A short-process resource treatment system and method for silver-containing waste liquid

Abstract

This invention discloses a short-process resource recovery system and method for silver-containing waste liquid, which can solve the technical problems of long process and low direct recovery rate of traditional "silver chloride precipitation-precipitated lead furnace" process for silver recovery. This invention innovatively proposes to mix high and low concentration silver-containing waste liquid to the optimal concentration window of 20-60 g / L, and then perform a first-stage sodium hydroxide oxidation precipitation and a second-stage directional precipitant deep precipitation. The high-grade silver oxide slag produced by this method can be directly returned to the silver separation furnace for smelting, eliminating the precious lead furnace process, thereby increasing the direct silver recovery rate from about 97.7% to more than 99%, and ensuring that the silver ion concentration in the liquid after silver precipitation is stably below 5 mg / L.

Description

Technical Field

[0001] This invention relates to the field of non-ferrous metal hydrometallurgy and secondary resource recovery, specifically to a short-process resource recovery system and method for treating silver-containing waste liquid. Background Technology

[0002] Silver electrolytic refining is a key process in the production of high-purity silver. During this process, two types of silver-containing waste liquid are continuously generated: one is a high-concentration silver-containing waste liquid (mainly composed of AgNO3 and Ag) produced from the boiling of silver anode mud with nitric acid. + The concentration is usually as high as 80-350 g / L, and it is strongly acidic; another type is low-concentration silver-containing wastewater generated during the production process, such as anode bag washing water, silver powder washing solution, floor washing solution, etc. (Ag + Concentrations are typically below 20 g / L.

[0003] Currently, the industry's conventional treatment method for these two types of waste liquids is to mix them and then use a combined process of "sodium chloride precipitation - steam evaporation - precious lead furnace smelting" to recover silver. Specifically, sodium chloride is added to the mild waste liquid to precipitate silver as AgCl. The precipitate slurry is evaporated to obtain silver-containing alkaline slag, which is then returned to the precious lead furnace and smelted together with lead to produce precious lead. The precious lead is then blown in a silver separation furnace to produce silver alloy plates, which are finally refined by electrolytic refining.

[0004] This traditional process has the following insurmountable drawbacks: First, the silver recovery process is lengthy: silver-containing materials need to undergo multi-stage pyrometallurgical smelting involving "precipitate slag → precious lead → silver alloy plate," resulting in a complex process and long production cycle. Second, the direct silver recovery rate is low: silver is dispersed in different intermediate products during circulation, and mechanical and chemical losses occur at each stage. In particular, the direct silver recovery rate in the precious lead furnace smelting section is only about 97.7%, becoming a bottleneck restricting the overall recovery rate. Third, the treatment of high-concentration waste liquid is incomplete: when the initial silver concentration of the waste liquid is too high (e.g., >120g / L), chlorination precipitation is prone to incomplete precipitation due to local supersaturation and encapsulation effects, resulting in the supernatant still containing silver at the g / L level. Fourth, equipment costs increase: the acidic environment exacerbates equipment corrosion.

[0005] Therefore, developing a new silver-containing waste liquid treatment technology that can directly produce high-value intermediate products that can be returned to the final refining process, thereby significantly shortening the process and increasing the direct silver recovery rate, has become an urgent need for the industry. Summary of the Invention

[0006] The present invention aims to solve the technical problems of existing silver-containing waste liquid processes, such as lengthy processes, low direct silver recovery rate, poor adaptability to high-concentration waste liquids, and high residual silver concentration in wastewater.

[0007] A short-process resource recovery system for silver-containing waste liquid, comprising: S1: Mixing and blending unit, configured to transport and mix low-silver-content waste liquid and high-silver-content waste liquid to form a mixed waste liquid with a silver ion concentration between 20g / L and 60g / L; S2: An oxidation precipitation tank connected to the outlet of the mixing and blending unit. The oxidation precipitation tank is equipped with an alkali dosing system and a pH detection device. S3: A two-stage deep sedimentation tank connected to the overflow or outlet of a first-stage oxidation sedimentation tank. The two-stage deep sedimentation tank is equipped with a sodium-based reagent dosing device. S4: A solid-liquid separation device connected to the slag discharge ports of a first-stage oxidation sedimentation tank and a second-stage deep sedimentation tank, respectively. S5: Silver oxide slag storage bin, which receives silver oxide slag from a section of the oxidation precipitation tank after solid-liquid separation.

[0008] Furthermore, the mixing and blending unit includes a low-silver-content waste liquid transport pump and a high-silver-content waste liquid transport pump. The low-silver-content waste liquid transport pump is connected to a low-silver-content waste liquid pit, and the high-silver-content waste liquid transport pump is connected to a high-silver-content waste liquid storage tank.

[0009] Furthermore, the system also includes a waste electrolyte purification reaction tank, which is equipped with a silver oxide slag feed port and a waste electrolyte inlet.

[0010] A short-process resource recovery method for silver-containing waste liquid includes the following steps: S1: Mixing and blending steps: Pump the low-silver-content waste liquid and the high-silver-content waste liquid into the mixing device for mixing to obtain a mixed waste liquid with a silver ion concentration of 20-60g / L; S2: First stage of silver oxide precipitation step: Add sodium hydroxide solution to the mixed waste liquid, control the final pH of the reaction system to be 10-14, carry out precipitation reaction under stirring, and after the reaction is completed, carry out the first solid-liquid separation to obtain the first precipitate residue rich in silver oxide and the first stage of silver precipitation liquid. S3: Two-stage deep silver precipitation step: Add a directional precipitant to the first-stage silver precipitation solution, and carry out a deep precipitation reaction under stirring. After the reaction is completed, perform a second solid-liquid separation to obtain a qualified liquid with a silver ion concentration of less than 5 mg / L and a second precipitate residue.

[0011] Furthermore, the final pH value of the reaction system in step S2 is 11 to 13.

[0012] Furthermore, the directional precipitant mentioned in step S3 is sodium chloride or sodium sulfide.

[0013] Furthermore, in step S3, the amount of sodium chloride added, based on the amount of chloride ions added, is 1.5 to 2.2 times the theoretical amount of chloride ions required for complete precipitation of residual silver ions in the liquid after silver precipitation, preferably 1.8 to 2.0 times.

[0014] Furthermore, in step S3, the amount of sodium sulfide added is 1.2 to 1.5 times the theoretical amount.

[0015] Furthermore, the above method also includes step S4: the silver oxide slag resource utilization step, in which all or part of the first precipitated slag rich in silver oxide is transported to a silver electrolytic refining furnace for smelting.

[0016] Furthermore, in step S4, a portion of the first precipitate slag rich in silver oxide is used to purify the waste silver electrolyte. Specifically, the silver oxide slag is added to the waste silver electrolyte, and the molar ratio of silver oxide to free nitric acid in the waste liquid is controlled to be 0.7~0.9:1. The mixture is stirred and reacted at 80-95℃ for 0.5-1.5 hours.

[0017] The present invention has the following advantages: 1. This invention, through extensive experimentation, creatively discovered that 20-60 g / L is the optimal concentration window. At this concentration, the waste liquid enters a first-stage oxidation precipitation tank, where, under strongly alkaline conditions (pH 10.0-12.5), the directional conversion of silver ions to silver oxide (Ag₂O) is achieved, while most impurity metals (such as Bi) are also eliminated. 3+ Cu 2+ The silver ions precipitate as hydroxides. The first stage of the precipitate then enters a second-stage deep sedimentation tank, where excess sodium chloride or sodium sulfide is added to perform a "sweeping" deep precipitation of residual trace and complexed silver ions, ensuring the effluent meets standards. This invention produces silver oxide slag that can be directly fed into the silver separation furnace, skipping the precious lead furnace process. It simplifies the traditional three-stage long process of "precipitation-precipitated lead-silver separation" into a two-stage short process of "precipitation-silver separation," increasing the direct silver recovery rate from 97.7% to over 99%, thus increasing economic benefits.

[0018] 2. Through extensive experiments, this invention has shown that at concentrations of 20-60 g / L, it can effectively avoid the encapsulation effect at high concentrations and the inefficiency at low concentrations. The precipitation reaction is complete, and the silver oxide slag crystallizes well, is easy to filter, and has a high grade (>80%).

[0019] 3. This invention employs a two-stage precipitation design of "oxidation conversion" and "chlorination sweeping," with clear division of labor and high efficiency, which can stably control the final effluent silver ion concentration below 5 mg / L. At the same time, the silver oxide slag can be directly returned to smelting or used as a purification agent for waste electrolyte treatment, realizing material circulation within the system and making it green and environmentally friendly.

[0020] 4. This invention is based on the transformation of existing production facilities, without the need for expensive and complex intelligent control equipment. Concentration window control can be achieved by adjusting the pump flow rate. It is simple to operate, stable in operation, and easy to promote and implement in existing factories. Attached Figure Description

[0021] Figure 1This is a schematic diagram of the process flow of the present invention.

[0022] Figure 2 The graph shows the change in the concentration of residual silver ions in the solution after two-stage deep precipitation under different sodium chloride dosing ratios. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this invention.

[0024] like Figure 1 As shown, in a specific implementation of the system of the present invention: low-silver-content waste liquid is pumped out from the pit 101 via the first transfer pump 103, and high-silver-content waste liquid is pumped out from the storage tank 102 via the second transfer pump 104. The two liquid streams are mixed in a pipeline or a dedicated mixing tank 105. By adjusting the flow rates of the two pumps, the silver concentration of the mixed liquid is stabilized within the range of 20-60 g / L.

[0025] The mixed waste liquid is either gravity-fed or pumped into a first-stage oxidation precipitation tank 201. The first agitator 204 is started, and simultaneously, a 30% sodium hydroxide solution is added via the sodium hydroxide dosing device 202. The pH is monitored by a pH meter 203, and the reaction endpoint is precisely controlled at 12.0. The reaction is continued for 4 hours at room temperature (approximately 20-25°C). The reaction slurry is pumped into a first filter press 205 for solid-liquid separation. The wet silver oxide slag (filter cake) falls into the silver oxide storage silo 401. Its dry basis composition, after testing, contains 85.2% silver and can be directly bagged and transported via transport path 402 to the silver separation furnace as feedstock. The liquid (filtrate) after the first-stage silver precipitation is Ag. + The concentration was reduced from the g / L level of the feed to 125 mg / L.

[0026] After silver precipitation, the liquid is pumped into the second-stage deep sedimentation tank 301. The second stirrer 303 is started, and industrial sodium chloride (1.8 times the theoretical amount, to achieve a complete precipitation of 125 mg / L) is added through the sodium chloride dosing device 302. + (Calculation). After reacting at room temperature for 4 hours, the slurry was pumped into a second filter press 304 for separation. The final purified liquid obtained was Ag. + Concentration < 5 mg / L, meeting emission / reuse standards. Secondary precipitate containing AgCl can be collected and treated separately.

[0027] In addition, a portion of silver oxide slag can be separated from the silver oxide slag storage silo 401 and fed into the waste electrolyte purification reactor 403. Stirred with the waste electrolyte at 90°C for 1 hour at a ratio of n(Ag₂O):n(HNO₃) = 0.8, this effectively neutralizes excess acid and deeply removes Cu. 2+ Bi 3+After removing impurities, the purified electrolyte can be returned to the electrolysis system.

[0028] Example 1: Treatment of ultra-high concentration acid boiling waste liquid

[0029] Raw materials: waste liquid from the boiling of silver anode mud with nitric acid, with an initial Ag⁺ concentration of 318.5 g / L and pH < 1.

[0030] Treatment process: (1) Mixing: The acid boiling waste liquid was pumped and mixed with low-concentration bag washing water (Ag⁺ ~10 g / L) at a volume ratio of about 1:6.5 to obtain a mixed liquid of about 7.5 m³. The Ag⁺ concentration after mixing was about 51.1 g / L; (2) First stage precipitation: The final pH was controlled at 12.0, and the reaction was carried out at room temperature for 5 h. The mixture was then filtered. Silver oxide slag (dry basis grade 85.2%) was obtained. The Ag⁺ concentration in the first stage liquid was 125 mg / L; (3) Second stage precipitation: 1.8 times the theoretical amount of NaCl was added, and the reaction was carried out at room temperature for 4 h. The mixture was then filtered.

[0031] Result: The final purified liquid Ag⁺ < 5 mg / L. The silver oxide slag was directly sent to the silver separation furnace.

[0032] Example 2: Treatment of medium-concentration mixed wastewater

[0033] Raw material: Normal mixed waste liquid in production, sampling volume 1 m³, initial Ag⁺ concentration 29.55 g / L.

[0034] Processing steps: (1) Mixing: The concentration is already at the optimal window, so it directly enters the precipitation stage; (2) First stage precipitation: Control the endpoint pH=11.8, react at room temperature for 4h, and filter under pressure. The Ag⁺ concentration of the first stage liquid is 89 mg / L; (3) Second stage precipitation: Add 2.0 times the theoretical amount of NaCl, react at room temperature for 3.5h, and filter under pressure.

[0035] Result: The final purified solution Ag⁺ < 5 mg / L.

[0036] Example 3: Purification of waste electrolyte by silver oxide slag

[0037] Raw material: 500 L of waste silver electrolyte containing free HNO3.

[0038] Processing procedure: Silver oxide slag from Example 1 was added at a ratio of n(Ag2O):n(HNO3)=0.8 and stirred at 90°C for 1 hour.

[0039] Results: After the reaction, the concentrations of Cu²⁺ and Bi³⁺ in the electrolyte both decreased to below 5 mg / L, indicating a significant purification effect.

[0040] The above embodiments demonstrate that the system and method of the present invention can efficiently treat silver-containing waste liquids of different concentrations and stably produce high-value intermediate products, thereby achieving a highly simplified and efficient silver recovery process.

Claims

1. A short-process resource utilization system for silver-containing waste liquid, characterized in that, The system includes: S1: Mixing and blending unit, configured to transport and mix low-silver-content waste liquid and high-silver-content waste liquid to form a mixed waste liquid with a silver ion concentration between 20g / L and 60g / L; S2: An oxidation precipitation tank connected to the outlet of the mixing and blending unit. The oxidation precipitation tank is equipped with an alkali dosing system and a pH detection device. S3: A two-stage deep sedimentation tank connected to the overflow or outlet of a first-stage oxidation sedimentation tank. The two-stage deep sedimentation tank is equipped with a sodium-based reagent dosing device. S4: A solid-liquid separation device connected to the slag discharge ports of a first-stage oxidation sedimentation tank and a second-stage deep sedimentation tank, respectively. S5: Silver oxide slag storage bin, which receives silver oxide slag from a section of the oxidation precipitation tank after solid-liquid separation.

2. The short-process resource utilization system for silver-containing waste liquid according to claim 1, characterized in that, The mixing and blending unit includes a low-silver-content waste liquid transport pump and a high-silver-content waste liquid transport pump. The low-silver-content waste liquid transport pump is connected to a low-silver-content waste liquid pit, and the high-silver-content waste liquid transport pump is connected to a high-silver-content waste liquid storage tank.

3. The short-process resource utilization system for silver-containing waste liquid according to claim 1, characterized in that, The system also includes a waste electrolyte purification reaction tank, which is equipped with a silver oxide slag feed port and a waste electrolyte inlet.

4. A short-process resource utilization method for silver-containing waste liquid, characterized in that, The method includes the following steps: S1: Mixing and blending steps: Pump the low-silver-content waste liquid and the high-silver-content waste liquid into the mixing device for mixing to obtain a mixed waste liquid with a silver ion concentration of 20-60g / L; S2: First stage of silver oxide precipitation step: Add sodium hydroxide solution to the mixed waste liquid, control the final pH of the reaction system to be 10-14, carry out precipitation reaction under stirring, and after the reaction is completed, carry out the first solid-liquid separation to obtain the first precipitate residue rich in silver oxide and the first stage of silver precipitation liquid. S3: Two-stage deep silver precipitation step: Add a directional precipitant to the first-stage silver precipitation solution, and carry out a deep precipitation reaction under stirring. After the reaction is completed, perform a second solid-liquid separation to obtain a qualified liquid with a silver ion concentration of less than 5 mg / L and a second precipitate residue.

5. The short-process resource utilization method for silver-containing waste liquid according to claim 4, characterized in that, The final pH value of the reaction system in step S2 is 11 to 13.

6. The short-process resource utilization method for silver-containing waste liquid according to claim 4, characterized in that, The directional precipitant mentioned in step S3 is sodium chloride or sodium sulfide.

7. The short-process resource utilization method for silver-containing waste liquid according to claim 6, characterized in that, In step S3, the amount of sodium chloride added is based on the amount of chloride ions added, which is 1.5 to 2.2 times the theoretical amount of chloride ions required for complete precipitation of residual silver ions in the solution after silver precipitation.

8. The short-process resource utilization method for silver-containing waste liquid according to claim 6, characterized in that, In step S3, the amount of sodium sulfide added is 1.2 to 1.5 times the theoretical amount.

9. The short-process resource utilization method for silver-containing waste liquid according to claim 4, characterized in that, The method further includes step S4: the silver oxide slag resource utilization step, in which all or part of the first precipitated slag rich in silver oxide is transported to a silver electrolytic refining furnace for smelting.

10. The short-process resource utilization method for silver-containing waste liquid according to claim 9, characterized in that, In step S4, a portion of the first precipitate rich in silver oxide is used to purify the waste silver electrolyte. Specifically, the silver oxide slag is added to the waste silver electrolyte, and the molar ratio of silver oxide to free nitric acid in the waste liquid is controlled to be 0.7~0.9:

1. The mixture is stirred and reacted at 80-95℃ for 0.5-1.5 hours.

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