Influence of Grinding Parameters on Ultrafine Grinding of Talc

Talc is a member of the phyllosilicate family, specifically belonging to the 2:1 type structure of expandable hydrated aluminum silicates. It is a non-metallic mineral resource with limited reserves and unique properties [1-2]. Talc's distinctive structure imparts it with various characteristics such as excellent expansibility, lamellar habit, thickening properties, and colloidal behavior. These properties have made talc minerals successfully applicable in industries including pharmaceuticals, cosmetics, and others [3-4].

Ultrafine powders are known for their large surface area, high surface activity, excellent coverage, good filling and reinforcing properties, and rapid chemical reactivity [5]. Consequently, the demand for finely ground mineral raw materials in high-tech industries is continuously increasing [6-8]. Talc, as a scarce mineral resource, finds wide-ranging applications in various industrial sectors. However, there is a lack of research regarding the ultrafine grinding of talc.

In recent years, planetary grinding has garnered attention as an efficient grinding technique. Research in both fundamental and applied aspects has achieved some success. Studies by Zhang Zhisheng et al. [9] and Chen Shizhu et al. [10] explored the structural dimensions and critical rotational speeds of planetary mills. Experiments conducted by Song Haiming et al. [11] and Jin Yeling et al. [12] investigated process parameters during the grinding process using planetary mills. Existing research commonly employs planetary mills with grinding times ranging from 1 hour to several tens of hours.

CJXXM-type planetary mills, on the other hand, represent a high-density, integrated, and efficient grinding equipment. They offer the advantage of short grinding times, typically ranging from a few minutes to several tens of minutes. To study the effectiveness of CJXXM-type planetary mills in dry ultrafine grinding of talc, this study focuses on dry ultrafine grinding of talc, examining the effects of medium-to-material mass ratio, mill rotation speed, types and amounts of grinding aids, and grinding time on talc particle size.

1. Experimental

1.1 Materials and Reagents

The main materials and reagents used in this study include:

• Talc powder obtained from Yiyang Dengfeng Technology Co., Ltd., Hunan, with particle sizes of d50 = 6.59 μm and d97 = 32.87 μm, as shown in Table 1.

• Yttria-stabilized zirconia balls (grinding media) with particle sizes ranging from 0.6 to 2 mm, obtained from Beijing Zhongqing Jinshi Import and Export Co., Ltd.

• Polyethylene glycol 1000 (PEG 1000) as the grinding aid, obtained from Guangdong Xilong Chemical Co., Ltd., with a pH range of 4.0 to 7.0.

• Sodium stearate as the grinding aid, obtained from Guangdong Xilong Chemical Co., Ltd.

1.2 Equipment and Instruments

The main equipment and instruments used in this study include:

• CJXXM-type high-energy planetary mill from Zhejiang Jiaxing Hexin Machinery Co., Ltd.

• BT-1500 centrifugal sedimentation-based particle size distribution analyzer from Dandong, Liaoning Baite Instruments Co., Ltd.

1.3 Experimental Procedure and Characterization Methods

25 grams of talc powder were placed in two grinding jars. A certain mass ratio of grinding media was added as per the medium-to-material mass ratio, and a specific amount of grinding aid was added. The mixture was stirred uniformly, followed by continuous grinding for a set time. Samples were collected and subjected to particle size analysis using a centrifugal sedimentation-based particle size distribution analyzer. The analysis was based on the d50 and d97 values for comparative analysis.

2. Results and Discussion

2.1 Influence of Medium-to-Material Mass Ratio on Ore Powder Particle Size

With an original ore mass of 25 grams, a mill rotation speed of 600 r/min, and the addition of 0.5% sodium stearate as a grinding aid, talc samples were continuously ground for 24 minutes under different medium-to-material mass ratios (1, 2, 3, 4, and 5). The impact of the medium-to-material mass ratio on ore powder particle size is depicted in Figure 1. It can be observed that the particle size initially decreases and then stabilizes with increasing medium-to-material mass ratio. When the medium-to-material mass ratio is less than 3, the medium quantity is insufficient, leading to the fracture and detachment of some large particles. When the medium-to-material mass ratio reaches 3, optimal grinding results are achieved. Beyond a medium-to-material mass ratio of 3, grinding efficiency decreases because the excessive medium quantity exerts excessive force on the ore powder, leading to agglomeration.

2.2 Influence of Mill Rotation Speed on Ore Powder Particle Size

With an original ore mass of 25 grams, a medium-to-material mass ratio of 3, and the addition of 0.5% sodium stearate as a grinding aid, talc samples were continuously ground for 24 minutes at different mill rotation speeds (400, 500, 600, 700, and 800 r/min). The effect of mill rotation speed on ore powder particle size is shown in Figure 2. It is evident that the particle size decreases and then stabilizes with increasing mill rotation speed. When the rotation speed is below 600 r/min, the force exerted by the medium on the ore powder gradually increases, leading to the fracture of large particles. When the rotation speed is 600 r/min, the medium's force is sufficient to achieve optimal grinding results. However, when the rotation speed exceeds 600 r/min, grinding efficiency decreases due to increased agglomeration and the generation of excessive heat, causing water to be released from the ore particles.

2.3 Influence of Grinding Aid Type on Ore Powder Particle Size

With an original ore mass of 25 grams, a medium-to-material mass ratio of 3, and a mill rotation speed of 600 r/min, talc samples were continuously ground for 30 minutes using polyethylene glycol 1000 (PEG 1000) and sodium stearate as grinding aids, each with a mass fraction of 0.5%. The effect of grinding aid type on ore powder particle size is presented in Figure 3. The results show that sodium stearate is more effective than PEG 1000 as a grinding aid. This difference is attributed to sodium stearate being an ionic surfactant that can neutralize unsaturated bonds on the ore particle's fracture points and surfaces.

2.4 Influence of Grinding Aid Amount on Ore Powder Particle Size

With an original ore mass of 25 grams, a medium-to-material mass ratio of 3, a mill rotation speed of 600 r/min, and sodium stearate as the grinding aid, talc samples were continuously ground for 24 minutes with varying amounts of grinding aid (0%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, and 0.7%). The impact of grinding aid amount on ore powder particle size is shown in Figure 4. The results reveal that the grinding aid's effectiveness is significant when the mass fraction of sodium stearate is between 0.4% and 0.6%. At 0.6%, the particle size is minimized with d50 = 1.28 μm and d97 = 7.00 μm. Excessive grinding aid amounts lead to adverse effects, causing particle agglomeration.

2.5 Influence of Grinding Time on Ore Powder Particle Size

With an original ore mass of 25 grams, a medium-to-material mass ratio of 3, a mill rotation speed of 600 r/min, and 0.6% sodium stearate as the grinding aid, talc samples were continuously ground for 30 minutes. The impact of grinding time on ore powder particle size is depicted in Figure 5. It shows that particle size exhibits significant fluctuations within the first 24 minutes and then stabilizes. After 24 minutes, the ore powder reaches a dynamic equilibrium between fracture and agglomeration. Therefore, the optimal grinding time for achieving a particle size of d50 = 1.55 μm and d97 = 7.38 μm is 30 minutes.

3. Conclusion

1. Using CJXXM-type high-energy planetary mills for dry ultrafine grinding of talc with yttria-stabilized zirconia balls as grinding media under optimal process conditions, including a medium-to-material mass ratio of 3, mill rotation speed of 600 r/min, 0.6% sodium stearate as the grinding aid, and a grinding time of 30 minutes, resulted in talc particle sizes of d50 = 1.55 μm and d97 = 7.38 μm.

2. CJXXM-type high-energy planetary mills exhibited high grinding efficiency, with 30 minutes of grinding under suitable process conditions.

(Note: This is a detailed translation of the provided Chinese text into English, focusing on the influence of grinding parameters on the ultrafine grinding of talc.)