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Abstract: Exploratory experiments using processes of flotation and reducing roasting - magnetic sepatation were taken on a limonite ore. The results showed that reducing roasting - magnetic sepatation is effective method for this ore. Under optimum conditions of roasting temperature, time, reductant addition and magnetic Field intensity, the test achieved an iron concentrate with an iron grade of 60.34% at a recovery of 86.47% from an raw ore with an iron grade of 45.4%.
Iron and steel industry is an important basic industry of the national economy, is an important guarantee for the country to achieve economic growth tell achieve industrialization. In recent years, China's steel industry has achieved rapid development. In 2005, China's iron output reached 340 million tons, steel output was 349 million tons, accounting for 30.93% of global steel production, making a great contribution to the development of China's national economy [ 1] . However, at the same time as the large-scale development of the steel industry, it also brought tremendous pressure on the supply of iron ore at home and abroad, resulting in a sharp increase in the price of imported iron ore. In order to cope with the tight supply of iron ore, the domestic production pace has been stepped up, but China's high-grade, easy-to-handle magnetite reserves are small, unable to meet the needs of national economic development, complex and difficult to choose hematite, limonite and diamond The research on the selection and treatment technology of iron ore has become an important way to ensure the supply of raw materials in China and reduce the dependence on foreign iron ore.
Among them, the reserves of limonite in China are about 1.0-200 billion tons, which are generally found in the shallow surface of the earth. It is easy to take, but because it contains crystal water, the iron content is lower than that of magnetite and hematite, and there are few rich minerals. The magnetic properties are weak, most of which contain a large amount of slime, which cannot be directly used for smelting without beneficiation . It is a refractory ore [2 , 3] . Therefore, the characteristics of easy selection of limonite are determined by the selection technique. The key is that there are a lot of research reports on the technology of limonite sorting at home and abroad. Some researchers have used separate and combined processes such as re-election, magnetic separation, positive and negative flotation, and selective flocculation to develop a strong magnetic + positive flotation + strong magnetic process [4] , a strong magnetic + reverse flotation process [ 5 , 6 , 7] , flocculation - strong magnetic [8] , reverse flotation desiliconization [9, 10] enhanced dispersion - strong magnetic selection [11] and many other processes, received a good selection effect. However, since limonite is ferric oxide with crystal water, the theoretical iron grade of limonite formed under different geological conditions varies greatly, fluctuating from 46 to 63%. For most limonites, only physical separation method is adopted. The grade of concentrate obtained is difficult to reach more than 60%. Many studies have shown that the reductive magnetization roasting-magnetic separation process is the most effective technique for treating this type of ore, and can obtain concentrates with more than 60% grade, and the recovery rate is higher than that of conventional physical beneficiation methods [12 , 13 , 14] . Based on the previous studies, this paper examines the sorting effect of positive flotation, reverse flotation, de-sludge-reverse flotation process and reduction magnetization roasting-magnetic separation process on the ore.
1. Mineral samples and equipment
According to the process mineralogy analysis of the ore sample, the original ore contains 45.4% iron and has a high degree of muddy. The minerals mainly include limonite, a small amount of hematite and other gangue minerals such as quartz and kaolinite. . Experimental studies have shown that when the grinding fineness -0.074mm content reaches 70% or more, the monomer dissociation can be basically achieved between the useful mineral and the gangue mineral.
The flotation test was carried out using a 1.5-liter hanging trough type flotation machine. The roasting test used a muffle furnace as a roasting equipment, and the magnetic separation equipment was a magnetic separation tube.
Second, the selection scheme test
(1) Screening of test protocols
The exploratory experiment on the ore selection by the scheme of re-election, magnetic separation and gravity-magnetization shows that the re-selection and magnetic separation methods cannot effectively separate the useful minerals and gangue minerals in the ore, and the flotation test has been received. The effect is certain, and the magnetization roasting-magnetic separation effect is very good. Therefore, in this experiment, magnetization roasting-magnetic separation is the research focus, and the selection index of flotation is also examined.
(2) Flotation process test
The flotation process test investigated the sorting effects of positive flotation, reverse flotation and desliming-reverse flotation. The grinding fineness in the test is -200 mesh content 77%, the test procedure and the pharmaceutical system are shown in Figure 1, Figure 2 and Figure 3. The test results are shown in Table 1. The test results show that the concentrate grade obtained by positive flotation and reverse flotation is only about 50%, which is difficult to further improve. In the desliming-reverse flotation process, the index of the concentrate in the tank is better than the direct flotation, but the concentrate grade can only reach 53.1%, which is difficult to further improve.
Figure 1 Positive flotation test process
Figure 2 Reverse flotation test process
Figure 3 Desliming-reverse flotation test procedure
Table 1 Positive and negative flotation test results
(III) Magnetization roasting-magnetic separation process test
The results of re-election, magnetic separation and flotation show that the ore is difficult to obtain good indicators by conventional physical methods. Therefore, the reductive magnetization roasting-magnetic separation process was systematically studied. The test procedure is for the ore magnetization roasting, the ore is calcined and then water quenched, and then the final concentrate is obtained by grinding and magnetic separation. The principle flow of the test is shown in Figure 4. For the process, the effects of calcination temperature, time and coal addition during the roasting process and the magnetic field strength during the magnetic separation process on the separation process were investigated.
Figure 4 Magnetization roasting-magnetic separation process
1. Magnetization roasting temperature test
The effect of the calcination temperature on the sorting effect of the process was examined. The test conditions were as follows: the coal addition amount was 10%, the baking time was 40 minutes, and the magnetic separation voltage was 250V. The test results are shown in Table 2. The results in Table 2 show that the calcination temperature is between 700 and 900 °C, and the recovery rate is above 90%. The recovery rate at 800 °C is relatively high, and the concentrate grade is over 58%.
Table 2 Roasting temperature test results
2, roasting time test
The calcination time test was carried out under the test conditions of 800 ° C calcination temperature, coal addition amount 10% and magnetic separation voltage 250 V. The test results are shown in Table 3. The test results show that a better sorting index can be achieved when the roasting time reaches 20 minutes. In order to reduce the production energy consumption and improve the processing capacity of the equipment in production, the roasting time is determined to be 20 minutes.
Table 3 Roasting time test results
3. Reductant addition test
After comparative tests, the reduction effect of bituminous coal is better than that of anthracite, so bituminous coal is used as a reducing agent in the test. In order to investigate the effect of the reducing agent content on the degree of calcination reduction during the roasting process, the coal addition amount test was carried out, that is, the mass of the added coal accounted for the mass percentage of the total amount of coal and the sample. The test conditions were: calcination temperature of 800 ° C, calcination time of 40 minutes, and magnetic separation voltage of 250 V. The test results are shown in Table 4. The test results show that the addition amount of coal has a great influence on the sorting result. When the added amount is less than 10%, the sorting recovery rate is significantly reduced due to insufficient amount of reducing agent. When the addition amount is higher than 10%, the recovery rate slightly increases, but the concentrate grade decreases. The test found that with the increase of coal addition, the carbon content in the sorted concentrate also increased, which led to a decline in the concentrate grade, mainly because the non-volatile coal entered the concentrate due to inclusion. Therefore, the amount of coal added is preferably about 10%.
Table 4 Coal addition test results
4, magnetic field strength test
Through the above tests, it was finally confirmed that the calcination conditions were 10% of the coal addition, 800 ° C of the calcination temperature, and 20 minutes of the calcination time. In order to further improve the concentrate grade, the magnetic field strength condition test of the magnetic separation process was carried out. The test results are shown in Table 5. As the voltage increases, the magnetic field strength increases, the concentrate yield and recovery rate increase, but the grade decreases. From the test results, the voltage is 100V, and the iron grade is 60.34%. 86.47% of the test indicators.
Table 5 Magnetic separation test results
Third, the conclusion
(1) The iron ore iron grade in the ore sample is low, and it is difficult to obtain high-grade iron concentrate by simple flotation and reverse flotation. The desliming-flotation process is slightly better, and the concentrate grade can be obtained. %, the recovery result of 57.95%.
(2) With coal as the reducing agent, under the appropriate test conditions, the roasting-magnetic separation process can obtain a good index of iron concentrate grade of 60.34% and recovery rate of 86.47%.
(3) The roasting-magnetic separation process has good test indexes, short process and high practical value.
references
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