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Zinc oxide before desliming flotation operations, resulting in significant loss of the zinc metal. The amount of slime directly affects the flotation index of zinc oxide ore. Therefore, the choice of reasonable grinding equipment and grinding process is particularly important for the flotation of zinc oxide ore. There are not many studies on how to reduce the secondary slime of zinc oxide ore. Kunming Metallurgical Research Institute has proposed preselection scheme for heavy media Lanping Lead Zinc oxide ore limestone, to reduce secondary sludge produced positive results. In October 2002, Lanping Nonferrous Metals Co., Ltd. entrusted our institute to carry out the grinding and grinding test on the recommendation of Dr. Gao Minglu, an Australian expert. This paper discusses the possibility of using agitating mill to reduce the secondary slime of Lanping zinc oxide ore and analyzes its mechanism.
First, the sample is taken and processed
The sample was collected from the 500t/d lead-zinc ore flotation industrial test plant of Lanping Lead-Zinc Mine. The pilot plant conducted a flotation industrial test in August-September 2002 using a mixed mine with a sand ash ratio of 1:1.5. The test found that the amount of secondary slime was large, which seriously affected the selection index. The principle of grinding principle adopted in industrial tests is shown in the figure below. The ore sample of this test is prepared by the fine particle size of -0.5mm in the figure and the coarse-grained ore of the incoming powder ore bin according to the particle size distribution of the ore. In addition, a total of 5 shifts (the overflow of Φ300mm cyclone) was collected from September 10 to 11, 2002, as a comprehensive sample of the final grinding products on site.
In this study, the two-stage grinding shown in Figure 1 was simulated by agitating mill. Therefore, the prepared samples were first processed to make the particle size composition close to the particle size composition of the second-stage grinding ore. The processed sample was used as a feed for the agitating mill, and its particle size composition is shown in Table 1.
Industrial test grinding principle process
Table 1 Particle size composition of the agitator mill
Second, test equipment and instruments
This test adopts vertical stirring mill, the inner diameter of the cylinder is 200mm, the depth of the cylinder is 220mm, and the volume is 6.9L. The agitator is rod type, that is, along the radial direction of the cylinder, several stirring rods are installed at different heights of the stirring shaft, and the end of the stirring rod is The gap between the inner walls of the cylinder is 20 mm, that is, the radius of rotation of the end of the stirring rod is 80 mm.
The stirrer speed is controlled by a Japanese-made FVR3.7E11S-4 inverter. The particle size characteristics of the product were determined using a continuous water analyzer and a Coulter Model LS100Q laser particle size analyzer.
Third, the test method
The following stirring mill conditions were fixed.
Grinding medium: Φ4～5mm ceramic ball, loading 5981g, medium filling rate 80%. Each time the ore loading is 2000g, the grinding concentration is 60%, and the agitator speed is 383.5r/min.
First, a set of agitating grinding test with different grinding time is carried out to determine the grinding time required to grind the final grinding fineness (measured by a continuous water analyzer with a sample size of 74 μm), and then carry out the on-site A comparison test of the grinding mill with the same fineness of grinding.
Fourth, test results and discussion
In this test, the particle size of the agitating mill is fine (-0.45mm), the grinding time of the grinding mill is only 20sec, and the fineness of the product reaches the fineness of the final grinding product (-74μm).
The particle size distribution of the product of the agitating mill for 20 sec and the final milled product of the test plant was measured by a continuous water analyzer. The comparison results are shown in Table 2. Meanwhile, the results of the laser particle size analyzer measurement are shown in Table 3.
Table 2 Product particle size comparison results (determined by water analyzer)
Table 3 Product particle size comparison results (laser particle size analyzer)
In the flotation of zinc oxide ore, the current deliming limit is generally -10 μm. Therefore, this study used a 10 μm particle size as a slime.
According to the comparison of the particle size distribution of Table 2 and Table 3, although the analysis results of the water analyzer and the laser particle size analyzer are quite different, from the overall trend, the slurry content of the agitated mill product is less than that of the final milled product at the site, and The content of the 19-74μm easy-to-select grade of the agitated mill product is significantly higher than that of the field, and the particle size distribution of the product is narrower. It shows that the quality of the agitated mill product is higher, which is more conducive to the subsequent flotation process.
So far, most researches on agitating mills at home and abroad have focused on the ultrafine pulverization of materials. However, from the results of this study, the application of agitating mills in ordinary beneficiation processing has certain potential. In fact, the two most important factors affecting the final particle size and particle size distribution characteristics of the product are the agitation speed and the size of the grinding media.
In the agitator mill, the motion state of the agitated slurry and the grinding medium is very complicated, and the influencing factors are as many as several dozen. Therefore, there is no systematic description of the pulverization mechanism of the agitating mill. The grinding medium and the slurry in the vertical agitating mill produce a rotary motion with the agitator. The linear velocity of the grinding medium moving in different radial directions is not equal; in the vertical direction, the speed of the grinding medium movement between the layers is not equal, there is a velocity gradient, which inevitably produces shearing force And the pressing force; the larger the speed gradient, the larger the shearing force and the pressing force, and the stronger the pulverizing effect. Near the agitator, the grinding medium moves most vigorously. In addition to the circular motion, the grinding medium in the agitating mill has different degrees of up and down turning, and a part of the grinding medium collides with the agitator, and there is a certain impact force near the agitator. In combination, the forces that pulverize throughout the grinding chamber are shear, squeezing, friction, and impact. The mixing mill operating parameters are different (such as the rotational speed, the diameter of the grinding medium), and the pulverizing force that plays a major role may be different. The main pulverizing force of the general agitating mill is the shearing force and the pressing force.
In this study, the linear velocity at the end of the stir bar was 6.42 m/s, where the grinding media moved at the fastest speed. In the vicinity of the cylinder wall, the moving speed of the grinding medium is small due to the friction of the cylinder wall. Therefore, in the annular region between the end of the stirring rod and the wall of the cylinder, the velocity gradient of the grinding medium is the largest, and the material pulverizing effect is the strongest. Since the material is subjected to high-speed agitation in the cylinder, under the action of the centrifugal force, the coarse-grained material preferentially moves toward the cylinder wall and enters the annular region with the strongest pulverization, so that the crushing is preferentially obtained. Finer materials tend to remain in the central region of the cylinder where the pulverization is weak. Therefore, the agitating mill has a certain self-grading and selective crushing effect, and the reduction of the amount of slime in this study is the result of this effect. In addition, consistent with the results of previous studies, the results of this study indicate that the particle size distribution of the agitated mill product is narrower, which is inseparable from the above effects.
V. Conclusion
It is initially seen through experiments that the agitated mill has certain application prospects in reducing secondary slime, and the particle size distribution of the agitated mill product is narrower. The main reason is that the agitating mill has selective crushing action and self-grading.
In this test, the mixing mill has a finer grain size and a short grinding time, which may affect the accuracy of the test.
This study failed to conduct detailed tests on the grinding media size, medium loading amount, ore feeding size, stirring speed and other parameters of the stirring mill, and further optimization of operating conditions is needed.
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