The milling time is 90min; dynamic equation as calcite wet superfine grinding: y (x, t) = 1- [1-y (x, 0)] e (- 0.01921t - 0.09363). Calcite is a carbonate minerals, mainly calcium carbonate, whose chemical composition, containing a very small amount of magnesium oxide, iron oxide, silica and the like [1]. Superfine heavy calcium carbonate calcite is one of the most important processing products, widely used in paper, plastics, rubber, cables, adhesives, etc. [2], is one of the largest market demand for non-metallic mineral processing products present. At present, the main production technology of ultrafine heavy calcium carbonate, especially paper-making pigment (slurry) grade calcium carbonate is wet superfine grinding [3 - 4] , and its main equipment is ultra-fine agitating mill or sand mill. Under the conditions determined by the grinding equipment, the pulp concentration, the grinding time, the type of the dispersing agent and the amount of the dispersing agent have an important effect on the ultrafine grinding effect of the calculus. In this experiment, the ultra-fine sand mill was used as the wet superfine grinding equipment. The effects of the variety and dosage of the dispersant, the concentration of the slurry and the grinding time of the ultrafine grinding effect of the calcite were studied. The calcite wet superfine grinding was obtained. According to the suitable process conditions, the grinding kinetics equation of calcite under suitable process conditions is summarized. First, the experimental part (1) Raw materials The calcite powder used in the experiment has the particle size composition of the raw material: D50=28.75μm, D97=115.17μm, and the content of -1μm is 2.76%, which is provided by Jiangsu Shuyang Non-Metallic Mineral Powder Factory. Grinding media used in the experiments alumina ceramic beads, having a density of 2.66g / cm 3, a particle size of 0.6 ~ 1mm. In the experiment, the grinding medium/material mass ratio was 4:1, and the mill rotation speed was constant at 2000 r/min. (2) Reagents Experiments with a dispersant: sodium polyacrylate, a density of 1.08, pH = 7.0, Rohm and Haas Company; sodium hexametaphosphate, AR grade, a density of 2.48g / cm 3, basic, Wuxi City of Hope Chemical Reagent factory. (3) Main experimental equipment and instruments Experimental SDF dispersion sand mill, Kunshan Leicheng Xingye Machinery Co., Ltd.; BT-9300H laser particle size distribution instrument, Dandong Baite Instrument Co., Ltd. Second, the results and discussion (1) Process condition test 1, the type of dispersant The sample was ground 200 g, the slurry concentration was 50%, and the dispersant was used in an amount of 0.5% by mass of the calcite powder. Grinding was carried out for 2 h, and the particle size was measured every 30 min during the grinding process. In this test, sodium polyacrylate and sodium hexametaphosphate were used for comparison test. The relationship between the median particle size D50 and the grinding time is shown in Fig. 1. Figure 1 Effect of dispersant type on grinding effect It can be seen from Fig. 1 that under the same grinding time, the sodium hexametaphosphate has a better grinding effect than the sodium polyacrylate. When the grinding time is 90 min, when the sodium hexametaphosphate is used as the dispersing agent, the material is in the middle position. The diameter D50 has reached 0.66μm, and sodium polyacrylate is used as the dispersing agent, which takes 120min to reach 0.68μm. Therefore, the dispersing agent of sodium hexametaphosphate as calcite is more efficient than sodium polyacrylate. 2, the amount of dispersant Grinding the sample 200g, the pulp concentration is 50%, the dispersing agent is sodium hexametaphosphate, the cumulative grinding is 90min, and the relationship between D50 and D97 and the grinding time is shown in Fig. 2. Figure 2 Effect of Dispersant Amount on Grinding Effect It can be seen from Fig. 2 that as the amount of dispersant increases, the fineness of the grinding sample decreases. When the dosage is 0.5%, the median particle size D50 of the material reaches a minimum of 0.66 μm; thereafter, with the amount of dispersant Increasing, the particle size reduction is not obvious, and continuing to increase the amount of dispersant has no significant improvement on ultrafine grinding, which only increases production costs. Therefore, a suitable amount of the dispersant is 0.5% by mass of the material. 3, pulp concentration Grinding sample 200g, the dispersing agent is sodium hexametaphosphate, the dosage is 0.5% of the mass of calcite powder, the cumulative grinding is 90min, the relationship between D50, D97 and grinding time is shown in Fig. 3. It can be seen from Fig. 3 that as the concentration of the slurry increases, the fineness of the material decreases in the same time (90 min), and the grinding efficiency increases. When the grinding concentration reaches 55%, the product median diameter D50 reaches 0.61 μm. Increasing the grinding concentration, the slurry and the grinding medium adhere together and cannot be stirred and ground. Therefore, the optimum slurry concentration is 55%. 4, grinding time The sample was ground 200g, the dispersing agent was sodium hexametaphosphate, the amount was 0.5% of the calcite mass, the grinding concentration was 55%, and the relationship between D50 and D97 and the grinding time is shown in Fig. 4. Figure 4 Effect of grinding time on grinding effect It can be seen from Fig. 4 that as the grinding time increases, D50 and D97 decrease. When the time reaches 90 min, the particle size of the material is no longer reduced, the specific surface area and surface free energy increase, and the particles reach the pulverization and agglomeration. Balanced state, and increased grinding time is just wasting energy. Therefore, the suitable grinding time is 90 min. From the above experiments, it can be concluded that the suitable process conditions for calcite wet superfine grinding are as follows: the dispersing agent is sodium hexametaphosphate, the dosage is 0.5% of calcite mass, the pulp concentration is 55%, and the grinding time is 90 min. (2) Grinding dynamics [5 - 7] Epstein proposed a selection function and a distribution function to describe the ultrafine pulverization process. Reid used these two functions to establish the dynamic differential equation of the intermittent superfine pulverization process: y(x,t)=1-[1-y(x,0)]e - s(x)t ,0≤x≤xmax (1) Where: y(x,0) is the mass percentage of the raw material smaller than the particle size X; y(x,t) is the mass percentage less than the particle size x at time t; s(x) is the pulverization selection function (representing the pulverization of a certain particle size) Specific rate). A study by South African scholar Tuzun found that the function is suitable for the description of the ultra-fine pulverization process of batch stirring mill, and gives the expression of the selection function: s(x)=αx β (2) Where: α is a constant; β is an index. Substituting (2) into (1) gives: y(x,t)=1-[1-y(x,0)]e - αxβt , 0≤x≤xmax (3) After transformation, and substituting (2), you can get: Ln{[(1-y(x,t)]/[1-y(x,0)]}=-s(x)t=-αx β t (4) The sample was ground 200 g, the slurry concentration was 55%, the grinding time was 90 min, the dispersing agent was sodium hexametaphosphate, and the amount was 0.5% of the calcite mass. The content of the sample at -1 μm (%) was measured at different times. The results are shown in Table 1. The grinding kinetics curve is calculated and plotted according to formula (4). The results are shown in Fig. 5. The dynamic points of the distribution in the graph are approximately linear, which is the first-order linear grinding dynamics relationship, ie ln{[(1-y(x,t)]/[1-y(x,0)]} The time t is linear. The comminution rate of the calcite (slope of the curve) s(x) is -0.01921 by regression analysis. Y=A+BX Where X is the grinding time t; Y is ln{[(1-y(x,t)]/[1-y(x,0)]}; A is the intercept, the value is -0.09363; B is the slope, the value Is -0.01921; x is the particle size; y (x, 0) is the mass percentage less than the particle size x in the raw material; y (x, t) is the mass percentage less than the particle size x in the sample after grinding t time. The curve equation is: Ln{[(1-y(x,t)]/[1-y(x,0)]}= A+BX=-0.09363-0.01921t By conversion, it can be concluded that the kinetic equation of calcite wet superfine grinding is: y(x,t)=1-[1-y(x,0)]e(-0.01921t-0.09363) Third, the conclusion 1. The suitable process conditions for calcite wet superfine grinding are: dispersing agent adopts sodium hexametaphosphate, the dosage is 0.5% of calcite mass, the pulp concentration is 55%, the grinding time is 90min, at this time, the sample D50 can reach 0.61. Μm, D97 can reach 1.46μm. The mathematical equation of calcite wet superfine grinding is obtained by mathematical regression analysis: y(x,t)=1-[1-y(x,0)]e(-0.01921t-0.09363). references [1] Zheng Shuilin. Non-metallic mineral processing and application [M]. Beijing: Chemical Industry Press, 2003: 17. [2] Li Jinfa. Calcite resources and development and utilization in Chizhou area [J]. Anhui Geology, 2000, 10 (4): 313-314. [3] Zheng Shuilin. Non-metallic mineral processing technology and equipment [M]. Beijing: Chemical Industry Press, 2009: 40-59. [4] Ding Hao, Xing Feng. Behavior and Action of Grinding Medium in Ultrafine Grinding of Mineral Powder Stirring and Wet Method[J]. China Powder Technology, 2000(8): 9-12. [5] Reid K J. A solution to the batch grinding equation [J]. Chem Eng Sci, 1965, 20: 953-963. [6] TuzunMA, etal. Effect of pintip velocity, ball density and ball size on grinding kinetics in a stirred ballmill [J]. Int JMinerProcess, 1995, 43: 179-191. [7] Pan Xinzhang, Ma Zhenhua. The Reverse of Mathematical Model of Micro-crushed Alumina by Stirring Mill[J].Journal of The Chinese Ceramic Society,1991,19(1):64-68. Thermal spray wires are used in thermal spraying processes, which involve the application of a coating material onto a surface. These wires are specifically designed to be melted and sprayed onto a substrate to create a protective or functional coating. Spray Wires,Arc Spray Coating,Thermal Arc Spray,Thermal Spray Wire Luoyang Golden Egret Geotools Co., Ltd , https://www.xtcwelding.com
Figure 3 Effect of slurry concentration on grinding effect
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Wet superfine grinding process and kinetics study of calcite