Experimental study on roasting and dressing of Wangjiatan siderite

As in recent years, the rapid development of China's iron and steel industry, China's domestic iron ore can not meet the needs of steel companies. In 2005, China's steel output was 349.36 million tons, and the finished iron ore was consumed by 512.1 million tons. Due to the rapid growth rate, the iron ore production at home and abroad has brought huge pressures that were unexpected, resulting in tight supply of iron ore and sharp increase in iron ore prices. In 2005, foreign iron ore prices rose by 71.50%. In 2006, the price increase in 2005 increased by 19.00%, which will inevitably lead to a significant increase in the production costs of China's steel companies. In order to cope with this situation, major domestic steel companies have increased their research efforts on difficult domestic ore dressing .

Siderite is one of the complex refractory minerals. China's siderite resources are very rich. The proven reserves are more than 1.8 billion tons, accounting for 14% of the total iron ore. It is mainly distributed in Shaanxi, Yunnan, Gansu, Qinghai and Xinjiang. Waiting for the place. Due to the low theoretical iron grade (TFe48.27%), the output varies greatly from place to place, and it often resembles calcium, magnesium and manganese , resulting in lower iron grade. In addition, the density of siderite is small (3.8 ~ 3.9g / cm ³ ), weak magnetic and other reasons make it difficult to obtain a higher grade iron concentrate by conventional ore dressing method, and because of the poor performance of the siderite of the siderite concentrate, the raw ball less intense, sintering hours of the liberation CO _2, resulting in poor sinter strength, chalks, to bring a number of metallurgical problems. Therefore, the current utilization of siderite is less than 10% of its total. However, in order to increase the self-sufficiency of ore, major steel companies have put on the agenda of how to rationally develop and utilize China's diamond resources. For example, Daxigou in Shaanxi has adopted the roasting magnetic separation-reverse flotation process of Changsha Research Institute of Mining and Metallurgy. The ore content of the siderite of Kunming Steel Wangjiatan during sintering shall not exceed 5% of the total amount of raw materials. With the development of Kunming Iron and Steel, the supply of iron ore is far from meeting the needs of its own development. The development of Wangjiatan siderite has been put on the agenda. Increasing the grade of iron ore and reducing the content of harmful impurities have important significance for the development of Wangjiatan siderite.

First, the nature of the ore

(1) The chemical composition of the ore

The results of multi-element chemical analysis of the ore were listed in Table 1, and the results of the iron phase analysis are shown in Table 2.

Table 1 Multi-element chemical analysis results of ore

Table 2 Analysis results of ore iron phase %

It can be seen from Tables 1 and 2 that the main component for ore recovery in ore is iron. Copper can be used as a comprehensive utilization target. The sulfur content is 2.00%. It can be seen that sulfur reduction must be used to ensure the quality of iron concentrate. . The occurrence of iron is relatively simple. The iron distributed in carbonate accounts for 85.88%, and the iron distributed in magnetite and red (brown) iron ore. The distribution rate is 87.13%, which is the ore dressing. The maximum theoretical recovery of iron in the selection of iron minerals in ore.

(II) Output characteristics of major minerals

The ore is mostly gray-yellow-yellow under the naked eye, and has a dense block structure, and some of them are net-like or plaque-like. After microscopic identification and X-ray diffraction analysis, the ore composition of ore is relatively simple. Iron minerals are mainly spironite and occasional limonite distribution. Metal sulfides are mainly pyrite, followed by chalcopyrite. and sphalerite; high gangue minerals are quartz content, followed by chlorite and sericite, other trace minerals include dolomite, calcite, zircon, monazite and apatite. Table 3 lists the mass content of the main minerals in the ore.

Table 3 % of main minerals in ore

Siderite is classified into two types: fine particles (particle diameter less than 0.2 mm) and medium coarse particles. The former are mostly self-shaped, semi-self-shaped granular, partially bamboo-like, and the crystal grain size is relatively uniform, mostly between 0.02 and 0.15 mm. The crystal grains are closely embedded in each other to form an aggregate or in a disseminated form with quartz and sericite. It is mixed with gangue minerals such as chlorite; the medium-thicked siderite is formed later than fine-grained fine iron ore, and its shape is relatively regular, but the crystal size changes greatly, and some can reach about 2.0mm and coarse grains. In the transition, the aggregates are often irregularly massive or fine veins, and the fine-grained fine iron ore in the early form is replaced, and the gangue minerals such as quartz can also be partially wrapped. The above two forms of the production of the siderite are mainly the first one, and the mineral content ratio of the two is about 75:25. Table 4 lists the multi-element chemical analysis results for the single mineral of siderite with a purity greater than 98%.

Table 4 Multi-element chemical analysis results of siderite

As seen from Table 4, siderite iron grade only 37.69%, wherein the metal cations other than Fe ^{2 +,} but also because the role of isomorphism containing higher Mg ^{2 +} and a small amount of Mn ^{2 +,} this firing process siderite With the decomposition of CO ₂ , the content of MgO will increase to a certain extent, resulting in low iron concentrate grade. The grade of roasting ore weak magnetic separation iron concentrate can only reach about TFe59.80%.

Second, laboratory test equipment

(1) SX-8 box type resistance furnace.

(2) Flash roaster.

(3) Ball mill . XMB-67φ200mm×240mm.

(4) Drum type wet weak magnetic separator. Φ300mm×200mm, surface magnetic field strength ≤127kA/m.

(5) XCGS-73 type magnetic separation tube. Φ50mm, magnetic field strength ≤ 240kA / m.

(6) XFD-63 series single-slot flotation machine.

(7) XFD-76 type trough flotation machine.

(8) Screening sieve for particle size. 16 mesh, aperture 1.16 mm; 150 mesh, aperture 0.1 mm; 200 mesh, mesh 0.074 mm; 325 mesh, mesh 0.045 mm.

Third, experimental research and main results

The roasting test is carried out in a box type electric resistance furnace. After the furnace temperature rises to the temperature set by the test, the stainless steel box of the ore is placed in the furnace, the furnace door is closed, and the roasting time is started after the constant temperature is reached; roasting The mine is discharged by water quenching. The test method for the calcination test index is to grind the ore to 97.54%-0.074 mm (92.23%-0.045 mm), and select it by XCGS-73 type magnetic separation tube, and the magnetic field strength is 143.23 kA/m.

(1) Roasting condition test

The calcination conditions play a key role in determining the ore dressing index of the roasting ore. Whether the calcination atmosphere is suitable, the temperature and time of calcination, and the thickness of the calcination to the ore layer are important factors.

1. Roasting atmosphere test

Under the conditions of calcination temperature of 750 ° C and calcination time of 80 min, the effects on the calcination index under different atmospheres were examined. The test results are shown in Table 5.

Table 5 % of calcination atmosphere test results

It can be seen from Table 5 that the calcination index under weak oxidation and neutral calcination atmosphere is better, and a higher metal recovery rate can be obtained, while the index of coal reduction reduction roasting is the worst. However, the calcination index is still not ideal, so the calcination conditions still need to be further optimized.

2, roasting temperature test

Theoretically, the siderite begins to decompose at 400 ° C and decomposes completely at 560 ° C. The chemical reaction is 3FeCO ₃ →Fe ₃ O ₄ +2CO ₂ +CO. Excessive temperature leads to the formation of richite and weakly magnetic iron silicate. The higher the temperature, the higher the amount of formation. The neutral roasting atmosphere was selected and the calcination time was 80 min. The effect of calcination temperature on the calcination index was examined. The test results are shown in Table 6.

Table 6 Roasting temperature test results

It can be seen from Table 6 that under the condition of calcination for 80 min, the calcination index obtained at the calcination temperature of 850 ° C is better, the yield of weak magnetic separation concentrate is 44.93%, the grade is TFe 55.94%, and the metal recovery rate is 68.92%. When the calcination temperature reaches 1000 °C, the tailings grade is greatly increased, and the recovery rate of iron is greatly reduced, which is an obvious over-burning characteristic.

3. Different thickness of the ore layer roasting test

Under the conditions of calcination temperature of 850 °C and calcination time of 80 min, the influence of different calcined ore thickness on the index was examined. The test results are shown in Table 7.

Table 7 % of the thickness of the ore layer roasting test

It can be seen from Table 7 that the thickness of the ore layer is good in the calcination index of 8.3 to 16.7 mm; when the thickness reaches 50 mm, the index is quickly deteriorated, which is mainly due to the fact that the ore layer is too thick to cause poor gas permeability, and the gas generated during roasting is difficult to discharge in time. Affects the extent to which the reaction phase transition progresses.

4, roasting time test

The thickness of the ore layer was selected to be 8.3 mm and the calcination temperature was 850 ° C. The calcination time test was carried out in a neutral roasting atmosphere to examine the effect of roasting time on the index. The results are shown in Table 8.

Table 8 Roasting time test results

It can be seen from Table 8 that as the calcination time is prolonged, the iron grade of the concentrate does not change much, but the recovery of iron increases. This is mainly due to the fact that the magnetite mineralization of the siderite is relatively complete.

(2) Roasting ore dressing test

1. Effect of grinding fineness on magnetic separation

The test of the effect of grinding fineness on the weak magnetic separation index was carried out on the calcined ore. The test results are shown in Table 9.

Table 9 Grinding fineness test results

It can be seen from Table 9 that the concentrate grade increases with the increase of grinding fineness; however, after the fineness of grinding reaches 99.27%-0.045 mm, the grade of tailings increases greatly and the recovery rate decreases drastically. This is mainly due to the inability to efficiently capture too fine particles under the magnetic field of sorting.

2, weak magnetic separation concentrate iron lifting test

For the weak magnetic separation concentrate, the iron ore concentrate was further extracted to explore the highest grade that can be achieved by iron concentrate. The cation and anion collector were used to carry out the reverse flotation test on the weak magnetic separation concentrate. The test results are shown in Table 10.

Table 10 Results of reverse flotation test of weak magnetic separation concentrate

Note: 1 type and amount of cationic reverse flotation agent: GE cation collector 300g / t, starch 500g / t; 2 anion reverse flotation agent type and dosage: NaOH regulator 800g / t, starch inhibitor 600g / t, The CaO activator was 600 g/t, and the RA-715 anion collector was 800 g/t.

It can be seen from Table 10 that the effect of iron removal and impurity reduction in weak magnetic separation concentrate is not obvious. When the operating yield of the concentrate is as low as 22.11% to 65.67%, the grade of the flotation concentrate iron can only be increased to 58.64% to 58.79%.

In order to ascertain the main chemical composition of the flotation concentrate, a multi-element chemical analysis of the concentrate reverse flotation concentrate was carried out. The results are shown in Table 11.

Table 11 Multi-element chemical analysis results of reverse flotation concentrates%

It can be seen from Table 11 that the reverse flotation concentrate reaches 58.79%, and the contents of impurities SiO ₂ , Al ₂ O ₃ and CaO are low, and the possibility of further reduction is small; and the content of MgO and MnO in the concentrate is small. Higher, which is related to the ore properties of the original siderite. It belongs to the similar phenomenon of crystal lattice substitution. It is currently impossible to remove by the beneficiation process, but MgO is the slag composition of blast furnace ironmaking, which can reduce the blast furnace ironmaking. The amount of slag used in the concentrate; the content of sulphur in the concentrate is high, and the spectroscopic observation is mainly pyrrhotite. Due to a series of complex physical and chemical changes in the ore during roasting, pyrite from the ore is produced. It is transformed and distributed in the form of fine particles, which is difficult to reduce.

3. Weak magnetic separation concentrate sulfur reduction test

In order to reduce the sulfur content in the roasting ore weak magnetic separation concentrate, SA is used as the activator, and BA is the main floating sulfur collector. The effect of different xanthate on sulfur reduction is examined. The test results are shown in Table 12.

Table 12 Results of sulfur reduction test of weak magnetic separation concentrate

Note: Y89 is a kind of xanthate anion collector.

As can be seen from Table 12, the effect of the addition of the SA activator on the sulfur reduction is apparent. After adding, the sulfur content in the concentrate can be greatly reduced. The sulfur reduction effect of BA+ Ding Huang is 300g/t, and the sulfur content in iron concentrate can be reduced to 0.63%. But this is still above the 0.30% requirement.

(3) Flash calcination test

Flash roasting is a national research project under the auspices of Academician Yu Yongfu. It is an effective roasting process for difficult-to-treat iron ore. In the state of full suspension, fine-grained minerals can achieve heat and mass transfer in a very short time, achieving the purpose of magnetization roasting. In order to examine the effect of flash calcination on the desulfurization of Wangjiatan siderite, the flash roasting test was carried out in a flash roaster, and the fineness of roasting was 65.14%-0.074mm. The regrind of the roasting ore was 90.30%-0.074mm, magnetic separation tube magnetic field strength is 143.24kA / m, the test results are shown in Table 13.

Table 13 Flash calcination test results

It can be seen from Table 13 that the flash calcination can also reach the iron grade of the weakly magnetically refined concentrate of conventional roasting, and the recovery rate of iron is increased to 90.75%, and the reduction of the sulfur content in the weak magnetic separation concentrate is large. It can be reduced to 0.15%, which is not possible with conventional calcination. Mainly because in the roasting process, the sulfur in the pyrite in the ore mine reacts into the gas phase in a short time, and with the exhaust gas, the iron in the pyrite is converted into magnetite, thus increasing the recovery of iron. rate.

Fourth, the conclusion

(1) The Wangjiatan siderite is a magnesia-manganese-like metamorphic iron ore, and the iron concentrate grade obtained from the roasting ore dressing is up to 59.80%.

(2) Treatment of Wangjiatan siderite by conventional roasting process will result in higher sulfur content of iron concentrate.

(3) Flash calcination can achieve the purpose of reducing sulfur in the roasting process. The iron concentrate has a sulfur content of less than 0.20%, and a recovery rate of 4.72% higher than that of conventional roasting can be obtained.

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