Method for removing fluorescein sodium from wastewater

Abstract

The present application belongs to the technical field of wastewater treatment, and particularly relates to a method for removing fluorescein sodium in wastewater. The method comprises the following steps: adding powdered activated carbon into the wastewater for adsorption treatment to obtain adsorbed wastewater; adding the adsorbed wastewater into anion polyacrylamide for flocculation treatment to obtain flocculated wastewater; and performing static sedimentation treatment on the flocculated wastewater. The present application provides a powdered activated carbon and polyacrylamide synergistic enhanced coagulation deep treatment process for acid mine wastewater containing fluorescein sodium, which has a high removal rate, fast solid-liquid separation, and sludge meeting general solid waste standards, and has a wide application value.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, and specifically relates to a method for removing sodium fluorescein from wastewater. Background Technology

[0002] Acidic mine wastewater is a typical highly polluting wastewater generated during mining operations. It is characterized by low pH, high acidity, a wide variety of heavy metal ions, and persistent pollution, making it a key and challenging issue in mine ecological restoration and water environment management. In projects such as hydrogeological exploration in mining areas, identification of groundwater runoff channels, and pollution source tracing, sodium fluorescein is widely used as a water tracer due to its high sensitivity, low detection limit, and strong visibility. However, after tracer tests, a large amount of sodium fluorescein remains in the acidic mine wastewater. Sodium fluorescein is a strongly hydrophilic, highly stable small organic molecule with extremely high water solubility, making it difficult to destabilize and remove using traditional coagulation methods. This results in significant challenges in the conventional treatment of sodium fluorescein-containing acidic mine wastewater, and a prominent problem of excessive residues in the effluent.

[0003] The current mainstream treatment process for acidic mine wastewater is a two-stage coagulation and sedimentation system consisting of lime slurry neutralization and polyacrylamide flocculation. Figure 1 The diagram shows the existing acidic mine wastewater treatment process. This process can effectively neutralize the acidity of the wastewater and remove most heavy metal ions through hydroxide precipitation. However, it has almost no effect on the removal of hydrophilic sodium fluorescein. Due to the thick hydration film and low interfacial activity of sodium fluorescein molecules, traditional flocculants have extremely weak adsorption, bridging, and sweeping capabilities. They can only remove a very small amount of tracer substances through weak physical entrainment. Under conventional processes, the removal rate of sodium fluorescein is generally less than 15%, resulting in a large amount of residual effluent, which seriously affects the stability of effluent water quality and interferes with subsequent water quality monitoring and water environment assessment.

[0004] In summary, existing acidic mine wastewater treatment technologies suffer from several technical defects, including extremely low sodium fluorescein removal efficiency, easy escape of powdered activated carbon leading to excessive turbidity in effluent, poor solid-liquid separation effect, high environmental risk of bottom sediment, and prominent secondary pollution hazards. There is an urgent need to develop a new enhanced coagulation treatment process that can efficiently remove sodium fluorescein, provide stable effluent quality, achieve rapid solid-liquid separation, and ensure safe and controllable bottom sediment. Summary of the Invention

[0005] The purpose of this invention is to provide a method for removing sodium fluorescein from wastewater. The method provided by this invention has extremely high sodium fluorescein removal efficiency, while effectively ensuring solid-liquid separation and clear effluent, as well as strong bottom sediment stability and no risk of secondary pollution from hazardous waste. It has broad application value for the treatment of acidic mine wastewater.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for removing sodium fluorescein from wastewater, comprising the following steps: Powdered activated carbon was added to the wastewater for adsorption treatment to obtain adsorption-treated wastewater, which contained sodium fluorescein. The wastewater after adsorption treatment was added to anionic polyacrylamide for flocculation treatment to obtain flocculated wastewater. The wastewater after flocculation treatment is allowed to settle and settle.

[0007] Preferably, the wastewater is acidic wastewater, and before adding the powdered activated carbon, the process further includes: adding an alkaline neutralizing agent to the acidic wastewater to adjust the pH value to ≥9.5 for alkaline treatment to obtain alkaline-treated wastewater; adding powdered activated carbon to the alkaline-treated wastewater; the alkaline neutralizing agent is lime milk, and the mass percentage of the lime milk is 5~10%.

[0008] Preferably, the pH value is 9.5~10.

[0009] Preferably, the alkali treatment is carried out under stirring conditions, with the stirring speed being 150~200 r / min.

[0010] Preferably, the dosage of the powdered activated carbon is 25~200 mg / L.

[0011] Preferably, the adsorption treatment time is 5 to 20 minutes; the adsorption treatment is carried out under stirring conditions, and the stirring speed is 50 to 100 r / min.

[0012] Preferably, the weight-average molecular weight of the anionic polyacrylamide is 10-15 million; the dosage of the anionic polyacrylamide is 2-3 mg / L.

[0013] Preferably, the flocculation treatment time is 20-30 minutes; the flocculation treatment is carried out under stirring conditions, and the stirring speed is 50-100 r / min.

[0014] Preferably, the settling time is 60-80 minutes.

[0015] Preferably, the wastewater is acidic mine wastewater; the concentration of sodium fluorescein in the wastewater is 100~300 μg / L.

[0016] This invention provides a method for removing sodium fluorescein from wastewater, comprising the following steps: adding powdered activated carbon to the wastewater for adsorption treatment to obtain adsorption-treated wastewater containing sodium fluorescein; adding anionic polyacrylamide to the adsorption-treated wastewater for flocculation treatment to obtain flocculated wastewater; and allowing the flocculated wastewater to settle. Compared with the prior art, this invention has the following advantages: This invention establishes a synergistic mechanism of adsorption enrichment and floc encapsulation through the physicochemical adsorption of powdered activated carbon (PAC) and the flocculation and trapping effect of polyacrylamide (PAM), overcoming the limitations of traditional coagulation processes that rely solely on charge neutralization and sweeping effects. Verification by examples shows that this invention significantly increases the removal rate of sodium fluorescein in acidic mine wastewater from less than 15% using traditional processes to approximately 99%, fundamentally solving the technical bottleneck of separating hydrophilic tracers from the aqueous phase and ensuring that the residual concentration of sodium fluorescein in the effluent meets environmental regulatory requirements.

[0017] This invention strictly employs a sequential dosing order of "first adding powdered activated carbon for adsorption, then adding polyacrylamide for flocculation," rather than simply adding them simultaneously or in reverse order. This specific sequence ensures that the PAM macromolecular chains can promptly and fully encapsulate the adsorbed sodium fluorescein PAC particles and heavy metal hydroxide flocs, forming high-density, large-particle flocs. By optimizing the reagent addition sequence, this invention effectively prevents the problem of excessive effluent turbidity caused by the escape of powdered activated carbon particles. While achieving highly efficient microscopic adsorption, it also ensures a significant improvement in macroscopic settling rate. Verification by examples shows that this invention achieves clear supernatant within 60 minutes of settling, significantly shortening the hydraulic retention time.

[0018] The composite sediment produced by this invention was verified by acid leaching tests according to the "Solid Waste Leaching Toxicity Leaching Method - Sulfuric Acid and Nitric Acid Method" (HJ / T 299-2007). The leaching concentrations of heavy metals and organic pollutants were far below the limits of the "Identification Standard for Hazardous Waste - Leaching Toxicity Identification" (GB 5085.3-2007). This indicates that the adsorbed and enriched sodium fluorescein and co-precipitated heavy metals have extremely high chemical stability in the sediment and are not prone to re-desorption under acidic rainfall or acidic leachate leaching conditions, eliminating the risk of secondary pollution. This allows the sediment to be disposed of or utilized as general industrial solid waste, significantly reducing hazardous waste disposal costs and environmental management burden.

[0019] Furthermore, this invention is based on the existing conventional two-stage coagulation process framework of alkali neutralization precipitation and PAM flocculation. It only requires the addition of a powdered activated carbon stock solution preparation and dosing unit, without the need for large-scale civil engineering modifications to the main structures such as sedimentation tanks. The operating parameters in the embodiments (pH 9.5~10.0, slow stirring time 25 minutes, and settling time 60 minutes) are all within the adjustable range of conventional water treatment equipment. The technology is mature and easily applied and promoted in existing acidic mine wastewater treatment plants.

[0020] In summary, this invention, based on the precipitation of heavy metal ions using alkali, utilizes the adsorption properties and large specific surface area of ​​PAC to provide additional coagulation nuclei for heavy metal hydroxide flocs. Simultaneously, the bridging effect of PAM intertwines the sodium fluorescein-containing PAC with the heavy metal precipitate into a unified large floc. This synergistic process not only removes sodium fluorescein but also further reduces the content of suspended heavy metals in the effluent through co-flocculation, achieving simultaneous deep treatment of organic tracers and inorganic heavy metal composite pollutants. Attached Figure Description

[0021] Figure 1 This is a flow chart of a traditional treatment process for acidic wastewater from mines in the existing technology. Figure 2 The flowcharts are shown for the conventional coagulation process in Comparative Example 1 and the powdered activated carbon-polyacrylamide enhanced coagulation process in Example 1 of this invention. Figure 3 This is an adsorption kinetic curve of sodium fluorescein under different concentration gradients of powdered activated carbon in Example 1 of the present invention; Figure 4 This invention illustrates the effect of different dosing sequences on the removal rate of sodium fluorescein. Figure 5 This invention provides a comparative example 1 of the conventional water treatment process for measuring the changes in sodium fluorescein concentration and pH. Figure 6 The changes in sodium fluorescein concentration and pH during the novel enhanced coagulation process in Example 2 of this invention are shown. Detailed Implementation

[0022] This invention provides a method for removing sodium fluorescein from wastewater, comprising the following steps: Powdered activated carbon was added to the wastewater for adsorption treatment to obtain adsorption-treated wastewater, which contained sodium fluorescein. The wastewater after adsorption treatment was added to anionic polyacrylamide for flocculation treatment to obtain flocculated wastewater. The wastewater after flocculation treatment is allowed to settle and settle.

[0023] In this invention, unless otherwise specified, all raw materials / components used in the preparation are commercially available products well known to those skilled in the art.

[0024] This invention involves adding powdered activated carbon to wastewater for adsorption treatment, resulting in adsorption-treated wastewater containing sodium fluorescein. In this invention, the wastewater is acidic. The acidic wastewater can be acidic mining wastewater. The concentration of sodium fluorescein in the wastewater is preferably 100-300 μg / L, more preferably 150-250 μg / L, and in the examples, it can be 200 μg / L.

[0025] In this invention, the wastewater is acidic wastewater. Before adding the powdered activated carbon, the invention preferably further includes: adding an alkaline neutralizing agent to the acidic wastewater to adjust the pH value to ≥9.5 for alkaline treatment, obtaining alkaline-treated wastewater; and adding powdered activated carbon to the alkaline-treated wastewater. In this invention, the alkaline neutralizing agent is preferably lime slurry. The mass percentage of the lime slurry is preferably 5-10%, and in the examples, it can be 8%. The invention preferably pre-filters the acidic wastewater, and the pre-filtration treatment preferably uses a screen. The alkaline treatment is preferably carried out under stirring conditions, and the stirring speed is preferably 150-200 r / min. The pH value is preferably 9.5-10. The alkaline treatment time is preferably 5-20 min, more preferably 5-10 min. This invention, through alkaline treatment and by optimizing the treatment time, causes heavy metal ions in the wastewater to precipitate as hydroxides, while simultaneously releasing the fluorescent response activity of sodium fluorescein. In this invention, the pH value of the acidic mining wastewater is preferably 2-3, more preferably 2.3-2.6. The water quality test results of the acidic mine wastewater used in the embodiments of the present invention are shown in Table 1.

[0026] Table 1. Water quality monitoring results of acidic mine wastewater

[0027] After obtaining the alkali-treated wastewater, this invention adds powdered activated carbon (PAC) to the alkali-treated wastewater for adsorption treatment, obtaining adsorption-treated wastewater. In this invention, the preferred dosage of the powdered activated carbon is 25-200 mg / L, and in the examples, it can be 25 mg / L, 50 mg / L, 75 mg / L, 100 mg / L, 150 mg / L, or 200 mg / L. The powdered activated carbon is preferably added in the form of a powdered activated carbon stock solution. The powdered activated carbon stock solution is an aqueous dispersion of powdered activated carbon. The preferred mass concentration of powdered activated carbon in the powdered activated carbon stock solution is 5-15 g / L, and in the examples, it can be 10 g / L. The preferred method for preparing the powdered activated carbon stock solution is to add the powdered activated carbon to deionized water and then disperse it under ultrasonic conditions. In this invention, the adsorption treatment time is preferably 5-20 min, more preferably 5-10 min. The adsorption treatment is preferably carried out under stirring conditions, and the stirring speed is preferably 50-100 r / min. In this invention, the powdered activated carbon relies on its high specific surface area and oxygen-containing functional groups on its surface to establish a monolayer chemical adsorption with sodium fluorescein, thereby rapidly capturing and enriching sodium fluorescein in the aqueous phase in a short time.

[0028] After obtaining the adsorption-treated wastewater, this invention adds anionic polyacrylamide (PAM) to the adsorption-treated wastewater for flocculation treatment, obtaining flocculated wastewater. In this invention, the weight-average molecular weight of the anionic polyacrylamide is preferably 10-15 million. The dosage of the anionic polyacrylamide is preferably 2-3 mg / L. In this invention, the flocculation treatment time is preferably 20-30 min. The flocculation treatment is carried out under stirring conditions, and the stirring speed is preferably 50-100 r / min. This invention utilizes the large molecular chain length of polyacrylamide to perform bridging and entanglement functions, connecting and entangled the powdered activated carbon particles that have adsorbed sodium fluorescein with heavy metal hydroxide flocs to form high-density large-particle flocs.

[0029] After obtaining the flocculation-treated wastewater, the present invention allows the wastewater to settle and settle. In the present invention, the settling time is 60-80 minutes. In this invention, after the static sedimentation treatment, the invention preferably further includes adjusting the pH value with acid. The acid is a sulfuric acid solution, and the adjusted pH value is preferably 6.5~7.5, and in the embodiment it can be 7. Preferably, this invention uses static sedimentation to allow the solid flocs containing sodium fluorescein to quickly settle to the bottom, and then adds acid to the overflow supernatant to adjust the pH to 6.5~7.5 for discharge compliance.

[0030] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0031] Example 1: PAC-PAM enhanced coagulation process with different PAC concentrations This embodiment uses a six-unit stirrer to conduct a simulated comparative experiment. According to... Figure 2 The process flow chart shows that 500 mL of acidic mining wastewater is first added to a sodium fluorescein stock solution at a rotation speed of 150 r / min to achieve a concentration of 200 μg / L. This yields acidic mining wastewater containing sodium fluorescein at a concentration of 200 μg / L. Under the condition of maintaining a rotation speed of 150 r / min, 8% lime milk with a mass fraction was added to acidic mining wastewater containing sodium fluorescein until the pH value rose to 9.5~10 to precipitate heavy metals. The alkali treatment (i.e. precipitation and neutralization) time was 5 min to obtain alkali-treated wastewater. 10 g of powdered activated carbon (PAC) was added to 1 L of deionized water and ultrasonically shaken in a water bath for 10 min to prepare a PAC stock solution. The stirring speed was then reduced to 50 r / min, and the PAC stock solution was added to the alkaline wastewater at concentrations of 25 mg / L, 50 mg / L, 75 mg / L, 100 mg / L, 150 mg / L, and 200 mg / L. After addition, the stirring speed was maintained at 50 r / min for surface adsorption reactions for 1 min, 2 min, 5 min, 10 min, 15 min, and 20 min, yielding the adsorption-treated wastewater. During the experiment, the content of sodium fluorescein in the water was measured at PAC concentrations of 25 mg / L, 50 mg / L, 75 mg / L, 100 mg / L, 150 mg / L, and 200 mg / L, and surface adsorption reaction times of 1 min, 2 min, 5 min, 10 min, 15 min, and 20 min. The results of the parallel gradient experiment are shown below. Figure 3 As shown. Figure 3 As shown, when the dosage of powdered activated carbon was 25 mg / L, 50 mg / L, 75 mg / L, 100 mg / L, 150 mg / L, and 200 mg / L, and the adsorption reaction time was 20 min, the residual concentrations of sodium fluorescein in the water were 99.1 μg / L, 10.83 μg / L, 9.19 μg / L, 0.8 μg / L, 0.33 μg / L, and 0.11 μg / L, respectively, with removal rates of 50.5%, 94.6%, 95.4%, 99.6%, 99.8%, and 99.9%, respectively.

[0032] Depend on Figure 3 It can be seen that as the dosage of powdered activated carbon increases, the adsorption rate of sodium fluorescein increases, and the concentration of sodium fluorescein in the aqueous solution decreases rapidly in a short time. Under the same adsorption time conditions, the higher the concentration of powdered activated carbon, the lower the concentration of residual sodium fluorescein at equilibrium, and the better the adsorption and removal effect. The residual sodium fluorescein concentration in the low dosage group is relatively high, and there is an adsorption saturation phenomenon. The high dosage can achieve rapid and efficient adsorption of sodium fluorescein, and the main adsorption process can be basically completed in 5~10 minutes.

[0033] This embodiment proposes a PAC adsorption-PAM coagulation process for the co-treatment of sodium fluorescein without altering the basic processes of the downstream water plant. This experiment determined the maximum adsorption capacity of activated carbon and the equilibrium time (i.e., when the concentration of sodium fluorescein in the solution stabilizes and no longer decreases over time) by introducing different concentrations (25 mg / L~200 mg / L) of activated carbon into an acidic wastewater system containing 200 μg / L sodium fluorescein. The desired effect was that the detection concentration of sodium fluorescein at the final effluent pH=7 was less than 1 μg / L (the instrument's detection limit); a value below this was considered as complete adsorption of sodium fluorescein. Figure 3 This is an adsorption kinetic curve of sodium fluorescein under different concentration gradients of powdered activated carbon in Example 1 of the present invention. Therefore, according to... Figure 3 As a result, this embodiment can determine that the optimal concentration of powdered activated carbon in the system is 100 mg / L.

[0034] Example 2: PAC-PAM enhanced coagulation process with optimal PAC concentration This embodiment uses a six-unit stirrer to conduct a simulated comparative experiment. According to... Figure 2 The process flow chart shows that 500 mL of acidic mining wastewater is first added to a sodium fluorescein stock solution at a rotation speed of 150 r / min to achieve a concentration of 200 μg / L. This yields acidic mining wastewater containing sodium fluorescein at a concentration of 200 μg / L. Under the condition of maintaining a rotation speed of 150 r / min, 8% lime milk with a mass fraction was added to acidic mining wastewater containing sodium fluorescein until the pH value rose to 9.5~10 to precipitate heavy metals. The precipitation and neutralization time was 5 min, and alkaline-treated wastewater was obtained. 10 g of powdered activated carbon (PAC) was added to 1 L of deionized water and ultrasonically shaken in a water bath for 10 min to prepare a powdered activated carbon stock solution. Then, the stirring speed was reduced to 50 r / min, and the powdered activated carbon stock solution was added to the alkaline wastewater at a dosage of 100 mg / L. After the addition was completed, the stirring speed was maintained at 50 r / min for a surface adsorption reaction for 5 min to obtain the adsorption-treated wastewater. PAM (15 million molecular weight) was added to the adsorption-treated wastewater at a stirring speed of 50 r / min, with a dosage of 2 mg / L. After the addition was completed, the stirring speed was maintained at 50 r / min for 20 min to carry out the flocculation reaction, and the flocculated wastewater was obtained. Turn off the agitator and let the flocculated wastewater settle for 60 minutes to allow the solid flocs containing sodium fluorescein to settle rapidly to the bottom. Add sulfuric acid solution to the overflow supernatant to adjust the pH back to 7.0 before discharging.

[0035] Figure 6 The changes in sodium fluorescein concentration and pH during the novel enhanced coagulation process in Example 2 of this invention are shown. Figure 6 The experimental conditions were: powdered activated carbon dosage 100 mg / L, surface adsorption reaction 5 min. Figure 6 As can be seen, in the PAC-PAM enhanced coagulation process provided in Example 2, the pH of the acidic mining wastewater containing sodium fluorescein was raised to the alkaline range of 9.5-10 after being adjusted to alkalinity with lime. During this stage, the concentration of sodium fluorescein decreased rapidly and significantly with adsorption by powdered activated carbon. In the subsequent flocculation and sedimentation stages, the concentration of sodium fluorescein remained at an extremely low level. Finally, during the process of adjusting the pH to neutral with sulfuric acid, the concentration of sodium fluorescein did not show a significant increase, indicating that the adsorbed sodium fluorescein was not easily desorbed. This example can stably maintain a low residual effluent effect after pH adjustment.

[0036] Comparative Example 1: Traditional coagulation process (PAM separate coagulation process) This comparative example uses a six-unit stirrer to conduct a simulated comparative experiment. According to... Figure 2 The process flow chart shows that 500 mL of acidic mining wastewater is first added to a sodium fluorescein stock solution at a rotation speed of 150 r / min to achieve a concentration of 200 μg / L. This yields acidic mining wastewater containing sodium fluorescein at a concentration of 200 μg / L. Under the condition of maintaining a rotation speed of 150 r / min, 8% lime milk with a mass fraction was added to acidic mining wastewater containing sodium fluorescein until the pH value rose to 9.5~10 to precipitate heavy metals. The precipitation and neutralization time was 5 min, and alkaline-treated wastewater was obtained. The stirring speed was then reduced to 50 r / min, and PAM (15 million molecular weight) was added to the alkaline wastewater at a dosage of 2 mg / L. After the addition was completed, the stirring speed was maintained at 50 r / min for 20 min to carry out the flocculation reaction, and the flocculated wastewater was obtained. After turning off the agitator, the wastewater after flocculation was allowed to settle for 60 minutes to allow the solid flocs containing sodium fluorescein to settle rapidly to the bottom. The overflow supernatant was then treated with sulfuric acid solution to adjust the pH to 7.0 before discharge. The sodium fluorescein concentration in the water was 170.8 μg / L, with a removal rate of 14.6%. In this comparative example, the sodium fluorescein response value and pH changes were monitored synchronously throughout the entire process. Figure 5 This illustrates the changes in sodium fluorescein concentration and pH during the conventional water treatment process in Comparative Example 1 of this invention. Figure 5It can be seen that the traditional water treatment process provided in Comparative Example 1 raises the pH to the alkaline range after lime alkali adjustment, but the concentration of sodium fluorescein in the system decreases only slightly. Sodium fluorescein remains at a high residual level throughout the entire process of coagulation, flocculation, and sedimentation. Subsequently, when sulfuric acid is used to restore the pH to the neutral stage, the concentration of sodium fluorescein does not decrease significantly. This confirms that relying solely on the traditional lime-polyacrylamide coagulation and sedimentation process cannot effectively remove sodium fluorescein from wastewater, and the residual concentration in the effluent remains high.

[0037] Comparative Example 2: PAM-PAC Enhanced Coagulation Process This comparative example uses a six-unit stirrer to conduct a simulated comparative experiment. 500 mL of acidic mine wastewater was taken and, at a stirring speed of 150 r / min, sodium fluorescein stock solution was added to achieve a concentration of 200 μg / L. This yielded acidic mine wastewater containing sodium fluorescein at a concentration of 200 μg / L. Under the condition of maintaining a rotation speed of 150 r / min, 8% lime milk with a mass fraction was added to acidic mining wastewater containing sodium fluorescein until the pH value rose to 9.5~10 to precipitate heavy metals. The precipitation and neutralization time was 5 min, and alkaline-treated wastewater was obtained. The stirring speed was then reduced to 50 r / min, and PAM (15 million molecular weight) was added to the alkaline wastewater at a dosage of 2 mg / L. After the addition was completed, the stirring speed was reduced to 50 r / min and the flocculation reaction was carried out for 20 min to obtain the flocculated wastewater. 10 g of powdered activated carbon (PAC) was added to 1 L of deionized water and ultrasonically shaken in a water bath for 10 min to prepare a PAC stock solution. Then, maintaining a stirring speed of 50 r / min, the PAC stock solution was added to the flocculated wastewater at a dosage of 100 mg / L. After addition, the surface adsorption reaction was carried out for 5 min while maintaining a stirring speed of 50 r / min to obtain the adsorption-treated wastewater. After turning off the agitator, the wastewater after adsorption treatment was allowed to settle for 60 minutes. Due to the fine particle size of the powdered activated carbon in the wastewater, it could not settle effectively after 60 minutes, resulting in high turbidity in the effluent. Sulfuric acid solution was added to the overflow supernatant to adjust the pH to 7.0. After filtration through a 0.45 μm PTFE membrane, the content of sodium fluorescein in the water was measured to be 8.4 μg / L, with a removal rate of 95.8%. However, this removal rate was measured after filtration, and the actual turbidity of the effluent did not meet the standard, therefore this method is not feasible.

[0038] Comparative Example 3: Simultaneous addition of PAM and PAC to enhance coagulation process This comparative example uses a six-unit stirrer to conduct a simulated comparative experiment. 500 mL of acidic mine wastewater was taken and, at a stirring speed of 150 r / min, sodium fluorescein stock solution was added to achieve a concentration of 200 μg / L. This yielded acidic mine wastewater containing sodium fluorescein at a concentration of 200 μg / L. Under the condition of maintaining a rotation speed of 150 r / min, 8% lime milk with a mass fraction was added to acidic mining wastewater containing sodium fluorescein until the pH value rose to 9.5~10 to precipitate heavy metals. The precipitation and neutralization time was 5 min, and alkaline-treated wastewater was obtained. 10 g of powdered activated carbon (PAC) was added to 1 L of deionized water and ultrasonically shaken in a water bath for 10 min to prepare a PAC stock solution. Then, the stirring speed was reduced to 50 r / min, and the PAC stock solution and PAM (15 million molecular weight) were simultaneously added to the alkaline wastewater. The dosage of PAC was 100 mg / L, and the dosage of PAM was 2 mg / L. After the addition was completed, the stirring speed was maintained at 50 r / min for 25 min to carry out the flocculation reaction, resulting in flocculated wastewater. Turn off the agitator and let the flocculated wastewater settle for 60 minutes to allow the solid flocs containing sodium fluorescein to settle rapidly to the bottom. Add sulfuric acid solution to the overflow supernatant to adjust the pH back to 7.0 before discharging. The sodium fluorescein content in the water is 24.2 μg / L, with a removal rate of 87.9%.

[0039] Figure 4 This study examines the effect of different dosing sequences on the removal rate of sodium fluorescein in Example 1 (experimental conditions: powdered activated carbon dosage 100 mg / L), Comparative Example 2, and Comparative Example 3 of this invention. Figure 4 It was found that the order of dosing had a limited impact on the thermodynamic adsorption removal rate of sodium fluorescein, with the maximum difference in removal rate among the three groups being approximately 11.7%. However, the order of dosing had a decisive influence on floc morphology, the solid-liquid separation effect of powdered activated carbon, and effluent turbidity. Dosing powdered activated carbon (PAC) first, followed by polyacrylamide (PAM), showed a superior removal effect for sodium fluorescein. PAC first captures a large amount of sodium fluorescein through its high-energy surface sites, and then polyacrylamide (PAM) further enhances the removal of the remaining sodium fluorescein and powdered activated carbon (PAC) through charge neutralization and netting / sweeping effects. From the perspective of practical engineering operation and improving effluent quality, the process arrangement of using powdered activated carbon (PAC) for adsorption first, followed by polyacrylamide (PAM) for coagulation, has significant advantages. The sweeping effect of polyacrylamide (PAM) can effectively encapsulate and settle the powdered activated carbon (PAC) added upstream. While deeply purifying sodium fluorescein, it significantly reduces the risk of turbidity problems in the effluent, providing the most suitable process solution for the enrichment and sedimentation removal of powdered activated carbon (PAC).

[0040] As demonstrated by the above embodiments, the method provided by this invention achieves extremely high sodium fluorescein removal efficiency. Compared to the extremely low sodium fluorescein removal rate of only 14.6% achieved by traditional coagulation processes, this invention significantly increases the sodium fluorescein removal rate to approximately 99% through the synergistic effect of powdered activated carbon adsorption and polyacrylamide flocculation. The specific dosing sequence of this invention ensures solid-liquid separation and clear effluent. This invention employs a sequential dosing strategy of first adding powdered activated carbon for adsorption and enrichment, followed by adding polyacrylamide for netting and sweeping. The rapid encapsulation and settling of powdered activated carbon particles by polyacrylamide eliminates the problem of excessive effluent turbidity caused by the escape of powdered activated carbon particles. This invention achieves strong sediment stability and eliminates the risk of secondary pollution from hazardous waste. The generated composite sediment, after acid leaching testing according to the "Solid Waste Leaching Toxicity Leaching Method - Sulfuric Acid and Nitric Acid Method" (HJ / T 299-2007), showed that the leaching concentrations of heavy metals and organic pollutants were far below the hazardous waste identification limits in GB 5085.3, demonstrating excellent environmental safety.

[0041] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for removing sodium fluorescein from wastewater, characterized in that, Includes the following steps: Powdered activated carbon was added to the wastewater for adsorption treatment to obtain adsorption-treated wastewater, which contained sodium fluorescein. The wastewater after adsorption treatment was added to anionic polyacrylamide for flocculation treatment to obtain flocculated wastewater. The wastewater after flocculation treatment is allowed to settle and settle.

2. The method for removing sodium fluorescein from wastewater according to claim 1, characterized in that, The wastewater is acidic wastewater. Before adding the powdered activated carbon, the process further includes: adding an alkaline neutralizing agent to the acidic wastewater to adjust the pH value to ≥9.5 for alkaline treatment, thereby obtaining alkaline-treated wastewater; adding powdered activated carbon to the alkaline-treated wastewater; the alkaline neutralizing agent is lime milk, and the mass percentage of the lime milk is 5~10%.

3. The method for removing sodium fluorescein from wastewater according to claim 2, characterized in that, The pH value is 9.5~10.

4. The method for removing sodium fluorescein from wastewater according to claim 2 or 3, characterized in that, The alkali treatment is carried out under stirring conditions, with a stirring speed of 150~200 r / min.

5. The method for removing sodium fluorescein from wastewater according to claim 1, characterized in that, The dosage of the powdered activated carbon is 25~200 mg / L.

6. The method for removing sodium fluorescein from wastewater according to claim 1 or 5, characterized in that, The adsorption treatment time is 5~20 min; the adsorption treatment is carried out under stirring conditions, and the stirring speed is 50~100 r / min.

7. The method for removing sodium fluorescein from wastewater according to claim 1, characterized in that, The weight-average molecular weight of the anionic polyacrylamide is 10-15 million; the dosage of the anionic polyacrylamide is 2-3 mg / L.

8. The method for removing sodium fluorescein from wastewater according to claim 1 or 7, characterized in that, The flocculation treatment time is 20-30 minutes; the flocculation treatment is carried out under stirring conditions, and the stirring speed is 50-100 r / min.

9. The method for removing sodium fluorescein from wastewater according to claim 1, characterized in that, The settling time is 60-80 minutes.

10. The method for removing sodium fluorescein from wastewater according to claim 1 or 2, characterized in that, The wastewater is acidic mine wastewater; the concentration of sodium fluorescein in the wastewater is 100~300μg / L.

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