Superfine magnesite powder, and preparation method and application thereof

Abstract

The application relates to a superfine magnesite powder and a preparation method and application thereof, and belongs to the technical field of refractory raw material manufacturing. A preparation method of a superfine magnesite powder comprises the following steps: simultaneously performing wet grinding and pulse electric field treatment on a magnesite flotation concentrate slurry, and drying to obtain the superfine magnesite powder; wherein the electric field strength of the pulse electric field is 150 V / mm-250 V / mm, a rectangular positive pulse is adopted, the pulse width is 20 mu s-30 mu s, the pulse frequency is 15000 Hz-25000 Hz, and the duty cycle is 40%-60%. The application combines pulse electric field induction and wet grinding to improve the grinding efficiency of the magnesite, reduce the grinding granularity of the magnesite particles, and break through the dual limitation of the magnesite powder granularity and efficiency.

Description

Technical Field

[0001] This invention belongs to the field of refractory raw material manufacturing technology, and relates to an ultrafine magnesite powder, its preparation method and application. Background Technology

[0002] Sintered magnesia is an important basic industrial raw material. Its quality and performance significantly impact product quality and economic benefits in related applications. Among these factors, bulk density is a crucial influence on the quality and performance of magnesia materials. Currently, the magnesia market typically considers materials with a bulk density ≥3.40 g / cm³ to be of high quality. 3 Sintered magnesia with a bulk density ≥ 3.40 g / cm³ is called high-density sintered magnesia. 3 High-density sintered magnesia requires the magnesite powder to be ground to below 2 μm. Currently, all magnesite in my country requires beneficiation to improve the performance of magnesia materials. The grinding particle size of magnesite before flotation is typically 10 μm to 200 μm, with particles smaller than 74 μm accounting for about 70%. Therefore, the magnesite powder after flotation cannot be directly used for the preparation of high-density sintered magnesia and needs to be further ground to below 2 μm.

[0003] Under normal conditions, when the flotation-processed magnesite slurry is transferred to an ultrafine grinder for ultrafine grinding, the viscosity of the magnesite slurry increases and its fluidity decreases as the magnesite particles shrink. This leads to increased resistance to the movement of the grinding media and a reduction in grinding efficiency. Grinding magnesite powder to a particle size of 2 μm is already the limit under normal grinding process conditions. Fundamentally, this phenomenon occurs because ultrafine magnesite particles adhere to the surface of the grinding media, reducing the friction and shearing action between the magnesite particles and the grinding media. Furthermore, during the ultrafine grinding process of magnesite, changes in the crystal structure and surface energy of magnesite cause the magnesite particles to become charged, becoming charged particles. At the same time, the flotation agents remaining in the flotation process (mainly including collectors, modifiers, and frothers) are mostly ionic substances, which are conductive in the magnesite slurry, further exacerbating particle agglomeration, leading to increased energy consumption, prolonged grinding time, and difficulty in obtaining ultrafine powder with uniform particle size distribution and good dispersion. Although existing technologies have attempted to improve this problem by optimizing grinding parameters or adding dispersants, none have been able to overcome the dual limitations of particle size and efficiency. Summary of the Invention

[0004] This invention provides an ultrafine magnesite powder, its preparation method, and its applications. Specifically, it provides a method for improving the grinding efficiency of magnesite and reducing the particle size of magnesite particles by combining pulsed electric field induction and wet grinding. Based on the current need to further improve the bulk density of sintered magnesia, this invention aims to minimize the particle size of the magnesite powder used as a raw material for sintered magnesia preparation during the ultrafine grinding process, thereby facilitating the improvement of the bulk density of sintered magnesia.

[0005] A method for preparing ultrafine magnesite powder includes the following steps: simultaneously subjecting magnesite flotation concentrate slurry to wet grinding and pulsed electric field treatment, followed by drying to obtain ultrafine magnesite powder; wherein the electric field strength of the pulsed electric field is 150 V / mm~250 V / mm, a rectangular positive pulse is used, the pulse width is 20 μs~30 μs, the pulse frequency is 15000 Hz~25000 Hz, and the duty cycle is 40%~60%.

[0006] Furthermore, the magnesite flotation concentrate slurry is loaded into a wet ultrafine grinding mill, and a pulsed electric field is applied to both ends of the ultrafine grinding mill. Under the action of the pulsed electric field, the magnesite slurry is intermittently contacted with the high-speed moving grinding media in the ultrafine grinding mill, so that the magnesite particles in the magnesite slurry are in full contact with the grinding media under the induction of the pulsed electric field, generating strong collision, friction and shearing effects, thereby improving the grinding efficiency of magnesite and reducing the grinding particle size of magnesite. After the treatment is completed, the pulsed electric field is unloaded, the ultrafine magnesite slurry is released from the ultrafine grinding mill, and it is dried to become ultrafine magnesite powder.

[0007] Furthermore, under the action of the pulsed electric field, the charged magnesite particles and the grinding media undergo a continuous intermittent contact-separation cycle, which increases the friction and shear force between the magnesite particles and the grinding media, improves the grinding efficiency of magnesite, and reduces the grinding particle size of magnesite.

[0008] In this invention, to measure the grinding particle size, the average particle size of the powder is represented by D50 (median particle size); to measure the grinding efficiency, the time required to grind the magnesite powder to a median particle size D50 of 2.5 μm is used as the evaluation index. The shorter the time required, the higher the grinding efficiency.

[0009] In the method described in this invention, the time for simultaneously performing wet grinding and pulsed electric field treatment is 15 min to 30 min, and the treatment temperature is 20℃ to 25℃.

[0010] Furthermore, the time for simultaneously performing wet grinding and pulsed electric field treatment as described in this invention can be adjusted according to the required average particle size of the magnesite powder.

[0011] In the method described in this invention, the wet grinding is carried out at a speed of 50 rpm to 70 rpm at 20℃ to 25℃ using zirconium oxide as the grinding medium, the ball-to-material ratio is 4 to 6:1, and the grinding time is 20 min to 40 min.

[0012] In the method described in this invention, the solid content of the magnesite concentrate slurry is 70%~76%.

[0013] In the method described in this invention, the main chemical components of the magnesite flotation concentrate slurry, by mass fraction, include: MgO 46.5%~47.5%, CaO 0.16%~0.57%, and SiO2 0.12%~0.20%.

[0014] Furthermore, the magnesite flotation concentrate slurry is obtained by purifying the magnesite using crushed magnesite ore as raw material through forward and reverse flotation.

[0015] Another object of the present invention is to provide an ultrafine magnesite powder obtained by the above method.

[0016] In the method described in this invention, the D50 of the ultrafine magnesite powder is 0.9 μm to 2.5 μm.

[0017] Another object of the present invention is to provide the application of the above-mentioned ultrafine magnesite powder in the preparation of high-density sintered magnesia.

[0018] The beneficial effects of this invention are as follows: During the ultrafine grinding process of magnesite, the pulsed electric field causes charged magnesite particles to undergo continuous intermittent contact-separation cyclic motion with the grinding media, increasing the friction and shear force between the magnesite particles and the grinding media, thereby improving the grinding efficiency of magnesite and reducing the particle size of the magnesite particles. Under the action of the pulsed electric field, the grinding efficiency of magnesite powder is increased by about 50% compared to when no electric field is applied. The particle size of the magnesite powder is reduced by about 60% compared to when no electric field is applied, even reaching below 1 μm. Detailed Implementation

[0019] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the invention, but do not limit the invention in any way.

[0020] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; the reagents and materials described are commercially available unless otherwise specified.

[0021] To improve the grinding efficiency of magnesite slurry and reduce the particle size of magnesite particles, this invention applies a pulsed electric field to an ultrafine magnesite grinder. This causes the magnesite slurry to be ground under a synergistic effect of pulsed electric field induction and wet grinding, achieving unexpected results in the experiment. The pulsed electric field induces intermittent contact-separation cycles between charged magnesite particles and the grinding media, increasing the friction and shear force between the magnesite particles and the grinding media.

[0022] Testing revealed that the grinding efficiency of magnesite powder was approximately 50% higher than when no electric field was applied, and the particle size of the magnesite powder was reduced by approximately 60%, even reaching below 1 μm. These results are significant for preparing high-density sintered magnesia, improving the service life of refractory materials, and increasing the economic benefits for enterprises.

[0023] This invention involves injecting the flotation-processed magnesite slurry into a wet ultrafine grinding mill, and applying a pulsed electric field with an intensity of 150 V / mm to 250 V / mm at both ends of the mill. Under the action of the pulsed electric field of the above intensity, the charged magnesite particles undergo intermittent contact-separation cyclic motion with the grinding media, increasing the friction and shear force between the magnesite particles and the grinding media. After grinding, the pulsed electric field is unloaded, and the magnesite slurry is dried into ultrafine magnesite powder.

[0024] This invention improves the grinding efficiency of magnesite powder by approximately 50% under the action of a pulsed electric field compared to when no electric field is applied. The particle size of the magnesite powder is reduced by approximately 60% compared to when no electric field is applied, even reaching below 1 μm.

[0025] Example 1 In this embodiment, magnesite flotation concentrate slurry was used as raw material, and its main chemical composition after drying is shown in Table 1.

[0026] Table 1. Main chemical composition (mass fraction) of magnesite flotation concentrate slurry in Example 1

[0027] Using crushed magnesite ore as raw material, the magnesite is purified by both direct and reverse flotation. Reverse flotation uses dodecylamine solution as the collector, prepared by mixing hydrochloric acid and dodecylamine (DDA) in a 1:1 molar ratio, with sodium polyacrylate (PAANa) solution as the depressant. Direct flotation uses sodium oleate (NaOL) as the collector, and a 1% NaOH solution as the pH adjuster. The resulting magnesite concentrate slurry is obtained after flotation.

[0028] The magnesite flotation concentrate slurry, with a solid content of 75%, was injected into a vertical wet ultrafine grinding mill. The mill was connected to a pulsed power supply at both ends, and a pulsed electric field was applied with a strength of 200 V / mm. Other pulse parameters were: rectangular positive pulse, pulse width of 25 μs, pulse frequency of 20000 Hz, and duty cycle of 50%. The mill was operated at 60 rpm at room temperature (25°C) using zirconium oxide grinding media, with a ball-to-material ratio of 5:1, for 30 min. After grinding, the electric field was removed, and the magnesite slurry was discharged from the mill. Subsequently, it was dried at 120°C for 12 h to obtain ultrafine magnesite powder.

[0029] After drying, the particle size of the magnesite powder was measured using a laser method, and the average particle size was expressed as D50 (median diameter). The grinding time required to achieve a D50 of 2.5 μm was used as the grinding efficiency indicator.

[0030] Example 2 The difference between this embodiment and Embodiment 1 is that the intensity of the pulsed electric field is 150 V / mm, while all other operations are the same as in Embodiment 1. The measurement results of Embodiment 2 are shown in Table 2. Comparing the results of Embodiment 2 and the comparative example in Table 2, it can be seen that changing the applied pulsed electric field intensity and setting it to 150 V / mm has a significant impact on the particle size of magnesite powder.

[0031] Example 3 The difference between this embodiment and Embodiment 1 is that the intensity of the pulsed electric field is 250 V / mm, while all other operations are the same as in Embodiment 1. The measurement results of Embodiment 3 are shown in Table 2. Comparing the results of Embodiment 3 and the comparative example in Table 2, it can be seen that changing the applied pulsed electric field intensity and setting it to 250 V / mm has no significant effect on the particle size of magnesite powder.

[0032] Example 4 The difference between this embodiment and Example 1 is that the magnesite slurry particles are ground to 2.5 μm before grinding is stopped; all other operations are the same as in Example 1. The measurement results of Example 4 are shown in Table 2. Comparing the results of Example 4 and the comparative example in Table 2, it can be seen that when using pulsed electric field grinding in this embodiment, the grinding time to obtain the same particle size is reduced from 30 min to 15 min, a reduction of 50%.

[0033] Comparative Example 1 The difference between this comparative example and Example 1 is that no pulsed electric field is applied, while all other operations are the same as in Example 1.

[0034] Table 2 shows the measurement results of the magnesite powders obtained in Examples 1-4 and Comparative Example 1. The results in the table show that the particle size of the magnesite powder milled using the pulsed electric field in this example was significantly reduced, with D50 decreasing from 2.5 μm without an electric field to 1.0 μm, a reduction of 60%.

[0035] Table 2 Results of Examples 1-4 and Comparative Example 1

Claims

1. A method for preparing ultrafine magnesite powder, characterized in that: Magnesite flotation concentrate slurry is simultaneously subjected to wet grinding and pulsed electric field treatment, followed by drying to obtain ultrafine magnesite powder; wherein the electric field strength of the pulsed electric field is 150V / mm~250V / mm, a rectangular positive pulse is used, the pulse width is 20μs~30μs, the pulse frequency is 15000 Hz~25000Hz, and the duty cycle is 40%~60%.

2. The method for preparing ultrafine magnesite powder according to claim 1, characterized in that: The simultaneous wet grinding and pulsed electric field treatment takes 15 to 30 minutes and the treatment temperature is 20°C to 25°C.

3. The method for preparing ultrafine magnesite powder according to claim 1, characterized in that: The wet grinding process is carried out at a speed of 50 rpm to 70 rpm and at a temperature of 20°C to 25°C using zirconium oxide as the grinding medium, with a ball-to-material ratio of 4 to 6:1 and a grinding time of 20 min to 40 min.

4. The method for preparing ultrafine magnesite powder according to claim 1, characterized in that: The solid content of the magnesite flotation concentrate pulp is 70%~76%.

5. The method for preparing ultrafine magnesite powder according to claim 1, characterized in that: The main chemical components of the magnesite flotation concentrate slurry, by mass fraction, include: MgO 46.5%~47.5%, CaO 0.16%~0.57%, and SiO2 0.12%~0.20%.

6. The method for preparing ultrafine magnesite powder according to claim 1, characterized in that: The drying conditions are as follows: drying at 110℃~120℃ for 10 h~14 h.

7. The ultrafine magnesite powder prepared by the method according to any one of claims 1 to 6.

8. The ultrafine magnesite powder according to claim 7, characterized in that: The D50 of the ultrafine magnesite powder is 0.9 μm to 2.5 μm.

9. The application of the ultrafine magnesite powder according to claim 7 in the preparation of high-density sintered magnesia.

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