Enrichment, separation and extraction method of selenium in waste gypsum

Abstract

The invention discloses a method for enriching, separating and extracting selenium in waste gypsum, and belongs to the field of extraction of valuable elements in solid waste. The method for enriching, separating and extracting selenium in waste gypsum comprises the following steps: mixing waste gypsum with water, and uniformly stirring to obtain mixed slurry; the mixed slurry is guided into a multi-cathode electrochemical reactor to be subjected to an electrolytic reaction, and generated anode mud is collected; transferring the anode mud into a closed reaction kettle, and introducing SO2 for reaction to obtain a selenium-containing suspension; and carrying out vacuum evaporation concentration on the selenium-containing suspension to obtain a selenium product. According to the method, electrochemical separation is adopted to replace traditional roasting or acid-base leaching, and efficient extraction of selenium in the waste gypsum is achieved through electrochemical directional regulation and control, waste gas synergistic reduction and resource recycling; the problems of low separation efficiency, high energy consumption and secondary pollution risk caused by tight combination of selenium and calcium sulfate when an existing selenium extraction process is applied to waste gypsum can be effectively solved.

Description

Technical Field

[0001] The present invention belongs to the field of extraction of valuable elements from solid waste, and relates to a method for enriching, separating and extracting selenium from waste gypsum. Background Art

[0002] The resource utilization of industrial solid waste is an important research direction in the chemical industry. Waste gypsum, as a typical industrial by-product, mainly includes phosphogypsum, flue gas desulfurization gypsum, titanium gypsum and fluorogypsum. Such waste gypsum often contains selenium. For example, the selenium content in flue gas desulfurization gypsum can reach 0.5% - 1%. As an important industrial raw material, selenium is widely used in fields such as electronics, metallurgy, and agriculture. Its efficient recovery has both economic value and environmental significance.

[0003] At present, the extraction technology of selenium mainly targets selenium-rich materials such as copper anode slime and smelting slag. Traditional methods include two categories: acid methods and alkali methods. Acid method processes such as sulfation roasting have a relatively high recovery rate, but there are problems of sulfur dioxide pollution and harsh reaction conditions; alkali method processes convert selenium into water-soluble salts through alkaline roasting, but require high-concentration selenium raw materials and are prone to waste liquid pollution.

[0004] For the recovery of selenium from waste gypsum, the existing technology faces the following challenges: First, selenium in waste gypsum is mostly combined with components such as calcium sulfate, and it is difficult for traditional roasting methods to selectively release selenium compounds; second, direct acid leaching easily dissolves a large amount of calcium-based impurities, resulting in difficulties in subsequent separation; third, the existing electrolysis or reduction processes are not optimized for the characteristics of waste gypsum, and there are problems such as low selenium recovery rate, high energy consumption or risk of secondary pollution. Therefore, it is urgent to develop a selenium recovery method suitable for the characteristics of waste gypsum to achieve the resource utilization goal of high efficiency, low consumption and environmental protection. Summary of the Invention

[0005] The technical problem to be solved by the present invention is the problems of low separation efficiency, high energy consumption and risk of secondary pollution caused by the tight combination of selenium and calcium sulfate when the existing selenium extraction process is applied to waste gypsum.

[0006] To achieve the above application purpose, the technical solution adopted in the present application is as follows.

[0007] In a first aspect, the present invention provides a method for enriching, separating and extracting selenium from waste gypsum, comprising the following steps:

[0008] S1. Mix waste gypsum with water and stir evenly to obtain a mixed slurry;

[0009] S2. Introduce the mixed slurry into a multi-cathode electrochemical reactor for electrolysis reaction, and collect the anode mud generated;

[0010] S3. Transfer the anode mud to a closed reaction kettle, introduce SO2 for reaction to obtain a selenium-containing suspension;

[0011] S4. Vacuum evaporative concentration is carried out on the selenium-containing suspension to obtain a selenium crystal product.

[0012] In the above step S1, the solid-liquid ratio of waste gypsum to water is 1 g: 5-20 mL; the stirring speed is 150-300 rpm, and the stirring time is 30-60 min.

[0013] In the above step S1, the waste gypsum is flue gas desulfurization gypsum containing selenium elements, or other industrial by-product gypsum containing selenium elements.

[0014] In the above step S2, the multi-cathode electrochemical reactor adopts a double-wall structure, the inner wall is the anode, and multiple cathodes are evenly distributed in the middle. Pure water is filled in the double-wall sandwich.

[0015] Furthermore, in the multi-cathode electrochemical reactor, the cathode material is an alloy, ruthenium iridium, graphite, titanium or platinum electrode, in the shape of a barb, stacked spiral or spiral, and the number is 2-8.

[0016] Furthermore, in the multi-cathode electrochemical reactor, the anode material is an alloy or a ruthenium iridium electrode.

[0017] In the above step S2, the electrolysis voltage is 0.4-36 V, and the electrolysis time is 15-60 min.

[0018] In the above step S3, SO2 is introduced from the bottom of the reaction kettle to form microbubbles; the concentration of the SO2 is 10%-100%, and the flow rate is 0.5-1.5 m 3 / min.

[0019] Furthermore, the SO2 is SO2 separated from smelting flue gas and coal-fired flue gas.

[0020] In the above step S3, the reaction temperature is 45-90 °C, and the pressure is 0.1-1.5 MPa.

[0021] In the above step S4, the temperature of vacuum evaporative concentration is 90-150 °C.

[0022] Furthermore, water is evaporated by vacuum evaporative concentration, and the water vapor is condensed and refluxed to step S1 to be mixed with the waste gypsum.

[0023] The beneficial effects of the present invention are as follows: The present invention provides a method for recovering selenium from selenium-containing waste gypsum. Aiming at the characteristics that selenium in waste gypsum is mainly combined with calcium sulfate in the form of selenate, a multi-cathode electrochemical reduction technology is adopted. During the electrolysis process, sulfuric acid is generated in the cathode area to dissolve selenate to form SeO2. At the same time, part of the selenium and SeO2 migrate to the anode with anions and are deposited as anode mud, realizing the directional enrichment of selenium elements. The selenium extraction rate of this method reaches 90%-98%, and the process is simple and the cost is controllable.

[0024] The present invention uses electrochemical separation to replace traditional roasting or acid-base leaching. Through electrochemical directional regulation, waste gas co-reduction, and resource recycling, the efficient extraction of selenium from waste gypsum is realized. At the same time, the problems of sulfur dioxide pollution and high energy consumption are avoided, providing a new way for the resource utilization of selenium-containing waste gypsum, and having both environmental benefits and resource recycling value. Specific Embodiments

[0025] In order to make the technical problems, technical solutions, and beneficial effects to be solved by the present application clearer, the present application will be further described in detail below in conjunction with the embodiments. Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those of ordinary skill in the art.

[0026] The present invention discloses a method for enriching, separating, and extracting selenium from waste gypsum, and the specific steps are as follows.

[0027] (1) Preparation of waste gypsum slurry: Mix waste gypsum and water at a solid-liquid ratio of 1 g:5 - 20 mL, and stir at a speed of 150 - 300 rpm for 30 - 60 min to form a uniform mixed slurry.

[0028] The above waste gypsum is flue gas desulfurization gypsum containing selenium elements, or other industrial by-product gypsum containing selenium elements.

[0029] (2) Multi-cathode electrochemical reduction: Feed the mixed slurry into a multi-cathode electrochemical reactor, and electrolyze at a voltage of 0.4 - 36 V for 15 - 60 min. The sulfuric acid generated in the cathode area dissolves the selenate ions in the waste gypsum to form SeO2, and at the same time, part of the SeO2 migrates to the anode surface with anions and deposits as anode mud containing SeO2.

[0030] The above reactor adopts a double-wall structure: the inner wall is an anode composed of alloy or ruthenium-iridium conductive material, and 2 - 8 thorn-shaped, stacked spiral-shaped or spiral-shaped cathodes (the material is alloy, ruthenium-iridium, graphite, titanium or platinum electrode) are evenly distributed inside the reaction, and the double-wall interlayer is filled with pure water. The present invention increases the effective reaction area through a multi-cathode layout. Structures such as thorns and spirals can strengthen the local current density, promote the rapid generation of sulfuric acid and dissolve selenate ions; at the same time, setting the double-wall structure anode has both conductive and heat dissipation functions, and directionally migrates selenium compounds to the anode to form enriched mud.

[0031] (3) Reduction of SO2 to extract elemental selenium: Transfer the anode mud containing SeO2 to a closed reaction kettle, and introduce SO2 gas (concentration 10% - 100%, flow rate 0.5 - 1.5 m 3 / min) from the bottom to form microbubbles to fully contact with SeO2, and react under the conditions of 45 - 90 °C and 0.1 - 1.5 MPa to reduce SeO2 to elemental selenium and obtain a selenium-containing suspension.

[0032] In the above reduction reaction, SO2 with strong reducibility is used to reduce SeO2 to elemental selenium in an acidic environment. The SO2 used is the SO2 separated from smelting flue gas and coal-fired flue gas (low-concentration SO2 is SO2 diluted by nitrogen), realizing "treating waste with waste" and reducing the reagent cost.

[0033] (4) Evaporation crystallization and resource recycling: The selenium-containing suspension is vacuum-evaporated and concentrated at 90-150 °C, and the water is evaporated to dryness to obtain selenium products; the evaporation condensate is returned to step (1) for recycling.

[0034] Specific embodiments will be listed below to explain the solution of the present invention. Those skilled in the art will understand that the following embodiments are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. For those without specific technical or conditions noted in the embodiments, the technologies or conditions described in the literature in this field or according to the product instructions are followed. For reagents or instruments without indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0035] Example

[0036] The chemical composition of the waste gypsum (flue gas desulfurization gypsum containing Se) used in this example is shown in Table 1.

[0037] Table 1 Chemical composition of waste gypsum

[0038]

[0039] Example 1: Enrichment, separation and extraction of selenium from waste gypsum. The specific test steps are as follows:

[0040] (1) Mix the flue gas desulfurization gypsum containing Se shown in Table 1 with water at a solid-liquid ratio of 1 g:5 mL, and stir at a speed of 150 rpm for 30 min to form a uniform mixed slurry.

[0041] (2) Feed the mixed slurry into a multi-cathode electrochemical reactor, electrolyze at a voltage of 0.4 V for 15 min, and collect the produced anode mud containing SeO2; the anode material of the multi-cathode electrochemical reactor is an alloy, and the cathode material is a spiky alloy, with a quantity of 2.

[0042] (3) Transfer the anode mud containing SeO2 to a closed reaction kettle, and introduce SO2 gas (concentration 10%, flow rate 0.5 m 3 / min) from the bottom to form microbubbles to fully contact with SeO2, and react under the conditions of 45 °C and 0.1 MPa to obtain a selenium-containing suspension.

[0043] (4) Vacuum-evaporate and concentrate the selenium-containing suspension at 90 °C, and evaporate the water to dryness to obtain selenium crystal products; after detection, the extraction efficiency of the selenium crystal products in Example 1 is 90%, and the purity of the selenium crystal products is 85%.

[0044] Example 2: Enrichment, separation and extraction of selenium from waste gypsum. The specific experimental steps are as follows:

[0045] (1) Mix the flue gas desulfurization gypsum containing Se shown in Table 1 with water at a solid-liquid ratio of 1 g:10 mL, and stir at a speed of 200 rpm for 60 min to form a uniform mixed slurry.

[0046] (2) Feed the mixed slurry into a multi-cathode electrochemical reactor, electrolyze at 18 V for 45 min, and collect the anodic mud containing SeO2; the anode material of the multi-cathode electrochemical reactor is ruthenium-iridium, and the cathode material is spiral ruthenium-iridium, with a quantity of 6.

[0047] (3) Transfer the anodic mud containing SeO2 to a closed reaction kettle, introduce SO2 gas (concentration 50%, flow rate 1 m 3 / min) from the bottom to form microbubbles in full contact with SeO2, and react under the conditions of 90 °C and 1 MPa to obtain a selenium-containing suspension.

[0048] (4) Vacuum-evaporate and concentrate the selenium-containing suspension at 150 °C, and evaporate the water to dryness to obtain a selenium crystal product; after detection, the extraction efficiency of the selenium crystal product in Example 2 is 98%, and the purity of the selenium crystal product is 90%.

[0049] Example 3: Enrichment, separation and extraction of selenium from waste gypsum. The specific experimental steps are as follows:

[0050] (1) Mix the flue gas desulfurization gypsum containing Se shown in Table 1 with water at a solid-liquid ratio of 1 g:20 mL, and stir at a speed of 300 rpm for 45 min to form a uniform mixed slurry.

[0051] (2) Feed the mixed slurry into a multi-cathode electrochemical reactor, electrolyze at 36 V for 60 min, and collect the anodic mud containing SeO2; the anode material of the multi-cathode electrochemical reactor is an alloy, and the cathode material is spiral titanium, with a quantity of 8.

[0052] (3) Transfer the anodic mud containing SeO2 to a closed reaction kettle, introduce SO2 gas (concentration 100%, flow rate 1.5 m 3 / min) from the bottom to form microbubbles in full contact with SeO2, and react under the conditions of 75 °C and 1.5 MPa to obtain a selenium-containing suspension.

[0053] (4) Vacuum-evaporate and concentrate the selenium-containing suspension at 100 °C, and evaporate the water to dryness to obtain a selenium crystal product; after detection, the extraction efficiency of the selenium crystal product in Example 2 is 95%, and the purity of the selenium crystal product is 81%.

Claims

1. Method for enriching, separating and extracting selenium from waste gypsum, characterized in that, It includes the following steps: S1. Mix waste gypsum with water and stir evenly to obtain a mixed slurry; S2. Introduce the mixed slurry into a multi-cathode electrochemical reactor for electrolysis reaction and collect the anode mud produced; S3. Transfer the anode mud to a closed reaction kettle, introduce SO2 for reaction to obtain a selenium-containing suspension; S4. Perform vacuum evaporation and concentration on the selenium-containing suspension to obtain a selenium product.

2. The method for enriching, separating and extracting selenium from waste gypsum according to claim 1, characterized in that: In step S1, the solid-liquid ratio of waste gypsum to water is 1g:5 - 20mL; the stirring speed is 150 - 300rpm, and the stirring time is 30 - 60min.

3. The method for enriching, separating and extracting selenium from waste gypsum according to claim 1, wherein: In step S1, the waste gypsum is flue gas desulfurization gypsum containing selenium elements or other industrial by-product gypsum containing selenium elements.

4. The method for enriching, separating and extracting selenium from waste gypsum according to claim 1, wherein: In step S2, the electrolysis voltage is 0.4 - 36V, and the electrolysis time is 15 - 60min.

5. The method for enriching, separating and extracting selenium from waste gypsum according to claim 1, characterized in that: In step S2, the multi-cathode electrochemical reactor adopts a double-wall structure, with the inner wall as the anode, and multiple cathodes are evenly distributed in the middle. Pure water is filled in the double-wall sandwich.

6. The method for enriching, separating and extracting selenium from waste gypsum according to claim 5, characterized in that: In the multi-cathode electrochemical reactor, the cathode material is an alloy, ruthenium-iridium, graphite, titanium or platinum electrode, in a barbed shape, stacked spiral shape or spiral shape, and the number is 2 - 8.

7. The method for enriching, separating and extracting selenium from waste gypsum according to claim 5, characterized in that: In the multi-cathode electrochemical reactor, the anode material is an alloy or ruthenium-iridium electrode.

8. The method for enriching, separating and extracting selenium from waste gypsum according to claim 1, wherein: In step S3, SO2 is introduced from the bottom of the reactor to form microbubbles; the concentration of the SO2 is 10% - 100%, and the flow rate is 0.5 - 1.5 m 3 / min.

9. The method for enriching, separating and extracting selenium from waste gypsum according to claim 1, characterized in that: In step S3, the reaction temperature is 45 - 90°C, and the pressure is 0.1 - 1.5MPa.

10. The method for enriching, separating and extracting selenium from waste gypsum according to claim 1, wherein: In step S4, the temperature of vacuum evaporation and concentration is 90 - 150°C.

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