Chromite ore dressing test

A chrome iron ore processing plant is treated grade chromium (Cr 2 O 3) 32% of high-grade ore, all-shaker grade sorting process can be obtained Cr 2 O 3 43% or more of chromium ore. As resources are diminishing , the recycling of lean mines is also on the agenda. There are different grades (Cr 2 O 3 5 ~ 30%) of chrome-poor iron ore near the mine . In order to provide a basis for the full use of resources in the future , we have carried out research on the beneficiation process and equipment selection of the skeletal iron ore . Four processes and three types of equipment were selected for chrome- depleted iron ore with a chromium grade of about 8% . The ideal sorting index has been achieved under different beneficiation processes and processes. Among them, the strong magnetic separation and tailing - shaker full-grain sorting process index is relatively good . Under the grinding grain size of -200 mesh 60% , the concentrate grade can be 39.98% , the yield is 13.28% , and the chromium recovery rate is 64.74%. good indicator, concentrate in the SiO 2 content of 4.07%.

1 Multi-element chemical analysis of raw ore

The results of multi-element chemical analysis of raw ore are shown in Table 1 .

From the chemical analysis results of the above table , the content of chromium in the ore in the ore is low , only 8.19% , which is a chrome-poor ore . It needs to be enriched by ore before it can be smelted into the furnace. Other metal element content of Mg is relatively high as 36.10%, if present as separate minerals, should be considered comprehensive recycling. The main gangue composition is SiO 2 , the content is up to 30.55% , the content of other components is lower , and the Al 2 O 3 content is only 1.78% . However, if Al 3+ and Cr 3+ are similar to each other , then the ore dressing process While enriched in chromium , aluminum will also be enriched in chromium concentrate. For the purposes of this study , the target element is Cr , while Mg and Si are the main targets that need to be removed in beneficiation.

2 ore grindability analysis

The grindability comparison was made with the wine ore as a standard ore sample. Results surface, relatively poor chromite steel mine mill liquor when the newborn content of 40% -200 mesh, the relative grindability 0.56.

3 dressing test

According to the high specific gravity (4.3 ~ 4.6) and weak magnetic properties ( specific magnetization coefficient 286 × 10 - 6 CGSM cm 3 / gram ) of chromite , it is determined that the re-election and magnetic separation methods are used for the beneficiation test.

3.1 Shaker beneficiation test

Shakers are currently the most commonly used equipment for chromite ore . Due to their high precision , many mines are willing to use them. To this end , we first carried out a shaker test for the chrome-poor ore.

3.1.1 Full grain selection

After grinding to the required fineness , go directly to the shaker to sort. In this test, the grinding size, flushing water volume, stroke, stroke and slope of the selected index were selected. According to the selected conditions , the process test is carried out . The selection process is : shaker rough selection - middle mine and then two selections. The selection process and results are shown in Figure 1 .

From the above results do not selected, in - using 60% 200 mesh particle size of the grinding sorting shaking period, to obtain grade 39.85%, yield of 11.82%, 56.83% recovery of chromium ore, SiO 2 content of 4.32% . The medium ore is re-selected to obtain a chromium concentrate with a yield of 2.68% and a grade of 32.69% . The silicon content is increased to 8.14% , which is combined with the coarse-concentrated concentrate as the final concentrate . The index is 14.50% , and the chromium grade. 38.53% , chromium recovery rate of 67.40% , silicon content of 5.03% , mineral processing ratio of 6.9 times.

3.1.2 Shaker graded ore dressing test

For shaker, the level of the narrower range of particle sizes in general, the more stable the sorting index higher separation efficiency. The grinding product using dry sieving for this approach sieved + 0.15mm, - 0.15 + 0.10mm, -0.1 + 0.074mm, - 0.074 + 0.038mm and - 0.038mm five levels, respectively, in which a suitable under shaking conditions for sorting, the sorting process for each level with FIG. 1, various size sorting products combined total sorting products. The test results are shown in Table 2 .

Table screening results, chromite minerals are present in 38 to 100 stages of Microparticles, these grain size grade is relatively high in chromium, chromium add up to 79.56% of the distribution. The grades of coarse and fine grades are lower , the grade of chromium in the grade of +0.15mm is 6.22% , and the grade of chromium in the grade of -38mm is only 5.93% , which is lower than the original ore , indicating that the gangue composition is in these two. Enriched in the grain size. From the results of separate sorting of each size , the selection efficiency of the intermediate size (0.038 ~ 0.010mm ) is higher , and the grade and recovery of the concentrate are ideal , especially 0.074 ~ 0.100mm. The grain grade , the chromium grade is 39.30% , and the recovery rate is 85.25% . Both indexes are the highest among the grain grades. Relatively speaking , the coarse-grained grade of +0.15mm and the fine- grained grade of -0.038mm are relatively poor . The former has a concentrate grade of only 34.07% , and the operation recovery rate is 52.75%, while the latter concentrate grade is only 26.09%. The recovery rate is also as low as 38.28% , and the grades of the two grades of tailings are also significantly higher than other grades. Analyze the reasons, that the coarse fraction is because low-grade mineral dissociation is not enough, not fully dissociated chromite and gangue, reach the purpose of separation, while the fine fraction index difference is due to the fine mud shaker for election Don't be inefficient. From the comprehensive results , the final concentrate grade is 36.09% , and the recovery rate is 73.97% . Compared with the whole-grain grade selection result , the concentrate grade is low and the recovery rate is relatively high. If the -0.038mm grain size is not incorporated into the concentrate , the concentrate grade can be increased to 37.22% . If the coarse fraction of +0.15mm or more is removed , the concentrate grade can be further improved. Taken together, the efficiency of the whole grain mineral grading and sorting process stage substantially close, whole grain selected stage has a simple process, without classification, advantages of simple operation, for this ore, because relatively thin grinding fineness, grain The level is relatively concentrated , and it is more suitable to use the full-grain level.

3.2 Spiral chute tailing - shaker beneficiation test Shaker has the advantages of high sorting precision , but at the same time has the disadvantages of large floor space and low processing capacity. For the ore , due to the low grade of raw ore chrome , a large amount of dissociated gangue minerals enter the shaker , which greatly increases the burden of the shaker . Therefore , it is necessary to explore the pre-spinning process and use a large amount of processing after grinding. Low-cost equipment throws out qualified tailings , which reduces the amount of minerals entering the shaker , saves the number of shakers , and reduces the interference of gangue, especially fine-grained gangue , creating favorable conditions for shaker sorting. For this purpose, a spiral chute tail - shake sorting test was carried out . The test procedure and results are shown in Fig. 2 .

It can be seen from the results in Fig. 2 that the spiral chute can discard the tailings with a yield of 43.91% and a chrome grade of 4.47% . After the tailing , the amount of minerals entering a shaker and the second-stage shaker is greatly reduced , and nearly half of the shaker equipment can be saved. With the floor space , and the efficiency of the shaker sorting after tailing is obviously improved , the same sorting process as the full-grain and graded sorting process can be used , and the final concentrate grade can be increased to 39.54%, only the recovery rate. The index is relatively low . The main reason is that when the spiral chute is thrown , a small part of fine-grained chromite enters the tailings due to centrifugal force , resulting in a slightly higher grade of tailings. The spiral chute has the advantages of large processing capacity per unit area, simple structure, no power, etc. , but the lower limit of the recovery particle size is about 30 microns . When the grinding particle size is fine, it is easy to cause the loss of useful minerals of fine particles.

3.3 Magnetic separation and tailing - shaker beneficiation test

According to the high specific magnetic susceptibility of chromite , a magnetic separation tailing - shaker selection test was carried out.

The magnetic separation equipment adopts the imitation Jones wet magnetic separator , and the strong magnetic separation tailing test is carried out under the condition of grinding grain size - 200 mesh 60% and magnetic field strength 5000 Oe . Since the magnetic separation tailings grade is low , it can be used as qualified tailings . Therefore, the magnetic separation is used for rough selection and tailing , and the shaker is used for selection to improve the grade. The test procedure and indicators are shown in Figure 3 .

From the results of FIG. 3, can be removed using a strong magnetic yield of 50.21% of qualified tailings, tailings grade of only 2.19%, so that the amount of ore into the shaker reduced by half, greatly reducing the number of shaker, while After the tailing, it created favorable conditions for the sorting of the shaker , which further improved the selection index , and finally obtained the ideal index of grade 39.98% , recovery rate 64.74% , SiO 2 content 4.07% , and spiral chute tailing - shaker Compared with the process , the strong magnetic separation process has a large throwing amount , the tailings grade is low , and the final concentrate recovery rate is relatively high.

4 indicators comparison analysis

From the selection indicators of the above processes , the final concentrate grade and recovery rate indicators are quite different . In comparison , the magnetic separation tailing - shaker selection process results are ideal. The grade of concentrate is significantly higher than other processes , and the recovery rate index is not much lower ; Spiral chute tailing - shaker sorting process can also obtain high-grade chromium concentrate , but due to the low recovery efficiency of fine-grained chromium minerals by spiral chute equipment , the grade of tailing tailings is slightly higher , resulting in concentrate recovery rate. Relatively low ; The index of the full-scale sorting process of the shaker is middle , and the graded selection index is relatively poor . The main performance is that the concentrate grade is low . If the concentrate belt width is further adjusted , the concentrate grade may increase , but the recovery rate will be decreased, the final index does not exceed the expected magnetic separation - shaker flow index (for example, the classification process of sorting grain size of 0.038 ~ 0.15mm ore sorting section together, which grade of 38.74% chromium, and The recovery rate is only 59.78%) .

From the process point of view , the number of shakers required for the full shaker selection is large , occupying a large area of ​​the plant . If the classification is selected , it is necessary to control the classification granularity more strictly ; Of the ore, because grinding fine-grained, smaller size range, and easy to manage from the point of view of operations, the process can be selected for full-size fraction. The spiral chute and strong magnetic separation tailing process can pre-delete the tailings with a yield of more than 43% , which creates favorable conditions for the next sorting of the shaker , and greatly reduces the number of shakers . The two tailing equipments operate reliably and have a large processing capacity. , consider using. Magnetic separation is the most suitable process . Due to the large processing capacity of the equipment , only a small number of units can be used to complete the workload of a large number of shakers , and the operation is simple , the operation is reliable , the index is stable , and the management is convenient . The disadvantage is that the equipment price is high . A single device consumes a lot of power. The above test procedures have their own advantages and disadvantages . The selection process that is suitable for the actual and low cost should be selected according to the construction conditions and economic comparison.

In this test, in order to recover as much chromite as possible , in the middle ore re-election of each sorting process , the amount of medium ore intercepted is large , so that the amount of minerals that are re-selected into the shaker is also large. From the selection index , the re-selected concentrate yield is very low , and most of the ore reserves re-enter the tailings , so in the actual production, the amount of minerals in a shaker can be reduced , thereby reducing the burden of the second-stage shaker.

5 product analysis

Multi-element chemical analysis was performed on the concentrate of the magnetic separation tail - shake full-grain process . The results are shown in Table 2 . Visible, the main ingredient concentrate as gangue Al 2 O 3 and MgO, both total content of up to 25.11%, a serious impact on concentrate grade. The content of MgO in the ore is higher , and there is a large decrease in the chromium concentrate after beneficiation , indicating that most of the Mg is present in the chromite ore as a separate mineral , which can be separated from the chromite by beneficiation. However, Al 2 O 3 is abundantly enriched in chromium concentrate, and the enrichment ratio is as high as 5.8 ( it is only 1.78% in the ore ) , indicating that Al is likely to enter the chromite ore and is similar to chromium. In phase , it cannot be separated from chromium by mechanical means.

6 conclusion

6.1 The content of Cr 2 O 3 in a chrome-poor iron ore is only 8.19% . After sorting suitable process can be obtained Cr 2 O 3 content of 39% or more qualified products, indicating that the lean chromite is optional.

6.2 Using the shaker selection process , the selection index of yield 14.50% , grade 38.53% , and chromium recovery rate 67.40% can be obtained at the full-grain level . When the fractionation grade is selected , the selection index of the yield of 16.91% , the grade of 36.09% , and the recovery rate of 73.97% can be obtained . Comprehensive comparison , the full-scale inclusion index is relatively better. The advantage of the full shaker process is that the sorting precision is high , and the disadvantage is that the processing amount is small , the number of equipment required is large , and the floor space is large.

6.3 Both the spiral chute and the strong magnetic separation process can remove more than 43% of the tailings in advance , creating conditions for the selection of the shaker , and greatly reducing the number of shaker equipment and the floor space of the plant. In comparison , the strong magnetic separation tailings have a low grade and can be directly discarded as qualified tailings , while the grade of the spiral chute tailings is relatively high. Both tailing devices have large processing capacity and reliable operation.

6.4 Adopt strong magnetic separation and throwing tail - shaker selection process

Obtained Yield 13.28%, 39.98% grade, 64.74% recovery of chromium ore, concentrate SiO 2 content of 4.07%. Spiral chute tailing - shaker sorting process can be obtained concentrate grade 39.54%, a yield of 12.50%, 60.28% chromium recovery index, concentrate in the SiO 2 content was 4.15%. The former has a relatively good selection index.

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