Ningxiang deposition type Oolitic hematite distributed in China, Hubei, Hunan, Sichuan, Guizhou and other provinces, the industry has proven reserves of more than thirty billion tons, of which only the western Hubei Hubei will account for about 58.7%. This type of ore minerals are complicated, disseminated fine, phosphorus, aluminum and silicon of high impurity content, it is difficult to world mineral stone. This study of western Hubei Oolitic iron ore samples were also metalization Roasting - magnetic separation tests, means to explore the feasibility of ore exploitation.
First, the nature of the ore
The test sample belongs to Ningxiang-type high-phosphorus hematite. The main iron mineral in the ore is hematite, followed by limonite, and a small amount of siderite, magnetic ore, etc.; the independent mineral of phosphorus is mainly apatite; the gangue mineral is mainly quartz , chlorite and kaolin. Stone, and other traces of amorphous carbon, calcite , zircon , etc. The main useful element in ore is iron, and the main harmful impurities are phosphorus and silicon.
The chemical multi-element analysis results of the samples are shown in Table 1. The chemical phase analysis of iron and phosphorus in ore is shown in Table 2 and Table 3, respectively.
The results of chemical multi-element analysis show that although the iron grade in the ore is 43.71%, the content of harmful elemental phosphorus is also high, reaching 0.93%.
The chemical phase analysis of iron and phosphorus in the ore indicates that the iron in the ore is mainly in the form of hematite, followed by iron silicate; the phosphorus in the ore is mainly distributed in the apatite, followed by the brown iron. In mines and hematite, there is very little phosphorus in gangue and other minerals.
The samples are hematite crystals, clay minerals such as clay minerals, colloidal phosphates, chlorites, and the likes of the hematite hematite ore which are closely symbiotic in the finely dispersed state. The size of the hematite and apatite in the ore is relatively fine and uneven. Among them, in the +0.074mm grain size, the hematite occupation rate is only 45.80%, and the -0.020mm grain size is the red iron. The mineral occupation rate is 21.47%; the apatite particle size is also extremely uneven, ranging from 0.015 to 0.25 mm.
Second, metallization roasting conditions test
The test scheme adopts carbonization and metallization roasting in a fixed bed, and then magnetic separation by fine grinding magnetic separation tube (8700e) to prepare high-grade iron powder or sponge iron. In order to maintain a sufficient reducing atmosphere and prevent oxidation of the secondary roasted ore, tests using excess reducing agent (coal powder). The reduction equipment used was a carbon resistance rod furnace.
(1) Metallization roasting temperature test
After uniformly mixing the -2 mm ore with the coal powder, the high-temperature calcination tank is placed in a muffle furnace at a preset temperature for calcination. After a certain period of time, the calcined ore is taken out and cooled by water quenching. The results of the metallization rate of the obtained calcined ore at different temperatures are shown in Fig. 1.
It can be seen from the figure that the metallization rate of the calcined ore at different holding times increases significantly with the increase of temperature below 1050 °C, and the metallization rate changes slowly after increasing the temperature. It shows that the elevated reaction temperature can promote the metallization of the calcined product, but when the temperature rises to a certain extent, it is restricted by the low melting point minerals in the mineral (2FeO·SiO 2 , FeO·Al 2 O 3 , etc.) and the reducing atmosphere. Attenuate the influence of other factors, thereby reducing the reduction rate of the ore, and thus affecting the progress of the reduction reaction. Therefore, in this test, the calcination temperature is preferably 1050 ° C, and the corresponding metallization ratio is above 95%.
(2) Metallization roasting holding time test
The roasting ore of different holding time at each calcination temperature was respectively ground for 10 min, and then magnetic separation was performed. The test results are shown in Fig. 2 and Fig. 3.
Figure 2 shows that the iron grade of the magnetically-selected iron concentrate obtained from the calcined ore at different holding times increases with the increase of the calcination temperature. Among them, compared with 1 h of heat preservation, the magnetic separation effect of the calcined ore kept for 3 h was obviously superior in the temperature range; however, the roasting ore of 5 h of heat preservation was between 950 and 1050 °C, and the iron grade and iron recovery rate did not change much. Moreover, at 1050 °C, the refined iron grade is similar to that obtained by holding for 3h, and the corresponding iron recovery rate is also very small. It is indicated that prolonging the roasting time within a certain temperature range does not promote the iron ore reduction reaction. It can be seen from Fig. 3 that the phosphorus content of the magnetically selected iron ore concentrate increases significantly above 1050 ° C with increasing temperature and prolonging the holding time. It can be seen that the calcination temperature is 1050 ° C, and the magnetic separation effect of the roasting ore for 3 h is relatively good.
(3) Metallization roasting test of different ore sizes
The raw ore of different particle sizes and the excess pulverized coal were uniformly mixed, finely ground by metallization and calcined [-0.074 mm (-200 mesh) 75.20%], and the test results are shown in Table 4.
It can be seen from the table that the iron grade of the calcined ore obtained by using the fine-grained ore is relatively superior, and the coarse-grain grade (-100mm) is second; the iron grade and iron recovery rate of the magnetically-selected iron concentrate are all increased with the decrease of the particle size. The phosphorus content is reversed. The results show that under laboratory conditions, the fine-grained ore shows relatively good results in both the quality of the calcined ore and the quality of the magnetically selected iron concentrate.
Third, the magnetic separation process test
In view of the industrial experimental experience, on the basis of the conditional test, the metallization roasting-magnetic separation process was carried out using coarse-grained lump ore (-10 mm). The test firstly mixes the ore and excess pulverized coal for reduction roasting, and the roasting ore is rapidly cooled, then thrown by permanent magnet block, and then finely ground magnetically. In order to obtain high-quality iron powder efficiently, the magnetic medium (the medium used is about 50% of the TCL of Panzhihua magnetite concentrate) was selected for the mud removal method. The test procedure is shown in Figure 4, and the magnetic separation test results are shown in Table 5.
It can be seen from the table that after the coarse-grained calcined ore is selected by the permanent magnet block tailing and the fine grinding magnetic medium deliming, the iron content of the obtained iron powder is more than 94%, the iron recovery rate is about 88%, and the phosphorus content is 0.38. %the above. From the chemical composition of iron powder, it can be used as a supplement to scrap steel resources, and is a high-quality raw material for electric steelmaking or powder metallurgy.
Fourth, the conclusion
(1) A braided hematite in western Hubei is a Ningxiang-type sedimentary braided hematite. The ore contains 43.71% iron and 0.93% phosphorus. Hematite crystals and clay minerals, phosphate rock and green in the ore. The gangue minerals such as mudstone are closely symbiotic in the finely dispersed state to form a braid, and the hematite and apatite have fine grain size and are uneven.
(2) The ore and the excess reducing agent (pulverized coal) are uniformly mixed, and calcined at 1050 °C for 3 hours, and the calcined ore is cooled by water quenching, and the metallization rate of the calcined ore is more than 95%.
(3) After the roasting ore is selected by the coarse-grain permanent magnet block tailing and the fine grinding magnetic medium deliming, the iron grade of the obtained iron powder is over 94%, and the iron recovery rate is about 88%. It can be used as a supplement to scrap steel resources and is a high-quality raw material for electric steelmaking or powder metallurgy.
(Author: Deng Jianguo bridge of ice Sun Zhiyong YANG Bing Zhang Qin)
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