A method for preparing iron-carbon filler from industrial green vitriol, a by-product of titanium dioxide production

Abstract

The invention discloses a method for preparing an iron-carbon filler based on industrial green vitriol, a by-product of titanium dioxide production. The method comprises the following steps: ferrous sulfate, a main component of the industrial green vitriol, is used as an iron source of the iron-carbon filler; some impurities in the industrial green vitriol are used as active additives of the iron-carbon filler and provide a bonding effect; graphite is used as a carbon source of the iron-carbon filler, suspended in a green vitriol aqueous solution, and co-precipitated into a precursor; and simultaneously, reaction gas generated during the calcination of the precursor plays a pore-forming role. Therefore, the iron-carbon filler prepared by the invention has well-developed pores and a porosity greater than 54%. The iron-carbon has sufficient contact, high reaction activity, and the method has the ability to efficiently treat industrial wastewater. Simulated printing and dyeing wastewater (containing 275 mg / L of methylene blue) is treated three times in succession, and the degradation rate of methylene blue in each treatment is greater than 87%. The method can be widely used in the treatment of industrial wastewater, thereby reducing environmental pollution.

Description

Technical Field

[0001] The invention relates to the field of solid waste recycling and wastewater treatment, and in particular to a method for preparing an iron-carbon filler based on industrial green vitriol, a by-product of titanium dioxide production. Background Art

[0002] Iron-carbon micro-electrolysis is a pretreatment process for wastewater treatment. It mainly uses the iron-carbon micro-electrolysis electrode reaction to degrade macromolecular organic matter in wastewater and improve the biodegradability of wastewater. At the same time, the Fe2+ and Fe3+ generated have a good flocculation effect and can adsorb and precipitate some difficult-to-degrade substances. It is widely used in the fields of printing and dyeing, petrochemicals, medicine, pesticides, etc.

[0003] Early iron-carbon microfillers were often prepared by mixing waste materials such as iron filings with activated carbon. While this was a low-cost method, the reaction was difficult to sustain and was prone to caking and passivation. To overcome these drawbacks, later fillers were typically made by high-temperature calcination of iron filings, activated carbon, and a binder to create spherical, solidified iron-carbon fillers. To further enhance the electrocatalytic effect, some laboratories have also used bimetallic fillers to improve the COD removal efficiency of iron-carbon fillers.

[0004] But no matter what, increasing the contact area between the cathode and anode in the iron-carbon filler, increasing the interface area between the iron-carbon filler and the solution, and improving the dispersion of the catalytically active components in the iron-carbon filler are beneficial to improving the efficiency of the iron-carbon filler in treating industrial wastewater. In the prior art, there are methods to reduce the size of the iron powder and the carbon source material (even using nano iron powder and carbon nanotubes) during the preparation of the iron-carbon filler to improve the contact area between the cathode and anode of the filler; there are also methods to add metals such as copper, manganese, aluminum and titanium or their compound powders as catalytically active components during the preparation of the iron-carbon filler; or to add a large amount of pore-forming agents during the preparation of the iron-carbon filler to increase the porosity of the filler. However, these technologies have greatly increased the production cost of the iron-carbon filler. There are also technologies that use sludge or iron ore powder with a high iron purity or blast furnace dust to prepare iron-carbon fillers in order to reduce the manufacturing cost of the iron-carbon filler. Although this has played a certain role, the contact between iron and carbon has not been significantly improved. Summary of the Invention

[0005] The purpose of the present invention is to solve the problem of high production cost of iron-carbon fillers with developed pores, sufficient iron-carbon contact and high reaction activity in the prior art, and to provide a method for preparing iron-carbon fillers based on industrial green vitriol, a by-product of titanium dioxide production.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows: a method for preparing an iron-carbon filler based on industrial green vitriol, a by-product of titanium dioxide production, comprising the following steps:

[0007] S1, dissolving industrial green vitriol to obtain a green vitriol solution, wherein the iron ion concentration in the green vitriol solution is 1.0-2.0M and the solution temperature is 60°C-90°C;

[0008] S2. Prepare a 5.0M ammonium carbonate solution, add graphite powder and additives under strong stirring, and continue stirring for 40 minutes to activate the graphite powder to form a uniformly dispersed suspension. The content of graphite powder in the suspension is 15-150g / L, and the temperature of the suspension is 60°C-90°C;

[0009] S3, slowly pouring the green vitriol solution prepared in S1 into the suspension prepared in S2 and reacting for 0.5 to 2.5 hours, the volume ratio of the green vitriol solution to the suspension is 3 to 5:1, maintaining the solution temperature at 60°C to 90°C during the reaction, and adjusting the pH of the reaction solution to 8 to 9 with a 1M to 10M ammonium carbonate solution. After the reaction is completed, filtering and repeatedly washing the filter residue, and drying the filter residue to a moisture content of 8 to 10%;

[0010] S4, crushing the filter residue dried in S3 to a particle size exceeding a 90-mesh sieve, and using a pelletizing device to form a particle precursor of uniform size;

[0011] S5. The particle precursor in S4 is calcined at a constant temperature in an inert atmosphere or a non-oxidizing atmosphere, the calcination temperature is 950° C. to 1350° C., and the calcination time is 60 min to 150 min. After the constant temperature calcination is completed, an iron-carbon filler is prepared.

[0012] Preferably, the industrial green vitriol is a by-product of titanium dioxide production, and the industrial green vitriol contains 7-10% magnesium, 5-6% titanium, and 1-2% manganese.

[0013] Preferably, in S2, the additive is one or both of calcium carbonate and sodium silicate, and the amount of the additive is 5 g / L to 30 g / L.

[0014] Preferably, in S2, the purity of the graphite powder is 90% to 99%, and the particle size is 150 mesh to 200 mesh.

[0015] Preferably, in S5, the precursor needs to be slowly heated step by step to a predetermined calcination temperature, and the specific heating process is: heating from room temperature to 120°C at a rate of 10°C / min and keeping warm for 1 hour; then heating to 600°C at a rate of 20°C / min and keeping warm for 1 hour; then heating to 950°C~1350°C at a rate of 25°C / min and calcining at a constant temperature for 60min~150min.

[0016] More preferably, in S5, the inert atmosphere is nitrogen; and the non-oxidizing atmosphere is a mixed gas of carbon monoxide and carbon dioxide.

[0017] The production of titanium dioxide produces a large amount of industrial green vitriol as a byproduct, with 4.5-5.0 tons of industrial green vitriol produced for every ton of titanium dioxide produced. This byproduct, green vitriol, typically contains a large amount of impurities, such as 7-10% magnesium, 5-6% titanium, and 1-2% manganese. Currently, the main approaches for the comprehensive utilization of industrial green vitriol include desulfurization to produce ironmaking raw materials and purification of the green vitriol to produce pigments, ferrite materials, or iron powder. However, these approaches face problems such as low product added value and limited market application. The present invention utilizes ferrous sulfate, the main component of industrial green vitriol, as the iron source for the iron-carbon filler, and utilizes the titanium, manganese, and magnesium components of the industrial green vitriol as active additives and bonding agents. Graphite is used as the carbon source for the iron-carbon filler, suspended in an aqueous solution of green vitriol, and co-precipitated under certain conditions to form a precursor. During co-precipitation, a layer of precursor formed by the hydrolysis of iron ions surrounds the suspended graphite. Compared to the traditional method of preparing the iron-carbon filler by mixing iron powder and carbon powder and then sintering, the co-precipitation of the precursor and subsequent calcination of the iron-carbon filler significantly improves the iron-carbon contact. In the traditional preparation of iron-carbon fillers, iron powder and carbon powder are mixed and sintered without reacting with each other to produce gas. To increase the porosity of the iron-carbon filler, it is usually necessary to add a large amount of carbonate to make it decompose during high-temperature calcination to produce gas to form pores. The precursor obtained by the co-precipitation of industrial green vitriol and graphite in the present invention contains a large amount of bound water. The water vapor released during the calcination of the precursor and the reaction gas generated by the reduction of iron oxide by graphite will play a pore-forming role. Therefore, the iron-carbon filler prepared by the present invention has developed pores, sufficient iron-carbon contact, and high reaction activity. Since the high-value raw materials used in the preparation of iron-carbon fillers in the present invention are provided by cheap industrial solid waste green vitriol, the production cost of iron-carbon is low. It opens up a new way for the comprehensive utilization of industrial green vitriol and realizes the green, environmentally friendly and sustainable development concept of waste-to-waste.

[0018] The beneficial effects of the present invention are:

[0019] (1) The present invention utilizes ferrous sulfate, the main component of industrial green vitriol, as the iron source of the iron-carbon filler, utilizes some impurities in the industrial green vitriol as the active additive component of the iron-carbon filler and provides a bonding effect, and uses graphite as the carbon source of the iron-carbon filler, which is suspended in a green vitriol aqueous solution and co-precipitated into a precursor. At the same time, the reaction gas generated during the calcination of the precursor plays a pore-forming role. Therefore, the iron-carbon filler prepared by the present invention has developed pores and a porosity greater than 54%. The iron-carbon contact is sufficient, the reaction activity is high, and it has the ability to efficiently treat industrial wastewater. The simulated printing and dyeing wastewater (containing 275 mg / L of methylene blue) was treated three times in a row, and the degradation rate of methylene blue was greater than 87% in each treatment. It can be widely used in the treatment of industrial wastewater to reduce environmental pollution.

[0020] (2) Since the present invention uses low-priced industrial solid waste green vitriol to prepare iron-carbon fillers, the raw material cost of the iron-containing component in the iron-carbon filler is almost negligible. Traditional iron-carbon fillers usually use iron powder to provide raw materials for the iron-containing component of the filler. The iron-carbon fillers on the market usually contain about 75% iron and about 15% carbon, that is, at least 0.75 tons of iron powder are consumed per ton of iron-carbon filler. According to the current lowest unit price of iron powder on the market (about 5,000 yuan / ton), the traditional iron-carbon filler preparation process using iron powder as raw material requires at least about 3,750 yuan more raw material cost to produce each ton of iron-carbon filler than the present invention. Obviously, the present invention greatly reduces the production cost of iron-carbon fillers, and realizes the reuse of solid waste industrial green vitriol, effectively reducing environmental pollution. DETAILED DESCRIPTION

[0021] The present invention will be further described below with reference to specific embodiments.

[0022] Example 1

[0023] 1. Coprecipitation: Add 278g of green vitriol to 670mL of water and heat in a 60°C waterbath with stirring until completely dissolved. Keep warm and set aside. This is Solution 1. Separately, add 96g of ammonium carbonate and 1.2g of sodium silicate to 200mL of water and heat in a 60°C waterbath with stirring until completely dissolved. Once completely dissolved, slowly add 10g of activated carbon while stirring rapidly. Once the activated carbon is evenly dispersed, add 4g of calcium carbonate to the suspension and stir rapidly until evenly dispersed. Stir the suspension in a 60°C waterbath for 40 minutes and keep warm. This is Solution 2. Slowly pour Solution 1 into Solution 2 while heating to 80°C. Continue the reaction for approximately 1.5 hours. Continuously add ammonium carbonate solution dropwise throughout the reaction to maintain a pH of 8-9. Once the reaction is complete, let the reaction cool for 10 minutes before filtering. Wash the filter residue at least three times. The resulting filter cake is dried to a moisture content of 8-10%.

[0024] 2. Pellet Formation: Crush the filter cake obtained in step 1 and pass it through a 90-mesh sieve. Use a disc pelletizer to form pellets with a particle size of approximately 30 mm. Add water as needed during the pelletizing process.

[0025] 3. Calcination: Place the pellets obtained in step 2 into a calcining furnace and continuously introduce nitrogen to begin heating. First, heat the temperature from room temperature to 120°C at a rate of 10°C / min and hold for 1 hour. Then, heat the temperature to 600°C at a rate of 20°C / min and hold for 1 hour. Finally, heat the temperature to 1150°C at a rate of 25°C / min. Calcinate at this constant temperature for 90 minutes, then cool naturally to room temperature to obtain an iron-carbon filler prepared from industrial green vitriol, a by-product of titanium dioxide production.

[0026] 4. The porosity of the iron-carbon filler was tested using the Archimedean drainage method, and was found to be 54.3%. Approximately 20g of the experimental sample was weighed and placed in a beaker with simulated printing and dyeing wastewater (containing 275mg / L of methylene blue) at a solid-to-liquid ratio of 1:10. The pH was adjusted to 3-5. The sample was then aerated for two hours using an aeration plate. After the aeration was completed, the methylene blue concentration in the wastewater was tested, indicating a methylene blue degradation rate of 89.4%. The used iron-carbon filler was then air-dried in the shade and then treated a second time with simulated printing and dyeing wastewater (containing 275mg / L of methylene blue) using the same method. The degradation rate was 87.3%. The used iron-carbon filler was then air-dried in the shade and then treated a third time with simulated printing and dyeing wastewater (containing 275mg / L of methylene blue) using the same method. The degradation rate remained at 87.5%. This demonstrates that the iron-carbon filler exhibits stable performance, exhibits almost no noticeable passivation, and has a long service life.

[0027] Example 2

[0028] 1. Coprecipitation: Add 290g of green vitriol to 670mL of water and heat in a 60°C waterbath with stirring until completely dissolved. Keep warm and set aside. This is Solution 1. Separately, add 96g of ammonium carbonate and 1.2g of sodium silicate to 200mL of water and heat in a 60°C waterbath with stirring until completely dissolved. Once completely dissolved, slowly add 15g of activated carbon while stirring rapidly. Once the activated carbon is evenly dispersed, add 4g of calcium carbonate to the suspension and stir rapidly until evenly dispersed. Stir the suspension in a 60°C waterbath for 40 minutes and keep warm. This is Solution 2. Slowly pour Solution 1 into Solution 2 while heating to 80°C. Continue the reaction for approximately 1.5 hours. Continuously add ammonium carbonate solution dropwise throughout the reaction to maintain a pH of 8-9. Once the reaction is complete, let the reaction cool for 10 minutes before filtering. Wash the filter residue at least three times. The resulting filter cake is dried to a moisture content of 8-10%.

[0029] 2. Pellet Formation: Crush the filter cake obtained in step 1 and pass it through a 90-mesh sieve. Use a disc pelletizer to form pellets with a particle size of approximately 30 mm. Add water as needed during the pelletizing process.

[0030] 3. Calcination: Place the pellets obtained in step 2 into a calcining furnace and continuously introduce nitrogen to begin heating. First, heat the temperature from room temperature to 120°C at a rate of 10°C / min and hold for 1 hour. Secondly, heat the temperature to 600°C at a rate of 20°C / min and hold for 1 hour. Finally, heat the temperature to 1200°C at a rate of 25°C / min, calcine at this constant temperature for 100 minutes, and then cool naturally to room temperature to obtain an iron-carbon filler prepared from industrial green vitriol, a by-product of titanium dioxide production.

[0031] 4. The porosity of the iron-carbon filler was tested using the Archimedean drainage method, and was found to be 69.1%. Approximately 20 g of the experimental sample was weighed and placed together with simulated printing and dyeing wastewater (containing 275 mg / L of methylene blue) at a solid-to-liquid ratio of 1:10 in a beaker, and the pH was adjusted to 3-5. The sample was then aerated for two hours using an aeration plate. After the aeration was completed, the methylene blue concentration in the wastewater was tested, and the degradation rate of methylene blue reached 96.7%. The used iron-carbon filler was naturally air-dried and then treated with simulated printing and dyeing wastewater (containing 275 mg / L of methylene blue) for a second time using the same method. The degradation rate of methylene blue was 95.1%. The used iron-carbon filler was further air-dried and then treated with simulated printing and dyeing wastewater (containing 275 mg / L of methylene blue) for a third time using the same method. The degradation rate of methylene blue was still 93.2%. This demonstrates that the iron-carbon filler has high activity, stable performance, and a long service life.

[0032] The description of the present invention is considered to be illustrative rather than restrictive. On the basis of the present invention, those skilled in the art can make some substitutions and modifications to some of the technical features according to the disclosed technical content without creative work, and all of them are within the scope of protection of the present invention.

Claims

1. A method for preparing an iron-carbon filler based on industrial green vitriol, a by-product of titanium dioxide production, characterized in that: The following steps are involved: S1. Dissolving industrial green vitriol to obtain a green vitriol solution, wherein the iron ion concentration in the green vitriol solution is 1.0-2.0M and the solution temperature is 60°C-90°C; the industrial green vitriol is a by-product of titanium dioxide production, and contains 7-10% magnesium, 5-6% titanium, and 1-2% manganese; S2. Prepare an ammonium carbonate solution with a concentration of 5.0M, add graphite powder and additives under strong stirring, and continue stirring for 40 minutes to activate the graphite powder to form a uniformly dispersed suspension, wherein the content of graphite powder in the suspension is 15-150g / L, and the temperature of the suspension is 60°C-90°C; the additive is one or both of calcium carbonate and sodium silicate, and the amount of the additive is 5 g / L-30g / L; S3. Slowly pour the green vitriol solution prepared in S1 into the suspension prepared in S2 and react for 0.5 to 2.5 hours. The volume ratio of the green vitriol solution to the suspension is 3 to 5:

1. During the reaction, the solution temperature is maintained at 60°C to 90°C. The pH of the reaction solution is adjusted to 8 to 9 with a 1M to 10M ammonium carbonate solution. After the reaction is completed, filter and repeatedly wash the filter residue, and dry the filter residue to a moisture content of 8 to 10%. S4, crushing the filter residue dried in S3 to a particle size exceeding a 90-mesh sieve, and using a pelletizing device to form a particle precursor of uniform size; S5. The particle precursor in S4 is calcined at a constant temperature in an inert atmosphere or a non-oxidizing atmosphere. The precursor needs to be slowly heated up step by step to a predetermined calcination temperature. The specific heating process is: heating from room temperature to 120°C at a rate of 10°C / min and keeping warm for 1 hour; then heating to 600°C at a rate of 20°C / min and keeping warm for 1 hour; then heating to 950°C~1350°C at a rate of 25°C / min and calcining at a constant temperature for 60min~150min. After the constant temperature calcination is completed, the iron-carbon filler is prepared.

2. The method according to claim 1, characterized in that In the S2, the purity of the graphite powder is 90% to 99%, and the particle size is 150 mesh to 200 mesh.

3. The method according to claim 1, characterized in that In S5, the inert atmosphere is nitrogen; and the non-oxidizing atmosphere is a mixed gas of carbon monoxide and carbon dioxide.