Study on Beneficiation Process of a Fine Grain Hematite

Our country is the world's red iron ore the most widely distributed, the largest reserves, one of the lowest grade hematite occupies a large proportion of the country's iron ore resources. Compared with magnetite, hematite has fine grain size, high mud content and difficult dressing . For a long time, domestic research on the ore dressing of complex and difficult to choose hematite has not been interrupted. After several generations of ore dressing workers' persistent efforts, China's hematite ore dressing technology has made great progress, and gradually formed a hematite beneficiation process with Chinese characteristics. At present, the most common typical beneficiation process for treating hematite is stage grinding or continuous grinding, coarse subdivision, re-election-weak magnetic separation-high gradient magnetic separation-anion reverse flotation process, continuous grinding, weak magnetic Selective-strong magnetic separation-anion reverse flotation process, roasting, stage grinding-high efficiency magnetic separation-cation reverse flotation process.

Based on the ore dressing practice of China's hematite, this study carried out a different ore dressing process test on a fine-grained hematite, and obtained a good index of iron concentrate grade 65.45% and iron recovery rate of 79.84%. The iron ore has certain reference significance.

First, the nature of the ore

(1) Multi-element analysis of raw ore chemistry and analysis of iron phase

The results of multi-element analysis and iron phase analysis of ore minerals are shown in Table 1, Table 2.

Table 1 Results of multi-element analysis of ore chemistry

Table 2 Results of ore phase analysis

As can be seen from Tables 1 and 2, the test ore has the following characteristics:

1. The main component for ore recovery in ore is iron. The iron grade is 36.56%, and there are no other recoverable valuable elements.

2. The slag-forming components that need to be removed by beneficiation are mainly SiO ₂ , and the harmful impurities such as phosphorus and sulfur are very low, which has little effect on the quality of iron concentrate. The ore has a basicity coefficient W(CaO+MgO) / w (SiO ₂ +A1 ₂ O ₃ ) of 0.18, which is a typical acid ore.

3. The ratio of ore W (TFe) to W (FeO) is 20.09, indicating that the ore is deeply oxidized and belongs to oxidized iron ore.

4. The state of occurrence of iron is not the same. The distribution of iron in magnetite, hematite and imaginary hematite accounts for more than 95% and is less distributed among other minerals.

(II) Particle size distribution characteristics of iron minerals

The grain size composition and distribution characteristics of iron minerals in the ore have a direct impact on determining the reasonable grinding size and beneficiation process. In order to ascertain the particle size distribution characteristics of iron minerals in the test ore samples, the embedding grain size of iron minerals was counted under the microscope, and the statistical results are shown in Table 3.

Table 3 Iron ore mineralization in the ore

It can be seen from Table 3 that in order to achieve a monomer dissociation degree of iron minerals of more than 90%, it must be finely ground to -0.043 mm to account for more than 90%. This indicates that the ore has the characteristics of fine-grained inlays. In order to obtain the ideal beneficiation index, it is necessary to pay attention to the grinding and grading process, so as to reduce the muddy reaction caused by over-crushing while achieving the better monomer dissociation of iron minerals. The impact of subsequent sorting operations.

Second, the test plan

For the nature of the ore, the following test plan was developed.

Scheme 1: Stage grinding, re-selection, weak magnetic separation, high gradient, strong magnetic separation, and reverse flotation. The scheme considers the characteristics of uneven size of iron mineral inlays, and re-selects the dissociated coarse-grained iron minerals in the relatively coarse grinding fineness to reduce the fine grinding amount and iron minerals. Mud. At present, China's Anshan District Concentrator and Hebei Sijiaying Concentrator have adopted a spiral chute to re-select a magnetic separation and flotation process. The advantage of this process is to obtain some high-grade concentrates preferentially, to achieve partial early harvest, and save certain The grinding cost, but the disadvantage is that the process is relatively complicated. At the same time, some high-quality iron minerals are recovered through re-election, resulting in lower flotation grade, which brings great difficulties to subsequent flotation operations.

Scheme 2: Stage grinding, weak magnetic separation, high gradient, strong magnetic separation, and reverse flotation. At present, the domestic treatment of hematite and limonite is generally adopted. The characteristic is that the raw ore firstly removes some of the dissociated low-grade gangue minerals by strong magnetic separation under the condition of coarse grinding fineness to reduce the grinding amount of the fine grinding; the magnetic separation coarse concentrate is fine Grinding, the iron minerals and gangue minerals obtain higher monomer dissociation degree, and finally the reverse flotation operation eliminates impurities, and achieves the purpose of improving the iron concentrate grade.

Third, the test results

(1) Test results of Option 1

1. Scheme 1 reselection test

The spiral chute is used to explore the conditions such as grinding fineness, sorting concentration and process structure. Finally, under the condition of grinding grain size of -0.076mm, 85%, and ore concentration of 12%, the ore is processed according to the flow of Figure 1. Perform a reselection test. The test results show that the raw ore can be selected by a spiral chute, and a part of the iron ore grade is 64.35%. The yield is 13.70% and the iron recovery rate is 24.31%.

Figure 1 Scheme 1 reselection test process

2. Scheme 1 magnetic separation test

Weak magnetic separation-strong magnetic separation for re-election of tailings. SLon vertical ring pulsating high gradient magnetic separator has the advantages of good deliming effect, high grade of working concentrate and good tailing effect, which can create good conditions for reducing flotation operation and obtaining high quality iron concentrate. To this end, the SLon type high gradient magnetic machine was selected as the strong magnetic separation device . On the basis of the magnetic field strength condition test, the magnetic separation test was carried out according to the flow of Fig. 2, and the test results are shown in Table 4.

Figure 2 Magnetic separation test procedure

Table 4 Results of the magnetic separation test of Scheme 1

3. Scheme 1 reverse flotation test

A qualified concentrate is obtained by reverse flotation of the magnetic separation concentrate. Due to the fine grain size of the iron mineral in the ore, the magnetic concentrate should be reground in order to meet the requirements of the final concentrate. The flotation temperature was controlled at 30 ° C, and the reverse flotation regrind test was carried out according to the flow and the chemical conditions of Fig. 3. The test results are shown in Fig. 4.

Figure 3 Reverse flotation regrind test procedure

Figure 4 Scheme 1 reverse flotation regrind test results

â– -iron recovery rate; â—†-iron grade

Can be seen from Figure 4. As the regrind becomes finer. The grade of concentrate iron is gradually increased. To achieve a grade of more than 65% of the concentrate iron grade, the regrind must be -0.043 mm to account for 95%. Therefore, it was confirmed that the regrind fineness was -0.043 mm, accounting for 95%.

Under the re-grinding degree of -0.043 mm and 95%, the reverse flotation reagent system test and the open circuit test were carried out. On this basis, the reverse flotation closed-circuit test is carried out according to the flow of Figure 5. The test results are shown in Table 5.

Figure 5 Reverse flotation closed circuit test procedure

Table 5 Scheme 1 reverse flotation closed circuit test results

Table 5 shows that after the re-selection of the magnetic separation concentrate of the tailings to 95% of -0.043mm, the iron grade can be increased from 47.81% to 65.15% by a coarse and fine three-sweeping flotation. The rate is 85.82%.

4, program 1 full process test

On the basis of the above tests, a full-flow test of phase grinding, re-selection, weak magnetic separation, high gradient, strong magnetic separation and reverse flotation was carried out. The test procedure is shown in Figure 6, and the test results are shown in Table 6.

Table 6 Test results of the whole process of Scheme 1

Figure 6 Scheme 1 test procedure

It can be seen from Table 6 that the ore is subjected to stage grinding, one re-selection, one weak magnetic separation, one high-gradient magnetic separation and one reverse flotation process, and the obtained iron concentrate iron grade is 64.88%, and the iron recovery rate is 79.91%. .

(2) Test results of program 2

1. Scheme 2 magnetic separation test

The SLon type high gradient magnetic machine is still used as the strong magnetic separation equipment. According to the same test procedure as in Fig. 2, the ore after the grinding is directly subjected to weak magnetic washing and strong magnetic separation.

Through conditional tests, it is determined that the grinding fineness is -0.076mm, which is 85%, the weak magnetic separation magnetic field strength is 159kA/m, the strong magnetic rough selection magnetic field strength is 637kA/m, and the strong magnetic sweeping magnetic field strength is 796kA/m. Under this condition, the obtained magnetic separation coarse concentrate yield was 65.50%, the iron grade was 50.68%, and the iron recovery was 91.43%.

2. Scheme 2 reverse flotation test

According to the same procedure as in Figure 3, at the flotation temperature of 30 ° C, the NaOH rough selection and the selected amount are 1.0 kg / t and 0.3 kg / t, the starch dosage is 1.2 kg / t, and the CaO dosage is 0.6 kg / t. Under the conditions of 0.6 kg/t and 0.4 kg/t of collector MZ, the coarse ore concentrate obtained by direct magnetic separation of raw ore is subjected to reverse flotation and regrind test. The results are shown in Figure 7.

Figure 7 Magnetic-floating process reverse flotation grinding particle size test results

It can be seen from Fig. 7 that as the fineness of regrind becomes finer, the grade of concentrate iron gradually increases. When the regrind fineness is -0.043mm, accounting for 90%, the concentrate grade is close to 66%. Therefore, scheme 2 The regrind fineness is -0.043mm, accounting for 90%.

Under the condition of -0.043 mm and 90% regrind, the crude flotation obtained by direct magnetic separation of raw ore was subjected to reverse flotation closed-circuit test by the same chemical structure and chemical system as in Figure 5. The results are shown in Table 7.

Table 7 Scheme 2 reverse flotation closed circuit test results%

Table 7 shows that after the crude ore obtained by direct magnetic separation of ore is re-ground to -0.043mm and 90%, the iron grade can be increased from 50.68% to 65.45% by a coarse-precision three-sweep reverse flotation. The recovery rate of reverse flotation operation It is 87.31%.

3, program 2 full process test

On the basis of the above tests, a full-flow test of stage grinding, weak magnetic separation, high gradient, strong magnetic separation and reverse flotation was carried out. The test procedure is shown in Figure 8, and the test results are shown in Table 8.

Figure 8 Scheme 2 test procedure

Table 8 Scheme 2 full process test results%

It can be seen from Table 8 that the raw ore is selected by the scheme 2 stage grinding, weak magnetic separation, high gradient strong magnetic separation and reverse flotation process, and the obtained iron concentrate iron grade reaches 65.45%, and the iron recovery rate is 79.84%. The indicator is better than option 1. According to the analysis, the index of the scheme 1 is worse than that of the scheme 2, because some of the coarse-grained iron minerals have entered the re-election concentrate, resulting in a low level of reverse flotation, which affects the quality of the reverse flotation concentrate.

Compared with the two schemes, the scheme 2 selection index is better, and the process structure is relatively simple and the regrind is relatively coarse. Therefore, the scheme 2, namely, stage grinding, weak magnetic separation, high gradient, strong magnetic separation and reverse flotation process is more reasonable.

Fourth, the conclusion

(1) Process mineralogical research shows that the test ore belongs to the fine-grained quartz -type oxidized ore, which must be finely ground to achieve monomer dissociation; the main useful minerals in the ore are magnetite, hematite, gangue minerals and quartz. Mainly.

(2) The test proves that the pulsating high gradient magnetic separation not only improves the grade of the flotation material, but also removes a large amount of necessary ore and slime, and improves the flotation conditions, which is the key to obtaining good mineral processing index.

(III) Stage grinding-weak magnetic separation-high gradient strong magnetic separation-reverse flotation process The test index is concentrate concentration 44.28%, iron grade 65.45%, grade 64.88%, recovery rate 79.91%. Considering the selection index, process structure and grinding cost, it is recommended to adopt the stage grinding-weak magnetic separation-high gradient strong magnetic separation-reverse flotation process.

(Iv) iron ore minerals fine grain size, only finely ground so that it can more fully monomer dissociation; but would cause excessive finely ground ore mud, thereby increasing the difficulty of sorting, recovery of losses caused by metal. Therefore, it is necessary to strengthen the grinding and grading process to avoid over-grinding.

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