A method for treating wastewater containing thallium

Abstract

The present application relates to a kind of methods for treating thallium-containing wastewater, including pH adjustment unit, thallium removal reaction unit, flocculation reaction unit, sludge backflow unit, precipitation reaction unit, sludge concentration unit and seed regeneration unit;The adjusting reagent of the pH adjustment unit is basic substance, and the pH adjustment unit is adjusted to 7.5~9.0;Thallium removal reagent and special seed are added in the thallium removal reaction unit, and thallium in water occurs chemical reaction to form water-insoluble under the action of special seed, the seed regeneration unit includes sludge separator and seed recovery device, sludge separator carries out primary separation to thallium insoluble precipitate adsorbed on the surface of special seed, and seed recovery device uses magnetic field to secondary separate special seed from water and thallium insoluble precipitate and make special seed recycle.The present application uses the way of adding reagent and special seed, and completes thallium removal by special seed reinforced coupling chemical precipitation and seed recovery.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment, and in particular to a method for treating thallium-containing wastewater. Background Technology

[0002] Thallium pollution sources mainly include weathering and leaching from mines, atmospheric deposition, industrial wastewater discharge, and soil erosion. The most significant sources are emissions from human activities and the release of thallium from parent materials. The mining of thallium-bearing ores releases large amounts of thallium into the environment. Simultaneously, abandoned tailings undergo long-term weathering, oxidation, decomposition, and water-acid-gas reactions, generating large quantities of acidic wastewater. Thallium dissolves and becomes activated in this acidic wastewater, subsequently transferring to water bodies. Dust pollution and its deposition during ore mining are also important sources of thallium pollution.

[0003] Currently, there are three main technologies for treating wastewater containing thallium ions: The first method is to remove thallium ions from wastewater through chemical reactions, mainly through sulfide precipitation.

[0004] The second method involves adsorption, concentration, and separation of thallium in wastewater, including adsorption and ion exchange.

[0005] The third method involves removing thallium from wastewater through the flocculation, absorption, accumulation, and enrichment of microorganisms or plants, including methods such as bioflocculation, bioadsorption, and phytoremediation.

[0006] Sulfide precipitation is a method for treating heavy metal pollution and is the most widely used method in industrial wastewater treatment. The principle of this method is to add lime to industrial wastewater to create an alkaline environment, then add sulfide substances to form sulfide precipitates, thereby reducing the concentration of heavy metals in the water. This method has relatively low processing costs and is widely used. The disadvantages are that this method requires the addition of large amounts of sulfide reagents, produces harmful gases such as H2S, generates a large amount of hazardous waste, can easily cause secondary environmental damage, and requires a large area.

[0007] The adsorption method mainly utilizes adsorbent materials with special functional groups. These materials have a high specific surface area and a loose structure, and use the interactions between van der Waals forces, Coulomb forces and chemical bonds to adsorb thallium from wastewater.

[0008] Activated carbon possesses advantages such as large pore size, high adsorption capacity, high strength, and good physicochemical properties, and is commonly used in the treatment of thallium-containing industrial wastewater. Its adsorption mechanism involves the complexation reaction between metal ions and the functional groups on the surface of activated carbon, resulting in proton or ion exchange and charge transfer. This process exhibits excellent adsorption performance, requires no chemical additives, and demonstrates significant adsorption effects and large adsorption capacities. Disadvantages include the large amount of adsorbent required, the inability to be reused multiple times, and high operating costs.

[0009] Ion exchange removes thallium by exchanging ions from an ion exchanger with thallium ions in wastewater. Ion exchange has advantages such as simple operation, no secondary pollution, and large adsorption capacity. Disadvantages include high cost, difficulty in storage, and low selectivity.

[0010] The mechanism of thallium removal using biological agents involves chelating and flocculating thallium metal in wastewater with biological agents, introducing thallium-removing functional groups to achieve deep removal of thallium ions from the wastewater. This process requires high parameter control, has strict process requirements, and its effectiveness is not entirely stable. Summary of the Invention

[0011] The purpose of this invention is to provide a method for treating thallium-containing wastewater, which employs the addition of reagents and proprietary seed crystals to enhance coupled chemical precipitation and recover the seed crystals in order to remove thallium.

[0012] The technical problem of this invention is mainly solved by the following technical solution: A method for treating thallium-containing wastewater includes a pH adjustment unit, a thallium removal reaction unit, a flocculation reaction unit, a sludge return unit, a sedimentation reaction unit, a sludge thickening unit, and a seed crystal regeneration unit. The pH adjusting agent in the pH adjusting unit is an alkaline substance, and the pH of the pH adjusting unit is adjusted to 7.5-9.0; The thallium removal reaction unit is equipped with a thallium removal agent and proprietary seed crystals. Under the action of the proprietary seed crystals, the thallium in the water undergoes a chemical reaction to form a water-insoluble substance. The thallium removal agent comprises the following components by weight: 100-300 parts sodium sulfide, 0-50 parts DTC sulfides, 10-30 parts sodium silicate, and 1-5 parts ascorbic acid. The proprietary seed crystal raw materials in the thallium removal reaction unit include Fe3O4 powder, petroleum coke, and Prussian blue. The seed regeneration unit includes a sludge separator and a seed recycler. The sludge separator performs initial separation of the thallium-insoluble precipitate adsorbed on the surface of the proprietary seed crystals. The seed recycler uses a magnetic field to perform secondary separation of the proprietary seed crystals from water and the thallium-insoluble precipitate, and allows the proprietary seed crystals to be recycled.

[0013] Preferably, the influent is pumped to the pH adjustment unit to adjust the pH to weakly alkaline, and then flows by gravity to the thallium removal reaction unit. Under mechanical stirring, the thallium removal agent and proprietary seed crystals fully react with the weakly alkaline thallium-containing wastewater and then flow by gravity to the flocculation reaction unit. Under the coagulation aid of the flocculant, the thallium in the wastewater is further adsorbed and grows on the surface of the proprietary seed crystals. The sludge then flows by gravity to the sludge return unit. The large amount of sludge formed is pumped to the seed crystal regeneration unit. Under the action of the seed crystal recoverer, the proprietary seed crystals are recycled back to the thallium removal reaction unit. The sludge-containing sludge enters the sludge thickening unit, where the sludge is filtered, stored, and transported off-site. The wastewater containing a small amount of sludge flows by gravity to the sedimentation reaction unit for sedimentation and is then discharged.

[0014] Preferably, the pH of the pH adjustment unit is adjusted to 8.0-8.5, and the alkaline substance in the pH adjustment unit includes one or more of quicklime, sodium hydroxide, sodium carbonate, sodium bicarbonate, and potassium hydroxide.

[0015] Preferably, the thallium removal agent comprises the following components in parts by weight: 200 parts sodium sulfide, 5 parts DTC-type sulfides, 20 parts sodium silicate, and 2 parts ascorbic acid. In the thallium removal reaction unit, sodium sulfide and DTC-type sulfides are the main agents for thallium removal, forming an insoluble precipitate with thallium, while sodium silicate and ascorbic acid are reaction aids.

[0016] Preferably, the thallium removal seed crystal in the thallium removal reaction unit is a proprietary seed crystal, which promotes the formation of thallium insoluble precipitate on the surface of the proprietary seed crystal by the thallium removal agent. The Fe3O4 powder has a particle size of 100-400 mesh, the petroleum coke is high-temperature needle-shaped petroleum coke with a particle size of 100-300 mesh, and the Prussian blue powder has a particle size of 100-250 mesh.

[0017] Preferably, the method for preparing the proprietary seed crystal is as follows: Material mixing: Weigh 100 parts Fe3O4 powder, 10-20 parts petroleum coke, and 1-8 parts Prussian blue by weight percentage, and then stir continuously at 80°C for 10-30 minutes. Coating: The above mixture is passed through a high-temperature reactor via a conveyor belt and intermittently stirred. The high-temperature reactor is heated to 400℃~600℃ at a heating rate of 3~10℃ / min, and held at the required temperature for 1~4 hours. Grinding: The heated intermediate product is fed out and cooled to room temperature, and then ground into powder using a Raymond mill; Screening: After crushing, the material is screened to the required mesh size.

[0018] Preferably, the flocculation reaction unit is used to further adsorb and bridge thallium insoluble precipitates onto the surface of proprietary seed crystals, and the flocculant used in the flocculation reaction unit is anionic PAM.

[0019] Preferably, the sedimentation reaction unit is used to reduce suspended solids in the effluent, and the surface loading of the sedimentation reaction unit is 5-12 m3 / (m2·h).

[0020] Preferably, the sludge thickening unit is a vertical flow sludge thickening tank with a surface loading rate of 1-2 m³ / (m²·h).

[0021] The beneficial effects of this invention are: 1. Under the synergistic effect of thallium removal agents and proprietary seed crystals, thallium dissolved in water is rapidly converted into nano-sized particles and adsorbed onto the surface of proprietary seed crystals through polarization, chelation, covalent bonding and adsorption. This rapidly forms a solid-liquid two-phase system. The thallium-containing fine particles grow from nano-sized particles to sub-nano-sized particles under secondary strong mixing. Then, through the adsorption, bridging and trapping effects of flocculants, a small amount of free thallium insoluble precipitate is adsorbed onto the surface of proprietary seed crystals, thereby rapidly separating mud and water and ensuring that the effluent meets discharge standards. 2. In the thallium removal reaction unit of the present invention, sodium silicate in the thallium removal agent undergoes a hydrolysis reaction under pH conditions of 7.5-9.0 and forms a thallium reaction nanocarrier. At the same time, under the promoting effect of ascorbic acid, sodium sulfide and DTC-type agents react rapidly with thallium in water, increasing the rate of thallium insoluble precipitate formation. 3. The proprietary seed crystal surface in the thallium removal reaction unit of the present invention has porous and electronegative properties, which makes it easy for nano-sized thallium insoluble precipitates to be adsorbed on the proprietary seed crystal surface, promoting a coupling effect with the thallium removal agent, promoting the growth of thallium insoluble precipitates on the proprietary seed crystal surface, and shortening the thallium removal reaction time.

[0022] 4. Under the action of strong centrifugation, shearing and magnetic field, the seed recovery unit of the present invention enables the proprietary seed to be recycled, which greatly reduces the amount of proprietary seed used and reduces operating costs. 5. The precipitation reaction unit of this invention has a high surface load, which greatly shortens the precipitation time, reduces the floor space, and saves fixed investment costs; Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is a top view of the present invention. Figure 3 This is a diagram showing the thallium removal effect of the thallium removal process system in this invention. Detailed Implementation

[0024] The technical solution of the present invention will be further described in detail below through embodiments and in conjunction with the accompanying drawings.

[0025] A method for treating thallium-containing wastewater includes a pH adjustment unit, a thallium removal reaction unit, a flocculation reaction unit, a sludge return unit, a sedimentation reaction unit, a sludge thickening unit, and a seed crystal recovery unit. The process flow is as follows: Influent is pumped to the pH adjustment unit, where a compound alkali is added to adjust the pH to weakly alkaline. The wastewater then flows by gravity to the thallium removal reaction unit. Under mechanical stirring, the thallium removal agent and proprietary seed crystals react fully with the weakly alkaline thallium-containing wastewater. The wastewater then flows by gravity to the flocculation reaction unit. With the aid of flocculant, thallium in the wastewater is further adsorbed and grows on the surface of the proprietary seed crystals. The wastewater then flows by gravity to the sludge return unit. The resulting large amount of sludge is pumped to the seed crystal recovery unit. Under the action of the seed crystal recovery unit, the proprietary seed crystals are recycled back to the thallium removal reaction unit. The sludge-containing sludge-water enters the sludge thickening unit. The sludge is then stored by pressure filtration and transported off-site. Wastewater containing a small amount of sludge flows by gravity to the sedimentation reaction unit. After sedimentation in inclined tubes, the effluent meets the discharge standards. The sedimentation reaction unit regularly discharges sludge.

[0026] The pH adjustment unit uses an alkaline substance as its adjusting agent, including one or more of quicklime, sodium hydroxide, sodium carbonate, sodium bicarbonate, and potassium hydroxide, preferably quicklime or sodium hydroxide. In this embodiment, the pH adjustment unit uses quicklime and sodium hydroxide to adjust the pH, with a mass ratio of 4:1, and the pH needs to be adjusted to 8.5. The pH adjustment unit regulates water quality by mechanical stirring, with the stirring rate controlled at 40~120 rpm. In this embodiment, the stirring rate is controlled at 80 rpm. The thallium removal reaction unit requires the addition of thallium removal agents and proprietary seed crystals; The thallium removal reaction unit uses a special thallium removal agent, which comprises the following raw materials and weight ratios: 100-300 parts sodium sulfide, 0-50 parts DTC sulfide, 10-30 parts sodium silicate, and 1-5 parts ascorbic acid. In this embodiment, the controlled ratio of the thallium removal agent is: 200 parts sodium sulfide, 5 parts sodium dimethyl dithiocarbamate, 20 parts sodium silicate, and 2 parts ascorbic acid. The thallium removal reaction unit uses proprietary seed crystals, which promote the formation of thallium-insoluble precipitates on the surface of the thallium removal agent. The proprietary seed material in the thallium removal reaction unit includes Fe3O4 powder, petroleum coke, and Prussian blue. The Fe3O4 powder particle size is controlled to be 100~400 mesh, and in this embodiment, the Fe3O4 powder particle size is controlled to be 200 mesh; The petroleum coke is high-temperature needle-shaped petroleum coke, and the petroleum coke particle size is controlled to be 100~300 mesh. In this embodiment, the petroleum coke particle size is controlled to be 200 mesh. The particle size of the Prussian blue powder is controlled to be 100-250 mesh, and in this embodiment, the particle size of the Prussian blue powder is controlled to be 200 mesh. The thallium removal seed crystal in the thallium removal reaction unit is a proprietary seed crystal, and the proprietary seed crystal is prepared as follows: Material mixing: Weigh 100 parts Fe3O4 powder, 10 parts petroleum coke, and 5 parts Prussian blue by weight percentage, and stir continuously at 80℃ for 10 minutes. Coating: The above mixture is passed through a high-temperature reactor with a conveyor belt and intermittently stirred. The heating program of the high-temperature reactor is 100℃-250℃-350℃-450℃, and the heating rate is controlled at 5℃ / min. The temperature is held at 100℃ for 30 minutes, then heated to 250℃, held at 250℃ for 20 minutes, then heated to 350℃, held at 350℃ for 20 minutes, then heated to 450℃, and held at 450℃ for 2 hours. Grinding: The intermediate product at 450℃ is fed into the mill and cooled to room temperature. The intermediate product is then ground into powder using a Raymond mill. Screening: After crushing, the material is screened to 200 mesh.

[0027] The thallium removal reaction unit includes a mechanical stirrer and a flow guiding center cylinder. The mechanical stirrer is an axial flow stirrer with a stirring rate controlled at 40~120 rpm. In this embodiment, the stirring rate is controlled at 50 rpm. The seed regeneration unit includes a sludge separator and a seed collector. The sludge separator controls the high-speed shearing speed to 1200 rpm, and the magnetic field strength in the seed collector is controlled to 0.6T. The flocculant used in the flocculation reaction unit is anionic PAM. In this embodiment, the molecular weight of the PAM used is above 8 million, and the amount of PAM added in this embodiment is 3 ppm. The flocculation reaction unit includes a mechanical stirrer and a flow guiding center cylinder. The mechanical stirrer is an axial flow stirrer, and the stirring speed is controlled at 20~80 rpm. In this embodiment, the stirring speed is controlled at 40 rpm. In this embodiment, the sludge pump flow rate in the sludge return unit is 3.5 m³ / s. 3 / h, the sludge is pumped to the seed crystal regeneration unit; The precipitation reaction unit includes a sludge storage hopper and an inclined tube. The angle of the sludge storage hopper is controlled between 55° and 60°. In this embodiment, the angle of the sludge storage hopper is 57°. The inclined tube is made of PP material, has a hole diameter of Φ80mm, and is installed at an angle of 60°. The surface load of the precipitation reaction unit is controlled at 5~12 m. 3 / (m 2 In this embodiment, the surface load is controlled at 10 m. 3 / (m 2 ·h); The sludge thickening unit is a vertical flow sludge thickening tank, with a surface loading rate controlled at 1~2m. 3 / (m 2In this embodiment, the surface load is controlled at 1.2m (h). 3 / (m 2 ·h).

[0028] This embodiment uses tailwater from a rare earth basin for thallium removal process verification. The thallium concentration is between 4 and 6 ug / l, the pH is around 6.5, and the wastewater flow rate is 30 m³ / L. 3 The concentration is calculated as follows: 20 ppm for compound alkali, 35 ppm for thallium removal agent, 5 ppm for proprietary seed crystals, 3 ppm for PAM, and the flow rate of the sludge return pump is controlled at 3.5 m³ / h. 3 The hydraulic retention time of the entire thallium removal process system is approximately 1.2 hours. After treatment, the thallium removal rate is basically above 80%, and the thallium content in the effluent is controlled below 1 ug / l, and can even reach below 0.1 ug / l.

[0029] The present invention has been described in detail above, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A method for treating thallium-containing wastewater, characterized in that: It includes a pH adjustment unit, a thallium removal reaction unit, a flocculation reaction unit, a sludge return unit, a sedimentation reaction unit, a sludge thickening unit, and a seed crystal regeneration unit; The pH adjusting agent in the pH adjusting unit is an alkaline substance, and the pH of the pH adjusting unit is adjusted to 7.5-9.0; The thallium removal reaction unit is equipped with a thallium removal agent and proprietary seed crystals. Under the action of the proprietary seed crystals, the thallium in the water undergoes a chemical reaction to form a water-insoluble substance. The thallium removal agent comprises the following components in parts by weight: 100-300 parts sodium sulfide, 0-50 parts DTC sulfide, 10-30 parts sodium silicate, and 1-5 parts ascorbic acid. The proprietary seed crystal raw materials in the thallium removal reaction unit include Fe3O4 powder, petroleum coke, and Prussian blue. The proprietary seed crystal preparation method is as follows: Material mixing: Weigh 100 parts Fe3O4 powder, 10-20 parts petroleum coke, and 1-8 parts Prussian blue by weight percentage, and then stir continuously at 80°C for 10-30 minutes. Coating: The mixture is conveyed to a high-temperature reactor via a conveyor belt and intermittently stirred. The high-temperature reactor is heated to 400℃~600℃ at a heating rate of 3~10℃ / min and held at the required temperature for 1~4 hours. Grinding: The heated intermediate product is fed out and cooled to room temperature, and then ground into powder using a Raymond mill; Screening: After crushing, the material is screened to the required mesh size; The seed regeneration unit includes a sludge separator and a seed recycler. The sludge separator performs initial separation of the thallium-insoluble precipitate adsorbed on the surface of the proprietary seed crystals. The seed recycler uses a magnetic field to perform secondary separation of the proprietary seed crystals from water and the thallium-insoluble precipitate, and allows the proprietary seed crystals to be recycled.

2. The method for treating thallium-containing wastewater according to claim 1, characterized in that: The influent is pumped to the pH adjustment unit to adjust the pH to weakly alkaline, and then flows by gravity to the thallium removal reaction unit. Under mechanical stirring, the thallium removal agent and proprietary seed crystals fully react with the weakly alkaline thallium-containing wastewater and then flow by gravity to the flocculation reaction unit. With the help of flocculant, the thallium in the wastewater is further adsorbed and grows on the surface of the proprietary seed crystals. The sludge flows by gravity to the sludge return unit, and the large amount of sludge formed is pumped to the seed crystal regeneration unit. Under the action of the seed crystal recovery device, the proprietary seed crystals are recycled back to the thallium removal reaction unit. The sludge-containing sludge water enters the sludge thickening unit, and the sludge is filtered, stored and transported off-site. The wastewater containing a small amount of sludge flows by gravity to the sedimentation reaction unit for sedimentation and then discharged.

3. The method for treating thallium-containing wastewater according to claim 1, characterized in that: The pH adjustment unit adjusts the pH to 8.0-8.5, and the alkaline substance in the pH adjustment unit includes one or more of quicklime, sodium hydroxide, sodium carbonate, sodium bicarbonate, and potassium hydroxide.

4. The method for treating thallium-containing wastewater according to claim 1, characterized in that: The thallium removal agent comprises the following components in parts by weight: 200 parts sodium sulfide, 5 parts DTC-type sulfides, 20 parts sodium silicate, and 2 parts ascorbic acid. In the thallium removal reaction unit, sodium sulfide and DTC-type sulfides are the main agents for thallium removal, forming an insoluble precipitate with thallium. Sodium silicate and ascorbic acid are reaction aids.

5. A method for treating thallium-containing wastewater according to claim 1, characterized in that: The thallium removal reaction unit uses proprietary seed crystals to promote the formation of thallium-insoluble precipitates on the surface of the proprietary seed crystals by the thallium removal agent. The Fe3O4 powder has a particle size of 100-400 mesh, the petroleum coke is high-temperature needle-shaped petroleum coke with a particle size of 100-300 mesh, and the Prussian blue has a particle size of 100-250 mesh.

6. A method for treating thallium-containing wastewater according to claim 1, characterized in that: The flocculation reaction unit is used to further adsorb and bridge thallium insoluble precipitates onto the surface of proprietary seed crystals. The flocculant used in the flocculation reaction unit is anionic PAM.

7. A method for treating thallium-containing wastewater according to claim 1, characterized in that: The sedimentation reaction unit is used to reduce suspended solids in the effluent, and the surface loading of the sedimentation reaction unit is 5–12 m³. 3 / (m 2 ·h).

8. A method for treating thallium-containing wastewater according to claim 1, characterized in that: The sludge thickening unit is a vertical flow sludge thickening tank with a surface loading rate of 1–2 m³ / h. 3 / (m 2 ·h).

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