Preparation method and application of nitrogen-doped steel slag-biochar composite for activating persulfate

Abstract

This application discloses a method for preparing and applying a nitrogen-doped steel slag-biochar composite material for activating persulfate, belonging to the field of environmental functional materials and advanced oxidation water treatment technology, and for environmental remediation. The method includes acid pretreatment of steel slag, alkali pretreatment of sugarcane bagasse, and drying; preparation of a mixed solution of ethanol, water, and urea; mixing the mixed solution with the acid-pretreated steel slag and alkali-pretreated sugarcane bagasse, stirring until a paste is formed, drying to obtain a precursor, calcining the precursor, and then cooling and grinding it. This application features low cost, simple preparation, and excellent catalytic performance, and can degrade organic pollutants such as phenol in water by activating persulfate.

Description

Technical Field

[0001] This application belongs to the field of environmental functional materials and advanced oxidation water treatment technology, and more specifically, it relates to a method for preparing and applying a nitrogen-doped steel slag-biochar composite material for activating persulfate. Background Technology

[0002] Phenolic wastewater is a typical type of recalcitrant organic wastewater, and the research and application of efficient treatment technologies for it has always been a focus of industry attention. Commonly used treatment methods mainly include physical, biological, and chemical methods. Among them, chemical methods, primarily oxidation methods, have advantages such as fast decomposition speed, strong oxidation capacity, high purification rate, compact equipment, and suitability for advanced treatment. Although traditional chemical oxidation methods have shortcomings, they still have application value in emergency treatment and pretreatment of low-concentration phenolic wastewater due to their mild reaction conditions and simple operation. Advanced oxidation methods, which use hydroxyl radicals as the main oxidant, have gained favor among domestic and foreign researchers in recent years due to their advantages such as thorough degradation, no secondary pollution, and short residence time.

[0003] Advanced oxidation technologies (AOPs) directly oxidize pollutants in wastewater into inorganic substances or convert them into low-toxicity, easily biodegradable intermediates using chemical or chemiphysical methods. AOPs such as Fenton oxidation, photocatalytic oxidation, and ozone oxidation have attracted widespread attention due to their powerful oxidizing capabilities. The Fenton reaction, as a mature advanced oxidation process, has advantages such as simplicity, high degradation efficiency, high organic loading capacity, and mild reaction conditions, and is widely used for the degradation of various organic pollutants in wastewater. However, traditional Fenton reactions suffer from drawbacks such as a narrow pH range and large sludge production. Fenton-like systems, on the other hand, can overcome the problems of narrow effective pH range, high iron content in wastewater, and low H2O2 utilization rate inherent in traditional Fenton systems.

[0004] Persulfate (PMS) ) is a type of substance containing peroxy bonds ( It is a strong oxidizing agent with a unique asymmetric molecular structure. The bond dissociation energy of the bond (140 kJ / mol) is significantly lower than that of persulfate (PDS). The PMS molecule contains a sulfate group (260 kJ / mol), making it more prone to breakage during activation and generating highly reactive oxygen species. ) and a hydroxyl group ( This gives it both hydrophilicity and a moderate redox potential (E°=1.82 V), allowing it to exist stably and exert its oxidizing effect over a wide pH range (pH=2~12).

[0005] Currently, commonly used PMS activation methods include thermal, ultraviolet light, alkali, carbon materials, and transition metals and their oxides. Among these, transition metal (such as Fe, Co, Mn, Cu, etc.) based materials have attracted much attention due to their high catalytic efficiency; however, homogeneous metal ions suffer from problems such as easy loss, difficulty in recovery, and potential secondary pollution. Steel slag, as a bulk solid waste from the metallurgical industry, is rich in elements such as iron, calcium, silicon, and aluminum, and is a potential source of inexpensive heterogeneous metals. However, single steel slag materials often suffer from drawbacks such as small specific surface area, easy aggregation of active sites, and limited catalytic efficiency.

[0006] On the other hand, biochar produced from the pyrolysis of biomass (such as agricultural waste) possesses abundant pore structures and surface functional groups, making it an excellent catalyst support. Combining biochar with metal-containing solid waste holds promise for constructing synergistic composite catalytic materials. Furthermore, nitrogen doping of carbon materials can modulate their electronic structure, enhancing their adsorption and activation capabilities for PMS.

[0007] Therefore, developing a high-performance, low-cost heterogeneous PMS activation material prepared from steel slag and agricultural waste (bagasse) through a simple process is of great significance for realizing "waste treatment" and promoting the practical application of advanced oxidation technologies. Summary of the Invention

[0008] The purpose of this application is to provide a method for preparing and applying a nitrogen-doped steel slag-biochar composite material for activating persulfate, which has the characteristics of low cost, simple preparation and excellent catalytic performance, and can degrade organic pollutants such as phenol in water by activating persulfate.

[0009] To achieve the above objectives, this application employs the following technical solution:

[0010] The method for preparing a nitrogen-doped steel slag-biochar composite material for activating persulfate as described in this application includes the following steps:

[0011] (1) Raw material pretreatment: Steel slag with a mesh size of 40-60 was soaked in a dilute sulfuric acid solution of 0.05-0.15 mol / L and ultrasonically treated for 30-60 minutes. After soaking and ultrasonic treatment, the solid was separated and washed with deionized water until neutral. The separated solid was then dried at a temperature of 100-105℃ to obtain acid-pretreated steel slag. Sugarcane bagasse with a mesh size of 60-80 was soaked in a dilute alkali solution of 0.05-0.15 mol / L for 30-60 minutes. After soaking, the solid was separated and washed with deionized water until neutral. The separated solid was then dried at a temperature of 100-105℃ to obtain alkali-pretreated sugarcane bagasse.

[0012] (2) Preparation of mixed solution: Prepare a mixed solution with a volume ratio of ethanol to water of 1:0.5 to 1:2, add urea and dissolve it to obtain a mixed solution; the amount of urea added is 40% to 60% of the total mass of the steel slag after acid pretreatment and the sugarcane bagasse after alkali pretreatment.

[0013] (3) Mixing and drying: The sugarcane bagasse pretreated in step (1) is added to the mixed solution obtained in step (2) and stirred for 0.5~1h to ensure full contact. Then, the acid pretreated steel slag obtained in step (1) is added and stirred at 50℃~60℃ until the mixture becomes a paste. Then, it is dried at 85℃~105℃ to obtain the composite material precursor.

[0014] (4) High-temperature calcination: The composite material precursor obtained in step (3) is placed in oxygen-limited conditions and calcined at a temperature of 500℃~700℃ for 1~2h. After calcination, it is naturally cooled to room temperature, ground and sieved to obtain nitrogen-doped steel slag-biochar composite material.

[0015] As one of the preferred technical solutions, the dry basis mass ratio of steel slag to bagasse in the steel slag-biochar composite material described in this application is 0.5:1 to 2:1.

[0016] As one of the preferred technical solutions, the dilute alkaline solution in step (1) of this application is a potassium hydroxide solution.

[0017] A nitrogen-doped steel slag-biochar composite material for activating persulfate is prepared using the method described above.

[0018] The use of a nitrogen-doped steel slag-biochar composite material for activating persulfate in the degradation of phenol.

[0019] Compared with the prior art, the beneficial effects of this application are:

[0020] 1. The raw material cost of this application is extremely low, enabling the high-value utilization of waste. The industrial waste such as steel slag and agricultural waste such as sugarcane bagasse used achieve the technical objective of "treating waste with waste," thus achieving both environmental and economic benefits. The preparation method described in this application is simple in process, does not require the use of complex preparation equipment, and is suitable for large-scale production.

[0021] 2. The composite material prepared in this application has a synergistic effect. The steel slag after acid pretreatment has an activated steel slag surface, and the bagasse after alkali treatment can remove its impurities and is easier to char. After calcination, the active metal components in the steel slag are highly dispersed in the biochar with a high specific surface area and porous structure, which can effectively prevent the agglomeration and leaching of metal components during the activation oxidation process. At the same time, the nitrogen doping introduced in this application can further optimize the electronic structure and surface properties of the biochar, introduce more defect sites and active sites, and significantly enhance the adsorption and electron transfer capabilities of the composite material for PMS.

[0022] 3. The composite material prepared in this application has the advantages of excellent catalytic performance and broad application prospects. It can efficiently and stably activate PMS to produce... •and It exhibits rapid degradation capabilities for typical organic pollutants such as phenol and has the potential to be used as a heterogeneous advanced oxidation catalyst for the treatment of recalcitrant organic wastewater. Attached Figure Description

[0023] Figure 1 This describes the effect of the amount of activator added (A) and the amount of PMS solid added (B) on the phenol degradation ability in Example 1. Detailed Implementation

[0024] The technical solution described in this application will be further described below with reference to embodiments. Steel slag is a major by-product of the iron and steel smelting process, and it includes calcium oxide, iron oxide (FeO / Fe2O3), silicon dioxide (SiO2), magnesium oxide (MgO), aluminum oxide (Al2O3), phosphorus pentoxide (P2O5), metallic iron, free calcium oxide (f-CaO), and others (TiO2, Cr2O3, V2O5, etc.). The content of each component varies slightly in different types of steel slag, such as converter slag (BOF), electric arc furnace oxidizing slag (EAF oxidizing), and electric arc furnace reducing slag (EAF reducing). Meanwhile, the oxides contained in steel slag do not exist independently, but are combined in the form of oxides, mainly including silicate phases (such as tricalcium silicate (C3S) and dicalcium silicate (C2S), totaling approximately 30-60%); iron phases (including magnesia ((Fe2, Mg)O) and calcium ferrite (Ca2Fe2O5)); magnesium phases (periacriticite (MgO)); and others (possibly including calcium aluminum feldspar, perovskite, etc.). As a multi-state polymetallic composite, steel slag contains multiple redox cycles (such as Fe... 2+ / Fe 3+ Cyclic lysis promotes sulfate formation •and Yes, it forms a "liquid-solid phase redox mechanism" that generates a variety of reactive oxygen species, which helps to efficiently degrade pollutants. Compared with traditional pure metal loading, it has significant advantages in terms of metal loading rate and release rate.

[0025] Example 1

[0026] A method for preparing nitrogen-doped steel slag-biochar composite material for activating persulfate, comprising the following steps:

[0027] (1) Raw material pretreatment: 1.0g of steel slag powder was passed through a 40-60 mesh sieve, soaked in 50mL of 0.1mol / L dilute sulfuric acid solution and ultrasonically treated for 30min-60min. After soaking and ultrasonic treatment, the solid was separated and washed with deionized water until neutral. It was then dried at 105℃ to obtain acid pretreated steel slag. 1.0g of dried sugarcane bagasse was passed through a 60-80 mesh sieve and soaked in 0.1mol / L potassium hydroxide solution for 30min-60min. After soaking, the solid was separated by filtration. The solid was washed with deionized water until neutral and then dried at 100-105℃ to obtain alkali pretreated sugarcane bagasse.

[0028] (2) Preparation of mixed solution: Measure 25 mL of anhydrous ethanol and 25 mL of deionized water, mix them evenly to form a mixed solution, add 1.0 g of urea and stir until completely dissolved to obtain mixed solution A;

[0029] (3) Mixing and drying: Add 1.0g of alkali-pretreated sugarcane bagasse obtained in step (1) to the mixed solution A obtained in step (2), stir at room temperature for 0.5~1h to ensure full contact, then add 1.0g of acid-pretreated steel slag obtained in step (1), and continue stirring at a water bath temperature of 55℃ until the mixture becomes a paste. Transfer the paste to a petri dish, and then dry at a temperature of 105℃ for 12h to obtain the dried composite material precursor;

[0030] (4) High-temperature calcination: The composite material precursor obtained in step (3) is placed in a muffle furnace and calcined under oxygen-limited conditions at 600℃ for 2 hours. After calcination, it is naturally cooled to room temperature, the sample is taken out and ground and sieved to obtain the nitrogen-doped steel slag-biochar composite material, labeled as N-SS@C-1.

[0031] Example 2

[0032] The only difference between this embodiment and embodiment 1 is that the amount of urea added in step (2) is 1.2g, and the resulting steel slag-biochar composite material is labeled as N-SS@C-2.

[0033] Example 3

[0034] The difference between this embodiment and embodiment 1 is that the stirring time in step (3) is 45 min, and the resulting steel slag-biochar composite material is labeled as N-SS@C-3.

[0035] Application Example 1

[0036] Application Example 1 was used to examine the performance of N-SS@C-1, N-SS@C-2, and N-SS@C-3 obtained in Examples 1 to 3 during the phenol degradation process.

[0037] A phenol-simulated wastewater with a concentration of 10 mg / L was prepared. 50 mL of this wastewater was placed in a 100 mL Erlenmeyer flask, and 50 mg of the N-SS@C-1 composite material prepared in Example 1 (concentration 1 g / L) was added. The flask was placed in a constant-temperature shaker (25℃, 100 rpm) for adsorption for 30 minutes. Then, 25.7 mg of potassium peroxymonosulfate composite salt (active ingredient KHSO5 content ≥47%, equivalent to a PMS:phenol molar ratio of approximately 15:1) was added, and timing was started. After 30 minutes of reaction, a sample was taken and filtered through a 0.22 μm filter membrane to determine the remaining phenol concentration and calculate the removal rate. The material in Example 1 (N-SS@C-1) achieved a phenol removal rate of 82.6% within 30 minutes, exhibiting the best performance. The materials in Examples 2 and 3 achieved removal rates of 74.6% and 76.9% respectively within 30 minutes under the same conditions.

[0038] Application Example 2

[0039] Application Example 2 was used to investigate the effect of different composite material dosages on phenol degradation.

[0040] Using N-SS@C-1 prepared in Example 1 as the activator, and fixing the PMS dosage (molar ratio 15:1) and the initial phenol concentration (10 mg / L, 50 mL), the activator dosage was set to 5, 10, 25, 50, 75, and 150 mg (i.e., 0.1, 0.2, 0.5, 1, 1.5, and 3 g / L). After reacting for 30 minutes, the phenol removal rate was measured. Figure 1 (A) The results showed that when the dosage increased from 0.1 g / L to 1 g / L, the removal rate increased significantly from 25.5% to over 75.9%; further increasing to 3 g / L did not significantly change the removal rate. Considering both efficiency and economy, the optimal dosage was 1 g / L.

[0041] Application Example 3

[0042] Application Example 3 was used to investigate the effect of different PMS dosages on phenol degradation.

[0043] Using N-SS@C-1 prepared in Example 1 as the activator, with a fixed activator dosage (1 g / L) and initial phenol concentration (10 mg / L, 50 mL), the molar ratio of PMS to phenol was controlled to be 5:1, 10:1, 20:1, 30:1, and 50:1 by varying the amount of solid PMS added. After reacting for 30 minutes, the phenol removal rate was measured. Figure 1 (B) The results showed that the removal efficiency was optimal (80.24%) at a molar ratio of 20:1, and the efficiency decreased at ratios lower or higher.

[0044] Comparative Example 1

[0045] Without adding composite materials, only the same amount of PMS (molar ratio 20:1) was added, and the reaction was carried out under the same conditions for 30 minutes. The phenol removal rate was 5.5%, which was significantly lower than the phenol degradation efficiency under the activation of the activator, indicating that PMS alone has a weak oxidizing effect on phenol.

[0046] Comparative Example 2

[0047] Using untreated raw steel slag (1.0 g) instead of N-SS@C-1 prepared in Example 1, the reaction was carried out under the same conditions (1 g / L, PMS:phenol = 20:1) for 30 minutes, and the phenol removal rate was 29.12%.

[0048] Comparative Example 3

[0049] Using biochar (excluding steel slag and urea) obtained solely from direct calcination of sugarcane bagasse at 600°C instead of the composite material prepared in Example 1, the phenol removal rate was 18.66% under the same conditions for 30 minutes.

[0050] Finally, although this specification describes embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing nitrogen-doped steel slag-biochar composite material for activating persulfate, characterized in that, The preparation method includes the following steps: (1) Raw material pretreatment: Steel slag with a mesh size of 40-60 was soaked in a dilute sulfuric acid solution of 0.05-0.15 mol / L and ultrasonically treated for 30-60 minutes. After soaking and ultrasonic treatment, the solid was separated and washed with deionized water until neutral. The separated solid was then dried at a temperature of 100-105℃ to obtain acid-pretreated steel slag. Sugarcane bagasse with a mesh size of 60-80 was soaked in a dilute alkali solution of 0.05-0.15 mol / L for 30-60 minutes. After soaking, the solid was separated and washed with deionized water until neutral. The separated solid was then dried at a temperature of 100-105℃ to obtain alkali-pretreated sugarcane bagasse. (2) Preparation of mixed solution: Prepare a mixed solution with a volume ratio of ethanol to water of 1:0.5 to 1:2, add urea and dissolve it to obtain a mixed solution; the amount of urea added is 40% to 60% of the total mass of the steel slag after acid pretreatment and the sugarcane bagasse after alkali pretreatment. (3) Mixing and drying: The sugarcane bagasse pretreated in step (1) is added to the mixed solution obtained in step (2) and stirred for 0.5~1h to ensure full contact. Then, the acid pretreated steel slag obtained in step (1) is added and stirred at 50℃~60℃ until the mixture becomes a paste. Then, it is dried at 85℃~105℃ to obtain the composite material precursor. (4) High-temperature calcination: The composite material precursor obtained in step (3) is placed in oxygen-limited conditions and calcined at a temperature of 500℃~700℃ for 1~2h. After calcination, it is naturally cooled to room temperature, ground and sieved to obtain nitrogen-doped steel slag-biochar composite material.

2. The preparation method according to claim 1, characterized in that, The dry weight ratio of steel slag to bagasse in the steel slag-biochar composite material is 0.5:1 to 2:

1.

3. The preparation method according to claim 1, characterized in that, The dilute alkaline solution in step (1) is a potassium hydroxide solution.

4. A nitrogen-doped steel slag-biochar composite material for activating persulfate, characterized in that, It is prepared by any one of the preparation methods according to claims 1 to 3.

5. The use of the nitrogen-doped steel slag-biochar composite material for activating persulfate as described in claim 4 in the degradation of phenol.

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