Low-coercivity iron oxide black magnetic powder and preparation method thereof

Abstract

The invention discloses low-coercivity iron oxide black magnetic powder and a preparation method thereof.The preparation method comprises the following steps that 1, solid ferrite serves as a raw material and is heated and dissolved in high-ammonia-nitrogen water, the ferrous content is 100-300 g / L, and then steam continues to be introduced for heating to 60-80 DEG C; (2) slowly adding a strong alkaline solution into a solution system in the step (1) while stirring until the content of ferrous ions in the solution is 4-20g / L, and keeping the temperature unchanged in the process; (3) keeping stirring for 1-2 hours, introducing steam, and raising the temperature to 90 DEG C; (4) compressed air is introduced for rapid oxidation; (5) when the pH value of the feed liquid in the step (4) is reduced to about 4.0, closing air, and slowly adding a strong alkaline solution to adjust the pH value to 8.0-10.0; (6) introducing air, and stopping the reaction when the pH value is reduced to 6.0 or above and is not reduced any more; and (7) filtering, rinsing and drying the feed liquid obtained in the step (6). The preparation method of the low-coercivity iron oxide black magnetic powder is mild in synthesis condition and low in production cost, and the product is nearly spherical, small in particle size and excellent in magnetic performance.

Description

Technical Field

[0001] The invention relates to the field of electrostatic developers, and in particular to low-coercivity iron oxide black magnetic powder and a preparation method thereof. Background Art

[0002] Developer, also known as toner, is an office consumable in the development process of copiers. It is expensive and its demand is increasing year by year. The main raw material is black ferroferric oxide magnetic powder.

[0003] Black ferroferric oxide magnetic powder is an important and widely used magnetic material. It has black pigment properties and superior magnetic properties. It is an indispensable main component in copy toner. Ferroferric oxide magnetic powder has the properties of magnetic materials and colorants. It is mainly used to prepare single-component magnetic toner and magnetic ink for copiers and laser printers. The main components of single-component toner are: resin, magnetic powder, dye, charge regulator, auxiliary additives. Since single-component toner does not use a carrier, a large amount of magnetic powder is added to the toner. Adding black magnetite powder or magnetic powder generated by chemical methods to black toner not only carries toner particles but also plays a dyeing role. Single-component laser printers must have both magnetic materials as carriers and black objects as pigments, so ferroferric oxide magnetic powder is selected. The ferroferric oxide magnetic powder must have high saturation magnetization, low coercive force and a certain particle size. The particle size characteristics of toner are important parameters that determine the performance of toner. To obtain high-quality development effects for fine lines and continuous images, the particle size of toner is usually required to be within 10 microns. In high-speed printers, the requirements for iron black magnetic powder particles are more stringent. The particle size distribution is required to be 0.2-0.5μm, with a narrow distribution, and the corresponding coercive force is required to be as low as possible, preferably below 40Oe, in order to show good application effects in the field of high-speed printing.

[0004] In addition, in order to prevent the magnetic iron oxide particles from falling off the surface of the carrier when used in the magnetic developer, causing the particle powder to fly and greatly reducing the development effect, and the printer toner requires the iron oxide magnetic particles to have good fluidity, the ideal Fe3O4 magnetic particles need to be spherical or nearly spherical and have multiple granular protrusions on the particle surface.

[0005] Patent application No. 2012102821140 discloses a method of using zinc plating pickling waste liquid to produce highly magnetic ferroferric oxide by adding a variety of organic additives. Although the ferroferric oxide magnetic powder prepared by this method has a nearly spherical morphology, its coercive force is relatively high and the operation process is complicated. Summary of the invention

[0006] To this end, the purpose of the present invention is to provide a low coercive force iron oxide black magnetic powder with a near-spherical shape and a preparation method thereof, which has the advantages of safe and reliable process, convenient operation, mild synthesis conditions, low production cost, good dispersibility, excellent magnetic properties, and low coercivity.

[0007] A method for preparing low coercive force iron oxide black magnetic powder comprises the following steps: (1) taking solid ferrous salt as a raw material, heating and dissolving it in high ammonia nitrogen water to make the ferrous content be 100-300 g / L, and then continuing to introduce steam to raise the temperature to 60°C-80°C; (2) slowly adding a strong alkaline solution to the solution system of step (1) while stirring, until the ferrous ion content in the solution is 4-20 g / L, and keeping the temperature unchanged during the process; (3) after stirring for 1-2 hours, introducing steam to raise the temperature to 90°C; (4) introducing compressed air for rapid oxidation; (5) when the pH value of the feed solution of step (4) drops to about 4.0, closing the air, and slowly adding a strong alkaline solution to adjust the pH value to 8.0-10.0; (6) introducing air, and when the pH value drops to above 6.0 and no longer drops, stopping the reaction; (7) filtering, rinsing and drying the feed solution obtained in step (6) to obtain nearly spherical low coercive force 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 produced in the preparation process of red iron oxide, that is, the high ammonia nitrogen wastewater produced by the iron oxide production plant, and its ferrous ion content is 10-30g / L, and the ammonia nitrogen mass concentration is 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, and the nitrate solution is a NaNO3 solution, a KNO3 solution or a NH4NO3 solution, and the addition amount thereof is 2-5% of the theoretical mass of the iron oxide magnetic powder.

[0010] In some embodiments, in step (1), the ferrous salt solution is FeCl 2· 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 step (2) and step (5), the strong alkaline solution is one or more of Na2CO3, K2CO3, NaOH, KOH or NH3·H2O.

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

[0013] In some embodiments, in step (2), the strong alkaline solution is added dropwise for 40-60 min; in step (5), the strong alkaline solution is added slowly for 10-30 min.

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

[0015] In some specific embodiments, the preparation steps are as follows: (1) dissolving solid ferrous sulfate in high ammonia nitrogen wastewater at 50°C to make the ferrous content 100-300 g / L, and then continuing to introduce steam to raise the temperature to 60°C-80°C; (2) slowly adding NaOH solution to the solution system of step (1) while stirring until the ferrous ion content in the solution is 4-20 g / L, and keeping the temperature unchanged during the process; (3) after stirring for 1-2 hours, introducing steam to raise the temperature to 90°C; (4) introducing compressed air for rapid oxidation; (5) when the pH of the step (4) feed solution 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) introducing air, and when the pH drops to above 6.0 and no longer drops, stop the reaction; (7) filtering, rinsing, and drying the feed solution obtained in step (6) to obtain low coercive force iron oxide black magnetic powder.

[0016] The low coercive force iron oxide black magnetic powder is prepared by the preparation method as described above.

[0017] The present invention has the following beneficial effects due to the adoption of the above technical solution:

[0018] (1) The method for preparing low coercive force iron oxide black magnetic powder of the present invention is more suitable for industrial-scale production because of its mild reaction conditions, simple process flow, low production cost, non-toxicity and pollution-free.

[0019] (2) In the method for preparing low coercive force iron oxide black magnetic powder described in the present invention, high ammonia nitrogen wastewater generated by an iron oxide production plant can be used as a raw material for dissolving solid ferrous sulfate, which not only avoids the waste of manpower, material resources, financial resources and other resources caused by treating high ammonia nitrogen wastewater, but also can efficiently recycle and reuse the wastewater. 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, greatly reducing the cost of treating wastewater.

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

[0021] (4) The low coercive force iron oxide black magnetic powder prepared by the present invention has a standard nearly spherical morphology, excellent dispersibility and fluidity, small particle size, low coercive force and high saturation magnetization, and can be well applied to electrostatic developer toner. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

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

[0026] Figure 5 This is the SEM image of the iron oxide black magnetic powder sample prepared in Comparative Example 1. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0028] Example 1

[0029] 10L of high ammonia nitrogen wastewater with a ferrous content of 15g / L produced by the iron oxide plant was put into a 30L reaction barrel. After steam was introduced to heat the temperature to 50°C, 3kg of solid ferrous sulfate was added and stirred until it was completely dissolved. The steam was heated to 60°C and maintained. Then, 432g / L of NaOH solution was slowly added dropwise while stirring. When the ferrous ion content in the solution reached 10g / L, the addition was stopped and the stirring was maintained for 1h. Then, the feed liquid was heated to 90°C and the air was turned on for rapid oxidation at an air flow rate of 90L / min. When the pH of the feed liquid dropped to 4.0, the air was stopped, and 432g / L of NaOH solution was slowly added dropwise until the pH was 8.5. The air was turned on again and the air flow rate was maintained at 90L / min. After 20min, the pH of the feed liquid dropped to 6.72. The air and steam were turned off to stop the reaction. The feed liquid was filtered and rinsed, and dried at 60°C for 12h to obtain an iron oxide black magnetic powder sample.

[0030] Example 2

[0031] 10L of high ammonia nitrogen wastewater with a ferrous content of 20g / L produced by the iron oxide plant was put into a 30L reaction barrel. After steam was introduced to heat the temperature to 50°C, 3kg of solid ferrous sulfate was added and stirred until it was completely dissolved. The steam was heated to 60°C and maintained. Then, 280g / L of KOH solution was slowly added dropwise while stirring. When the ferrous ion content in the solution was 8g / L, the addition was stopped and the stirring was maintained for 1h. Then, the feed liquid was heated to 90°C and the air was turned on for rapid oxidation at an air flow rate of 200L / min. When the pH of the feed liquid dropped to 4.0, the air was stopped, and 280g / L of KOH solution was slowly added dropwise to a pH of 8.5. The air was turned on again with an air flow rate of 200L / min. After 20min, the pH of the feed liquid dropped to 7.3. The air and steam were turned off to stop the reaction. The feed liquid was filtered, rinsed, and dried at 60°C for 12h to obtain an iron oxide black magnetic powder sample.

[0032] Example 3

[0033] The 0.7m 3 High ammonia nitrogen wastewater with ferrous content of 20g / L was put into 2m 3 In the reaction barrel, steam is introduced and heated to 50°C, then 210kg of solid ferrous sulfate is added and stirred until it is completely dissolved, and the steam temperature is raised to 60°C and maintained, then 432g / L of NaOH solution is slowly added dropwise while stirring, until the ferrous ion content in the solution reaches 8g / L, then the addition is stopped and stirring is maintained for 1h, then the feed liquid is heated to 90°C and air is turned on for rapid oxidation, with an air flow rate of 200m 3 / h, when the pH of the feed solution drops to 4.0, stop introducing air, slowly add 432g / L NaOH solution until the pH reaches 8.5, and start the air again, with the air flow rate maintained at 200m3 / h, after 20 minutes, the pH value of the feed liquid dropped to 7.2, the air and steam were turned off, the reaction was stopped, the feed liquid was filter-filtered, rinsed, and dried at 60°C for 12 hours to obtain an iron oxide black magnetic powder sample.

[0034] Example 4

[0035] 10L of tap water and 15g of ammonium nitrate were successively put into a 30L reaction barrel, stirred to dissolve, and steam was introduced to heat up to 50°C. Then, 3kg of solid ferrous sulfate was added and stirred until completely dissolved, and the steam was heated to 60°C and maintained. Then, 432g / L of NaOH solution was slowly added dropwise while stirring. When the ferrous ion content in the solution was 8g / L, the addition was stopped and stirring was maintained for 1h. Then, the feed liquid was heated to 90°C and air was turned on for rapid oxidation at an air flow rate of 120L / min. When the pH of the feed liquid dropped to 4.0, the air was stopped, and 432g / L of NaOH solution was slowly added dropwise until the pH was 8.5. The air was turned on again and the air flow rate was maintained at 200L / min. After 20min, the pH of the feed liquid dropped to 7.6. The air and steam were turned off to stop the reaction. The feed liquid was filtered and rinsed, and dried at 60°C for 12h to obtain an iron oxide black magnetic powder sample.

[0036] Comparative Example 1

[0037] 10L of tap water was added to a 30L reaction barrel, the steam temperature was raised to 50°C, 3kg of solid ferrous sulfate was added and stirred until it was completely dissolved, and the steam temperature was raised to 60°C and maintained, and 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 1h, and then the feed liquid was heated to 90°C and air was turned on for rapid oxidation, with an air flow rate of 120L / min. After 10 minutes of air, 15g of sodium nitrate was slowly added, and air oxidation was continued. When the pH value of the feed solution dropped to 4.5, the air was stopped, and 432g / L NaOH solution was slowly added dropwise until the pH value reached 8.5. The air was turned on again, and the air flow rate was maintained at 120L / min. After 20 minutes, the pH value of the feed solution dropped to 6.8. The air and steam were turned off to stop the reaction. The feed solution was filtered, rinsed, and dried at 60°C for 12h to obtain an iron oxide black magnetic powder sample.

[0038] The black iron oxide samples obtained in Examples 1-4 and Comparative Example 1 were subjected to SEM testing to obtain Figure 1-Figure 5 ,in, Figure 1 This is the SEM image of the iron oxide black magnetic powder sample prepared in Example 1. Figure 2 This is the SEM image of the iron oxide black magnetic powder sample prepared in Example 2. Figure 3This is the SEM image of the iron oxide black magnetic powder sample obtained in Example 3. Figure 4 This is the SEM image of the iron oxide black magnetic powder sample obtained in Example 4. Figure 5 This is the SEM image of the iron oxide black magnetic powder sample prepared in Comparative Example 1.

[0039] like Figure 1-5 As shown, the particle morphology of the iron oxide black magnetic powder samples prepared in Examples 1-4 of the present invention is close to spherical, and there are many granular protrusions on the particle surface, so that the application in the toner will not cause the particles to fall off and affect its final color tone, and the prepared iron oxide magnetic powder shows good dispersibility, fluidity and stable magnetism, thereby ensuring that high-definition images can be produced when applied to the developer. However, compared with the use of ammonium nitrate solution to dissolve solid ferrous sulfate in Example 4, the use of high ammonia nitrogen wastewater produced by the iron oxide production plant as the raw material for dissolving solid ferrous sulfate in Examples 1-3 makes the particle size of the prepared iron oxide black magnetic powder samples smaller, more uniform, and the particle size distribution is narrower. In Comparative Example 1, since sodium nitrate is added to the system at a later stage, the morphology of part of the prepared iron oxide black magnetic powder sample is nearly square, the particles are seriously agglomerated, and the particle size distribution is large and uneven.

[0040] Morphology and magnetic testing:

[0041] Morphology detection method: The surface morphology of the samples was observed using a S4800 scanning electron microscope (SEM: Scanning Electron Micrographs) produced by Hitachi, Japan; magnetic detection method: The magnetism of the samples was measured using a LakeShore 7410 vibrating-sample magnetometer (VSM: Vibrating-sample Magnetometer).

[0042] The above method was used to test the magnetism of the black iron oxide samples prepared in Examples 1-4 and Comparative Example 1. The test results are shown in Table 1 below:

[0043] Table 1: Magnetic test table of black iron oxide samples prepared in Examples 1-4 and Comparative Example 1

[0044] sample Particle size (D50, μm) Saturation magnetism (emu / g) Remanence (emu / g) Coercivity(Oe) 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] It can be seen from the data in Table 1 that the particle size of the iron oxide black magnetic powder samples prepared in Examples 1-4 of the present invention does not exceed 0.504 μm, the particle size is small, the saturation magnetization is high, the residual magnetization is low, and the electrostatic developer toner can be well applied. However, compared with the use of ammonium nitrate solution to dissolve solid ferrous sulfate in Example 4, the use of high ammonia nitrogen wastewater produced by the iron oxide production plant as the raw material for dissolving solid ferrous sulfate in Examples 1-3 makes the particle size of the prepared iron oxide black magnetic powder samples smaller and the coercive force lower. Therefore, the introduction of high ammonia nitrogen wastewater can obtain iron oxide black magnetic particles with excellent dispersibility and low coercive force. Experiments have shown that the particle size of the iron oxide black magnetic powder sample prepared by ammonium nitrate solution is larger than that of the iron oxide black magnetic powder sample prepared by sodium nitrate solution. However, by comparing Example 4 with Comparative Example 1, it can be seen that since sodium nitrate is added to the system in the later stage of Comparative Example 1, the particle size of the iron oxide black magnetic powder sample in Comparative Example 1 increases to 0.745 μm, agglomerates severely, and has a coercive force of up to 42.96 Oe, which cannot meet the performance requirements of high-speed printers for iron black magnetic powder particles.

[0046] After testing, the ferroferric oxide magnetic powder provided in Example 1 has an iron content of up to 99.10%, an average particle size D50 of up to 0.26 μm at best, a nearly spherical morphology, and a plurality of granular protrusions on the particle surface, so that it will not fall off during toner application, a saturation magnetization of 96.69 emu / g, a remanence as low as 2.48 emu / g, and a coercive force as low as 28.04 Oe, which is well suitable for electrostatic developer toner.

[0047] In the present invention, the preparation method of low coercive force iron oxide black magnetic powder has mild reaction conditions, simple process flow, low production cost, is non-toxic and pollution-free, and can use high ammonia nitrogen wastewater generated by an iron oxide production plant as a raw material for dissolving solid ferrous sulfate, thereby avoiding the waste of human, material and financial resources caused by treating high ammonia nitrogen wastewater, and can efficiently recycle and reuse the wastewater. The process means can reduce the ammonia nitrogen content of up to 10,000 to 50,000 mg / L to below 1,000 mg / L, greatly reducing the cost of treating wastewater, and being more suitable for industrial-scale clean production.

[0048] In the present invention, the experimental conditions of the examples cited are not limited to this. The numerical values ​​exemplified above are reference values ​​in the experimental process and are only preferred embodiments of the present invention and are not used to limit the present invention. All modifications, replacements and improvements made based on the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing low coercive force iron oxide black magnetic powder, characterized in that: The preparation steps are as follows: (1) solid ferrous salt is used as a raw material, heated and dissolved in high ammonia nitrogen water to make the ferrous content 100-300 g / L, and then steam is continuously introduced to raise the temperature to 60°C-80°C; (2) slowly adding a strong alkaline solution to the solution system of step (1) while stirring until the ferrous ion content in the solution is 4-20 g / L, and keeping the temperature constant during the process; (3) After stirring for 1-2 hours, steam is introduced to raise the temperature to 90°C; (4) introducing compressed air for rapid oxidation; (5) When the pH of the feed 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) Allow air to flow in, and stop the reaction when the pH drops to above 6.0 and does not drop any further; (7) filtering, rinsing and drying the liquid obtained in step (6) to obtain low coercive force iron oxide black magnetic powder.

2. The method for preparing low coercive force iron oxide black magnetic powder according to claim 1, characterized in that: In step (1), the high ammonia nitrogen water is the untreated high ammonia nitrogen mother liquor water produced in the preparation process of red iron oxide, and its ferrous ion content is 10-30 g / L, and the ammonia nitrogen mass concentration is as high as 10,000-50,000 mg / L.

3. The method for preparing low coercive force iron oxide black magnetic powder according to claim 1, characterized in that: In the step (1), the high ammonia nitrogen water is a nitrate solution, and the nitrate solution is a NaNO3 solution, a KNO3 solution or a NH4NO3 solution, and the addition amount thereof is 2-5% of the theoretical mass of the iron oxide magnetic powder.

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

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

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

7. The method for preparing low coercive force iron oxide black magnetic powder according to claim 1, characterized in that: In the step (2), the strong alkaline solution is added dropwise for 40-60 minutes; in the step (5), the strong alkaline solution is added dropwise for 10-30 minutes.

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

9. The method for preparing low coercive force iron oxide black magnetic powder according to claim 1, characterized in that: The preparation steps are as follows: (1) dissolving solid ferrous sulfate in high-ammonia nitrogen wastewater at 50° C. to make the ferrous content 100-300 g / L, and then continuing to introduce steam to raise the temperature to 60° C.-80° C.; (2) slowly adding NaOH solution to the solution system of step (1) while stirring until the ferrous ion content in the solution is 4-20 g / L, and keeping the temperature unchanged during the process; (3) After stirring for 1-2 hours, steam is introduced to raise the temperature to 90°C; (4) introducing compressed air for rapid oxidation; (5) When the pH of the feed 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) Allow air to flow in, and stop the reaction when the pH drops to above 6.0 and does not drop any further; (7) filtering, rinsing and drying the liquid obtained in step (6) to obtain low coercive force iron oxide black magnetic powder.

10. Low coercivity iron oxide black magnetic powder prepared by the preparation method according to any one of claims 1 to 9.

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