Composite molten iron pretreatment agent and application

Abstract

The invention discloses a composite molten iron pretreatment agent and application. The composite molten iron pretreatment agent comprises the following chemical components in percentage by mass: 58-71% of CaCO3, 5-13% of Fe2O3, 7-11% of C, 8-10% of NaCl and the balance of unavoidable impurities. In the inevitable impurities, SiO2 is less than or equal to 4%, and Al2O3 is less than or equal to 2%. The invention further provides application of the composite molten iron pretreatment agent to desulfurization and dephosphorization in the molten iron treatment process. According to the invention, the limestone powder, the iron oxide, the carbon powder and the sodium chloride are selected and proportioned, so that high-alkalinity desulfurization of the whole slag system can be maintained, and the functions of decarburization, dephosphorization, desilicication and desulfurization can be achieved during molten iron treatment.

Description

Technical Field

[0001] The invention relates to the technical field of ironmaking pretreatment, and more specifically to a composite molten iron pretreatment agent and application thereof. Background Art

[0002] In the whole process of steel enterprises, molten iron pretreatment and molten steel refining have developed rapidly in recent years. In the molten iron tank or refining furnace, powder spraying and stirring are usually used to make the removal rate of sulfur and phosphorus reach 80-90%. The technical principle of molten iron desulfurization is that the desulfurizer reacts with the sulfur in the molten iron to form sulfides that are insoluble or low-soluble in iron, thereby reducing the sulfur content of the molten iron, and the sulfur enters the slag phase and is separated out of the system by slagging or pouring, so as to obtain low-sulfur molten iron.

[0003] At present, hot metal desulfurizers include soda series, calcium carbide (calcium carbide) series, lime series and magnesium series, and each series has auxiliary materials added to improve the desulfurization performance. The desulfurization product of soda series desulfurizer used as a desulfurizer is Na2S at low oxygen level and Na2SO4 at high oxygen level; desulfurization at hot metal temperature will cause a large amount of smoke and dust; increasing the temperature and reducing the silicon content of hot metal will cause an increase in smoke and dust, which will reduce the utilization rate of Na2CO3 and cause environmental pollution. The sensible heat taken away by a large amount of smoke and dust will reduce the temperature of hot metal by 30 to 50°C; although adding lime powder, limestone or cement to the soda series can improve the desulfurization effect to a certain extent, soda is an important industrial raw material, and it is difficult to supply in large quantities and the cost is high. In addition, if it cannot be effectively recovered during use, it will bring a series of environmental problems to the comprehensive utilization of subsequent slag. Calcium carbide (calcium carbide) is a desulfurizing agent whose desulfurizing ability and speed are all higher than the lime system and soda system, and is applicable to fast processing of a large amount of molten iron; The calcium carbide that is used for desulfurization is powdery, very easily generates acetylene with the moist air effect, and has explosion danger, so calcium carbide needs sufficient drying and sealing storage; When using calcium carbide for desulfurization, although smoke dust is few, temperature drop is few, the utilization rate of CaC2 is only 50%, and the price is higher, therefore with CaC2 and CaCO3, Ca (OH)2 and colemanite (2CaO3B2O35H2O) etc. are mixed and used, or add calcium cyanamide, all can improve desulfurization effect, reduce consumption; But because the production area of ​​calcium carbide is relatively concentrated, the material of inconvenient storage and transportation, very easy moisture absorption deterioration and higher use price has limited the use of calcium carbide desulfurizing agent. Lime-based desulfurizer is a widely available and low-cost desulfurizer, which includes lime and a mixture of lime as the main component. The lime used for molten iron desulfurization is generally powdered, so the water content is an important parameter. Lime powder with high water content is easy to stick to the wall of the conveying pipe or block the throat of the manure spraying tank, affecting the normal conveying or desulfurization treatment; lime particles that are too fine will affect the conveying performance and increase the loss during the spraying desulfurization; lime particles that are too large will reduce the desulfurization speed; and because lime powder has very strong water absorption, its processing and storage must be moisture-proof, and it must be baked before use; in addition, when using lime-based desulfurizer, the molten iron temperature is reduced by about 25 to 50°C before and after treatment, and the temperature drop during the treatment process is relatively large. Magnesium-based desulfurizers react quickly with sulfur and are suitable for large-scale processing of molten iron, including magnesium, magnesium alloys, and mixtures of magnesium and other materials. At the molten iron processing temperature, the metallic magnesium added to the molten iron first turns into steam and reacts with the sulfur in the metal to form MgS. At 1400°C, the equilibrium pressure of magnesium vapor is equal to 0.80Mpa. Such high-pressure magnesium vapor in the molten iron causes violent turbulence in the molten iron, which is beneficial to the desulfurization reaction, but also causes splashing. Excessive use of magnesium-based desulfurizers will cause splashing of the molten iron. Magnesium is extremely easy to oxidize, and it must be sealed during transportation and storage. In addition, the price of metallic magnesium is much higher than other desulfurizers, and it is mostly used in special steel types for deep desulfurization of molten steel.In addition to the above four series, there are some other substances, such as the rare earth element cerium, which has a strong affinity with sulfur, but its desulfurization ability is lower than that of magnesium and its cost is high, so it is not suitable for treating large amounts of molten iron; a mixture of table salt and manganese carbonate ore can also be desulfurized, but a large amount of brown smoky salt vapor and chlorine gas is volatilized during desulfurization, which seriously pollutes the environment, so it has not been widely used. Summary of the invention

[0004] In view of the defects existing in the prior art, the purpose of the present invention is to provide a composite molten iron pretreatment agent and its application, which selects four materials, namely limestone powder, iron oxide, carbon powder and sodium chloride, to have the functions of decarbonization, dephosphorization, desiliconization and desulfurization when treating molten iron while maintaining high alkalinity desulfurization of the entire slag system.

[0005] To achieve the above object, the present invention adopts the following technical solution:

[0006] The first aspect of the present invention provides a composite molten iron pretreatment agent, the chemical composition and mass percentage of which are as follows: CaCO3 58-71%, Fe2O3 5-13%, C 7-11%, NaCl 8-10%, and the balance is unavoidable impurities;

[0007] Among the inevitable impurities, SiO2≤4%, Al2O3≤2%.

[0008] Preferably, the CaCO3 is made of limestone powder with a CaCO3 content of ≥96% as raw material; the particle size of the limestone powder is ≤0.075mm;

[0009] The Fe2O3 uses iron oxide powder with a Fe2O3 content of ≥85% as raw material; the particle size of the iron oxide powder is ≤0.075mm;

[0010] The C uses carbon powder with a fixed carbon content of more than 80% as raw material; the particle size of the carbon powder is ≤0.075mm;

[0011] The NaCl adopts sodium chloride industrial salt with NaCl content greater than 90% as raw material; the particle size of the sodium chloride industrial salt is less than or equal to 0.075 mm.

[0012] Preferably, the iron oxide powder is selected from iron oxide scale powder or low-silicon hematite powder or water-treated iron mud.

[0013] Preferably, the following raw materials are used: limestone powder, iron oxide powder, carbon powder and sodium chloride industrial salt, and the amount of carbon powder added is the sum of 1 / 3 of the amount of iron oxide added and 20% of the amount of sodium chloride industrial salt added.

[0014] Preferably, the mass ratio of the limestone powder, iron oxide powder, carbon powder and sodium chloride industrial salt is 7:1:1:1.

[0015] The second aspect of the present invention provides an application of the composite molten iron pretreatment agent as described in the first aspect of the present invention in desulfurization and dephosphorization during molten iron treatment.

[0016] Preferably, the usage of the composite molten iron pretreatment agent is 4-15 kg / ton of molten iron.

[0017] Preferably, in the molten iron treated with the composite molten iron pretreatment agent, the sulfur content is ≤0.009%, and the phosphorus content is ≤0.009%.

[0018] The effects of the present invention are as follows:

[0019] 1. The limestone powder selected in the present invention can be decomposed into CaO and CO2 at high temperature. The decomposed CaO is a newly generated calcium oxide with excellent reaction activity and has a good desulfurization ability. At the same time, the released CO2 plays a role in stirring the molten pool, which can improve the mass transfer conditions and accelerate the desulfurization speed. At the same time, a certain amount of carbon powder can be equipped to ensure a reducing atmosphere during desulfurization;

[0020] 2. The iron oxide selected in the present invention will react with carbon to form a ferrous phase, which has a good effect on slag removal. At the same time, it can react with silicon and carbon in molten iron to play a role in decarburization and desiliconization;

[0021] 3. The sodium chloride used in the present invention undergoes a thermochemical reaction at high temperature. The generated metallic sodium has high chemical activity and hardens with the generated calcium chloride to form metallic calcium. Since the activity of metallic calcium is higher than that of iron at high temperature, it can be directly removed from the FeS component in the molten iron phase. DETAILED DESCRIPTION

[0022] In order to better understand the above technical solution of the present invention, the technical solution of the present invention is further described below in conjunction with embodiments.

[0023] The invention provides a composite molten iron pretreatment agent, whose chemical composition and mass percentage are as follows: CaCO3 58-71%, Fe2O3 5-13%, C 7-11%, NaCl 8-10%, and the remainder is inevitable impurities; among the inevitable impurities, SiO2≤4%, Al2O3≤2%.

[0024] CaCO3 uses limestone powder with a CaCO3 content of ≥96% as raw material, with the purpose of utilizing the active calcium oxygen formed by the high-temperature decomposition of calcium carbonate. The particle size of the limestone powder is ≤0.075mm.

[0025] NaCl uses sodium chloride industrial salt with a NaCl content of more than 90% as raw material; the particle size of the sodium chloride industrial salt is ≤0.075mm.

[0026] Fe2O3 uses iron oxide powder with a Fe2O3 content of ≥85% as raw material; the particle size of the iron oxide powder used is ≤0.075mm; the above-mentioned iron oxide powder can be selected from iron oxide scale powder or low-silicon hematite powder or water-treated iron mud.

[0027] C uses carbon powder with a fixed carbon content of more than 80% as raw material; the particle size of the carbon powder used is ≤0.075mm.

[0028] In summary, the composite molten iron pretreatment agent of the present invention adopts the following raw materials: limestone powder, iron oxide powder, carbon powder and sodium chloride industrial salt, and the mass percentage thereof can be 7:1:1:1.

[0029] The composite molten iron pretreatment agent of the present invention utilizes powdered limestone powder, which decomposes instantly at high temperature to form calcium oxide, and belongs to soft-burned lime. Compared with hard-burned lime (steel-making lime is used for molten iron pretreatment and steelmaking desulfurization in the prior art), it has strong chemical activity at high temperature. Secondly, sodium chloride is selected, mainly because NaCl will undergo a thermochemical reaction at high temperature to generate metallic sodium, and metallic sodium can be desulfurized to form sodium sulfide. At the same time, the released chlorine and calcium oxide generate calcium chloride, and the thermal reaction replaces to obtain metallic calcium, which generates calcium sulfide with the iron sulfide in the molten iron phase and dissolves in the slag layer composed of the lime phase, changing the distribution ratio of sulfur in the molten iron-slag layer, thereby completing the desulfurization of molten iron; the composite molten iron pretreatment agent of the present invention has better desulfurization effect than conventional steelmaking quicklime, and has high desulfurization efficiency; and has a long storage period, and is not as easy to deteriorate as steelmaking lime; in addition, it is more convenient to use when the steel ladle or iron ladle in the small foundry industry is simply desulfurized.

[0030] The composite molten iron pretreatment agent of the present invention undergoes the following reaction after being added into molten iron:

[0031] (I) When the composite molten iron pretreatment agent is sprayed into the high-temperature molten iron layer, when the carbon and silicon content in the molten iron is high, the following reactions occur:

[0032] CaCO3→CaO+CO2 (1)

[0033] 2CaO +[S]+1 / 2[Si]→CaS+1 / 2Ca2S iO3 (2)

[0034] When the silicon content is low, the following reaction occurs:

[0035] 2CaO + [S] + [C] → CaS + CO (3)

[0036] The above-mentioned desulfurization reaction proceeds relatively rapidly under reducing conditions.

[0037] In addition, the CaO generated by reaction (1) also undergoes conventional quicklime desulfurization reaction:

[0038] CaO+ FeS→CaS+FeO (4)

[0039] (II) At the moment of spraying the composite molten iron pretreatment agent, the following chemical reactions will also occur:

[0040]

[0041] 2Na+CaCl2→2NaCl+Ca (6)

[0042] FeS+Ca→CaS+Fe (7)

[0043] Reaction (5) is mainly to reduce NaCl to generate Na by C in the presence of calcium oxide; reaction (6) exists at high temperature, and the metal calcium generated by this reaction is in the same main group as metal magnesium, and the chemical reaction properties are very similar; since metal magnesium is an efficient sharp sulfur agent, the property of metal calcium is also similar to that of magnesium. This is one of the main reactions of particularly efficient desulfurization. Reaction (7) is the main reaction of hot metal desulfurization.

[0044] (III) When the composite molten iron pretreatment agent is sprayed with powder, the Fe2O3 in it has the following reaction:

[0045] Fe2O3+Si→SiO2+FeO (8)

[0046] Fe2O3+C→CO+2FeO (9)

[0047] In addition to the above-mentioned desiliconization and decarburization reactions, the generated FeO and CaO also react at the same time, namely the "slagging effect", which promotes the desiliconization and desulfurization. The specific reactions are as follows:

[0048] CaO+FeO+SiO2→CaO·SiO2·FeO (10)

[0049] The low melting point fayalite mineral phase generated above has a slag-forming effect and promotes the reaction of CaO;

[0050] In addition, if the phosphorus content in the molten iron is high, the phosphorus in the molten iron reacts with CaO and FeO generated in reactions (8) and (9) as follows:

[0051] 2P+5FeO+4CaO→4CaO·P2O5+5Fe (11)

[0052] The principles of the components of the composite molten iron pretreatment agent of the present invention are as follows:

[0053] CaCO3 will decompose into CaO and CO2 under high temperature of molten iron. The decomposition product CaO has good desulfurization ability. At the same time, the released CO2 plays the role of stirring the molten pool, which can improve mass transfer conditions and accelerate the desulfurization speed. At the same time, a certain amount of carbon (ie C) can ensure a reducing atmosphere during desulfurization.

[0054] NaCl will undergo a thermochemical reaction at high temperature, and the generated metallic sodium has high chemical activity. The metallic sodium continues to react with the generated calcium chloride to generate metallic calcium. At high temperature, the activity of metallic calcium is higher than that of iron, and it can directly remove sulfur from FeS; this is an important basis for the present invention.

[0055] In high-temperature molten iron, carbon powder has a short residence time and it is difficult to add carbon to the molten iron to form Fe-C alloy. It exists in the molten iron phase. Even if excessive carbon powder is used, it will enter the slag layer to reduce iron oxide to elemental iron. Another function of C is to ensure the reducing atmosphere during desulfurization.

[0056] At high temperatures, Fe2O3 will reduce with carbon to form ferrous phase, which has a good effect on chemical slag; it also reacts with silicon and carbon in molten iron to decarbonize and desiliconize. In practical applications, the reaction of Fe2O3 is related to various factors such as molten iron temperature and the depth of the spray gun insertion; in addition, the decarbonization and desiliconization of Fe2O3 in the composite molten iron pretreatment agent at high temperatures is much faster than the usual operation of using lime + oxygen blowing, and the process slag detection data before the furnace found that the phosphorus content was high. It can be seen that the composite molten iron pretreatment agent can remove phosphorus quickly while efficiently desulfurizing.

[0057] When the composite molten iron pretreatment agent of the present invention is used to desulfurize the molten iron smelted in the cupola of melting steel slag iron, powder is sprayed into a simple molten iron ladle, and it is found that the iron oxide from different sources has obvious differences in the removal speed of carbon and silicon; the composite molten iron pretreatment agent using the byproduct iron oxide scale of steel rolling and the coarse granular sludge of the converter as the source of iron oxide has a desiliconization and decarburization speed that is significantly slower than the composite molten iron pretreatment agent using the fine powder of hematite as the source of iron oxide, and faster than the composite molten iron pretreatment agent using the water treatment iron mud as the source of iron oxide. When the above-mentioned materials are used as the source of iron oxide, the composition of the iron oxide is basically similar before processing, and the difference in the raw materials themselves is not large, so the difference in the desiliconization and decarburization speed may be related to the mineral phase composition of the iron oxide.

[0058] In addition, the four materials used in the present invention are obviously different from the existing soda-based, lime-based, and calcium carbide-based desulfurizers; the present invention has the advantages of a lime-based desulfurizer and can maintain high alkalinity desulfurization of the entire slag system; at the same time, the thermochemical reaction of sodium chloride can promote the generation of metallic sodium and metallic calcium, both of which can directly react with FeS in molten iron.

[0059] In the raw materials of the composite molten iron pretreatment agent of the present invention, except for limestone, the content of other raw materials can be changed within a range, which basically does not affect the use, but no matter how it is adjusted, the amount of carbon powder added should be excessive. In a specific embodiment, the amount of carbon powder added can be the sum of 1 / 3 of the amount of iron oxide powder added and 20% of the amount of sodium chloride industrial salt added. In this way, when used, the effects of desulfurization and desiliconization are more obvious.

[0060] The invention also provides an application of the composite molten iron pretreatment agent in desulfurization and dephosphorization during molten iron treatment.

[0061] The four raw materials of the composite molten iron pretreatment agent of the present invention are fully mixed in a mixer and the roughly mixed materials are ground and mixed in a ball mill. The latter has better use effect than the former. After the high-temperature molten iron is first sprayed with powder for desiliconization and desulfurization, it is convenient to manually scrape off the upper slag. In the powder spraying dephosphorization and deep desulfurization, sulfur and phosphorus in the molten iron can be removed to less than 0.009%. The removal operation is carried out in two stages, which can obviously achieve a better molten iron treatment effect.

[0062] The dosage of the composite molten iron pretreatment agent is 4-15 kg / ton of molten iron. For example, in the early stage of powder spraying, it is controlled at 4-6 kg / ton of molten iron, and in the later stage it can be controlled at 5-6 kg / ton of molten iron, and the overall cost is relatively low.

[0063] In summary, the sulfur content in the molten iron treated with the composite molten iron pretreatment agent of the present invention is ≤0.009%, and the phosphorus content is ≤0.009%.

[0064] The following is a detailed description of the composite molten iron pretreatment agent and its application in combination with specific embodiments. The raw materials of the following embodiments are roughly prepared according to the mass ratio of limestone powder: coke powder: iron powder: industrial salt of 7:1:1:1, and the chemical composition of the obtained composite molten iron pretreatment agent is shown in Table 1.

[0065] Table 1 Composition and mass percentage content of composite molten iron pretreatment agent

[0066] <![CDATA[Fe2O3%]]> <![CDATA[C 固 %]]> <![CDATA[CaCO3%]]> NaCl% <![CDATA[SiO2%]]> <![CDATA[Al2O3%]]> Sample 1 9.13 8.25 65.42 8.91 3.57 1.23 Sample 2 8.53 8.01 66.42 9.25 2.68 1.57 Sample 3 8.46 8.82 64.39 9.37 1.56 0.98 Sample 4 11.23 10.2 58.75 10 1.13 0.56 Sample 5 5.21 7.15 70.52 8.64 1.12 0.63

[0067] Example 1

[0068] This embodiment adopts the composite molten iron pretreatment agent corresponding to Sample 1 and Sample 3 in Table 1.

[0069] In the 2T slag iron cupola, the molten iron is desulfurized by flushing the molten iron with a ladle (small lifting ladle).

[0070] The ladle can hold 70 kg of molten iron (part of its components are shown in Table 2). Due to the short desulfurization time, it cannot be stirred. Therefore, about 3 kg of the composite molten iron pretreatment agent corresponding to Sample 1 or Sample 3 is placed at the bottom of the ladle, and the molten iron is poured in. After leaving it for 10 minutes, the upper slag is scraped off before pouring.

[0071] At the same time, 3 kg of metallurgical lime powder with a CaO content of 91% was used to desulfurize molten iron under the same conditions as a comparison.

[0072] As shown in Table 2, compared with the molten iron treated with metallurgical lime, the composite molten iron pretreatment agent of this embodiment has obvious desulfurization and dephosphorization effects, and can reduce the S content in the molten iron to below 0.008%, and the P content to below 0.007%, which can meet the desulfurization treatment in front of a small casting furnace, especially the desulfurization when the carbon content of the molten iron is high, and the carbon powder in the composite molten iron pretreatment agent does not add carbon to the molten iron.

[0073] Table 2

[0074]

[0075] Example 2

[0076] This embodiment adopts the composite molten iron pretreatment agent corresponding to Sample 2 and Sample 5 in Table 1.

[0077] 1T steel casting medium frequency furnace, ladle flushing molten steel desulfurization. The usage of composite molten iron pretreatment agent is 12 kg.

[0078] In addition, during the same period, 12 kg of metallurgical lime powder with a CaO content of 91% was used for desulfurization under the same conditions as a comparison.

[0079] As shown in Table 3, compared with the molten iron treated with metallurgical lime, the composite molten iron pretreatment agent of this embodiment has significantly reduced C, S, P and Mn contents in the molten steel during desulfurization treatment of molten steel under low carbon, wherein the S content is reduced to below 0.006%, and the P content is reduced to below 0.006%; in addition, the hot slag on the molten steel treated with this embodiment has better fluidity than that treated with metallurgical lime, is easy to skim, is more convenient to operate than metallurgical lime, and is basically a "one-pot" production operation, which reduces the intensity of smelting operation.

[0080] Table 3

[0081]

[0082] Example 3

[0083] This embodiment adopts the composite molten iron pretreatment agent corresponding to Sample 3 and Sample 4 in Table 1.

[0084] 40T LF refining furnace, LF furnace is responsible for the task of rapid deep desulfurization, which requires the incoming molten steel with a sulfur content of 0.010% to 0.025% to be quickly desulfurized to less than 0.005% in the shortest time. Due to the smelting of low-carbon and low-sulfur steel, the average sulfur content of converter steel is 0.018%, so the sulfur content of the outgoing molten steel is required to be less than 0.005%, and the desulfurization rate is greater than 80%.

[0085] Before using the composite molten iron pretreatment agent, each furnace of molten steel was about 35 tons, using 450 kg of metallurgical lime, 30 kg of fluorite, 70 kg of pre-melted refined slag, 70 to 90 kg of bauxite, and about 10 to 25 kg of aluminum wire for deoxidation.

[0086] Using 500kg of composite molten iron pretreatment agent of sample 3 and sample 4 instead of metallurgical lime, and using 70kg of bauxite to assist slag making, the on-site tracking results after three months are as follows: desulfurization rate 80% to 87%, hit rate increased by 3.1%, slag volume reduced by about 15% to 20%, argon volume reduced by 12%, aluminum wire for deoxidation reduced to less than 10kg, refining time is easy to control, which can be reduced by 2 minutes / furnace compared with the use of metallurgical lime, and the refining cost per furnace is reduced by about 65 yuan. In addition, the fluidity of the refined slag is moderate, and the foam slag is stable. Although the composite treatment agent contains carbon, it reacts in the foam slag layer and does not add carbon to the molten steel.

[0087] Those skilled in the art should recognize that the above embodiments are only used to illustrate the present invention, and are not intended to limit the present invention. As long as they are within the spirit of the present invention, any changes or modifications to the above embodiments will fall within the scope of the claims of the present invention.

Claims

1. A composite molten iron pretreatment agent, characterized in that: Its chemical composition and mass percentage are as follows: CaCO3 58-71%, Fe2O3 5-13%, C 7-11%, NaCl 8-10%, and the balance is inevitable impurities; Among the inevitable impurities, SiO2≤4%, Al2O3≤2%.

2. The composite molten iron pretreatment agent according to claim 1, characterized in that: The CaCO3 is made of limestone powder with a CaCO3 content of ≥96% as raw material; the particle size of the limestone powder is ≤0.075mm; The Fe2O3 uses iron oxide powder with a Fe2O3 content of ≥85% as raw material; the particle size of the iron oxide powder is ≤0.075mm; The C uses carbon powder with a fixed carbon content of more than 80% as raw material; the particle size of the carbon powder is ≤0.075mm; The NaCl adopts sodium chloride industrial salt with NaCl content greater than 90% as raw material; the particle size of the sodium chloride industrial salt is less than or equal to 0.075 mm.

3. The composite molten iron pretreatment agent according to claim 2, characterized in that: The iron oxide powder is selected from iron oxide scale powder, low-silicon hematite powder or water-treated iron mud.

4. The composite molten iron pretreatment agent according to claim 2, characterized in that: The following raw materials are used: limestone powder, iron oxide powder, carbon powder and sodium chloride industrial salt. The amount of carbon powder added is the sum of 1 / 3 of the amount of iron oxide added and 20% of the amount of sodium chloride industrial salt added.

5. The composite molten iron pretreatment agent according to claim 4, characterized in that: The mass ratio of the limestone powder, iron oxide powder, carbon powder and sodium chloride industrial salt is 7:1:1:

1.

6. Use of the composite molten iron pretreatment agent as claimed in any one of claims 1 to 5 for desulfurization and dephosphorization in the process of molten iron treatment.

7. The use according to claim 6, characterized in that: The dosage of the composite molten iron pretreatment agent is 4-15 kg / ton of molten iron.

8. The use according to claim 6, characterized in that: In the molten iron treated with the composite molten iron pretreatment agent, the sulfur content is ≤0.009%, and the phosphorus content is ≤0.009%.

Images