Method for preparing high-purity silver nitrate from silver-containing waste

Abstract

The invention relates to the technical field of industrial waste treatment and silver nitrate preparation, in particular to a method for preparing high-purity silver nitrate from silver-containing waste. The method comprises the following steps: reducing the silver-containing waste by adopting a liquid phase reduction method, pickling to remove impurities, putting the silver-containing waste into a medium-frequency induction furnace, performing high-temperature smelting and ingot casting, performing electrolytic purification to obtain crude silver powder, and performing smelting and ingot casting on the crude silver powder to obtain a raw material national standard No.1 silver ingot for preparing silver nitrate; the method comprises the following steps: putting a national standard No.1 silver ingot and a nitric acid solution into a reaction kettle according to a certain proportion for dissolving silver, carrying out adsorption and impurity removal on a dissolved solution through ion exchange resin, carrying out adsorption and impurity removal on a primary filtrate through chelating type adsorption resin, and carrying out centrifugation, evaporative crystallization, drying and other processes on a secondary filtrate to obtain the high-purity silver nitrate. The method is easy to implement, the recovery rate of the silver-containing waste materials is high, the high-purity silver nitrate product can reach the premium-grade pure standard, and the technological process is environmentally friendly.

Description

Technical Field

[0001] The invention relates to the technical field of industrial waste treatment and silver nitrate preparation, and in particular to a method for preparing high-purity silver nitrate by utilizing silver-containing waste. Background Art

[0002] Silver-containing waste is waste generated during the production of silver products. The waste contains a certain amount of precious metal silver and has a high recycling value. At present, the main methods for recycling and purifying silver-containing waste are wet reduction and pyrometallurgical reduction. For example, Chinese patent CN109536726A proposes a method for recycling silver-containing waste catalysts. First, silver is leached with dilute nitric acid, then silver is precipitated with sodium chloride, and finally hydrogen is used to reduce it to obtain silver powder. Silver can be efficiently recovered, but the use of dilute nitric acid to selectively leach silver can only be used when other impurities in the material to be treated are insoluble in dilute nitric acid. Otherwise, the grade of the recovered silver will be reduced. In addition, the process of reducing silver chloride with hydrogen is unsafe and prone to explosion, which is not suitable for industrial use. It is widely used in the industry; Chinese patent CN118497511A proposes a method for recovering metallic silver from waste photovoltaic cells by a fire-wet method. First, concentrated nitric acid is used for acid leaching to obtain silver nitrate, and then sodium chloride is added to precipitate the silver. The precipitate is then mixed with sodium carbonate powder for reduction smelting to obtain metallic silver. The invention adopts a fire-wet combined process to reduce the discharge of waste liquid. The reduction residue generated during the recovery process is converted into sodium chloride, and the discharged carbon dioxide is converted into sodium carbonate. The two are returned to the invention process for recycling, but the purity of the silver recovered in the invention is less than 99.5%.

[0003] When the silver content in the silver-containing waste does not exceed 65%, there are many other impurities and the content is high. It is difficult to achieve photographic grade purity of silver nitrate prepared by the above method, and the yield is low. The grade of the obtained silver nitrate product is not high enough, and a new impurity removal and purification process needs to be developed to improve the quality of silver nitrate. Therefore, it is very necessary to find an environmentally friendly, high-purity method for preparing silver nitrate using silver-containing materials. Summary of the invention

[0004] The present invention provides a new method for preparing high-purity silver nitrate from silver-containing waste materials, so as to solve the problems of large environmental pollution, poor safety, low recovery efficiency, low purity and high cost when silver is recovered from silver-containing waste materials with a silver content of no more than 65% by traditional processes. The specific technical scheme of the present invention is as follows:

[0005] A method for preparing high-purity silver nitrate using silver-containing waste comprises the following steps:

[0006] Step 1: crush and screen the silver-containing waste material with a silver content of no more than 65%, adjust the pH value thereof to 13-14 with a 20% mass concentration sodium hydroxide solution, add a reducing agent solution, heat and stir to reduce, and then filter to obtain a coarse silver powder;

[0007] Step 2: Add a dilute hydrochloric acid solution with a concentration of 2-5 mol / L to the crude silver powder obtained in step 1 for pickling, filter the silver powder after pickling, wash it with pure water and filter it to obtain a filtrate and a filter cake, wherein the conductivity of the filtrate is less than 20 μs / cm, and dry the filter cake;

[0008] Step 3: Smelt a mixture of a certain proportion of the filter cake obtained in step 2, sodium carbonate and borax, and then cast an ingot to obtain a silver ingot;

[0009] Step 4: The silver ingot obtained in step 3 is used as an anode plate, and the electrolyte is a silver nitrate solution, and high-purity silver powder is obtained on the cathode plate. The high-purity silver powder is washed with deionized water for several times until the conductivity of the washed water is less than 5μs / cm, and the high-purity silver powder is dried;

[0010] Step 5: The high-purity silver powder obtained in step 4 is mixed with sodium carbonate and borax for smelting, and then cast into an ingot to obtain a national standard No. 1 silver ingot;

[0011] Step 6: adding the national standard No. 1 silver ingot obtained in step 5 and a nitric acid solution in a mass ratio of 1:1.0-1.6 into a reaction kettle to dissolve silver to obtain a silver nitrate solution, wherein the mass concentration of nitric acid in the nitric acid solution is 60-75%;

[0012] Step 7: The silver nitrate solution obtained in step 6 is subjected to ion exchange resin adsorption and impurity removal, and then filtered through a precision filter with an accuracy of 2 nm to obtain a primary filtrate, and the primary filtrate is subjected to secondary adsorption and impurity removal by a chelating adsorption resin, and then centrifuged and dried to obtain high-purity silver nitrate, wherein the silver nitrate yield is more than 85% and the purity is more than 99.8%.

[0013] Furthermore, the silver-containing waste in step 1 is waste generated in the process of producing silver-containing products, and its main components range from: Ag: 50%-65%, Si: 20-30%, S: 2-4%, Cl: 0.3-0.5%, As: 0.03-0.08%, Pb: 0.01-0.06%, Ni: 0.002-0.004%.

[0014] Furthermore, in step 1, the heating temperature is 80-90° C., the stirring speed is 300 rpm, the reaction time is 0.5-1 hour, and the mass concentration of the reducing agent solution is 40-50%.

[0015] Furthermore, the reducing agent in step 1 may be hydrazine hydrate, formaldehyde, or glucose.

[0016] Furthermore, in step 2, the temperature during the pickling process is 55-60° C., and the pickling time is 1 hour.

[0017] Furthermore, step 3 is smelted in a medium frequency induction furnace, the mass ratio of borax to sodium carbonate is 1-1.5:1, the mass ratio of the borax and sodium carbonate mixture to the filter cake is 1:110-160, the smelting temperature is 1000-1100 degrees Celsius, and the smelting time is 1-2h.

[0018] Furthermore, the concentration of the silver nitrate solution in step 4 is controlled at 150-200 g / L, and the pH value is 1-1.5.

[0019] Furthermore, step 5 is smelted in a medium frequency induction furnace, the mass ratio of borax to sodium carbonate is 1-1.5:1, the mass ratio of the borax and sodium carbonate mixture to the filter cake is 1:100-150, the smelting temperature is 1000-1100 degrees Celsius, and the smelting time is 1-2h.

[0020] Furthermore, in step 6, the reaction temperature of dissolving silver is 60-80° C., and the reaction time is 1-2 h.

[0021] Furthermore, in step 7, the ion exchange resin is a gel-type cation exchange resin, the mass ratio of the ion exchange resin to the silver nitrate solution is 1:0.5-1.5, the stirring time is 2-3h, the chelating adsorption resin is a side chain chelating resin, the functional groups contained in the side chain chelating resin are at least one of oximes, hydroxyquinolines or pyridines, and the mass ratio of the chelating adsorption resin to the primary filtrate is 1:0.2-0.6.

[0022] The invention first reduces the silver compound to elemental silver through a wet reduction process, and then performs pickling. The pickling process can remove other base metal impurities that can be dissolved in dilute hydrochloric acid, and the metal ions are removed with the filtrate. Then, pyrometallurgy is performed. The main purpose of adding borax and sodium carbonate is to form slag. The slag floating on the surface of the molten silver liquid can be removed by slagging to remove refractory impurities, and obtain a high-purity national standard No. 1 silver ingot. Then, the silver ingot is acid-dissolved to prepare silver nitrate. Ion exchange resin and chelating resin are used to remove impurities such as Cu, Fe, Pb, sulfate and silicate in the silver nitrate mother liquor. After the national standard No. 1 ingot is prepared by wet reduction, pyrometallurgy combined with electrolytic purification, the present invention uses an adsorption resin to adsorb and remove impurities from the dissolved silver liquid, which can greatly improve the grade of silver nitrate. The final silver nitrate yield is more than 85%, and the purity is more than 99.8%. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The embodiments of the present invention are further described below with reference to the accompanying drawings, in which:

[0024] Figure 1 The process flow chart of the present invention is shown. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below through specific embodiments in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0026] Implementation 1

[0027] (1) Liquid phase reduction: 12.2 kg of silver-containing waste (silver content: 60.1%) was taken, crushed and sieved, and then 2 L of water was added to wet the waste. The pH value was adjusted to 13-14 with a 20% sodium hydroxide solution, and a 45% hydrazine hydrate solution was added thereto. The reduction temperature was 90° C. and the mixture was stirred at a speed of 300 rpm. The reduction reaction was carried out for 1 hour. The end point of the reaction was determined when no more bubbles were generated. The reaction solution was filtered to separate the solid and liquid to obtain a coarse silver powder.

[0028] (2) acid washing and impurity removal: adding 200 mL of 10% (2.8 mol / L) dilute hydrochloric acid solution to the crude silver powder of step 1 for acid washing, the reaction temperature is 60° C., the reaction time is 1 hour, the acid washed silver powder is filtered, and then washed with pure water and filtered to obtain a filtrate and a filter cake, the conductivity of the filtrate is less than 20 μs / cm, and the filter cake is dried;

[0029] (3) Melting ingot: add all 7.0 kg of the filter cake obtained in step 2 into a medium frequency induction furnace for smelting, add 20 g of sodium carbonate and 30 g of borax, and melt at 1100° C. for 1 hour, and separate the smelting slag to obtain a silver ingot;

[0030] (4) Electrolytic purification: The silver ingot obtained in step 3 is used as the anode plate, the electrolyte concentration is 200 g / L silver nitrate solution, and the pH value is 1. High-purity silver powder is obtained on the cathode plate. The high-purity silver powder is washed several times with deionized water until the conductivity of the washed water is less than 5 μs / cm, and the high-purity silver powder is dried.

[0031] (5) Melting and re-ingot casting: 6.8 kg of high-purity electrolytic silver powder obtained in step 4 was added to a medium-frequency induction furnace for smelting, and 60 g of a 1:1 mixture of sodium carbonate and borax was added again. The mixture was smelted at a temperature of 1000-1100° C. for 1-2 h and then ingot casting was performed to obtain 6.78 kg of national standard No. 1 silver ingot, and the silver recovery rate was 92.5%;

[0032] (6) putting the national standard No. 1 silver ingot obtained in step 5 and 60% nitric acid solution into a reaction kettle at a mass ratio of 1:1.6 to dissolve the silver at a temperature of 60-80° C. for a reaction time of 1-2 h to obtain a silver nitrate solution;

[0033] (7) The silver nitrate solution obtained in step 6 is subjected to ion exchange resin adsorption and impurity removal, and then filtered through a precision filter (precision of 2 nm) to obtain a primary filtrate, the mass ratio of the ion exchange resin to the silver nitrate solution is 1:0.5-1.5, and the stirring time is 2-3 hours; the primary filtrate is subjected to secondary adsorption and impurity removal by a chelating adsorption resin, the chelating adsorption resin is a side chain chelating resin, the functional group contained in the side chain chelating resin is oxime, the mass ratio of the chelating adsorption resin to the primary filtrate is 1:0.2-0.6, and then centrifuged in a centrifuge, evaporated and crystallized, dried and packaged to obtain 10.56 kg of high-purity silver nitrate product, the silver nitrate yield is 91.7%, and the silver nitrate purity can reach 99.84%. The test results are shown in Table 1.

[0034] Table 1

[0035] name Test results <![CDATA[AgNO3 / %]]> 99.84 Appearance qualified pH value (50g / L, 25℃) 5.45 Clarity test, ＜2 Chloride (Cl) (w%) ＜0.0005 <![CDATA[Sulfate (SO4) (w%)]]> ＜0.002 Fe / % ＜0.00003 Cu / % ＜0.00001 Pb / % ＜0.00004 Hydrochloric acid no precipitation (w%) ＜0.005

[0036] Implementation 2

[0037] (1) Liquid phase reduction: 23 kg of silver-containing waste (silver content of 57.8%) was taken, crushed and sieved, and then 2 L of water was added to wet the waste. The pH value was adjusted to 13-14 with a 20% mass concentration of sodium hydroxide solution, and a 45% concentration of hydrazine hydrate solution was added thereto. The reduction temperature was 90° C. and the mixture was stirred at a speed of 300 rpm. The reduction reaction was carried out for 1 hour. The end point of the reaction was determined when no more bubbles were generated. The reaction solution was filtered to separate the solid and liquid to obtain a coarse silver powder;

[0038] (2) acid washing and impurity removal: adding 200 mL of 10% (2.8 mol / L) dilute hydrochloric acid solution to the crude silver powder of step 1 for acid washing, the reaction temperature is 60° C., the reaction time is 1 hour, the acid washed silver powder is filtered, and then washed with pure water and filtered to obtain a filtrate and a filter cake, the conductivity of the filtrate is less than 20 μs / cm, and the filter cake is dried;

[0039] (3) Melting ingot: add all 13.1 kg of filter cake obtained in step 2 into a medium frequency induction furnace for smelting, add 40 g of sodium carbonate and 60 g of borax, and heat at 1100° C. for 1 hour, and separate the smelting slag to obtain a silver ingot;

[0040] (4) Electrolytic purification: The silver ingot obtained in step 3 is used as the anode plate, the electrolyte concentration is 200 g / L silver nitrate solution, and the pH value is 1. High-purity silver powder is obtained on the cathode plate. The high-purity silver powder is washed several times with deionized water until the conductivity of the washed water is less than 5 μs / cm, and the high-purity silver powder is dried.

[0041] (5) Melting and re-ingot casting: 12.9 kg of high-purity electrolytic silver powder obtained in step 4 was added to a medium-frequency induction furnace for smelting, and a certain amount of a mixture of sodium carbonate and borax (120 g) was added again. The mixture was smelted at a temperature of 1000-1100° C. for 1-2 h and then ingot casting was performed to obtain 12.8 kg of national standard No. 1 silver ingot, and the silver recovery rate was 96.3%;

[0042] (6) putting the national standard No. 1 silver ingot obtained in step 5 and 70% nitric acid solution into a reaction kettle at a mass ratio of 1:1.2 to dissolve the silver at a temperature of 60-80° C. for a reaction time of 1-2 h to obtain a silver nitrate solution;

[0043] (7) The silver nitrate solution obtained in step 6 is subjected to ion exchange resin adsorption and impurity removal, and then filtered through a precision filter (precision of 2 nm) to obtain a primary filtrate, the mass ratio of the ion exchange resin to the silver nitrate solution is 1:0.5-1.5, and the stirring time is 2-3 hours; the primary filtrate is subjected to secondary adsorption and impurity removal by a chelating adsorption resin, the chelating adsorption resin is a side chain chelating resin, the functional group contained in the side chain chelating resin is oxime, the mass ratio of the chelating adsorption resin to the primary filtrate is 1:0.2-0.6, and then centrifugal separation is performed in a centrifuge, evaporation and crystallization are performed, and after drying and packaging, 19.85 kg of high-purity silver nitrate product is obtained, the silver nitrate yield is 94.7%, and the silver nitrate purity can reach 99.85%. The test results are shown in Table 2.

[0044] Table 2

[0045]

[0046]

[0047] Some exemplary embodiments of the present invention are described above. It can be understood that the above embodiments are only used to explain the present invention and do not constitute a limitation on the protection scope of the present invention. The features in these embodiments can be recombined in a suitable manner, and the scheme obtained thereby is still within the protection scope required by the present invention. Based on the above embodiments, all other embodiments obtained by those skilled in the art without making creative work, that is, all modifications, equivalent substitutions and improvements made within the spirit and principles of this application, fall within the protection scope required by the present invention.

Claims

1. A method for preparing high-purity silver nitrate using silver-containing waste, characterized in that: The following steps are involved: Step 1: crush and screen the silver-containing waste material with a silver content of no more than 65%, adjust the pH value thereof to 13-14 with a 20% mass concentration sodium hydroxide solution, add a reducing agent solution, heat and stir to reduce, and then filter to obtain a coarse silver powder; Step 2: Add a dilute hydrochloric acid solution with a concentration of 2-5 mol / L to the crude silver powder obtained in step 1 for pickling, filter the silver powder after pickling, wash it with pure water and filter it to obtain a filtrate and a filter cake, wherein the conductivity of the filtrate is less than 20 μs / cm, and dry the filter cake; Step 3: Smelting the filter cake obtained in step 2 with a mixture of sodium carbonate and borax in a certain proportion, and then casting the mixture to obtain a silver ingot; Step 4: The silver ingot obtained in step 3 is used as an anode plate, and the electrolyte is a silver nitrate solution, and high-purity silver powder is obtained on the cathode plate. The high-purity silver powder is washed with deionized water for several times until the conductivity of the washed water is less than 5μs / cm, and the high-purity silver powder is dried; Step 5: The high-purity silver powder obtained in step 4 is mixed with sodium carbonate and borax for smelting, and then cast into an ingot to obtain a national standard No. 1 silver ingot; Step 6: adding the national standard No. 1 silver ingot obtained in step 5 and a nitric acid solution in a mass ratio of 1:1.0-1.6 into a reaction kettle to dissolve silver to obtain a silver nitrate solution, wherein the mass concentration of nitric acid in the nitric acid solution is 60-75%; Step 7: The silver nitrate solution obtained in step 6 is subjected to ion exchange resin adsorption and impurity removal, and then filtered through a precision filter with an accuracy of 2 nm to obtain a primary filtrate. The primary filtrate is subjected to secondary adsorption and impurity removal by a chelating adsorption resin, and then centrifuged and evaporated, crystallized and dried to obtain high-purity silver nitrate with a purity of more than 99.8%.

2. A method for preparing high-purity silver nitrate using silver-containing waste according to claim 1, characterized in that: The silver-containing waste in step 1 is the waste generated in the process of producing silver-containing products, and its main components range from: Ag: 50%-65%, Si: 20-30%, S: 2-4%, Cl: 0.3-0.5%, As: 0.03-0.08%, Pb: 0.01-0.06%, Ni: 0.002-0.004%.

3. A method for preparing high-purity silver nitrate using silver-containing waste according to claim 1, characterized in that: In step 1, the heating temperature is 80-90° C., the stirring speed is 300 rpm, the reaction time is 0.5-1 hour, and the mass concentration of the reducing agent solution is 40-50%.

4. A method for preparing high-purity silver nitrate using silver-containing waste according to claim 1 or 3, characterized in that: The reducing agent in step 1 is hydrazine hydrate, formaldehyde, and glucose.

5. A method for preparing high-purity silver nitrate using silver-containing waste according to claim 1, characterized in that: The temperature during the pickling process in step 2 is 55-60° C. and the pickling time is 1 hour.

6. A method for preparing high-purity silver nitrate using silver-containing waste according to claim 1, characterized in that: Step 3 is to carry out smelting in a medium frequency induction furnace, the mass ratio of borax to sodium carbonate is 1-1.5:1, the mass ratio of the borax and sodium carbonate mixture to the filter cake is 1:110-160, the smelting temperature is 1000-1100 degrees Celsius, and the smelting time is 1-2h.

7. A method for preparing high-purity silver nitrate using silver-containing waste according to claim 1, characterized in that: The concentration of the silver nitrate solution in step 4 is controlled at 150-200 g / L, and the pH value is 1-1.

5.

8. A method for preparing high-purity silver nitrate using silver-containing waste according to claim 1, characterized in that: Step 5 is to carry out smelting in a medium frequency induction furnace, the mass ratio of borax to sodium carbonate is 1-1.5:1, the mass ratio of the borax and sodium carbonate mixture to the filter cake is 1:100-150, the smelting temperature is 1000-1100 degrees Celsius, and the smelting time is 1-2h.

9. A method for preparing high-purity silver nitrate using silver-containing waste according to claim 1, characterized in that: The reaction temperature of step 6 for dissolving silver is 60-80°C, and the reaction time is 1-2h.

10. A method for preparing high-purity silver nitrate using silver-containing waste according to claim 1, characterized in that: In step 7, the ion exchange resin is a gel-type cation exchange resin, the mass ratio of the ion exchange resin to the silver nitrate solution is 1:0.5-1.5, the stirring time is 2-3h, the chelate adsorption resin is a side chain chelate resin, the functional groups contained in the side chain chelate resin are at least one of oximes, hydroxyquinolines or pyridines, and the mass ratio of the chelate adsorption resin to the primary filtrate is 1:0.2-0.6.

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