Method for treating silver-containing wastewater

Abstract

This invention relates to the field of environmental protection technology and discloses a method for treating silver-containing wastewater. The method is carried out in a wastewater treatment device, which includes: a silver precipitation reaction tank, a membrane separation filter, a settling tank, and a centrifuge connected in sequence. The method includes: contacting and reacting a chlorine-containing precipitant with the silver-containing wastewater in the silver precipitation reaction tank; then sending the wastewater to the membrane separation filter for membrane separation to obtain a solid slurry and a first filtrate; then sending the solid slurry to the settling tank for settling; and finally sending the entire settling material to the centrifuge for centrifugation to obtain a precipitate solid and a second filtrate. The silver content of the silver-containing wastewater is 0.2-5000 mg / L. The treatment method provided by this invention has a simple process, is easy to operate, and can significantly shorten the treatment time and improve the treatment efficiency.

Description

Technical Field

[0001] This invention relates to the field of environmental protection technology and discloses a method for treating silver-containing wastewater. Background Technology

[0002] Currently, the main methods for treating silver-containing wastewater include electrolysis, ion exchange, adsorption, and precipitation. Electrolysis is often used for waste fixing solutions and silver plating wastewater, but it cannot be performed under low metal ion concentration conditions and is unsuitable for silver-containing wastewater with low silver ion concentrations. Ion exchange has the advantage of recovering trace amounts of silver from wastewater, but ion exchange resins are easily contaminated or oxidized, leading to ineffectiveness, frequent regeneration, high operating costs, and high requirements for the adsorbent, thus limiting its practical application. Adsorption recovers silver from silver-containing wastewater through physicochemical effects on the active surface of the adsorbent. Its adsorption effect mainly depends on the performance of the adsorbent used and is not suitable for large wastewater volumes or high silver content. Precipitation involves adding sodium sulfide solution under specific pH conditions to form silver sulfide precipitate, thus removing silver ions. However, because silver sulfide precipitate particles are small and easily form colloids, natural gravity sedimentation is ineffective, and it also introduces sulfur pollution into the wastewater and complicates subsequent treatment.

[0003] It is evident that the above method is not applicable to silver-containing wastewater with different silver ion concentrations, and its recovery capacity is limited. Summary of the Invention

[0004] The purpose of this invention is to overcome the problem of the lack of a simple and efficient method for recovering silver from silver-containing wastewater in the prior art, and to provide a method for treating silver-containing wastewater. The method provided by this invention has a simple treatment process and is convenient to operate, which can significantly shorten the treatment time and improve the treatment efficiency. It not only ensures that the silver content in the treated filtrate is stable below 0.1 mg / L, but also effectively recovers silver from the wastewater, simultaneously achieving compliant discharge of silver-containing wastewater and recycling of silver resources.

[0005] This invention provides a method for treating silver-containing wastewater. The method is carried out in a silver-containing wastewater treatment device, which includes: a silver precipitation reaction tank, a membrane separation filter, a settling tank, and a centrifuge connected in sequence. The method includes: reacting a chlorine-containing precipitant with the silver-containing wastewater in the silver precipitation reaction tank, then sending it to the membrane separation filter for membrane separation to obtain a solid slurry and a first filtrate, then sending the solid slurry to the settling tank for settling, and then sending the entire settling material to the centrifuge for centrifugation to obtain a precipitate solid and a second filtrate; the silver content of the silver-containing wastewater is 0.2-5000 mg / L.

[0006] The method provided by this invention requires fewer pieces of equipment and has lower raw material costs. The processing steps are simple and easy to operate, which can significantly shorten the processing time, improve the processing efficiency, and ultimately achieve a stable and controllable treatment process for silver-containing wastewater.

[0007] This invention enables continuous treatment of silver-containing wastewater by using a simple device that connects a silver precipitation reaction tank, a membrane separation filter, a settling tank, and a centrifuge. It can also keep the silver content in the treated filtrate below 0.1 mg / L and effectively recover silver from the wastewater. This invention can simultaneously achieve the standard discharge of silver-containing wastewater and the recycling of silver resources.

[0008] Furthermore, by setting a settling tank after the membrane separation filter, the present invention can significantly reduce centrifugation time and energy consumption. Moreover, the method of the present invention can ensure that the silver content of various silver-containing wastewaters is stabilized below 0.1 mg / L after treatment. Attached Figure Description

[0009] Figure 1 This is a flowchart of the treatment process for silver-containing wastewater. Detailed Implementation

[0010] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0011] This invention provides a method for treating silver-containing wastewater. The method is carried out in a silver-containing wastewater treatment device, which includes: a silver precipitation reaction tank, a membrane separation filter, a settling tank, and a centrifuge connected in sequence. The method includes: reacting a chlorine-containing precipitant with the silver-containing wastewater in the silver precipitation reaction tank, then sending it to the membrane separation filter for membrane separation to obtain a solid slurry and a first filtrate, then sending the solid slurry to the settling tank for settling, and then sending the entire settling material to the centrifuge for centrifugation to obtain a precipitate solid and a second filtrate; the silver content of the silver-containing wastewater is 0.2-5000 mg / L.

[0012] According to a preferred embodiment of the present invention, a first recovery pipe is provided between the membrane separation filter and the silver precipitation reaction tank for selectively returning the first filtrate to the silver precipitation reaction tank for further reaction.

[0013] According to a preferred embodiment of the present invention, a second recovery pipe is provided between the centrifuge and the silver precipitation reaction tank for selectively returning the second filtrate to the silver precipitation reaction tank for further reaction.

[0014] In this invention, there are no special requirements for the type of membrane separation filter. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the membrane separation filter is an expansion membrane filter; preferably, the expansion membrane filter is capable of automatic backwashing and continuous feeding.

[0015] In this invention, a first pump body is provided on the connecting pipeline between the silver precipitation reaction tank and the membrane separation filter, for sending the suspension in the silver precipitation reaction tank into the membrane separation filter for filtration.

[0016] In this invention, a second pump body is provided on the connecting pipeline between the settling tank and the centrifuge, for sending the sediment in the settling tank into the centrifuge for centrifugal separation.

[0017] According to a preferred embodiment of the present invention, the silver precipitation reaction tank is equipped with a stirrer for stirring the materials in the silver precipitation reaction tank so that the silver-containing wastewater and the chlorine-containing precipitant are fully mixed and reacted.

[0018] According to a preferred embodiment of the present invention, the silver precipitation reaction tank is provided with a dosing device for adding a chlorine-containing precipitant to the silver precipitation reaction tank.

[0019] In this invention, the silver-containing wastewater treatment device further includes a clear liquid storage tank, which is connected to a membrane separation filter and is used to store the first filtrate.

[0020] In this invention, silver-containing wastewater of various concentrations and sources can be treated using the method of this invention. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the silver content of the silver-containing wastewater is 600-1500 mg / L, preferably 900-1100 mg / L.

[0021] In this invention, the silver-containing wastewater mainly contains only silver ion impurities, and the content of other impurities is low and does not affect its discharge after treatment.

[0022] In this invention, there are no special requirements for the type of chlorine-containing precipitant. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the chlorine-containing precipitant is one or more of sodium chloride, potassium chloride, and sodium hypochlorite, preferably one or more of sodium chloride and potassium chloride.

[0023] In this invention, the ratio of chlorine-containing precipitant to silver-containing wastewater can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the ratio of chlorine-containing precipitant to silver-containing wastewater is 0.01-3 g / L, preferably 2.3-2.7 g / L.

[0024] In this invention, the contact reaction is carried out under dynamic conditions. There are no special requirements for the dynamic conditions. For example, the contact reaction can be carried out under stirring conditions. There are no special requirements for the stirring speed, which can be selected according to actual needs. This will not be elaborated here.

[0025] In this invention, there are no special requirements for the contact reaction time, which can be selected according to actual needs. For example, the reaction time can be 25-600 min, preferably 30-240 min.

[0026] In this invention, after the contact reaction is completed in the silver precipitation reaction tank, the suspension in the silver precipitation reaction tank can be sent to the membrane separation filter by a slurry pump for membrane separation. There are no special requirements for the type of slurry pump. Commonly used pumps are all suitable for this invention and can be selected according to actual needs. This will not be elaborated here.

[0027] In this invention, there are no special requirements for the sedimentation method. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the sedimentation is natural sedimentation. By using natural sedimentation, the solids in the slurry first settle to the bottom under the action of gravity, and then further solid-liquid separation is carried out. This facilitates faster completion of the subsequent solid-liquid separation and reduces energy consumption during the subsequent solid-liquid separation, avoiding unnecessary energy waste.

[0028] In this invention, there are no special requirements for the type of centrifuge. Commonly used centrifuges are all applicable to this invention, and can be selected according to actual needs. Further details will not be provided here.

[0029] In this invention, after the solid slurry settles in the settling tank, it can be pumped to a centrifuge for centrifugation. There are no special requirements for the type of slurry pump; any commonly used pump can be used in this invention and can be selected according to actual needs. Further details are omitted here.

[0030] In this invention, after the centrifugation process is completed, the solid precipitate silver chloride is recovered, and the second filtrate is reused in the contact reaction.

[0031] In this invention, the silver content of the first filtrate can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the silver content of the first filtrate is below 0.1 mg / L, preferably below 0.05 mg / L. Using the treatment method of this invention, the silver content of the filtrate can be stably maintained below 50% of the discharge standard of 0.2 mg / L, achieving stable compliance with discharge standards for silver-containing wastewater and efficient recovery of the precious metal silver.

[0032] According to a preferred embodiment of the present invention, the method for treating the silver-containing wastewater further includes: returning the first filtrate to the contact reaction or discharging it directly; and returning the second filtrate to the contact reaction.

[0033] In this invention, after centrifugation, the first filtrate is tested for silver content. Different treatments are applied based on the silver content analysis. If the silver content of the filtrate is within acceptable limits, it can be discharged or reused in the contact reaction. If the silver content is below acceptable, it is reused in the contact reaction again. In this invention, a silver content below 0.2 mg / L is considered acceptable.

[0034] The treatment method provided by this invention requires fewer pieces of equipment and has lower raw material costs. The treatment process is simple and easy to operate, significantly reducing treatment time and improving efficiency, ultimately achieving a stable and controllable treatment process for silver-containing wastewater. This method not only ensures that the silver content in the treated filtrate is consistently below 0.1 mg / L, but also effectively recovers silver from the wastewater, simultaneously achieving compliant discharge of silver-containing wastewater and the recycling of silver resources.

[0035] Example 1

[0036] Silver-containing wastewater is taken from a catalyst production process; the treatment process is as follows: Figure 1 As shown, the specific steps include:

[0037] 1) Take 800 ml of silver-containing wastewater samples twice, and label them A1 and A2 respectively. Keep the original sample A1 as a control sample.

[0038] 2) Transfer sample A2 to the silver precipitation reaction tank for silver precipitation reaction. Add 1.76 g of sodium chloride, a chlorine-containing precipitant, by the automatic dosing device, stir thoroughly, and react for 30 minutes.

[0039] 3) After the reaction, the suspension in the silver precipitation reaction tank is sent to an expansion membrane filtration device that can automatically backwash and continuously feed through a slurry pump for expansion membrane filtration.

[0040] 4) The filtered liquid separated by the diaphragm filter enters the clear liquid storage tank and its silver content is analyzed. If the silver content is qualified, it is discharged or reused in the silver precipitation reaction. If the silver content is not qualified, it is reused in the silver precipitation reaction again. A sample of the clear liquid is taken and labeled A3. A3 is sent to a testing agency to test its silver content. The results are shown in Table 1.

[0041] 5) The concentrated slurry separated by the diaphragm filter is transferred to a settling tank (not shown in the figure). After standing for 4 hours, it separates into layers. The slurry sediment is pumped to a centrifuge for centrifugal filtration. The silver chloride precipitate is recycled as a solid phase, and the filtrate is returned to the silver precipitation reaction tank for further reaction.

[0042] Example 2

[0043] Another type of silver-containing wastewater is taken from the production process of a certain catalyst, and the treatment process is as follows: Figure 1 As shown, the specific steps include:

[0044] 1) Take two 800 ml samples of the silver-containing wastewater, labeled B1 and B2 respectively, and keep the original sample B1 as a control sample.

[0045] 2) Transfer sample B2 to the silver precipitation reaction tank for silver precipitation reaction. Add 1.76 g of sodium chloride, a chlorine-containing precipitant, by the automatic dosing device, stir thoroughly, and react for 30 minutes.

[0046] 3) After the reaction, the suspension in the silver precipitation reaction tank is sent to an expansion membrane filtration device that can automatically backwash and continuously feed through a slurry pump for expansion membrane filtration.

[0047] 4) The filtered liquid separated by the diaphragm filter enters the clarified liquid storage tank and its silver content is analyzed. If the silver content is qualified, it is discharged or reused in the silver precipitation reaction. If the silver content is not qualified, it is reused in the silver precipitation reaction again. A sample of the clarified liquid is taken and labeled B3. B3 is sent to a testing agency to test its silver content. The results are shown in Table 1.

[0048] 5) The concentrated slurry separated by the diaphragm filter is transferred to a settling tank (not shown in the figure). After standing for 4 hours, it separates into layers. The slurry sediment is pumped to a centrifuge for centrifugal filtration. The silver chloride precipitate is recycled as a solid phase, and the filtrate is returned to the silver precipitation reaction tank for further reaction.

[0049] Example 3

[0050] The difference compared to Example 1 is that 1.94 grams of sodium chloride, a chlorine-containing precipitant, was added.

[0051] A sample of the clear liquid separated by the diaphragm filter was taken and labeled A4. A4 was sent to a testing institution to test its silver content. The results are shown in Table 1.

[0052] Example 4

[0053] The difference compared to Example 2 is that 2.11 grams of sodium chloride, a chlorine-containing precipitant, was added.

[0054] A sample of the clear liquid separated by the diaphragm filter was taken and labeled B4. B4 was sent to a testing institution to test its silver content. The results are shown in Table 1.

[0055] Example 5

[0056] The difference from Example 1 is that the added chlorine-containing precipitant is potassium chloride.

[0057] A sample of the clear liquid separated by the diaphragm filter was taken and labeled A5. A5 was sent to a testing institution to test its silver content. The results are shown in Table 1.

[0058] Example 6

[0059] The difference from Example 2 is that the added chlorine-containing precipitant is potassium chloride.

[0060] A sample of the clear liquid separated by the diaphragm filter was taken and labeled B5. B5 was sent to a testing institution to test its silver content. The results are shown in Table 1.

[0061] Comparative Example 1

[0062] The difference from Example 1 is that the added precipitant is sodium sulfide.

[0063] A sample of the clear liquid separated by the diaphragm filter was taken and labeled A6. A6 was sent to a testing institution to test its silver content. The results are shown in Table 1.

[0064] Comparative Example 2

[0065] The difference from Example 2 is that potassium sulfide was added as the precipitant.

[0066] A sample of the clear liquid separated by the diaphragm filter was taken and labeled B6. B6 was sent to a testing institution to test its silver content. The results are shown in Table 1.

[0067] Table 1

[0068] Sample number Sample properties Silver content, mg / L A1 Colorless, clear 974 A3 Colorless, clear 0.06 A4 Colorless, clear 0.03 A5 Colorless, clear 0.04 A6 Light gray, clear 0.11 B1 Colorless, clear 1010 B3 Colorless, clear 0.08 B4 Colorless, clear 0.02 B5 Colorless, clear 0.03 B6 Light gray, clear 0.12

[0069] The preferred embodiments of the present invention have been described above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various specific technical features in any suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for treating silver-containing wastewater, characterized in that, The method is carried out in a silver-containing wastewater treatment device, which includes: The silver precipitation reaction tank, membrane separation filter, settling tank and centrifuge are connected in sequence; The method includes: Chlorine-containing precipitant and silver-containing wastewater are reacted in a silver precipitation reaction tank, and then sent to a membrane separation filter for membrane separation to obtain a solid slurry and a first filtrate. The solid slurry is then sent to a settling tank for settling, and the settling material is then sent to a centrifuge for centrifugation to obtain a precipitate solid and a second filtrate. The silver content of the silver-containing wastewater is 0.2-5000 mg / L.

2. The method according to claim 1, wherein, A first recovery pipe is provided between the membrane separation filter and the silver precipitation reaction tank, which is used to selectively send the first filtrate back to the silver precipitation reaction tank for further reaction; A second recovery pipe is provided between the centrifuge and the silver precipitation reaction tank, which is used to selectively send the second filtrate back to the silver precipitation reaction tank for further reaction.

3. The method according to claim 1 or 2, wherein, The membrane separation filter is an expandable membrane filter; Preferably, the diaphragm filter is capable of automatic backwashing and continuous feeding.

4. The method according to any one of claims 1-3, wherein, A first pump body is installed on the connecting pipeline between the silver precipitation reaction tank and the membrane separation filter; and / or A second pump body is installed on the pipeline connecting the settling tank and the centrifuge; and / or The silver immersion reaction tank is equipped with a stirrer; and / or The silver immersion reaction tank is equipped with a dosing device.

5. The method according to any one of claims 1-4, wherein, The device also includes a clear liquid storage tank, which is connected to the membrane separation filter and is used to store the first filtrate.

6. The method according to any one of claims 1-5, wherein, The silver content of the silver-containing wastewater is 600-1500 mg / L, preferably 900-1100 mg / L.

7. The method according to any one of claims 1-6, wherein, The chlorine-containing precipitant is one or more of sodium chloride, potassium chloride, and sodium hypochlorite, preferably one or more of sodium chloride and potassium chloride.

8. The method according to any one of claims 1-7, wherein, The ratio of the chlorine-containing precipitant to the silver-containing wastewater is 0.01-3 g / L, preferably 2.3-2.7 g / L.

9. The method according to any one of claims 1-8, wherein, The silver content of the first filtrate is below 0.1 mg / L, preferably below 0.05 mg / L.

10. The method according to any one of claims 1-9, wherein, The method also includes: The first filtrate can be returned to undergo the contact reaction or directly discharged. The second filtrate is returned to carry out the contact reaction.

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