Low-coercivity iron oxide black magnetic powder and method for producing the same

Abstract

The application discloses a kind of low coercivity iron oxide black magnetic powder and preparation method thereof, and preparation steps are as follows: (1) solid ferrous salt is used as raw material, dissolved in high ammonia nitrogen water by heating, so that the ferrous content is 100-300g / L, then continue to pass in steam to heat to 60-80 DEG C;(2) slowly add strong alkaline solution to solution system of step (1) while stirring, until the ferrous ion content in solution is 4-20g / L, temperature is kept unchanged during the process;(3) keep stirring for 1-2h, then pass in steam to heat to 90 DEG C;(4) pass in compressed air to carry out rapid oxidation;(5) when the pH of material liquid in step (4) is reduced to about 4.0, close air, slowly add strong alkaline solution to adjust pH to 8.0-10.0;(6) pass in air, when pH is reduced to more than 6.0 and no longer decline, stop reaction;(7) filter, rinse, dry the material liquid obtained in step (6).The preparation method of low coercivity iron oxide black magnetic powder provided by the application has mild synthesis condition and low production cost, the product is near-spherical, small in particle size, and has superior magnetic properties.

Description

Technical Field

[0001] This invention relates to the field of electrostatic developers, specifically to a low coercivity iron oxide black magnetic powder and its preparation method. Background Technology

[0002] Developer, also known as toner, is an office consumable used in the developing process of photocopiers. It is expensive, and its demand is increasing year by year. Its main raw material is black iron oxide magnetic powder.

[0003] Black magnetite (Fe3O4) magnetic powder is an important and widely used magnetic material. It possesses the properties of black pigment and superior magnetic properties, making it an indispensable main component in copier toners. Magnetite (Fe3O4) magnetic powder combines the properties of magnetic materials and colorants, primarily used in the preparation of single-component magnetic toners and magnetic inks for copiers and laser printers. The main components of single-component toners include: resin, magnetic powder, dye, charge regulator, and auxiliary additives. Because single-component toners do not use a carrier, a large amount of magnetic powder is added. Adding black magnetite powder or chemically generated magnetic powder to black toner both carries the toner particles and provides coloring. Single-component laser printers require both a magnetic material as a carrier and a black pigment, hence the selection of magnetite (Fe3O4) magnetic powder. This magnetite (Fe3O4) magnetic powder must have high saturation magnetization, low coercivity, and a specific particle size. The particle size characteristics of the toner are a crucial parameter determining its performance; to achieve high-quality development of fine lines and continuous images, the particle size of the toner is typically required to be within the range of 10 micrometers. In high-speed printers, the requirements for iron black magnetic powder particles are even more stringent. The particle size distribution is required to be 0.2 to 0.5 μm with a narrow distribution, and the corresponding coercivity is required to be as low as possible, preferably below 40 Oe, in order to achieve good application results in the field of high-speed printing.

[0004] In addition, in order to prevent the magnetic iron oxide particles from falling off the carrier surface when applied to magnetic developers, causing the particle powder to scatter and greatly reducing the developing effect, and because printer toner requires the ferric oxide magnetic particles to have good flowability, the ideal Fe3O4 magnetic particles need to be based on a spherical or near-spherical shape and have multiple granular protrusions on the particle surface.

[0005] Patent application number 2012102821140 discloses a method for producing high magnetic iron oxide by adding a variety of organic additives to zinc pickling waste liquid. Although the morphology of the iron oxide magnetic powder prepared by this method is nearly spherical, its coercivity is relatively high and the operation process is complicated. Summary of the Invention

[0006] Therefore, the purpose of this invention is to provide a low-coercivity iron oxide black magnetic powder with a near-spherical shape that is safe and reliable in process, convenient in operation, mild in synthesis conditions, low in production cost, good in dispersion performance, excellent in magnetic properties, and has good magnetic properties, as well as a method for its preparation.

[0007] A method for preparing low coercivity iron oxide black magnetic powder, the preparation steps are as follows: (1) Solid ferrous salt is used as raw material and heated to dissolve in high ammonia nitrogen water to make the ferrous content 100-300g / L, and then steam is continuously introduced to raise the temperature to 60℃-80℃; (2) While stirring, a strong alkaline solution is slowly added to the solution system of step (1) until the ferrous ion content in the solution is 4-20g / L, and the temperature is kept constant during the process; (3) After stirring for 1-2 hours, steam is introduced to raise the temperature to 90℃; (4) Compressed air is introduced for rapid oxidation; (5) When the pH of the material solution in step (4) drops to about 4.0, the air is turned off and a strong alkaline solution is slowly added to adjust the pH to 8.0-10.0; (6) Air is introduced, and when the pH drops to above 6.0 and no longer drops, the reaction is stopped; (7) The material solution obtained in step (6) is filtered, rinsed and dried to obtain near-spherical low coercivity iron oxide black magnetic powder.

[0008] In some embodiments, in step (1), the high ammonia nitrogen water is the untreated high ammonia nitrogen mother liquor water generated during the preparation of iron oxide red, that is, the high ammonia nitrogen wastewater generated by the iron oxide production plant, with a ferrous ion content of 10-30 g / L and an ammonia nitrogen mass concentration as high as 10,000-50,000 mg / L.

[0009] In some embodiments, in step (1), the high ammonia nitrogen water is a nitrate solution, which is a NaNO3 solution, KNO3 solution or NH4NO3 solution, and the amount added is 2-5% of the theoretical mass of iron oxide magnetic powder.

[0010] In some embodiments, in step (1), the ferrous salt solution is FeCl₂. 2· One or more of 4H2O, Fe(NO3)2·6H2O, FeSO4·7H2O, or ferrous acetate. In some specific embodiments, the ferrous salt is preferably FeSO4·7H2O.

[0011] In some embodiments, in steps (2) and (5), the strongly alkaline solution is one or more of Na2CO3, K2CO3, NaOH, KOH or NH3·H2O.

[0012] In some embodiments, in steps (4) and (6), the air velocity is 10-360 m / s. 3 / h.

[0013] In some embodiments, in step (2), the strong alkaline solution is added over a time of 40-60 minutes; in step (5), the strong alkaline solution is added slowly over a time of 10-30 minutes.

[0014] In some embodiments, the drying temperature in step (7) is 60-70°C.

[0015] In some specific embodiments, the preparation steps are as follows: (1) Dissolve solid ferrous sulfate in high ammonia nitrogen wastewater at 50°C to make the ferrous content 100-300g / L, and then continue to pass steam to raise the temperature to 60°C-80°C; (2) While stirring, slowly add NaOH solution to the solution system of step (1) until the ferrous ion content in the solution is 4-20g / L, and keep the temperature constant during the process; (3) After stirring for 1-2 hours, pass steam to raise the temperature to 90°C; (4) Pass compressed air to carry out rapid oxidation; (5) When the pH of the solution in step (4) drops to about 4.0, turn off the air and slowly add a strong alkaline solution to adjust the pH to 8.0-10.0; (6) Pass air, and when the pH drops to above 6.0 and no longer drops, stop the reaction; (7) Filter, rinse and dry the solution obtained in step (6) to obtain low coercivity iron oxide black magnetic powder.

[0016] The low coercivity iron oxide black magnetic powder is prepared by the method described above.

[0017] The present invention, by adopting the above technical solution, has the following beneficial effects:

[0018] (1) The preparation method of low coercivity iron oxide black magnetic powder of the present invention is more suitable for industrial-scale production because the reaction conditions involved are mild, the process is simple, the production cost is low, and it is non-toxic and pollution-free.

[0019] (2) In the preparation method of low coercivity iron oxide black magnetic powder of the present invention, high ammonia nitrogen wastewater generated by iron oxide production plant can be used as raw material for dissolving solid ferrous sulfate. This not only avoids the waste of manpower, material resources and financial resources caused by treating high ammonia nitrogen wastewater, but also enables the wastewater to be recycled and reused in a high-efficiency manner. Through this process, the ammonia nitrogen content of up to 10,000-50,000 mg / L can be reduced to below 1,000 mg / L, which greatly reduces the cost of wastewater treatment.

[0020] (3) In the preparation method of low coercivity iron oxide black magnetic powder of the present invention, the nitrogen oxide contained in the high ammonia nitrogen wastewater produced by the iron oxide production plant has a catalytic and auxiliary effect on the synthesis of near-spherical morphology of iron oxide black, and the high ammonia nitrogen wastewater produced by the iron oxide production plant acts as a dispersant in the Fe3O4 synthesis process, so that the Fe3O4 particles formed have a lower particle size and a narrower particle size distribution, thereby obtaining low coercivity iron oxide magnetic powder.

[0021] (4) The low coercivity iron oxide black magnetic powder prepared by the present invention has a regular near-spherical morphology, excellent dispersibility and flowability, small particle size, and low coercivity and high saturation magnetization intensity, which can be well applied to electrostatic developer toner. Attached Figure Description

[0022] Figure 1 SEM image of the iron oxide black magnetic powder sample prepared in Example 1;

[0023] Figure 2 SEM image of the iron oxide black magnetic powder sample prepared in Example 2;

[0024] Figure 3 SEM image of the iron oxide black magnetic powder sample prepared in Example 3;

[0025] Figure 4 SEM image of the iron oxide black magnetic powder sample prepared in Example 4;

[0026] Figure 5 The image shows the SEM image of the iron oxide black magnetic powder sample prepared in Comparative Example 1. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0028] Example 1

[0029] 10L of high-ammonia nitrogen wastewater with a ferrous content of 15g / L from an iron oxide plant was added to a 30L reaction vessel. Steam was introduced to raise the temperature to 50℃, and then 3kg of solid ferrous sulfate was added and stirred until completely dissolved. The steam temperature was raised to 60℃ and maintained. Then, 432g / L of NaOH solution was slowly added dropwise while stirring until the ferrous ion content in the solution reached 10g / L. The addition was stopped, and stirring was maintained for 1 hour. The solution was then heated to 90℃, and air was turned on for rapid oxidation at a flow rate of 90L / min. When the pH of the solution dropped to 4.0, the air supply was stopped, and 432g / L of NaOH solution was slowly added dropwise until the pH reached 8.5. The air supply was turned on again, and the air flow rate was maintained at 90L / min. After 20 minutes, the pH of the solution dropped to 6.72. The air and steam were turned off, and the reaction was stopped. The solution was filtered, rinsed, and dried at 60℃ for 12 hours to obtain iron oxide black magnetic powder samples.

[0030] Example 2

[0031] 10L of high-ammonia nitrogen wastewater with a ferrous content of 20g / L from an iron oxide plant was added to a 30L reaction vessel. Steam was introduced to raise the temperature to 50℃, and then 3kg of solid ferrous sulfate was added and stirred until completely dissolved. The steam temperature was raised to 60℃ and maintained. Then, 280g / L of KOH solution was slowly added dropwise while stirring until the ferrous ion content in the solution reached 8g / L. The addition was stopped, and stirring was maintained for 1 hour. The solution was then heated to 90℃, and air was turned on for rapid oxidation at a flow rate of 200L / min. When the pH of the solution dropped to 4.0, the air supply was stopped, and 280g / L of KOH solution was slowly added dropwise until the pH reached 8.5. The air supply was turned on again, and the air flow rate was maintained at 200L / min. After 20 minutes, the pH of the solution dropped to 7.3. The air and steam were turned off, and the reaction was stopped. The solution was filtered, rinsed, and dried at 60℃ for 12 hours to obtain iron oxide black magnetic powder samples.

[0032] Example 3

[0033] The 0.7m produced by the iron oxide plant 3 High ammonia nitrogen wastewater with ferrous content of 20 g / L was added to a 2m³ 3 In the reaction vessel, steam was introduced and the temperature was raised to 50°C. Then, 210 kg of solid ferrous sulfate was added and stirred until completely dissolved. The steam temperature was then raised to 60°C and maintained. Subsequently, a 432 g / L NaOH solution was slowly added dropwise while stirring until the ferrous ion content in the solution reached 8 g / L. The addition was then stopped, and stirring was maintained for 1 hour. Afterward, the solution was heated to 90°C, and air was introduced for rapid oxidation at a flow rate of 200 m³ / h. 3 Continue the process at a rate of 1 h until the pH of the feed solution drops to 4.0. Stop aeration and slowly add 432 g / L NaOH solution until the pH reaches 8.5. Then restart the aeration process, maintaining an air flow rate of 200 m³ / h.3 After 20 minutes, the pH of the solution dropped to 7.2. The air and steam were turned off, the reaction was stopped, the solution was pressure filtered and rinsed, and then dried at 60°C for 12 hours to obtain iron oxide black magnetic powder samples.

[0034] Example 4

[0035] 10L of tap water and 15g of ammonium nitrate were added sequentially to a 30L reaction vessel and stirred until dissolved. Steam was introduced to raise the temperature to 50℃, then 3kg of solid ferrous sulfate was added and stirred until completely dissolved. The temperature was raised to 60℃ and maintained. Then, 432g / L of NaOH solution was slowly added dropwise while stirring until the ferrous ion content in the solution reached 8g / L. The addition was stopped, and stirring was maintained for 1 hour. The solution was then heated to 90℃ and air was turned on for rapid oxidation at a flow rate of 120L / min. When the pH of the solution dropped to 4.0, the air supply was stopped, and 432g / L of NaOH solution was slowly added dropwise until the pH reached 8.5. The air supply was turned on again, and the flow rate was maintained at 200L / min. After 20 minutes, the pH of the solution dropped to 7.6. The air and steam were turned off, and the reaction was stopped. The solution was filtered, rinsed, and dried at 60℃ for 12 hours to obtain the iron oxide black magnetic powder sample.

[0036] Comparative Example 1

[0037] 10L of tap water was added to a 30L reaction vessel. The steam temperature was raised to 50°C, and 3kg of solid ferrous sulfate was added and stirred until completely dissolved. The steam temperature was then raised to 60°C and maintained. While stirring, a 432g / L NaOH solution was slowly added dropwise until the ferrous ion content in the solution reached 8g / L. The addition was then stopped, and stirring was maintained for 1 hour. Afterward, the solution was heated to 90°C, and air was turned on for rapid oxidation at a flow rate of 120L / min. After 10 minutes of air circulation, 15g of sodium nitrate was slowly added, and air oxidation continued until the pH of the solution dropped to 4.5. At this point, air circulation was stopped, and 432g / L NaOH solution was slowly added dropwise until the pH reached 8.5. Air circulation was then restarted, with the air flow rate maintained at 120L / min. After 20 minutes, the pH of the solution dropped to 6.8. Air and steam were then turned off, and the reaction was stopped. The solution was filtered, rinsed, and dried at 60℃ for 12 hours to obtain the iron oxide black magnetic powder sample.

[0038] SEM analysis was performed on the iron oxide black samples obtained in Examples 1-4 and Comparative Example 1 to obtain... Figures 1-5 ,in, Figure 1 This is a SEM image of the iron oxide black magnetic powder sample prepared in Example 1. Figure 2 This is a SEM image of the iron oxide black magnetic powder sample prepared in Example 2. Figure 3This is a SEM image of the iron oxide black magnetic powder sample prepared in Example 3. Figure 4 This is a SEM image of the iron oxide black magnetic powder sample prepared in Example 4. Figure 5 The image shows the SEM image of the iron oxide black magnetic powder sample prepared in Comparative Example 1.

[0039] like Figure 1-5 As shown, the iron oxide black magnetic powder samples prepared in Examples 1-4 of this invention have a near-spherical particle morphology and numerous granular protrusions on the particle surface. This prevents particle shedding when applied to toner, thus avoiding impact on the final color tone. Furthermore, the prepared iron oxide magnetic powder exhibits good dispersibility, flowability, and stable magnetism, ensuring high-resolution images when used in developers. However, compared to Example 4, which uses ammonium nitrate solution to dissolve solid ferrous sulfate, Examples 1-3 use high-ammonia nitrogen wastewater from an iron oxide production plant as the raw material for dissolving solid ferrous sulfate. This results in smaller, more uniform particle sizes and a narrower particle size distribution in the prepared iron oxide black magnetic powder samples. In contrast, in Comparative Example 1, because sodium nitrate was added to the system later, some of the prepared iron oxide black magnetic powder samples had a near-square morphology, severe particle agglomeration, and a large and uneven particle size distribution.

[0040] Morphology and magnetic properties testing:

[0041] Morphology detection method: The surface morphology of the samples was observed using a Hitachi S4800 scanning electron microscope (SEM). Magnetic detection method: The magnetic properties of the samples were measured using a LakeShore 7410 vibrating-sample magnetometer (VSM).

[0042] The magnetic properties of the iron oxide black samples prepared in Examples 1-4 and Comparative Example 1 were tested using the above method. The test results are shown in Table 1 below:

[0043] Table 1: Magnetic Detection Table of Iron Oxide Black Samples Prepared in Examples 1-4 and Comparative Example 1

[0044] Example 1 0.263 96.69 2.48 28.04 Example 2 0.364 92.67 2.83 27.58 Example 3 0.294 93.94 2.19 28.45 Example 4 0.504 94.58 4.27 36.48 Comparative Example 1 0.745 97.55 5.64 42.96

[0045] As shown in Table 1, the iron oxide black magnetic powder samples prepared in Examples 1-4 of this invention have a particle size of no more than 0.504 μm. This small particle size results in high saturation magnetization and low remanent magnetization, making them well-suited for use with electrostatic developer toners. However, compared to Example 4, which used ammonium nitrate solution to dissolve solid ferrous sulfate, Examples 1-3 used high-ammonia nitrogen wastewater from an iron oxide production plant as the raw material for dissolving solid ferrous sulfate. This resulted in even smaller particle size and lower coercivity in the prepared iron oxide black magnetic powder samples. Therefore, the introduction of high-ammonia nitrogen wastewater can yield iron oxide black magnetic particles with excellent dispersion performance and low coercivity. Experiments have shown that the particle size of the iron oxide black magnetic powder sample prepared with ammonium nitrate solution is larger than that prepared with sodium nitrate solution. However, comparing Example 4 with Comparative Example 1, it can be seen that because sodium nitrate was added to the system later in Comparative Example 1, the particle size of the iron oxide black magnetic powder sample in Comparative Example 1 increased to 0.745 μm, with severe agglomeration and a coercivity as high as 42.96 Oe, which cannot meet the performance requirements of high-speed printers for iron oxide black magnetic powder particles.

[0046] Testing revealed that the iron content of the ferric oxide magnetic powder provided in Example 1 is as high as 99.10%, the average particle size D50 is optimally 0.26μm, its morphology is nearly spherical, and the particle surface has multiple granular protrusions, which prevent it from falling off in toner applications. The saturation magnetism reaches 96.69 emu / g, the remanence is as low as 2.48 emu / g, and the coercivity is as low as 28.04 Oe, making it well-suited for electrostatic developer toners.

[0047] In this invention, the preparation method of low coercivity iron oxide black magnetic powder has mild reaction conditions, simple process flow, low production cost, and is non-toxic and pollution-free. It can also use high ammonia nitrogen wastewater generated by iron oxide production plants as raw material for dissolving solid ferrous sulfate, which avoids the waste of manpower, material resources and financial resources caused by treating high ammonia nitrogen wastewater, and can also efficiently recycle and reuse the wastewater. Through this process, the ammonia nitrogen content, which is as high as 10,000-50,000 mg / L, can be reduced to below 1,000 mg / L, which greatly reduces the cost of wastewater treatment and is more suitable for industrial-scale clean production.

[0048] In this invention, the experimental conditions of the examples are not limited to those described above. The numerical values ​​mentioned above are reference values ​​during the experiment and are only preferred embodiments of this invention. They are not intended to limit this invention. All modifications, substitutions, and improvements made in accordance with the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for preparing low coercivity iron oxide black magnetic powder, characterized in that, The preparation steps are as follows: (1) Use solid ferrous salt as raw material, heat it up and dissolve it in high ammonia nitrogen water to make the ferrous content 100-300g / L, and then continue to pass steam to heat it to 60℃-80℃. (2) While stirring, slowly add a strong alkaline solution to the solution system of step (1) until the ferrous ion content in the solution is 4-20 g / L, and keep the temperature constant during the process; (3) After stirring for 1-2 hours, introduce steam to raise the temperature to 90℃; (4) Introduce compressed air for rapid oxidation; (5) When the pH of the solution in step (4) drops to about 4.0, turn off the air and slowly add a strong alkaline solution to adjust the pH to 8.0-10.0; (6) Introduce air and stop the reaction when the pH drops to above 6.0 and stops decreasing. (7) The liquid obtained in step (6) is filtered, rinsed and dried to obtain low coercivity iron oxide black magnetic powder. The particle morphology of the low coercivity iron oxide black magnetic powder is close to spherical and the particle surface has multiple granular protrusions. In step (1), the high ammonia nitrogen water is the untreated high ammonia nitrogen mother liquor water produced during the preparation of iron oxide red, with a ferrous ion content of 10-30 g / L and an ammonia nitrogen mass concentration as high as 10,000-50,000 mg / L.

2. The method for preparing low coercivity iron oxide black magnetic powder according to claim 1, characterized in that, In step (1), the ferrous salt is one or more of FeCl2·4H2O, Fe(NO3)2·6H2O, FeSO4·7H2O or ferrous acetate.

3. The method for preparing low coercivity iron oxide black magnetic powder according to claim 1, characterized in that, In steps (2) and (5), the strongly alkaline solution is one or more of Na2CO3, K2CO3, NaOH, KOH or NH3·H2O.

4. The method for preparing low coercivity iron oxide black magnetic powder according to claim 1, characterized in that, In the steps (4) and (6), the air flow rate is 10-360 m 3 / h.

5. The method for preparing low coercivity iron oxide black magnetic powder according to claim 1, characterized in that, In step (2), the strong alkaline solution is added over a period of 40-60 minutes; in step (5), the strong alkaline solution is added over a period of 10-30 minutes.

6. The method for preparing low coercivity iron oxide black magnetic powder according to claim 1, characterized in that, In step (7), the drying temperature is 60-70°C.

7. The method for preparing low coercivity iron oxide black magnetic powder according to claim 1, characterized in that, The preparation steps are as follows: (1) Dissolve solid ferrous sulfate in high ammonia nitrogen wastewater at 50°C to make the ferrous content 100-300g / L, and then continue to pass steam to raise the temperature to 60°C-80°C. (2) While stirring, slowly add NaOH solution to the solution system of step (1) until the ferrous ion content in the solution is 4-20 g / L, and keep the temperature constant during the process; (3) After stirring for 1-2 hours, introduce steam to raise the temperature to 90℃; (4) Introduce compressed air for rapid oxidation; (5) When the pH of the solution in step (4) drops to about 4.0, turn off the air and slowly add a strong alkaline solution to adjust the pH to 8.0-10.0; (6) Introduce air and stop the reaction when the pH drops to above 6.0 and stops decreasing. (7) The liquid obtained in step (6) is filtered, rinsed and dried to obtain low coercivity iron oxide black magnetic powder.

Images