A method for promoting fenton-like oxidation effect of ferrous silicate under weak acid condition

Abstract

The application discloses a method for promoting the Fenton-like oxidation effect of ferrous silicate under weak acid conditions, which comprises the following steps: adjusting the pH of organic wastewater to 4.5-5.5, adding ferrous silicate catalytic material and a promoter (sodium bisulfite and / or disodium malonate), and then slowly adding hydrogen peroxide for oxidation reaction. The method uses ferrous silicate catalytic material and sodium bisulfite or disodium malonate as the promoter, can catalyze the rapid and complete oxidation and degradation of hydrogen peroxide to organic wastewater under weak acid conditions, and solves the technical problems of the existing Fenton-like oxidation, such as the limitation to strong acid environment, low reaction rate under weak acid conditions, unstable effect of the promoter and low activity of the catalytic material, and is especially suitable for the treatment of dye wastewater, beneficiation wastewater and other water bodies containing refractory organic matters.

Description

Technical Field

[0001] This invention relates to a Fenton-like oxidation method, and more particularly to a method for promoting the Fenton oxidation effect of ferrous silicate under weakly acidic conditions, belonging to the field of organic wastewater treatment technology. Background Technology

[0002] Traditional homogeneous Fenton systems typically rely on strong acidic conditions, resulting in technical problems such as a narrow operating pH window, excessive iron sludge, and high process adjustment costs.

[0003] In recent years, heterogeneous Fenton-like catalytic materials have become a research hotspot, among which iron-based catalytic materials have attracted attention due to their broad and good interfacial catalytic capabilities. With the development of Fenton system regulation strategies, the addition of small-molecule Fenton promoters has become an effective way to enhance the reaction activity under weak acid and near-neutral conditions. Compared with redesigning catalysts, Fenton promoters have advantages such as short screening cycles, flexible addition methods, easy coupling with existing reaction systems, and rapid regulation around the iron cycle and interfacial reactions, showing promising application prospects. For example, Chinese patent (CN101792205A) discloses a Fenton and Fenton-like system enhancer. By using ascorbic acid, sodium sulfite, lithium sulfite, potassium sulfite, magnesium sulfite, calcium sulfite, hydroxylamine hydrochloride, hydroxylamine perchlorate, hydroxylamine sulfate, hydrazine, N,N-diethylhydroxylamine, carbazide, aminoethanolamine, hydroxylamine solution, or nitrogen-tetrasubstituted phenylenediamine, it can solve the current limitations of pH value in Fenton and Fenton-like reactions, and the Fenton reaction's Fe... 2+ It has drawbacks such as excessive dosage and low Fenton-like reaction rate. However, its Fenton-like reaction efficiency is still relatively low, with an oxidation degradation efficiency of about 80% for organic pollutants in wastewater after 10 minutes, and its optimal Fenton-like reaction pH range is 4-5. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a method for promoting the Fenton oxidation effect of ferrous silicate under weakly acidic conditions. This method employs ferrous silicate as a catalytic material and special sodium bisulfite or disodium malonate with hydroxylamine hydrochloride as a promoter. It can catalyze the rapid and thorough oxidation and degradation of organic wastewater by hydrogen peroxide under weakly acidic conditions, achieving an oxidation and degradation efficiency of over 97% within 2.5 minutes. This solves the technical problems of existing Fenton oxidation methods, such as being limited to strongly acidic environments, having low reaction rates under weakly acidic conditions, unstable promoter effects, and low activity of catalytic materials.

[0005] To achieve the above-mentioned technical objectives, the present invention provides a method for promoting the Fenton oxidation effect of ferrous silicate under weakly acidic conditions. The method involves adjusting the pH of organic wastewater to 4.5-5.5, first adding ferrous silicate catalyst and promoter, and then slowly adding hydrogen peroxide to carry out the oxidation reaction. The promoter includes sodium bisulfite and / or disodium malonate.

[0006] This invention relates to an advanced oxidative degradation process for organic wastewater. By employing a Fenton-like catalytic oxidation system of ferrous silicate-hydrogen peroxide, and using sodium bisulfite and / or disodium malonate as promoters, the Fenton-like catalytic oxidation effect can be significantly amplified. This enables better catalytic oxidation degradation under weakly acidic conditions and in a shorter time, effectively addressing the shortcomings of existing Fenton-like oxidation methods that rely on strongly acidic environments and have low catalytic oxidation efficiency under weakly acidic conditions.

[0007] This invention selects sodium bisulfite or disodium malonate as an accelerator. In an environment with pH ≈ 5, sodium bisulfite can pass through HSO3... - Selective reduction of Fe(III) accelerates the Fe(III) / Fe(II) cycle to promote the Fe2SiO4 / H2O2-like Fenton oxidation system, while disodium malonate can act as a medium-strength ligand, stabilizing iron species through complexation and promoting the formation of surface-homogeneous synergistic reaction pathways. Both can effectively avoid the side reactions or complexation failure problems common under neutral or alkaline conditions under weakly acidic conditions, thus showing a significant promoting effect.

[0008] As a preferred embodiment, the ferrous silicate catalyst is prepared by the following method: a sodium silicate solution is slowly and uniformly added to a ferrous sulfate solution, and the reaction is stirred at pH 5-7. The reaction product is then filtered, washed, and dried to obtain the catalyst. The molar ratio of sodium silicate in the sodium silicate solution to ferrous sulfate in the ferrous sulfate solution is 0.5:1 to 0.75:1. The ferrous silicate catalyst obtained by the preferred method has an amorphous crystalline structure, nanoparticle morphology, and a positively charged surface. It can achieve rapid enrichment of organic pollutants, especially anionic organic pollutants, on its surface. Simultaneously, the ferrous silicate catalyst exhibits higher catalytic activity due to its nanostructure and amorphous crystal form. Based on the synergistic effect of "rapid enrichment" and "highly efficient catalysis" of organic pollutants, the catalytic oxidation efficiency of organic pollutants is greatly improved. This invention, by synergistically controlling the feeding method, pH conditions, and material ratio, can control the morphology and crystal phase of the synthesized ferrous silicate to obtain a ferrous silicate catalyst with good adsorption performance and high catalytic activity. On the one hand, by adjusting the molar ratio of sodium silicate to ferrous sulfate, the isoelectric point of the ferrous silicate material can be adjusted. By controlling the ratio within a suitable range, a ferrous silicate material with a high isoelectric point can be obtained, making its surface positively charged, thus exhibiting high adsorption activity for anionic organic pollutants and demonstrating adsorption effect. On the other hand, by controlling the feeding method and pH conditions of the sodium silicate solution and ferrous sulfate solution during the reaction process, the particle morphology and crystal phase structure of the ferrous silicate catalyst material can be effectively controlled. Under optimized conditions, it can be ensured that the obtained ferrous silicate catalyst material has an amorphous crystal phase and a regular particle morphology, which is conducive to obtaining a ferrous silicate catalyst material with high catalytic activity. The reaction pH of this invention is preferably controlled within the range of 5 to 7. The higher the pH of the reaction, the lower the catalytic activity of the ferrous silicate catalyst, and the lower the pH of the reaction, the higher the catalytic activity of the ferrous silicate catalyst. However, when the pH is less than 5, the amount of ferrous silicate catalyst produced is very low and has no production value. For example, the yield of ferrous silicate catalyst at pH=5 is only about one-tenth of that at pH=7.

[0009] As a preferred embodiment, the concentration of the ferrous sulfate solution is 150~250 g / L;

[0010] As a preferred embodiment, the concentration of the sodium silicate solution is 50~150g / L.

[0011] As a preferred embodiment, the reaction conditions are: room temperature and a reaction time of 0.5 h to 1 h. If the temperature is too high, highly crystalline ferrous silicate material is easily obtained, while controlling the temperature at room temperature yields amorphous ferrous silicate material. A reaction time of 0.5 h indicates the reaction is essentially complete, and extending the reaction time has little effect on the performance of the ferrous silicate material. As a further preferred embodiment, the reaction time is 0.5 h to 1.0 h.

[0012] As a preferred embodiment, the drying process employs either oven drying or natural air drying. The oven drying temperature is 95-105℃, and the time is 1-2 hours; the natural air drying time is 1-3 days. During the drying process, ferrous silicate materials undergo not only "dehydration" but also condensation polymerization and structural rearrangement. Inappropriate drying methods can easily lead to a decrease in specific surface area (possibly due to further condensation polymerization (-OH / -OR) during drying) and pore structure collapse caused by surface tension. Condensation polymerization results in "smoothing / densification of pore walls," directly reducing the usable surface area and accessibility of active sites. More importantly, the Si–OH (silanol) group on the silicon surface is the core group determining surface hydrophilicity and adsorption behavior. Conventional drying methods can retain the silanol group on the dried xerogel surface, and high-density silanol makes the surface hydrophilic and a molecular adsorption center; however, removing the hydroxyl group significantly alters the surface properties. Vacuum drying will cause the silanols on the surface / inside the pores of ferrous silicate to undergo further dehydroxylation and condensation to form Si–O–Si, making the surface "drier, less polar, and with fewer hydrogen bond donors." This will result in a reduction of hydroxyl groups, a decrease in surface polarity, and a denser pore structure. This will directly reduce the enrichment of organic matter at the interface (decreased adsorption and poorer mass transfer) and weaken the effective activation of H2O2 at the interface (decreased contact probability and fewer interfacial reaction zones).

[0013] As a preferred embodiment, the amount of ferrous silicate catalyst added is controlled to have a concentration of 0.1–1.0 g / L in the organic wastewater.

[0014] As a preferred embodiment, the amount of hydrogen peroxide added is controlled to maintain its concentration in the organic wastewater at 5–10 mM.

[0015] As a preferred embodiment, the amount of the promoter added is controlled to maintain its concentration in the organic wastewater at 0.1–1.0 mM. As a more preferred embodiment, when sodium bisulfite is selected as the promoter, its amount added is controlled to maintain its concentration in the organic wastewater at 0.4–0.6 mM. When disodium malonate is selected as the promoter, its amount added is controlled to maintain its concentration in the organic wastewater at 0.1–0.3 mM. If the dosage of sodium bisulfite is low, it is insufficient to effectively promote the Fe(III) / Fe(II) cycle, while a high dosage inhibits the reaction due to the removal of ·OH and non-productive consumption of H2O2. If the dosage of disodium malonate is low, its complexation regulation effect is limited; if the dosage is high, it may reduce the reactivity by excessively complexing iron ions, thereby inhibiting the effective activation of H2O2. Both exhibit typical "optimal dosage window" characteristics, but their high-dose failure mechanisms stem from enhanced side reactions and inactivation of active centers, respectively.

[0016] The organic wastewater of this invention includes mineral processing wastewater, dye wastewater, antibiotic wastewater, etc. Generally, the concentration of organic matter in the organic wastewater is in the range of 60~220 mg / L.

[0017] Compared with the prior art, the beneficial technical effects of the technical solution of the present invention are as follows:

[0018] This invention introduces sodium bisulfite or disodium malonate promoters into a Fenton-like catalytic oxidation system of ferrous silicate-hydrogen peroxide. This can significantly amplify the Fenton-like catalytic oxidation effect under weakly acidic conditions, achieving near-complete short-time removal, such as achieving an oxidation degradation efficiency of over 97% within 2.5 minutes, and demonstrating a high efficiency / dosage ratio.

[0019] The ferrous silicate catalytic material used in this invention has an amorphous crystal phase structure, nanoparticle morphology, and a positively charged surface. It not only has high adsorption activity for anionic organic pollutants, but also can catalyze the efficient oxidation and degradation of organic pollutants by peroxides. Based on the synergistic effect of "rapid enrichment" and "efficient catalysis" of organic pollutants, the catalytic oxidation efficiency of organic pollutants is greatly improved.

[0020] This invention enables the advanced oxidation process of organic wastewater to be carried out in a weakly acidic pH environment, breaking the constraint that traditional Fenton catalysis requires acidic conditions for degradation and reducing the consumption of acid and alkali reagents. Attached Figure Description

[0021] Figure 1 The image shows the XRD pattern of the ferrous silicate catalyst prepared in Example 1.

[0022] Figure 2 The image shows a scanning electron microscope (SEM) image of the ferrous silicate catalyst prepared in Example 1.

[0023] Figure 3 The graph shows the degradation effect of methyl orange solution at different concentrations of sodium bisulfite or disodium malonate.

[0024] Figure 4 The graph shows the degradation effect of methyl orange solution when using different accelerators.

[0025] Figure 5 A comparison chart showing the degradation effect of methyl orange solution when using sodium bisulfite or disodium malonate versus when not using sodium bisulfite or disodium malonate. Detailed Implementation

[0026] The following examples are intended to further illustrate the content of the present invention, but should not be construed as limiting the scope of protection of the claims of the present invention.

[0027] Example 1

[0028] 1) Dissolve 20.00g of ferrous sulfate heptahydrate in 100ml of pure water to obtain a ferrous sulfate solution;

[0029] 2) Dissolve 10.22g of sodium silicate nonahydrate in 100ml of pure water to obtain a sodium silicate solution;

[0030] 3) The sodium silicate solution was slowly and uniformly added to the ferrous sulfate solution using an injection device while stirring. The pH of the solution was controlled at 7, and the reaction time was 1 hour. After the reaction, the mixture was filtered, and the filter residue was washed with water and then dried in an oven at 100°C for 1.5 hours. Five groups of experiments were set up according to different molar ratios of sodium silicate to ferrous sulfate: 0.5:1, 0.75:1, and 1:1, respectively. The obtained ferrous silicate catalysts were designated as A-1, A-2, and A-3, respectively.

[0031] A-1 and A-2 are mainly black granules, primarily composed of amorphous ferrous silicate. However, as the molar ratio of sodium silicate to ferrous sulfate increases, the ferrous silicate gradually transforms into waxy yellow lumps, such as A-3, which has relatively high crystallinity and is brittle.

[0032] This invention provides ferric silicate prepared by varying molar ratios of sodium silicate to ferrous sulfate, which exhibit different adsorption capacities. When the molar ratios of sodium silicate to ferrous sulfate are 0.5:1 and 0.75:1, the isoelectric point of ferrous silicate is higher. Under the same pH conditions, such as pH=7, the surfaces of materials prepared by the 0.5:1 and 0.75:1 molar ratios are positively charged, thus exhibiting strong adsorption for anionic pollutants. The concentration of pollutants increases per unit area of ​​the material, resulting in higher reaction efficiency between the surface and the pollutants, and consequently, superior degradation ability.

[0033] Add A-1, A-2, and A-3 to 1L of 20mg / L methyl orange solution at a concentration of 0.2g / L, adjust the pH to 7, add hydrogen peroxide dropwise and stir to react. The amount of hydrogen peroxide used is 10mM, and the stirring time is 30min.

[0034]

[0035] As can be seen from Table 1, ferrous silicate catalyst A-1 has the highest removal efficiency, reaching over 99.82%, making it the most preferred ferrous silicate catalyst, followed by A-2.

[0036] from Figure 1 The XRD results show that the ferrous silicate catalyst is mainly amorphous, which can provide active sites with continuous energy distribution.

[0037] from Figure 2 The scanning electron microscope images show that the ferrous silicate catalyst is formed by the stacking of nanoparticles and has a large specific surface area.

[0038] Examples 2-4 below illustrate the Fenton-like catalytic oxidation degradation of organic wastewater using methyl orange solution as a model.

[0039] Unless otherwise specified, the following examples all use methyl orange as a model pollutant. A methyl orange solution with a concentration of 20 mg / L was prepared to simulate organic wastewater. The pH of the methyl orange solution was adjusted to 5. The dosage of ferrous silicate catalyst (A-1) was 0.2 g / L, and the concentration of hydrogen peroxide was 10 mM.

[0040] Specific operating procedure: First, adjust the pH of the methyl orange solution to weakly acidic (pH about 5.0), then add ferrous silicate catalyst (A-1) and stir to disperse for 5 minutes. Next, add sodium bisulfite or disodium malonate promoter, immediately adjust the pH to the initial pH range, and then add hydrogen peroxide (industrial grade 30%) and stir to react for 10 minutes.

[0041] Example 2

[0042] The removal rates of sodium bisulfite or disodium malonate in methyl orange solution were investigated at concentrations of 0.1 mM, 0.5 mM, and 1.0 mM, respectively, after a reaction time of 10 min. The results are shown in [Figure number missing]. Figure 3 .

[0043] Depend on Figure 3It is evident that sodium bisulfite or disodium malonate exhibits a clear dose-response relationship under weakly acidic conditions. Furthermore, sodium bisulfite achieves efficient degradation at a low dosage of 0.1 mM, while disodium malonate requires a higher dosage of 0.5 mM to achieve efficient degradation. Therefore, it is determined that sodium bisulfite exhibits better properties in promoting the degradation of ferrous silicate by oxidation-peroxide under weakly acidic conditions.

[0044] Example 3

[0045] Sodium malonate, oxalic acid, tartaric acid, sodium citrate, and sodium bisulfite were added at 0.5 mM or 1.0 mM, and the absorbance and removal rate after 5 min of reaction were investigated. The results are shown in [Figure number missing]. Figure 4 (Note: For the same accelerator, the left side of the bar chart represents the dosage of 0.5 mM, and the right side represents the dosage of 1 mM.) Figure 4 As can be seen, in the screening of different accelerators over 5 minutes, sodium bisulfite and disodium malonate both showed the best short-time removal effect, significantly better than oxalic acid, tartaric acid, and sodium citrate. This further proves that these two agents are suitable as the main accelerators of this invention.

[0046] Example 4

[0047] Using 0.5 mM sodium bisulfite and disodium malonate, the changes in absorbance and C / CO ratio at different reaction time points were investigated in the optimal dosage group and the blank group. The results are shown in [Figure number missing]. Figure 5 .Depend on Figure 5 It is evident that, under optimal dosage conditions, both sodium bisulfite and disodium malonate significantly reduced the C / CO value at various time points in the system. Calculated as the apparent reaction rate over the 0–2.5 min period, based on the absorbance decrease divided by time, the sodium bisulfite group and the disodium malonate group showed rates approximately 1.65 times and 1.64 times higher than the control group, respectively, indicating that both had a significant rate-increasing effect.

Claims

1. A method for promoting the Fenton oxidation effect of ferrous silicate under weakly acidic conditions, characterized in that: After adjusting the pH of the organic wastewater to 4.5–5.5, ferrous silicate catalyst and promoter are added first, and then hydrogen peroxide is slowly added to carry out the oxidation reaction. The accelerator includes sodium bisulfite and / or disodium malonate.

2. The method for promoting the Fenton oxidation effect of ferrous silicate under weakly acidic conditions according to claim 1, characterized in that: The ferrous silicate catalyst is prepared by the following method: sodium silicate solution is slowly and uniformly added to ferrous sulfate solution, and the reaction is stirred at pH 5-7. The reaction product is then filtered, washed and dried to obtain the catalyst. The molar ratio of sodium silicate in the sodium silicate solution to ferrous sulfate in the ferrous sulfate solution is 0.5:1 to 0.75:

1.

3. The method for promoting the Fenton oxidation effect of ferrous silicate under weakly acidic conditions according to claim 2, characterized in that: The concentration of the ferrous sulfate solution is 150~250 g / L; The concentration of the sodium silicate solution is 50~150g / L.

4. The method for promoting the Fenton oxidation effect of ferrous silicate under weakly acidic conditions according to claim 2, characterized in that: The reaction conditions are: room temperature and 0.5h to 1h. The drying process is carried out by oven drying or natural air drying; the oven drying temperature is 95~105℃ and the time is 1~2 hours; the natural air drying time is 1~3 days.

5. A method for promoting the Fenton oxidation effect of ferrous silicate under weakly acidic conditions according to any one of claims 1 to 4, characterized in that: The amount of ferrous silicate catalyst added is controlled so that its concentration in the organic wastewater is 0.1-1.0 g / L.

6. The method for promoting the Fenton oxidation effect of ferrous silicate under weakly acidic conditions according to claim 1, characterized in that: The amount of hydrogen peroxide added is controlled to maintain its concentration in the organic wastewater at 5–10 mM.

7. A method for promoting the Fenton oxidation effect of ferrous silicate under weakly acidic conditions according to claim 1, 2, 3, 4 or 6, characterized in that: The amount of the accelerator added is controlled so that its concentration in the organic wastewater is 0.1 to 1.0 mM.

8. The method for promoting the Fenton oxidation effect of ferrous silicate under weakly acidic conditions according to claim 7, characterized in that: When sodium bisulfite is selected as the accelerator, its addition amount is controlled to maintain its concentration in the organic wastewater at 0.4–0.6 mM. When sodium malonate is selected as the accelerator, its addition amount is controlled to maintain its concentration in the organic wastewater at 0.1–0.3 mM.

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