Chromium is an important strategic resource and an important raw material for the stainless steel industry. It is also widely used in refractory materials, chemicals and light industry. With the development of China’s national economy, the demand for chromite ore has grown rapidly. However, there is a serious shortage of chromite resources in China. The retained reserves are only 10.779 million tons (ores), and the rich ore accounts for only 1/2 of them. Most of them are distributed in Tibet, Xinjiang and other regions. They are difficult to use due to imperfect infrastructure. In recent years, more than 85% of the chromite ore needs in China each year have depended on imports, and the resource supply situation is very tight. Therefore, while strengthening the domestic geological prospecting of chromite resources, researches on sorting technology for chromite resources and improving resource utilization have attracted increasing attention of researchers.

At present, in the production practice of chromite ore separation, heavy separation methods such as shaking table and jigging are widely used, and there are also laboratory research reports on dry strong magnetic separation, wet strong magnetic separation, flotation and various chemical beneficiation methods. , But rarely used in production. In this paper, for a certain chromite ore with high iron content, the process of separating magnetite with weak magnetic separation and recovering chromite with strong magnetic separation is determined. While recovering chromite, comprehensive utilization of iron resources is realized.

1. Nature of

the ore The ore belongs to the type of seashore placer of high-iron chromite ore. The grade of Cr203 in the raw ore is 31.20%, and the grade of total iron (TFe) is 29.11%. The metal minerals in the ore are mainly chromite, chromium spinel and magnetite, followed by hematite and ilmenite; gangue minerals are mainly olivine, pyroxene and amphibole, followed by serpentine. The chromium mineral content is 60.3%, of which chromium spinel accounts for a larger proportion, and the mineral content ratio of chromite and chromium spinel is approximately 35:65. It is inferred that it is difficult to obtain high-grade chromium concentrate from the sample. The content of magnetite reaches 27.6%, and part of the magnetite belongs to the category of chromium magnetite because of its high content of Cr203. The composition analysis of the energy spectrum of the scanning electron microscope showed that the average content of Cr203 in the chromium mineral of the sample was 43.58%, and the average iron content of the magnetite was 60.66%.

The main particle size in the ore sample is 0.1～0.5mm, of which the yield of +0.5mm particle size is only about 0.3%, the yield of -0.1mm particle size is less than 3%, and the dissociation degrees of chromium mineral and magnetite are 93.7 respectively. % And 90.2%.

The ore chemical composition, chromium phase analysis and main mineral quality content analysis results

2. The experimental research

process mineralogy results show that the main component of the sample for beneficiation recovery is Cr203, and iron can be used as an object for comprehensive utilization. That is, the gangue minerals that need to be removed are mainly silicate minerals such as olivine, and the useful minerals chromite, chromium spinel and magnetite are separated. Compared with gangue minerals, magnetite, chromite and chromium spinel are denser, and some gangue minerals can be thrown away by gravity separation; magnetite is a strong magnetic mineral, and chromite is a weakly magnetic mineral. Weak magnetic separation can realize the separation of the two, the weak magnetic separation concentrate is iron concentrate, and the weak magnetic separation tailings are chromium coarse concentrate; the chromium coarse concentrate can be separated by strong magnetic separation to improve the chromium concentrate grade. It should be noted that because the mineral silicate gangue mineral content is less, and it is a non-magnetic mineral, it can also be separated from useful minerals during the magnetic separation process. Therefore, the gravity separation operation can be selected according to the separation effect. Sexual adoption.

(1)

Gravity separation test Gravity separation test examined the sorting effect of shaker, jig and chute on raw ore. The test results show that jig and chute operation has poor separation effect on the ore, and shaker sorting can remove Light minerals such as olivine and pyroxene can improve the grade of the concentrate to a certain extent. The grade of Cr203 of the raw ore can be increased from 31.04% to 33.68%, and the recovery rate is 84.47%. However, since the ore contains less low-density gangue minerals, the enrichment effect of the gravity separation operation on useful minerals is not obvious.

(2) Weak magnetic separation test

The weak magnetic separation process is shown in Figure 1. The weak magnetic separation test mainly examines the influence of factors such as the strength of the weak magnetic separation magnetic field, the selected particle size, and the roller speed of the magnetic separator on the separation effect.

1. In the weak magnetic separation magnetic field strength test,

the grinding particle size is -0.074mm, accounting for 62%, and the drum speed is 50r/min. The weak magnetic separation magnetic field strength test is carried out. The recovery rate is shown in Figure 2. It can be seen from Figure 2 that as the field strength increases, although the TFe grade of the iron concentrate does not change much, the recovery rate is significantly improved. At the same time, the Cr203 grade in the crude chromium concentrate has a certain increase. Therefore, it is determined that the weak magnetic separation field strength is 0.12T, and the TFe grade of the iron concentrate at this time is 55.38%.

2. Selected particle size test for weak magnetic field

In order to examine the effect of mineral dissociation on the separation of magnetite (Fe304) and chromite (Cr203), the particle size test was conducted under the conditions of magnetic field strength of 0.12T and drum speed of 50r/min. The separation of magnetite and chromite in the experiment is shown in Figure 3. The results in Figure 3 show that when the particle size of the material becomes finer, the Fe304 content in the iron concentrate and the Cr203 recovery rate in the chromium crude concentrate both decrease significantly. It shows that fine grinding of ore may cause mechanical entrainment during magnetic separation. Therefore, the ore sample does not need to be ground (-0.074mm particle size content is about 2%), and can be directly subjected to weak magnetic separation. At this time, an iron concentrate containing Fe304 69.24% can be obtained, and the Fe304 recovery rate during operation is 97.91%; For the crude chromium concentrate, the Cr203 content is 41.55%, and the operating recovery rate is 80.61%.

3. Weak magnetic separator roller speed test

When the magnetic field intensity is 0.12T, the magnetic separator roller speed test is carried out on the raw ore without grinding. The separation of magnetite and chromite in the test is shown in Figure 4. It can be seen from Figure 4 that as the roller speed increases, the Fe304 content in the iron concentrate increases slightly, but the grade of the crude chromium concentrate decreases. Therefore, the appropriate roller speed is determined to be 50r/min.

(3) In the strong magnetic separation test, when the

raw ore is directly separated by weak magnetic field, the strong magnetic magnetite enters the iron concentrate, while the weakly magnetic chromium-containing minerals and non-magnetic gangue minerals enter the tailings together. Both use strong magnetic separation. Separation, the test process is shown in Figure 5. The strong magnetic separation test is mainly aimed at the tailings of the raw ore directly without grinding, and the influence of factors such as selected particle size and magnetic field strength on the separation effect is examined.

1. In

order to examine the influence of mineral dissociation on the chromite index in the tailings of weak magnetic separation , a strong magnetic separation particle size test was carried out. The magnetic separation intensity in the test was 0.9T, and the test results are shown in Figure 6. . It can be seen from Figure 6 that the selected particle size of the strong magnetic separation has little effect on the Cr2O3 grade and recovery rate in the chromium concentrate, but the recovery rate will be reduced when the ore is too fine. Therefore, the weak magnetic separation tailings can be directly strengthened without grinding. magnetic separation.

2. Field strength test

of strong magnetic separation The test results of strong magnetic separation of tailings of weak magnetic separation under different field strengths are shown in Figure 7. It can be seen from Figure 7 that with the increase of the magnetic field strength, the recovery rate of chromite ore greatly increases; but after the field strength reaches 0.7T, the magnetic field strength continues to increase, and the grade of the chromium concentrate decreases. Comprehensive considerations determine the strong magnetic separation field strength It is 0.9T. At this time, the Cr2O3 grade in the chromium concentrate is 41.43%, and the operating recovery rate is 93.01%.

(4) Whole-process test

According to the above-mentioned test results, it is determined that the raw ore does not undergo grinding and gravity separation, but directly uses weak magnetic separation to recover magnetite and weak magnetic separation tailings to carry out the entire process of strong magnetic separation and recovery of chromite. The test process is shown in Figure 8, and the test results are shown in Table 4. It can be seen from Table 4 that using the weak magnetic separation-strong magnetic separation process, chromium concentrate and TFe grade with a Cr2O3 grade of 41.43% and a recovery rate of 79.31% can be obtained from a raw ore containing 31.23% Cr2O3 and 28.81% Fe. It is 55.89% of iron ore with a recovery rate of 58.71%.

3. Conclusion The

key to the separation of a high-iron chromite ore is to use the magnetic difference between chromite, magnetite and gangue minerals. A weak magnetic separation and a strong magnetic separation process can effectively separate the ore and realize the comprehensive utilization of chromite and magnetite. The raw ore does not need to be ground. When the magnetic field strength of the weak magnetic separation is 0.12T and the drum speed is 50r/min, magnetite with a TFe grade of 55.89% and a recovery rate of 58.71% can be obtained; With 0.9T strong magnetic separation, the grade of chromium concentrate Cr203 obtained is 41.43%, and the recovery rate is 79.31%.

Link to this article：Experiment on the separation of high-iron chromite by weak magnetic-strong magnetic technology

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