Chromite beneficiation experiment

A chromite ore concentrator is currently processing rich ore with a chromium grade (Cr2O3) of more than 32%. Using a full shaking table classification and separation process, a chromium concentrate with more than 43% Cr2O3 can be obtained. As resources are dwindling, the recycling of lean minerals has also been put on the agenda. There are also poor chromite ores of different grades (Cr2O35~30%) near the mine. In order to provide a basis for full utilization of resources in the future, we conducted a study on the selection of mineral processing technology and equipment for the poor chromite ore in the mine. The chromium grade is: About 8% of the lean chromite ore has been selected from four processes and three types of equipment. Relatively ideal separation indicators have been achieved under different mineral processing processes and techniques. Among them, the strong magnetic separation and tailing-shaking table full-grain separation process indicators are relatively good. At a grinding particle size of -200 mesh of 60%, a concentrate grade of 39.98%, a yield of 13.28%, and a chromium recovery rate of 64.74% can be obtained. A better indicator is that the SiO2 content in the concentrate is 4.07%.
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1 Multi-element chemical analysis of raw ore

From the chemical analysis results in the table above, it can be seen that the content of the target element chromium in the ore is relatively low, only 8.19%. It is a chromium-poor ore and needs to be processed and enriched before it can be smelted in the furnace. The content of other metallic elements Mg is also relatively high, at 36.10%. If it exists as a separate mineral, comprehensive recycling should be considered. The main gangue component is SiO2, with a content as high as 30.55%. The contents of other components are low, and the Al2O3 content is only 1.78%. However, if Al3+ and Cr3+ exist in the same quality, while chromium is enriched during the mineral processing process, aluminum It will also be enriched in chromium concentrates. For this study, the target element is Cr, while Mg and Si are the main objects that need to be eliminated in mineral processing.

2. Ore grindability analysis

Jiji Iron and Steel Ore was used as a standard ore sample for grindability comparison. The results show that poor chromite ore is more difficult to grind than Jiuxing Iron parts. When the content of Xinsheng-200 mesh reaches 40%, its relative grindability is 0.56.

3 Ore dressing test

According to the properties of chromite’s high specific gravity (4.3~4.6) and weak magnetism (specific magnetization coefficient 286×10-6C.G.S.M cm3/g), it was decided to use gravity separation and magnetic separation methods for the mineral Cnc Machining test.

3.1 Shaking table mineral processing test

Shaking table is currently a commonly used equipment for sorting chromite ore. Due to its high sorting accuracy, many mines are often willing to use it. To this end, we first conducted a shaking table separation test on the poor chromite ore.

3.1.1 Full grain level selection

After grinding the ore to the required fineness, it directly enters the shaking table for sorting. In this test, the grinding particle size, flushing water volume, stroke, number of strokes and slope that affect the separation index were selected. According to the selected conditions, a process test is carried out. The separation process is: shaking table rough separation – medium ore selection and then two stages of separation. The selection process and results are shown in Figure 1.

From the above separation results, it can be seen that using a shaking table to separate at a grinding particle size of -200 mesh and 60%, a chromium concentrate with a grade of 39.85%, a yield of 11.82%, a recovery rate of 56.83%, and a SiO2 content of 4.32% can be obtained. By re-selecting the medium ore, a chromium concentrate with a yield of 2.68% and a grade of 32.69% can be obtained. The silicon content is increased to 8.14%. It is combined with the rough concentrate as the final concentrate. The indicators are a yield of 14.50% and a chromium grade of 14.50%. The chromium recovery rate is 38.53%, the chromium recovery rate is 67.40%, the silicon content is 5.03%, and the mineral processing ratio is 6.9 times.

3.1.2 Shaking table classification mineral processing test

For shakers, generally speaking, the narrower the particle size range, the more stable the sorting index and the higher the sorting efficiency. To this end, the grinding products are screened into five levels using dry screening: +0.15mm, – 0.15 +0.10mm, -0.1+0.074mm, – 0.074+0.038mm and – 0.038mm, respectively at their appropriate Shaker sorting is carried out under the conditions. The sorting process of each level is the same as Figure 1. The sorted products of each particle level are combined into the total sorted product. The test results are shown in Table 2.

Judging from the surface screening results, chromite minerals mainly exist in the 38-100 micron particle size. The chromium grades in these particle sizes are relatively high, and the total chromium distribution rate reaches 79.56%. The chromium grades of the coarse-grained and fine-grained grades are both low, with the +0.15mm grade having a chromium grade of 6.22% and the -38mm grade having a chromium grade of only 5.93%, which are both lower than the original ore, indicating that the gangue composition in these two Enriched in particle size. Judging from the separate separation results of each particle size, the separation efficiency of the middle particle size (0.038 ~ 0.010mm) is relatively high, and the chromium grade and recovery rate of the concentrate are relatively ideal, especially the 0.074 ~ 0.100mm particle size, the chromium grade is 39.30%, recovery rate 85.25%, both indicators are the highest among all particle grades. Relatively speaking, the separation effect of +0.15mm coarse particle size and -0.038mm fine particle size is relatively poor. The former concentrate grade is only 34.07% and the operating 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 tailings grades of these two particle sizes are also significantly higher than other particle sizes. Analyzing the reasons, it is believed that the low grade of the coarse-grained grade is due to the insufficient degree of mineral dissociation, the chromite and gangue are not fully dissociated, and the purpose of separation cannot be achieved, while the poor index of the fine-grained grade is due to the selection of fine mud by the shaking table. Not due to low efficiency. Judging from the comprehensive results, the final concentrate grade is 36.09% and the recovery rate is 73.97%. Compared with the full particle size separation results, the concentrate grade is low and the recovery rate is relatively high. If the -0.038mm particle size is not incorporated into the concentrate, the concentrate grade can be increased to 37.22%. If the coarse particle size above +0.15mm is removed, the concentrate grade can be further improved. Taken together, the beneficiation efficiencies of the full-grain grade and graded separation processes are basically close. The full-grain grade selection has the advantages of a simple process, no need for classification, and easy operation. For this ore, due to the relatively fine grinding particle size, the Grain grades are relatively concentrated, and it is more appropriate to select all grain grades.

3.2 Spiral chute tailing-shaking table mineral processing test The shaking table has the advantage of high separation accuracy, but it also has the disadvantages of large floor space and low processing capacity. For this ore, due to the low chromium grade of the raw ore, a large amount of dissociated gangue minerals enter the shaking table, which greatly increases the burden on the shaking table. For this reason, it is necessary to explore the pre-tailing process and adopt a large processing capacity after grinding. , Low-cost equipment is used to throw away qualified tailings, which not only reduces the amount of ore entering the shaking table, saves the number of shaking tables, but also reduces the interference of gangue, especially fine-grained gangue, creating favorable conditions for shaking table sorting. To this end, a spiral chute tail throwing-shaking table selection test was carried out. The test process and results are shown in Figure 2.

It can be seen from the results in Figure 2 that the spiral chute can throw away tailings with a yield of 43.91% and a chromium grade of 4.47%. After the tailings are thrown out, the amount of ore entering the first-stage shaking table and the second-stage shaking table is greatly reduced, and nearly half of the shaking table equipment can be saved. Compared with the floor space, the efficiency of shaker separation after tailing is significantly improved. Using the same shaker separation process as full-grain and graded separation, the final concentrate grade can be increased to 39.54%, but the recovery rate is The indicator is relatively low. The main reason is that when the spiral chute throws tail, a small amount of fine-grained chromite ore 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, and no need for power. However, the lower limit of its recovery particle size is about 30 microns. When the grinding particle size is fine, it is easy to cause the loss of fine-grained useful minerals.

3.3 Magnetic separation tailing-shaking table mineral processing test

According to the property of chromite having a high specific magnetization coefficient, a magnetic separation tailing-shaking table separation test was carried out.
The magnetic separation equipment adopts an imitation Jones wet strong magnetic separator. The strong magnetic separation tailing test is carried out under the conditions of grinding particle size – 200 mesh 60% and magnetic field strength 5000Oe. Due to the low grade of the magnetic separation tailings, it can be used as qualified tailings. Therefore, magnetic separation is used for rough selection and tailing, and a shaker is used for selection to improve the quality. The test process and indicators are shown in Figure 3.

From the results in Figure 3, strong magnetic separation can be used to remove qualified tailings with a yield of 50.21%, and the tailings grade is only 2.19%, thus reducing the amount of ore entering the shaking table by half, greatly reducing the number of shaking tables, and at the same time The tailing created favorable conditions for the shaking table sorting, further improving the sorting index, and finally obtained the ideal index of grade 39.98%, recovery rate 64.74%, and SiO2 content 4.07%, which is consistent with the spiral chute tailing-shaking technology. In comparison, the strong magnetic separation process has a large amount of tailings, low grade tailings, and a relatively high final concentrate recovery rate.

4 Comparative analysis of indicators

Judging from the separation indicators of the above processes, the final concentrate grade and recovery rate indicators are quite different. From a comparison point of view, the results of the magnetic separation and shaker separation process are more ideal. The concentrate grade is significantly higher than other processes, and the recovery rate index does not drop much; the spiral chute tailing-shaking table separation process can also obtain high-grade chromium concentrate, but due to the spiral chute equipment’s recovery efficiency of fine-grained chromium minerals On the low side, the grade of the tailings thrown out is slightly higher, resulting in a relatively low concentrate recovery rate; the indicators of the shaking table full-grain separation process are in the middle, and the classification and separation indicators are relatively poor, which is mainly reflected in the low chromium grade of the concentrate. Low. If the width of the concentrate belt is further adjusted, the concentrate grade may increase, but the recovery rate will decrease significantly. It is expected that the final index will not exceed the index of the magnetic separation-shaking table process (for example, the grading separation process will be 0.038 The chromium grade of the first-stage separation concentrate with ~0.15mm particle size is 38.74%, but the recovery rate is only 59.78%).
From a process perspective, full shaker separation requires a large number of shakers and occupies a large plant area. If grading is used for selection, stricter control of the grading particle size is required; for this ore, due to the finer grinding particle size, the particle size The scope is smaller, and from the perspective of convenient management and operation, a full granular selection process can be adopted. The spiral chute and strong magnetic separation tailing process can pre-throw the tailings with a yield of more than 43%, creating favorable conditions for the next step of shaking table sorting, while greatly reducing the number of shakers. The two tailing equipment are reliable in operation and have a large processing capacity. , can be considered for use. Magnetic separation is the most suitable process. Due to the large processing capacity of this equipment, only a small number of shakers can be used to complete the workload of a large number of shakers. It is also simple to operate, reliable in operation, stable in indicators, and easy to manage. The disadvantage is that the equipment is expensive. A single device consumes a lot of power. The above test processes each have their own advantages and disadvantages, and a suitable and low-cost selection process should be selected based on the plant construction situation and economic comparison.
In this test, in order to recover as much chromite as possible, during the re-selection of mid-range ore in each separation process, a large amount of mid-range ore was intercepted, so that the amount of mid-range ore re-selected into the shaking table was also large. From the perspective of separation indicators, the re-selection concentrate yield is very low, and most of the ore re-enters the tailings. Therefore, in actual production, the amount of medium ore in the first stage of the shaking table can be reduced, thereby reducing the burden on the second stage of the shaking table.

5 Product Analysis

Multi-element chemical analysis was performed on the concentrate separated by the magnetic separation and tailing-shaking table full particle size process. The results are shown in Table 2. It can be seen that the main gangue components in the concentrate are Al2O3 and MgO, and their total content is as high as 25.11%, which seriously affects the grade of the concentrate. The content of MgO in the raw ore is relatively high. After beneficiation, the content of MgO in the chromite concentrate is greatly reduced, indicating that most of the Mg exists in the chromite as a separate mineral and can be separated from the chromite after beneficiation. However, Al2O3 is enriched in large quantities in chromite concentrate, with an enrichment ratio as high as 5.8 (its content in raw ore is only 1.78%), indicating that Al element is likely to enter the chromite lattice and exist in the same phase as chromium element. It cannot be separated from chromium using mechanical methods.

6 Conclusion

6.1 The Cr2O3 content in a certain poor chromite ore is only 8.19%. After proper selection process, qualified products with a Cr2O3 content of more than 39% can be obtained, indicating that this poor chromite ore is optional.
6.2 Using the shaking table sorting process, the sorting indicators of yield 14.50%, grade 38.53%, and chromium recovery rate 67.40% can be obtained when the whole particle size is selected. When selected by particle classification, the selection indicators of yield 16.91%, grade 36.09%, and recovery rate 73.97% can be obtained. Comprehensive comparison, the selection index of the whole grain level is relatively better. The advantage of the full shaking table process is high sorting accuracy, but the disadvantage is that the processing volume is small, the number of equipment required is large, and the floor space is large.
6.3 The use of spiral chute and strong magnetic separation technology can remove more than 43% of the tailings in advance, creating conditions for shaker selection, while greatly reducing the number of shaker equipment and the floor space of the factory. Comparing the two, the strong magnetic separation tailings have a low grade and can be directly discarded as qualified tailings, while the spiral chute tailings have a relatively higher grade. The two types of tail throwing equipment have large processing capacity and reliable operation.
6.4 Use strong magnetic separation to remove tails – shaking table selection process
A chromium concentrate with a yield of 13.28%, a grade of 39.98%, and a recovery rate of 64.74% can be obtained. The SiO2 content in the concentrate is 4.07%. The spiral chute tailing-shaking table separation process can obtain indicators of concentrate grade 39.54%, yield 12.50%, chromium recovery rate 60.28%, and SiO2 content in the concentrate is 4.15%. The former has relatively better selection indicators.