A method and device for treating thallium- and arsenic-containing waste acid

Abstract

The present invention discloses a method for treating acid wastewater containing thallium and arsenic, comprising the following steps: S1 adding the acid wastewater to limestone for neutralization, and controlling the pH value of the effluent after filtration to be 2-4; S2 feeding the effluent in step S1 into the first reaction tank of the first-stage oxidation section, adding ferrous sulfate in the first reaction tank, and the effluent enters the second reaction tank of the first-stage oxidation section, and adding hydrogen peroxide in the second reaction tank; S3 feeding the effluent from the second reaction tank of the first-stage oxidation section into the first-stage neutralization tank, adding lime milk, and controlling the pH value of the effluent after filtration to be 8.5-9.5; S4 feeding the effluent from the first-stage neutralization section in step S3 into the first reaction tank of the second-stage oxidation section, adding lime milk and ferrous sulfate, the effluent is fed into the second reaction tank of the second-stage oxidation section, introducing compressed air, controlling the pH value to be 8.5-9.5, and filtering after the reaction to obtain the treated acid wastewater. The method of the present invention can effectively remove thallium and arsenic in the acid wastewater, and the removal rate can reach more than 99.9%.

Description

Technical Field

[0001] The present invention belongs to the technical field of waste acid treatment, and particularly relates to a method for treating waste acid containing thallium and arsenic. In particular, the present invention also relates to an apparatus for treating waste acid containing thallium and arsenic. Background Art

[0002] During the metal smelting process, a large amount of waste acid is generated, which generally contains high concentrations of harmful components such as acid, thallium, arsenic, etc., and is extremely harmful to humans and organisms. Therefore, it is necessary to carry out environmental protection treatment. The most commonly used methods for treating sewage and waste acid are chemical deposition methods. Generally, alkaline substances such as hydroxides and sulfides, as well as coagulants such as iron salts and alum (aluminum sulfate) are selected. After multi-stage neutralization, aeration, sedimentation, and filtration, through solid-liquid separation, the sediments are removed, and the sewage and waste acid are purified and discharged up to standard. At present, it is difficult to carry out environmental protection treatment on heavily polluted sewage and waste acid. Although there are various treatment methods, there are still many disadvantages, such as high operating costs, large floor areas, poor working environments, etc. Moreover, the quality of the supernatant after separation is poor, making it difficult to meet the discharge standards or quickly return as industrial water for recycling, resulting in environmental pollution and waste of water resources.

[0003] Therefore, there is an urgent need to develop an efficient, convenient, and environmentally friendly method for treating waste acid. Summary of the Invention

[0004] The present invention is based on the inventor's discovery and understanding of the following facts and problems: The treatment method of waste acid has always been a difficult problem in the smelting industry. With the increasingly severe environmental protection situation, the conventional treatment process of waste acid often fails to meet the discharge requirements. For the treatment process of waste acid with high contents of thallium and arsenic, it usually needs to adopt multi-stage oxidation, neutralization and combine with sulfidation or flocculation processes, with complex processes, long treatment flows, and high costs.

[0005] The present invention aims to solve at least one of the technical problems in the related technologies to some extent. For this purpose, an embodiment of the first aspect of the present invention provides a method for treating waste acid containing thallium and arsenic, which can effectively remove thallium and arsenic in the waste acid, has a short process flow, the treated water quality is stably up to standard, is easy to maintain, the medicaments are commonly available, and the amount of slag is small, having a good ecological environment effect, and finally achieving the purpose of reducing slag and zero discharge.

[0006] A method for treating waste acid containing thallium and arsenic according to an embodiment of the first aspect of the present invention includes the following steps:

[0007] S1. Waste acid neutralization section

[0008] Add waste acid to limestone for neutralization, and control the pH value of the liquid discharged after filtration to be 2 - 4;

[0009] S2. First-stage oxidation section

[0010] Feed the liquid discharged in step S1 into the first reaction tank of the first-stage oxidation section. Add ferrous sulfate to the first reaction tank, and the effluent enters the second reaction tank of the first-stage oxidation section. Add hydrogen peroxide to the second reaction tank.

[0011] S3. First-stage neutralization section

[0012] Feed the effluent from the second reaction tank of the first-stage oxidation section into the first-stage neutralization tank. Add lime milk, and control the pH value of the filtered effluent to be 8.5 - 9.5.

[0013] S4. Second-stage oxidation section

[0014] Feed the effluent from the first-stage neutralization section in step S3 into the first reaction tank of the second-stage oxidation section. Add lime milk and ferrous sulfate. The effluent is sent to the second reaction tank of the second-stage oxidation section, and compressed air is introduced. Control the pH value to be 8.5 - 9.5. After the reaction, filter to obtain the treated liquid of the waste acid.

[0015] The advantages and technical effects brought by the independent claims of the embodiment according to the first aspect of the present invention are as follows: 1. For waste acid containing arsenic and thallium, first use limestone for neutralization, and then perform first-stage oxidative Fenton oxidation to oxidize low-valent thallium into trivalent thallium and trivalent arsenic into pentavalent arsenic. Add lime milk in the first-stage neutralization section to remove most of the thallium, control the pH value of the effluent from the first-stage neutralization section to be 8.5 - 9.5, and perform second-stage oxidation. Add lime milk and ferrous sulfate in the second-stage oxidation to oxidize divalent iron into trivalent iron. Trivalent iron reacts with calcium hydroxide to form ferric hydroxide, which adsorbs and co-precipitates with iron arsenate, calcium arsenate, thallium hydroxide that has not been separated in the first-stage neutralization, etc., to solidify arsenic and thallium, achieve solid-liquid separation, effectively remove thallium and arsenic in the waste acid. By controlling the pH value in the second-stage oxidation section to be 8.5 - 9.5, the best adsorption co-precipitation of ferric hydroxide with iron arsenate, calcium arsenate, thallium hydroxide, etc. is achieved. The solidification and separation of thallium and arsenic are directly completed in the second-stage oxidation section, reducing process steps such as the neutralization section, sulfidation section, and flocculation section after the second-stage oxidation section in the traditional process, reducing the consumption of chemicals, and controlling the pH at 8.5 - 9.5, which has little corrosion to the equipment and can extend the service life of the equipment; 2. The method of the embodiment of the present invention can effectively remove thallium and arsenic in the waste acid, with a removal rate reaching more than 99.9%. The process flow is short, the effluent meets the standards stably, it is easy to maintain, the chemicals are commonly available, and the amount of slag is small, having a good ecological environment effect, and finally achieving the purpose of reducing slag and zero discharge.

[0016] According to the method for treating waste acid containing thallium and arsenic of the embodiment of the first aspect of the present invention, in step S1, the sludge obtained by filtration is fed into the smelting furnace.

[0017] A method for treating thallium- and arsenic-containing waste acid according to an embodiment of the first aspect of the present invention further includes a step S5 membrane treatment section, where the post-treatment liquid of the waste acid in step S4 is sent to a membrane treatment device for treatment. The fresh water obtained from the membrane treatment device is returned for use as process water, and the high-salt water is used for slag flushing makeup water.

[0018] A method for treating thallium- and arsenic-containing waste acid according to an embodiment of the first aspect of the present invention further includes a step S6 evaporation and crystallization section, where the high-salt water generated in step S5 is sent to an evaporation and crystallization device for treatment, and the condensed water generated by evaporation and crystallization is returned for use as process water.

[0019] A method for treating thallium- and arsenic-containing waste acid according to an embodiment of the first aspect of the present invention, wherein in step S2, the oxidation-reduction potential of the second reaction tank is 600 - 800 mv.

[0020] A method for treating thallium- and arsenic-containing waste acid according to an embodiment of the first aspect of the present invention, wherein in step S4, the mass ratio of Fe in the added ferrous sulfate to As in the waste acid is 10 - 14:1.

[0021] An embodiment of the second aspect of the present invention also provides a device for treating thallium- and arsenic-containing waste acid, which can effectively remove thallium and arsenic in the waste acid, and the removal rate reaches more than 99.9%.

[0022] A device for treating thallium- and arsenic-containing waste acid according to an embodiment of the second aspect of the present invention includes a waste acid neutralization reaction tank, a first reaction tank in the first-stage oxidation section, a second reaction tank in the first-stage oxidation section, a first-stage neutralization tank, a first-stage filtration device, a first reaction tank in the second-stage oxidation section, a second reaction tank in the second-stage oxidation section, and a second-stage filtration device connected in sequence. Among them, the waste acid neutralization reaction tank is provided with a limestone inlet, the first reaction tank in the first-stage oxidation section is provided with a ferrous sulfate inlet, the second reaction tank in the first-stage oxidation section is provided with a hydrogen peroxide inlet, the first-stage neutralization tank is provided with a lime milk inlet, the first reaction tank in the second-stage oxidation section is provided with a lime milk and ferrous sulfate inlet, and the second reaction tank in the second-stage oxidation section is provided with a compressed air inlet.

[0023] The advantages and technical effects brought by the independent claims according to an embodiment of the second aspect of the present invention are as follows: The device of the embodiment of the present invention can effectively remove thallium and arsenic in the waste acid, the removal rate reaches more than 99.9%, the effluent meets the standards stably, it is easy to maintain, the medicaments are commonly available, and the amount of slag is small, having a good ecological environment effect, and finally achieving the purpose of reducing slag and zero discharge.

[0024] A device for treating thallium- and arsenic-containing waste acid according to an embodiment of the second aspect of the present invention further includes a membrane treatment device. The liquid inlet of the membrane treatment device is connected to the liquid outlet of the second-stage filtration device. The fresh water obtained from the membrane treatment device is returned for use as process water, and the high-salt water is used for slag flushing makeup water.

[0025] The device for treating thallium- and arsenic-containing waste acid according to the embodiment of the second aspect of the present invention further includes an evaporation and crystallization device. The liquid inlet of the evaporation and crystallization device is connected to the high-salt water outlet of the membrane treatment device, and the condensed water generated by evaporation and crystallization is returned for use as process water.

[0026] The device for treating thallium- and arsenic-containing waste acid according to the embodiment of the second aspect of the present invention, wherein the membrane treatment device includes a regulating tank, a first reaction tank, a second reaction tank, a coagulation sedimentation tank, a pressurized water tank, a filter, an ultrafiltration device, a security filtration device, a first-stage reverse osmosis device, and a second-stage reverse osmosis device, which are connected in sequence. Description of the Drawings

[0027] Figure 1 is a schematic diagram of the device for treating thallium- and arsenic-containing waste acid according to the embodiment of the present invention;

[0028] Figure 2 is a schematic diagram of the device for treating thallium- and arsenic-containing waste acid according to another embodiment of the present invention;

[0029] Figure 3 is the present invention Figure 2 schematic diagram of the membrane treatment device in the embodiment. Detailed Embodiments

[0030] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the drawings. The embodiments described below with reference to the drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0031] A method for treating thallium- and arsenic-containing waste acid according to the embodiment of the first aspect of the present invention includes the following steps:

[0032] S1. Waste acid neutralization stage

[0033] Add waste acid to limestone for neutralization, and control the pH value of the filtered effluent to be 2-4;

[0034] S2. First-stage oxidation stage

[0035] Feed the effluent from step S1 into the first reaction tank of the first-stage oxidation stage, add ferrous sulfate in the first reaction tank, and the effluent enters the second reaction tank of the first-stage oxidation stage, where hydrogen peroxide is added in the second reaction tank;

[0036] S3. First-stage neutralization stage

[0037] Feed the effluent from the second reaction tank of the first-stage oxidation stage into the first-stage neutralization tank, add lime milk, and control the pH value of the filtered effluent to be 8.5-9.5;

[0038] S4. Second-stage oxidation stage

[0039] Feed the effluent from a neutralization stage in Step S3 into the first reaction tank of the second-stage oxidation stage, add lime milk and ferrous sulfate, send the effluent into the second reaction tank of the second-stage oxidation stage, introduce compressed air, control the pH value to be 8.5 - 9.5, and after the reaction, filter to obtain the treated effluent of the waste acid.

[0040] The advantages and technical effects brought by the independent claims according to the embodiments of the first aspect of the present invention are as follows: 1. For waste acid containing arsenic and thallium, first use limestone for neutralization, and then perform first-stage oxidation Fenton oxidation to oxidize low-valent thallium into trivalent thallium and trivalent arsenic into pentavalent arsenic. Add lime milk in the first-stage neutralization stage to remove most of the thallium, control the pH value of the effluent from the first-stage neutralization stage to be 8.5 - 9.5, and perform second-stage oxidation. Add lime milk and ferrous sulfate in the second-stage oxidation to oxidize divalent iron into trivalent iron and trivalent arsenic into pentavalent arsenic. Eventually, pentavalent arsenic forms iron arsenate, calcium arsenate or calcium arsenite, etc., and trivalent iron reacts with calcium hydroxide to form iron hydroxide, which adsorbs and co-precipitates with iron arsenate, calcium arsenate, thallium hydroxide that was not separated in the first-stage neutralization, etc., to achieve the solidification of arsenic and thallium and realize solid-liquid separation, effectively removing thallium and arsenic in the waste acid. The inventor found that by controlling the pH value in the second-stage oxidation stage to be 8.5 - 9.5 and performing second-stage oxidation, the best adsorption co-precipitation of iron hydroxide with iron arsenate, calcium arsenate, thallium hydroxide, etc. can be achieved, directly completing the solidification and separation of thallium and arsenic in the second-stage oxidation stage, reducing process steps such as the neutralization stage, sulfidation stage, and flocculation stage after the second-stage oxidation stage in the traditional process, reducing the consumption of reagents, and controlling the pH to be 8.5 - 9.5, which has little corrosion to the equipment and can extend the service life of the equipment; 2. The method of the embodiments of the present invention can effectively remove thallium and arsenic in the waste acid, with a removal rate of over 99.9%. The process flow is short, the effluent meets the standards stably, it is easy to maintain, the reagents are commonly available, and the amount of slag is small, having a good ecological environment effect, and finally achieving the purpose of reducing slag and zero discharge.

[0041] According to the method for treating waste acid containing thallium and arsenic according to the embodiments of the first aspect of the present invention, wherein, in the step S1, the sludge obtained by filtration is fed into a smelting furnace. In the method of the embodiments of the present invention, the sludge generated after the waste acid neutralization reaction is returned to the smelting furnace for batching, and the sludge is effectively utilized, achieving the purpose of reducing slag.

[0042] The method for treating thallium- and arsenic-containing waste acid according to the embodiment of the first aspect of the present invention further includes a step S5 membrane treatment section, where the post-treatment liquid of the waste acid in step S4 is sent to a membrane treatment device for treatment. The fresh water obtained from the membrane treatment device is returned for use as process water, and the high-salt water is used for slag flushing makeup water. In the embodiment of the present invention, the post-treatment liquid of the waste acid is sent to the membrane treatment section for membrane treatment. This section can reduce the total hardness of the wastewater and concentrate the salts in the wastewater. After the membrane treatment section, the quality of the fresh water reaches the quality of softened water, with a TDS of less than 150 mg / L. The generated fresh water is recycled for process makeup water in the factory area, and a part of the discharged high-salt water can be returned for use in slag flushing makeup water in the factory area, and a part can be sent to the subsequent evaporation and crystallization section.

[0043] The method for treating thallium- and arsenic-containing waste acid according to the embodiment of the first aspect of the present invention further includes a step S6 evaporation and crystallization section, where the high-salt water generated in step S5 is sent to an evaporation and crystallization device for treatment, and the condensed water generated by evaporation and crystallization is returned for use as process water. In the embodiment of the present invention, the high-salt water generated in the membrane treatment section is sent to the evaporation and crystallization device for treatment to separate the salts in the high-salt water, and the generated condensed water is recycled for process water in the factory area. After the evaporation and crystallization section, the water quality reaches the quality of softened water, with a TDS of less than 100 mg / L.

[0044] In the method for treating thallium- and arsenic-containing waste acid according to the embodiment of the first aspect of the present invention, in step S2, the oxidation-reduction potential of the second reaction tank is 600 - 800 mv; in step S4, the mass ratio of Fe in the added ferrous sulfate to As in the waste acid is 10 - 14:1. In the embodiment of the present invention, the oxidation-reduction potential in the Fenton oxidation section and the iron-to-arsenic ratio in the second-stage oxidation section are preferably controlled, improving the removal rates of thallium and arsenic in the waste acid, so that the present invention can achieve the removal of high contents of thallium and arsenic in the waste acid with a short process flow.

[0045] The embodiment of the second aspect of the present invention further provides a device for treating thallium- and arsenic-containing waste acid, which can effectively remove thallium and arsenic in the waste acid, and the removal rate reaches more than 99.9%.

[0046] As Figure 1As shown in the figure, the device for treating thallium- and arsenic-containing waste acid according to the embodiment of the second aspect of the present invention includes a waste acid neutralization reaction tank 1, a first reaction tank 2 in the first-stage oxidation section, a second reaction tank 3 in the first-stage oxidation section, a first-stage neutralization tank 4, a first-stage filtration device 5, a first reaction tank 6 in the second-stage oxidation section, a second reaction tank 7 in the second-stage oxidation section, and a second-stage filtration device 8, which are connected in sequence. Among them, the waste acid neutralization reaction tank 1 is provided with a limestone inlet, the first reaction tank 2 in the first-stage oxidation section is provided with a ferrous sulfate inlet, the second reaction tank 3 in the first-stage oxidation section is provided with a hydrogen peroxide inlet, the first-stage neutralization tank 4 is provided with a lime milk inlet, the first reaction tank 6 in the second-stage oxidation section is provided with a lime milk and ferrous sulfate inlet, and the second reaction tank 7 in the second-stage oxidation section is provided with a compressed air inlet.

[0047] The advantages and technical effects brought by the independent claims of the embodiment according to the second aspect of the present invention are as follows: The device of the embodiment of the present invention can effectively remove thallium and arsenic in the waste acid, and the removal rate reaches more than 99.9%. The effluent meets the standards stably, is easy to maintain, the medicaments are commonly available, and the amount of slag is small, having a good ecological environment effect, and finally achieving the purpose of reducing slag and zero discharge.

[0048] As Figure 2 shown in the figure, the device for treating thallium- and arsenic-containing waste acid according to the embodiment of the second aspect of the present invention further includes a membrane treatment device 9. The liquid inlet of the membrane treatment device is connected to the liquid outlet of the second-stage filtration device 8. The fresh water obtained through the membrane treatment device is returned for use as process water, and the high-salt water is used for slag flushing makeup water. In the embodiment of the present invention, the post-treatment liquid of the waste acid after two-stage oxidation and filtration is sent to the membrane treatment device for membrane treatment. This stage can reduce the total hardness of the wastewater and concentrate the salts in the wastewater at the same time. The quality of the fresh water after the membrane treatment stage reaches the soft water quality, with a TDS less than 150 mg / L. The generated fresh water is reused for the process makeup water of the factory area, and a part of the discharged high-salt water can be returned for use in the slag flushing makeup water of the factory area, and a part can be sent to the subsequent evaporation and crystallization section.

[0049] The device for treating thallium- and arsenic-containing waste acid according to the embodiment of the second aspect of the present invention further includes an evaporation and crystallization device 10. The liquid inlet of the evaporation and crystallization device is connected to the high-salt water outlet of the membrane treatment device 9. The condensed water generated by evaporation and crystallization is returned for use as process water. In the embodiment of the present invention, the high-salt water generated by the membrane treatment device is sent to the evaporation and crystallization device for treatment to separate the salts in the high-salt water, and the generated condensed water is reused for the process water of the factory area. The water quality after the evaporation and crystallization section reaches the soft water quality, with a TDS less than 100 mg / L.

[0050] The device for treating thallium- and arsenic-containing waste acid according to the embodiment of the second aspect of the present invention, wherein the membrane treatment device 9 includes an adjustment tank 910, a first reaction tank 911, a second reaction tank 912, a coagulation sedimentation tank 913, a pressure water tank 914, a filter 915, an ultrafiltration device 916, a security filtration device 917, a first-stage reverse osmosis device 918 and a second-stage reverse osmosis device 919 which are connected in sequence. In the embodiment of the present invention, the membrane treatment device is preferably selected. After the waste acid is subjected to two-stage oxidation and filtration, it is pressurized by a pump to the adjustment tank, and the wastewater in the adjustment tank is lifted by a pump to the first reaction tank and the second reaction tank to remove the temporary hardness and permanent hardness in the water respectively. The effluent enters the coagulation sedimentation tank to further remove various impurities in the water, and the underflow is pressurized by a sludge pump to a filter press. The supernatant flows into the pressure water tank by gravity and is sent to a multi-media filter by a pressure pump. The effluent enters the ultrafiltration device. Under a certain pressure, water, inorganic salts and small-molecule substances pass through the membrane, and suspended solids, colloids and microorganisms are intercepted. After the wastewater treated by ultrafiltration is filtered by a 5μ security filtration device, it is sent to the reverse osmosis device by a high-pressure pump for desalination treatment, and preferably two-stage reverse osmosis devices are provided. The fresh water generated after membrane treatment can be returned for process water make-up in the factory area. The high-salt water discharged from the reverse osmosis device flows into the high-salt water tank 920 by gravity. Part of it is used for slag flushing and make-up water in the factory area, and part of it is sent to the subsequent evaporation crystallization device by a lift pump.

[0051] The specific embodiments of the present invention will be described below with reference to the accompanying drawings.

[0052] Example 1

[0053] The waste acid of a smelter contains 956 mg / L of arsenic, 10.3 mg / L of thallium, 29 g / L of sulfuric acid, and the total amount of waste acid is 400 t / d.

[0054] S1 Waste acid neutralization section

[0055] As Figure 1 shown, the thallium- and arsenic-containing waste acid is sent to the waste acid neutralization reaction tank 1, and a limestone solution with a mass concentration of 25% is added to the waste acid neutralization reaction tank 1 for neutralization reaction. The pH of the effluent supernatant is controlled to be 2.5, and the bottom sludge is sent to a filter press for filtration. The obtained sludge is sent to the smelting furnace for batching, which can effectively utilize the sludge and reduce the discharge of sludge.

[0056] S2. First-stage oxidation section

[0057] The effluent obtained in S1 is sent to the first reaction tank 2 in the first-stage oxidation section, ferrous sulfate is added to the first reaction tank 2 in the first-stage oxidation section and stirred evenly. The effluent flows into the second reaction tank 3 in the first-stage oxidation section by gravity, hydrogen peroxide is added to the second reaction tank 3 in the first-stage oxidation section, the oxidation-reduction potential is controlled to be 650 mv, and it is stirred for 30 - 40 minutes to oxidize the low-valent thallium into trivalent thallium and the trivalent arsenic into pentavalent arsenic.

[0058] S3. First neutralization stage

[0059] The liquid discharged from the second reaction tank 3 of the first oxidation stage flows by gravity to the first neutralization tank 4, where lime milk is added and stirred evenly. Thallium(III) forms thallium hydroxide. The liquid then flows by gravity to the first filtration device 5. The first neutralization stage takes a total of 35 - 45 minutes. The pH value of the liquid discharged from the first filtration device 5 is 8.5, and most of the low-valent thallium is removed in the first neutralization stage.

[0060] S4. Second oxidation stage

[0061] The liquid discharged from the first filtration device 5 flows by gravity to the first reaction tank 6 of the second oxidation stage, where lime milk and ferrous sulfate are added and stirred evenly. The liquid then flows by gravity to the second reaction tank 7 of the second oxidation stage, and compressed air is introduced to continue oxidizing ferrous iron to ferric iron and arsenite to arsenate. Eventually, arsenate forms iron arsenate, calcium arsenate or calcium arsenite, and ferric iron reacts with calcium hydroxide to form ferric hydroxide, which adsorbs and co-precipitates with iron arsenate, calcium arsenate, and thallium hydroxide that was not separated in the first neutralization stage. The pH is controlled at 8.5, and the mass ratio of Fe in the added ferrous sulfate to As in the waste acid is controlled at 12:1. This stage takes a total of 40 minutes. The liquid then flows by gravity to the second filtration device 8, and the treated liquid of the waste acid is obtained by filtration.

[0062] The treated liquid of the waste acid obtained in this example contains 0.2 mg / L of arsenic and 0.003 mg / L of thallium, meeting the discharge standard of thallium content not exceeding 0.005 mg / L in the "Discharge Standard of Thallium Pollutants in Industrial Wastewater of Hunan Province" (DB43 / 968 - 2014) and the discharge standard of arsenic content not exceeding 0.3 mg / L in the "Discharge Standard of Pollutants for Lead and Zinc Industries" (GB25466—2010).

[0063] Example 2

[0064] As Figure 2 and 3As shown in the figure, the post-treatment liquid of the waste acid obtained in Example 1 is sent into the membrane treatment device 9. The post-treatment liquid of the waste acid is pressurized by a pump to the adjustment tank 910. The wastewater in the adjustment tank 910 is lifted by a pump to the first reaction tank 911. Calcium hydroxide is added to the first reaction tank 911 to remove the temporary hardness in the water. The effluent enters the second reaction tank 912. Sodium carbonate is added to the second reaction tank 912 to remove the permanent hardness in the water. The effluent enters the coagulation sedimentation tank 913. A coagulant is added to the coagulation sedimentation tank 913 to further remove various impurities in the water. The underflow is pressurized by a sludge pump to the filter press. The supernatant flows into the pressurized water tank 914 by gravity, is sent to the filter 915 by a pressurizing pump, and the effluent enters the ultrafiltration device 916. Under a certain pressure of the system, water, inorganic salts, and small molecule substances pass through the membrane, while suspended solids, colloids, and microorganisms are intercepted. The wastewater after ultrafiltration treatment is filtered by a 5μ security filter device 917 and then sent to a first-stage reverse osmosis device 918 and a second-stage reverse osmosis device 919 for desalination treatment. The fresh water produced by the first-stage reverse osmosis device 918 and the second-stage reverse osmosis device 919 can be returned for use as process water in the plant area. The high-salt water discharged from the second-stage reverse osmosis device 919 flows into the high-salt water tank 920 by gravity. Part of it is returned for use as flushing water for slag cleaning in the plant area, and part of it is sent to the subsequent evaporation crystallization device 10 by a lift pump. After the high-salt water is treated by the evaporation crystallization device, the salt in the high-salt water is separated, and the produced condensed water is returned for use as process water in the plant area.

[0065] The fresh water quality after treatment by the membrane treatment device reaches the soft water quality, with a TDS of less than 150 mg / L. The water quality after treatment in the evaporation crystallization section reaches the soft water quality, with a TDS of less than 100 mg / L.

[0066] The total amount of waste acid in this smelter is 400 t / d. The amount of fresh water produced in the membrane treatment device is 319.4 t / d, and this part is returned for use as process water in the plant area. The amount of high-salt water produced is 80 t / d, and this part is returned for use as slag flushing in the plant area. The amount of condensed water produced in the evaporation crystallization device is 0.6 t / d, and this part is recycled for use as process water in the plant area.

[0067] The fresh water obtained after treatment in this example meets the soft water quality requirements, can be returned for use as process water in the plant area, effectively utilizes the wastewater resources, and avoids the waste of water resources.

[0068] Examples 3 - 4

[0069] The method is the same as that in Example 1, except that the contents of thallium and arsenic in the waste acid are different, and the pH values are controlled differently in steps S3 and S4. The contents of arsenic and thallium in the post-treatment liquid of the waste acid are shown in Table 1 in detail.

[0070] Comparative Examples 1 - 2

[0071] The method is the same as that of Example 1, except that the pH value is controlled differently in Steps S3 and S4. The contents of arsenic and thallium in the treated waste acid solution are shown in Table 1 in detail.

[0072] Comparative Example 3

[0073] The method is the same as that of Example 1, except that the order of the method steps is different. The order of Comparative Example 3 is S1, S4, S3, and S2, that is, lime milk, ferrous sulfate, and compressed air are used for oxidation in the first-stage oxidation, and Fenton oxidation is used in the second-stage oxidation. The pH value of Fenton oxidation is controlled at 2.5. The contents of arsenic and thallium in the treated waste acid solution are shown in Table 1 in detail.

[0074] Comparative Example 4

[0075] The method is the same as that of Example 1, except that Fenton oxidation is also used in Step S4, and the pH of Fenton oxidation is controlled at 2.5. The contents of arsenic and thallium in the treated waste acid solution are shown in Table 1 in detail.

[0076] Table 1

[0077]

[0078] It can be seen from the data in Table 1 that in the examples of the present invention, in the first-stage oxidation section, Fenton oxidation is first used, and then in the second-stage oxidation section, lime-iron salt-air oxidation is used, and the pH value of the second-stage oxidation section is strictly controlled to be 8.5-9.5, so that the treated high-content arsenic and thallium waste acid can meet the discharge requirements by using a short-process technology, without the need to further treat thallium and arsenic by subsequent treatment processes such as the second-stage neutralization section, sulfidation section, and flocculation section in the traditional process. The thallium content in the treated waste acid meets the discharge standard of not more than 0.005 mg / L of thallium content in the "Hunan Provincial Industrial Wastewater Thallium Pollutant Discharge Standard" (DB43 / 968-2014), and the arsenic content meets the discharge standard of not more than 0.3 mg / L of arsenic content in the "Lead and Zinc Industrial Pollutant Discharge Standard" (GB25466-2010).

[0079] In addition, the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of these features. In the description of the present invention, the meaning of "a plurality" is at least two, such as two, three, etc., unless otherwise specifically defined.

[0080] In the present invention, unless otherwise clearly defined or limited, terms such as "installed", "connected", "joined", "fixed", etc. shall be construed broadly. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection, an electrical connection, or capable of communicating with each other; it may be directly connected, or indirectly connected through an intermediate medium, and it may be the communication inside two elements or the interaction relationship between two elements, unless otherwise clearly defined. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0081] In the present invention, unless otherwise clearly defined or limited, the first feature being "on" or "under" the second feature may be that the first and second features are in direct contact, or the first and second features are indirectly in contact through an intermediate medium. Moreover, the first feature being "above", "over" and "on top of" the second feature may be that the first feature is directly above or obliquely above the second feature, or merely indicates that the first feature has a higher horizontal height than the second feature. The first feature being "under", "beneath" and "underneath" the second feature may be that the first feature is directly below or obliquely below the second feature, or merely indicates that the first feature has a lower horizontal height than the second feature.

[0082] In the present invention, terms such as "an embodiment", "some embodiments", "examples", "specific examples", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic descriptions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0083] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for treating thallium- and arsenic-containing waste acid, characterized in that, it comprises the following steps: S1. Waste acid neutralization section Add the waste acid to limestone for neutralization, control the pH value of the filtrate to be 2 - 4 after filtration, and send the filtered sludge to the smelting furnace; S2. First-stage oxidation section Send the filtrate from step S1 to the first reaction tank in the first-stage oxidation section, add ferrous sulfate in the first reaction tank, and the effluent enters the second reaction tank in the first-stage oxidation section. Add hydrogen peroxide in the second reaction tank to oxidize thallium in the lower valence state to trivalent thallium and arsenite in the third valence state to pentavalent arsenic; S3. First-stage neutralization section Send the effluent from the second reaction tank in the first-stage oxidation section to the first-stage neutralization tank, add lime milk to remove part of the thallium, and control the pH value of the filtrate to be 8.5 - 9.5 after filtration; S4. Second-stage oxidation section Send the effluent from the first-stage neutralization section in step S3 to the first reaction tank in the second-stage oxidation section, add lime milk and ferrous sulfate, and the effluent is sent to the second reaction tank in the second-stage oxidation section. Introduce compressed air, control the pH value to be 8.5 - 9.5, oxidize divalent iron to trivalent iron, oxidize trivalent arsenic to pentavalent arsenic, pentavalent arsenic generates iron arsenate, calcium arsenate or calcium arsenite, and trivalent iron reacts with calcium hydroxide to form ferric hydroxide, which adsorbs and co-precipitates with iron arsenate, calcium arsenate, and thallium hydroxide that was not separated in the first-stage neutralization section. After the reaction, filter to obtain the treated waste acid solution.

2. The method for treating thallium- and arsenic-containing waste acid according to claim 1, characterized in that, it further comprises step S5 membrane treatment section. Send the treated waste acid solution from step S4 to the membrane treatment device for treatment. The fresh water obtained from the membrane treatment device is returned for use as process water, and the high-salt water is used for slag flushing makeup water.

3. The method for treating thallium- and arsenic-containing waste acid according to claim 2, characterized in that, it further comprises step S6 evaporation and crystallization section. Send the high-salt water generated in step S5 to the evaporation and crystallization device for treatment, and the condensed water generated by evaporation and crystallization is returned for use as process water.

4. The method for treating thallium- and arsenic-containing waste acid according to claim 1, characterized in that, in step S2, the redox potential of the second reaction tank is 600 - 800 mv.

5. The method for treating thallium- and arsenic-containing waste acid according to claim 1, characterized in that, in step S4, the mass ratio of Fe in the added ferrous sulfate to As in the waste acid is 10 - 14:1.

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