The smectite mineral is a general term for a class of clay minerals mainly composed of montmorillonite. It is a 2:1 layered hydrous silicon composed of two layers of silicon-oxygen tetrahedron sandwiched with an aluminum ( magnesium )-oxyoctahedron. Acid salt minerals [1] .
Due to the crystal structure of layered silicate minerals, smectite minerals have special physical and chemical properties [2] , widely used in pharmaceuticals, cosmetics, fine ceramics, paper, food, petroleum extraction, detergents, rubber, Plastics and other industries. In addition, the smectite mineral represented by montmorillonite is the mineral that is the easiest to achieve nano-scale exfoliation and dispersion in layered silicate minerals, and will become an important and promising nano-dispersed inorganic material of nanocomposites [3] .
The ultrafine powder has excellent physical and chemical properties such as large specific surface area, high surface activity, fast chemical reaction speed, low sintering temperature, high strength of sintered body, good filling and reinforcing performance, and high hiding rate [4] . At present, almost all of the powdery mineral raw materials required for high-tech industries require ultra-fine processing. For example, the preparation of high-performance and high-purity fine ceramics requires ultrafine alumina powder as raw material [5-7] , high-performance magnetic recording material. need ultrafine Fe 2 O 3 powder as the raw material, the United States developed ultrafine dry powder of iron oxide catalyst has been used as a rocket booster with ultraviolet radiation absorber success [8].
The application prospect of ultra-fine pulverization processing is extremely broad, and the industrial requirements for the miniaturization of materials are endless. In recent years, the development of ultrafine powders has been extremely active, and its application fields have been expanding [9-10] . Therefore, it is of great significance to carry out ultrafine pulverization research on smectite.
First, the experimental part
(1) Raw materials
Smectite powder, manufactured by Hanson Haicheng talc flour mill, its chemical composition (wt%) of: SiO 2, 32.45; A1 2 O 3, 18.1; Fe 2 O 3, 0.19; CaO, 0.069; MgO, 35.58.
(2) Reagents
Dispersant: hexametaphosphate, sodium phosphate, molecular weight 611.72, analytical grade, commercially available.
(3) Experimental equipment
Horizontal sander: Sand mill manufactured by NETZSCH (Shanghai) Co., Ltd., model MiniZeta 03E-993.03.
(4) Experimental methods
Firstly, 3 factors (slurry concentration A, grinding time B, dispersant dosage C) 3 levels were obtained (the pulp mass concentrations were 35%, 45%, 55%, respectively, and the grinding time was 10 min, 15 min, 20 min, respectively, and the dispersant mass concentrations were respectively Orthogonal test of O.2%, 0.5%, 0.8%, the level of each level from small to large is l, 2, 3); then the single-factor test method is used to determine the suitable process conditions of smectite wet superfine pulverization The speed of the sander during the test was constant at 3490r/min.
Second, the results and discussion
(1) Orthogonal test results
The effects of various factors of orthogonal test on the D50 and specific surface area of ​​the ground sample are shown in Fig. 1 and Fig. 2, respectively. It can be seen from Fig. 1 and Fig. 2 that the grinding sample D50 decreases significantly with the increase of the pulp concentration, and increases after exceeding a certain value; D50 gradually decreases with the increase of the grinding time; D50 with sodium hexametaphosphate Significantly reduced by increasing the amount. The specific surface area did not change much with the slurry concentration and grinding time; it increased significantly with the increase of the amount of sodium hexametaphosphate. The interaction between the three factors is complex.
(2) Single factor test results
1. Slurry concentration:
When the fixed grinding time is 20 min and the dispersant dosage is 0.5%, the appropriate slurry concentration is determined. The test results are shown in Fig. 3. The slurry concentration was determined to be 50% from Figure 3. When the concentration is too high, the slurry flow rate is slow, and the impact of the grinding medium becomes weak. The grain size of the ore discharge product may become coarser, and the coarse fraction will increase. When the concentration is too thin, the slurry flow rate will increase, and the ore and grinding medium will be increased. The number of impacts is reduced, which reduces the grinding efficiency and increases the wear of the lining steel balls, so the slurry concentration is controlled within an appropriate range.
2, grinding time:
The amount of fixed dispersant is 0.5%, and the concentration of pulp is 50%. The suitable grinding time is determined. The test results are shown in Figure 4. The grinding time was determined to be 25 min from Figure 4. As the grinding time increases, the fineness of the product becomes smaller and smaller, the specific surface area becomes smaller and smaller, and the grinding effect becomes better and better. However, as time goes on, the viscosity of the slurry is getting larger and larger, which causes the dispersed materials to agglomerate, which in turn makes the grinding effect worse. When it exceeds a certain period of time, the slurry may be clogged due to excessive viscosity and the grinding may not continue.
3. Dispersant dosage:
The fixed slurry concentration is 50%, the grinding time is 25 min, and the appropriate dispersant dosage is determined. The test results are shown in Fig. 5. From Figure 5, the amount of dispersant was determined to be 0.6%. The dispersant is adsorbed on the surface of the mineral in the slurry, reduces the free energy of the mineral surface, and penetrates into the micro-crack to play the role of splitting, reducing the viscosity of the slurry and improving the rheology of the pulp, thereby improving the process of superfine pulverization. Dispersibility, producing more fine fractions under the same conditions.
4. Verify the pulp concentration again:
The fixed grinding time was 25 min, the dispersant dosage was 0.6%, and the slurry concentration was determined again. The test results are shown in Fig. 6. The slurry concentration was finally determined from Figure 6 to be 30%. In general, the grinding effect is related to factors such as slurry concentration, grinding time and amount of dispersant. It can be seen from Fig. 6 that the use of sodium hexametaphosphate as a dispersing agent, the pulp concentration is 30%, the grinding time is 25 min, and the dispersant dosage is 0.6%, the grinding effect is the best. At this time, the sample had a fineness D50 of 1.35 μm and a specific surface area of ​​25.449 m 2 /g.
Third, the conclusion
The process condition of smectite wet superfine pulverization is preferably: sodium hexametaphosphate is a dispersing agent, the pulp concentration is 30%, the grinding time is 25 min, and the dispersant dosage is 0.6%. Grinding under the conditions of the process, the sample had a fineness D50 of 1.35 μm and a specific surface area of ​​25.449 m 2 /g.
references
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[4] Zheng Shuilin, Yuan Jizu. Non-metallic mineral processing technology and application manual [M]. Beijing: Metallurgical Industry Press. 2005: 7, 126-127, 193-198.
[5] Huang Dongsheng, et al. Development of high purity ultrafine a-A12O3 powder [J] Journal of Central South Institute of Mining and Metallurgy, 1993 (5): 24.
[6] Yang Huaming, et al. Progress in ultrafine pulverization technology [J]. Metal Mine, 1998 (9): 20-27.
[7] Masato K, Gary L M. Controlled transformation and sintering of a boehmite sol-gel by α-A12O3 seeding [J]. J Am Ceram Soc, 1985, 68(9): 500.
[8] Iwata H. Ultra fine iron oxide [J]. Int J Powder Metal, 1990, 26(2): 103.
[9] Yuan Jiazhong, et al. Microwave absorption rate of ultrafine metal powder multilayer composites [J]. Powder Metallurgy Technology, 1992 (4): 243-248.
[10] Zhou X, Peter J. Novel uses for metal powders [J]. Metal Powder Report, 1989, 44(9): 575.
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