Study on the combined technology of a high-phosphorus limonite ore in Yunnan

With the rapid development of China's iron and steel industry, domestic iron ore resources are increasingly strained, the availability of iron ore resources are increasingly tend to be poor, fine, miscellaneous. In order to improve the self-sufficiency rate of China's iron ore resources and ease the pressure of imported iron ore, it is necessary to research and develop a large number of refractory iron ore. China's iron ore resources have high levels of harmful impurities such as sulfur, phosphorus and silica. The impurities are closely symbiotic with useful iron minerals, which makes it difficult to remove iron concentrate. Phosphorus is one of the main harmful elements in the iron and steel smelting process, which seriously affects the steelmaking process and the quality of steel products. With the implementation and development of new metallurgical technology industry, the quality of the iron ore is increasingly high demand for phosphorus content is also strictly limited, so efficient dephosphorization iron ore imminent ^[1-3].

At present, domestic and foreign selection of low-grade high-impurity limonite is dominated by strong magnetic separation-positive flotation, weak magnetic separation-strong magnetic separation-positive flotation, classification-re-selection-fine-grain flotation, flocculation- Strong magnetic separation, reverse flotation - roasting - weak magnetic separation, roasting - weak magnetic separation - reverse flotation and other joint processes ^[4] .

A certain amount of limonite ore resources in Yunnan is good. The iron ore mineral size is complicated to be embedded, the phosphorus content is high, and the muddy phenomenon is serious. It is difficult to select ore and has not been developed for a long time. In order to develop and utilize mineral resources and improve the self-sufficiency rate of mineral resources of enterprises, the company entrusted Kunming University of Science and Technology to conduct research on the ore of this ore. After a series of exploratory experiments, it was found that the concentrate iron grade obtained by conventional single strong magnetic separation, re-election and flotation method is difficult to reach more than 48%, but phosphorus content is above 0.8%. Aiming at this situation, the combined process of reverse flotation-magnetization reduction roasting-ultrafine magmatic flocculation was studied. Finally, an iron concentrate with an iron grade of 69.57% and a recovery rate of 71.62% was obtained, of which 0.29% was phosphorus. It has a satisfactory technical index with 0.17% sulfur and 5.75% silicon.

I. Research on ore process mineralogy

An iron ore mine in Yunnan is a multi-period, multi-cause, multi-type superimposed large-scale iron deposit with complex characteristics, with a geological reserve of 1.994 billion tons, mainly divided into two major categories: primary ore and oxidized ore. The oxidized ore is distributed in the open pit of the ore body, accounting for 16% of the total reserves. The mineral component of the oxidized ore is mainly limonite, and the molecular formula is 2Fe ₂ O ₃ •3H ₂ O, which accounts for about 70%. The limonite in the ore is usually a multi-mineral aggregate composed of goethite, fibrite, water needle iron ore, hydrofibrite, and mechanically mixed characters such as water-containing silica and mud. Granular limonite often has irregular, mesh, cloth embedded in quartz gum, since most of the mineral particle size of fine monomers, most of them were each other mutually indistinguishable disseminated distribution; gangue minerals quartz and chlorite , followed by colloidal phosphate and montmorillonite. The limonite has a particle size of generally 0.004 to 0.15 mm and a minimum of 0.002 mm. The limonite in the ore has two genetic types, one is sedimentary limonite, which is formed during the formation of sedimentary rocks, often distributed in the form of cement between quartz crumbs, often mixed in small Montmorillonite, chlorite. The sedimentary limonite is a cryptocrystalline aggregate; the second genetic type of limonite is an oxidative hydrolysis to form a limonite aggregate under exogenous action. The composition of this type of limonite is quite different, and the phosphorus content also has a large change. The quartz inlay is uneven in thickness and the output grain size is 0.015 to 1 mm. There are three kinds of quartz formed in the ore. The first one is sedimentary siliceous rock and recrystallized to form granular fine quartz; the second is quartz crumb; the third is epigenetic quartz, and the grain size is relatively large. It is often distributed in a veined strip. The harmful elemental phosphorus in the ore is in the form of colloidal phosphate ore. The colloidal phosphate ore is composed of a very fine apatite aggregate, and the output size of the colloidal phosphate is 0.003 to 0.2 mm. The ore contains higher phosphorus, and phosphorus does not exist as a separate mineral, but more than 90% of it is in the form of a homogeneous and very fine mechanical mixture present in the carrier mineral limonite.

The analysis results of the main chemical elements of the ore are shown in Table 1. It can be seen from Table 1 that the total iron content of the ore is 43.75%, the impurity silicon and phosphorus content are higher, and the sulfur content is lower.

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

In view of the research on ore processing minerals and on the basis of similar iron ore research, it has been found that a single beneficiation or metallurgy is not the best method. Only through the organic combination of mineral processing and metallurgy can a better economy be obtained. Benefits, the main ideas of the following research work: through the method of mineral processing, try to reduce the phosphorus content in the ore, and at the same time ensure the recovery rate of iron, and then carry out the magnetization reduction roasting-weak magnetic separation or magnetic flocculation test on the obtained dephosphorization coarse concentrate. Get qualified iron concentrate.

Second, the study of mineral processing technology

(1) Strong magnetic separation process test

The magnetic difference between limonite and gangue minerals is large, and there is a strong magnetic separation sorting condition, so the strong magnetic separation process is tested. Grinding the original ore to -0.074mm accounted for 90%, mediating the flushing water, the concentration of the ore and the sorting time, and then performing strong magnetic separation at a magnetic field strength of 880 kA/m. The test results are shown in Table 3.

It can be seen from Table 3 that the iron concentrate grade and recovery obtained by the strong magnetic separation operation are 45.35% and 69.03%, respectively, and the phosphorus is enriched in the concentrate. The reason is twofold. On the one hand, the iron phase analysis results show that the iron silicate occupancy rate is 17.67%, which is not well recovered in the strong magnetic selection. On the other hand, due to the very fine grain size of the apatite in the ore, it cannot be dissociated well from the iron ore, so the phosphorus content in the concentrate cannot be reduced. Finally, the phosphorus is enriched with the enrichment of iron concentrate. . After the ore is ground, the grain size polarization of the iron mineral is severe, which causes some fine-grained iron minerals to be lost in the tailings. Therefore, the strong magnetic separation operation does not achieve the effect of pre-pitching iron-preserving and phosphorus-reducing.

(II) Direct reverse flotation dephosphorization process test

Under certain flotation conditions, using the difference in surface properties between weak magnetic iron minerals and apatite minerals, an anionic collector was used for direct reverse flotation dephosphorization test ^[5] to achieve "protection of iron and impurities" Objectives: Exploratory experiments were carried out on the flotation conditions and rational pharmaceutical systems of this process.

1. Grinding fineness test

The fineness of grinding has a great influence on the standard of mineral processing. For fine-grained iron ore, grinding not only makes the minerals reach the purpose of monomer dissociation, but also can not make the ore muddy and affect the sorting index. The grinding fineness test was carried out under the condition that the natural pH of the slurry was 6.5. The test procedure is a rough selection of reverse flotation dephosphorization. The test results are shown in Table 4.

It can be seen from Table 4 that as the fineness of the grinding increases, the iron grade of the iron concentrate does not change much, but the recovery rate of iron decreases. The phosphorus grade has increased and the rate of dephosphorization is not high. When the grinding fineness increases, the dissociation degree of phosphorus-containing minerals will increase, and limonite will also be easily muddy, which makes the collector selectivity worse. In addition, since the phosphorus-containing minerals are basically the same type And in the form of very fine mechanical admixtures present in limonite, the phosphorus-containing mineral monomers cannot be cleaved by fine grinding. Comprehensive consideration, the anti-flotation grinding fineness -0.074mm accounted for 90% is more suitable.

2, Na ₂ CO ₃ dosage test

In the grinding fineness of -0.074mm accounted for 90%, in order to eliminate the influence of harmful ions such as Ca ²⁺ and Mg ²⁺ in the slurry, and the reverse flotation dephosphorization should be carried out in alkaline pulp, the test adopts Na ₂ CO ₃ adjusts the pH value of the slurry and conducts the Na ₂ CO ₃ dosage test. The test results are shown in Table 5.

It can be seen from Table 5 that with the increase of the amount of Na ₂ CO ₃ , the iron grade in the iron concentrate is increasing, the phosphorus grade is not changed, the iron recovery rate is increased, and the phosphorus grade in the tailings is increased. Considering that the dosage of Na ₂ CO ₃ is 6.5-7.4kg/t, the pH of the slurry is between 9 and 10, the iron concentrate is 0.75%, and the iron recovery is 93.61%.

3, collector type test

In the grinding fineness of -0.074mm accounted for 90%, pH = 9 ~ 10, new conditioning agent (1) 240g / t, water glass 4 000g / t, starch 800g / t, the collector type test, test The results are shown in Table 6.

It can be seen from Table 6 that the anti-flotation dephosphorization effect of the collector M is relatively good, and M is a fatty acid collector which is prepared according to a certain ratio. When the dosage is 600 g/t, the concentrate iron grade is obtained as 44.86%. The phosphorus content was 0.74%, and the iron recovery rate was 93.23%.

4, two-stage reverse flotation dephosphorization test

The exploratory test of rough selection conditions showed that after a 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 procedure and conditions are shown in Figure 1. The test results are shown in Table 7.

It can be seen from Table 7 that the rough selection 2 does not further reduce the concentrate phosphorus in the tank, and the tailings still contain 0.84% ​​of phosphorus, and the phosphorus removal rate is low, and the iron mineral recovery rate of nearly 4 percentage points is lost. Therefore, the effect of reducing the phosphorus content in the iron concentrate in the tank by multi-stage reverse flotation is not obvious. In addition, the exploratory test results of the inhibitor and collector dosage indicate that the ore is difficult to reduce phosphorus by reverse flotation. The phosphorus content in the concentrate is about 0.75%, and the recovery rate of iron mineral is about 90%. .

Third, the study of magnetization reduction roasting technology

(1) Calcination temperature test

The above-mentioned mineral processing technology research results show that the phosphorus removal rate of the whole 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 iron concentrate grade and reduce the phosphorus content in the iron concentrate, the dephosphorization iron concentrate was subjected to a magnetization reduction roasting test. Magnetization reduction roasting-weak magnetic separation is to add reducing agent carbon powder and auxiliary agent Na ₂ CO ₃ to the ore to be calcined to reduce weak magnetic iron such as limonite into ferromagnetic iron mineral. The additive Na ₂ CO ₃ changes the phase composition of the harmful impurities, and then the iron concentrate is sorted by the weak magnetic separation method. There are many factors affecting roasting, such as ore properties, calcination temperature, calcination time, particle size, calcination atmosphere, and types and amounts of additives. After a series of exploratory test conditions to determine the amount of pulverized coal is 15%, additives in an amount of Na ₂ CO ₃ 10%, conditions of roasting time of 120min. The effect of the calcination temperature was examined under the optimal combination of conditions. The dehydrogenation concentrate reduction roasting test procedure is shown in Figure 2, and the calcination temperature test results are shown in Table 8.

It can be seen from Table 8 that at different temperatures, the dephosphorization concentrate has a burn-out rate of 5% to 8% after magnetization reduction roasting, and the iron grade can be increased by 1% to 3% after calcination. At the same time, the phosphorus content increased from 0.75% to about 0.8%. The reduction roasting temperature also has a great influence on the sorting index. The temperature increases from 800 °C to 1 070 °C, the concentrate iron grade rises from 51.52% to 63.80%, and the iron recovery rate rises from 34.76%. 74.31%. However, the content of phosphorus in iron concentrates exceeded the standard. When the calcination temperature is 1 070 °C, the phosphorus content of the iron concentrate is also as high as 0.63%. After the temperature is found to exceed 1 100 °C in the test, the ore is reflowed, and the recovery rate of the weak magnetic separation operation is very low, so the calcination temperature is taken. It is 1 070 ° C.

(2) Magnetic flocculation test

In order to reduce the phosphorus content in the final iron concentrate, superfine grinding of the calcined ore sample to increase the dissociation degree of the iron mineral and the phosphorus mineral, considering that the conventional weak magnetic separation equipment can not recover the fine fraction. Iron minerals, magnetic flocculation was used to separate magnetic minerals, and magnetic flocculation and magnetic separation tubes were compared. The test results of the effect of grinding fineness on magnetic flocculation are shown in Table 9.

It can be seen from Table 9 that the grinding fineness has a great influence on the magnetic flocculation index. As the fineness of the grinding increases, the final concentrate iron grade increases and the phosphorus content decreases significantly. When the fineness of grinding is 38μm and 90%, the iron grade of 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 the magnetic flocculation can obtain higher iron recovery rate than the magnetic separation tube, the phosphorus content of the concentrate is reduced from 0.63% to 0.30%; at the same time, the roasting ore sample of 38% of 90% is magnetic. In the tube selection test, the crude iron concentrate grade was 70.12%, the phosphorus content was 0.28%, and the iron recovery rate was 60.59% after one rough selection at a magnetic field strength of 96 kA/m. This indicates that the superfine grinding of the calcined ore sample increases the dissociation degree of iron minerals and phosphorus minerals. The magnetic flocculation can reduce the phosphorus content in the concentrate. In addition, during the magnetic flocculation process, the fine-grained iron mineral is magnetized by the applied magnetic field to form flocculation, which increases the sorting granularity, overcomes the disadvantages of weak magnetic separation equipment for poor recovery of fine-grained iron minerals, and thus obtains higher iron recovery. rate.

Fourth, the whole process test

On the basis of the above experiments, the whole process of reverse flotation-magnetization reduction roasting-magnetic flocculation was carried out. The whole process of the experiment is shown in Fig. 3. The main chemical element analysis results of the concentrate are shown in Table 10.

The test results show that in the reverse flotation-magnetization reduction roasting-magnetic flocculation process, an iron concentrate with a grade of 69.57% and a recovery of 71.62% can be obtained. The iron concentrate contains 0.29% phosphorus, 0.17% sulfur and 5.75% silicon.

V. Conclusion

(1) Process mineralogical studies show that: a limonite ore in Yunnan is complex in nature, with fine mineral grain size, serious muddy phenomenon, high phosphorus content, and most of the phosphorus is similar to the same type and very fine mechanical mixture. The form exists in limonite, which is difficult to select ore.

(2) Conventional single strong magnetic separation, re-election, and flotation processes have almost no sorting effect on the ore. To this end, the ore was treated by reverse flotation-magnetization reduction roasting-ultrafine grinding flocculation process, and the iron grade was 69.57%, the recovery rate was 71.62%, the iron concentrate was 0.29%, and the sulfur content was 0.17. %, silicon content is 5.75%, and the technical indicators are satisfactory.

(3) Ultra-fine grinding-magnetic flocculation can well reduce the phosphorus content in the concentrate, improve the concentrate grade, and solve the problem that the conventional weak magnetic separation equipment can not effectively recover the fine-grained iron minerals. This process provides a new method for the iron and phosphorus reduction of refractory high-phosphorus iron ore. The determination of the best parameters in the test requires further study.

(4) With the increasing tension of ore resources and the increasing demand for smelting raw materials, it is becoming more and more difficult to deal with refractory ore with a simple physical beneficiation process. It is particularly important to seek new beneficiation processes. This study provides a new idea for the sorting of similarly difficult brown iron ore.

references

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[2] æ°¸ Yong, Li Yuping. Discussion on the equilibrium price of international iron ore resources market [J]. Metal Mine, 2008 (2): 13-15.

[3] Sun Keji, Lu Shouci, et al. Experimental study on dephosphorization of weak magnetic iron ore [J]. China Mining, 1999 (6): 61-64

[4] Sun Bingquan. Recent developments in complex refractory iron ore beneficiation technology in China [J]. Metal Mine, 2006 (3): 11-14

[5] Hu Weibai. Flotation [M]. Beijing: Metallurgical Industry Press. 1997.

[6] Luo Liqun, Zhang Yusheng, Gao Yuanyang, et al. Study on dry cooling magnetization roasting technology of siderite [J]. Metal Mine, 2004 (10): 28-31.

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