A method for treating thallium-containing wastewater

Abstract

The application discloses a treatment method of thallium-containing wastewater and belongs to the technical field of wastewater treatment. The treatment method of the thallium-containing wastewater comprises the following steps: adding soda ash into the wastewater to adjust the pH to 7-7.5; then adding sodium sulfide and keeping the pH at 8-8.5; then adding a trapping agent; then adding lime to adjust the pH to 9.5-10.5; and finally adding PAM to obtain the treated wastewater. The treatment method can efficiently remove thallium in the wastewater, and the content of thallium in the treated wastewater is as low as below 5 ug / L.

Description

Technical Field

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

[0002] Thallium (Tl) is a highly toxic heavy metal, far exceeding the toxicity of common heavy metals such as arsenic (As) and cadmium (Cd). Even trace amounts of thallium can enter the human body through the food chain or skin contact, leading to neurological damage, organ failure, and even death. Thallium is commonly found in sulfide ores, and the strategic metal antimony is also frequently found in sulfide ores. Therefore, in the mining, beneficiation, and smelting processes of antimony minerals, in addition to generating large amounts of antimony- and arsenic-containing wastewater, some thallium-containing wastewater is also frequently produced. Furthermore, some thallium-containing wastewater is generated during the indium hydrometallurgical process. The compliant treatment of thallium-containing wastewater is crucial for the sustainable and green development of the industry.

[0003] my country has extremely strict discharge standards for thallium-containing wastewater (≤5 μg / L). However, current research on the treatment of high-concentration thallium-containing wastewater, both domestically and internationally, is limited. The main methods include direct precipitation, ion exchange, electrochemical deposition, coagulation, microbial methods, and adsorption. While each method has its advantages, they all have limitations. For example, direct precipitation, although simple and low-cost, consumes large amounts of reagents and struggles to consistently achieve concentrations below 5 μg / L. Adsorption methods often use activated carbon or metal oxides (such as hydrated iron oxide) as adsorbents; while offering high adsorption capacity, they suffer from material agglomeration and regeneration difficulties, limiting their practical application. Other treatment methods also suffer from excessively long treatment times, high costs, or secondary pollution. In particular, treatment methods for wastewater containing antimony, arsenic, and lead are rare. Therefore, research on efficient treatment methods for high-concentration thallium-containing wastewater is urgently needed. Developing an economical, simple, and efficient method for treating thallium-containing wastewater is of particular importance in order to solve the industry-wide problem that currently hinders the sustainable development of the antimony and indium smelting industry.

[0004] CN118684375A provides a method and system for removing thallium from thallium-containing wastewater. The method includes: adding calcium hydroxide solution to the thallium-containing wastewater to adjust its pH, so that the pH of the thallium-containing wastewater after pH adjustment is a preset target pH value; adding sodium sulfide solution to the pH-adjusted thallium-containing wastewater to remove thallium, obtaining a first effluent; and performing solid-liquid separation treatment on the first effluent. Although this method is simple to operate and has a concise process, it is only suitable for low-concentration thallium-containing wastewater and can remove thallium from the wastewater, but it is not suitable for treating complex multi-metallic thallium-containing wastewater generated by the antimony and indium industry.

[0005] CN118724372A discloses a process for treating industrial thallium-containing wastewater, comprising the following steps: adding thallium-containing wastewater to a sedimentation tank, adjusting the pH of the wastewater to alkaline by adding alkali, and precipitating to remove trivalent thallium ions; adjusting the pH of the supernatant obtained after removing trivalent thallium ions back to neutral; then adding it to a magnetic coagulation sedimentation tank, adding magnetic adsorbent material, PAC, and PAM, and after the addition is completed, performing flocculation sedimentation and filtration; wherein, the magnetic adsorbent material is a mixture of Fe3O4 and Co3O4. Although this method achieves efficient thallium removal through short-process staged treatment by optimizing and controlling the process, and can treat high-concentration thallium-containing wastewater, the thallium content can only be reduced to below 50 μg / L, which cannot effectively meet the national emission standard of below 5 μg / L.

[0006] How to efficiently remove thallium from wastewater is a technical problem that existing technologies need to solve. Summary of the Invention

[0007] The purpose of this invention is to overcome the above-mentioned technical deficiencies and provide a method for treating thallium-containing wastewater, thereby solving the technical problem of how to efficiently remove thallium from wastewater in the prior art.

[0008] To achieve the above-mentioned technical objectives, the present invention provides a method for treating thallium-containing wastewater, comprising the following steps: adding soda ash to the wastewater to adjust the pH to 7-7.5; then adding sodium sulfide and maintaining the pH at 8-8.5; then adding a precipitating agent; then adding lime to adjust the pH to 9.5-10.5; and finally adding PAM for treatment.

[0009] In any embodiment, the reaction time for adding the soda ash is 50-130 minutes; and / or, the reaction time for adding sodium sulfide is 60-130 minutes.

[0010] In any embodiment, the trapping agent is PFS.

[0011] In any implementation, the PAM treatment time is 30-40 minutes.

[0012] In any implementation, the PAM treatment is followed by a settling treatment.

[0013] In any embodiment, the settling and rinsing process takes 2-3 hours.

[0014] In any embodiment, the process further includes removing particulate impurities from the wastewater before adding soda ash to the wastewater.

[0015] In any embodiment, acid is added to the water obtained from sedimentation to adjust the pH to 7-8.

[0016] In any embodiment, the acid is sulfuric acid.

[0017] Compared with the prior art, the beneficial effects of the present invention include: The method for treating thallium-containing wastewater proposed in this invention includes the following steps: adding soda ash to the wastewater to adjust the pH to 7-7.5. Adding soda ash to control the pH can react lead salts to generate lead oxides, which are then precipitated and separated; then adding sodium sulfide and maintaining the pH at 8-8.5. The sodium sulfide reacts with monovalent thallium in the water to generate Tl2S, which is insoluble in water and precipitates and is removed. At the same time, fine heavy metals are further removed by sulfidation. Then, a trapping agent is added to further adsorb, bridge, and precipitate the fine particles that have not yet precipitated in the above process. Then, lime is added to adjust the pH to 9.5-10.5 to trap pentavalent arsenic in the wastewater and precipitate it. Then, PAM is added for treatment. Through organic macromolecular bridging and coagulation, suspended fine particles in the water are further trapped and rapidly precipitated, thereby achieving efficient removal of thallium from the wastewater. The thallium content in the treated wastewater is as low as below 5 ug / L. Attached Figure Description

[0018] Figure 1 This is a schematic flowchart of a method for treating thallium-containing wastewater according to a specific embodiment of the present invention. Detailed Implementation

[0019] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is understood that ranges of 60–110 and 80–120 are also expected. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0020] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0021] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0022] Combination Figure 1 This specific embodiment provides a method for treating thallium-containing wastewater, including the following steps: removing particulate impurities from the wastewater; adding soda ash to the wastewater to adjust the pH to 7-7.5 and reacting for 50-130 minutes; then adding sodium sulfide and maintaining the pH at 8-8.5 for 60-130 minutes; then adding a trapping agent PFS (i.e., polyferric sulfate); then adding lime to adjust the pH to 9.5-10.5; and finally adding PAM (i.e., polyacrylamide) for 30-40 minutes to obtain the final product.

[0023] In some embodiments, the PAM treatment is followed by a settling treatment of 2-3 hours.

[0024] In some embodiments, sulfuric acid is added to the water obtained from sedimentation to adjust the pH to 7-8.

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0026] In this invention, the terms "some embodiments," "this embodiment," and examples are used to describe a subset of all possible embodiments. However, it is understood that "some embodiments" can be the same subset or different subsets of all possible embodiments and can be combined with each other without conflict.

[0027] If the application documents contain similar descriptions such as "first / second", the following explanation shall be added: In the following description, the terms "first / second / third" are used only to distinguish similar objects and do not represent a specific ordering of objects. It is understood that "first / second / third" may be interchanged in a specific order or sequence where permitted, so that the embodiments described herein can be implemented in an order other than that illustrated or described herein.

[0028] In this embodiment, the term "and / or" is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, object A and / or object B can represent three situations: object A exists alone, object A and object B exist simultaneously, and object B exists alone.

[0029] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products. In the following embodiments or comparative examples, the amount of PAM added is 3 ppm.

[0030] Example 1

[0031] This embodiment proposes a method for treating thallium-containing wastewater. The wastewater is collected from a primary indium extraction process in a tin mine area. It contains thallium, as well as heavy metals such as antimony, arsenic, and lead. Its composition is: Thallium 3.24 mg / L, Sb 77.44 mg / L, Pb 85.34 mg / L, As 31.57 mg / L, and the pH value is 6. The treatment steps are as follows:

[0032] Wastewater enters the wastewater pretreatment tank, where mechanical and large particulate impurities are first removed. It then enters the heavy metal removal reaction tank, where soda ash is added, stirred, and the pH is adjusted to 7. The reaction is carried out for approximately 60 minutes. The treated wastewater then flows from the bottom of the tank into the thallium removal sulfide precipitation reaction tank. Sodium sulfide is added to the thallium removal sulfide precipitation reaction tank, and the reaction is carried out for 60 minutes to maintain the pH at 8. Afterward, the wastewater flows from the bottom of the reaction tank into the sedimentation and collection tank. PFS (polysulfide precipitant) is then added to the sedimentation and collection tank to capture antimony and arsenic. Finally, the wastewater flows from the bottom into the pH adjustment and impurity removal tank. Fine lime was added to the wastewater tank to adjust the pH to 9.5, further removing pentavalent arsenic. The treated wastewater then entered a coagulation and clarification tank from the bottom. PAM was added to the coagulation and clarification tank, and after reacting for about 30 minutes and settling for about 2 hours, water samples were sent for testing. Atomic fluorescence spectrometry analysis showed that the TL in the water was 0.11 ug / L, Sb was 0.11 mg / L, Pb was 0.23 mg / L, As was 0.05 mg / L, and the pH was 9.5. After settling, the overflow water flowed into a pH adjustment tank where 98% concentrated sulfuric acid was added to adjust the pH to 7 before discharge. The precipitated sludge automatically flowed into a collection tank, and then was pumped into a membrane plate and frame filter press. The filter water was returned to the pretreatment tank, and the filter residue was sent to a slag yard for storage and then to a specialized disposal unit.

[0033] Example 2

[0034] This embodiment proposes a method for treating thallium-containing wastewater. The wastewater is collected from a primary indium extraction process in a tin mine area. It contains thallium, as well as heavy metals such as antimony, arsenic, and lead. Its composition is: Thallium 216 mg / L, Sb 821.67 mg / L, Pb 462 mg / L, As 586 mg / L. The pH value of the wastewater is 5. The treatment steps are as follows:

[0035] Wastewater enters the wastewater pretreatment tank, where large particulate impurities are first removed. It then enters the heavy metal removal reaction tank, where soda ash is added, stirred, and the pH is adjusted to 7. The reaction is carried out for approximately 120 minutes. The wastewater then flows from the bottom of the tank into the thallium sulfide precipitation tank, where sodium sulfide is added and the reaction is carried out for 120 minutes to maintain the pH at 8. The treated water flows from the bottom of the reaction tank into the sediment collection tank, where antimony and arsenic trapping agent PFS is added to capture antimony and arsenic. The treated water then flows from the bottom into the pH adjustment and impurity removal tank. Fine lime is added to the pH adjustment and impurity removal tank to adjust the pH to 10, further removing pentavalent arsenic. The treated water then enters the coagulation and clarification sedimentation tank from the bottom, where PAM is added and reacted for about 30 minutes, followed by settling for about 3 hours. Water samples are then sent for testing. Atomic fluorescence spectrometry analysis shows that the water contains TL 2.18 ug / L, Sb 0.15 mg / L, Pb 0.47 mg / L, As 0.07 mg / L, and has a pH of 10. After settling, the overflow water flows into the pH adjustment tank where 98% concentrated sulfuric acid is added to adjust the pH to 8 before discharge. The precipitated sludge automatically flows into the collection tank, then is pumped into a membrane plate and frame filter press. The filter water is returned to the pretreatment tank, and the filter residue is sent to a slag yard for storage and then to a specialized disposal unit.

[0036] Example 3

[0037] This embodiment proposes a method for treating thallium-containing wastewater. The wastewater is collected from a primary indium extraction process in a tin mine area. It contains thallium, as well as heavy metals such as antimony, arsenic, and lead. Its composition is: Thallium 115 mg / L, Sb 492.36 mg / L, Pb 181 mg / L, As 223 mg / L. The pH value of the wastewater is 5. The treatment steps are as follows:

[0038] Wastewater enters the wastewater pretreatment tank, where large particulate impurities are first removed. It then enters the heavy metal removal reaction tank, where soda ash is added, stirred, and the pH is adjusted to 7. The reaction is carried out for approximately 90 minutes. The treated water then flows from the bottom of the tank into the sulfide precipitation and thallium removal reaction tank. Sodium sulfide is then added to the sulfide precipitation and thallium removal reaction tank, and the reaction is carried out for 90 minutes, maintaining the pH at 8. The treated water then flows from the bottom of the reaction tank into the sedimentation and collection tank, where the collecting agent PFS is added to capture antimony and arsenic. Finally, the treated water flows from the bottom into the pH adjustment and impurity removal tank. In the pH removal tank, fine lime is added to adjust the pH to 10.5 to further remove pentavalent arsenic. The treated water then enters the coagulation and clarification tank from the bottom. PAM is added to the coagulation and clarification tank, and after reacting for about 30 minutes and settling for about 4 hours, water samples are sent for testing. Atomic fluorescence spectrometry analysis shows that the water contains TL 1.86 ug / L, Sb 0.23 mg / L, Pb 0.43 mg / L, As 0.08 mg / L, and has a pH of 10.5. The overflow water after settling flows into the pH adjustment tank, where 98% concentrated sulfuric acid is added to adjust the pH to 9 before discharge. The precipitated sludge flows automatically into the collection tank and is then pumped into a membrane plate and frame filter press. The filter water is returned to the pretreatment tank, and the filter residue is sent to the slag yard for storage and then to a specialized disposal unit.

[0039] Comparative Example 1

[0040] This comparative example proposes a method for treating thallium-containing wastewater. The main difference from Example 1 is the change in the order of the wastewater treatment steps. Wastewater collected during an indium extraction process in a tin mine area is used. The wastewater contains thallium, as well as heavy metals such as antimony, arsenic, and lead. Its composition is: Thallium 3.24 mg / L, Sb 77.44 mg / L, Pb 85.34 mg / L, As 31.57 mg / L, and the pH value is 6. The treatment steps are as follows:

[0041] Wastewater enters the wastewater pretreatment tank, where large particulate impurities are first removed. It then enters the heavy metal removal reaction tank, where soda ash is added, stirred, and the pH is adjusted to 7. The reaction is carried out for approximately 60 minutes. After treatment, the wastewater enters the sedimentation and collection tank from the bottom, where PFS (polysulfide precipitate) is added to collect antimony and arsenic. It then enters the pH adjustment and impurity removal tank from the bottom, where fine lime is added to adjust the pH to 8. Finally, it enters the sulfidation thallium removal precipitation reaction tank from the bottom. Sulfidation thallium removal precipitation reaction tank is then filled with sulfidation thallium... Sodium was added and reacted for 60 minutes to maintain a pH of 9. The solution then flowed from the bottom of the reaction tank into a coagulation and clarification tank. PAM was added to the coagulation and clarification tank, and the reaction continued for approximately 30 minutes, followed by settling for about 2 hours. Water samples were then sent for testing. Atomic fluorescence spectrometry analysis showed that the water contained TL 11.23 ug / L, Sb 0.13 mg / L, Pb 0.26 mg / L, As 0.08 mg / L, and a pH of 9. The overflow water after settling flowed into a pH adjustment tank where 98% concentrated sulfuric acid was added to adjust the pH to 7 before discharge. The precipitated sludge automatically flowed into a collection tank, and was then pumped into a membrane plate and frame filter press. The filter water was returned to the pretreatment tank, and the filter residue was sent to a slag yard for storage and then to a specialized disposal unit.

[0042] Comparative Example 2

[0043] This comparative example proposes a method for treating thallium-containing wastewater. The main difference from Example 1 is that no refined lime was added. Wastewater collected during indium extraction in a tin mine area was used. The wastewater contains thallium, as well as heavy metals such as antimony, arsenic, and lead. Its composition is: Thallium 3.24 mg / L, Sb 77.44 mg / L, Pb 85.34 mg / L, As 31.57 mg / L, and the pH value is 6. The treatment steps are as follows:

[0044] Wastewater enters the wastewater pretreatment tank, where mechanical and large particulate impurities are first removed. It then enters the heavy metal removal reaction tank, where soda ash is added, stirred, and the pH is adjusted to 7. The reaction is carried out for approximately 60 minutes. The treated wastewater then flows from the bottom of the tank into the thallium sulfide precipitation reaction tank. Sodium sulfide is added to the thallium sulfide precipitation reaction tank, and the reaction is carried out for 60 minutes to maintain the pH at 8. Afterward, the wastewater flows from the bottom of the reaction tank into the sedimentation and collection tank. PFS (Potassium Sulfate) is then added to the sedimentation and collection tank to collect antimony and arsenic. The wastewater then flows from the bottom into the pH adjustment and impurity removal tank, and then from the bottom into the coagulation and clarification tank. PAM is added to the coagulation and clarification tank, and the reaction is carried out for approximately 30 minutes. After settling for approximately 2 hours, water samples are sent for testing. Atomic fluorescence spectrometry analysis shows that the TL in the water is 6.08 ug / L, Sb is 0.21 mg / L, Pb is 0.36 mg / L, As is 0.68 mg / L, and the pH is 8. After settling, the overflow water flows into the pH adjustment tank where 98% concentrated sulfuric acid is added to adjust the pH to 7 before discharge. The sludge automatically flows into the collection tank, and is then pumped into the membrane plate and frame filter press. The filter water is returned to the pretreatment tank, and the filter residue is sent to the slag yard for storage and then to a specialized disposal unit.

[0045] Other beneficial effects:

[0046] 1. The purified water treated by the method proposed in this invention meets national treatment standards, namely, effluent containing TL ≤ 5 ug / L, Pb ≤ 0.5 mg / L, Sb ≤ 0.3 mg / L, As ≤ 0.1 mg / L, and pH between 6 and 9. This method is very suitable for the treatment of thallium-containing wastewater generated during the antimony-indium smelting process.

[0047] 2. The wastewater pretreatment effect of this invention is very good, effectively blocking particulate impurities and coarse sludge from subsequent treatment.

[0048] 3. This invention has a good effect on the treatment of thallium-containing wastewater, with short treatment time and high treatment efficiency.

[0049] 4. The thallium-containing wastewater treated by this invention can fully meet the discharge standards without generating secondary pollution, thus having excellent environmental benefits.

[0050] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for treating thallium-containing wastewater, characterized by, The thallium-containing wastewater also contains antimony, arsenic, and lead. The treatment includes the following steps: adding soda ash to the wastewater to adjust the pH to 7-7.5 to react with lead salts and form a precipitate for separation; then adding sodium sulfide and maintaining the pH at 8-8.5 to react with monovalent thallium in the water to form a water-insoluble Tl2S precipitate for removal; then adding a trapping agent PFS; then adding lime to adjust the pH to 9.5-10.5 to trap pentavalent arsenic in the wastewater; then adding PAM for treatment; and finally, precipitation treatment.

2. The method of treating thallium-containing wastewater of claim 1, wherein, The reaction time after adding the soda ash is 50-130 minutes; and / or, the reaction time after adding sodium sulfide is 60-130 minutes.

3. The method of treating thallium-containing wastewater of claim 1, wherein, The PAM treatment time is 30-40 minutes.

4. The method of treating thallium-containing wastewater of claim 1, wherein, The settling and rinsing process takes 2-3 hours.

5. The method of treating thallium-containing wastewater of claim 1, wherein, Before adding soda ash to wastewater, the process also includes removing particulate impurities from the wastewater.

6. The method of treating thallium-containing wastewater of claim 1, wherein, This also includes adding acid to the water obtained from sedimentation to adjust the pH to 7-8.

7. The method of treating thallium-containing wastewater of claim 6, wherein, The acid is sulfuric acid.

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