A treatment method for efficiently removing selenium from waste acid

Abstract

The application discloses a treatment method for efficiently removing selenium from waste acid, and specifically comprises the following steps: preheating waste acid to be treated for removing selenium, adding sulfuric acid to adjust the H + concentration of 4-6 mol / L, then adding a reducing agent sodium sulfite Na2SO3, and fully stirring and mixing; controlling the temperature to be 55-70 DEG C to perform a first-stage reaction, then adding a composite catalyst prepared by mixing sodium thiosulfate Na2S2O3 and iodine I2, stirring and mixing, continuing to perform a deep reaction, and performing solid-liquid separation after filtration when the reaction is completed. The application uses sodium sulfite reduction, iodine and sodium thiosulfate catalysis as a substitute for the traditional SO2 reduction mode, solves the problem that the traditional SO2 reduction method is limited by pH liquid, accelerates the reaction rate through iodine and sodium thiosulfate catalysis, simultaneously solves the problem that the traditional sulfite cannot reduce selenium-containing substances other than selenite, and improves the reduction effect of selenium.

Description

Technical Field

[0001] This invention relates to the field of resource recycling technology, specifically to a method for efficiently removing selenium from waste acid. Background Technology

[0002] During copper smelting, the smelting flue gas is rich in SO2 due to the sulfur content of the copper concentrate. After dust collection, washing, and purification, it is sent to the acid production system. The dilute sulfuric acid produced during the washing process contains heavy metals and impurities, requiring periodic open-circuit treatment. This portion of the open-circuit acidic wastewater is also known as waste acid. Waste acid contains 15-20 mg / L of selenium, mainly in the form of selenite, which is toxic to organisms. Common waste acid treatment methods, such as sulfide precipitation and arsenic removal with iron salts, primarily remove metal elements through precipitation, making it difficult to treat selenium. The treated liquid does not meet national emission standards.

[0003] Current methods for treating selenium-containing wastewater include physical, chemical, and biological methods. Physical methods utilize the high specific surface area or porous structure of adsorbent materials to remove selenium; however, these materials are difficult to regenerate and require periodic replacement. Adsorption selectivity is also limited by coexisting ions, particularly SO42-. 2- Significant interference. Biological methods degrade selenium through the metabolism of microorganisms, but the types of reducing bacteria are limited, and the reaction conditions, such as waste liquid composition and pH, are highly demanding, resulting in long reaction times and difficulties in industrial application. Chemical methods, however, are currently a more mature approach in industrial applications. (Fe...) 3+ Al 3+ Plasma flocculation coprecipitation and SO2 reduction are the most widely used methods. Flocculation coprecipitation produces a large amount of coprecipitated sludge, requiring secondary treatment of pollutants. SO2 reduction has good recovery efficiency, but it is only suitable for wastewater with a pH around 6. It has low reduction efficiency for acidic liquids and poses risks of gaseous reducing agent storage and spillage. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the present invention aims to provide a method for efficiently removing selenium from waste acid.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for efficiently removing selenium from waste acid, the specific process of which is as follows:

[0007] The waste acid to be deselenized is preheated, and sulfuric acid is added to adjust the pH to H₂. + The concentration is 4-6 mol / L. Then, sodium sulfite (Na2SO3) is added as a reducing agent and stirred thoroughly. The temperature is controlled to rise to 55-70℃ for a first-stage reaction. Then, a composite catalyst prepared by mixing sodium thiosulfate (Na2S2O3) and iodine (I2) is added, stirred, and the reaction continues. After the reaction is completed, the solid and liquid are separated by filtration.

[0008] Furthermore, the waste acid to be deselenized is preheated to 40°C.

[0009] Furthermore, the molar amount of the reducing agent sodium sulfite (Na2SO3) is 1.1-1.2 times the theoretical value.

[0010] Furthermore, the reaction time is 5 minutes.

[0011] Furthermore, the amount of I2 used is 0.3-0.5 mol of I2 per liter of waste acid, and the molar ratio of Na2S2O3 to I2 is (3-5):1.

[0012] Furthermore, at room temperature, I2 was completely dissolved in an appropriate amount of water, and then Na2S2O3 was slowly and uniformly added and stirred until the solution was completely decolorized to obtain the composite catalyst.

[0013] Furthermore, the deep reaction time is 10-15 minutes.

[0014] The beneficial effects of this invention are as follows:

[0015] This invention utilizes the stepwise hydrolysis of solid sodium sulfite in acidic solutions, producing sulfurous acid with strong reducing properties under strongly acidic conditions. This sulfurous acid can be used as a substitute for sulfur dioxide reduction in acidic media, solving safety issues related to the storage and transportation of reducing agents and the environmental pollution problem of SO2 gas leakage during the reduction process. Preheating the liquid before adding sodium sulfite prevents excessively rapid local temperature increases and avoids the amount of SO2 generated by sodium sulfite decomposition exceeding the liquid's soluble capacity, thus preventing SO2 leakage and avoiding environmental pollution and reducing agent loss, ensuring the reduction effect.

[0016] Utilizing the catalytic properties of halide ions, iodine and sodium thiosulfate are pre-mixed at room temperature, allowing all iodine to be oxidized to iodide ions beforehand. This oxidizes the reduction of selenium in waste acid, increasing the reaction rate. Furthermore, it can reduce Se(VI) in selenic acid, which sodium sulfite cannot reduce, to Se(IV), achieving deep arsenic removal. The reaction equation is as follows:

[0017] I₂ + 2S₂O₃ 2- =2I - +S4O6 2-

[0018] SeO3 2- +4I - +6H + →2I₂ + Se + 3H₂O

[0019] SeO4 2- +4I - +4H + →SeO3 2-+2I₂ + 2H₂O

[0020] The addition of sodium thiosulfate does not introduce new elements. Furthermore, excess sodium thiosulfate can re-oxidize the iodine generated in the selenium reduction reaction back into iodide ions, achieving a cyclic catalytic effect and further promoting the selenium reduction reaction. The stepwise addition of the composite catalyst prepared by mixing iodine and sodium thiosulfate with sodium sulfite can also minimize the risk of selenium being oxidized to sulfate before being reduced by sulfite, thus preventing the loss of reducing agent and affecting the selenium reduction efficiency.

[0021] Using sodium sulfite reduction and iodine and sodium thiosulfate catalysis as an alternative to the traditional SO2 reduction method solves the problem of pH-limited liquids in the traditional SO2 reduction method. Iodine and sodium thiosulfate catalysis accelerate the reaction rate and solve the problem that traditional sulfites cannot reduce selenite-containing substances other than selenite, thus improving the selenium reduction effect. Attached Figure Description

[0022] Figure 1 This is a flowchart illustrating the methods of various embodiments of the present invention. Detailed Implementation

[0023] The present invention will be further described below with reference to the accompanying drawings. It should be noted that this embodiment is based on the present technical solution and provides detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to this embodiment.

[0024] Example 1

[0025] like Figure 1 As shown, the waste acid to be deselenized is preheated to 40°C, and sulfuric acid is added to adjust the acidity to H₂. + Se(VI) in selenic acid was reduced by adding Na₂SO₃ at a concentration of 4 mol / L, 1.1 times the theoretical molar amount. After stirring for 5 min, the temperature was slowly increased to 55 °C, and a prepared composite catalyst was added, with I₂ added at a rate of 0.5 mol per liter of waste acid, and the molar ratio of Na₂S₂O₃:I₂ being 3:1. After thorough mixing, the reaction was allowed to proceed for 10 min, followed by filtration. The selenium concentration in the filtrate was 89 μg / L, and the selenium reduction removal rate was 99.41%.

[0026] Example 2

[0027] like Figure 1 As shown, the waste acid to be deselenized is preheated to 40°C, and sulfuric acid is added to adjust the acidity to H₂. +Se(VI) in selenic acid was reduced by adding Na₂SO₃ at a concentration of 6 mol / L, 1.2 times the theoretical molar amount. After stirring for 5 min, the temperature was slowly increased to 70℃, and a prepared composite catalyst was added, with I₂ added at a rate of 0.5 mol per liter of waste acid, and a Na₂S₂O₃:I₂ ratio of 5:1 (molar ratio). After thorough mixing, the reaction was allowed to proceed for 15 min, followed by filtration. The selenium concentration in the filtrate was 44 μg / L, and the selenium reduction removal rate was 99.75%.

[0028] Example 3

[0029] like Figure 1 As shown, the waste acid to be deselenized is preheated to 40°C, and sulfuric acid is added to adjust the acidity to H₂. + Se(VI) in selenic acid was reduced by adding Na₂SO₃ at a concentration of 4 mol / L, 1.2 times the theoretical molar amount. After stirring for 5 min, the temperature was slowly increased to 55℃, and a prepared composite catalyst was added, with I₂ added at a rate of 0.3 I₂ per liter of waste acid, and a Na₂S₂O₃:I₂ ratio of 4:1 (molar ratio). After thorough mixing, the reaction was allowed to proceed for 15 min, followed by filtration. The selenium concentration in the filtrate was 44 μg / L, and the selenium reduction removal rate was 99.82%.

[0030] For those skilled in the art, various corresponding changes and modifications can be made based on the above technical solutions and concepts, and all such changes and modifications should be included within the protection scope of the claims of this invention.

Claims

1. A method for efficiently removing selenium from waste acid, characterized in that, The specific process is as follows: The waste acid to be deselenized is preheated, and sulfuric acid is added to adjust the pH to H₂. + The concentration is 4-6 mol / L. Then, sodium sulfite (Na2SO3) is added as a reducing agent and stirred thoroughly. The temperature is controlled to rise to 55-70℃ for a first-stage reaction. Then, a composite catalyst prepared by mixing sodium thiosulfate (Na2S2O3) and iodine (I2) is added, stirred, and the reaction continues. After the reaction is completed, the solid and liquid are separated by filtration. The amount of I2 used is 0.3-0.5 mol of I2 per liter of waste acid, and the molar ratio of Na2S2O3 to I2 is (3-5):

1. At room temperature, I2 is first completely dissolved in an appropriate amount of water, and then Na2S2O3 is slowly and uniformly added. The mixture is stirred until the solution is completely decolorized to obtain the composite catalyst.

2. The processing method according to claim 1, characterized in that, Preheat the waste acid to be deselenized to 40°C.

3. The processing method according to claim 1, characterized in that, The molar amount of the reducing agent sodium sulfite (Na2SO3) is 1.1-1.2 times the theoretical value.

4. The processing method according to claim 1, characterized in that, The reaction time is 5 minutes.

5. The processing method according to claim 1, characterized in that, The deep reaction time is 10-15 minutes.

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