Technical experiments and technological transformation plans for super iron concentrates

With the development of the steel industry and chemical industry, the uses of super iron concentrate are becoming more and more extensive. Research and development of super iron concentrate have become another development direction for mining enterprises and various research departments. Super iron concentrate generally refers to iron concentrate with TF e≥71% and SiO2≤1.5%. It is not only a deep-processing product of mineral processing, but also a new functional material with great development potential.

It is mainly used for powder metallurgy and production metallization. It has huge application value and market potential in the fields of pellets, magnetic materials, chemical industry, environmental protection, food preservation and sewage treatment. Up to now, domestic powder metallurgy, magnetic materials and other industries mainly rely on iron scale as raw materials. Because iron scale has unstable performance, complex chemical composition and limited supply, it is difficult to meet the demand for high-end powder metallurgy products. Due to its large production scale, stable composition and low harmful impurities, super iron concentrate is used as raw material in many developed countries to produce powder metallurgy products and magnetic materials. With the continuous development of my country’s high-tech industry, the demand for high-grade reduced iron powder and ferrite will also increase.
Super iron ore concentrate powder is high-purity magnetite powder metallurgy obtained by fully purifying ordinary iron ore concentrate powder. Both magnetite and hematite in iron ore can effectively extract super iron concentrate. Generally, the ore dressing process and method are determined based on the gangue type, embedded particle size and symbiotic relationship with iron minerals of ordinary concentrates in the ore dressing plant. The main beneficiation methods include: flotation, magnetic separation, electric separation and fine screening. Production technology can use the original equipment of mining enterprises to upgrade their products through transformation and expansion, thereby increasing the economic value of the products.
The process flow of the main plant of the mineral processing plant of Banshi Mining Company is “stage grinding, stage separation, fine screening and self-circulation process”. The grinding plant and filtering plant of the mineral processing plant are about 200 meters apart. The grinding concentrate flows into the filtering plant through pipelines. After concentration and magnetic separation, it enters the filter for dehydration. The grinding and separation workshop uses a magnetic separation column as the final check to ensure that the concentrate grade is above 67%. In the actual production process, because the magnetic separation column can effectively reduce undissociated particles from entering the concentrate, more than 68% of the concentrate is often produced, and even more than 69% of the concentrate may occur.
1. Sample overview
The iron concentrate produced by the concentrator is magnetite, with a concentrate grade of 67.63%, a main impurity SiO2 content of 4.05%, a relatively low S and P content, and a fineness of -200 mesh (-0.074mm) accounting for 87%. Analyzed under a microscope, the iron-containing minerals include magnetite minerals and a small amount of hematite. The undissociated iron minerals are mostly euhedral and semi-euhedral crystals embedded in the gangue. Magnetite is mainly associated with Quartz grows continuously, and larger particles are often wrapped in quartz. There are also a very small amount of magnetite wrapped in small gangues. Magnet minerals are mainly disseminated structures with fewer veins. The complete chemical analysis of iron concentrate is shown in Table 1.

2. Determination of test plan
According to the workshop space and actual layout of the concentrator, the concentrator only separates a part of the concentrate in the filtration plant for purification by adding screening and magnetic separation processes, and the concentrate is regrinded, reseparated, or flotation. It is difficult to achieve for mineral cnc machining plants. Therefore, the entire test plan only considers the method of combining screening and weak magnetism to purify the concentrate.
3. Test methods
In order to further clarify the composition and binding state of the test concentrate, it is judged whether the concentrate grade can be improved through magnetic separation under the existing particle size. First, a magnetic separation tube was used to conduct a low-field magnetic separation test on the sample. The test results are shown in Table 2. It can be seen from the test results that the concentrate grade cannot reach the target grade through magnetic separation method under the existing particle size.

(1) Fineness test under sieve
In order to further improve the grade of the concentrate, the concentrate is improved to the target grade through screening and magnetic separation processes without regrinding. Screening tests were conducted using 200-mesh, 300-mesh, and 400-mesh inspection sieves. The grades of iron ore in the upper and lower sieve grades are shown in Table 3.

It can be seen from the sieving test results that as the particle size under the sieve gradually becomes finer, the grade of the concentrate under the sieve also increases significantly. When observed under a microscope, the basic monomers of the ore particles under the sieve are dissociated.
(2) Magnetic separation tests under different conditions
In order to further reduce the impurity SiO2 content and improve the iron grade, low-field magnetic separation tests were conducted on three products under the screen. The test results are shown in Table 4. It can be seen from the test results that low field strength magnetic separation improves the grade by about 0.5% on average, and the field strength has little impact on the grade. Through the above tests, it can be determined that when the particle size under the sieve reaches below -400 mesh, the concentrate grade can meet the requirements of super iron concentrate, and the concentrate grade can be increased by about 0.5% through magnetic separation. Therefore, the best test conditions are for the particle size under the sieve to reach -400 mesh, and then conduct magnetic separation to improve the concentrate grade.

4. Proposed transformation plan
(1) Proposal of plan
Based on the analysis of multi-condition test results and the actual situation of the mineral cnc machining plant, it is believed that a diverter valve can be added to the ore feeding part of the concentrated magnetic separation to divert a small part of the concentrate for purification, and a Derrck high-frequency fine screen and a magnetic field can be added to the filtration plant. Select the column and enter the concentrate pool on the screen. Since the grade is still around 65%, you can use a pump to directly return to the concentrated magnetic separation and mix it with the ordinary concentrate. Since its amount is relatively small and has little impact on the grade of ordinary concentrate, it can still be used. To ensure that the concentrate grade of the ordinary concentrate is above 67%, it is fed into the magnetic separation column under the screen. The magnetic separation column concentrate enters the filtration system as the final super concentrate. The medium ore is returned to the concentrate pool and mixed with the concentrate on the screen to return to the concentrated magnetic select. The proposed transformation process flow is as follows:

(2) Equipment selection
Among fine particle classification equipment, the Derrck high-frequency fine screen and its 0.05mm polyester screen produced by the American company Derrck have achieved good classification results in applications in other mines at home and abroad, and can effectively control the screen size. The particle size -0.038mm reaches more than 90%. Therefore, it is strongly recommended to use Derrck high-frequency fine screen as a classification equipment for ultra-fine particles.
Among weak magnetic separation equipment, conventional magnetic separation equipment (cylindrical magnetic separator) has a strong “magnetic agglomeration” effect on the magnetite separation process due to its large magnetic field force. Magnetic agglomeration reduces the selectivity of the magnetic separation process and produces “magnetic inclusions” and “non-magnetic inclusions”. Magnetic inclusions cause conjoined bodies to enter the magnetic separation concentrate, while non-magnetic inclusions cause single gangue to enter the magnetic separation concentrate. Therefore, it is difficult to obtain high-grade magnetite concentrate using a single magnetic separation method. The magnetic separation column is an electromagnetic low-magnetic field and high-efficiency magnetic gravity separation equipment that can fully disperse magnetic agglomeration and make full use of magnetic agglomeration. In the Anshan Design and Research Institute’s test of using a magnetic separation column to purify super iron concentrate, more than 72% of super iron concentrate was effectively produced through reasonable control of the ascending water flow, magnetic field strength, magnetic field conversion period and ore discharge valve size of the magnetic separation column. mine. Magnetic separation column is the best separation equipment for magnetite purification of super iron concentrate. ​
There are five filters in the filtration plant, two are currently used for production and three are in reserve. The transformation process can use a spare filter, which not only saves investment costs but also makes full use of existing equipment without affecting existing production.
5. Conclusion
(1) Magnetite in raw iron concentrate is mainly composed of fine-grained disseminated structures, which are fine-grained and embedded. Its crystal structure is complete. Fine-grained useful minerals and gangue minerals can easily achieve complete dissociation. After separation, The final magnetic particles are relatively pure and are ideal magnetic raw materials.
(2) Due to the limitations of the mineral processing process and the location of the plant, the test can only use screening and magnetic separation processes for purification without adding additional grinding equipment.
(3) After the raw concentrate is screened, the -400 mesh grade can reach the required grade of super iron concentrate, and then part of the medium ore is thrown out through a magnetic separation column with better magnetic separation effect to obtain TFe71.76 %, SiO2 ≤ 0.50% super iron concentrate, while ensuring that the grade of ordinary concentrate is above 67%, with no tailings thrown out and no metal loss.
(4) The key to this process is to select the classification particle size. In order to meet the classification needs, the Derrck high-frequency fine screen with good fine-grained screening effect is used for screening and the magnetic separation column with good magnetic separation effect is used for selection.
(5) The proposed transformation plan is formulated based on the actual conditions of the concentrator and avoids improving the concentrate grade through grinding and flotation processes.
(6) This solution is easy to modify and basically does not affect the existing production process. The new equipment quoted has the advantages of advanced technology, low energy consumption, and large improvement in concentrate grade.
references:
(1) Zhang Jinrui On the research status and direction of super iron ore (M) Mining and Metallurgical Engineering 2000-12.