Experimental Study on Alumina Grinding Balls as Regrinding Media

Abstract

Taking Wushan copper ore as the research object, the grinding and flotation tests were carried out by using metal ball and alumina ball respectively. The results show that alumina ball has the same grinding performance compared with metal ball under the grinding fineness of -0.074mm 90%, and the former grinding product is lighter when overground. The suitable medium sizes of φ 30mm and φ 15mm and the ratio of 4:1 were calculated by using the section semi-theoretical formula. With ma-1 + MOS-2 as a combination reagent and pulp pH=12.0, copper flotation was carried out after one roughing, two scavenging and two cleaning. A copper concentrate grade of 23.26% and copper recovery of 95.31% were obtained, and the copper recovery was increased by 1.12%.

Ⅰ. Introduction

There are many factors affecting the grinding operation, including the nature of the grinding material, operating conditions and mill structure, etc., the nature of the grinding material and the mill structure is relatively fixed, operating conditions mainly include the grinding concentration, the speed of the mill and the size, shape, filling rate, type and ratio of the grinding medium. Too large size of grinding medium causes too large crushing force, which is prone to over-crushing phenomenon. At the same time, large size of medium reduces the number of filling medium, reduces the crushing probability of medium and ore, which is not conducive to the monomer dissociation of useful minerals. Grinding medium is too small resulting in insufficient crushing force, low grinding efficiency, energy consumption is greatly improved, the optimal size of grinding medium conditions can improve the grinding efficiency of 30%. Grinding media usually use spherical steel balls, in addition to cylindrical, hexagonal, steel forging and other shapes of grinding media. The results show that the spherical medium is the most effective and the lowest energy consumption in the normal size range, and can obtain the most fine-grained grinding products, while the cylindrical medium grinding products have uniform particle size, light mud, but poor rolling property, suitable for coarse grinding but not for fine grinding. Steel ball as grinding medium will cause iron pollution, affect pulp potential, affect the flotation effect, therefore, mineral processing workers at home and abroad actively seek new grinding medium, mainly stone, porcelain ball, etc.. Stone as grinding medium can remove iron pollution, but the shape of stone is irregular, the lining plate wear is large and the work of stone addition is large. Porcelain ball has the advantages of high hardness, high wear resistance, no pollution and corrosion resistance. Using porcelain as grinding medium can greatly reduce energy consumption and has broad application prospects.

In this paper, the middling ore after the tailings of copper cleaning ⅰ and the concentrate of scavenging ⅰ of Wushan Copper Mine are combined as the research object, and the experimental study of the middling ore regrinding process of alumina grinding ball replacing metal ball is carried out, and the differences of grinding products and flotation indexes between the two grinding media are analyzed.

Ⅱ. Experiment

1.Experimental Samples

The multi-element analysis results of middling ore are shown in Table 1, and the copper dissociation analysis results of each middling product are shown in Table 2. Table 1 Results of multi-element chemical analysis of middling ore.

Table 1

Table 1 shows that the main valuable minerals in middling ores are Cu and S, with grades of 1.74% and 27.38%. The grade of gold and silver is 0.97g/t and 64.21g/t, which can be recovered as associated metals and enriched into copper concentrate with higher valuation coefficient as far as possible. The content of lead and zinc is low, which has little effect on concentrate.

Table 2

As can be seen from Table 2, the monomer dissociation degree of copper minerals from scavenging CONCENTRATE I and cleaning tailings I is low, accounting for only 28.64% and 39.97%, mainly associated with gangue and sulfide. Table 3 shows the results of screening analysis of middling ore.

The sieve analysis results show that the middling ore size is fine, and the proportion of -0.074mm is 78.05%. The yield of +0.038mm grain is 27.74%, the copper grade is high, and the copper distribution rate is 41.88%. The copper in this part of the ore is closely connected with gangue and sulfide, and the copper in this part of the ore needs to realize monomer dissociation through regrinding and flotation to recover.

2. The Grinding Media

A φ 240mm×90mm ball mill with a volume of 6.25L was used for grinding. Metal balls and alumina balls were used as grinding media respectively. The physical properties of metal balls and high aluminum balls are shown in Table 4 and Table 5.

3. Test Procedure

This experiment is mainly for alumina grinding balls instead of the metal ball feasibility study, referring to the process flow in Wushan copper mine site, advance screening grade is 0.038 mm, on the screen with different grinding media for grinding, grinding through inspection sieve, sieve under again return to the mill grinding, qualified grade and classification of undersize combined flotation experiment was carried out in advance. Fixed different grinding media grinding fineness of -0.074mm accounted for 90%, grinding products slurry to 35%, add lime to adjust pH=12.0, ma-1 + MOS-2 as flotation reagent after one roughing, two scavenging, two cleaning, copper coarse concentrate, flotation middling and copper tailings. The particle size characteristics of grinding products under different grinding media and their influence on flotation behavior were analyzed.

Ⅲ. Result And Discussion

1.Filling Rate Test of Alumina Grinding Ball

Referring to the actual production, the filling rate of metal ball is 35%, the ball diameter (diameter) is 12mm, and the ball diameter of alumina grinding ball with equivalent mass conversion is 15mm. It has been pointed out that the filling rate of alumina grinding ball is higher than that of metal ball. With a fixed grinding fineness of -0.074mm 90%, the particle size characteristics of alumina grinding ball grinding products under different filling rates were investigated. The test results are shown in Table 6.

As can be seen from Table 6, when the filling rate is low, it takes longer grinding time to reach the specified grinding fineness, which is easy to make qualified grain products overgrind. With the increase of filling rate from 35% to 45%, the yield of fine grain (-0.020mm) of grinding product gradually decreases, and overcomminution slows down. The filling rate of grinding medium is increased, and the fineness of the product is increased again, indicating that the filling rate of grinding medium should not be too high, which is consistent with the actual production, so the filling rate of alumina grinding ball is determined to be 45%.

2. Grain Size Distribution Characteristics of Grinding Products

Laboratories use the same grinding machine, the different grinding media to grinding experiment of sample, grinding parameters, grinding fineness of 0.074 mm, grinding concentration 50%, 90% of metal ball, alumina grinding balls filling rate is 35%, 45% respectively, the grinding particle size distribution characteristics of different grinding media analysis results are shown in table 7, the grinding particle size is the cumulative results as shown in figure 1.

It can be seen from Figure 1 that at the grinding fineness of 90% -0.074mm, metal ball and alumina ball have similar particle size distribution characteristics, indicating that the two different grinding media have the same grinding performance. Compared with the grain size distribution characteristic curve of grinding products, the particle size of grinding products using metal ball as grinding medium is finer, mainly because of the small size and heavy ratio of steel ball, which has stronger grinding effect on ore and produces more secondary slime. The grinding performance of alumina grinding ball is better than that of metal ball, which is beneficial to the subsequent flotation operation.

3. Grinding Media Ratio

The ball diameter semi-theoretical formula is the most accurate formula used in China to calculate the size of grinding medium required for grinding ore of different particle size. See Formula 1.

Where, k – filling rate, 45%; φ — ratio of the radius of the innermost sphere to the outermost sphere, 0.508; R1 outermost sphere radius, 95cm, then D0=173.44cm. The results of particle size analysis of middling ore show that the overall particle size of the ore is relatively fine, and the +0.15mm particle size only accounts for 7.02%, indicating that the medium with small size is suitable for middling fine grinding to achieve the purpose of fine grinding. Taking 0.074mm and 0.038mm as reference, the suitable ball diameter of grinding medium was calculated.

It can be seen from the calculation results in Table 9 that the appropriate ball diameter of alumina grinding ball is φ 30mm and φ 15mm, and the ratio of the two is determined as 4∶1 according to the grain yield. In order to further verify the calculation results of grinding medium ratio, a verification test was carried out, and the reagent system was as follows: Copper concentrate was obtained with ma-1 + MOS-2 dosage of 30+30g/t, terpinol oil dosage of 10g/t and regulator Ca(OH)2 dosage of 2500g/t through an open circuit process of one roughing and two blank cleaning. The test results are shown in Table 10.

It can be seen from Table 9 that with the increase of grinding medium ratio (φ 30mm: φ 15mm), the ratio of coarse and refined minerals increases gradually, and copper grade increases first and then decreases. The reason is that when the proportion of grinding media is low, the proportion of grinding media with large ball diameter is small, the grinding and stripping effect of ore is weak, the proportion of fine grain size is low, and some copper minerals are not dissociated. With the increase of the ratio, more grinding fine mud is produced and the copper grade of coarse concentrate is reduced. Considering the indexes comprehensively, the ratio of grinding medium was determined as 4:1, and the copper grade of copper concentrate was 26.51% and the copper recovery was 86.54%.

4. Experimental Study on Flotation

Flotation test was conducted on metal ball and alumina grinding ball grinding products to investigate the influence of different grinding media on copper flotation. The test flow diagram is shown in Figure 2, and the test results are shown in Table 11.

As can be seen from Table 10, copper concentrate with higher yield can be obtained by using alumina grinding ball as grinding medium, copper recovery increased from 94.19% to 95.31%, sulfur grade and recovery slightly increased. After flotation, gold and silver in the ore are enriched to a certain extent. After using alumina grinding ball instead of metal ball as grinding medium, gold recovery in copper concentrate decreases from 25.69% to 23.52%, while silver recovery increases from 52.98% to 58.05%. Considering the value of copper, gold and silver, using alumina grinding ball instead of metal ball is beneficial to improve the flotation index.

4. Conclusion

  • The grade of copper and sulfur in Wushan Copper mine is 1.74% and 27.38%, and the dissociation degree of copper minerals is low, mainly associated with gangue and sulfide.
  • Alumina grinding ball and metal ball as grinding medium has the same grinding performance, metal ball size is small, than significant, the ore grinding effect is stronger, in -0.074mm 90% fineness, two -0.020mm grain yield is 60.49%, 66.94%, the overcomminution of alumina grinding ball grinding products is light.

There are many factors affecting the grinding operation, including the nature of the grinding material, operating conditions and mill structure, etc., the nature of the grinding material and the mill structure is relatively fixed, operating conditions mainly include the grinding concentration, the speed of the mill and the size, shape, filling rate, type and ratio of the grinding medium. Taking Wushan copper ore as the research object, the grinding and flotation tests were carried out by using metal ball and alumina ball respectively. The results show that alumina ball has the same grinding performance compared with metal ball under the grinding fineness of -0.074mm 90%, and the former grinding product is lighter when overground. The suitable medium sizes of φ 30mm and φ 15mm and the ratio of 4:1 were calculated by using the section semi-theoretical formula. With ma-1 + MOS-2 as a combination reagent and pulp pH=12.0, copper flotation was carried out after one roughing, two scavenging and two cleaning. A copper concentrate grade of 23.26% and copper recovery of 95.31% were obtained, and the copper recovery was increased by 1.12%. The results show that the spherical medium is the most effective and the lowest energy consumption in the normal size range, and can obtain the most fine-grained grinding products, while the cylindrical medium grinding products have uniform particle size, light mud, but poor rolling property, suitable for coarse grinding but not for fine grinding.

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