Research and development of a common process for beneficiation and smelting of a certain high-phosphorus limonite ore in Yunnan

With the rapid development of my country’s steel industry, domestic iron ore resources are becoming increasingly scarce, and the available iron ore resources are becoming increasingly poor, fine, and miscellaneous. In order to improve my country’s self-sufficiency rate in iron ore resources and ease the pressure on imported iron ore, it is necessary to research, develop and utilize a large amount of refractory iron ore. The content of harmful impurities such as sulfur, phosphorus, and silica in my country’s iron ore resources is high. The impurities are closely symbiotic with useful iron minerals, which makes it difficult to remove impurities from iron concentrates. Phosphorus is one of the main harmful elements in the steel smelting process, which seriously affects the carbon steel making process and the quality of steel products. With the development of the metallurgical industry and the implementation of new processes, the quality requirements for iron concentrates are getting higher and higher, and the phosphorus content is also strictly limited. Therefore, it is urgent to efficiently reduce phosphorus in iron concentrates [1-3].
At present, at home and abroad, strong magnetic separation-positive flotation, weak magnetic separation-strong magnetic separation-positive flotation, classification-gravity separation-fine-grained flotation, and flocculation-are used for the beneficiation of difficult-to-select low-grade and high-impurity limonite. Strong magnetic separation, reverse flotation-roasting-weak magnetic separation, roasting-weak magnetic separation-reverse flotation and other combined processes [4].
A certain limonite ore in Yunnan has good resources, complex particle size distribution of iron minerals, high phosphorus content, and serious muddying phenomenon. It is a difficult-to-select ore and has not been developed for a long time. In order to develop and utilize mineral resources and improve the company’s self-sufficiency rate in mineral resources, the company entrusted Kunming University of Science and Technology to conduct a trial study on the selection and smelting of the ore. After a series of exploratory experimental studies, it was found that the iron grade of the concentrate obtained by using conventional single strong magnetic separation, gravity separation and flotation methods is difficult to reach more than 48%, but the phosphorus content is more than 0.8%. In view of this situation, the combined process of reverse flotation – magnetization reduction roasting – ultrafine grinding and magnetic flocculation was studied, and finally an iron concentrate with an iron grade of 69.57% and a recovery rate of 71.62% was obtained, which contained 0.29% phosphorus. , containing 0.17% sulfur and 5.75% silicon, achieving satisfactory technical indicators.
1. Research on ore process mineralogy
An iron ore in Yunnan is a large-scale iron ore deposit with complex characteristics that is multi-stage, multi-factor and multi-type superimposed. The geological reserves reach 1.994 billion tons and are mainly divided into two categories: primary ore and oxidized ore. Oxidized ore is distributed in the open-pit ore body, accounting for 16% of the total reserves. The mineral component of the oxidized ore is mainly limonite, with a molecular formula of 2Fe2O3·3H2O and a content of approximately 70%. Limonite in the ore is usually a multi-mineral aggregate, consisting of goethite, lepidocrocite, hydrogoethite, hydrolepidocrocite, as well as water-containing silica, mud and other mechanical mixtures. Limonite is often embedded in quartz in the form of irregular granular, reticulated, and colloidal shapes. Since most of the individual minerals have small particle sizes, most of them are disseminated with each other and are difficult to distinguish; the gangue minerals are mainly quartz and chlorite. , followed by collophosphate and montmorillonite. The particle size of limonite is generally 0.004~0.15mm, with the minimum being 0.002mm. There are two types of limonite in this ore. One is sedimentary limonite, which is formed during the formation of sedimentary rocks. It is often distributed between quartz debris in the form of cement, and is often mixed with fine particles. Montmorillonite, chlorite. Sedimentary limonite is a cryptocrystalline aggregate; the second type of origin of limonite is limonite aggregates formed by oxidative hydrolysis under exogenous action. The composition of this type of limonite varies greatly, and the phosphorus content also varies greatly. The thickness of the quartz embedded cloth is uneven, and the output particle size is 0.015~1mm. There are three types of quartz formed in the ore. The first is siliceous rock formed by sedimentation and then recrystallized to form microgranular quartz; the second is quartz debris; and the third is epigenetic quartz with relatively large particle size. Often distributed in vein-like strips. The harmful element phosphorus in the ore exists in the form of collophosphate rock, which is composed of extremely fine apatite aggregates. The particle size of collophosphate rock produced is 0.003 to 0.2 mm. The ore contains high phosphorus, and phosphorus does not exist in the form of independent minerals. Instead, more than 90% of the phosphorus exists in the form of isomorphous and extremely fine mechanical admixtures in the carrier mineral limonite.
The analysis results of the main chemical elements of the raw ore are shown in Table 1. It can be seen from Table 1 that the total iron content of the raw ore is 43.75%, the content of impurities silicon and phosphorus is high, and the sulfur content is low.

The results of the iron phase analysis of the raw ore are shown in Table 2. It can be seen from Table 2 that the main iron-containing mineral in the raw ore is limonite. The iron in limonite accounts for 69.10%, and the iron in other minerals is very small.

In view of the research on raw ore process mineralogy and on the basis of research on similar iron ores, it has been concluded that neither mineral Machining Shop nor metallurgy alone is the best method. Only through the organic combination of mineral processing and metallurgy can we obtain better economic results. Benefits, the main idea of the following research work is to reduce the phosphorus content in the raw ore as much as possible through mineral processing methods, and at the same time ensure the recovery rate of iron, and then conduct magnetization reduction roasting-weak magnetic separation or magnetic flocculation test on the obtained dephosphorized rough concentrate, and finally Obtain qualified iron ore concentrate.
2. Research on mineral processing technology
(1) Strong magnetic separation process test
The magnetic properties of limonite and gangue minerals are quite different, and they have the sorting conditions for strong magnetic separation, so a test of the strong magnetic separation process was carried out. Grind the raw ore to -0.074mm and account for 90%. After adjusting the conditions such as flushing water, ore concentration and separation time, perform strong magnetic separation at a magnetic field intensity of 880kA/m. The test results are shown in Table 3.

It can be seen from Table 3 that the grade and recovery rate of the iron concentrate obtained by the strong magnetic separation operation are 45.35% and 69.03% respectively, and phosphorus is enriched in the concentrate. The reason for this is twofold. On the one hand, the iron phase analysis results show that the occupancy rate of iron silicate is 17.67%. This part of iron cannot be recovered well in strong magnetic selection. On the other hand, because the apatite particles in the raw ore are very fine, they cannot be well dissociated from the iron ore, so the phosphorus content in the concentrate cannot be reduced. Eventually, phosphorus is enriched with the enrichment of the iron ore. . After the raw ore is ground, the particle size of the iron minerals is severely polarized, causing some of the fine-grained iron minerals to be lost in the tailings. Therefore, the strong magnetic separation operation does not achieve the effect of retaining iron and reducing phosphorus by discarding the tailings in advance.
(2) Direct reverse flotation dephosphorization process test
Under certain flotation conditions, using the difference in surface properties of weakly magnetic iron minerals and apatite minerals, anionic collectors were used to conduct direct reverse flotation dephosphorization experiments [5] to achieve the goal of “preserving iron and reducing impurities” For the purpose, an exploratory test was carried out below on the flotation conditions and reasonable pharmaceutical system of this process.
1. Grinding fineness test
The fineness of grinding has a great influence on the mineral separation standards. For fine-grained iron ore, grinding must not only achieve the purpose of monomer dissociation of the minerals, but also must not muddy the ore and affect the separation indicators. The grinding fineness test was conducted under the condition that the natural pH of the slurry is 6.5. The test process is a stage of reverse flotation, dephosphorization and rough separation. The test results are shown in Table 4.

It can be seen from Table 4 that as the grinding fineness increases, the iron grade of the iron concentrate does not change much, but the iron recovery rate decreases. The phosphorus grade has increased and the dephosphorization rate is not high. When the grinding fineness increases, the dissociation degree of phosphorus-containing minerals will increase. At the same time, limonite is also easy to sludge, making the collector selectivity worse. In addition, since phosphorus-containing minerals are basically homogeneous in nature, It exists in limonite in the form of extremely fine mechanical admixtures, and the phosphorus-containing mineral monomer cannot be cleaved out by fine grinding. Comprehensive consideration, the reverse flotation grinding fineness -0.074mm accounting for 90% is more appropriate.
2. Na2CO3 dosage test
When the grinding fineness is -0.074mm accounting for 90%, in order to eliminate the influence of harmful ions such as Ca2+ and Mg2+ in the slurry, reverse flotation dephosphorization should be carried out in alkaline slurry. The test uses Na2CO3 to adjust the pH value of the slurry. Carry out Na2CO3 dosage test, and the test results are shown in Table 5.

It can be seen from Table 5 that as the amount of Na2CO3 increases, the iron grade in the iron concentrate shows an upward trend, the phosphorus grade changes little, the iron recovery rate increases, and the phosphorus grade in the tailings increases. Comprehensive consideration, the dosage of Na2CO3 is 6.5-7.4kg/t, which is more suitable. At this time, the pH of the slurry is between 9 and 10, the iron concentrate contains 0.75% phosphorus, and the iron recovery rate is 93.61%.
3. Collectant type test
When the grinding fineness is -0.074mm accounting for 90%, pH=9~10, new adjuster (1) 240g/t, water glass 4000g/t, starch 800g/t, the collector type test is carried out. The results are shown in Table 6.

It can be seen from Table 6 that the reverse flotation dephosphorization effect of collector M is relatively good. M is a fatty acid collector prepared in a certain proportion. When the dosage is 600g/t, the iron grade of the obtained concentrate is 44.86%. Containing 0.74% phosphorus, the iron recovery rate is 93.23%.
4. Second-stage reverse flotation dephosphorization test
The exploratory test of roughing conditions showed that after one-stage reverse flotation dephosphorization, the phosphorus content of the iron concentrate in the tank was 0.74%. In order to further reduce the phosphorus content in the iron concentrate in the tank, a two-stage flotation dephosphorization test was carried out. The test process and conditions are shown in Figure 1. The test results are shown in Table 7.
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It can be seen from Table 7 that roughing 2 did not further reduce the phosphorus of the concentrate in the tank, and the phosphorus content of the tailings was still 0.84%. The phosphorus removal rate was low, and nearly 4 percentage points of iron mineral recovery rate were lost. Therefore, the effect of reducing the phosphorus content in the iron concentrate in the tank through multi-stage reverse flotation is not obvious. In addition, exploratory test results on the dosage of inhibitors and collectors show that it is very difficult to reduce phosphorus through deep reverse flotation of this ore. The phosphorus content of the concentrate in the tank is about 0.75%, and the iron mineral recovery rate is about 90%. .
3. Research on magnetization reduction roasting technology
(1) Roasting temperature test
The above-mentioned mineral processing technology research results show that the phosphorus removal rate of the entire operation is not high, the iron concentrate grade is less than 45%, and the phosphorus content is about 0.75%. In order to improve the grade of iron concentrate and reduce the phosphorus content in the iron concentrate, a magnetization reduction roasting test was conducted on the dephosphorized iron concentrate. Magnetization reduction roasting-weak magnetic separation is to add reducing agent carbon powder and additive Na2CO3 to the ore for roasting, so that weak magnetic iron such as limonite is reduced into strongly magnetic iron minerals. The additive Na2CO3 changes the phase composition of harmful impurities, and then the weak magnetic separation method is used to separate the iron concentrate. There are many factors that affect roasting, including ore properties, roasting temperature, roasting time, roasting particle size, roasting atmosphere, and types and amounts of additives. After a series of conditional exploratory tests, it was determined that the dosage of pulverized coal was 15%, the dosage of additive Na2CO3 was 10%, and the roasting time was 120 minutes. Under the optimal combination of conditions, the effect of calcination temperature was investigated. The reduction roasting test process of dephosphorization concentrate is shown in Figure 2, and the roasting temperature test results are shown in Table 8.
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It can be seen from Table 8 that at different temperatures, the dephosphorization concentrate has an ignition loss rate of 5% to 8% after magnetization reduction roasting, and the iron grade after roasting can be increased by 1% to 3%. At the same time, the phosphorus content increased from 0.75% to about 0.8%. The reduction roasting temperature also has a great impact on the sorting index. When the temperature increases from 800°C to 1070°C, the iron grade of the concentrate increases from 51.52% to 63.80%, and the iron recovery rate increases from 34.76% to 74.31%. However, the phosphorus grade content in the iron concentrate exceeds the standard. When the roasting temperature is 1070°C, the phosphorus content of the iron concentrate is also as high as 0.63%. In the test, it was found that after the temperature exceeds 1100°C, the ore reflows and the iron recovery rate in the weak magnetic separation operation is very low, so the roasting temperature is is 1070℃.
(2) Magnetic flocculation test
In order to reduce the phosphorus content in the final iron concentrate, the roasted ore samples were ultrafinely ground to increase the degree of dissociation of iron minerals and phosphorus minerals. Considering that conventional weak magnetic separation equipment cannot recover fine particles well For iron minerals, magnetic flocculation was used in the test to sort magnetic minerals, and a comparative test between magnetic flocculation and magnetic separation tubes was conducted. The test results of the influence of grinding fineness on magnetic flocculation are shown in Table 9.

It can be seen from Table 9 that the grinding fineness has a greater impact on the magnetic flocculation index. As the grinding fineness increases, the iron grade of the final concentrate increases and the phosphorus content decreases significantly. When the grinding fineness is 38 μm and accounts for 90%, the iron grade of the magnetic flocculation concentrate is 68.06%, the phosphorus content is 0.3%, and the iron recovery rate is 82.74%. At the same time, it can be seen from the comparison of the data in Table 8 that magnetic flocculation can obtain a higher iron recovery rate than the magnetic separator, and the phosphorus content of the concentrate is reduced from 0.63% to 0.30%; at the same time, magnetic analysis was performed on the roasted ore samples with 38 μm accounting for 90%. In the tube selection test, after one rough selection under a magnetic field intensity of 96kA/m, the final iron concentrate had an iron grade of 70.12%, a phosphorus content of 0.28%, and an iron recovery rate of 60.59%. This shows that after ultrafine grinding of roasted ore samples, the dissociation degree of iron minerals and phosphorus minerals is increased, and magnetic flocculation can effectively reduce the phosphorus content in the concentrate. In addition, during the magnetic flocculation CNC Milling 1684, fine-grained iron minerals are magnetized by an external magnetic field to form flocculation, thereby increasing the separation particle size and overcoming the disadvantages of poor recovery of fine-grained iron minerals by weak magnetic separation equipment, thereby achieving higher iron recovery. Rate.
4. Full process test
On the basis of the above tests, a full process test of reverse flotation – magnetization reduction roasting – magnetic flocculation was carried out. The whole test process is shown in Figure 3. The analysis results of the main chemical elements of the concentrate are shown in Table 10.

The test results show that in the full process test of reverse flotation-magnetic reduction roasting-magnetic flocculation, iron concentrate with a grade of 69.57% and a recovery rate of 71.62% can be obtained. The iron concentrate contains 0.29% phosphorus, 0.17% sulfur and 5.75% silicon.
5. Conclusion
(1) Research on technological mineralogy shows that: the ironstone of a limonite in Yunnan has complex properties, fine mineral particle size, severe mud formation, high phosphorus content, and most of the phosphorus is in the form of homogeneous and extremely fine mechanical mixtures. It exists in limonite in the form of limonite and is a difficult-to-select ore.
(2) Conventional single strong magnetic separation, gravity separation, and flotation CNC Drilling Services have almost no separation effect on this ore. To this end, the technological process of reverse flotation – magnetization reduction roasting – ultra-fine grinding magnetic flocculation was used to process the ore, and the iron grade was 69.57%, the recovery rate was 71.62%, the phosphorus content of the iron concentrate was 0.29%, and the sulfur content was 0.17 %, the silicon content is 5.75%, and the technical indicators are satisfactory.
(3) Ultra-fine grinding-magnetic flocculation can effectively reduce the phosphorus content in the concentrate, improve the grade of the concentrate, and at the same time solve the problem that conventional weak magnetic separation equipment cannot effectively recover fine-grained iron minerals. This process provides a new method for improving iron ore and reducing impurities from difficult-to-select high-phosphorus iron ores. Determination of the optimal parameters in the experiments requires further study.
(4) With the increasing shortage of ore resources and the increasing requirements for smelting raw materials, it is becoming more and more difficult to treat refractory ores with simple physical beneficiation processes, and it is particularly important to seek new beneficiation processes. This study provides a new idea for the sorting of similar refractory limonite ores.
references
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