are carried out in sequence. The temperature is controlled at 95°C during the heating and residual liquid discharge stage to discharge the sodium-containing mother liquor trapped in the crystals and obtain high-purity silver nitrate crystals. S4. Drying and Packaging: The high-purity silver nitrate crystals obtained in step S3 are centrifuged, washed and dried to obtain a low-sodium, high-purity silver nitrate product.

[0037] In step S2, the nanofiltration membrane of the nanofiltration system is a polyamide composite membrane with a molecular weight cutoff of 300 Da, an operating pressure of 2.5 MPa, a silver nitrate rejection rate of ≥95%, and a sodium ion rejection rate of ≤20%.

[0038] In step S2, the addition of a nanofiltration pretreatment agent, wherein the pretreatment agent is an aluminum salt and the amount added is 0.05% of the mass of silver nitrate.

[0039] The aluminum salt is aluminum nitrate, which is added to adjust the pH of the solution to 6.0.

[0040] In step S3, the cooling rate of layer crystallization is 5℃ / min, and the final crystallization temperature is 25℃.

[0041] In step S3, the heating rate for raising the temperature and draining the residual liquid is 10℃ / min, and the final temperature is 90℃.

[0042] In step S3, the cleaning process uses high-purity water or a high-purity silver nitrate saturated solution with a sodium content of less than 0.1 ppm.

[0043] In this process, nanofiltration membrane separation in step S2 and layered monolithic crystallization in step S3 can be performed in a multi-stage series operation.

[0044] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of the invention and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the invention should be included within the protection scope of the invention. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. A combined purification method for removing impurities from silver nitrate, characterized in that, Includes the following steps: S1. Silver dissolving process: Add pure water and silver raw material to the reaction vessel. The mass ratio of silver raw material to pure water volume is 1:(0.5-1). Heat to 50-70℃ and slowly add nitric acid. The volume ratio of nitric acid to silver raw material mass is (0.8-1.2):

1. After the reaction is completed, silver nitrate solution is obtained. S2. Nanofiltration membrane separation: The silver nitrate solution obtained in step S1 is pumped into the nanofiltration system. Taking advantage of the selective separation characteristics of the nanofiltration membrane for monovalent ions, the sodium ions in the silver nitrate solution pass through the nanofiltration membrane of the nanofiltration system along with some water molecules and enter the permeate, while the silver nitrate is retained and enters the concentrate. S3, Layered integral crystallization: The concentrated liquid obtained in step S2 is pumped into the layered crystallization device, and the cooling crystallization, draining, heating and residual liquid discharge, washing and dissolving material discharge operations are carried out in sequence. The temperature is controlled at 55-95℃ during the heating and residual liquid discharge stage to discharge the sodium-containing mother liquor trapped in the crystals and obtain high-purity silver nitrate crystals. S4. Drying and Packaging: The high-purity silver nitrate crystals obtained in step S3 are centrifuged, washed and dried to obtain a low-sodium, high-purity silver nitrate product.

2. The combined purification method for removing impurities from silver nitrate according to claim 1, characterized in that, In step S2, the nanofiltration membrane of the nanofiltration system is a polyamide composite membrane with a molecular weight cutoff of 200-300 Da, an operating pressure of 1.0-2.5 MPa, a silver nitrate rejection rate of ≥95%, and a sodium ion rejection rate of ≤20%.

3. The combined purification method for removing impurities from silver nitrate according to claim 1, characterized in that, Step S2 further includes adding a nanofiltration pretreatment agent, which is an aluminum salt, and the amount added is 0.01%-0.05% of the mass of silver nitrate.

4. The combined purification method for removing impurities from silver nitrate according to claim 3, characterized in that, The aluminum salt is aluminum nitrate, which is added to adjust the pH of the solution to 5.0-6.

0.

5. The combined purification method for removing impurities from silver nitrate according to claim 1, characterized in that, In step S3, the cooling rate of layer crystallization is 0.5-5℃ / min, and the final crystallization temperature is 10-25℃.

6. The combined purification method for removing impurities from silver nitrate according to claim 1, characterized in that, In step S3, the heating rate for raising the temperature and draining the residual liquid is 1-10℃ / min, and the final temperature is 70-90℃.

7. The combined purification method for removing impurities from silver nitrate according to claim 1, characterized in that, In step S3, the cleaning process uses high-purity water or a high-purity silver nitrate saturated solution with a sodium content of less than 0.1 ppm.

8. The combined purification method for removing impurities from silver nitrate according to claim 1, characterized in that, The nanofiltration membrane separation in step S2 and the layered monolithic crystallization in step S3 can be carried out in two or more stages in series.