Experimental Study on Comprehensive Recovery of Iron from an Iron Tailings in Jiangxi Province

Jiangxi Province, a place rich in iron ore resources, currently there are 300 million tons of iron ore, nearly 100 million tons of ore was mined, in addition to more than ten kilometers long such iron ore belt, and suitable Open pit mining. Due to the long-term use of the screening and washing process to recover the lump ore, a large amount of iron resources are lost to the tailings. The comprehensive utilization of the tailings not only has high development value, but also meets the current resource situation of China and the cycle advocated by the government. Economic and industrial policy.

First, the nature of the ore

(1) Main components and characteristics of minerals

Ore mineral composition is relatively simple, the main metallic minerals limonite, hematite, magnetite, manganese soft pyrite, sphalerite, galena, covellite, malachite; gangue Minerals include opal (chalcedony), quartz , feldspar , clay minerals, chlorite, calcite , hydromica (sericite), tremolite, and the like.

1. Iron oxide minerals

Iron is mainly found in limonite and hematite, with limonite being dominant. The particle size is fine, mostly below 0.04mm, and is widely distributed in the sample. In addition to the monomer particles, it is often adhered to other mineral surfaces.

2, sulfide

The sulfide in the sample is mainly pyrite, and most of the oxidized residue is encapsulated in hematite and limonite. The monomer is rare, and the particle size is more than 0.04 mm.

3. Hard manganese ore and pyrolusite

It is mostly mixed with limonite and hematite. It is difficult to identify under the microscope, and the particle size is mostly 0.01~0.05mm.

4, quartz, opal

Quartz is relatively small, mainly opal, which is cryptocrystalline fine particles, mostly contaminated with limonite.

5. Silicate minerals such as hornblende

The content is very small, and it is needle-shaped or granular, and some of the particles have gypsum adhesion on the surface.

6, clay minerals such as kaolinite

The particle size is very fine, mostly below 0.02mm, distributed in dusty form, or mixed with limonite, showing flocculent particles.

(2) Chemical composition

Table 1 Multi-element analysis results of raw ore

The multi-element analysis of the ore shows that the main chemical components of the ore are iron, SiO ₂ and Al ₂ O ₃ , and the valuable components are mainly iron, lead, zinc, copper and cobalt .

2. Experimental study on reduction magnetization roasting

(1) The main principle of conversion of limonite into magnetite

Under high temperature conditions, coal is used as a reducing agent to convert limonite into magnetite. The chemical reaction is:

Fe ₂ O ₃ ·nH ₂ O—Fe ₂ O ₃ +nH ₂ O (1)

3Fe ₂ O ₃ +CO—2Fe ₃ O ₄ ++CO ₂ (2)

The conversion process is mainly:

1. Limonite loses crystal water under high temperature conditions and converts ferric oxide;

2. The ferric oxide is reduced to triiron tetroxide in a reducing atmosphere. The reduction reaction process is a heterogeneous reaction process. The same gas phase (reducing gas) reacts. The magnetization roasting reaction is carried out in three stages:

(1) Diffusion and adsorption. The reducing gas molecules are adsorbed by the surface of the ore due to convection or molecular diffusion of the gas.

(2) Chemical reaction. The adsorbed reducing gas interacts with the oxygen atoms of the ore to carry out a chemical reaction.

(3) Desorption of chemical products. The gas product produced by the reaction leaves the surface of the ore and diffuses into the gas phase in the opposite direction.

During the calcination process, the newly formed reducing material first forms an outer shell, which surrounds the unreduced portion, and the reaction proceeds gradually inward, and the reaction speed is controlled by the interface of the reducing substance and the reducing product.

The process of converting Fe ₂ O ₃ to Fe ₃ O ₄ was carried out in the following manner. The oxygen in the outer layer of the αFe ₂ O ₃ ore is removed by a reducing agent, and the lattice of the iron oxide crystal is locally deformed, so that αFe ₂ O _{3 is} converted into γFe ₂ O ₃ containing a certain number of fine pores, and a spinel type is formed. A cubic lattice of γFe ₂ O ₃ outer layer. Continued deoxidation on the surface of the ore will result in excess iron ions, and excess iron ions will fill the missing nodes. When all the points on the outer layer are full, they become magnetite. These magnetites have the same crystal lattice as γFe ₂ O ₃ . This spreads from the outer layer to the inner layer, and this process continues to the hematite in the center of the ore, until the hematite disappears.

(2) Magnetization roasting temperature test

Mix the ore and pulverized coal into the magnetic ring roasting furnace, raise the temperature to the set temperature, keep the temperature constant for 2h, change the magnetization roasting temperature, 900°C, 950°C, 1000°C, 1050°C, and grind the product after natural cooling 85%- 74μm, then magnetic separation tube magnetic separation operation, the magnetic field strength is 87.55kA / m, the test results are shown in Figure 1, this test uses anthracite. The proportion of pulverized coal is 20% of the weight of the ore sample. According to the test results, 950 ~ 1000 ° C is the best temperature.

Figure 1 Magnetization roasting temperature test results

1-iron grade; 2-iron recovery rate;

(3) Test of coal type and dosage

The anthracite and lignite were compared. The magnetization roasting temperature was 950 °C and the calcination was 2 h. The proportion of coal powder was 8%, 15% and 20% respectively. The results showed that under the same conditions, lignite effect was significantly better than anthracite; In the coal, with the decrease of the amount of coal powder, the total iron content of the iron concentrate is reduced. In addition, anthracite is used, and the total iron content of the magnetized roasting ore is not different from that of the original ore. When the lignite is used, the total iron content of the magnetized roasting ore is higher than that of the ore. Nearly 10%, the weight of the ore sample after magnetization roasting is also reduced by 20%. Considering the cost comprehensively, lignite is selected, and the amount of coal powder is preferably 15% to 20% of the original ore. The test results are shown in Figure 2.

Figure 2 Coal test results

(4) Magnetization roasting time condition test

The calcination temperature was determined to be 950 ° C, the proportion of coal was 20%, and the magnetization roasting time was changed, which was 1 h, 1.5 h, 2 h, and 3 h, respectively. After the product is naturally cooled, it is ground 85%-74μm, and then magnetic separation is performed by magnetic separation tube. The magnetic field strength is 87.55kA/m, and the test result is shown in Fig. 3.

Figure 3 Test results of magnetization roasting time conditions

(5) Magnetic field strength test

It was confirmed that the magnetization roasting temperature was 950 ° C, the amount of coal was still 20%, and the product of the constant temperature magnetization roasting for 2 h was subjected to the magnetic field strength condition test. The product was naturally cooled and ground to 85%-74 μm, and the magnetic separation operation was performed, and the magnetic fields were changed to 71.63 kA/m, 87.55 kA/m, and 103.46 kA/m, respectively. The test results are shown in Figure 4. Considering the comprehensive technical and economic indicators, the magnetic field strength of magnetic separation operation is 87.55kA/m.

Figure 4 Magnetic field strength test results

(6) Grinding fineness condition test

The separation effect of iron minerals and gangue minerals is poor when the calcined products are directly sorted, and grinding is required before sorting. The other conditions were the same, and the magnetic baking test was carried out on the magnetized roasting products which were not ground (-74μm was 68%) and the grinding fineness was -74μm 80%, 85%, 90%, 98%, respectively. In the grinding products, the increase of -74μm particle size, the iron concentrate yield decreased, and the total iron content increased. When the content of -74μm was more than 85%, the change rate slowed down. Therefore, it is better to take -74 μm to 85%. The test results are shown in Figure 5.

Figure 5 results of grinding fineness conditions test

(7) Process test

According to the above test results, the best conditions are determined in Table 2. The process test is carried out according to the best condition test. The mass quality flow chart is shown in Fig. 6.

Table 2 Roasting-magnetic separation process conditions

Figure 6 Magnetization roasting - magnetic selection quality process

Third, the conclusion

(A) as the main mineral in limonite ore beneficiation hard metal material, such magnetic ore roasting - magnetic separation is the best technical indicators dressing method, both grade and recovery.

(2) The lignite is sorted by a magnetization roasting-magnetic separation process to obtain an iron concentrate having a yield of 51.46%, a total iron content of 64.83%, and a total iron recovery rate of 78.88%. All indicators met the requirements. Moreover, the magnetization roasting-magnetic separation process has the characteristics of reasonable process, reliability, strong adaptability and easy implementation in production.

(3) From the economic point of view, the cost of magnetizing roasting is high, and it can only be considered when there are cheap coal resources in the local area. Under normal circumstances, the joint process, such as: weak magnetic separation - strong magnetic selection - positive flotation, classification - re-election - flotation, etc., although these processes are more complicated, the operating costs are much lower than the magnetization roasting.