Method for removing selenium from wastewater through self-control of oxidation-reduction potential

Abstract

The invention provides a method for removing selenium from wastewater through self-control of oxidation-reduction potential. The method comprises the following steps: adjusting the pH of selenium-containing wastewater to be 1t; the method comprises the following steps: 1, adding a first-stage reducing agent sodium sulfite, reacting for 20-40 minutes, adding a second-stage reducing agent for reduction, ending the reaction when the oxidation-reduction potential of the solution reaches the end-point potential, and carrying out solid-liquid separation to obtain selenium-removed wastewater; and the secondary reducing agent is selected from one or more of thiourea, iron powder, copper powder and other reducing agents. According to the method for conveniently and rapidly indicating the key point of the reaction, the reaction process is controlled through ORP indication, the situation that the reagent is added excessively is avoided, and the reagent cost is saved; the wastewater treatment condition can be judged through ORP indication, the water outlet process is simplified, the repeated treatment and water outlet detection times are reduced, the wastewater outlet time consumption is reduced, and the overall treatment cost is saved; the selenium removal rate is high.

Description

Technical Field

[0001] The invention belongs to the technical field of water treatment, and in particular relates to a method for removing selenium from wastewater with automatic redox potential control. Background Art

[0002] Selenium has a wide range of uses, mainly in metallurgy, electronics industry, photovoltaics and other fields. In the metallurgical industry, the application of selenium accounts for about 30% of the total demand; in the electronics industry and photovoltaics, the application of selenium accounts for about 5% of the total demand. Because selenium has photosensitivity and semiconductor properties, it is often used to manufacture photoreceptors, laser devices, infrared controllers, etc. Therefore, wastewater generated by the metallurgical and electronics industries often contains a high concentration of selenium, which can easily cause surface water and groundwater pollution. As a second-class pollutant, the first, second and third level standards of selenium in the comprehensive sewage discharge standard are: 0.1mg / L, 0.2mg / L, 0.5mg / L. Therefore, the discharge of selenium-containing wastewater is strict and difficult to treat.

[0003] Selenium is located in the sixth main group of the fourth period in the periodic table. Its chemical properties are between sulfur and tellurium, and its main valence states are -2, +4 and +6. Selenium can directly combine with hydrogen, oxygen, sulfur and other elements except iodine, and the resulting selenide has certain toxicity; selenium is easily generated into toxic selenium dioxide when heated in air; selenium is insoluble in dilute sulfuric acid or hydrochloric acid, but can react with concentrated sulfuric acid and concentrated nitric acid with strong oxidizing properties to generate selenious acid.

[0004] Among the current wastewater selenium removal processes, one type of process is to intercept, adsorb or ion exchange selenate and selenite to achieve the purpose of selenium removal, including adsorption process, membrane separation process, biological treatment process and other processes. The adsorption treatment materials can be adsorbents such as ion exchange resins, activated carbon and carbon-based adsorbents. Among them, the exchange capacity of ion exchange resins is limited, and the treatment effect of high-concentration selenium wastewater is poor; the adsorption efficiency of activated carbon for selenium is low, and it is not selective, and the selenium removal effect is poor, while the cost of carbon-based adsorbents is high, which limits its wide application. The membrane separation process can remove other anions and cations while removing selenium, and the effluent water quality is excellent, but the treatment effect is not good when it contains suspended matter and complex water quality. The scope of application of biological treatment processes is small, and the treatment effect is poor. Another type of process is to reduce selenate and selenite to elemental selenium or degrade them into selenium-containing organic matter, including chemical reduction process, flocculation precipitation process, etc. The reducing agent can be: zero-valent iron, copper-nickel alloy, thiourea, sodium sulfite, etc. Among them, the processing cost of zero-valent iron and copper-nickel alloy is relatively high, and the selenium removal effect of thiourea and sodium sulfite is affected by factors such as selenium concentration and impurities, and the selenium removal effect is unstable.

[0005] Most of the existing processes are suitable for treating low-concentration selenium wastewater, and there is a lack of processes suitable for treating high-concentration selenium wastewater. There are problems such as unstable treatment effects, lack of indicators for judging the reaction endpoint, high wastewater treatment costs, and inconvenient use. Summary of the invention

[0006] In view of this, the purpose of the present invention is to provide a method for removing selenium from wastewater by automatic control of redox potential, which method can quickly and conveniently indicate the reaction endpoint, simplify the water discharge process, reduce the number of repeated treatments and water discharge detection times, reduce the time consumption for wastewater discharge, save overall treatment costs, and efficiently and stably remove high-concentration selenium in wastewater.

[0007] The present invention provides a method for removing selenium from wastewater by automatic redox potential control, comprising the following steps:

[0008] The selenium-containing wastewater is adjusted to pH <1, a primary reducing agent, sodium sulfite, is added, the reaction is carried out for 20 to 40 minutes, and then a secondary reducing agent is added for reduction. When the redox potential of the solution reaches the end potential, the reaction is terminated, the solid and liquid are separated, and the selenium-removed wastewater is obtained;

[0009] The secondary reducing agent is selected from one or more of thiourea, iron powder and copper powder.

[0010] In certain specific embodiments of the present invention, the secondary reducing agent is thiourea, and the endpoint potential is 148-152 mV.

[0011] In certain specific embodiments of the present invention, when the secondary reducing agent is iron powder or copper powder, the endpoint potential is 248-252 mV.

[0012] In certain specific embodiments of the present invention, the secondary reducing agent is thiourea, and the temperature of the reduction reaction is 75-85°C.

[0013] In certain specific embodiments of the present invention, the secondary reducing agent is copper powder or iron powder, the temperature of the reduction reaction is 15 to 35° C., and the time of the reduction reaction is 1.5 to 2.5 hours.

[0014] In certain specific embodiments of the present invention, the temperature of the reaction of adding the primary reducing agent sodium sulfite is 70-80°C.

[0015] In certain specific embodiments of the present invention, the amount of the primary reducing agent sodium sulfite added is 1.0 to 1.2 times the theoretical amount.

[0016] In certain specific embodiments of the present invention, the amount of the secondary reducing agent added is 1.5 to 3.0 times the theoretical amount.

[0017] In certain specific embodiments of the present invention, the selenium ion content in the selenium-containing wastewater is 1 to 10 g / L.

[0018] In certain specific embodiments of the present invention, if the secondary reducing agent is iron powder, magnetic absorption is performed to recover the iron after the reaction is completed.

[0019] The present invention provides a method for removing selenium from wastewater by self-controlled redox potential, comprising the following steps: adjusting the selenium-containing wastewater to pH <1, adding a primary reducing agent, sodium sulfite, reacting for 20 to 40 minutes, and then adding a secondary reducing agent for reduction, when the redox potential of the solution reaches the end potential, terminating the reaction, and performing solid-liquid separation to obtain the wastewater after deselenium removal; the secondary reducing agent is selected from one or more of thiourea, iron powder and copper powder reducing agents. The present application provides a method for conveniently and quickly indicating the focus of the reaction, that is, controlling the reaction process by ORP indication, avoiding the situation of excessive reagent addition, and saving reagent costs; the wastewater treatment situation can be judged by ORP indication, simplifying the effluent process, reducing the number of repeated treatments and effluent detection times, reducing the time consumption of wastewater effluent, and saving overall treatment costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The figure is a schematic diagram of the process of removing selenium from wastewater in certain embodiments of the present invention. DETAILED DESCRIPTION

[0021] The present invention provides a method for removing selenium from wastewater by automatic redox potential control, comprising the following steps:

[0022] The pH value of selenium-containing wastewater is adjusted to below 1, and a primary reducing agent, sodium sulfite, is added to react for 20 to 40 minutes; a secondary reducing agent is added for reduction, and when the redox potential of the solution reaches the end potential, the reaction is terminated, and the solid-liquid is separated to obtain selenium-removed wastewater; the secondary reducing agent is selected from one or more reducing agents such as thiourea, iron powder and copper powder.

[0023] The selenium ion content in the selenium-containing wastewater of the present invention is 1-10 g / L; the selenium-containing wastewater includes Se(IV) and Se(VI); and also includes arsenic ions, zinc ions, calcium ions and other impurities, all of which have a concentration less than 0.1 g / L. In a specific embodiment, the selenium concentration is 2.81 g / L, 0.529 g / L or 1.15 g / L.

[0024] The present invention uses sulfuric acid or hydrochloric acid to adjust the pH value of selenium-containing wastewater to less than 1. Sodium sulfite is added to the solution for reaction for 20 to 40 minutes; sodium sulfite is used as a primary reducing agent to perform a primary reduction reaction with the selenium-containing wastewater, and the reaction temperature is 70 to 80° C. The amount of sodium sulfite added is 1.0 to 1.2 times the theoretical amount. In a specific embodiment, sodium sulfite is added for reaction for 30 minutes.

[0025] After the primary reduction reaction is completed, a secondary reducing agent is added to continue the secondary reduction reaction; the secondary reducing agent is selected from one or more reducing agents such as thiourea, iron powder, and copper powder. The secondary reducing agent can be thiourea, and the temperature of the reduction reaction is 75 to 85°C; the secondary reducing agent can be copper powder or iron powder, and the temperature of the reduction reaction is 15 to 35°C; the time of the reduction reaction is 1.5 to 2.5 hours. The amount of the secondary reducing agent added is 1.5 to 3.0 times the theoretical amount. The present invention can improve the treatment efficiency of selenium-containing wastewater by selecting a specific type of secondary reducing agent for the secondary reduction reaction.

[0026] When the redox potential of the solution reaches the endpoint potential, the reaction is terminated. The present invention preferably uses a redox potentiometer to detect the potential change of the solution. When the secondary reducing agent is thiourea, the endpoint potential is 145-160mV, preferably 148-154mV. When the secondary reducing agent is iron powder or copper powder, the endpoint potential is 220-265mV, preferably 224-264mV; in a specific embodiment, the endpoint potential is 224mV, 241mV or 264mV.

[0027] The present invention adopts a primary reducing agent, sodium sulfite, as a primary reduction, and continues to adopt a specific type of secondary reducing agent to continue the reduction reaction, and controls the reaction process through ORP indication, thereby avoiding excessive reagent addition and saving reagent costs; the wastewater treatment situation can be judged through ORP indication, the water outlet process is simplified, the number of repeated treatments and water outlet detection times is reduced, the wastewater outlet time is reduced, and the overall treatment cost is saved.

[0028] Compared with the adsorption method and the biological method, the equipment required for this application is a continuous stirred tank reactor, which is a common hydrometallurgical industrial equipment, and the overall process is very easy to realize industrial application; the reagents required for this application are conventional industrial reagents, among which copper powder and iron powder can be recycled and reused through industrial waste slag, further saving reagent costs and improving resource utilization.

[0029] After the reaction is finished, a multi-media filter is used for solid-liquid separation to obtain selenium-free wastewater. If iron powder is used as the reducing agent, after the reduction reaction is finished, the magnetic recovery device is turned on to recover the iron powder to achieve resource recovery, effectively avoid the mixing of iron powder and selenium residue in the filter residue, and improve the purity of the recovered selenium resources.

[0030] The selenium concentration in the selenium removal wastewater is 0.2-0.4 mg / L, and the selenium removal rate is 99.9%.

[0031] Figure 1 This is a schematic diagram of the process of removing selenium from selenium-containing wastewater in certain embodiments of the present invention:

[0032] The selenium-containing wastewater is subjected to primary reduction using a primary reducing agent, and then to secondary reduction using a secondary reducing agent. The endpoint potential is indicated by a redox potential indicating system, and the reaction is terminated after the endpoint potential is reached. If iron powder is used as a reducing agent for secondary reduction, the magnetic recovery device is turned on, and then the solid-liquid separation is carried out through a multi-media filter, and finally the selenium is recovered and the discharge meets the standards.

[0033] In order to further illustrate the present invention, a method for removing selenium from wastewater by self-controlling redox potential provided by the present invention is described in detail below in conjunction with embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0034] Example 1

[0035] The selenium-containing acidic wastewater from a wet smelting production line was taken, in which the selenium concentration was 2.81g / L, and other impurities included arsenic ions, zinc ions, calcium ions, etc., and the concentrations were all less than 0.1g / L.

[0036] 1) Take 1L of the above wastewater, heat it to 85℃±2℃, stir it at 410±5r / min, add sulfuric acid to adjust the pH to 0.7-0.75, and react for 30min.

[0037] 2) Add 9.8 g of sodium sulfite to the solution in step 1), and stir and react for 30 min.

[0038] 3) Add 3.2 g of thiourea to the solution in step 2) and stir to react for 3 hours.

[0039] 4) Use a redox potentiometer to detect the potential change of the solution in step 3). When the potential is 154 mV, stop the reaction.

[0040] 5) Solid-liquid separation was performed to obtain selenium-removed wastewater. The selenium concentration in the treated wastewater was detected by ICP method and was 0.4 mg / L, with a selenium removal rate of 99.9%.

[0041] Example 2

[0042] The selenium-containing acidic wastewater from a wet smelting production line was taken, in which the selenium concentration was 0.529g / L, and other impurities included arsenic ions, zinc ions, calcium ions, etc., and the concentrations were all less than 0.1g / L.

[0043] 1) Take 1L of the above wastewater, heat it to 80℃±2℃, stir it at 450±5r / min, add sulfuric acid to adjust the pH to 0.9-1.0, and react for 30min.

[0044] 2) Add 1.6 g of sodium sulfite to the solution in step 1), and stir and react for 30 min.

[0045] 3) Add 1.43 g of thiourea to the solution in step 2), and stir and react for 2 hours.

[0046] 4) Using a redox potentiometer to detect the potential change of the solution in step 3), when the potential is 148 mV, the reaction is stopped, and solid-liquid separation is performed to obtain selenium-removed wastewater. The selenium concentration in the treated wastewater is 0.3 mg / L using the ICP method, and the selenium removal rate is 99.9%.

[0047] Example 3

[0048] The selenium-containing acidic wastewater from a wet smelting production line was taken, in which the selenium concentration was 1.15g / L, and other impurities included arsenic ions, zinc ions, calcium ions, etc., and the concentrations were all less than 0.1g / L.

[0049] 1) Take 1L of the above wastewater, heat it to 75℃±2℃, stir it at 410±5r / min, add sulfuric acid to adjust the pH to 0.5-0.6, and react for 30min.

[0050] 2) Add 3.47 g of sodium sulfite to the solution in step 1), and stir and react for 30 min.

[0051] 3) Add 0.96 g of Fe powder to the solution in step 2), and stir and react at the temperature for 1.5 hours.

[0052] 4) Use a redox potentiometer to detect the potential change of the solution in step 3). When the potential is 241 mV, stop the reaction.

[0053] 5) Turn on the magnetic recovery device, shut it down after 10 to 15 minutes, separate the solid and liquid to obtain the selenium-removed wastewater, and detect the selenium concentration in the treated wastewater by ICP method, which is 0.2 mg / L, and the selenium removal rate is 99.9%.

[0054] Example 4

[0055] The selenium-containing acidic wastewater from a wet smelting production line was taken, in which the selenium concentration was 3.19g / L, and other impurities included arsenic ions, zinc ions, calcium ions, etc., and the concentrations were all less than 0.1g / L.

[0056] 1) Take 1L of the above wastewater, heat it to 90℃±2℃, stir it at 450±5r / min, add sulfuric acid to adjust the pH to 0.6-0.5, and react for 30min.

[0057] 2) Add 14.45 g of sodium sulfite to the solution in step 1), and stir and react for 30 min.

[0058] 3) Add 3.83 g of Fe powder to the solution in step 2) and stir at room temperature for 2 hours.

[0059] 4) Use a redox potentiometer to detect the potential change of the solution in step 3). When the potential is 224 mV, stop the reaction.

[0060] 5) Turn on the magnetic recovery device, shut it down after 10 to 15 minutes, separate the solid and liquid to obtain the selenium-removed wastewater, and detect the selenium concentration in the treated wastewater by ICP method, which is 0.2 mg / L, and the selenium removal rate is 99.9%.

[0061] Example 5

[0062] The selenium-containing acidic wastewater from a wet smelting production line was taken, in which the selenium concentration was 2.56g / L, and other impurities included arsenic ions, zinc ions, calcium ions, etc., and the concentrations were all less than 0.1g / L.

[0063] 1) Take 1L of the above wastewater, heat it to 90℃±2℃, stir it at 410±5r / min, add sulfuric acid to adjust the pH to 0.5-0.4, and react for 30min.

[0064] 2) Add 9.8 g of sodium sulfite to the solution in step 1), and stir and react for 30 min.

[0065] 3) Add 4.21 g of Cu powder to the solution in step 2), set the reaction temperature at 60°C ± 2°C, and stir for 1.5 hours.

[0066] 4) Use a redox potentiometer to detect the potential change of the solution in step 3). When the potential is 264 mV, stop the reaction.

[0067] 5) Solid-liquid separation was performed to obtain selenium-removed wastewater. The selenium concentration in the treated wastewater was detected by ICP method and was 0.2 mg / L, with a selenium removal rate of 99.9%.

[0068] From the above examples, it can be seen that the present invention provides a method for removing selenium from wastewater by automatic redox potential control, two-stage reducing agent reduction, and ORP indicating the reaction end point. The example results show that the selenium removal rate of the present invention is 99.9%, and the selenium concentration of the wastewater meets the standard.

[0069] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for removing selenium from wastewater by automatic redox potential control, comprising the following steps: The selenium-containing wastewater is adjusted to pH <1, a primary reducing agent, sodium sulfite, is added, the reaction is carried out for 20 to 40 minutes, and then a secondary reducing agent is added for reduction. When the redox potential of the solution reaches the end potential, the reaction is terminated, the solid and liquid are separated, and the selenium-removed wastewater is obtained; The secondary reducing agent is selected from one or more of thiourea, iron powder and copper powder.

2. The method according to claim 1, characterized in that: The secondary reducing agent is thiourea, and the endpoint potential is 148-152 mV.

3. The method according to claim 1, characterized in that When the secondary reducing agent is iron powder or copper powder, the endpoint potential is 248-252 mV.

4. The method according to claim 1, characterized in that: The secondary reducing agent is thiourea, and the temperature of the reduction reaction is 75-85°C.

5. The method according to claim 1, characterized in that The secondary reducing agent is copper powder or iron powder, the temperature of the reduction reaction is 15 to 35° C., and the time of the reduction reaction is 1.5 to 2.5 hours.

6. The method according to claim 1, characterized in that The reaction temperature of adding the primary reducing agent sodium sulfite is 70-80°C.

7. The method according to claim 1, characterized in that The amount of sodium sulfite added as the primary reducing agent is 1.0 to 1.2 times the theoretical amount.

8. The method according to claim 1, characterized in that The amount of the secondary reducing agent added is 1.5 to 3.0 times the theoretical amount.

9. The method according to claim 1, characterized in that: The selenium ion content in selenium-containing wastewater is 1 to 10 g / L.

10. The method according to claim 1, characterized in that If the secondary reducing agent is iron powder, magnetic absorption is performed to recover the iron after the reaction is completed.

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