With the development of China's steel industry, demand for iron ore is growing. Imported iron ore under the monopoly of the three major mining companies abroad, the price continues to push up, making the survival of China's steel companies very difficult, diversified imports will be the future development trend. The imported South African iron ore grade is relatively low and cannot be directly used for smelting. It needs to be processed by mineral processing to meet the demand of China's ironmaking process.

First, the nature of the ore

(1) Multi-element analysis of raw ore

The results of multi-element chemical analysis of an iron ore in South Africa are shown in Table 1.

Table 1 Multi-element chemical analysis results of ore

(II) Analysis of ore phase of iron ore

The iron phase analysis results of an iron ore in South Africa are shown in Table 2.

Table 2 Analysis results of ore phase of iron ore

It can be seen from Table 2 that the ore is mainly composed of magnetic iron minerals, and the content of other iron minerals is very low, and the magnetic separation can be selected by purification.

(3) Raw ore screening test

The results of the ore screening are shown in Table 3.

Table 3 Raw ore screening results

It can be seen from Table 3 that the ore particles are coarser and the content of +200 mesh accounts for 55.70%.

Second, the beneficiation test

(1) Direct magnetic separation test

1, 1 magnetic separation test

In the case of non-grinding, a GX-167 drum magnetic separator is used, the specification is φ327 mm×180 mm, and the magnetic field strength is 79.578 kA/m, and magnetic separation is performed to obtain a magnetic separation coarse concentrate once. The test results are shown in Table 4.

Table 4 Results of 1 magnetic separation test %

It can be seen from Table 4 that after one magnetic separation, the iron concentrate grade is only 63.56%, which cannot meet the requirements.

2, 2 times magnetic separation test

The magnetic separation of the primary concentrate was carried out for the second time, and the magnetic separation concentrate was obtained twice. The test results are shown in Table 5.

Table 5 Results of 2 times magnetic separation test %

It can be seen from Table 5 that after grinding for 2 times, the concentrate grade is 64.48%, which is obviously low. Considering that the ore size is coarser and the ore monomer is not sufficiently dissociated, it is necessary to carry out the grinding test.

(2) Grinding fineness test

1. Influence of grinding time on grinding fineness

The ore sample was taken 500g, and the XMQ-φ240mm×90mm cone ball mill was used . The grinding concentration was 70%, and the grinding time was 1, 2, 3, 5, 7 min, respectively. The effect of grinding time on the fineness of grinding was investigated. The test results are shown in Figure 1.

Figure 1 Relationship between grinding time and -200 mesh in grinding products

It can be seen from Fig. 1 that with the increase of grinding time, the fineness of grinding increases, the content of 2min -200 mesh reaches 70.54%, and the 7min -200 mesh reaches 96.94%.

2. Influence of grinding fineness on magnetic separation

The XCS-73 type φ50mm magnetic separation tube was used, and the magnetic field strength was 95.493kA/m. One section of open-circuit grinding was performed, and one magnetic separation was performed to investigate the influence of grinding fineness on the magnetic separation index. The test results are shown in Table 6.

Table 6 Magnetic separation tube test results under different grinding fineness

It can be seen from Table 6 that as the fineness of the grinding increases, the grade of the iron concentrate increases and the recovery rate gradually decreases. But the change in recovery rate is not very large. Grinding fineness - 200 mesh accounted for 70.54% and 79.04%, the iron concentrate grade has reached the requirements. Considering that as the grinding fineness increases, the energy consumption also increases, which is uneconomical in the industry. Therefore, the grinding time is 2 min, and the grinding fineness - 200 mesh accounts for 70.54%.

(3) Process test

Grinding was carried out by XMQ-φ240mm×90mm cone ball mill. The grinding fineness-200 mesh accounted for 70.54%. The GX-167 drum magnetic separator was used, and the magnetic field strength was 79.578 kA/m. The process is shown in Figure 2, and the test results are shown in Table 7.

Figure 2 Test procedure

Table 7 Process test results %

It can be seen from Table 7 that through the process test, the concentrate grade is 65.96% after two magnetic separations, the recovery rate is 98.30%, and the beneficiation index is better. The results of the final multi-element chemical analysis of concentrates are shown in Table 8.

Table 8 Results of multi-element chemical analysis of final concentrates %

It can be seen from Table 8 that the content of SiO ₂ , S and P in iron concentrate is low, and the grade of iron concentrate can meet the demand of ironmaking process in China.

(4) Magnetic separation test of raw ore-100 mesh products

As can be seen from Table 3, the ore-100 mesh fraction content reached 68.40%. In order to investigate the feasibility of pre-classification before ore grinding, a magnetic separation test was carried out on a magnetic separator with a magnetic field strength of 79.577 kA/m for a -100 mesh grade material. The test results are shown in Table 9.

Table 9 Magnetic ore test results of ore-100 mesh materials

It can be seen from Table 9 that after 2 times of magnetic separation of the ore-100 mesh material, the concentrate grade is 65.60%, and the recovery rate is 98.47%, which fully meets the requirements of pre-screening.

(5) Recommended process

According to the above test, the recommended process for the ore is shown in Figure 3.

Figure 3 Recommended Process

Third, the conclusion

An iron ore in South Africa passes through a section of grinding. When the grinding fineness -200 mesh accounts for 70.54%, after 2 magnetic separations, an iron concentrate with a yield of 88.46%, a grade of 65.96% and a recovery rate of 98.30% can be obtained. The silicon, sulfur and phosphorus in the concentrate are not exceeded, which can meet the needs of China's ironmaking process.

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