Chromium is an important strategic resource and an important raw material for the stainless steel industry. It is also widely used in refractory materials, chemicals and light industry. With the development of our national economy, the demand for ferrochrome mine is growing rapidly. However, China's chromite resources are in serious shortage. The reserves are only 10.779 million tons (ores), and the rich ore only accounts for 1/2 of them. Most of them are distributed in Tibet, Xinjiang and other areas, and it is difficult to use due to the imperfect infrastructure. In recent years, more than 85% of the chromite ore required in China is imported, and the resource supply situation is very tight. Therefore, while strengthening the domestic chromite ore resource geological prospecting, research on the selection technology of chromite ore resources and improving the resource utilization rate have increasingly attracted the attention of researchers. At present, in the production practice of chromite ore selection, re-election methods such as shaker and jigging are widely used. Dry magnetic separation, wet magnetic separation, flotation and various chemical beneficiation methods are also reported in laboratory research. However, there are few applications in production. In this paper, for a chromite ore with high iron content, the process of selecting magnetite by weak magnetic separation and recovering chromite by strong magnetic separation is determined. The chromite ore is recovered and the comprehensive utilization of iron resources is realized. First, the nature of the ore The ore is a type of high-iron chromite ore beach sand mine. The original ore contains Cr 2 0 3 grade of 31.20% and the total iron grade (TFe) of 29.11%. Metal ore minerals are chromite, chrome spinel, and magnetite, hematite and secondary iron titanium; gangue minerals olivine, pyroxene and amphibole, followed serpentine. The content of chromium minerals is 60.3%, of which chrome spinel accounts for a large proportion, and the mineral content ratio of chromite or chrome spinel is roughly 35..65. It is concluded that it is difficult to obtain high-grade chromium concentrate from the sample. The magnetite content reached 27.6%, and some magnetites belonged to the category of chrome magnetite due to the high Cr 2 0 3 content. Scanning electron microscopy analysis of the composition of the micro-area shows that the average content of Cr 2 0 3 in the sample chromium mineral is 43.58%, and the average iron content in magnetite is 60.66%. The main fraction in the ore sample is 0.1-0.5mm, of which the +0.5mm fraction yield is only about 0.3%, the -0.1mm fraction yield is less than 3%, and the chromium mineral and magnetite dissociation are 93.7 respectively. % and 90.2%. The ore chemical composition, chromium phase analysis and main mineral mass content analysis results are listed in Table 1, Table 2 and Table 3, respectively. Table 1 Main chemical composition of raw ore (mass fraction) /% Cr 2 0 3 TFe FeO Fe 2 0 3 SiO 2 Ti0 2 A1 2 0 3 Mg0 CaO other 31.20 29.11 19.81 19.61 5.36 0.39 9.44 9.42 3.01 1.76 Table 2 Analysis results of ore chromium phase Chromium phase content/% Distribution rate /% Cr 2 0 3 in chromite ore and chrome spinel 28.05 89.90 Cr 2 0 3 in magnetite 0.99 3.17 Cr 2 0 3 in silicate 2.16 6.93 total 31.20 100.00 Table 3 Mineral composition and relative content (mass fraction) /% Chromite, chrome spinel magnetite Hematite Ilmenite Peridot, pyroxene, hornblende Serpentine other 60.3 27.6 2.9 0.5 7.8 0.7 0.2 Second, experimental research The results of process mineralogical studies show that the main component available for beneficiation recovery in the sample is Cr 2 0 3 , and iron can be used as a comprehensive utilization target. That is, the gangue minerals that the mineral needs to be removed are mainly silicate minerals such as olivine, and the useful mineral chromite, chrome spinel and magnetite are separated. Compared with gangue minerals, magnetite, chromite and chrome spinel are denser, and some gangue minerals can be removed by re-election; magnetite is a strong magnetic mineral, and chromite is a weak magnetic mineral. Weak magnetic separation can achieve separation between the two, weak magnetic separation concentrate is iron concentrate, weak magnetic separation tailings is chromium coarse concentrate; chromium coarse concentrate can use strong magnetic separation to improve chromium concentrate grade. It should be noted that since the mineral silicate gangue mineral content is small and it is a non-magnetic mineral, the separation from the useful mineral can also be realized in the magnetic separation process, so the re-election operation can be selected according to the selection effect. Adoption. (1) Re-election test The re-election test examined the sorting effect of the shaker, jigging and chute on the ore. The test results show that the jigging and chute operations have a poor effect on the ore sorting, and the shaker sorting can remove the olivine, pyroxene, etc. Light minerals have a certain improvement on the grade of concentrate, which can increase the grade of raw ore Cr 2 0 3 from 31.04% to 33.68%, and the recovery rate is 84.47%. However, due to the low density of gangue minerals in the ore, the enrichment effect of re-election operations on useful minerals is not obvious. (2) Weak magnetic separation test The process of weak magnetic separation is shown in Figure 1. The weak magnetic separation test mainly investigated the influence of factors such as the weak magnetic separation magnetic field strength, the selected particle size, and the magnetic separator roller speed on the separation effect. 1. Weak magnetic separation magnetic field strength test The weak magnetic separation field strength test was carried out under the condition that the grinding size was -0.074mm, the particle size was 62%, and the drum rotation speed was 50r/min. The grade and recovery rate of iron concentrate and chromium coarse concentrate are shown in Fig. 2. It can be seen from Fig. 2 that with the increase of field strength, although the TFe grade of iron concentrate does not change much, the recovery rate is obviously improved, and at the same time, the Cr 2 0 3 grade in chromium coarse concentrate is improved. Therefore, it is determined that the weak magnetic field strength is 0.12T, and the iron concentrate TFE grade is 55.38%. 2, weak magnetic selection into the particle size test In order to examine the dissociation of minerals, the effect of separation of magnetite (Fe 3 0 4 ) and chromite (Cr 2 0 3 ) was weakened with a magnetic field strength of 0.12 T and a drum rotation speed of 50 r/min. The magnetic separation was selected into the particle size test. The separation of magnetite from chromite in the test is shown in Fig. 3. The results in Fig. 3 show that the Fe 3 0 4 content in the iron concentrate and the Cr 2 0 3 recovery rate in the chromium concentrate are significantly reduced when the material size is fine. It indicates that fine grinding of ore may result in mechanical entrainment during magnetic separation. Therefore, the ore sample does not need to be ground (-0.074mm particle size content is about 2%), and can be directly subjected to weak magnetic separation. At this time, an iron concentrate containing Fe 3 0 4 69.24% can be obtained, and Fe 3 0 4 is in operation. The recovery rate was 97.91%; for the chromium coarse concentrate, the Cr 2 0 3 content was 41.55%, and the work recovery rate was 80.61%. 3, weak magnetic separation roller speed test When the magnetic field strength is 0.12T, the magnetic separator roller speed test is carried out on the unmilled ore. The separation of magnetite and chromite in the test is shown in Fig. 4. It can be seen from Fig. 4 that as the roller speed increases, the Fe 3 0 4 content in the iron concentrate increases slightly, but the grade of the chromium coarse concentrate decreases, so it is determined that the suitable roller speed is 50 r/min. (3) Strong magnetic separation test When the ore is directly weakly magnetically selected, the ferromagnetic magnetite enters the iron concentrate, and the weakly magnetic chromium-containing mineral enters the tailings together with the non-magnetic gangue mineral, and the two are separated by strong magnetic separation. The test flow is shown in Fig. 5. . The strong magnetic separation test is mainly for the tailings of the original mine without direct grinding and weak magnetic separation. The effects of the selected particle size and magnetic field strength on the separation effect are investigated. 1. Strong magnetic separation and particle size test In order to examine the effect of mineral dissociation on the chromite index in weak magnetic separation tailings, a strong magnetic inclusion particle size test was carried out. The magnetic separation strength was 0.9T in the test. The test results are shown in Fig. 6. It can be seen from Fig. 6 that the selection of the particle size of the strong magnetic field has little effect on the Cr 2 O 3 grade and recovery rate in the chromium concentrate, but the recovery rate is reduced when the grinding is too fine, so the weak magnetic separation tailings can be ground without grinding. Direct magnetic separation. 2, strong magnetic field strength test The experimental results of strong magnetic separation of weak magnetic separation tailings at different field strengths are shown in Fig. 7. It can be seen from Fig. 7 that the recovery rate of chromite is greatly increased with the increase of magnetic field strength; however, after the field strength reaches 0.7T, the magnetic field strength is continuously increased, and the grade of chromium concentrate is reduced. Considering the comprehensive consideration, the strong magnetic field selection is determined. It is 0.9T. At this time, the Cr 2 O 3 grade in the chromium concentrate is 41.43%, and the operation recovery rate is 93.01%. (4) Full process test According to the above test results, the whole process test of the original ore without grinding and re-election, directly recovering magnetite by weak magnetic separation, and weak magnetic separation tailings for strong magnetic separation and recovery of chromite is determined. The test procedure is shown in Figure 8, and the test results are shown in Table 4. It can be seen from Table 4 that the weak magnetic separation-strong magnetic separation process can obtain the Cr 2 O 3 grade of 41.43% and the recovery rate of 79.31% from the ore containing Cr 2 O 3 of 31.23% and containing Fe of 28.81%. The iron concentrate with a chromium concentrate and a TFe grade of 55.89% and a recovery rate of 58.71%. Table 4 Full process test results product name Yield/% grade/% Recovery rate/% Cr 2 O 3 TFe Cr 2 O 3 TFe Iron concentrate 30.26 15.21 55.89 14.74 58.71 Chromium concentrate 59.77 41.43 17.47 79.31 36.25 Tailings 9.96 18.64 14.58 5.95 5.04 Raw ore 100.00 31.23 28.81 100.00 100.00 Third, the conclusion The key to the selection of a high-speed ferrochrome is the use of magnetic differences between chromite, magnetite and gangue minerals. The weak magnetic separation and strong magnetic separation process can effectively select the ore and realize the comprehensive utilization of chromite and magnetite. The ore is not required to be ground. When the weak magnetic separation magnetic field strength is 0.12T and the drum rotation speed is 50r/min, magnetite with a TFe grade of 55.89% and a recovery rate of 58.71% can be obtained. The magnetic field strength of the weak magnetic separation tailings is With strong magnetic separation of 0.9T, the obtained chromium concentrate Cr 2 0 3 grade is 41.43%, and the recovery rate is 79.31%. Double layer shutter door forming machine,we can tell from its name.This machine can make double layer shutter door with pu insulation or nimeral wool.This double layer shutter door are used a lot for shpping mall.
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