The beneficiation of ilmenite involves two processes: typically, iron is first extracted, followed by the selection of titanium from the iron tailings. Various methods, including gravity separation, magnetic separation, electrostatic separation, and flotation, are employed for titanium selection. In this case, the TiO2 grade in the iron tailings is low, with a high content of gangue minerals, making it unfavorable for flotation recovery. Hence, a strong magnetic pre-selection of titanium is introduced before flotation, resulting in the final beneficiation process: weak magnetic separation - strong magnetic pre-selection - flotation process.
The primary metallic minerals in the original ore are ilmenite, magnetite, and small amounts of hematite and goethite. Key gangue minerals include augite, feldspar, garnet, with minor quartz and mica.
The particle size of the ilmenite ore sample ranges mainly between 0.178 mm and 0.056 mm, with a relatively even distribution. The overall granularity is fine, with a low content of coarse and extremely fine mineral particles and low clay content.
Due to the intimate association of ilmenite and magnetite, with a poor dissociation degree, grinding is necessary to achieve the individual dissociation of target minerals. It is essential to avoid excessive comminution to prevent material and energy losses.
Grinding fineness experiments revealed that a fineness of -200 mesh, accounting for 85%, provides a balance between increasing the grade of magnetic iron in the concentrate and minimizing the loss in recovery rates for titanium dioxide.
Iron, mainly present as magnetic iron, needs to be weakly magnetically separated before the selection of titanium. During strong magnetic separation, magnetic iron tends to aggregate, forming clusters and magnetic chains that encapsulate iron minerals, preventing the settling of iron in ilmenite. Therefore, weak magnetic iron selection is performed before ilmenite selection.
Through beneficiation experiments, it was found that a magnetic field intensity of 77.10 kA/m yields favorable indicators for the grade and recovery rate of magnetic iron in the iron concentrate, meeting the national standards for iron concentrate. Additionally, the recovery rate of titanium dioxide in the magnetic separation tailings is high, indicating that this magnetic field intensity is conducive to subsequent operations.
In this case, the titanium content in the iron tailings is low, and the gangue mineral content is high, hindering effective flotation recovery of ilmenite. Therefore, a magnetic pre-selection is carried out, utilizing a strong magnetic selection process due to the weak magnetic nature of ilmenite.
Through beneficiation experiments, the magnetic field intensity for strong magnetic pre-selection of titanium was determined to be 378.12 kA/m. At this intensity, the indicators for TiO2 grade and recovery rate in the titanium rough concentrate are satisfactory.
The advantage of using strong magnetic selection for titanium is that it effectively discards a significant amount of gangue minerals, allowing for the pre-enrichment of ilmenite before flotation. This reduces the feed quantity for flotation operations, consequently lowering flotation costs.
The titanium rough concentrate obtained from high-gradient magnetic separation is used as the input for flotation operations. The dosage of flotation reagents is determined through beneficiation experiments, and after one roughing, two cleaning, and one scavenging operation, the total TiO2 recovery rate reaches 93.99%, with a titanium concentrate grade of 48.15%.
In addition to open circuit flotation, a closed circuit test is conducted with one roughing, two cleaning, one scavenging, and the return of middlings in sequence. The resulting titanium concentrate has a grade of 47.74%, with a TiO2 recovery rate of 79.28%.
Through this case study, it is evident that when the TiO2 grade in the iron tailings is low, and the gangue mineral content is high, the introduction of strong magnetic pre-selection before flotation is beneficial. This process allows for the pre-enrichment of titanium, effectively removing a significant amount of gangue minerals before flotation, positively impacting the final flotation results.
