Synchronous Dephosphorization Process Technology for Reduction and Roasting of High Phosphorus Oxide Hematite
However, about 1/9 of China's iron ore resource reserves are braided hematite, and the effective use of braided hematite ore is of great significance in China.
A lot of research work has been carried out on this kind of ore at home and abroad. Kunming University of Science and Technology conducted experiments on re-election, but the effects of iron enrichment and phosphorus removal were not obvious; Wuhan University of Technology used direct reduction to treat this type of ore, which can obtain higher iron grade and recovery rate. However, the effect of dephosphorization is not very satisfactory, and the phosphorus grade in the final product is about 0.5%; Ji Jun et al. conducted a pilot study on the dispersion-selective agglomeration dephosphorization-reverse flotation dephosphorization process, through appropriate adjustment of the pharmaceutical system. And the process structure, the phosphorus content in the iron concentrate can be reduced to less than 0.25%, the iron recovery rate reaches 90.57%, but the iron concentrate grade is only about 50%; domestic units have carried out flotation and magnetic separation test on the ore. However, the iron grade in the iron concentrate is lower than that of the low phosphorus grade.
In summary, for the Ningxiang-type high-phosphorus-like hematite, it is difficult to obtain satisfactory results by the commonly used beneficiation method. Studies have shown that the direct reduction roasting-magnetic separation method with the addition of dephosphorization agent can obtain better indicators, but no detailed process conditions have been studied. In this paper, the effects of direct reduction roasting-magnetic separation process parameters of dephosphorization agent were studied, and the optimal conditions for direct reduction roasting-magnetic separation of ore were determined, which provided a new way for the effective utilization of such ore.
First, the nature of the sample and test methods
The grades of iron and phosphorus in the high-phosphorus-like hematite ore in western Hubei are 43.65% and 0.83%, respectively. The main useful minerals are hematite and a small amount of limonite, and the iron of the limonite is 97.82%.
The reduction roasting uses coal as a reducing agent and simultaneously adds a dephosphorization agent NCP to achieve the purpose of simultaneous dephosphorization by reduction roasting. Both the test sample and the coal were broken to -2 mm. The test procedure is shown in Figure 1. The main factors investigated include coal dosage, dephosphorization agent dosage, reduction calcination temperature and reduction roasting time.
Figure 1 Direct reduction roasting-magnetic separation test procedure
The iron in the final product obtained by direct reduction roasting-magnetic separation is greater than 90%. To avoid confusion with conventional iron concentrates, the product is named as a reduced iron product. Test large changes in the total mass of the product after firing as compared with prior to firing, so that the ratio of the absolute amount of the metal with the absolute amount of gold metal iron in the reduced iron product with added test firing ore recovery calculated. The amount of coal and NCP refers to the ratio of coal or NCP to ore quality, expressed in mass percent.
Second, the test results and discussion
(1) Two-stage grinding time test
Firstly, the influence of grinding grain size on the test results during the roasting process was investigated. In the previous stage of the test, it was found that the improvement of iron grade and the reduction of phosphorus grade were achieved by fine grinding, so the experimental procedure was determined to be two-stage grinding magnetic separation. A detailed examination of the time of regrind of the concentrate was carried out. The fixed conditions are: coal dosage 40%, NCP dosage 20%, roasting temperature 1000 ° C, roasting time 60 min, grinding concentration 70%, first grinding particle size -0.074 mm grain size 55%, magnetic field strength 87.6 kA/m, concentrate regrind. The results are shown in Figure 2.
Figure 2 Two-stage grinding time test results
It can be seen from Fig. 2 that the grade and recovery rate of iron increase when the second-stage grinding time increases, but the phosphorus grade has a large decrease when the grinding time is 20min, which should be finer in the size of the inlay. The gangue mineral can be sufficiently dissociated from the iron mineral at this time, and no agglomeration occurs. Therefore, it is determined that the second grinding time is 20 min, the particle size is -16 μm, the grain size is 100%, and the -8.93 μm particle size is 90%.
(2) Coal consumption test
The other conditions were fixed, and the influence of coal consumption during the roasting process was examined. The results are shown in Fig. 3.
Figure 3 Coal dosage test results
It can be seen from Figure 3 that as the amount of coal increases, the grade and recovery of iron increase, and the grade of phosphorus decreases. In this process, coal can fully react with the ore to reduce Fe 2 O 3 in the ore, but when When the coal consumption exceeds 40%, the coal is excessive in the reaction. Although the recovery rate of iron is still somewhat improved, it will affect the dephosphorization effect of the dephosphorization agent, and the iron grade is slightly reduced. Therefore, the optimum amount of coal is determined to be 40%.
(III) Dephosphorization agent dosage test
Other conditions are unchanged, and the amount of NCP is changed to test. The results are shown in Fig. 4.
Figure 4 NCP dosage test results
It can be seen from Figure 4 that before the NCP dosage is 15%, the iron grade and recovery rate are significantly improved, and the phosphorus grade is significantly reduced. When the NCP dosage exceeds 20%, the effect on the results becomes smaller, so the NCP is determined. The optimum dosage is 20%. The main function of NCP is to react with the ore during the roasting process, thereby removing phosphorus during the magnetic separation process, and at the same time reducing the temperature of reduction of iron during roasting, which has a certain promoting effect on reduction.
(4) Calcination temperature test
Other conditions were unchanged, and the firing temperature was changed to test. The results are shown in Fig. 5.
Figure 5 Calcination temperature test results
It can be seen from Fig. 5 that when the calcination temperature is lower than 1000 °C, the recovery of iron increases with the increase of temperature, and the grade of phosphorus decreases, indicating that at this temperature, raising the temperature is beneficial to the reduction of iron. And the removal of phosphorus; when the temperature exceeds 1000 ° C and continues to rise, the grade of phosphorus is obviously increased, and the recovery rate of iron is decreased accordingly, so that in this range, the effect of the dephosphorization agent on the temperature is disadvantageous. influences. When the temperature is higher than 1000 °C in the test, the product after calcination is agglomerated seriously, and large iron particles are formed, and the grade of phosphorus in the reduced iron product is increased. It is inferred that some of the iron is melted and combined with phosphorus during the calcination process, making dephosphorization more difficult to achieve. Therefore, it was determined that the optimum temperature was 1000 °C.
(5) Roasting time test
Other conditions were unchanged, and the firing time was changed to test. The results are shown in Fig. 6.
Figure 6 Roasting time test results
It can be seen from Fig. 6 that as the calcination time is prolonged, the grade and recovery rate of iron increase, and the grade of phosphorus decreases. However, when the calcination time exceeds 60 min, the effect becomes smaller. It can be determined that when the time is 60 min, the reduction is performed. The reaction was basically completed, so the calcination time was determined to be 60 min.
The optimum conditions for the determination of high-phosphorus-like hematite roasting and reduction magnetic separation in western Hubei were as follows: reducing agent coal dosage 40%, NCP dosage 20%, calcination temperature 1000 °C, roasting time 60 min, and a grinding particle size of -0.074 mm. The particle size accounts for 55%, the second-stage grinding particle size is -16μm, the grain size is 100%, the -8.93μm particle size is 90%, and the magnetic separation field is 87.6kA/m. After repeated tests, the average iron grade of the reduced iron product was 90.09%, the iron recovery rate was 88.91%, and the phosphorus grade was 0.06%.
Third, the conclusion
(1) Adding dephosphorization agent during the reduction roasting process of the braided high-phosphorus hematite ore can reduce the phosphorus content to 0.06% while obtaining the high-grade reduced iron product. It provides a new way to make rational use of refractory high-phosphorus hematite.
(2) In the process of reduction roasting, the dephosphorization agent NCP plays the role of dephosphorization, and at the same time, the calcination temperature can be lowered.
(3) The reduction roasting temperature should be controlled at 1000 °C. If the temperature is too high, the iron mineral will recombine with phosphorus, and if the temperature is too low, the reduction effect will not be achieved.
(4) Since the size of the inlaid hematite itself is extremely fine, the products subjected to reduction and roasting require sufficient fine grinding to be effectively sorted.
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