A comprehensive recovery method of silver and impurity elements in silver electrolytic wastewater and silver electrolytic old liquid

Abstract

The application provides a comprehensive recycling method of silver in silver electrolytic wastewater and silver electrolytic old liquid and comprehensive recovery of impurity elements, and comprises the following steps: most of metal elements in the silver electrolytic wastewater are precipitated by using an organic strong base, and all of the metal elements in the electrolytic wastewater are precipitated and hydrolyzed by continuously using sodium carbonate; the precipitated and hydrolyzed slag is put into the electrolytic old liquid which needs to be purified, and then most of silver oxide is dissolved by readjusting nitric acid after reaching a certain pH value; the filtered slag after purification is reduced by using hydrazine hydrate and filtered; the filtered slag is put into a pressure kettle again for leaching by matching copper anode slime. The method greatly improves the silver direct recovery rate, simplifies the silver wastewater treatment process, and reduces environmental pollution.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of metallurgy, and relates to a comprehensive recovery method of silver and impurity elements in silver electrolysis wastewater and silver electrolysis old liquid. BACKGROUND

[0002] The electrolysis method is a commonly used method for producing silver in silver production enterprises at present. The silver powder prepared by the electrolysis method can reach a purity of 99.9-99.999 wt%, and has the advantages of simple operation, less reagent consumption, short realization cycle, high and stable product purity, and recoverable platinum group metals in the anode plate. According to the characteristics of the upstream anode mud, the rough silver anode plate after enrichment generally contains about 90% or more of silver, and has complex chemical composition. In the electrolysis process, part of impurity elements such as palladium, copper, lead, selenium, tellurium and bismuth will enter the solution. With the prolongation of the electrolysis time, the impurity elements will be accumulated to a certain concentration and be deposited on the cathode to enter the silver powder, which affects the purity of the electrolytic Ag powder. Therefore, the electrolyte needs to be disposed or purified and reused by removing impurities after aging. With the progress of the silver electrolysis industry, the rapid realization of silver products and the reduction of the intermediate tank pressure have become a trend. Therefore, it is very important to study the high-efficiency recycling technology of silver electrolyte and the comprehensive recovery technology of impurity elements.

[0003] The traditional silver electrolyte purification treatment or recycling technology mainly includes the following methods: (1) sodium chloride or hydrochloric acid precipitation method, using sodium chloride aqueous solution or hydrochloric acid to precipitate silver in silver electrolyte waste liquid as AgCl, so as to separate silver from impurity elements, AgCl is replaced by iron into crude silver and then returned to the kaldor furnace for treatment, or AgCl is directly returned to the kaldor furnace for treatment, and then cast into anode plate for electrolysis again; (2) displacement method, using copper to displace silver in waste electrolyte, and the displaced crude silver powder is returned to the kaldor furnace for smelting into silver anode plate for electrolysis again. The above two methods have simple process and convenient operation, but have the disadvantages of low yield and large intermediate tank; (3) thermal decomposition method, using the different decomposition temperatures of nitric acid and other base metals to separate them, controlling a certain temperature to make the base metal nitrate decompose into oxide while silver nitrate does not decompose, then heating water to dissolve silver nitrate, and the base metal oxide is insoluble in water, so that the silver nitrate solution can be reused, and the base metal oxide is sent to the fire system for treatment. This method has the defects of long process, complicated operation, high cost, safety hazards and the like; (4) hydrolysis method, using sodium hydroxide to adjust the pH value of the electrolyte, and hydrolyzing and precipitating impurity elements in silver electrolyte waste liquid. According to the principle that Ag+ and Cu2+, Pb2+, Bi3+ and Sb3+ have large difference in hydrolysis pH value, by adding sodium hydroxide and controlling the pH value, Cu2+, Pb2+, Bi3+ and Sb3+ impurity ions are hydrolyzed to form precipitates, and Ag+ remains in the solution, so as to separate silver from impurity elements. At present, the hydrolysis method has become the most widely used method for purification treatment of silver electrolyte waste liquid. The disadvantage of this method is that sodium hydroxide is a strong base, and the pH value is not easy to control. SUMMARY

[0004] The present application aims at the problems existing in the prior art, and provides a comprehensive recovery method for silver and impurity elements in silver electrolytic wastewater and silver electrolytic old liquid.

[0005] To this end, the present application adopts the following technical solutions:

[0006] A comprehensive recovery method for silver and impurity elements in silver electrolytic wastewater and silver electrolytic old liquid, comprising the following steps:

[0007] (1) using an organic strong base to adjust the pH value of the silver electrolytic wastewater to 5-6;

[0008] (2) slowly adding sodium carbonate to the silver electrolytic waste liquid to make the pH value reach 8-8.4, and then filtering to obtain a first filtrate and a first filter residue;

[0009] (3) slowly add the primary filter residue into silver electrolysis old liquid with temperature of 55-60 DEG C and stir at the same time for 40 min-1h, when the pH value of silver electrolysis old liquid reaches 6.2-6.5, stop adding the primary filter residue, then slowly add nitric acid with concentration of 2-2.5 mol / L to adjust the pH value of silver electrolysis old liquid to 4.2-4.4;

[0010] (4) filter the silver electrolysis old liquid after pH value adjustment to obtain secondary filter residue and secondary filter liquid, slurry the secondary filter residue, then add hydrazine hydrate to adjust the pH value to 8.2-8.5, then filter to obtain tertiary filter residue;

[0011] (5) mix the tertiary filter residue after washing and filtering with copper anode slime, put into a pressure kettle to carry out pressure leaching reaction, and finally carry out smelting.

[0012] Further, the organic strong base in the step (1) is hydrazine hydrate.

[0013] Further, in the step (2), the primary filter liquid is mixed with chlorine-containing wastewater and stirred for 20-30 min, then filtered to obtain silver-containing filter residue, and the silver-containing filter residue is put into a fire furnace to recover silver.

[0014] Further, in the step (4), the acidity of the secondary filter liquid is adjusted to 0.15-0.18 mol / L by using concentrated nitric acid to obtain new electrolyte.

[0015] Further, in the step (4), water is added to the secondary filter residue to slurry, and the solid-liquid ratio of the secondary filter residue and water is 1:2.

[0016] The present application has the following advantages:

[0017] (1) Compared with the traditional method, the present application has high silver direct recovery rate and good environmental protection effect. The traditional silver electrolyte recovery method often uses silver chloride precipitation method. Since the silver chloride particles are small, part of the silver chloride enters the exhaust pipe after being put into the furnace, which leads to the decrease of the direct recovery rate. The present application realizes the recycling of most of the silver in the electrolytic wastewater and electrolytic old liquid, and avoids the generation of a large amount of nitrogen oxides in nitric acid solution.

[0018] (2) The present application maximizes the recovery of platinum, palladium and other precious metal elements in the electrolytic wastewater and electrolytic old liquid. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The process flow chart of the present application is shown in the figure; DETAILED DESCRIPTION

[0020] The present application will be described in detail below in combination with examples:

[0021] Example 1

[0022] (1) As shown in Figure 1 9m3 silver electrolysis wastewater was taken for treatment, and the chemical composition of the silver electrolysis wastewater was as shown in Table 1:

[0023] Table 1

[0024]

[0025] At 26℃ room temperature, the pH value of 9m3 silver electrolysis wastewater was adjusted to 5.5 by using organic strong base hydrazine hydrate.

[0026] (2) At 26℃ room temperature, sodium carbonate was slowly added to the electrolysis wastewater after the alkali adjustment in step (1) to make the pH reach 8.2, and all metal elements in the silver electrolysis wastewater were hydrolyzed to produce a precipitate, and a first filtrate and a first filter residue were obtained by filtration. Then the first filtrate was mixed with the chlorine-containing wastewater produced by the system for 25min, and trace silver ions in the first filtrate combined with chlorine to form silver chloride. After the reaction was completed, filtration was performed, the filtrate was discharged, and a silver-containing filter residue was obtained, which was a small amount of silver chloride and was put into a fire furnace for silver recovery.

[0027] (3) 2.5m3 silver electrolysis old liquid was heated to 55℃, and the chemical composition of the silver electrolysis old liquid was as shown in Table 2. The first filter residue obtained in step (2) was stirred into the old silver electrolysis liquid, and the reaction time was 40min. When the pH value of the silver electrolysis old liquid reached 6.3, the addition of the first filter residue was stopped. At this time, the copper in the silver electrolysis old liquid had been completely hydrolyzed and precipitated, and the silver electrolysis old liquid was clear and colorless. Then 2mol / L nitric acid was slowly added to the reaction kettle, and the pH value of the silver electrolysis old liquid began to drop. When the pH value reached 4.4, the silver electrolysis old liquid began to show blue, and the addition of dilute nitric acid was stopped.

[0028] Table 2

[0029]

[0030] The silver electrolysis old liquid after pH adjustment was filtered to obtain a second filtrate and a second filter residue. The second filter residue mainly contained copper hydroxide, silver oxide, and a small amount of palladium hydroxide and other impurity element compounds. Then concentrated nitric acid was added to the second filtrate to adjust the acidity to 0.17mol / L, and a new electrolyte was obtained. The silver ion concentration in the new electrolyte increased by 74.8%, and the copper ion concentration was less than 0.1g / L, so the new electrolyte could be used for silver electrolysis. The chemical composition of the purified new electrolyte was as shown in Table 3.

[0031] Table 3

[0032]

[0033] (4) Slurry the secondary filter residue by adding water to the secondary filter residue, the solid-liquid ratio of the secondary filter residue and water being 1:2 (for example, 100 kg of secondary filter residue is mixed with 200 L of water), then add hydrazine hydrate to the slurry to adjust the pH value for reduction, and stop adding hydrazine hydrate when the pH value reaches 8.4, and continuously stir during the adding process, and then filter to obtain tertiary filter residue;

[0034] (5) Wash and filter the tertiary filter residue, then mix the tertiary filter residue with copper anode slime and put them into a pressure kettle for pressure leaching reaction, the mass of the copper anode slime being the same as that of the tertiary filter residue, and the silver, palladium and platinum and other high-value metal elements in the copper anode slime are enriched and then melted in a fire furnace again, and the copper in the copper anode slime is leached out to realize the leaching of copper.

[0035] Example 2

[0036] (1) Take 10 m³ of silver electrolysis wastewater for treatment, and the chemical composition of the silver electrolysis wastewater is shown in Table 4:

[0037] Table 4

[0038]

[0039] At 26°C, use organic strong base hydrazine hydrate to adjust the pH value of 10 m³ of silver electrolysis wastewater to 5.4.

[0040] (2) At 26°C, slowly add sodium carbonate to the silver electrolysis wastewater after the pH value is adjusted in step (1) to make the pH value reach 8.3, and all the metal elements in the silver electrolysis wastewater are hydrolyzed to produce a precipitate, and then filter to obtain a first filtrate and a first filter residue, then mix the first filtrate with the chlorine-containing wastewater produced by the system for 30 min, and the trace silver ions in the first filtrate combine with the chlorine to generate silver chloride, and after the reaction is completed, filter, and the filtrate is discharged, and at the same time, silver-containing filter residue is obtained, which is a small amount of silver chloride, and is put into a fire furnace for silver recovery.

[0041] (3) Heat 2.5 m³ of silver electrolysis old liquid to 58°C, and the chemical composition of the silver electrolysis old liquid is shown in Table 5, and put the first filter residue obtained in step (2) into the silver electrolysis old liquid for stirring, and the reaction time is 50 min, and when the pH value of the silver electrolysis old liquid reaches 6.5, stop adding the first filter residue, at this time, the copper in the silver electrolysis old liquid has been completely hydrolyzed and precipitated, and the silver electrolysis old liquid is clear and colorless, then continue to slowly add concentrated nitric acid with a concentration of 2.3 mol / L to the reaction kettle, and the pH value of the silver electrolysis old liquid begins to drop, and when the pH value reaches 4.6, the silver electrolysis old liquid begins to show blue, and stop adding the dilute nitric acid.

[0042] Table 5

[0043]

[0044] The silver electrolysis old liquid after pH value adjustment is filtered to obtain secondary filtrate and secondary filter residue, the secondary filter residue mainly contains copper hydroxide and silver oxide, and also contains a small amount of palladium hydroxide and other impurity element compounds; then concentrated nitric acid is added to the secondary filtrate to adjust the acidity to 0.15 mol / L to obtain new electrolyte, the silver ion concentration in the new electrolyte is increased by 62.3%, and the copper ion concentration is less than 0.1 g / L, so that the new electrolyte can be continuously used for silver electrolysis; the chemical composition of the new electrolyte after purification is shown in Table 6;

[0045] Table 6

[0046]

[0047] (4) The secondary filter residue is slurried, specifically, water is added to the secondary filter residue to slurry, the solid-liquid ratio of the secondary filter residue and water is 1:2 (for example, 100 kg of secondary filter residue is mixed with 200 L of water), then hydrazine hydrate is added to the slurry to adjust the pH value for reduction, the addition of hydrazine hydrate is stopped when the pH value reaches 8.2, and the slurry is continuously stirred during the addition, then the slurry is filtered to obtain tertiary filter residue;

[0048] (5) The tertiary filter residue is washed and filtered, then mixed with copper anode slime and placed in a pressure kettle for pressure leaching reaction, the mass of the copper anode slime is the same as that of the tertiary filter residue, the high-value metal elements such as silver, palladium and platinum in the copper anode slime are enriched, and then melt in a fire furnace for smelting, and the copper in the copper anode slime is leached out by pressure leaching to realize the leaching of copper.

Claims

1. A comprehensive method for recovering silver and impurity elements from silver electrolysis wastewater and old silver electrolysis solution, characterized in that, Includes the following steps: (1) Use strong organic bases to adjust the pH of silver electrolysis wastewater to 5-6; (2) Add sodium carbonate slowly to the silver electrolysis wastewater to make the pH reach 8-8.4, and then filter to obtain primary filtrate and primary filter residue; (3) Slowly add the primary filter residue to the old silver electrolysis solution at a temperature of 55℃-60℃ and stir for 40min-1h during the addition process. When the pH value of the old silver electrolysis solution reaches 6.2-6.5, stop adding the primary filter residue, and then slowly add nitric acid with a concentration of 2-2.5mol / L to adjust the pH value of the old silver electrolysis solution to 4.2-4.

4. (4) After filtering and adjusting the pH value of the old silver electrolysis solution, a secondary filter residue and a secondary filtrate are obtained. The secondary filter residue is slurried, and then hydrazine hydrate is added to adjust the pH value to 8.2-8.

5. Then, the solution is filtered to obtain a tertiary filter residue. (5) After washing and filtering the filter residue three times, mix it with copper anode mud and put it into a pressure vessel for pressure leaching reaction, and finally smelt it.

2. The comprehensive recovery method for silver and impurity elements from silver electrolysis wastewater and old silver electrolysis solution according to claim 1, characterized in that, The strong organic base in step (1) is hydrazine hydrate.

3. The comprehensive recovery method for silver and impurity elements from silver electrolysis wastewater and old silver electrolysis solution according to claim 1, characterized in that, In step (2), the filtrate is mixed with chloride-containing wastewater for 20-30 minutes and then filtered to obtain silver-containing filter residue. The silver-containing filter residue is then fed into a pyrometallurgical furnace to recover silver.

4. The comprehensive recovery method for silver and impurity elements from silver electrolysis wastewater and old silver electrolysis solution according to claim 1, characterized in that, In step (4), the acidity of the secondary filtrate is adjusted to 0.15-0.18 mol / L with concentrated nitric acid to obtain a new electrolyte.

5. The comprehensive recovery method for silver and impurity elements from silver electrolysis wastewater and old silver electrolysis solution according to claim 1, characterized in that, In step (4), water is added to the secondary filter residue to slurry it, and the solid-liquid ratio of the secondary filter residue and water is 1:2.

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