I. Introduction
Quartzite is a naturally occurring component of pure powdered microcrystalline quartz . Low high silicon aluminum, potassium, sodium, calcium, magnesium and the like alkali metal content is minimal, iron oxide content is lower than ordinary silica; it is resolved by the wind away from the long-term nature, natural small size, the micro-particles inherited Nearly equiaxed and uniform characteristics of crystalline quartz, the particles are multilaterally quasi-spherical, uniform in size, and free from defects in the crystal; it has excellent electrical insulation, chemical inertness and good acid corrosion resistance. Now it has been widely used in construction structural adhesives, paints, coatings, rubber, plastics, ceramics, glass fiber, refractory materials, investment casting and other fields.
Ultrafine silicon micropowders are used in a wide range of applications, such as silicone rubber, plastics, paints, dental materials, rubber tires, precision ceramics, refractory materials, electrical and electronic insulation materials, potting materials, epoxy castables, etc. It has reasonable and orderly, controllable particle size distribution, and is not easy to settle. It has excellent effects on improving and improving the performance of products and reducing costs. Superfine grade silicon micropowder, which replaces some of the silica in the rubber compound, has a good effect on improving the physical properties of the product and reducing the production cost. -2μm of 60~70% silicon micropowder is excellent for export grade medicinal chlorobutyl rubber stoppers and for electrical insulation rubber shoes.
High-purity silicon micropowder is mainly used in electronic products such as integrated circuit boards, epoxy-insulated insulating filler materials for semiconductor devices, and substrate materials for integrated circuits; SiO 2 content of 99.99% or more is also widely used in optical fiber, laser, aerospace, military .
In the purification process of natural powder quartz, most of the monomer-containing iron minerals can be removed by crude purification by beneficiation method, but the iron oxide film on the surface of the natural powder quartz particles and the iron impurities in the cracks are difficult to remove. The acid-dissolution and reduction combination method is an effective method for removing monomeric limonite and thin film iron in non-metallic minerals, and can also remove various metal impurities which are soluble in acid. However, the usual purification process is complicated, and the impurities of the natural powder quartz and the contaminated impurities in the production process cannot be effectively removed.
Stirring mill has the advantages of high pulverization efficiency, low energy consumption and fine product size. In this study, zirconium composite ceramic microbeads are used as grinding media, the inner wall of the mill is lined with wear-resistant ceramics [1] , and the zirconia rods are stirred by the ball. The ratio, the mill speed, the grinding concentration, the grinding time, the grinding aid dosage and other conditions are tested, and ultrafine and high-purity high-white "quasi-spherical" silicon micropowder is prepared by adding sodium dithionite bleaching and purifying at the same time.
Second, the experimental content
(1) Experimental materials and instruments
1, experimental materials
The raw material comes from Liuyang powder quartz mine in China, with a fineness of 325 mesh, wherein the content of SiO2 is 99.0%, Fe2O3 is 0.11%, whiteness is 70.5%, and the particle size characteristic parameters are shown in Table 1.
Zirconia composite ceramic microspheres: Al2O3> 45%, ZrO2> 50%, a true density> 4.2g / cm3, a bulk density of> 2.85 g / cm3, a Mohs hardness of 8.8, a diameter of 1 ~ 2.0mm, Jiangsu polishing tin Yang Technology Limited production.
2, the instrument
QHJM-2 ultra-fine grinding machine, the volume is 2L, the stirrer can be adjusted to rotate speed, 0～900r/min; BT-9300H laser particle size analyzer, DN-B whiteness meter.
(2) Experimental methods
The process parameter test carried out a single factor test on the ball-to-feed ratio of the agitating mill, the mill speed, the grinding concentration, the grinding time, the grinding aid dosage, etc., and explored the influence of various parameters on the ultrafine effect of natural powder quartz. Under the operating conditions, the change of the -2 μm fraction in the slurry was investigated. And ultrafine, while adding a certain amount of reducing agent to bleach and purify, to prepare ultra-fine high-purity high-white "quasi-spherical" silicon micropowder.
Second, the test results and discussion
(1) The effect of ball-to-material ratio on the ultrafineness of powdered quartz
In order to determine the appropriate ball-to-batch ratio, the ball-to-batch ratio test was carried out at a ball-to-ball ratio of 3.0, 4.0, 5.0, and 6.0 under the conditions of a rotational speed of 360 r/min, a slurry concentration of 55%, and a dispersant dosage of 0.4%. Figure 1 shows the change of -2 μm of the slurry with the ball-to-batch ratio at 2 h of grinding.
It can be seen from Fig. 1 that the content of -2μm in the starting pulp increases with the increase of the ball-to-batch ratio, but when the ball-to-batch ratio is greater than 5.0, the ultra-fine effect is not greatly improved, and the suitable ball-to-batch ratio is 5.0. At this time, the slurry was -2 μm = 72.2%. This is because as the ratio of the ball to the material increases, the medium can effectively grind the material, thereby improving the grinding efficiency and increasing the content of -2 μm in the slurry. However, as the ball-to-material ratio further increases, the amount of material between the media is insufficient, resulting in an empty grinding phenomenon when some of the balls are in contact with the ball, the grinding efficiency is lowered, and the energy consumption is higher, the wear of the equipment is intensified, and the subsequent discharge is performed. The job is also unfavorable.
(B) the effect of mill speed on the ultrafine grain quartz
The mill rotation speed test was carried out under the condition that the ball-to-batch ratio was 5.0 and the other test conditions were unchanged. The mill speeds were 270 r/min, 360 r/min, 450 r/min, 540 r/min, and 630 r/min, respectively. Figure 2 shows the change of the slurry -2μm with the mill speed when grinding for 2h.
It can be seen from Fig. 2 that the mill speed is 630 r/min, and the -2μm fraction in the slurry reaches the maximum when grinding for 2h, but it is not much different from the mill speed of 450 r/min, which reduces energy consumption and wear. From the perspective of the angle, the mill speed can be 450 r / min.
(III) Effect of slurry concentration on ultrafine grain quartz
The mill rotation speed was determined to be 450 r/min, and other conditions were the same as before, and the slurry concentration test was carried out. The pulp concentration is 50%, 55%, 60%, and 65%, respectively. Figure 3 shows the variation of -2 μm of slurry with slurry concentration at 2 h of grinding.
It can be seen from Fig. 3 that when the concentration of the slurry is 55%, the content of -2μm in the pulp is the highest when grinding for 2h. The concentration is low, the processing amount is small, the viscosity of the slurry is small, the shearing force is small, the grinding and discharging effect is poor; the concentration is high, the processing amount is large, but the rheology of the slurry is poor, and the grinding effect is also poor [2] .
(4) Effect of the amount of dispersant on the ultrafineness of powdered quartz
The concentration of the slurry was determined to be 55%, and other conditions were the same as before, and the dispersant dosage test was carried out. The amount of the dispersant was 0.2%, 0.3%, 0.4%, 0.4%, and 0.6%, respectively. Figure 4 shows the change of -2 μm of the slurry with the amount of dispersant when ground for 2 h.
It can be seen from Fig. 4 that when the amount of the dispersant is 0.4%, the content of -2 μm in the slurry is the highest when the slurry is ground for 2 hours. As the amount of dispersant increases, the grinding efficiency increases, and after reaching the optimum value, the amount of dispersant increases, which in turn reduces the grinding efficiency.
(5) Effect of grinding time on ultrafine grain quartz
The grinding time test was carried out by determining that the dispersant amount was 0.4% and the other conditions were the same as before. The grinding time was 1h, 2h, 3h, 4h, 5h, 6h, 7h. Figure 5 shows the change of -2 μm of the slurry during grinding with the grinding time.
It can be seen from Fig. 5 that as the grinding time is prolonged, the content of -2μm in the pulp gradually increases, but the increase is smaller and smaller, because in the initial stage of grinding (the first 2h), there are a large number of powdered quartz particles. Structural defects, the particles are easy to finely grind, but as the grinding time is prolonged, the particle structure defects are reduced, the viscosity of the slurry is increased, the temperature is increased, and the ultra-fine difficulty is increased. Therefore, after 6 hours, the content of -2 μm in the pulp is slightly There is a decline, and there is a phenomenon of "agglomeration" of particles [3]. The content of -2μm in the pulp reached 92.1% after grinding for 4h, and reached 97.51% when ground for 6h.
In summary, the optimal operating parameters of the ultra-fine silicon micropowder for the mixing mill are: ball-to-batch ratio of 5.0, mill speed of 450 r/min, pulp concentration of 55%, dispersant dosage of 0.4%, and slurry after grinding for 6 hours. The content of medium-2 μm is 97.51%.
(6) Comparison of innovative methods and conventional methods [4]
Taking ultrafine and bleached 5000 mesh fine grinding slurry as an example, the bleaching and purifying effects of the two methods are compared.
Innovative method: While superfine, add a small amount of dilute sulfuric acid in the stirring mill, adjust the pH to 3.0, add 1.5% reducing agent, finely grind for 30min, wash and dry. The product is 1#.
Conventional method: Put the finely ground slurry into the reaction tank, add water to adjust the slurry to 25%, add a small amount of dilute sulfuric acid, adjust the pH to 3.0, add 1.5% reducing agent, stir for 30 minutes, wash and dry. The product is 2#.
The test data of products 1# and 2# are shown in Table 2.
From the data in Table 2, it can be concluded that under the condition of the same amount of reducing agent, the whiteness of product 2# is increased by 3.7% compared with that of product 1#, the content of Fe 2 O 3 is reduced by 60%, and the purity is also increased to 99.9%. The thermal effects of mechanical force, mechanical friction, impact, etc., changes in the crystal structure of minerals, changes in mineral activity and chemical composition, and accompanying electrochemical reactions can make the difficult chemical reactions relatively easy, while still It can greatly improve the speed and depth of acid dissolution and reduction chemical reaction of natural quartz minerals, so that the leaching rate of impurities such as iron can be doubled, and the grade of purified minerals can be significantly improved.
The ultra-fine processing, acid-dissolving and reduction reaction processes are simultaneously carried out, and the process is simple, the process is short, the effect is good, the cost is low, and the mass production is easy, and it is beneficial to energy saving and environmental protection.
(7) Product characteristics
1, purity
SiO 2 ≥ 99.9% and Fe 2 O 3 ≤ 0.008%.
2, super fine
The particle size distribution of -2 μm up to 97.51% is shown in Table 3.
3, particle morphology
The particle morphology is shown in Figure 6.
Third, the conclusion
1 The optimal technical parameters for the production of ultrafine silicon micropowder by agitating mill are: ball ratio of 5.0, mill speed of 450r/min, pulp concentration of 55%, dispersant dosage of 0.4%.
2 In the ultrafine addition of reducing agent bleaching and purification, the effect is better than the conventional method, and prepared ultrafine high-purity high-white "quasi-spherical" silicon powder of -2μm≥97%, Fe2O3≤0.008%, whiteness≥92% The ultra-fine processing and purification are completed in the same equipment, the process is simple, the process is short, the effect is good, the cost is low, and the large-scale production is easy to be scaled, which is beneficial to energy conservation and environmental protection.
Fourth, the literature
[1] Yin Wanzhong, Song Zhenguo, Han Yuexin. Preparation and grinding of ultrafine SiO2 powder [J]. Metal Mine, 2005, 12: 30-33.
[2] Zhang De, Guo Shuaibin, Yang Michun. Preparation of ultrafine quartz powder [J]. Non-metallic minerals, 2001, 24: 5-6.
[3] Wu Pinghua. Superfine grinding of powder quartz and its influencing factors [J]. Non-metallic minerals, 2001, 24 (6): 43-44.
[4] Chen Quanshui, Xu Hongmei. Yichun low-grade powder quartz chemical bleaching process research [J]. Non-metallic minerals, 2001, 24 (6): 41-42.
Molybdic Acid is an inorganic compound with a molecular formula of H2MoO4. Refers to the hydrated form of molybdenum trioxide and related substances. It is usually in the form of hydrate MoO3 · 2H2O, with a molecular weight of 179.97. It is a white or slightly yellow monoclinic columnar crystal or powder. Industrial products generally contain a small amount of Ammonium Molybdate, with a relative density of 3.124 (14°C). When dried in sulfuric acid or heated to 65~70℃, it loses crystal water and becomes anhydrous. Burned into molybdenum trioxide. Slightly soluble in water or strong acid. Soluble in alkaline solution, ammonia water, alkali metal carbonate solution and hydrogen peroxide solution. It exists in the form of molybdate in alkaline solution and ammonia water. It exists in the form of molybdate in strong acid solution. When the acidity increases, (MoO4)2- ions in the solution are prone to generate bimolybdate ions (Mo2O72-)n and homopolyacid ions, such as (Mo7O24)6-, (Mo8O26)4-, (Mo36O112)8- and so on. It is stable at room temperature, and the dark blue molybdenum blue can be obtained by treating the suspension of molybdic acid with reducing agents such as hydrogen sulfide, sulfur dioxide and zinc. Ammonium molybdate is obtained by oxidizing and roasting molybdenite sand with ammonia water, and then acidifying with nitric acid to obtain ammonium molybdate. Used in the manufacture of molybdenum-containing catalysts, molybdenum salts, molybdenum trioxide, Molybdenum Powder, ceramic glazes, blue pigments, coatings, medicines, etc.
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