1 REC + SiO ==== 1 [RE]si + CO ( 18 ) 2 2 We are a China-based factory offering DTF Film for DTF printer, we are looking for buyers and global agent. Hot Peeling Film,Laminated Roll Film,Film Pet Rolls,Hot Peeling Pet Film Guangzhou YESUN Digital Technology Limited , https://www.dtffilmcn.com
18 , Tsinghua University Rare Earth Cast Iron Research Group . Rare Earth Ferroalloys and Alkaline Earth Ferrous Alloys, Beijing: Metallurgical Industry Press, 1991
19 , Tu Yufeng, Ren Cunzhi, etc., calcination decomposition of fluorocarbon bismuth concentrate, nonferrous mining and metallurgy, 1999 , 6 : 18 ～ 20
20 , Zhang Shirong, Tu Yufeng et al. Study on the thermal decomposition behavior of bastnasite, Rare Metals, 1998 , 22 ( 3 ): 185 ～ 187
21 , Tu Yifeng, Zhang Shirong et al. Kinetic model of thermal decomposition of powdered bastnasite ore, Chinese Journal of Rare Earths, 2000 , 18 ( 1 ): 24 ~ 26
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Basic principle of preparing rare earth ferrosilicon alloy by carbothermal reduction method
Carbothermic production is widely used in the reduction of iron silicon alloy Preparation process is characterized by: using a relatively inexpensive bastnaesite ore containing greater than 55% REO; a using prioritized reinforcing calcined fluorocarbon bastnaesite The carbonization process of the rare earth in the mine improves the insulation performance of the false lining; uses a lower operating voltage and a higher core power; selects a suitable composition during the smelting process, and operates the carbon deep into the charge. Ensure that the bottom of the furnace has a higher temperature, prevent the formation and accumulation of carbides at the bottom of the furnace, and achieve the effect of smoothing the furnace condition, no rising of the furnace bottom, and no slag smelting; the alloy composition of the product is uniform, no slag inclusion, no powdering; rare earth reduction The yield of entering the alloy is higher than 95%; the rare earth silicide alloy containing 30% rare earth metal has a power consumption per ton of less than 9500 kW·h, which is equivalent to the power consumption of one ton of FeSi75 alloy.
Basic principle of preparing rare earth ferrosilicon alloy by carbothermal reduction method
The reduction mechanism of metal oxides interacting with carbon is complicated. Even for a metal, the main reactions are different under different conditions and at different stages of the reaction, and sometimes several reduction mechanisms exist simultaneously. In general, the main process of carbothermal reduction is nothing more than the following three processes: the interaction of the gas phase; the interaction of the solid phase; the opposite interaction of the liquid. The reaction of the gas phase in the rare earth intermediate alloy smelting process may be of great significance. That is to say, the agglomerated oxide and the gaseous reducing agent, the gaseous oxide and the agglomerated reducing agent, and the interaction between the gaseous oxide and the gaseous reducing agent are all possible.
The main reaction of carbothermal reduction to obtain rare earth intermediate alloy can be expressed as:
MxOy+C ====MxO y -1 +CO↑ (1)
MxOy+(z+y)C ====MxCz+yCO↑ (2)
zMxOy+yMxCz ==== x(z+y)M+xyCO↑ (3)
In the formula, M is an alloy element such as rare earth, silicon or calcium. The low oxide can be further reduced until a metal is formed. Intermediate product carbon oxides are also present. It can further react with oxides and carbon to form a metal. For example, the process of reducing silicon from silica by a well-studied carbon can be simply listed as follows: [18]
SiO 2(s)
C
SiO (g )
C
SiC (s)
SiO 2 , SiO
Si (1)
SiO 2
SiO ( g )
(4)
→
→
→
→
>1600°C
<1800°C
1800 ~ 1580 ° C
>1850°C
 Â
Thermodynamic and kinetic studies of the Si-OC-Ce(Y) system indicate that the following reactions are present:
Ce 2 O 3 +7C ==== 2CaC 2 +3CO↑ (5)
Y 2 O 3 +7C ==== 2YC 2 +3CO↑ (6)
SiC+SiO ==== 2Si+CO↑ (7)
SiC+SiO 2 ==== Si+SiO+CO↑ (8)
CeC 2 +2SiO ==== CeSi 2 +2CO↑ (9)
SiC+CeO ==== CeSi+CO↑ (10)
When the temperature is higher than 1600 ° C, silicon is initially reduced, and intermediate products of SiO, SiC, and rare earth carbides are formed. Reducing rare earth metals requires higher temperatures (above 1800 ° C).
The intermediate agglomerated product of the reduced silicon and the rare earth metal is a carbide which can be decomposed by interaction with silicon monoxide or silicon dioxide. Under the same conditions, the formation of silicon carbide is easier than the formation of rare earth carbides; with the formation of rare earth silicide, rare earth carbides are more easily decomposed than silicon carbide. The aggregation of silicon carbide, etc., if not decomposed in time, can easily cause the bottom of the furnace to accumulate and form a furnace. The ratio of the amount of rare earth metal and silicon formed and decomposed under the actual conditions of the carbothermal reduction process will be the sum of thermodynamic and kinetic factors. Decide.
When carbon reduction is used, a large amount of silica is always added . On the one hand, the reduction product silicon can form stable silicide with rare earth and calcium, which reduces the initial reduction temperature of these difficult original elements; on the other hand, it will inevitably be stable. Silicates and other complex oxides that deteriorate the thermodynamic and kinetic conditions of the reducing elements.
The basic principle of producing rare earth silicide alloy by carbothermal reduction method mainly includes the reduction of silicon dioxide by carbon to silicon and silicon monoxide and the carbonization of rare earth compound to form carbide and the reduction of rare earth by SiO2 into rare earth metal. Of course, there are other side reactions and intermediate reactions, such as the formation and destruction of silicon carbide, the decomposition and reduction of barium sulfate, the reduction of calcium and aluminum compounds, and the formation of rare earth silicides from rare earth metals and silicon.
(1) Basic chemical process of carbon-reduced silica The basic chemical theory of carbon-reduced silica has been well studied by many scholars since the advent of ferrosilicon and industrial silicon. It is a relatively mature theory. It is summarized into the following basic chemical reactions.
SiO 2 +2 C ==== Si+2CO (11)
SiO 2 +C ==== SiO+CO (12)
SiO+2C ==== SiO+CO (13)
2SiO ==== Si+SiO 2 (14)
2SiC+3SiO 2 ==== Si+4SiO+2CO (15)
Formula (11) is the total reaction formula. Under the condition of insufficient carbon content, the reaction of silica is insufficient, and a large amount of silicon monoxide [formula (12)] can be formed; in the case of excess carbon, a large amount of silicon carbide is formed [formula (13)] . In fact, in the submerged arc furnace, the first generation of SiO formed by the furnace charge filtration and the coke carbon fall reaction is SiC [Formula (13)], which is then decomposed and reduced to form silicon. Formula (14) is a disproportionation reaction, and many scholars have proved that this reaction exists in the furnace.
(2) Chemical reaction of rare earth concentrate in furnace The chemical formula of bastnasite is in principle REFCO 3 , which is a composite mineral of rare earth carbonate and rare earth fluoride, which exists in nature as a crystal. Under certain temperature conditions, the rare earth carbonates decomposed to produce rare earth oxyfluoride [19 to 21].
REFCO 3 ====REFO+CO 2
(16)
â–³
Equation (17) is the chemical equation for the rare earth carbonization reaction.
In the submerged arc furnace, the actual system is Si-OC-RE system, and the following main reactions occur [2 2 ~ 26] :
           Â
REFO+3C ==== REC 2 +CO+[F] (17)
Whether the rare earth carbonization reaction in the formula (17) is to generate REC 2 or RE 2 C 3 or to generate REC is to be further studied and confirmed, but the reaction of the rare earth with carbon to form a carbide has been proved by practice. .
The reduced rare earth metal and silicon form a rare earth silicide alloy, and fluorine is combined with silicon dioxide or silicon monoxide to form a fluorosilicide discharged with the furnace gas.
Before the rare earth concentrate is put into the furnace, it is calcined to liberate carbon dioxide [formula (16)] to increase the activity of the rare earth compound; at the same time, it avoids the liberation of carbon dioxide from the fluorocarbon strontium ore after the rare earth pellets are put into the furnace. The pellets are pulverized.
In order to accelerate the formation of rare earth carbides, high-reactive reducing agents-coke powder and charcoal powder are added during the formation of rare earth concentrates, so that the rare earth compounds are fully contacted with carbon, and the rare earths first form carbides at high temperatures in the furnace. [Formula (17)]. In order to strengthen the process of rare earth formation of carbides in the agglomerates, when the rare earth calcined ore is combined with the carbon reducing agent, the carbon amount is the amount of carbon required for the complete conversion of the rare earth compound into the rare earth carbide (REC 2 ). 1 to 3 times.
Starting from the requirements of the reaction [formula (18)], conditions for generating sufficient SiO are caused in the furnace to facilitate reduction of the rare earth carbide by silicon monoxide. To cause the SiO atmosphere, it must be under the condition of insufficient carbon, which is the basic chemical principle that requires carbon deficit operation in the process.
Of course, in the furnace, the reaction of reducing the rare earth oxide by silicon also exists, but does not constitute a main reaction.
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