A process for treating wastewater containing thallium

Abstract

The present application relates to the field of wastewater treatment, and specifically discloses a thallium-containing wastewater treatment process, comprising the following steps: Step 1, passing the thallium-containing wastewater into an alkali adjustment reaction tank and a sedimentation tank in sequence, and adjusting the pH of the thallium-containing wastewater to alkaline in the alkali adjustment reaction tank; Step 2, sending the supernatant of the sedimentation tank into a pre-oxidation tank provided with an ultraviolet light source, and the bottom mud of the sedimentation tank is discharged to the thallium sludge tank; Step 3, the effluent of the pre-oxidation tank is discharged to the ozone catalytic reaction tank for reaction, and the effluent of the ozone catalytic reaction tank enters the flotation separation unit; Ozone bubbles are passed into the ozone catalytic reaction tank, and the ozone bubbles include micron bubbles with a particle size of 10-50 μm and nano bubbles with a particle size of less than 200 nm; Step 4, adding coagulants and flocculants to the flotation separation unit, and one-third to two-thirds of the effluent after treatment by the flotation separation unit is returned to the pre-oxidation tank, and the remaining water flows to the clear water tank by gravity. The above-mentioned treatment process has excellent thallium removal effect on wastewater.

Description

Technical Field

[0001] The present application relates to the field of wastewater treatment, and more specifically, to a process for treating thallium-containing wastewater. Background Art

[0002] Thallium is a rare metal element. Thallium and its compounds are highly toxic substances. Their toxicity is second only to methylmercury and more than three times that of methylarsenic. They are cumulative and can cause lasting harm. Large amounts of thallium enter the environment through mining, metal smelting, industrial production and other channels, which can easily cause cross-regional and large-scale environmental abnormalities and affect the ecological environment.

[0003] Thallium usually exists in wastewater in the form of monovalent thallium and trivalent thallium. At present, the main methods for treating thallium-containing wastewater in my country are precipitation, adsorption and ion exchange.

[0004] The precipitation method mainly converts thallium ions in the wastewater into precipitates and enters the solid phase through physical and chemical reactions, thereby reducing the thallium concentration in the wastewater. However, it is difficult for the effluent to meet the discharge standards after treatment with a single chemical precipitation method.

[0005] The ion exchange method uses ion exchangers such as ion exchange resins, zeolites, molecular sieves, etc. to separate thallium ions. However, the selectivity of ion exchangers is not high, and wastewater usually contains a large amount of other conventional ions, which makes the exchangers easily ineffective.

[0006] The adsorption method uses porous solid phase materials to adsorb and separate thallium pollutants in water. Currently, the widely used thallium removal adsorbents mainly include activated carbon, nano-metal oxides, biomaterials and composite materials. However, this type of adsorbent has poor adaptability to composite wastewater, the adsorption material is difficult to regenerate, the thallium removal efficiency is low, and the cost is high.

[0007] Therefore, it is extremely important to develop a thallium-containing wastewater treatment process with good thallium removal effect. Summary of the invention

[0008] In order to effectively improve the treatment effect of thallium-containing wastewater, the present application provides a thallium-containing wastewater treatment process.

[0009] The present application provides a thallium-containing wastewater treatment process using the following technical solutions:

[0010] A process for treating thallium-containing wastewater comprises the following steps:

[0011] Step 1, passing the thallium-containing wastewater into an alkali adjustment reaction tank and a sedimentation tank in sequence, and adjusting the pH of the thallium-containing wastewater to alkaline in the alkali adjustment reaction tank;

[0012] Step 2, sending the supernatant of the sedimentation tank to a pre-oxidation tank equipped with an ultraviolet light source, and discharging the bottom sludge of the sedimentation tank to a thallium sludge tank;

[0013] Step 3, the effluent from the pre-oxidation tank is discharged to the ozone catalytic reaction tank for reaction, and the effluent from the ozone catalytic reaction tank enters the flotation separation unit; ozone bubbles are introduced into the ozone catalytic reaction tank, and the ozone bubbles include micron bubbles with a particle size of 10-50 μm and nano bubbles with a particle size of less than 200 nm, and the content of the nano bubbles is not less than 400 million / mL;

[0014] Step 4, adding coagulant and flocculant to the flotation separation unit, one third to two thirds of the effluent after treatment by the flotation separation unit is returned to the pre-oxidation tank, and the remaining water flows to the clear water tank by gravity; the effluent returned to the pre-oxidation tank contains nano-scale ozone bubbles, and the content of nano-scale ozone bubbles is not less than 80 million / mL.

[0015] Furthermore, the flotation separation unit adopts a dissolved air flotation machine, the dosage of the coagulant is 30-50 mg / L, the dosage of the flocculant is 1-2 mg / L, and the scum of the flotation separation unit is discharged to the thallium sludge pool.

[0016] By adopting the above technical scheme, the thallium-containing wastewater is first adjusted to alkalinity, and most of the thallium ions are precipitated by chemical precipitation to perform preliminary thallium removal. Flocs are formed under the action of flocculants, which can effectively remove part of the thallium ions and suspended matter in the wastewater. After solid-liquid separation in the sedimentation tank, the supernatant of the sedimentation tank still contains a certain concentration of thallium ions, which is sent to the pre-oxidation tank for pre-oxidation. Since the solubility product of trivalent thallium hydroxide is much lower than that of monovalent thallium hydroxide, after oxidizing monovalent thallium to trivalent thallium, thallium hydroxide precipitation can be quickly generated in an alkaline solution, so that the thallium ions in the solution are greatly reduced.

[0017] The supernatant of the sedimentation tank is mixed with the water returned from the flotation separation unit to the pre-oxidation tank, which contains a large number of nano-scale ozone bubbles. Under the synergistic effect of ultraviolet light, ozone quickly produces hydroxyl free radicals with higher oxidation ability and induces the production of other ground-state substances and free radicals. Hydroxyl free radicals are excellent strong oxidants. Under the action of hydroxyl free radicals, part of the monovalent thallium ions are pre-oxidized. The wastewater after pre-oxidation enters the ozone catalytic reaction tank.

[0018] In the ozone catalytic reaction pool, the average diameter of ozone bubbles is less than 100 microns, and it contains a large number of nano-scale ozone bubbles. Ozone is introduced into the water in the form of micro-nano bubbles, which prolongs the retention time of ozone in the water and increases the reaction contact area. It also has a slow-release effect in the wastewater, greatly improving the utilization rate of ozone. It can also more effectively oxidize monovalent thallium ions into trivalent thallium ions, so that the thallium ions are precipitated in an alkaline environment, and the thallium ions can still be effectively removed when the thallium content in the wastewater is very low.

[0019] In the flotation separation unit, under the action of flocculants and coagulants, the solid flocs formed by the suspended matter adhered to the micro-nano bubbles can be further floated to the liquid surface with the bubbles to form a scum layer and scraped off by a scraper and discharged to the thallium sludge pool as hazardous waste treatment. The concentration of unreacted nano-ozone bubbles in the effluent of the flotation separation unit is still relatively high. The flotation separation unit is returned to the pre-oxidation tank, and the unreacted ozone nano-bubbles can be further fully utilized, so that the unreacted ozone and ultraviolet light can synergistically enhance the pre-oxidation of thallium ions, further improving the removal effect of thallium ions.

[0020] In this field, the thallium content in wastewater can generally be treated to 10-15μg / L. The lower the thallium concentration in the wastewater, the more difficult it is to remove the thallium ions. When the thallium ion content in the wastewater is lower than 10μg / L, continuously reducing the thallium ion content has always been a technical problem in this field, and the requirements for process flow, equipment, etc. are extremely stringent. The present application utilizes a pre-oxidation tank, an ozone catalytic reaction tank and a process step formed by a coordinated flotation separation unit to reduce the thallium content in the wastewater to below 1μg / L.

[0021] Preferably, the mass ratio of the ozone to the thallium content in the thallium-containing wastewater is (1-1.5):1.

[0022] Preferably, the ultraviolet light wavelength of the ultraviolet light source is 220-260 nm, and the ultraviolet light wavelength is further preferably 250-260 nm.

[0023] By adopting the above technical solutions and optimizing the corresponding process conditions, it is helpful to improve the thallium removal effect on wastewater. Optimizing the ultraviolet wavelength of the ultraviolet light source helps ozone to produce hydroxyl free radicals with stronger oxidizing ability to pre-oxidize thallium ions in wastewater.

[0024] Furthermore, in the ozone catalytic reaction tank, an air-entrained dispersed micro-nano ultrafine bubble device is used to suck ozone under negative pressure and add it to the thallium-containing wastewater in the form of micro-nano ultrafine bubbles. Putting ozone gas into the reaction tank in the form of micro-nano bubbles not only improves the ozone utilization efficiency, but also further simplifies the process flow, so that the purpose of good thallium removal can still be achieved in wastewater with low thallium content.

[0025] Preferably, a manganese dioxide catalyst layer is provided in the ozone catalytic reaction tank.

[0026] Furthermore, the manganese dioxide catalyst layer is columnar as a whole and is located in the middle of the ozone reaction tank.

[0027] By adopting the above technical solution, the catalyst layer can further accelerate the oxidation reaction rate and help improve the treatment effect of thallium-containing wastewater.

[0028] Furthermore, an ozone tail gas destroyer is provided at the end of the ozone catalytic reaction pool, and the ozone tail gas destroyer is used to safely treat the incompletely reacted ozone before discharging. The ozone treated by the ozone tail gas destroyer can be safely discharged, thereby improving the safety of the process.

[0029] Preferably, in step 1, sulfide and flocculant are respectively added to the alkali adjustment reaction tank for stirring reaction.

[0030] Preferably, sodium hydroxide or potassium hydroxide is used in the alkali adjustment reaction tank to adjust the pH of the thallium-containing wastewater to 9-11.

[0031] Preferably, in step 1, based on the thallium-containing wastewater, the dosage of the sulfide is 5-15 mg / L, and the dosage of the flocculant is 2-3 mg / L.

[0032] Preferably, the flocculant is polyacrylamide, and the coagulant is polyaluminium chloride.

[0033] By adopting the above technical scheme and selecting suitable flocculants and coagulants, the removal effect of sediment and suspended matter in thallium-containing wastewater is guaranteed, and the treatment effect of thallium-containing wastewater is improved.

[0034] Preferably, the sulfide includes one of sodium sulfide, potassium sulfide and ammonium sulfide.

[0035] Furthermore, the sulfide is preferably sodium sulfide.

[0036] By adopting the above technical solution and selecting a mixture of sulfide and flocculant, the thallium content in the wastewater can be greatly reduced.

[0037] In summary, this application has the following beneficial effects:

[0038] 1. The treatment process of this application can reduce the thallium content in wastewater to below 1 μg / L, and the treatment effect on wastewater is excellent. The entire treatment process does not require manual operation and is fully automatically controlled.

[0039] 2. Adding ozone in the form of micro-nano ozone bubbles and coordinating with the pre-oxidation process, under the synergistic effect of ultraviolet light, the utilization rate of ozone has been significantly improved, reducing the scale of the ozone generating device. The suspended matter and tiny bubbles in the effluent of the ozone catalytic reaction tank have high viscosity and entangle each other. Combined with the flotation separation process, the effluent effect is good and the dosage of flocculant can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a flowchart of the thallium-containing wastewater treatment process of this application. DETAILED DESCRIPTION

[0041] The embodiments of the present invention will be described in detail below in conjunction with examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. The specific conditions not specified in the examples are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used without indicating the manufacturer are all conventional products that can be purchased commercially.

[0042] Example

[0043] Example 1

[0044] A process for treating thallium-containing wastewater comprises the following steps:

[0045] Step 1, passing the thallium-containing wastewater into an alkali adjustment reaction tank, adjusting the pH of the thallium-containing wastewater to 10 with a sodium hydroxide solution with a mass concentration of 10%, adding sodium sulfide, stirring and reacting for 20 minutes, and then adding flocculant polyacrylamide, and then entering a sedimentation tank for solid-liquid separation; the addition amount of sodium sulfide is 10 mg / L, and the addition amount of polyacrylamide is 3 mg / L;

[0046] Step 2, sending the supernatant of the sedimentation tank to a pre-oxidation tank equipped with an ultraviolet light source, stirring the reaction in the pre-oxidation tank and staying for 30 minutes, wherein the ultraviolet light wavelength of the ultraviolet light source is 250-260nm, and the bottom mud of the sedimentation tank is discharged to the thallium sludge tank;

[0047] Step 3, the effluent from the pre-oxidation tank is discharged to the ozone catalytic reaction tank for reaction, the reaction time is 1h, the mass ratio of ozone to the thallium content in the thallium-containing wastewater is 1:1, the ozone concentration is not less than 120mg / L, and an air-entrained dispersed micro-nano ultrafine bubble device is used to inhale ozone under negative pressure and add it to the thallium-containing wastewater in the form of micro-nano ultrafine bubbles. The ozone bubbles include micron bubbles with a particle size of 10-50μm and nano bubbles with a particle size of less than 200nm, and the nano bubble content is not less than 400 million / mL;

[0048] A columnar manganese dioxide catalyst layer is laid in the middle of the ozone catalytic reaction tank, and an ozone tail gas destroyer is arranged at the end of the ozone catalytic reaction tank, and the ozone tail gas destroyer is used to safely treat the incompletely reacted ozone before discharging; the water discharged from the ozone catalytic reaction tank enters the flotation separation unit;

[0049] Step 4, the flotation separation unit adopts a dissolved air flotation machine, and a coagulant polyaluminum chloride and a flocculant polyacrylamide are added to the dissolved air flotation machine. The dosage of the coagulant is 40 mg / L, and the dosage of the flocculant is 2 mg / L. 1 / 2 of the effluent of the flotation separation unit is returned to the pre-oxidation tank. The effluent returned to the pre-oxidation tank contains nano-scale ozone bubbles, and the content of nano-scale ozone bubbles is not less than 80 million / mL. The remaining water flows by gravity to the clear water tank, and the scum of the flotation separation unit is discharged to the thallium sludge tank.

[0050] Example 2

[0051] The difference from Example 1 is that, in step 1, the thallium-containing wastewater is passed into an alkali adjustment reaction tank, the pH of the thallium-containing wastewater is adjusted to 9 with a potassium hydroxide solution with a mass concentration of 15%, potassium sulfide is added, the reaction is stirred for 15 minutes, and then a flocculant polyacrylamide is added, the dosage of sodium sulfide is 15 mg / L, and the dosage of polyacrylamide is 2 mg / L; then the wastewater enters a sedimentation tank for solid-liquid separation; the rest is the same as Example 1.

[0052] Example 3

[0053] The difference from Example 1 is that, in step 2, the supernatant of the sedimentation tank is sent to a pre-oxidation tank equipped with an ultraviolet light source, stirred and reacted in the pre-oxidation tank and stayed for 10 minutes, wherein the ultraviolet light wavelength of the ultraviolet light source is 220-240nm, and the bottom sludge of the sedimentation tank is discharged into the thallium sludge tank; the rest is the same as Example 1.

[0054] Example 4

[0055] The difference from Example 1 is that, in step 3, the mass ratio of ozone to the thallium content in the thallium-containing wastewater is 1.5:1, and no manganese dioxide catalyst layer is provided in the ozone reaction tank. The rest is the same as Example 1.

[0056] Example 5

[0057] The difference from Example 1 is that, in step 4, the flotation separation unit adopts a mechanical stirring flotation machine, and coagulant polyaluminum chloride and flocculant polyacrylamide are added to the mechanical stirring flotation machine, the dosage of the coagulant is 30 mg / L, the dosage of the flocculant is 1 mg / L, 1 / 3 of the effluent of the flotation separation unit is returned to the pre-oxidation tank, and the remaining water flows to the clear water tank by gravity, and the scum of the flotation separation unit is discharged to the thallium sludge tank. The rest is the same as Example 1.

[0058] Example 6

[0059] The difference from Example 1 is that in step 1, the sulfide is aluminum sulfate, the dosage of aluminum sulfate is 5 mg / L, the dosage of flocculant is 5 mg / L, and the rest is the same as Example 1.

[0060] Example 7

[0061] The difference from Example 1 is that in step 4, ferric chloride is used as the coagulant, the dosage of ferric chloride is 26 mg / L, the dosage of flocculant is 4 mg / L, and the rest is the same as Example 1.

[0062] Comparative Example

[0063] Comparative Example 1

[0064] The difference from Example 1 is that in step 1, the pH value of the thallium-containing wastewater is not adjusted, and the rest is the same as Example 1.

[0065] Comparative Example 2

[0066] The difference from Example 1 is that in step 2, no ultraviolet light source is provided in the pre-oxidation tank, and the rest is the same as Example 1.

[0067] Comparative Example 3

[0068] The difference from Example 1 is that in step 3, large ozone bubbles with an average diameter of 0.1 mm are introduced into the ozone catalytic reaction tank, and the rest are the same as Example 1.

[0069] Comparative Example 4

[0070] The difference from Example 1 is that in step 3, the mass ratio of ozone to the thallium content in the thallium-containing wastewater is 1:3; the rest is the same as Example 1.

[0071] Comparative Example 5

[0072] The difference from Example 1 is that in step 4, the water discharged from the flotation separation unit flows to the clean water tank by gravity and does not flow back to the pre-oxidation tank. The rest is the same as Example 1.

[0073] Performance testing

[0074] The thallium-containing wastewater was treated by the treatment processes of Examples 1-7 and Comparative Examples 1-5. The thallium content in the thallium-containing wastewater before treatment was 5 mg / L. The thallium content in the clear water tank after treatment was detected, and the results are recorded in Table 1.

[0075] Table 1

[0076] Thallium content Example 1 0.41 μg / L Example 2 0.78 μg / L Example 3 0.86 μg / L Example 4 0.93 μg / L Example 5 0.74 μg / L Example 6 1.87 μg / L Example 7 0.88 μg / L Comparative Example 1 3.15mg / L Comparative Example 2 0.82mg / L Comparative Example 3 1.83mg / L Comparative Example 4 1.11mg / L Comparative Example 5 0.96mg / L

[0077] In combination with Examples 1-6 and Table 1, it can be seen that the treatment process of the present application can effectively remove the thallium content in the wastewater, and the thallium concentration in the effluent can be reduced to below 1 μg / L. The treatment effect on thallium-containing wastewater is excellent. The entire treatment process does not require manual operation and is fully automated and controlled, and the enterprise operating cost is low.

[0078] Combining Example 1 and Comparative Example 1 and Table 1, it can be seen that the pH value of the thallium-containing wastewater was not adjusted in Comparative Example 1, resulting in the inability of subsequent processes to cooperate, a high thallium content in the effluent, and a significant decrease in the thallium removal effect.

[0079] Combining Example 1 and Comparative Example 2 and Table 1, it can be seen that in Comparative Example 2, no ultraviolet light source is provided in the pre-oxidation tank, and the removal effect of thallium is also reduced. This is because part of the water flowing back from the flotation separation unit to the pre-oxidation tank also contains a large amount of ozone bubbles. Ozone quickly produces hydroxyl radicals with higher oxidation ability under the synergistic effect of ultraviolet light and induces the production of other ground state substances and free radicals. Hydroxyl radicals are excellent strong oxidants with a higher redox potential than simple ozone. More thallium ions are pre-oxidized under the action of hydroxyl radicals, so that the thallium ions are precipitated in an alkaline environment to achieve the purpose of removing thallium.

[0080] Combining Example 1 and Comparative Examples 3-5 and Table 1, it can be seen that the ozone bubbles introduced in Comparative Example 3 are large, rise fast in water, have a short residence time, cannot be effectively utilized, and the utilization rate of ozone is significantly reduced. The same amount of ozone is introduced but the thallium content in the effluent is significantly increased. This is because the micro-nano ozone bubbles extend the retention time of ozone in water, increase the reaction contact area, and have a slow release effect in wastewater, greatly improving the utilization rate of ozone. It can also more effectively oxidize monovalent thallium ions to trivalent thallium ions, so that thallium ions are precipitated in an alkaline environment. In Comparative Example 4, the amount of ozone is too small, which also leads to the inability to achieve a good thallium removal effect. In Comparative Example 5, part of the effluent from the flotation separation unit was not refluxed for reuse, the pre-oxidation reaction was weak, and the thallium content in the effluent increased. This is because in the flotation separation unit, the concentration of unreacted ultrafine ozone bubbles is still relatively high. Part of the water that flows back from the flotation separation unit to the pre-oxidation tank can utilize residual ozone and ultraviolet light to synergistically enhance the pre-oxidation of thallium ions, further improving the removal effect of thallium ions.

[0081] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A process for treating thallium-containing wastewater, characterized in that: The following steps are involved: Step 1, passing the thallium-containing wastewater into an alkali adjustment reaction tank and a sedimentation tank in sequence, and adjusting the pH of the thallium-containing wastewater to alkaline in the alkali adjustment reaction tank; Step 2, sending the supernatant of the sedimentation tank to a pre-oxidation tank equipped with an ultraviolet light source, and discharging the bottom sludge of the sedimentation tank to a thallium sludge tank; Step 3, the effluent from the pre-oxidation tank is discharged to the ozone catalytic reaction tank for reaction, and the effluent from the ozone catalytic reaction tank enters the flotation separation unit; Ozone bubbles are introduced into the ozone catalytic reaction pool, wherein the ozone bubbles include microbubbles with a particle size of 10-50 μm and nanobubbles with a particle size of less than 200 nm, and the content of the nanobubbles is not less than 400 million / mL; the mass ratio of the ozone to the thallium content in the thallium-containing wastewater is (1-1.5):1; Step 4, adding coagulant and flocculant to the flotation separation unit, one third to two thirds of the effluent after treatment by the flotation separation unit is returned to the pre-oxidation tank, and the remaining water flows to the clear water tank by gravity; the effluent returned to the pre-oxidation tank contains nano-scale ozone bubbles, and the content of nano-scale ozone bubbles is not less than 80 million / mL.

2. The thallium-containing wastewater treatment process according to claim 1, characterized in that: The ultraviolet light wavelength of the ultraviolet light source is 220-260nm.

3. The thallium-containing wastewater treatment process according to claim 1, characterized in that: A manganese dioxide catalyst layer is arranged in the ozone catalytic reaction pool.

4. The thallium-containing wastewater treatment process according to claim 1, characterized in that: In the step 1, sulfide and flocculant are respectively added to the alkali adjustment reaction tank for stirring reaction.

5. The thallium-containing wastewater treatment process according to claim 4, characterized in that: In the alkali adjustment reaction tank, sodium hydroxide or potassium hydroxide is used to adjust the pH of the thallium-containing wastewater to 9-11.

6. The thallium-containing wastewater treatment process according to claim 4, characterized in that: In step 1, based on the thallium-containing wastewater, the dosage of the sulfide is 5-15 mg / L, and the dosage of the flocculant is 2-3 mg / L.

7. The thallium-containing wastewater treatment process according to claim 6, characterized in that: The sulfide includes one of sodium sulfide, potassium sulfide and ammonium sulfide.

8. The process for treating thallium-containing wastewater according to claim 1, characterized in that: The flocculant is polyacrylamide, and the coagulant is polyaluminium chloride.

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