Fine rare earth smelting slag is an important raw material of the rare earth silicon iron alloy. The rare earth concentrate is obtained from the tailings of the Baiyun Obo rare earth iron ore after iron ore processing. With the continuous improvement and improvement of mineral processing technology , the rare earth oxide content of rare earth concentrates can reach more than 60%. However, the smelting of rare earth ferrosilicon alloys with high-grade rare earth concentrates is economically unreasonable and thus has not been applied in industrial scale production. At present, a large number of low-grade rare earth concentrates from Baiyun Obo are used to smelt rare earth ferrosilicon alloys. The chemical compositions are shown in Table 1.
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Table 1 Chemical composition of Baotou rare earth concentrate : %
Grade | REO | CaO | CaF2 | SiO2 | MnO | TiO2 | P2O5 | TFe | BaO | ThO2 | S |
Middle grade Low grade | 54.18 30.42 | 0.95 1.12 | 15.83 23.00 | 1.31 1.02 | 0.29 0.66 | 0.11 0.27 | 5.74 7.68 | 3.49 10.30 | 5.67 8.81 | 0.11 0.13 | 1.80 2.60 |
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Low-grade rare earth concentrate from the chemical composition can be seen, rare earth concentrate contains more impurities, especially phosphorus-containing higher amounts of these oxides, in addition to reductant in the smelting process to consume a certain amount, is not conducive to Improve the rare earth content of rare earth ferrosilicon alloy, and have a very bad impact on product quality. Therefore, rare earth concentrates must be treated to reduce the cost of slagging.
The medium and low grade rare earth concentrates generally have a particle size of less than 200 mm and contain high moisture. Therefore, the rare earth concentrate must be agglomerated and dried before it can be desulfurized and dephosphorized.
(1) Agglomeration of rare earth concentrates Commonly used methods for agglomerating rare earth concentrates include pellet method and briquetting method.
1 Preparation of rare earth concentrate pellets According to the different consolidation temperature of rare earth concentrate pellets, they are divided into low temperature solidified pellets and high temperature calcined pellets.
Preparation of low temperature consolidated pellets The preparation process of rare earth concentrate pellets is shown in Table 2.
Time/min | 0 | 2.5 | 5 | 10 | 15 | 30 | 40 | 50 | 75 | 120 |
Alloy calcium content /% | 0.39 | 15.93 | 21.53 | 21.15 | 22.33 | 21.87 | 21.30 | 19.05 | 15.20 | |
Alloy silicon content /% | 75.70 | 67.50 | 59.10 | 56.10 | 56.10 | 55.70 | 55.80 | 57.00 |
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Low-temperature consolidated rare earth concentrate pellets need to be selected with suitable binders, such as water glass (Na 2 SiO 3 ) and hydrated lime [Ca(OH) 2 ]. The spheroidal process is simple and easy, first entering the rare earth concentrate with less than 8% moisture into its concentrate pellets. The raw ball is dried in a drying oven for 40 minutes, and the temperature of the pellet at the bottom of the drying oven is controlled to be 120 to 150 °C. The dried rare earth concentrate pellets can have a compressive strength of 390 N/ball or more.
Another method of preparing low temperature consolidated rare earth concentrate pellets is carbonation cold consolidation. The process is to add 10% to 15% of slaked lime and a small amount of glass to the dried rare earth concentrate, and mix uniformly, and then use a pelletizer to make pellets of φ15 to 25 mm, and the ball formation rate is 70% to 80%. After natural drying, the green ball has a compressive strength greater than 50 N/ball, and the dried pellets are put into a carbonation tank and passed into a hot furnace exhaust gas (CO2 > 20%, 50 to 80 ° C). The treated pellets can have a compressive strength of 30 to 50 N/ball. The slaked lime in the rare earth concentrate pellets not only participates in the carbonation reaction, but also acts as a flux to increase the alkalinity of the pellets.
Rare earth concentrate | Solid water glass | |||
 ↓ | ↓ | |||
Silo | Crusher | |||
     ↓ | ↓ | |||
Mixer | Ball mill | |||
↓ | ↓ | |||
Ball machine | Silo | |||
↓ | ||||
Rare earth concentrate pellet | ||||
Figure 1 Schematic diagram of the preparation process of low temperature consolidated pellets
Figure 2 Schematic diagram of the sintering furnace
1-furnace; 2-exhaust port; 3-dust valve 4-handwheel
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Preparation of high temperature calcined pellets Rare earth concentrates are free of binders or only a small amount of flux. After mixing, a pellet of φ15 to 25 mm is formed by a pelletizer, and is calcined at a high temperature to achieve the purpose of consolidation by the slag phase formed by the ball group itself. There are various methods for high-temperature calcination, and rare earth concentrate pellets are commonly used in a sintering furnace roasting method and a rotary kiln roasting method.
The pelletizing and roasting of the rare earth concentrate was carried out using a φ1600 mm disc pelletizer and a 0.24 m 3 sintering furnace [15] , and the pelletizer disc tilting was 45°. With a side height of 180mm and a rotational speed of 17r/min, a 1.0-1.1t green pellet can be produced per ton of rare earth concentrate with a productivity of 900kg/(m 2 ·h). The ball performance is listed in Table 3. The sintering furnace is shown in Figure 2. The wind pressure of the fan used is 4000Pa, the rotational speed is 2850r/min, and the power is 2.8kW. Each furnace can produce rare earth concentrate balls 0.8~1.0t, and the return rate is 5%~8%. The technical conditions of the calcination and the properties of the cooked balls are shown in Tables 3 and 4, respectively.
 Table 3 Performance of rare earth concentrate ball
Slaked lime added amount% | Raw ball diameter / mm | Compressive strength / (N / ball) | Impact strength / (time / 50mm) | Bulk density / (t / m3) | Water content /% |
9 to 10 | 10~15 | 5.36 | 3.6 | 1.72~1.81 | 9.5 to 10.5 |
Table 4 Roasting technical conditions
Roasting time | Maximum exhaust gas temperature / °C | Material layer thickness / mm | Vertical firing rate (mm/min) | Maximum calcination temperature / °C |
45～55 | 450～500 | 350~400 | 6-8 | 1140～1150 |
Table 5 performance of roasting cooked balls
Bulk density / (t / m 3 ) | Compressive strength / (N / ball) | Index of rotation (>5mm) /% |
1.543 | 950 | 89.6 |
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The main parameters of the rotary kiln are: kiln body diameter 700mm, length 12000mm, effective volume 4.6m 3 , lining refractory brick thickness 115mm, kiln body inclination angle 5°, rotation speed 0.465r/min, 0.58r/min and 1.2r/ respectively Min. Coal to coke oven gas as fuel. Air combustion. The kiln maintains a weak negative pressure, and the flame is weakly oxidized. A bell feeder is provided at the end of the kiln. The pellet is fed into the kiln through a φ120mm discharge elbow, and the finished pellet discharged from the kiln head is stored in the hopper. Practice shows that when the rotary kiln is inclined at 5°, the rotational speed is 0.58r/min, and the baking temperature is 115～1130°C, the utilization coefficient can be 1.45～1.54t/(m 3 ·d ), and the yield is 87.4%～91.1%. The production index, the pellet compressive strength is about 1100N / ball.
In actual production, roasting of rare earth concentrate pellets by rotary kiln or baking furnace can meet the needs of de-ironing and phosphorus removal and smelting rare earth ferrosilicon alloy.
2 rare earth concentrate briquettes Rare earth concentrate briquetting process is simple and easy. The rare earth concentrate and slaked lime (added in an amount of 8% to 10% of the concentrate) are uniformly mixed in a mixer, and then sent to a briquetting machine for press molding. The size of the rare earth concentrate compact can be changed according to the production requirements by changing different molds, generally controlled at 65mm × 110mm × 240mm. After the natural compaction of the compact, the strength can meet the requirements of iron removal in the electric furnace. This method is simple and convenient to operate, but the strength of the compact is low, which may cause damage during long-term storage and transportation, and thus the use is limited.
3 Mineral composition of rare earth concentrate pellets The mineral composition of rare earth concentrate pellets depends largely on their calcination temperature and alkalinity. Consolidation low rare earth mineral concentrate pellets substantially maintaining the original composition of the rare earth ore, the main mineral monazite, bastnaesite, hematite (Fe 2 O 3), magnetite (Fe 3 O 4) , fluorite (CaF 2 ) and barite (BaSO 4 ).
The mineral composition of the high-alkali rare earth concentrate pellets at high temperature is different from that of low-temperature consolidation pellets. The main reason is that under the high temperature roasting conditions, some physical and chemical changes have taken place inside the pellets, and the mineral composition is mainly red iron. Mineral (Fe 2 O 3 ), calcium ferrite (CaO·Fe 2 O 3 ), fluorite (CaF 2 ), barite (BaSO 4 ), gunite (3CaO·CaFe 2 ·SiO 2 ) and 铈 needle Stone (Ce 2 O 3 ) and the like. The appearance of tassel is apparently caused by the decomposition of monazite and bastnasite during roasting. The high alkalinity (CaO/SiO2>1.87) and high temperature (1100-1200 °C) roasting are the core conditions for the production of stellite. High-alkalinity high-temperature calcined rare earth concentrate pellets are very beneficial for the production of high-quality rare earth concentrate slag and smelting soil ferrosilicon alloy, which should be promoted in industrial production.
references
references
15. JI.B.CлeпoBa и дp..CMaJIb 1980,6:507
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