Method for treating chlorine ions in circulating water of steel industry by lime-alum salt precipitation

Abstract

The application relates to the technical field of chlorine-containing wastewater treatment and environmental protection, and specifically discloses a method for treating chlorine ions in circulating water in the steel industry by a lime-aluminum salt precipitation method. The method comprises the following steps: S1, preparing a chlorine-containing wastewater simulation water sample, wherein the obtained simulation water sample is a sodium chloride solution; S2, simultaneously adding calcium oxide and sodium metaaluminate into the simulation water sample, so that calcium ions and aluminum ions are in contact with chlorine ions in the simulation water sample to generate a chlorine-containing precipitation mixture; S3, allowing the chlorine-containing precipitation mixture to stand and stratify, and separating supernatant and wet-state precipitate; S4, filtering and diluting the supernatant, and detecting the chlorine ion concentration in the filtrate; and S5, sequentially filtering, washing, drying and grinding and screening the wet-state precipitate to obtain a powdery dechlorination by-product. The method can be used to solve the problem of excessive chlorine ions caused by the increase of the concentration multiple of circulating water, and has the advantage of improving the chlorine ion capturing capacity of a unit medicament.

Description

Technical Field

[0001] This application relates to the field of chlorine-containing wastewater treatment and environmental protection technology, and more specifically, it relates to a method for treating chloride ions in circulating water of the iron and steel industry by lime-aluminum salt precipitation. Background Technology

[0002] To achieve water conservation and emission reduction, the circulating cooling water system in the steel industry generally adopts an operation strategy that increases the concentration ratio. However, this leads to the continuous accumulation of chloride ions in the system. To address the risk of equipment corrosion caused by excessive chloride ions, the industry widely uses chemical precipitation methods for treatment. Among them, lime softening and aluminum salt coagulation are considered mature control methods due to their wide availability of reagents, relatively simple operation, and low initial investment. These methods mainly remove some suspended solids and colloids by generating calcium hydroxide or aluminum hydroxide flocs and using physical adsorption or sweeping action. To a certain extent, this can alleviate the problem of water quality deterioration and provide a basis for subsequent solid-liquid separation. They have long played a role in maintaining the basic stable operation of the circulating water system.

[0003] However, most related processes use a single reagent, which cannot form a lattice structure conducive to chloride ion fixation. This makes it difficult for aluminum ions to hydrolyze and form charged hydroxyl complexes that match the lattice of slightly soluble calcium ions, thus failing to provide sufficient active sites for chloride ion insertion and replacement. Conventional treatment methods often rely solely on physical adsorption on the floc surface, resulting in low reagent utilization and loose, unstable precipitates. Under conditions of wide concentration fluctuations, these precipitates are difficult to maintain high dechlorination efficiency and cannot meet increasingly stringent industrial water treatment standards and low-cost operation requirements. Summary of the Invention

[0004] To address the problem of maintaining high dechlorination efficiency due to the use of single reagents in related processes, this application provides a method for treating chloride ions in circulating water of the steel industry using lime-aluminum salt precipitation.

[0005] This application provides a method for treating chloride ions in circulating water of the iron and steel industry using lime-aluminum salt precipitation, employing the following technical solution: A method for treating chloride ions in circulating water of the iron and steel industry using lime-aluminum salt precipitation includes the following steps: S1. Prepare a simulated water sample containing chlorine wastewater. The obtained simulated water sample is a sodium chloride solution. S2. Calcium oxide and sodium aluminate are added to the simulated water sample at the same time. Calcium oxide dissociates to provide calcium ions, and sodium aluminate dissociates to provide aluminum ions. The calcium ions and aluminum ions react with chloride ions in the simulated water sample to generate a chloride-containing precipitate mixture. S3. Allow the chlorine-containing precipitate mixture to stand and separate into layers to obtain a supernatant and a wet precipitate; S4. Filter and dilute the supernatant, and detect the chloride ion concentration in the filtrate; S5. The wet precipitate is sequentially filtered, washed, dried, ground, and sieved to obtain a powdered dechlorination byproduct.

[0006] By adopting the above technical solution, the use of calcium oxide and sodium aluminate as composite reagent sources, and the synergistic precipitation effect of calcium and aluminum ions in the aqueous phase, replaces the limitations of single reagents, resulting in a more compact floc structure. Therefore, a highly efficient solid-liquid separation basis is obtained, providing a feasible process path for reducing the chloride ion concentration in the circulating water system.

[0007] Preferably, in step S1, the preparation step of the chlorine-containing wastewater simulated water sample includes: dissolving sodium chloride in deionized water and adjusting the initial chloride ion concentration of the resulting sodium chloride solution to 300-2000 mg / L.

[0008] By adopting the above technical solution, and by using sodium chloride as a simulated solute and controlling the initial concentration range, it is ensured that the simulated water sample matches the ionic strength and osmotic pressure characteristics of the actual circulating cooling water in the steel industry, thus avoiding precipitation kinetic errors caused by concentration deviations. Therefore, experimental data that can truly reflect the on-site working conditions are obtained, improving the reliability of industrialization.

[0009] Preferably, in step S2, before adding calcium oxide and sodium aluminate, a pretreatment step is included to adjust the initial pH value of the simulated water sample: the initial pH value of the simulated water sample is adjusted to 4~10 using 0.1 mol / L sulfuric acid solution and 0.1 mol / L sodium hydroxide solution.

[0010] By adopting the above technical solution, the pH of the reaction system is locked within a suitable range in advance, which inhibits the premature formation of inactive aluminum hydroxide colloids by aluminum ions under alkaline conditions. At the same time, it also avoids the obstruction of calcium ion precipitation caused by excessive acidity. Therefore, a stable pre-reaction environment is obtained, ensuring that calcium ions and aluminum ions can participate in the crystal nucleation process simultaneously after the subsequent addition of reagents.

[0011] Preferably, in step S2, the dosage of calcium oxide and sodium aluminate satisfies: n(Ca 2+ ):n(Al 3+ ):n(Cl - )=5:(2~4):1, where n(Ca 2+ ) originates from the dissociation of calcium oxide, n(Al 3+ ) originates from the dissociation of sodium aluminate, n(Cl - () represents the amount of initial chloride ions in the simulated water sample.

[0012] By adopting the above technical solution, the molar ratio of calcium, aluminum and chloride ions is controlled, so that the charged hydroxyl complex generated by the hydrolysis of aluminum ions can match the slightly soluble salt lattice formed by calcium ions. This provides sufficient active sites for the insertion and replacement of chloride ions, thus achieving a precipitation conversion effect driven by charge balance and improving the chloride ion capture capacity per unit reagent.

[0013] Preferably, in step S2, the contact reaction conditions for calcium ions, aluminum ions and chloride ions are: reaction temperature 30~40℃, stirring rate 200~400r / min, and reaction time 30min.

[0014] By adopting the above technical solution, the reaction temperature is controlled within the thermodynamically stable range, which not only ensures the diffusion kinetic energy of ions but also prevents excessive evaporation of water. Combined with the shear force generated by medium- and high-speed stirring, the precipitated particles are in a suitable collision growth state. Therefore, the generation, growth and aging process of crystal nuclei are completed within a reasonable reaction time of thirty minutes, thus taking into account both processing efficiency and energy consumption control.

[0015] Preferably, in step S2, when treating simulated water samples with an initial chloride ion concentration of 300–2000 mg / L, the chloride ion removal rate is 80% ± 2%.

[0016] By adopting the above technical solution, the kinetic stability of the precipitation reaction under the molar ratio and reaction conditions was verified, as it maintained a stable removal efficiency over a wide concentration range. It was unaffected by fluctuations in the initial chloride ion load, thus achieving shock resistance to changes in the concentration ratio of circulating water in steel enterprises and ensuring the continuous compliance of effluent quality.

[0017] Preferably, in step S3, the settling time is 30 min; when separating the supernatant, the supernatant is filtered using a 0.45 μm filter membrane, the filtrate is collected and diluted with deionized water to a set ratio, and the chloride ion concentration in the filtrate is detected by ion chromatography or silver nitrate titration.

[0018] By adopting the above technical solution, sufficient gravity settling time is provided, allowing fine suspended particles to fully aggregate and settle. Combined with the precise retention effect of the filter membrane, the interference of residual solids on photometric or titration detection is eliminated. Therefore, accurate liquid-phase chloride ion concentration data are obtained, providing a precise analytical basis for evaluating the dechlorination effect.

[0019] Preferably, in step S4, the filtration is carried out using a 0.45 μm filter membrane. After collecting the filtrate, it is diluted 10 to 100 times with deionized water. The mass concentration of chloride ions in the diluted filtrate is determined by ion chromatography or silver nitrate titration, and the chloride ion removal rate is calculated using a formula: ;in, To simulate the initial chloride ion mass concentration of the water sample, The mass concentration of residual chloride ions in the filtrate after treatment.

[0020] By adopting the above technical solution, a standardized sampling, testing and data processing procedure is established. By combining dilution factor with quantitative analysis method, the interference of high concentration salt on detection electrode or indicator is eliminated. Therefore, repeatable and verifiable quantitative evaluation index is obtained, ensuring the comparability and scientific validity of experimental results between different batches.

[0021] Preferably, in step S5, the washing uses deionized water and is performed 2-4 times; the drying is carried out at 50-70℃ for 10-14 hours; and the grinding and sieving are performed by grinding and then passing the product through a 100-mesh sieve to obtain a powdered dechlorination byproduct with a particle size ≤150μm.

[0022] By adopting the above technical solution, the wet precipitate is washed multiple times with deionized water, effectively removing impurities such as free sodium ions and sulfate ions adsorbed on the precipitate surface. The subsequent medium-low temperature long-term drying strategy avoids the loss of crystal water and phase transformation caused by high temperature. The final grinding and sieving process eliminates particle agglomeration. Therefore, a powder sample with high purity and uniform particle size is obtained, which meets the standard requirements for the physical properties of the sample for subsequent precision instrument characterization.

[0023] Preferably, step S5 further includes structural characterization of the powdered dechlorination byproduct: X-ray diffraction is used to analyze the crystal structure of the powdered dechlorination byproduct, and scanning electron microscopy-energy dispersive spectroscopy is used to analyze its microstructure and elemental composition. Based on the characterization results, it is inferred that the dechlorination mechanism is a synergistic effect of adsorption and anion exchange.

[0024] By adopting the above technical solution, and by comprehensively utilizing X-ray diffraction and electron microscopy, the essential properties of the precipitate products were revealed from two dimensions: macroscopic phase composition and microscopic morphology. This confirmed that chloride ions are removed by entering the interior of the precipitate lattice rather than by simple surface physical adsorption. Therefore, a clear dechlorination mechanism of adsorption and anion exchange was obtained, providing support for the process optimization and industrial application of this method.

[0025] In summary, this application has the following beneficial effects: 1. In this application, the preferred technical solution is to regulate the molar ratio of calcium ions, aluminum ions and chloride ions. The charged hydroxyl complex generated by the hydrolysis of aluminum ions can match the microsoluble salt lattice formed by calcium ions, providing sufficient active sites for the insertion and replacement of chloride ions. Therefore, a precipitation conversion effect based on charge balance is obtained, which significantly improves the chloride ion capture capacity of unit reagent. Moreover, the raw materials used are widely available and inexpensive, making them suitable for large-scale promotion and application.

[0026] 2. The method of this application, by controlling the reaction temperature within the thermodynamically stable range and coordinating with appropriate stirring shear force, promotes the precipitated particles to be in a suitable collision growth state, and completes the entire process of crystal nucleus generation, growth and aging within a reasonable reaction time. Therefore, it achieves an operational effect that balances processing efficiency and energy consumption control. The process flow is simple and controllable, does not rely on complex special equipment, and is suitable for the continuous operation needs of circulating water in steel enterprises.

[0027] 3. The method of this application maintains the kinetic stability of the precipitation reaction within a wide concentration range, unaffected by fluctuations in the initial chloride ion load. Combined with a well-defined synergistic dechlorination mechanism of adsorption and anion exchange, it achieves shock resistance to changes in the concentration ratio of circulating water. While achieving compliant treatment of chlorinated wastewater, it aligns with the concept of green industrial development and possesses both high economic and environmental value.

[0028] 4. Since this application uses calcium oxide and sodium aluminate to construct a composite precipitation system, it utilizes the synergistic precipitation effect of calcium ions and aluminum ions in the aqueous phase to replace the limitations of using a single reagent, resulting in a more compact floc structure. Therefore, it obtains a highly efficient solid-liquid separation basis, provides a practical and feasible process route for reducing the chloride ion concentration in the circulating water system, and ensures the safe operation of industrial production equipment. Attached Figure Description

[0029] Figure 1 XRD images of the precipitates under different reaction conditions obtained by this method; Figure 2 (a), (b), and (c) represent the results of this method in n(Ca) 2+ ):n(Al 3+ ):n(Cl - SEM images of the precipitate at a ratio of 5:(2~4):1; Figure 3 (a), (b), and (c) are SEM images of the precipitate products obtained by this method at 30-40℃; Figure 4 This method is used for different concentrations of Cl - The impact on the removal effect; Figure 5 This is a flowchart of a method for treating chloride ions in circulating water of the iron and steel industry using lime-aluminum salt precipitation, as proposed in this application. Detailed Implementation

[0030] The present application will be further described in detail below with reference to the accompanying drawings and embodiments.

[0031] Technical concept: This application discloses a method for treating chloride ions in circulating water of the iron and steel industry using lime-aluminate precipitation. The method includes the following steps: S1, preparing a simulated water sample containing chloride wastewater, wherein the simulated water sample is a sodium chloride solution; S2, simultaneously adding calcium oxide and sodium aluminate to the simulated water sample, where calcium ions and aluminum ions react with chloride ions in the simulated water sample to generate a chloride-containing precipitate mixture; S3, allowing the chloride-containing precipitate mixture to stand and separate into layers, obtaining a supernatant and a wet precipitate; S4, filtering and diluting the supernatant, and detecting the chloride ion concentration in the filtrate; S5, sequentially filtering, washing, drying, and grinding and sieving the wet precipitate to obtain a powdered dechlorination byproduct.

[0032] This application preferably employs a technical solution that regulates the molar ratio of calcium ions, aluminum ions, and chloride ions. The charged hydroxyl complex generated by the hydrolysis of aluminum ions can match the microsoluble salt lattice formed by calcium ions, providing sufficient active sites for the insertion and replacement of chloride ions. Therefore, a precipitation conversion effect driven by charge balance is obtained, which significantly improves the chloride ion capture capacity per unit of reagent. Moreover, the raw materials used are widely available and inexpensive, making them suitable for large-scale promotion and application.

[0033] Example 1: This example provides a method for treating chloride ions in circulating water of the iron and steel industry using lime-aluminum salt precipitation, comprising the following steps: S1. Prepare a simulated water sample containing chlorine wastewater by dissolving sodium chloride in deionized water. The resulting simulated water sample is a sodium chloride solution.

[0034] The initial chloride ion concentration of the resulting sodium chloride solution was adjusted to 300 mg / L.

[0035] S2. Calcium oxide and sodium aluminate are added to the simulated water sample simultaneously. Calcium oxide dissociates to provide calcium ions, and sodium aluminate dissociates to provide aluminum ions. The calcium ions and aluminum ions react with the chloride ions in the simulated water sample to form a chloride-containing precipitate mixture.

[0036] Before adding calcium oxide and sodium aluminate, the initial pH of the simulated water sample was adjusted to 4.0 using 0.1 mol / L sulfuric acid solution and 0.1 mol / L sodium hydroxide solution. The dosage of calcium oxide and sodium aluminate met the molar ratio of calcium ions, aluminum ions and chloride ions of 5:2:1. The contact reaction conditions for calcium ions, aluminum ions and chloride ions were a reaction temperature of 30℃, a stirring rate of 200 r / min and a reaction time of 30 min. When treating a simulated water sample with an initial chloride ion concentration of 300 mg / L, the chloride ion removal rate was measured to be 82%.

[0037] S3. Allow the chlorine-containing precipitate mixture to stand and separate into layers to obtain the supernatant and wet precipitate.

[0038] The settling time for stratification was 30 min. When separating the supernatant, a 0.45 μm filter membrane was used to filter the supernatant. After collecting the filtrate, it was diluted with deionized water to a set ratio, and the chloride ion concentration in the filtrate was detected by ion chromatography.

[0039] S4. Filter and dilute the supernatant, and detect the chloride ion concentration in the filtrate.

[0040] The filtration was carried out using a 0.45 μm filter membrane. After collecting the filtrate, it was diluted 10 times with deionized water. The mass concentration of chloride ions in the diluted filtrate was determined by ion chromatography, and the chloride ion removal rate was calculated using a formula. ;in, To simulate the initial chloride ion mass concentration of the water sample, The mass concentration of residual chloride ions in the filtrate after treatment.

[0041] S5. The wet precipitate is sequentially filtered, washed, dried, ground, and sieved to obtain a powdered dechlorination byproduct.

[0042] The washing process involved washing with deionized water twice; drying at 50°C for 10 hours; and grinding and sieving the powdered dechlorination byproduct with a particle size of less than or equal to 150 μm. The process also included structural characterization of the powdered dechlorination byproduct: X-ray diffraction was used to analyze the crystal structure, and scanning electron microscopy-energy dispersive spectroscopy was used to analyze its microstructure and elemental composition. Based on the characterization results, the dechlorination mechanism was confirmed to be a synergistic effect of adsorption and anion exchange.

[0043] Example 2: This example provides a method for treating chloride ions in circulating water of the iron and steel industry using lime-aluminum salt precipitation, comprising the following steps: S1. Prepare a simulated water sample containing chlorine wastewater by dissolving sodium chloride in deionized water. The resulting simulated water sample is a sodium chloride solution.

[0044] The initial chloride ion concentration of the resulting sodium chloride solution was adjusted to 1000 mg / L.

[0045] S2. Calcium oxide and sodium aluminate are added to the simulated water sample simultaneously. Calcium oxide dissociates to provide calcium ions, and sodium aluminate dissociates to provide aluminum ions. The calcium ions and aluminum ions react with the chloride ions in the simulated water sample to form a chloride-containing precipitate mixture.

[0046] Before adding calcium oxide and sodium aluminate, the initial pH of the simulated water sample was adjusted to 7.0 using 0.1 mol / L sulfuric acid solution and 0.1 mol / L sodium hydroxide solution. The dosage of calcium oxide and sodium aluminate met the molar ratio of calcium ions, aluminum ions and chloride ions of 5:3:1. The contact reaction conditions for calcium ions, aluminum ions and chloride ions were a reaction temperature of 35℃, a stirring rate of 300 r / min and a reaction time of 30 min. When treating a simulated water sample with an initial chloride ion concentration of 1000 mg / L, the chloride ion removal rate was measured to be 80%.

[0047] S3. Allow the chlorine-containing precipitate mixture to stand and separate into layers to obtain the supernatant and wet precipitate.

[0048] The settling time for stratification was 30 minutes. When separating the supernatant, a 0.45 μm filter membrane was used to filter the supernatant. After collecting the filtrate, it was diluted with deionized water to a set ratio, and the chloride ion concentration in the filtrate was detected by silver nitrate titration.

[0049] S4. Filter and dilute the supernatant, and detect the chloride ion concentration in the filtrate.

[0050] The filtration was carried out using a 0.45 μm filter membrane. After collecting the filtrate, it was diluted 50 times with deionized water. The mass concentration of chloride ions in the diluted filtrate was determined by silver nitrate titration, and the chloride ion removal rate was calculated using a formula. ;in, To simulate the initial chloride ion mass concentration of the water sample, The mass concentration of residual chloride ions in the filtrate after treatment.

[0051] S5. The wet precipitate is sequentially filtered, washed, dried, ground, and sieved to obtain a powdered dechlorination byproduct.

[0052] The washing process involved washing with deionized water three times; drying at 60°C for 12 hours; and grinding and sieving the powdered dechlorination byproducts to obtain powdered dechlorination byproducts with a particle size of less than or equal to 150 μm. The process also included structural characterization of the powdered dechlorination byproducts: X-ray diffraction was used to analyze the crystal structure of the powdered dechlorination byproducts, and scanning electron microscopy-energy dispersive spectroscopy was used to analyze their microstructure and elemental composition. Based on the characterization results, it was confirmed that the dechlorination mechanism was a synergistic effect of adsorption and anion exchange.

[0053] Example 3: This example provides a method for treating chloride ions in circulating water of the iron and steel industry using lime-aluminum salt precipitation, comprising the following steps: S1. Prepare a simulated water sample containing chlorine wastewater by dissolving sodium chloride in deionized water. The resulting simulated water sample is a sodium chloride solution.

[0054] The initial chloride ion concentration of the resulting sodium chloride solution was adjusted to 2000 mg / L.

[0055] S2. Calcium oxide and sodium aluminate are added to the simulated water sample simultaneously. Calcium oxide dissociates to provide calcium ions, and sodium aluminate dissociates to provide aluminum ions. The calcium ions and aluminum ions react with the chloride ions in the simulated water sample to form a chloride-containing precipitate mixture.

[0056] Before adding calcium oxide and sodium aluminate, the initial pH of the simulated water sample was adjusted to 10.0 using 0.1 mol / L sulfuric acid solution and 0.1 mol / L sodium hydroxide solution. The dosage of calcium oxide and sodium aluminate met the molar ratio of calcium ions, aluminum ions and chloride ions of 5:4:1. The contact reaction conditions for calcium ions, aluminum ions and chloride ions were a reaction temperature of 40℃, a stirring rate of 400 r / min and a reaction time of 30 min. When treating a simulated water sample with an initial chloride ion concentration of 2000 mg / L, the chloride ion removal rate was measured to be 78%.

[0057] S3. Allow the chlorine-containing precipitate mixture to stand and separate into layers to obtain the supernatant and wet precipitate.

[0058] The settling time for stratification was 30 min. When separating the supernatant, a 0.45 μm filter membrane was used to filter the supernatant. After collecting the filtrate, it was diluted with deionized water to a set ratio, and the chloride ion concentration in the filtrate was detected by ion chromatography.

[0059] S4. Filter and dilute the supernatant, and detect the chloride ion concentration in the filtrate.

[0060] The filtration was carried out using a 0.45 μm filter membrane. After collecting the filtrate, it was diluted 100 times with deionized water. The chloride ion concentration in the diluted filtrate was determined by ion chromatography, and the chloride ion removal rate was calculated using a formula. ;in, To simulate the initial chloride ion mass concentration of the water sample, The mass concentration of residual chloride ions in the filtrate after treatment.

[0061] S5. The wet precipitate is sequentially filtered, washed, dried, ground, and sieved to obtain a powdered dechlorination byproduct.

[0062] The washing process involved using deionized water, repeated four times; drying at 70°C for 14 hours; and grinding and sieving, followed by passing the powdered dechlorination byproduct through a 100-mesh sieve to obtain a particle size of less than or equal to 150 μm. The process also included structural characterization of the powdered dechlorination byproduct: X-ray diffraction was used to analyze the crystal structure, and scanning electron microscopy-energy dispersive spectroscopy was used to analyze its microstructure and elemental composition. Based on the characterization results, the dechlorination mechanism was confirmed to be a synergistic effect of adsorption and anion exchange.

[0063] Example 4: A beaker containing 100 ml of chlorine-containing wastewater was placed on a heat-collecting, constant-temperature magnetic stirrer. Under specific stirring rates and temperatures, appropriate amounts of CaO and NaAlO2 were simultaneously added to the beaker. The mouth of the beaker was sealed with sealing film. After a specific reaction time, stirring was stopped, and the mixture was allowed to settle for 30 minutes. After the solution separated into layers, the supernatant was filtered through a 0.45 μm filter membrane, and the filtrate was collected, diluted, and the removal of Cl in the effluent after the reaction was determined. - The concentration of Cl was calculated. - The removal rate was determined; the generated precipitate was filtered, washed three times with deionized water, dried at 60℃ for 12 hours, and ground through a 100-mesh sieve to obtain a powder sample, which was then analyzed by XRD and SEM-EDS.

[0064] (1) Effect of CaO and NaAlO2 dosage on chloride ion removal efficiency Using chloride ion content as the base value 1, n(Ca) was fixed respectively. 2+ ):n(Cl - ) ratio, change Al 3+ Percentage, fixed n(Al) 3 + ):n(Cl - The ratio changes Ca 2+ The optimal n(Ca) ratio was used to determine the highest chloride ion removal efficiency. 2+ ):n(Al 3+ ):n(Cl - Molar ratio and optimal dosing method.

[0065] a. Fixed n (Al 3+ ):n(Cl - ), change the CaO dosage Fixed n(Al) 3+ ):n(Cl - The solutions were 1, 2, 3, and 4, with an initial chloride ion concentration of 500 mg / L. The solutions were reacted for 30 min at a stirring speed of 200-400 r / min in a thermostatically heated magnetic stirrer at 30-40℃, followed by 30 min of settling. The pH of the solution was 4-10. The amount of CaO added was varied to investigate the effect of CaO addition on chloride ion removal rate.

[0066] b. Fix n(Ca) 2+ ):n(Cl - ), change the NaAlO2 dosage Fixed n(Ca) 2+ ):n(Cl -The following groups were selected as 1, 2, 3, 4, and 5, with an initial chloride ion concentration of 500 mg / L. The mixture was reacted for 30 min at a stirring speed of 200-400 r / min in a heat-collecting constant-temperature magnetic stirrer at 30-40℃, followed by 30 min of settling. The pH of the solution was 4-10. The dosage of NaAlO2 was varied to investigate the effect of NaAlO2 dosage on chloride ion removal rate.

[0067] (2) Effect of reaction time on chloride ion removal efficiency Fixed n(Ca) 2+ ):n(Al 3+ ):n(Cl - The initial chloride ion concentration was 500 mg / L, and the mixture was reacted for 10, 20, 30, 40, 50, 60, 90, and 120 min at a stirring speed of 200-400 r / min in a thermostatically heated magnetic stirrer at 30-40℃. After settling for 30 min, the pH of the solution was 4-10. The effect of reaction time on chloride ion removal rate was investigated.

[0068] (3) Effect of reaction temperature on chloride ion removal efficiency Fixed n(Ca) 2+ ):n(Al 3+ ):n(Cl - The reaction mixture was 5:(2~4):1, with an initial chloride ion concentration of 500 mg / L. Under experimental conditions of stirring speed of 200~400 r / min, reaction time of 30 min, solution pH of 4~10, and reaction temperatures of 25℃, 30℃, 35℃, 40℃, 45℃, and 50℃, the effect of reaction temperature on effluent chloride ion concentration and chloride ion removal rate was investigated.

[0069] (4) Effect of stirring speed on chloride ion removal efficiency Fixed n(Ca) 2+ ):n(Al 3+ ):n(Cl - The reaction mixture was 5:(2~4):1, with an initial chloride ion concentration of 500 mg / L, a reaction temperature of 30~40℃, a reaction time of 30 min, a settling time of 30 min, a solution pH of 4~10, and stirring speeds of 100, 200, 300, 400, 500, and 600 r / min, to investigate the effect of stirring speed on the effluent chloride ion concentration and chloride ion removal efficiency.

[0070] (5) Effect of initial solution pH on chloride ion removal efficiency 100 mL of simulated wastewater was measured at room temperature, with an initial chloride ion concentration of 500 mg / L. The initial pH values ​​of the simulated wastewater were adjusted to 2, 4, 6, 8, 10, and 12 respectively using 0.1 mol / L H₂SO₄ and NaOH. n(Ca) was then added. 2+ ):n(Al 3+ ):n(Cl - CaO and NaAlO2 with a ratio of 5:(2~4):1 were mixed, and the stirring speed was controlled at 200~400 r / min, the reaction temperature at 30~40℃, the reaction time at 30 min, and the sedimentation time at 30 min. The effect of the initial pH value of the solution on the chloride ion concentration in the effluent and the chloride ion removal effect was investigated.

[0071] (6) Effect of initial chloride ion concentration in solution on chloride ion removal efficiency 100 mL of simulated wastewater was measured at room temperature, with an initial chloride ion concentration of 500 mg / L and a fixed n(Ca) concentration. 2+ ):n(Al 3+ ):n(Cl - The reaction ratio was 5:(2~4):1, the stirring speed was 200~400 r / min, the reaction temperature was 30~40℃, the reaction time was 30 min, and the initial solution concentrations were 300, 500, 800, 1000, 1500, and 2000 mg / L, respectively. The initial Cl- concentration of the solution was investigated. - The effect of concentration on effluent chloride ion concentration and chloride ion removal efficiency.

[0072] Comparative Example 1: This comparative example refers to the content of Example 1, except that only calcium oxide is added in step S2, and sodium aluminate is not added. The rest of the content is the same as that of Example 1.

[0073] Comparative Example 2: This comparative example refers to the content of Example 1, except that the pretreatment step of adjusting the initial pH value of the simulated water sample is omitted in step S2. The initial pH value of the simulated water sample is the natural pH value of 7.5. The rest of the content is the same as Example 1.

[0074] Comparative Example 3: This comparative example refers to the content of Example 1, except that in step S2, the amount of calcium oxide and sodium aluminate added satisfies the molar ratio of calcium ions, aluminum ions and chloride ions of 1:1:1. The rest of the content is the same as that of Example 1.

[0075] Comparative Example 4: This comparative example refers to the content of Example 1, except that the contact reaction conditions of calcium ions, aluminum ions and chloride ions in step S2 are 10°C. The rest of the content is the same as that of Example 1.

[0076] Comparative Example 5: This comparative example is based on the content of Example 1, except that the contact reaction conditions of calcium ions, aluminum ions and chloride ions in step S2 are a stirring rate of 50 r / min. The rest of the content is the same as that of Example 1.

[0077] Comparative Example 6: This comparative example is based on the content of Example 1, except that the contact reaction time of calcium ions, aluminum ions and chloride ions in step S2 is 5 minutes. The rest of the content is the same as that of Example 1.

[0078] Performance testing Sample preparation: The supernatant of each example and comparative example was collected separately, and 500 mL of each collected liquid was placed in a stoppered glass bottle and sealed for storage. It was used for the detection of chloride ion concentration and physicochemical index in liquid phase. The corresponding wet precipitates were washed with deionized water, dried to constant weight at the corresponding temperature, ground and passed through a 100-mesh sieve. The powdered dechlorination byproducts were collected and stored in a desiccator for solid phase microstructure and composition characterization.

[0079] Chloride ion removal rate detection: Take the supernatant prepared above and filter it using a 0.45 μm pore size filter membrane. Collect the clear filtrate and dilute it with deionized water to the preset multiple. Use an ion chromatograph or an automatic potentiometric titrator to determine the mass concentration of residual chloride ions in the filtrate. The chloride ion removal rate is calculated according to the formula: the difference between the initial concentration and the residual concentration is divided by the initial concentration and multiplied by 100%. The arithmetic mean of three parallel determinations is taken as the final result. The silver nitrate titration method is performed in accordance with GB / T11896, and the ion chromatography method is performed in accordance with HJ84-2016.

[0080] Floc settling performance test: After the reaction of the chlorine-containing precipitate mixture in the examples and comparative examples is completed, it is immediately transferred to a 1000mL graduated cylinder. The stopwatch is started to record the time, and the initial position of the mud-water interface is observed and recorded as 100% scale. During the settling process, the height of the mud-water interface drop is recorded every 2 minutes until the interface height no longer changes within 30 minutes. The settling rate per unit time and the final sludge volume percentage are calculated. This process is carried out in accordance with the settling observation method in the cup and tank test method of GB / T16881-2008.

[0081] Reagent utilization and precipitate characterization: The prepared powdered dechlorination by-product sample was analyzed for its crystal structure using X-ray diffraction with a scanning angle range of 5° to 80° and a step size of 0.02°. The microstructure and agglomeration state of the sample were observed using scanning electron microscopy, and the elemental types and relative contents on the sample surface were qualitatively or semi-quantitatively analyzed using energy dispersive spectroscopy. By comparing the characteristic peak positions and changes in elemental composition, it was determined whether chloride ions successfully entered the precipitate lattice. The BET specific surface area was determined in accordance with GB / T19587-2017.

[0082] Process operation stability and shock load resistance testing: Simulated water samples with initial chloride ion concentrations of 300 mg / L, 1000 mg / L, and 2000 mg / L were prepared. Ten batches of circulating treatment tests were conducted continuously under the same process parameters. After each batch of treatment, the chloride ion concentration in the effluent was measured, and the relative standard deviation of the removal rate of each batch was calculated to evaluate the operational stability and shock load resistance of the process under different influent loads. The chloride ion control index was implemented in accordance with GB / T50050-2017 Industrial Circulating Cooling Water Treatment Design Specification.

[0083] Environmental compatibility and leaching toxicity testing: The powdered dechlorination byproduct after grinding and sieving was mixed with deionized water at a liquid-to-solid ratio of 10:1, and extracted by shaking at room temperature for 18 hours. After filtration, the leachate was obtained. The concentrations of heavy metal ions and chloride ions in the leachate were detected by inductively coupled plasma mass spectrometry to assess the environmental risks of the solidified body during long-term stockpiling or resource utilization. The leaching test was performed according to the horizontal shaking method of HJ557-2010 Solid Waste Leaching Toxicity Leaching Method. The chloride ion concentration in the leachate was determined according to GB / T15453.

[0084] Table 1: Results of Chloride Ion Removal Efficiency and Process Stability Tests

[0085] Table 2: Results of Floc Sedimentation Performance Test

[0086] Table 3: Characterization and Environmental Compatibility Test Results of Dechlorination Byproducts

[0087] Example Conclusion: As can be seen from Examples 1-3 and Comparative Example 1, and Tables 1 and 3, the composite precipitation system constructed by calcium oxide and sodium aluminate can induce chloride ions to be effectively embedded in the precipitate lattice, rather than relying solely on physical adsorption, thereby obtaining structurally stable dechlorination byproducts. Compared with single reagent systems, this composite system reduces the leaching risk of chloride ions and provides a safety guarantee for solid-liquid separation and subsequent byproduct disposal.

[0088] Based on Examples 1-3 and Comparative Example 2, and in conjunction with Tables 1 and 2, it can be seen that pretreatment and adjustment of the initial pH value before the reaction can optimize the hydrolysis morphology of aluminum ions in the aqueous phase, promote the formation of dense flocs with larger particle sizes with calcium ions; this pretreatment step effectively accelerates the settling rate and reduces the sludge volume, improves the degree of solid-liquid separation, and ensures the clarity of the effluent.

[0089] Based on Examples 1-3 and Comparative Example 3, and in conjunction with Tables 1 and 3, it can be seen that adjusting the specific molar ratio of calcium ions, aluminum ions, and chloride ions can meet the requirements of charge balance-driven precipitation conversion, allowing chloride ions to occupy the anion exchange sites in the crystal lattice more fully. The product under this ratio has a higher chloride ion fixation rate, reflecting the improvement of raw material utilization and the specificity of the reaction mechanism, thereby achieving the effect of improving dechlorination efficiency.

[0090] As can be seen from Examples 1-3 and Comparative Example 4, and Table 2, controlling the reaction temperature within the thermodynamically stable range can provide a suitable energy environment for the generation and aging of crystal nuclei, promoting the orderly crystal growth of precipitated particles. Suitable temperature conditions avoid the problem of small particles caused by insufficient power, ensuring that the flocs have good mechanical strength and sedimentation performance, which is conducive to maintaining the continuity of process operation.

[0091] As can be seen from Examples 1-3 and Comparative Example 5, and Table 2, with appropriate stirring shear force, reasonable fluid dynamic conditions can be formed in the reaction system, which not only promotes uniform contact of reactant molecules, but also avoids the crushing effect of excessive shear force on newly formed flocs; this stirring condition helps to form precipitated particles with concentrated particle size distribution and dense structure, thereby improving the treatment efficiency per unit volume.

[0092] As can be seen from Examples 1-3 and Comparative Example 6, and Table 1, under a reasonable reaction time, the precipitation reaction can complete the entire process from crystal nucleus formation to growth, ensuring that the generated solid phase material has a stable chemical structure; sufficient reaction time ensures the full realization of the dechlorination mechanism, enabling the process to maintain a stable removal effect in a wide concentration range, demonstrating good resistance to shock loads.

[0093] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for treating chloride ions in circulating water of the iron and steel industry using lime-aluminum salt precipitation, characterized in that, Includes the following steps: S1. Prepare a simulated water sample containing chlorine wastewater. The obtained simulated water sample is a sodium chloride solution. S2. Calcium oxide and sodium aluminate are added to the simulated water sample at the same time. Calcium oxide dissociates to provide calcium ions, and sodium aluminate dissociates to provide aluminum ions. The calcium ions and aluminum ions react with chloride ions in the simulated water sample to generate a chloride-containing precipitate mixture. S3. Allow the chlorine-containing precipitate mixture to stand and separate into layers to obtain a supernatant and a wet precipitate; S4. Filter and dilute the supernatant, and detect the chloride ion concentration in the filtrate; S5. The wet precipitate is sequentially filtered, washed, dried, ground, and sieved to obtain a powdered dechlorination byproduct.

2. The method for treating chloride ions in circulating water of the iron and steel industry by lime-aluminate precipitation according to claim 1, characterized in that, In step S1, the preparation of the simulated chlorine-containing wastewater sample includes: dissolving sodium chloride in deionized water and adjusting the initial chloride ion concentration of the resulting sodium chloride solution to 300–2000 mg / L.

3. The method for treating chloride ions in circulating water of the iron and steel industry by lime-aluminate precipitation according to claim 1, characterized in that, In step S2, before adding calcium oxide and sodium aluminate, a pretreatment step is also included to adjust the initial pH value of the simulated water sample: the initial pH value of the simulated water sample is adjusted to 4~10 using 0.1 mol / L sulfuric acid solution and 0.1 mol / L sodium hydroxide solution.

4. The method for treating chloride ions in circulating water of the iron and steel industry by lime-aluminum salt precipitation according to claim 1, characterized in that, In step S2, the dosages of calcium oxide and sodium aluminate satisfy: n(Ca 2+ ):n(Al 3+ ):n(Cl - )=5:(2~4):1, where n(Ca 2+ ) originates from the dissociation of calcium oxide, n(Al) 3+ ) originates from the dissociation of sodium aluminate, n(Cl - () represents the amount of initial chloride ions in the simulated water sample.

5. The method for treating chloride ions in circulating water of the iron and steel industry by lime-aluminate precipitation according to claim 1, characterized in that, In step S2, the contact reaction conditions for calcium ions, aluminum ions and chloride ions are: reaction temperature 30~40℃, stirring rate 200~400r / min, and reaction time 30min.

6. The method for treating chloride ions in circulating water of the iron and steel industry by lime-aluminum salt precipitation according to claim 1, characterized in that, In step S2, when treating simulated water samples with an initial chloride ion concentration of 300–2000 mg / L, the chloride ion removal rate was 80% ± 2%.

7. The method for treating chloride ions in circulating water of the iron and steel industry by lime-aluminate precipitation according to claim 1, characterized in that, In step S3, the settling time is 30 min; when separating the supernatant, the supernatant is filtered using a 0.45 μm filter membrane, and the filtrate is collected and diluted with deionized water to a set ratio. The chloride ion concentration in the filtrate is detected by ion chromatography or silver nitrate titration.

8. The method for treating chloride ions in circulating water of the iron and steel industry by lime-aluminum salt precipitation according to claim 1, characterized in that, In step S4, filtration is performed using a 0.45 μm filter membrane. After collecting the filtrate, it is diluted 10 to 100 times with deionized water. The chloride ion concentration in the diluted filtrate is determined by ion chromatography or silver nitrate titration, and the chloride ion removal rate is calculated using the following formula: ;in, To simulate the initial chloride ion mass concentration of the water sample, The mass concentration of residual chloride ions in the filtrate after treatment.

9. The method for treating chloride ions in circulating water of the iron and steel industry by lime-aluminate precipitation according to claim 1, characterized in that, In step S5, the washing uses deionized water and is performed 2-4 times; the drying is carried out at 50-70℃ for 10-14 hours; and the grinding and sieving involves grinding the product and then passing it through a 100-mesh sieve to obtain a powdered dechlorination byproduct with a particle size ≤150μm.

10. The method for treating chloride ions in circulating water of the iron and steel industry by lime-aluminum salt precipitation according to claim 1, characterized in that, Step S5 also includes structural characterization of the powdered dechlorination byproducts: X-ray diffraction is used to analyze the crystal structure of the powdered dechlorination byproducts, and scanning electron microscopy-energy dispersive spectroscopy is used to analyze their microstructure and elemental composition. Based on the characterization results, it is inferred that the dechlorination mechanism is a synergistic effect of adsorption and anion exchange.

Images