Preparation method of sponge-based ferrous silicate reducing agent for wastewater treatment

Abstract

This invention belongs to the field of wastewater treatment technology, specifically relating to a method for preparing a sponge iron-based ferrous silicate reducing agent for wastewater treatment. Sponge iron is activated in a dilute phosphoric acid solution to obtain activated sponge iron; the activated sponge iron is washed and then immersed in a ferrous solution, removed and washed, and then matured in a sodium silicate solution to obtain matured sponge iron; the matured sponge iron is washed and freeze-dried to obtain the sponge iron-based ferrous silicate reducing agent. The sponge iron-based ferrous silicate reducing agent prepared by this invention is easily separated from the effluent and has excellent and long-lasting reducing performance. It solves the problems of high reducing agent dosage, high salinity of the treated effluent, generation of large amounts of iron sludge, and the need for continuous addition of reducing agent in traditional reduction processes. Furthermore, the preparation method is simple, requiring no complex equipment or catalysts, and the raw material, sponge iron, is inexpensive and widely available, resulting in low production costs and suitability for large-scale preparation and engineering applications.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, and specifically relates to a method for preparing a sponge-based ferrous silicate reducing agent for wastewater treatment. Background Technology

[0002] Organic wastewater containing pollutants such as nitro compounds, organic peroxides, halogenated hydrocarbons, or heavy metals is a major challenge in wastewater treatment due to its high toxicity and difficulty in biodegradation. These pollutants not only severely damage aquatic ecosystems but also endanger human health through the food chain. Therefore, developing efficient and environmentally friendly wastewater treatment technologies is of great significance. Reduction methods, as an effective wastewater treatment technology, work by using a reducing agent to provide electrons, converting biotoxic and recalcitrant high-valence organic pollutants in wastewater into low-toxicity and easily degradable small molecules for subsequent biological treatment. Simultaneously, reduction wastewater treatment technology can also convert heavy metal pollutants in wastewater into easily separated or non-toxic forms, thus achieving efficient pollutant removal. Therefore, reduction wastewater treatment technology has received widespread attention.

[0003] However, the widely used traditional reduction methods still have many drawbacks. Commonly used reducing agents in existing technologies are mostly chemical reagents such as ferrous sulfate or sulfites, as well as elemental metals such as aluminum, iron, and zinc. These reducing agents generally suffer from high consumption in practical applications, and the reaction process easily generates large amounts of secondary pollutants such as iron sludge. This not only increases the processing load of subsequent solid-liquid separation but may also cause new environmental problems. Furthermore, the high salinity of the effluent after treatment by traditional reduction methods can adversely affect the stability of subsequent biological treatment processes, limiting further improvement in water quality. The short duration of the reactivity of traditional reducing agents necessitates continuous replenishment of reducing agents to maintain treatment effectiveness, resulting in cumbersome operation procedures and high treatment costs, making it difficult to meet the needs of large-scale industrial wastewater treatment.

[0004] Chinese patent CN103193336A discloses a combined treatment method for toxic organic wastewater. The method involves adding a sponge-based iron-based reducing agent to the toxic organic wastewater solution and reacting it under ultrasonic conditions. The sponge-based iron-based reducing agent is then magnetically separated and recycled. The treated wastewater solution is then subjected to deep adsorption treatment by activated carbon. The adsorbed activated carbon is then regenerated and activated by microwave radiation for reuse. However, this patent does not consider the increase in salinity and the formation of iron sludge caused by the ferrous and ferric iron produced after the sponge-based iron reduces pollutants and then entering the wastewater. Chinese patent CN115520951A discloses a method for simultaneously removing hexavalent chromium ions and organic micropollutants from wastewater. This method utilizes ferrous salts to reduce hexavalent chromium ions, achieving intermediate-state reduction of chromium. Simultaneously, it leverages the high selectivity of intermediate pentavalent and tetravalent chromium species generated during the reduction of hexavalent chromium ions by ferrous salts, which exhibit high reactivity with organic micropollutants, to simultaneously remove coexisting organic micropollutants. Low-valent chromium ions in the system can also be removed simultaneously via co-precipitation. However, this patent generates iron sludge after the addition of ferrous salts during the treatment process. This iron sludge requires hazardous waste treatment in subsequent processes, increasing economic costs and environmental pressure. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a sponge-based ferrous silicate reducing agent for wastewater treatment. The sponge-based ferrous silicate reducing agent prepared by this method is easy to separate from the effluent and has excellent and long-lasting reducing performance. It solves the problems of high reducing agent dosage, high salinity of the treated effluent, generation of a large amount of iron sludge, and the need for continuous addition of reducing agent in traditional reduction processes.

[0006] The preparation method of the sponge-based ferrous silicate reducing agent for wastewater treatment according to the present invention includes the following steps:

[0007] (1) Sponge iron is activated in dilute phosphoric acid solution to obtain activated sponge iron;

[0008] (2) After washing the activated sponge iron, it was immersed in ferrous solution, taken out and washed, and then placed in sodium silicate solution for aging to obtain aging sponge iron;

[0009] (3) Wash the aged sponge iron and freeze dry it to obtain sponge iron-based ferrous silicate reducing agent.

[0010] In step (1), the concentration of the dilute phosphoric acid solution is 3-7 wt.%, the activation time is 10-40 min, and the activation temperature is room temperature.

[0011] In step (1), the ratio of sponge iron to dilute phosphoric acid solution is 1:3-5, where sponge iron is expressed in g and dilute phosphoric acid solution is expressed in mL.

[0012] In step (2), the soaking time is 6-24 hours and the soaking temperature is room temperature.

[0013] In step (2), the concentration of the ferrous solution is 10-20 wt.%, and the ferrous solution is either ferrous sulfate or ferrous chloride. The solvent in the ferrous solution is deoxygenated water, and the washing is done by rinsing with deoxygenated water until neutral.

[0014] In step (2), the curing time is 6-24 hours and the curing temperature is 40-60℃.

[0015] In step (2), the solvent in the sodium silicate solution is deoxygenated water, the concentration of the sodium silicate solution is 0.5-1.5 mol / L, the pH of the sodium silicate solution is 2-4, and the ratio of sodium silicate solution to sponge iron in step (1) is 1:0.2-0.6, where sponge iron is expressed in g and sodium silicate solution is expressed in mL.

[0016] In step (2), the ratio of ferrous solution to sponge iron in step (1) is 1:0.2-0.6, where sponge iron is expressed in g and ferrous solution in mL.

[0017] In step (3), the washing process involves rinsing with deoxygenated water until the solution is neutral.

[0018] In step (3), the freeze-drying temperature is -45 to -43°C, preferably -45°C, and the freeze-drying time is 18 to 24 hours.

[0019] This invention involves first immersing sponge iron activated with dilute phosphoric acid in a ferrous solution, then aging it in a pH-adjusted sodium silicate solution, and finally removing and freeze-drying it to obtain a sponge iron-based ferrous silicate reducing agent. The prepared sponge iron-based ferrous silicate reducing agent can utilize ferrous iron to reduce pollutants in wastewater and generate ferric iron. The generated ferric iron can then be reduced back to ferrous iron through electron exchange with elemental iron in the sponge iron, giving the sponge iron-based ferrous silicate reducing agent continuous reducing performance.

[0020] The beneficial effects of this invention are as follows:

[0021] (1) In the preparation process, the present invention utilizes dilute phosphoric acid to activate sponge iron, which can dissolve the inert iron oxide on the surface of sponge iron. At the same time, some phosphate ions remain on the surface of sponge iron. Phosphate ions can enhance the adsorption capacity of ferrous ions in the subsequent ferrous solution through electrostatic adsorption or coordination binding, promote the impregnation of ferrous ions on the surface of sponge iron, and improve the loading amount and loading uniformity. Subsequently, ferrous ions and silicate ions undergo precipitation reaction to generate ferrous silicate solid product and firmly load it on sponge iron. This solid loading form avoids ferrous ions entering the wastewater in a free ionic state, thereby avoiding the problems of generating a large amount of iron sludge and high salinity of effluent. On the other hand, the ferric ions generated by the oxidation reaction of ferrous ions can undergo electron transfer with the elemental iron in sponge iron, so that the ferric ions are reduced back to ferrous ions, realizing the in-situ regeneration of active ferrous ions and ensuring that the sponge iron-based ferrous silicate reducing agent can play a long-term reducing role.

[0022] (2) Sponge iron is porous, and when it comes into direct contact with wastewater, it will undergo large-scale electrochemical corrosion and oxidation reactions. The elemental iron inside and outside the porous structure of the sponge iron will be consumed in large quantities and rapidly, resulting in the fragmentation and pulverization of the porous skeleton of the sponge iron, and eventually its collapse. In this invention, ferrous silicate is firmly loaded on the surface of the sponge iron in a solid state, which can serve as a protective layer to prevent the sponge iron from directly contacting the wastewater, thereby avoiding the problem of sponge iron collapse; at the same time, it can also prevent ferrous silicate from combining with anions in the wastewater in a free ionic state to form iron sludge, reducing the problem of increased solid waste disposal costs caused by iron sludge. In addition, the porous structure of the sponge iron provides effective loading sites with high specific surface area for ferrous silicate, ensuring uniform loading of ferrous silicate; on the other hand, it facilitates the flow of wastewater inside and on the surface of the sponge iron-based ferrous silicate reducing agent, providing a good physical channel for the mass transfer process and ensuring efficient reduction reaction.

[0023] (3) The present invention controls the pH of the sodium silicate solution between 2 and 4, which can effectively prevent the sodium silicate from polymerizing and forming solid silica gel during the dissolution and preparation process, thus ensuring the effectiveness of the reactants; at the same time, it avoids the ferrous silicate solid product formed during the aging process from being too large in volume and too densely packed, thus blocking the porous structure of the sponge iron, ensuring the mass transfer effect inside and outside the sponge iron-based ferrous silicate reducing agent, and thus ensuring the full play of the reducing performance of the sponge iron-based ferrous silicate reducing agent.

[0024] (4) The preparation method of the present invention is simple, requires no complex equipment or catalyst, the raw material sponge iron is inexpensive and widely available, the production cost is low, and it is suitable for large-scale preparation and engineering application.

[0025] (5) The sponge iron-based ferrous silicate reducing agent prepared in this invention is a solid reducing agent, which is easy to separate from the effluent and can be used in wastewater reduction treatment processes such as decolorization of azo dye wastewater. Detailed Implementation

[0026] The present invention will be further described below with reference to embodiments.

[0027] Example 1

[0028] (1) Place 10g of sponge iron in 50mL of 3wt.% dilute phosphoric acid solution and activate it at room temperature for 40min to obtain activated sponge iron;

[0029] (2) The activated sponge iron obtained in step (1) was rinsed with deoxygenated water until neutral and then placed in 50 mL of 20 wt.% ferrous sulfate solution at room temperature for 6 h. After that, it was taken out and rinsed with deoxygenated water until neutral. Then it was placed in 50 mL of 1.5 mol / L sodium silicate solution with pH=2 and aged at 60 °C for 24 h to obtain aged sponge iron.

[0030] (3) The aged sponge iron obtained in step (2) is rinsed with deoxygenated water until neutral, and then freeze-dried at -45°C for 24 hours to obtain sponge iron-based ferrous silicate reducing agent.

[0031] Example 2

[0032] (1) Place 20g of sponge iron in 80mL of 7wt.% dilute phosphoric acid solution and activate it for 10min at room temperature to obtain activated sponge iron;

[0033] (2) The activated sponge iron obtained in step (1) was rinsed with deoxygenated water until neutral and then placed in 50 mL of 10 wt.% ferrous sulfate solution at room temperature for 24 h. After that, it was taken out and rinsed with deoxygenated water until neutral. Then it was placed in 50 mL of 0.5 mol / L sodium silicate solution with pH=4 and aged at 40 °C for 6 h to obtain aged sponge iron.

[0034] (3) The aged sponge iron obtained in step (2) is rinsed with deoxygenated water until neutral and freeze-dried at -43°C for 18 hours to obtain sponge iron-based ferrous silicate reducing agent.

[0035] Example 3

[0036] (1) Place 30g of sponge iron in 90mL of 5wt.% dilute phosphoric acid solution and activate it for 20min at room temperature to obtain activated sponge iron;

[0037] (2) The activated sponge iron obtained in step (1) was rinsed with deoxygenated water until neutral and then placed in 50 mL of 15 wt.% ferrous chloride solution at room temperature for 12 h. After that, it was taken out and rinsed with deoxygenated water until neutral. Then it was placed in 50 mL of 1 mol / L sodium silicate solution with pH=3 and aged at 50 °C for 12 h to obtain aged sponge iron.

[0038] (3) The aged sponge iron obtained in step (2) is rinsed with deoxygenated water until neutral, and then freeze-dried at -44℃ for 20h to obtain sponge iron-based ferrous silicate reducing agent.

[0039] Comparative Example 1

[0040] Without using dilute phosphoric acid solution, the other steps are the same as in Example 1 to obtain the reducing agent.

[0041] Comparative Example 2

[0042] Without using ferrous sulfate solution, the other steps are the same as in Example 1 to obtain the reducing agent.

[0043] Comparative Example 3

[0044] Without using sodium silicate solution, the other steps are the same as in Example 1 to obtain the reducing agent.

[0045] Comparative Example 4

[0046] Under stirring conditions, 50 mL of sodium silicate solution with a concentration of 1.5 mol / L and pH=2 was slowly added dropwise to 50 mL of ferrous sulfate solution with a concentration of 20 wt.%, and the mixture was aged at 60 °C for 24 h. After centrifugation, a solid phase was obtained, and the solid phase was freeze-dried at -45 °C for 24 h to obtain ferrous silicate reducing agent.

[0047] Weigh 1g of each of the reducing agent prepared in Examples 1-3 and Comparative Examples 1-4 and add them to 50mL of Acid Red solution (concentration of 10mg / L). Stir on a shaker for 30min at 200rpm. Then, filter the supernatant through a 0.45μm membrane and measure the absorbance at a characteristic wavelength of 510nm. Compared with the absorbance of Acid Red solution with a concentration of 10mg / L, the decolorization rates of Examples 1-3 were 99.3%, 98.8%, and 99.2%, respectively, while the decolorization rates of Comparative Examples 1-4 were 83.3%, 80.2%, 85.6%, and 88.4%, respectively.

[0048] 1 g each of the reducing agent prepared in Example 1 and Comparative Example 4 was added to 50 mL of Acid Red solution (concentration 10 mg / L). The mixture was stirred on a shaker for 30 min at 200 rpm. The supernatant was then filtered through a 0.45 μm membrane, and the absorbance was measured at a characteristic wavelength of 510 nm. The absorbance was compared with that of the 10 mg / L Acid Red solution to obtain the first decolorization rate. The effluent was centrifuged to obtain a solid. The solid was used as the reducing agent to repeat the above experiment twice to obtain the second and third decolorization rates. The first to third decolorization rates of Example 1 were 99.1%, 98.3%, and 97.8%, respectively, while those of Comparative Example 4 were 88.0%, 38.1%, and 10.3%, respectively. This indicates that the sponge-based ferrous silicate reducing agent in this invention can exert a sustained reducing effect.

Claims

1. A method for preparing a sponge-based ferrous silicate reducing agent for wastewater treatment, characterized in that... Includes the following steps: (1) Sponge iron is activated in dilute phosphoric acid solution to obtain activated sponge iron; (2) After washing the activated sponge iron, it was immersed in ferrous solution, taken out and washed, and then placed in sodium silicate solution for aging to obtain aging sponge iron; (3) Wash the aged sponge iron and freeze-dry it to obtain a sponge iron-based ferrous silicate reducing agent; The pH of the sodium silicate solution in step (2) is 2-4.

2. The preparation method of the sponge-based ferrous silicate reducing agent for wastewater treatment according to claim 1, characterized in that... In step (1), the concentration of the dilute phosphoric acid solution is 3-7 wt.%, the activation time is 10-40 min, and the activation temperature is room temperature.

3. The preparation method of the sponge-based ferrous silicate reducing agent for wastewater treatment according to claim 1, characterized in that... In step (1), the ratio of sponge iron to dilute phosphoric acid solution is 1:3-5, where sponge iron is expressed in g and dilute phosphoric acid solution is expressed in mL.

4. The preparation method of the sponge-based ferrous silicate reducing agent for wastewater treatment according to claim 1, characterized in that... In step (2), the soaking time is 6-24 hours and the soaking temperature is room temperature.

5. The method for preparing the sponge-based ferrous silicate reducing agent for wastewater treatment according to claim 1, characterized in that... In step (2), the concentration of the ferrous solution is 10-20 wt.%, and the ferrous solution is either ferrous sulfate or ferrous chloride. The solvent in the ferrous solution is deoxygenated water, and the washing is done by rinsing with deoxygenated water until neutral.

6. The method for preparing the sponge-based ferrous silicate reducing agent for wastewater treatment according to claim 1, characterized in that... In step (2), the curing time is 6-24 hours and the curing temperature is 40-60℃.

7. The method for preparing the sponge-based ferrous silicate reducing agent for wastewater treatment according to claim 1, characterized in that... In step (2), the solvent in the sodium silicate solution is deoxygenated water, the concentration of the sodium silicate solution is 0.5-1.5 mol / L, and the ratio of sodium silicate solution to sponge iron in step (1) is 1:0.2-0.6, where sponge iron is expressed in g and sodium silicate solution is expressed in mL.

8. The method for preparing the sponge-based ferrous silicate reducing agent for wastewater treatment according to claim 1, characterized in that... In step (2), the ratio of ferrous solution to sponge iron in step (1) is 1:0.2-0.6, where sponge iron is expressed in g and ferrous solution in mL.

9. The method for preparing the sponge-based ferrous silicate reducing agent for wastewater treatment according to claim 1, characterized in that... In step (3), the washing process involves rinsing with deoxygenated water until the solution is neutral.

10. The method for preparing the sponge-based ferrous silicate reducing agent for wastewater treatment according to claim 1, characterized in that... In step (3), the freeze-drying temperature is -45 to -43°C, and the freeze-drying time is 18 to 24 hours.