The vast majority of limonite in nature exists in the form of 2Fe2O3 · 3H2O, in the form of amorphous, cryptocrystalline, or colloidal form. Its exterior color is yellow brown, dark brown to brownish black, and weakly to moderately magnetic. Limonite has very few rich ores, with lower iron content than magnetite and hematite, and most of them contain a large amount of slime, which cannot be directly used for smelting without beneficiation, making it a difficult to select ore. However, with the increasing demand for steel and rising prices in the market, research on the selection of limonite has become increasingly important. At present, the main beneficiation processes for limonite include:
① single gravity separation process, which results in low iron recovery rate and serious resource waste due to large changes in limonite mineral density.
② The single wet high intensity magnetic separation process has poor separation effect on fine-grained ore slime The single flotation process, including positive flotation and reverse flotation, focuses on the impact of fine-grained ore slime. ④ Selective flocculation flotation utilizes starch, humic acid salts, etc. to selectively flocculate limonite, and then removes silicate minerals through desliming or reverse flotation. With the development of research on the beneficiation process of Jieshan Iron Mine, numerous types of combined processes have emerged, including high magnetic separation positive flotation high magnetic separation process, high magnetic separation amine reverse flotation process, reduction roasting magnetic separation leaching process, etc. Based on the characteristics of a certain area’s limonite ore, an iron concentrate with a grade of 54.12% and a recovery rate of 62.16% was obtained using an enhanced dispersion strong magnetic separation process.
1、 Ore properties
The mineralogical analysis of the ore sample process shows that the iron containing minerals in the raw ore are mainly limonite and hematite; The main gangue minerals are kaolinite, illite, as well as a small amount of calcite and calcium magnesium minerals. The results of multi-element chemical analysis and cast iron phase analysis of the ore.
2、 Selection Scheme Test
（1） Re-selection process test
There is a significant difference in density and hardness between silicate minerals and iron containing minerals in the raw ore, which requires good gravity separation conditions. Therefore, gravity separation experiments were conducted. Grind the raw ore to 75%~0.074mm and use a slot shaker for sorting. Adjust the conditions such as stroke, impact rate, bed inclination angle, water volume, and ore feeding rate. The experimental results show that the iron concentrate grade and recovery rate obtained by the gravity separation process are low, indicating that it is difficult to achieve good sorting indicators after gravity separation. The reason is that after grinding the raw ore, the particle size of iron minerals is severely polarized, and some fine-grained iron minerals are lost in the tailings.
（2） Single flotation test
The siliceous minerals in the raw ore are mainly difficult to float kaolinite and illite, which are prone to mud and have a significant impact on subsequent flotation. Therefore, they need to be pre screened and removed. This experiment has developed pre screening grinding cation reverse flotation and pre screening grinding anion positive flotation processes.
The experimental results show that the pre screening grinding anionic positive flotation process yields higher grade iron concentrate. The test results are shown in Table 4, and the process is shown in Figures 1 and 2.
It can be seen that the consumption of anionic and cationic collectors in both processes is high, which fully indicates that the ore is prone to mud formation. After pre screening and desliming, some of the ore mud still enters the flotation operation, increasing the consumption of reagents. Comparatively speaking, the pre screening grinding anionic positive flotation test has achieved ideal indicators, but its process is complex, the consumption of reagents is too high, the iron recovery rate is low, and the loss of fine iron ore through pre screening is severe with the slime. However, the cationic agent dodecylamine has poor collection ability and sorting ability, and cannot effectively separate silicate minerals, possibly due to the influence of ore mud. In summary, the experimental results indicate that a single flotation scheme is difficult to obtain ideal comprehensive indicators.
（3） Selective flocculation test
In order to reduce the impact of silicate mud on subsequent experiments and examine the feasibility of the flocculation and desliming process, selective flocculation experiments were conducted. By preliminarily determining the grinding fineness and sodium carbonate dosage, changing the dosage of water glass and PD one by one, the optimal conditions for the desliming test were ultimately determined. The best test results are shown in Table 5, and the best process conditions
The grinding fineness ranges from 75% to 0.074mm. When 3000 g/t sodium carbonate and 2000 g/t sodium silicate are added during the grinding process, the slurry can be well dispersed. According to existing research literature, the zero point of limonite is basically around 6, while the zero point of silicate minerals is between 2-4. When the pH value is between 4-6, there will be a phenomenon of anomalous condensation between limonite and gangue minerals. When 3000 g/t of sodium carbonate is added, the pH value of the slurry can be adjusted to between 8.5 and 10, resulting in negative charges on the surfaces of different minerals and good dispersion. PD is an anionic starch that preferentially adsorbs on the surface of malleable cast iron with relatively lower negative charge in the slurry to form selective flocs, thus achieving the purpose of separating iron minerals. However, from Table 5, it can be seen that using selective flocculation is still difficult to significantly improve the grade of concentrate iron, only increasing by about 3 percentage points.
（4） Selective Flocculation Strong Magnetic Separation Process Test
Under the conditions of grinding fineness of 75%~0.074mm, sodium carbonate of 3000g/t, water glass of 2000g/t, and PD flocculant of 200g/t, selective flocculation strong magnetic separation coarse selection strong magnetic separation selection and selective flocculation strong magnetic separation reverse flotation test plans have been formulated. It can be seen that a single strong magnetic separation process is significantly better than the combined process of strong magnetic separation flotation. After flocculation and desliming, the raw ore undergoes one strong magnetic separation coarse selection (1.5T) and one strong magnetic separation fine selection (0.9T), An iron concentrate with a grade of 53.43% and a recovery rate of 66.99% can be obtained. The enrichment efficiency and recovery rate of high intensity magnetic separation are much better than flotation, indicating that there is a significant magnetic difference between useful minerals and gangue minerals in iron ore. High intensity magnetic separation is an effective method for separating the two. In the selective flocculation strong magnetic separation reverse flotation experiment, 1231 showed better sorting performance than dodecylamine, but still failed to obtain ideal sorting indicators, indicating that even after desliming, the useful minerals (iron minerals) were difficult to enrich and separate during cationic reverse flotation. The iron ore is embedded with fine particle size and difficult to dissociate. HSiO3- and HSiO3 formed by the hydrolysis of water glass added during the selective flocculation process adsorb on the surface of the ore mud, making it hydrophilic and inhibited. These reasons may have led to poor sorting of the cationic reverse flotation process. Therefore, for this type of limonite, using a single high intensity magnetic separation should be the most effective method.
（5） Enhanced dispersion strong magnetic separation process test
The above experimental results indicate that a single magnetic separation scheme has significant advantages. In order to further investigate the impact of desliming factors on single high intensity magnetic separation, experiments were conducted on the processes of non desliming, enhanced dispersion, and high intensity magnetic separation.
The experimental results have shown that by high strength small powder metallurgy gears slurry dispersion without desliming, ideal indicators can still be obtained for high intensity magnetic separation. Therefore, the enhanced slurry dispersion high intensity magnetic separation scheme has been further optimized. The experimental results are shown in Table 7, and the experimental processes are shown in Figure 7 and Figure 8, respectively.
Through optimization experiments, the optimal grinding fineness is determined to be 85%~0.074mm, the magnetic separation feed concentration is 20%, and the process structure is one rough selection, one sweeping selection, and two cleaning. The experiment obtained good indicators such as concentrate grade of 54.12% and iron recovery rate of 62.16%. Based on the above experimental results, the optimal process for the experimental treatment of limonite is the enhanced dispersion strong magnetic separation process.
（1） The useful minerals of this iron ore are limonite and hematite, while the gangue minerals are silicate minerals such as kaolinite, which are difficult to select. There are significant magnetic differences between useful minerals and gangue minerals in the ore, and ideal separation indicators can be obtained through strong magnetic separation methods.
（2） When the fineness of the raw ore grinding is between 85% and 0.074mm, sodium carbonate and water glass dispersed slurry are used, and a high intensity magnetic separation process is adopted, including one rough separation (H=1.25 T), one sweeping separation (H=1.25 T), and two cleaning (H=1.0 T). Finally, an iron concentrate with an iron grade of 54.12% and a recovery rate of 62.16% can be obtained, with good separation indicators.
（3） Adding sodium carbonate and water glass dispersants to enhance slurry dispersion during the raw ore grinding process is a key technology to improve the efficiency of high intensity magnetic separation.
Link to this article：Processing Techniques for a Certain Limonite Ore Dressing
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