One-step carbon thermal reduction method for smelting rare earth silicide alloys in DC submerged arc furnace
March 13, 2024
In the process of smelting rare earth intermediate alloys in a DC submerged arc furnace, the quality of the furnace material includes its chemical composition, physical and mechanical properties, particle size composition, which plays an important role in the furnace condition, electrical energy consumption, and product quality. The new process of one-step carbon thermal reduction for smelting rare earth silicide alloys is carried out in a 4150kVA DC submerged arc furnace.
1. Raw materials
(1) Rare earth raw materials: The rare earth raw materials used in this process are fluorocarbon cerium type rare earth concentrates, with the main chemical components being: ReO>5% BaO<8%. The particle size of rare earth concentrate is generally less than 0.5mm for gravity ore and 200 mesh for flotation ore. From the performance of pelletizing, flotation ore is better.
(2) Silicon stone: In principle, the silicon stone used in the smelting of ferrosilicon alloys can be used as the silicon containing raw material for this process, with SiO2>98%, Al2O3<0.5%, and P2O5<0.02%. The block size of silica is 25-80mm.
(3) Carbon reducing agent: Various types of coke (such as metallurgical coke, coal coke, petroleum coke, etc.), charcoal, wood blocks, etc. can be used as carbon reducing agents for this process. Considering the needs of the smelting process, it is necessary to use carbon reducing agents with good reactivity and high specific resistance, while also considering production costs. In actual production, it is often used in combination.
① Coke: Metallurgical coke has a high fixed carbon content, high coke block strength, and low volatile content, but its reactivity is not as good as gas coke, and its specific resistance is low. This process prioritizes the selection of coke particles under the sieve, with a particle size of 1-25mm, of which 3-8mm accounts for more than half. The fixed carbon content is greater than 80%.
Gas coke is actually a type of semi coke with good reactivity, high specific resistance, but relatively high volatile content. The fixed carbon content is generally around 78% and the strength is relatively low, but it is not affected when used in a DC submerged arc furnace.
② Charcoal and wooden blocks: The use of charcoal is mainly to adjust the permeability of the furnace charge. Use hardwood charcoal with a block size of 3-50mm, and the quantity of less than 10mm should not exceed 20%. The wooden blocks are made from wood processing plant scraps or dry branches, preferably hardwood. The block size is 20-60mm, and the fixed carbon content is generally>26%.
2. Technological process
The main advantages of carbon thermal reduction method are that it can be directly reduced in one step, the reducing agent is cheap, the energy utilization is reasonable, and it can be continuously produced in large quantities. The silicon thermal reduction method has a fast reaction rate, and the product is easy to adjust and control, making it suitable for small-scale production of multiple varieties. When the carbon thermal method achieves error free operation, the rare earth recovery rate is above 90%. The silicon thermal method has added a secondary recovery process, and its recovery rate can only reach 80%. The production of rare earth intermediate alloys by silicon thermal method consumes more than 30% of the corresponding raw materials and electrical energy compared to the carbon thermal method.
