Method for efficiently recovering elemental selenium from selenium-containing wastewater

Abstract

The invention discloses a method for efficiently recovering elemental selenium from selenium-containing wastewater, and belongs to the field of scattered metal resource recovery and electrochemistry. The method comprises the following steps: adding an electrolyte sodium hydroxide solution into selenium-containing wastewater to adjust the pH value to 1-4, carrying out electrolysis by taking graphite as an anode material and a stainless steel sheet as a cathode material and controlling current and voltage, carrying out electrochemical reduction reaction on selenium ions in the solution on the cathode, and cleaning and drying pure selenium sediments separated out from the cathode to obtain elemental selenium. According to the method, a closed electrolyte circulating system is constructed, electrolysis conditions are optimized, effective deposition of selenium in the selenium-containing wastewater is achieved in an electrochemical mode, and metal selenium with the purity and the recovery rate reaching 99.9% or above is obtained. The method is simple in process, low in cost, high in efficiency and especially suitable for recycling selenium in wastewater in the heavy metal smelting industry, environmental pollution is reduced, and the utilization rate of selenium resources can be effectively increased.

Description

Technical Field

[0001] The invention belongs to the field of rare metal resource recovery and electrochemistry, and in particular relates to a method for efficiently recovering elemental selenium from selenium-containing wastewater. Background Art

[0003] Selenium can usually be recovered from selenium-containing wastewater through chemical precipitation, adsorption, membrane separation, biological methods or electrochemical technology. Chemical precipitation is one of the most commonly used methods. By adjusting the pH value of the wastewater or adding low-valent sulfide (Na2S, H2S) reducing agents, selenium is converted from the wastewater into a sparingly soluble compound precipitate (SeS2), or sulfur dioxide (SO2) sulfite is used to reduce selenium to elemental selenium. However, chemical precipitation is prone to introduce other pollutants and requires a large amount of secondary treatment. Adsorption technology uses the selective adsorption of selenium by adsorbent materials, such as activated carbon, iron oxides, aluminum oxides, manganese oxides, etc., to achieve the removal and recovery of selenium. Although the adsorbent can be recycled, it is mainly suitable for low-concentration wastewater. Membrane separation separates selenides through nanofiltration, reverse osmosis or electrodialysis technology, but membrane pollution and membrane cleaning problems are more prominent.

[0004] The copper smelting process is often accompanied by the generation of selenium-containing wastewater. The form of selenium in the wastewater is mainly in the form of selenite. Direct discharge will have a negative impact on the environment and cannot fully recover selenium resources. How to efficiently and environmentally friendly recover elemental selenium from selenium-containing wastewater has always been an urgent problem to be solved in the industry. Traditional methods for recovering selenium from selenium wastewater are often complicated to operate, costly and unfriendly to the environment. Therefore, it is of great practical significance to develop a simple, efficient and environmentally friendly method for recovering selenium. Summary of the invention

[0005] In view of the deficiencies of the above technical problems, the present invention proposes a method for efficiently recovering elemental selenium from selenium-containing wastewater. By optimizing the electrolyte concentration, electrolysis voltage, and current density, efficient recovery of selenium is achieved, and a set of process flow suitable for industrial application is provided, which has the characteristics of simple operation, low cost, and environmental friendliness.

[0006] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a method for efficiently recovering elemental selenium from selenium-containing wastewater, comprising the following steps: adding an electrolyte sodium hydroxide solution to the selenium-containing wastewater solution to adjust the pH; using graphite as the anode material and copper or alloy as the cathode material, controlling the voltage, current density, time and temperature for electrolysis; washing and drying the pure selenium deposit precipitated on the cathode to obtain elemental selenium.

[0007] As a preferred embodiment of the present invention, the electrolyte is composed of a selenium-containing wastewater solution and an electrolyte, the concentration of the electrolyte sodium hydroxide solution is 3 to 5 mol / L, and the sodium hydroxide solution adjusts the pH of the electrolyte to 1 to 4. The pH of the electrolyte of 1 to 4 can promote the ionization of selenous acid and enhance the conductivity; inhibit the side reaction of the combination of selenite ions and hydroxide ions, ensure the output and purity of selenium; and stabilize the electrode environment, reduce corrosion and passivation, and help the electrolysis to be continuous and stable.

[0008] As a preferred embodiment of the present invention, the voltage is 1.5 to 3V. When the voltage exceeds the range of 1.5-3V, it is difficult to obtain pure selenium cathode deposits. If the voltage is too low, the electrolysis reaction rate is too slow, or may not even occur, resulting in an extremely low recovery rate of selenium; if the voltage is too high, it will trigger a variety of side reactions, such as hydrogen ions may discharge in large quantities at the cathode to produce hydrogen, which reduces the recovery rate of selenium; at the same time, other impurity ions may also discharge and deposit at the cathode, thereby reducing the purity of elemental selenium. For example, under excessively high voltage, metal impurity ions in the solution may precipitate simultaneously with selenium, resulting in an impure product.

[0009] As a preferred embodiment of the present invention, the current density is 50-100 mA / cm 2 More preferably, the current density is 75 mA / cm 2 A current density that is too high will cause water electrolysis to produce hydrogen and oxygen, consume too much electricity, and make the electrolysis of selenious acid incomplete, thereby reducing the recovery rate of elemental selenium. A high current density may make the reaction on the electrode surface too intense, causing impurity ions to participate in the reaction and be mixed in the generated selenium, reducing the purity of elemental selenium; a current density that is too low will cause the electrolysis reaction rate to be too slow.

[0010] As a preferred embodiment of the present invention, the electrolysis temperature is 20-40°C. More preferably, the electrolysis temperature is 25°C. When the temperature is too high, the hydrogen evolution overpotential becomes small, resulting in a large amount of hydrogen precipitation, the pH rises and causes side reactions, the ion thermal motion intensifies and reduces the current efficiency, and the quality of the selenium deposit deteriorates; when the temperature is too low, the solution viscosity increases, making ion migration difficult, the resistance increases, the electrolysis rate decreases, and crystal precipitation is easy to block the electrode or diaphragm, hindering the electrolysis process.

[0011] As a preferred embodiment of the present invention, the electrolysis time is 1-24h. More preferably, the electrolysis time is 5 hours. The reaction time is too long, and the amount of elemental selenium generated per unit time decreases. Under the condition that other losses remain unchanged, it will cause the recovery rate to be difficult to improve. The system is in the electrolysis environment for a long time, which will increase the probability of impurities mixing into, thereby affecting the purity of elemental selenium.

[0012] The principle of the method for efficiently recovering elemental selenium from selenium-containing wastewater of the present invention is as follows: by controlling the voltage, current, concentration and pH of the electrolyte in the electrolytic circulation system to jointly maintain the stable operation and excellent reaction selectivity of the circulation system, the effect of precipitating high-purity and high-yield elemental selenium on the cathode is synergistically achieved.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] (1) The present invention constructs an electrolytic circulation system, and selenium ions in selenium-containing wastewater migrate to the cathode under the action of direct current, obtain electrons at the cathode, generate selenium element and adhere to the cathode.

[0015] (2) The present invention achieves efficient deposition of selenium by simplifying the process and optimizing the electrolysis conditions. The present invention obtains metallic selenium with a recovery rate and purity of more than 99.9%, is easy to operate, and is environmentally friendly, and is particularly suitable for industrial occasions where selenium needs to be extracted from selenium-containing wastewater. At the same time, the present invention also provides an electrolytic recovery system, which has a simple structure, is easy to operate, and has good stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The present invention is a flow chart of a method for efficiently recovering elemental selenium from selenium-containing wastewater.

[0017] Figure 2 This is the XRD pattern of elemental selenium prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0018] The present invention is not limited to the following embodiments, and various modifications and improvements can be made without departing from the spirit and scope of the present invention. For example, the electrolysis conditions can be adjusted and optimized according to actual conditions. In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0019] The present invention comprises an electrolytic cell, a power source, an anode, a cathode and an electrolyte to form a closed electrolytic circulation system; the electrolytic cell is used to accommodate the anode, the cathode and the electrolyte, the power source is used to provide the electric energy required for electrolysis, the anode and the cathode are respectively connected to the positive and negative electrodes of the power source, and the electrolyte circulation system is used to circulate the electrolyte to the electrolytic cell to maintain the uniformity and stability of the electrolyte.

[0020] Example 1

[0021] A method for efficiently recovering elemental selenium from selenium-containing wastewater comprises the following steps:

[0022] Appropriate anode and cathode materials are arranged in the electrolytic cell, graphite is used as the anode, and stainless steel sheet is used as the cathode; a selenious acid solution of selenium-containing wastewater with a concentration of 0.01 g / mL is added to the electrolytic cell as an electrolyte, and an appropriate amount of 3 mol / L electrolyte sodium hydroxide solution is added to adjust the pH to 1-4; the power supply is turned on to perform electrolysis, and the electrolysis conditions are: voltage 1.5 V, electrolysis current density 50 mA / cm 2 , electrolysis temperature 25°C, electrolysis time 24 hours; after the electrolysis, the pure selenium sediment was scraped off from the cathode, washed and dried to obtain elemental selenium. The filtrate after electrolysis was tested, and no selenium ions were detected. The purity of elemental selenium was as high as 99.9% or more by ICP-AES, and the recovery rate was as high as 99.9% or more.

[0023] Example 2

[0024] A method for efficiently recovering elemental selenium from selenium-containing wastewater comprises the following steps:

[0025] Appropriate anode and cathode materials are arranged in the electrolytic cell, graphite is used as the anode, and stainless steel sheet is used as the cathode; a selenious acid solution of selenium-containing wastewater with a concentration of 0.5 g / mL is added to the electrolytic cell as the electrolyte, and an appropriate amount of 4 mol / L electrolyte sodium hydroxide solution is added to adjust the pH to 1-4; the power supply is turned on to perform electrolysis, and the electrolysis conditions are: voltage 3V, electrolysis temperature 25°C, electrolysis current density 75 mA / cm 2 , electrolysis time 24 hours; after the electrolysis is completed, the pure selenium sediment is scraped off from the cathode, washed and dried to obtain elemental selenium. The filtrate after electrolysis is tested, no selenium ions are detected, and the purity of elemental selenium is as high as 99.9% or more by ICP-AES, and the recovery rate is more than 99.9%.

[0026] Example 3

[0027] A method for efficiently recovering elemental selenium from selenium-containing wastewater comprises the following steps:

[0028] Appropriate anode and cathode materials are arranged in the electrolytic cell, graphite is used as the anode, and a stainless steel sheet is used as the cathode; a selenious acid solution of selenium-containing wastewater with a concentration of 1 g / mL is added to the electrolytic cell as an electrolyte, and an appropriate amount of 5 mol / L electrolyte sodium hydroxide solution is added to adjust the pH to 1-4; the power supply is turned on to perform electrolysis, and the electrolysis conditions are: voltage 1.5 V, electrolysis temperature 25 ° C, electrolysis current density 75 mA / cm 2 , electrolysis time 24 hours; after the electrolysis is completed, the pure selenium sediment is scraped off from the cathode, washed and dried to obtain elemental selenium. The filtrate after electrolysis is tested, and no selenium ions are detected. The purity of elemental selenium is as high as 99.9% or more by ICP-AES, and the recovery rate is as high as 99.9% or more.

[0029] Example 4

[0030] A method for efficiently recovering elemental selenium from selenium-containing wastewater comprises the following steps:

[0031] The electrolytic cell was equipped with suitable anode and cathode materials, with graphite as the anode and stainless steel sheet as the cathode; a selenium-containing selenious acid solution with a concentration of 1 g / mL was added to the electrolytic cell as the electrolyte, and an appropriate amount of 3 mol / L electrolyte sodium hydroxide solution was added to adjust the pH to 1-4; the power supply was turned on to perform electrolysis, and the electrolysis conditions were: voltage 3 V, electrolysis temperature 40 ° C, electrolysis current density 75 mA / cm 2 , electrolysis time 24 hours; after the electrolysis is completed, the pure selenium sediment is scraped off from the cathode, washed and dried to obtain elemental selenium. The filtrate after electrolysis is tested, and no selenium ions are detected. The purity of elemental selenium is as high as 99.9% or more by ICP-AES, and the recovery rate is as high as 99.9% or more.

[0032] Example 5

[0033] A method for efficiently recovering elemental selenium from selenium-containing wastewater comprises the following steps:

[0034] The electrolytic cell was equipped with suitable anode and cathode materials, with graphite as the anode and stainless steel sheet as the cathode; a selenium-containing selenious acid solution with a concentration of 0.5 g / mL was added to the electrolytic cell as the electrolyte, and an appropriate amount of 4 mol / L electrolyte sodium hydroxide solution was added to adjust the pH to 1-4; the power supply was turned on to perform electrolysis, and the electrolysis conditions were: voltage 1.5 V, electrolysis temperature 40 ° C, electrolysis current density 75 mA / cm 2 , electrolysis time 24 hours; after the electrolysis is completed, the pure selenium sediment is scraped off from the cathode, washed and dried to obtain elemental selenium. The filtrate after electrolysis is tested, and no selenium ions are detected. The purity of elemental selenium is as high as 99.9% or more by ICP-AES, and the recovery rate is as high as 99.9% or more.

[0035] Comparative Example 1

[0036] The only difference between the method for efficiently recovering elemental selenium from selenium-containing wastewater described in this comparative example and the embodiment is that the current density in the electrolytic cell is 25 mA / cm 2 , the electrolysis temperature is 40° C. The purity of elemental selenium is above 49.9% and the recovery rate is 59.9%.

[0037] Comparative Example 2

[0038] A method for efficiently recovering elemental selenium from selenium-containing wastewater comprises the following steps:

[0039] Appropriate anode and cathode materials were set in the electrolytic cell, with graphite as the anode and stainless steel sheet as the cathode; a selenium-containing selenious acid solution with a concentration of 0.5 g / mL was added to the electrolytic cell as the electrolyte, and an appropriate amount of 4 mol / L sodium hydroxide solution was added to adjust the pH to 5; the power was turned on and electrolysis was performed, with the electrolysis temperature at 25°C, the voltage at 4V, and the electrolysis current density at 25 mA / cm 2 , electrolysis time 24 hours; after the electrolysis is completed, the elemental selenium is scraped off from the cathode, washed and dried to obtain the elemental selenium. The filtrate after electrolysis is tested, and the test results and the purity of selenium are shown in Table 1. The purity of the elemental selenium is above 49.9% and the recovery rate is 49.9%.

[0040] Effect example

[0041] The elemental selenium content was detected by testing the electrolytic deposits on the cathode sheets obtained in Examples 1-5 and Comparative Examples 1-2, and the results are shown in Table 1.

[0042] Table 1 Elemental selenium content detected by electrolytic deposition on cathode sheet

[0043]

[0044]

[0045] As can be seen from Table 1, the recovery rate of selenium in Examples 1-5 of the present invention is much higher than that in Comparative Examples 1-2; By comparing Examples 1-5 with Comparative Example 1, it can be seen that too low current density will lead to too slow electrolysis reaction rate, too long reaction time, and less elemental selenium generated per unit time, which will make it difficult to improve the recovery rate when other losses remain unchanged. When the temperature is too high, the hydrogen evolution overpotential becomes smaller, resulting in a large amount of hydrogen precipitation, the pH rises and triggers side reactions, the ion thermal motion intensifies and reduces the current efficiency, and the quality of the selenium deposit deteriorates.

[0046] According to Examples 1-5 and Comparative Example 2, as the pH increases, selenite is prone to side reactions, generating other forms of selenium and causing losses, thereby reducing the selenium recovery rate and purity; when the voltage is too high, water ionization intensifies, a large amount of hydrogen is released at the cathode, changing the solution pH and ion balance, and inducing side reactions, such as the formation of complex selenium compounds, which reduces the selenium purity and recovery rate and destroys the chemical stability of the electrolyte cycle.

[0047] The above is the entire content of the present invention. Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the protection scope of the present invention. Although the present invention is described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A method for efficiently recovering elemental selenium from selenium-containing wastewater, characterized in that: The method comprises adding electrolyte sodium hydroxide solution to the selenium-containing wastewater solution to adjust the pH, using graphite as the anode material and copper or alloy as the cathode material, controlling the voltage, current density, time and temperature for electrolysis; washing and drying the pure selenium sediment precipitated in the cathode to obtain elemental selenium.

2. A method for efficiently recovering elemental selenium from selenium-containing wastewater according to claim 1, characterized in that: The selenium-containing wastewater solution comprises a selenious acid solution, and the concentration of the electrolyte sodium hydroxide solution is 3-5 mol / L; the pH value is 1-4.

3. A method for efficiently recovering elemental selenium from selenium-containing wastewater according to claim 1, characterized in that: The alloy is stainless steel.

4. A method for efficiently recovering elemental selenium from selenium-containing wastewater according to claim 1, characterized in that: The voltage is 1.5 to 3V.

5. A method for efficiently recovering elemental selenium from selenium-containing wastewater according to claim 1, characterized in that: The current density is 50-100 mA / cm 2 .

6. A method for efficiently recovering elemental selenium from selenium-containing wastewater according to claim 1, characterized in that: The electrolysis temperature is 20-40°C.

7. A method for efficiently recovering elemental selenium from selenium-containing wastewater according to claim 1, characterized in that: The electrolysis time is 1-24h.

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