Synthesis method of high-purity fayalite

Abstract

The invention discloses a high-purity fayalite synthesis method which comprises the following steps: mixing FeCO3 powder and SiO2 powder to obtain a FeCO3-SiO2 mixture; placing the FeCO3-SiO2 mixture in a high-purity fayalite synthesis device, and roasting the FeCO3-SiO2 mixture; and cooling to room temperature along with the furnace to obtain the fayalite. The method has the advantages of relatively simple process, low equipment requirement, short synthesis time, high raw material utilization rate, high product purity and the like, an inert gas atmosphere is not needed in the reaction process, and no toxic or harmful gas is generated in the preparation process. By preferably controlling the reaction conditions, the proportion of the alpha-fayalite crystal phase in the fayalite product prepared by the invention is higher than 95%. Compared with an existing fayalite synthesis method, multi-step heating and secondary purification of a prepared product are not needed.

Description

Technical Field

[0001] The invention relates to a method for preparing fayalite, in particular to a method for synthesizing high-purity fayalite, and belongs to the field of inorganic non-metallic material engineering. Background Art

[0002] Fayalite is an iron silicate with the molecular formula of Fe2SiO4 and an olivine-type crystal structure. Fayalite can be used in the industry to prepare refractory materials, metal surface coating materials, and ceramic preparation. In the field of geological research, fayalite is widely distributed in syenite, granite and other rock phases, mainly in the lower mantle, and is an important reference material for studying rock phase transitions. In addition, in the field of metallurgical engineering, fayalite is the main form of iron in non-ferrous metallurgical solid wastes such as copper and nickel, with an iron content of up to 54.8 wt.%, and is a potential available iron resource.

[0003] Related research on fayalite requires high-purity fayalite as a raw material basis. However, the synthesis method of fayalite in existing research is complicated, the conditions are relatively harsh, and the product purity is relatively low. For example, Shi Xiaoyan et al. from Shanghai University mixed Fe2O3, SiO2 and Fe, and kept them in an inert atmosphere at 1350℃ for 2 h. The purity of the obtained fayalite was only 72.59%, and its impurities were mainly silicon dioxide. Liu Hui et al. from Central South University published a method for preparing fayalite (CN106829978B), which mixed Fe3O4, FeS, and SiO2 after ball milling, placed them in an inert atmosphere, and sintered them for the first time at 1100-1600℃, and the sintered product was leached and purified with an acid solution and then sintered for the second time at 1000-1300℃, so that the relative content of fayalite in the product was higher than 95%. However, this method requires the use of an acid solution to purify the product, and there is a toxic gas SO2 overflow during the preparation process, which requires an additional waste gas absorption device. Other methods for preparing fayalite include chemical coprecipitation and sol-gel methods, but the above methods have low production yields and small particle sizes of fayalite, which are not suitable for research in the fields of industry and geology. So far, there has been no report on the one-step synthesis of high-purity fayalite with simple process and low cost. Summary of the invention

[0005] Therefore, the technical problem to be solved by the present invention is to provide a method for synthesizing high-purity fayalite with relatively simple process, low equipment requirements, short synthesis time, high raw material utilization rate and high product purity.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions: A method for synthesizing high-purity fayalite comprises the following steps: (1) mixing FeCO3 and SiO2 powder to obtain a FeCO3-SiO2 mixture; (2) placing the FeCO3-SiO2 mixture in a high-purity fayalite synthesis device for roasting; (3) Cool down to room temperature in the furnace to obtain fayalite.

[0007] During the heating process, the decomposition reaction of FeCO3 occurs first, and the reaction process can be expressed as: FeCO3→ FeO + CO2↑.

[0008] The CO2 gas produced by the reaction enters the tube of the tubular furnace to form an inert atmosphere, which can protect the reaction products from oxidation. The excess gas inside the tube of the tubular furnace can be discharged by the one-way valve. As the temperature rises further, the FeO produced by the decomposition of FeCO3 will react with SiO2, that is: FeO + SiO2→ Fe2SiO4, and the product is fayalite.

[0009] By adopting the method of cooling with the furnace, the synthetic product is always in the closed environment of the furnace during the cooling process, which can avoid the oxidation of fayalite and improve the purity of fayalite. After the reaction is completed, if it is cooled outside the furnace, the prepared fayalite is at a high temperature and is easy to react with oxygen in the air, causing oxidation, thereby reducing the purity of the fayalite.

[0010] In the above-mentioned method for synthesizing high-purity fayalite, the molar ratio of FeCO3 to SiO2 is 2:1. The reaction product of FeO and SiO2 exists in various forms depending on the molar ratio of the two. When the molar ratio of FeO to SiO2 is 2:1, the reaction product is fayalite. If the molar ratio of the two is greater than or less than 2:1, the reactant will remain and enter the roasted product, and will exist as an impurity. Only by synthesizing at the preferred ratio can high-purity fayalite be obtained.

[0011] In the above-mentioned method for synthesizing high-purity fayalite, the particle size of FeCO3 and SiO2 is less than or equal to 0.075 mm.

[0012] In the above-mentioned high-purity fayalite synthesis method, FeCO3 and SiO2 are mixed evenly without local component segregation. After being fully mixed, the raw material particles are evenly distributed, which can effectively promote the synthesis reaction.

[0013] In the above-mentioned method for synthesizing high-purity fayalite, FeCO3 and SiO2 are dry-milled for 30 to 60 minutes at room temperature. Ferrous carbonate is stable in dry air and low temperature. Dry-mixed ball milling at room temperature can achieve full mixing. If the ball milling time is short, the mixing is not uniform enough, and if the ball milling time is long, time is wasted.

[0014] The above-mentioned method for synthesizing high-purity fayalite has a calcination temperature of 700-1200 °C and a holding time of 0.5-4 h. When the calcination temperature is lower than 700 °C, the synthesis reaction is not sufficient, which will cause the reactants to remain. When the temperature is higher than 1200 °C, the reactants are prone to oxidation. At the same time, at too high a temperature, fayalite will melt into a liquid state, making it difficult to separate the product from the crucible. The preferred synthesis conditions are: a calcination temperature of 800-900 °C and a holding time of 1-2 h. Under the preferred conditions, the reaction product has high purity, the overall reaction time is short, and the synthetic product is not easily oxidized.

[0015] The above-mentioned method for synthesizing high-purity fayalite and the device for synthesizing high-purity fayalite include a tubular furnace body and a tubular furnace tube; the tubular furnace tube is placed inside the tubular furnace body, and both ends of the tubular furnace tube are located outside the tubular furnace body; a sealing flange is provided at one end of the tubular furnace tube, and a vent flange is provided at the other end of the tubular furnace tube, and a one-way valve is connected to one end of the vent flange facing the outside of the tubular furnace tube. The sealing flange is tightly connected to one end of the tubular furnace tube to ensure the airtightness inside the synthesis device during the synthesis process; one end of the vent flange is connected to the other end of the tubular furnace tube, and the other end of the vent flange is connected to the one-way valve.

[0016] In the above-mentioned method for synthesizing high-purity fayalite, a tube furnace plug is provided on both sides of the tube furnace tube, a refractory brick base is provided at the center of the tube furnace tube, a corundum crucible is provided on the refractory brick base, and the synthetic raw materials are placed in the corundum crucible. During the synthesis process, the raw materials are placed in the corundum crucible; in order to reduce the temperature gradient of the synthesis environment and ensure the accuracy of the synthesis temperature, the corundum crucible needs to be raised with a refractory brick base and placed in the center of the tube furnace tube, and plugs are placed on both sides of the tube furnace tube.

[0017] In the above-mentioned high-purity fayalite synthesis method, the one-way valve opens when the internal pressure of the synthesis device is greater than the external pressure. The sealing flange and the vent flange are respectively connected to the two ends of the tubular furnace tube, and a one-way valve is installed at the end of the vent flange facing outward. The one-way valve opens when the internal pressure of the synthesis device is greater than the external pressure to ensure that the gas inside the synthesis device flows from the inside to the outside in one direction. To avoid excessive pressure inside the synthesis device, the opening pressure of the one-way valve is not greater than 0.02 MPa.

[0018] In the above-mentioned method for synthesizing high-purity fayalite, the FeCO3-SiO2 mixture is placed in a corundum crucible, and then the corundum crucible is wrapped with iron foil before being roasted. Since CO2 has a certain oxidizing property at high temperature, and it is difficult to avoid residual air in the furnace tube, wrapping the corundum crucible with iron foil can prevent the residual gas in the furnace tube of the tubular furnace at high temperature from entering the corundum crucible and reacting with the synthetic product, which helps to improve the relative purity of the synthetic product.

[0019] The technical solution of the present invention achieves the following beneficial technical effects: 1. The synthesis device of high-purity fayalite of the present invention comprises a tubular furnace body, a tubular furnace tube, a sealing flange, a vent flange, a one-way valve, a corundum crucible required for holding the reaction raw materials, a refractory brick base required for adjusting the position of the corundum crucible, and a tubular furnace plug required for ensuring uniform reaction temperature. The one-way valve is used to control the internal pressure of the tubular furnace tube. The one-way valve opens when the internal pressure of the synthesis device is greater than the external pressure to ensure that the gas inside the synthesis device flows from the inside to the outside in a one-way manner. The opening pressure of the one-way valve is set to be no more than 0.02 MPa to avoid the internal pressure of the synthesis device being too high and causing explosion.

[0020] 2. Synthesis principle of the present invention: With FeCO3 and SiO2 as raw materials, during the heating process, the decomposition reaction of FeCO3 occurs first, and the reaction process can be described as follows: FeCO3→ FeO + CO2↑.

[0021] The CO2 gas produced by the reaction enters the tube of the tubular furnace to form an inert atmosphere, and the air in the tube of the tubular furnace is discharged through a one-way valve, which can protect the reaction products from oxidation under low temperature conditions.

[0022] As the temperature rises further, FeO produced by the decomposition of FeCO3 will react with SiO2. The reaction product of FeO and SiO2 is ferrosilicate, and the types of synthetic products vary with the stoichiometric ratio of the two. When the stoichiometric ratio of the two is 2:1, the synthetic product is fayalite, that is: 2FeO + SiO2= Fe2SiO4.

[0023] When the molar ratio of FeO to SiO2 is greater than or less than 2:1, reactants will remain or other ferrosilicates will be formed, which will enter the calcined product as impurities.

[0024] 3. FeCO3 powder and SiO2 powder are dry-milled and mixed at room temperature. FeCO3 powder is stable at room temperature. Dry-mixed ball milling at room temperature can achieve sufficient mixing and is simple to operate.

[0025] The preferred calcination temperature is 800-900°C and the holding time is 1-2 hours. Under the preferred conditions, the reaction product has high purity and the overall reaction time is short.

[0026] 4. The method of the present invention has the advantages of relatively simple process, low equipment requirements, short synthesis time, high raw material utilization rate, and high product purity. The reaction process does not require an inert gas atmosphere, and no toxic or harmful gases are generated during the preparation process. By optimizing the reaction conditions, the proportion of α-fayalite crystal phase in the fayalite product prepared in this application is higher than 95%.

[0027] Compared with the existing fayalite synthesis method, there is no need for multi-step heating and secondary purification of the prepared product. This method can provide research materials for many disciplines such as geology and materials science, especially for iron resource recovery research related to fayalite-type non-ferrous metallurgical solid waste, and can provide high-purity fayalite raw materials. It is conducive to general scientific research institutions to use existing instruments and equipment to prepare high-purity fayalite, which is of great significance for basic research in related disciplines. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A high-purity fayalite synthesis device of the present invention; Figure 2 X-ray diffraction pattern of the synthetic product of Example 2; Figure 3 X-ray diffraction pattern of the synthetic product of Example 3; Figure 4 X-ray diffraction pattern of the synthetic product of Example 4; Figure 5 Scanning electron microscope image of Example 2; Figure 6 Surface scan of Si element distribution of Example 2; Figure 7 The Fe element distribution surface scan of Example 2; Figure 8 The surface scan of the O element distribution of Example 2; Fig. 9 Energy spectrum of Example 2; Fig.10 Scanning electron microscope image of Example 3; Fig.11 Surface scan of Si element distribution of Example 3; Fig.12 The Fe element distribution surface scan of Example 3; Fig.13 The surface scan of the O element distribution of Example 3; Fig.14 Energy spectrum of Example 3; Fig.15 Scanning electron microscope image of Example 4; Fig.16 Scanning image of Si element distribution in Example 4; Fig.17The Fe element distribution surface scan of Example 4; Fig.18 The surface scan of the O element distribution of Example 4; Fig.19 Energy spectrum of Example 4.

[0029] Among them, the accompanying drawings are marked as: 1-tube furnace body; 2-tube furnace tube; 3-sealing flange; 4-vent flange; 5-check valve; 6-tube furnace plug; 7-refractory brick base; 8-corundum crucible. DETAILED DESCRIPTION

[0030] Embodiment 1, High purity fayalite synthesis device, such as Figure 1 As shown, it includes a tubular furnace body 1 and a tubular furnace tube 2; the tubular furnace tube 2 is placed inside the tubular furnace body 1, and both ends of the tubular furnace tube 2 are located outside the tubular furnace body 1; a sealing flange 3 is provided at one end of the tubular furnace tube 2, and a vent flange 4 is provided at the other end of the tubular furnace tube 2, and a one-way valve 5 is connected to the vent flange 4 at one end facing the outer side of the tubular furnace tube 2.

[0031] A one-way valve is provided at one end of the vent flange, and the one-way valve opens when the internal pressure of the synthesis device is greater than the external pressure. The opening pressure of the one-way valve is less than or equal to 0.02 MPa to avoid excessive internal pressure of the synthesis device.

[0032] Tube furnace plugs 6 are provided on both sides of the tube furnace tube 2; a refractory brick base 7 is provided at the center of the tube furnace tube 2, and a corundum crucible 8 is provided on the refractory brick base 7, and the synthetic raw materials are placed in the corundum crucible 8. The refractory brick base 7 can be provided to raise the corundum crucible and place it at the center of the tube furnace tube. Placing the raw materials in the corundum crucible can reduce the temperature gradient of the synthesis environment and ensure the accuracy of the synthesis temperature.

[0033] Examples 2 to 4 are about synthesizing α-fayalite using the synthesis device of Example 1.

[0034] Example 2 Weigh 7.94 g and 2.06 g of FeCO3 and SiO2 with a particle size of less than or equal to 0.075 mm (passing a 200-mesh sieve) at a mass ratio of 2:1, respectively, dry-mill for 30 minutes at room temperature, and place in a 20 mL corundum crucible. Wrap the crucible with iron foil and place it on the refractory brick base in the tube furnace. Close the tube furnace body, heat to 900 ° C and roast. After roasting for 1 hour, cool to room temperature with the furnace. The X-ray diffraction pattern of the obtained product ( Figure 2 )、Scanning electron microscope images( Figure 5 )、Element distribution surface scan( Figure 6-Figure 8) and the corresponding energy spectrum ( Fig. 9 ) As shown in the figure. The test results show that the synthetic product is in a loose solid state, with the main component being α-ferroitite, accounting for 96.8% of the total, and the rest being ferrosilicon spinel (γ-Fe2SiO4), accounting for 3.2%.

[0035] Example 3 Weigh 7.94 g and 2.06 g of FeCO3 and SiO2 with a particle size of less than or equal to 0.075 mm (passing a 200-mesh sieve) respectively according to the molar ratio of 2:1, dry-mill for 30 minutes at room temperature, and place in a 20 mL corundum crucible. Wrap the crucible with iron foil and place it on the refractory brick base in the tube furnace tube. Close the tube furnace body, heat to 900 ° C and roast. After roasting for 2 hours, cool to room temperature with the furnace. The X-ray diffraction spectrum of the obtained product ( Figure 3 )、Scanning electron microscope images( Fig.10 )、Element distribution surface scan( Figure 11-13 ) and the corresponding energy spectrum ( Fig.14 ) As shown in the figure. The test results show that the synthetic product is in a loose solid state, with the main component being α-fayalite, accounting for 97.2% of the total, and the rest being ferrosilicon spinel (γ-Fe2SiO4), accounting for 2.8%.

[0036] Example 4 Weigh 7.94 g and 2.06 g of FeCO3 and SiO2 with a particle size of less than or equal to 0.075 mm (passing a 200-mesh sieve) respectively according to a molar ratio of 2:1, dry-mill for 30 minutes at room temperature, and place in a 20 mL corundum crucible. Wrap the crucible with iron foil and place it on the refractory brick base in the tube furnace. Close the tube furnace body, heat to 1000 ° C and roast. After roasting for 1 hour, cool to room temperature with the furnace. The X-ray diffraction pattern of the obtained product ( Figure 4 )、Scanning electron microscope images( Fig.15 )、Element distribution surface scan( Figure 16-18 ) and the corresponding energy spectrum ( Fig.19 ) As shown in the figure. The test results show that the main component of the synthetic product is α-ferroitite, accounting for 93.8% of the total, and the rest is ferrosilicon spinel (γ-Fe2SiO4), accounting for 6.2%.

[0037] It can be seen from the above-mentioned Examples 2 to 4 that the method of the present invention has the advantages of relatively simple process, low equipment requirements, short synthesis time, high raw material utilization rate, and high product purity. The reaction process does not require an inert gas atmosphere, and no toxic or harmful gas is generated during the preparation process. Compared with the existing fayalite synthesis method, there is no need for multi-step heating and secondary purification of the prepared product. This method can provide research materials for research work in many disciplines such as geology and materials science, and can especially provide high-purity fayalite raw materials for research work related to iron resource recovery of fayalite-type non-ferrous metallurgical solid waste, which is beneficial for general scientific research institutions to use existing instruments and equipment to prepare high-purity fayalite, and is of great significance for basic research in related disciplines.

[0038] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the claims of this patent application.

Claims

1. A method for synthesizing high-purity fayalite, characterized in that: The steps include: (1) mixing FeCO3 powder and SiO2 powder to obtain a FeCO3-SiO2 mixture; (2) placing the FeCO3-SiO2 mixture in a high-purity fayalite synthesis device for roasting; (3) Cool down to room temperature in the furnace to obtain fayalite.

2. The method for synthesizing high-purity fayalite according to claim 1, characterized in that: The molar ratio of FeCO3 to SiO2 is 2:

1.

3. The method for synthesizing high-purity fayalite according to claim 1, characterized in that: The particle size of FeCO3 and SiO2 is less than or equal to 0.075 mm.

4. The method for synthesizing high-purity fayalite according to claim 1, characterized in that: FeCO3 and SiO2 are mixed until they are uniform and there is no local component segregation.

5. The method for synthesizing high-purity fayalite according to claim 4, characterized in that: Under room temperature, dry-mill FeCO3 and SiO2 for 30 to 60 min.

6. The method for synthesizing high-purity fayalite according to claim 1, characterized in that: The calcination temperature is 700-1200 °C and the holding time is 0.5-4 h.

7. The method for synthesizing high-purity fayalite according to claim 1, characterized in that: A high-purity fayalite synthesis device comprises a tubular furnace body (1) and a tubular furnace tube (2); the tubular furnace tube (2) is placed inside the tubular furnace body (1), and both ends of the tubular furnace tube (2) are located outside the tubular furnace body (1); a sealing flange (3) is provided at one end of the tubular furnace tube (2), a vent flange (4) is provided at the other end of the tubular furnace tube (2), and a one-way valve (5) is connected to one end of the vent flange (4) facing the outside of the tubular furnace tube (2).

8. The method for synthesizing high-purity fayalite according to claim 7, characterized in that: Tubular furnace plugs (6) are provided on both sides of the tubular furnace tube (2), respectively; a refractory brick base (7) is provided at the center of the tubular furnace tube (2), a corundum crucible (8) is provided on the refractory brick base (7), and synthetic raw materials are placed in the corundum crucible (8).

9. The method for synthesizing high-purity fayalite according to claim 7, characterized in that: The one-way valve opens when the pressure inside the synthesis device is greater than the external pressure.

10. The method for synthesizing high-purity fayalite according to claim 8, characterized in that: The FeCO3-SiO2 mixture is placed in a corundum crucible, and then the corundum crucible is wrapped with iron foil and then calcined.

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