Pure iron material for lithium iron phosphate battery and preparation method thereof

Abstract

The invention discloses a pure iron material for lithium iron phosphate battery and a preparation method thereof. The method comprises: using iron ore and sintered ore as raw materials to carry out blast furnace ironmaking; casting a part of molten iron into cast iron blocks, carrying out oxygen blowing pretreatment for removing chromium and manganese on the remaining part of the molten iron, and slagging after the pretreatment, wherein the slagging amount is greater than 80% of the total slag amount; using the cast iron blocks as coolant and molten iron as raw material to carry out converter steelmaking, wherein the weight of the cast iron blocks is 10-13% of the weight of the molten iron, and the converter slag making is carried out in two steps, and a slag pouring operation is carried out after the first slag making is completed, and the total converter smelting time is 35-40 minutes, and slag is blocked when the converter is tapped, and the slag amount in the ladle is not greater than 1.5% of the weight of the molten steel; slagging treatment is carried out on the molten steel, and the residual slag amount in the ladle after slagging is not greater than 20% of the original slag amount; blowing oxygen into the molten steel after RH refining treatment for 4-5 minutes, and then maintaining a vacuum degree within 100Pa until the treatment is completed; and continuously casting the molten steel into continuous casting billets. The chromium, nickel and manganese contents in the pure iron material meet the composition requirements of pure iron for lithium iron phosphate batteries.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and in particular relates to a pure iron material for lithium iron phosphate batteries and a preparation method thereof. Background Art

[0002] In recent years, the rapid development of the new energy electric vehicle industry has led to an increase in the demand for pure iron for lithium iron phosphate batteries. At the same time, it has also put forward more stringent composition requirements for pure iron for lithium iron phosphate batteries in order to obtain higher performance battery products. Pure iron for lithium iron phosphate batteries specifically requires the chromium, nickel and manganese content to be: Cr≤0.006%, Ni≤0.004%, Mn≤0.008%.

[0003] However, the existing pure iron preparation process for lithium iron phosphate batteries cannot meet the product quality requirements due to the following technical difficulties: chromium and iron have similar properties. When chromium is oxidized to a certain extent during the smelting process, it is very difficult to remove it by oxidation; there is a problem of manganese recycling during the smelting process; and nickel is difficult to remove by oxidation during the steelmaking process. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a method for preparing pure iron material for lithium iron phosphate battery, comprising the following steps:

[0005] S1, blast furnace ironmaking: blast furnace ironmaking is carried out with iron ore and sinter as raw materials, wherein the contents of chromium, nickel and manganese in the iron ore and sinter are controlled to be: Cr≤0.025%, Ni≤0.0035%, Mn≤0.08% by mass percentage, and the composition of molten iron prepared by blast furnace ironmaking is: Cr≤0.03%, Ni≤0.0036%, Mn≤0.10% by mass percentage, and the rest is Fe and unavoidable impurities;

[0006] S2, molten iron pretreatment: a part of the molten iron prepared by the step S1 is cast into cast iron blocks, which are used as cooling materials for subsequent converter steelmaking instead of scrap steel; the rest of the molten iron prepared by the step S1 is pretreated with oxygen blowing to remove chromium and manganese, and used as raw materials for subsequent converter steelmaking. In the oxygen blowing to remove chromium and manganese, 10-15 kg of lime and red mud balls are added to each ton of molten iron for slag making, wherein the FeO content of the red mud balls is controlled to be ≥80%, and the oxygen supply intensity is controlled to be 1.2-1.5 Nm 3 / (t·min), oxygen blowing time is controlled at 15-25 minutes, slag removal operation is carried out after oxygen blowing chromium removal and manganese removal pretreatment is completed, and the slag removal amount is greater than 80% of the total slag amount, and the composition of molten iron by mass percentage is: Cr≤0.015%, Ni≤0.0035%, Mn≤0.04%, and the rest is Fe and unavoidable impurities;

[0007] S3, converter steelmaking: using the cast iron block obtained in step S2 as a coolant and the molten iron pre-treated by oxygen blowing to remove chromium and manganese in step S2 as a raw material, converter steelmaking is carried out, and the weight of the cast iron block is 10-13% of the weight of the molten iron; converter slag making in converter steelmaking is carried out in two steps: the first step is to add 18-20kg / t of lime and 11-15kg / t of raw dolomite according to the weight of the molten steel in the converter furnace to make slag, and the converter is blown for 5-7 minutes before the slag is discharged, and the amount of residual slag in the furnace is controlled to not exceed 30% of the total slag; the second step, according to the weight of the molten steel in the converter, add 15-20kg / t of lime and 10-15kg / t of raw dolomite to make slag, and continue oxygen blowing smelting; the total smelting time of the converter is 35-40 minutes, and after the smelting is completed, the converter tapping slag is blocked, and the slag amount in the ladle is controlled to be no more than 1.5% of the weight of the molten steel. The composition of the converter tapping steel is as follows: Cr≤0.005%, Ni≤0.0036%, Mn≤0.006%, and the rest is Fe and unavoidable impurities;

[0008] S4, slag removal: slag removal is performed on the molten steel in the converter, and the amount of residual slag in the ladle after slag removal is controlled to be no more than 20% of the original slag amount;

[0009] S5, RH refining: After RH refining for 4 to 5 minutes, oxygen is blown into the molten steel to further remove residual chromium and manganese elements. The oxygen blowing amount is controlled at 1.0 to 1.2 Nm per ton of molten steel. 3 After oxygen blowing, the vacuum degree is maintained within 100Pa until the RH refining treatment is completed. After the RH refining is completed, the composition of the molten steel is as follows: Cr≤0.0045%, Ni≤0.0036%, Mn≤0.0055% by mass percentage, and the rest is Fe and unavoidable impurities;

[0010] S6, continuous casting: continuously casting the molten steel prepared according to the above steps into a continuous casting billet to prepare the pure iron material for lithium iron phosphate battery.

[0011] As an embodiment, in the method for preparing the pure iron material for lithium iron phosphate battery, the size of the cast iron block is 100 mm×100 mm×100 mm.

[0012] As an embodiment, in the method for preparing the pure iron material for lithium iron phosphate battery:

[0013] In the step S1, the contents of chromium, nickel and manganese in the iron ore are controlled by mass percentage as follows: Cr 0.023%, Ni 0.0030%, Mn 0.06%, the contents of chromium, nickel and manganese in the sintered ore are controlled by mass percentage as follows: Cr 0.024%, Ni 0.0033%, Mn 0.07%, and the composition of the molten iron prepared by blast furnace ironmaking is by mass percentage as follows: Cr 0.02%, Ni 0.0031%, Mn 0.07%, and the rest is Fe and unavoidable impurities;

[0014] In step S2, during the oxygen blowing chromium and manganese removal pretreatment, 13 kg of lime and red mud balls are added per ton of molten iron to make slag, wherein the FeO content of the red mud balls is controlled to be 85%, and the oxygen supply intensity is controlled to be 1.2 Nm 3 / (t·min), oxygen blowing time is controlled to be 19 minutes, the slag removal amount in the slag removal operation is 89% of the total slag amount, and the composition of the molten iron by mass percentage is: Cr 0.01%, Ni 0.0030%, Mn 0.039%, and the rest is Fe and unavoidable impurities;

[0015] In the step S3, the weight of the cast iron block is 11% of the weight of the molten iron; in the first step of converter slag making, 20kg / t of lime and 15kg / t of raw dolomite are added according to the weight of the molten steel in the converter to make slag, and the converter is blown for 5 minutes before the slag is poured, and the amount of residual slag in the furnace is controlled to be 21% of the total slag; in the second step of converter slag making, 18kg / t of lime and 13kg / t of raw dolomite are added according to the weight of the molten steel in the converter to make slag, and oxygen blowing smelting is continued; the total converter smelting time is 38 minutes, and after the smelting is completed, the converter is tapped to block the slag, and the amount of slag in the ladle is controlled to be 1.5% of the weight of the molten steel, and the components of the converter tapped steel are as follows by mass percentage: 0.005% Cr, 0.0033% Ni, 0.0056% Mn, and the rest are Fe and unavoidable impurities;

[0016] In step S4, the amount of residual slag in the ladle after slagging is controlled to be 16% of the original slag amount;

[0017] In step S5, oxygen is blown into the molten steel after RH refining for 5 minutes, and the oxygen blowing amount is controlled to be 1.2 Nm per ton of molten steel. 3 After RH refining, the composition of molten steel is as follows by mass percentage: Cr 0.0044%, Ni 0.0033%, Mn 0.0053%, and the rest is Fe and unavoidable impurities.

[0018] As an embodiment, in the method for preparing the pure iron material for lithium iron phosphate battery:

[0019] In the step S1, the contents of chromium, nickel and manganese in the iron ore are controlled by mass percentage as follows: Cr 0.025%, Ni 0.0031% and Mn 0.075%, the contents of chromium, nickel and manganese in the sintered ore are controlled by mass percentage as follows: Cr 0.023%, Ni 0.0034% and Mn 0.078%, and the composition of the molten iron prepared by blast furnace ironmaking is by mass percentage as follows: Cr 0.025%, Ni 0.0035% and Mn 0.08%, and the rest is Fe and unavoidable impurities;

[0020] In step S2, during the oxygen blowing chromium and manganese removal pretreatment, 14 kg of lime and red mud balls are added per ton of molten iron to make slag, wherein the FeO content of the red mud balls is controlled to be 83%, and the oxygen supply intensity is controlled to be 1.5 Nm 3 / (t·min), oxygen blowing time is controlled to be 16 minutes, the slag removal amount in the slag removal operation is 86% of the total slag amount, and the composition of the molten iron by mass percentage is: Cr 0.014%, Ni 0.0035%, Mn 0.038%, and the rest is Fe and unavoidable impurities;

[0021] In the step S3, the weight of the cast iron block is 13% of the weight of the molten iron; in the first step of converter slag making, 19kg / t of lime and 14kg / t of raw dolomite are added according to the weight of the molten steel in the converter to make slag, and the converter is blown for 6 minutes before the slag is poured, and the amount of residual slag in the furnace is controlled to be 25% of the total slag; in the second step of converter slag making, 16kg / t of lime and 15kg / t of raw dolomite are added according to the weight of the molten steel in the converter to make slag, and oxygen blowing smelting is continued; the total converter smelting time is 39 minutes, and after the smelting is completed, the converter is tapped to block the slag, and the amount of slag in the ladle is controlled to be 1.3% of the weight of the molten steel, and the components of the converter tapped steel are as follows by mass percentage: 0.0049% Cr, 0.0035% Ni, 0.0059% Mn, and the rest are Fe and unavoidable impurities;

[0022] In step S4, the amount of residual slag in the ladle after slagging is controlled to be 19% of the original slag amount;

[0023] In step S5, oxygen is blown into the molten steel after RH refining for 4 minutes, and the oxygen blowing amount is controlled to be 1.1 Nm per ton of molten steel. 3 After RH refining, the composition of molten steel is as follows by mass percentage: Cr 0.0045%, Ni 0.0036%, Mn 0.0054%, and the rest is Fe and unavoidable impurities.

[0024] In addition, the present invention also provides a pure iron material for a lithium iron phosphate battery, and the pure iron material for a lithium iron phosphate battery is prepared by the above-mentioned method for preparing the pure iron material for a lithium iron phosphate battery.

[0025] The beneficial effects of the pure iron material for lithium iron phosphate batteries and the preparation method thereof of the present invention include: the control level of chromium, nickel and manganese content in the pure iron material is significantly improved, and the composition requirements of Cr≤0.006%, Ni≤0.004%, and Mn≤0.008% of pure iron for lithium iron phosphate batteries are fully met. The product has high purity, low smelting cost, and strong production operability, which is helpful to promote the development and technological progress of my country's new energy battery and new energy automobile industries, and has good social significance and application prospects. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0027] The method for preparing the pure iron material for lithium iron phosphate battery of the present invention comprises the following steps:

[0028] S1, blast furnace ironmaking: blast furnace ironmaking is carried out with iron ore and sinter as raw materials, wherein the contents of chromium, nickel and manganese in the iron ore and sinter are controlled to be: Cr≤0.025%, Ni≤0.0035%, Mn≤0.08% by mass percentage, and the composition of molten iron prepared by blast furnace ironmaking is: Cr≤0.03%, Ni≤0.0036%, Mn≤0.10% by mass percentage, and the rest is Fe and unavoidable impurities;

[0029] S2, molten iron pretreatment: a part of the molten iron prepared by the above step S1 is cast into cast iron blocks, which are used as cooling materials for subsequent converter steelmaking instead of scrap steel. The size of the cast iron blocks can be, for example, 100 mm×100 mm×100 mm; the rest of the molten iron prepared by the above step S1 is pretreated by oxygen blowing to remove chromium and manganese, and used as raw materials for subsequent converter steelmaking. In the oxygen blowing to remove chromium and manganese pretreatment, 10-15 kg of lime and red mud balls are added per ton of molten iron to make slag, wherein the FeO content of the red mud balls is controlled to be ≥80%, and the oxygen supply intensity is controlled to be 1.2-1.5 Nm 3 / (t·min), oxygen blowing time is controlled at 15-25 minutes, after oxygen blowing to remove chromium and manganese pretreatment is completed, slag removal operation is carried out, and the slag removal amount is greater than 80% of the total slag amount. The composition of molten iron by mass percentage is: Cr≤0.015%, Ni≤0.0035%, Mn≤0.04%, and the rest is Fe and unavoidable impurities;

[0030] S3, converter steelmaking: using the cast iron block obtained in the above step S2 as a coolant and the molten iron pretreated by oxygen blowing to remove chromium and manganese in the above step S2 as a raw material, converter steelmaking is carried out, and the weight of the cast iron block is 10-13% of the weight of the molten iron; converter slag making in converter steelmaking is carried out in two steps: the first step is to add 18-20kg / t of lime and 11-15kg / t of raw dolomite to make slag according to the weight of the molten steel in the converter, and after the converter is blown for 5-7 minutes, the slag is poured, and the amount of residual slag in the furnace is controlled to be no more than 30% of the total slag; the second step is to add 15-20kg / t of lime and 10-15kg / t of raw dolomite to make slag according to the weight of the molten steel in the converter, and continue oxygen blowing smelting; the total converter smelting time is 35-40 minutes, and after the smelting is completed, the converter steel is tapped with slag, and the slag amount in the ladle is controlled to be no more than 1.5% of the weight of the molten steel. The composition of the steel out of the converter is as follows by mass percentage: Cr≤0.005%, Ni≤0.0036%, Mn≤0.006%, and the rest is Fe and unavoidable impurities;

[0031] S4, slag removal: slag removal is performed on the molten steel from the converter. After slag removal, the residual slag in the ladle is controlled to be no more than 20% of the original slag. Slag removal is performed before RH refining to prevent the converter slag from reacting with steel slag in subsequent production, and elements such as chromium and manganese are reduced and enter the steel, causing the chromium and manganese elements to exceed the standard;

[0032] S5, RH refining: After RH refining for 4 to 5 minutes, oxygen is blown into the molten steel to further remove residual elements such as chromium and manganese. The oxygen blowing amount is controlled at 1.0 to 1.2 Nm per ton of molten steel. 3 After oxygen blowing, the vacuum degree is maintained within 100Pa until the RH refining treatment is completed. After the RH refining, the composition of the molten steel is as follows: Cr≤0.0045%, Ni≤0.0036%, Mn≤0.0055% by mass, and the rest is Fe and unavoidable impurities;

[0033] S6, continuous casting: continuously casting the molten steel prepared according to the above steps into a continuous casting billet, thereby preparing the pure iron material for lithium iron phosphate battery. The composition of the pure iron material for lithium iron phosphate battery is as follows by mass percentage: Cr≤0.006%, Ni≤0.004%, Mn≤0.008%, and the rest is Fe and unavoidable impurities.

[0034] After actual testing, the pure iron material prepared by the preparation method of the pure iron material for lithium iron phosphate battery of the present invention has significantly improved control levels of chromium, nickel and manganese content, Cr≤0.006%, Ni≤0.004%, Mn≤0.008%, which fully meets the requirements of pure iron for lithium iron phosphate batteries and is beneficial to improving the performance of battery products.

[0035] The preparation method of the pure iron material for lithium iron phosphate battery of the present invention is described in detail below in conjunction with specific embodiments.

[0036] Example 1

[0037] The method for preparing the pure iron material for lithium iron phosphate battery of Example 1 of the present invention comprises the following steps:

[0038] S1, blast furnace ironmaking: blast furnace ironmaking is carried out with iron ore and sintered ore as raw materials, wherein the contents of chromium, nickel and manganese in the iron ore are controlled by mass percentage as follows: Cr 0.023%, Ni 0.0030%, Mn 0.06%, the contents of chromium, nickel and manganese in the sintered ore are controlled by mass percentage as follows: Cr 0.024%, Ni 0.0033%, Mn 0.07%, and the composition of molten iron prepared by blast furnace ironmaking is as follows: Cr 0.02%, Ni 0.0031%, Mn 0.07%, and the rest is Fe and unavoidable impurities;

[0039] S2, molten iron pretreatment: a part of the molten iron prepared by the above step S1 is cast into a cast iron block of 100mm×100mm×100mm, and used as a coolant for subsequent converter steelmaking instead of scrap steel; the rest of the molten iron prepared by the above step S1 is pretreated by oxygen blowing to remove chromium and manganese, and used as a raw material for subsequent converter steelmaking. In the oxygen blowing to remove chromium and manganese pretreatment, 13kg of lime and red mud balls are added to each ton of molten iron for slag making, wherein the FeO content of the red mud balls is controlled to be 85%, and the oxygen supply intensity is controlled to be 1.2Nm 3 / (t·min), oxygen blowing time is controlled to be 19 minutes. After the oxygen blowing chromium and manganese removal pretreatment is completed, slag removal operation is carried out, and the slag removal amount is 89% of the total slag amount. The composition of molten iron by mass percentage is: Cr 0.01%, Ni 0.0030%, Mn 0.039%, and the rest is Fe and unavoidable impurities;

[0040] S3, converter steelmaking: using the cast iron block obtained in the above step S2 as a coolant and the molten iron pretreated by oxygen blowing to remove chromium and manganese in the above step S2 as a raw material, converter steelmaking is carried out, and the weight of the cast iron block is 11% of the weight of the molten iron; converter slag making in converter steelmaking is carried out in two steps: the first step is to add 20kg / t of lime and 15kg / t of raw dolomite to slag according to the weight of the molten steel in the converter, and after 5 minutes of converter blowing, the slag is poured, and the amount of residual slag in the furnace is controlled to be 21% of the total slag; the second step is to add 18kg / t of lime and 13kg / t of raw dolomite to slag according to the weight of the molten steel in the converter, and continue oxygen blowing smelting; the total converter smelting time is 38 minutes, and after the smelting is completed, the converter steel is tapped with slag, and the slag amount in the ladle is controlled to be 1.5% of the weight of the molten steel. The composition of the steel out of the converter is as follows by mass percentage: Cr 0.005%, Ni 0.0033%, Mn 0.0056%, and the rest is Fe and unavoidable impurities;

[0041] S4, slag removal: slag removal is performed on the molten steel in the converter, and the amount of residual slag in the ladle after slag removal is controlled to be 16% of the original slag amount;

[0042] S5, RH refining: After RH refining for 5 minutes, oxygen is blown into the molten steel, and the oxygen blowing amount is controlled to 1.2Nm per ton of molten steel. 3 After oxygen blowing, the vacuum degree is maintained within 100Pa until the RH refining treatment is completed. After the RH refining, the composition of the molten steel is as follows: Cr 0.0044%, Ni 0.0033%, Mn 0.0053% by mass, and the rest is Fe and unavoidable impurities;

[0043] S6, continuous casting: continuously casting the molten steel prepared according to the above steps into a continuous casting billet, thereby completing the preparation of pure iron material for lithium iron phosphate battery.

[0044] After actual detection, the contents of chromium, nickel and manganese in the pure iron material prepared by the method for preparing pure iron material for lithium iron phosphate battery of Example 1 of the present invention are as follows: Cr 0.0043%, Ni 0.0037%, Mn 0.005% by mass, which fully meets the composition requirements of pure iron for lithium iron phosphate battery that Cr≤0.006%, Ni≤0.004%, Mn≤0.008%.

[0045] Example 2

[0046] The method for preparing the pure iron material for lithium iron phosphate battery of embodiment 2 of the present invention comprises the following steps:

[0047] S1, blast furnace ironmaking: blast furnace ironmaking is carried out with iron ore and sintered ore as raw materials, wherein the contents of chromium, nickel and manganese in the iron ore are controlled by mass percentage as follows: Cr 0.025%, Ni 0.0031%, Mn 0.075%, the contents of chromium, nickel and manganese in the sintered ore are controlled by mass percentage as follows: Cr 0.023%, Ni 0.0034%, Mn 0.078%, and the composition of molten iron prepared by blast furnace ironmaking is as follows: Cr 0.025%, Ni 0.0035%, Mn 0.08%, and the rest is Fe and unavoidable impurities;

[0048] S2, molten iron pretreatment: a part of the molten iron prepared by the above step S1 is cast into a cast iron block of 100mm×100mm×100mm, and used as a coolant for subsequent converter steelmaking instead of scrap steel; the rest of the molten iron prepared by the above step S1 is pretreated by oxygen blowing to remove chromium and manganese, and used as a raw material for subsequent converter steelmaking. In the oxygen blowing to remove chromium and manganese pretreatment, 14kg of lime and red mud balls are added to each ton of molten iron for slag making, wherein the FeO content of the red mud balls is controlled to be 83%, and the oxygen supply intensity is controlled to be 1.5Nm 3 / (t·min), oxygen blowing time is controlled to be 16 minutes. After oxygen blowing to remove chromium and manganese pretreatment is completed, slag removal operation is carried out, and the slag removal amount is 86% of the total slag amount. The composition of molten iron by mass percentage is: Cr 0.014%, Ni 0.0035%, Mn 0.038%, and the rest is Fe and unavoidable impurities;

[0049] S3, converter steelmaking: using the cast iron block obtained in the above step S2 as a coolant and the molten iron pretreated by oxygen blowing to remove chromium and manganese in the above step S2 as a raw material, converter steelmaking is carried out, and the weight of the cast iron block is 13% of the weight of the molten iron; converter slag making in converter steelmaking is carried out in two steps: the first step is to add 19kg / t of lime and 14kg / t of raw dolomite to make slag according to the weight of the molten steel in the converter, and after 6 minutes of converter blowing, the slag is poured, and the amount of residual slag in the furnace is controlled to be 25% of the total slag; the second step is to add 16kg / t of lime and 15kg / t of raw dolomite to make slag according to the weight of the molten steel in the converter, and continue oxygen blowing smelting; the total converter smelting time is 39 minutes, and after the smelting is completed, the converter steel is tapped with slag, and the slag amount in the ladle is controlled to be 1.3% of the weight of the molten steel. The composition of the steel out of the converter is as follows by mass percentage: Cr 0.0049%, Ni 0.0035%, Mn 0.0059%, and the rest is Fe and unavoidable impurities;

[0050] S4, slag removal: slag removal is performed on the molten steel in the converter. After slag removal, the amount of residual slag in the ladle is controlled to be 19% of the original slag amount;

[0051] S5, RH refining: After RH refining for 4 minutes, oxygen is blown into the molten steel, and the oxygen blowing amount is controlled to 1.1Nm per ton of molten steel. 3 After oxygen blowing, the vacuum degree is maintained within 100Pa until the RH refining treatment is completed. After the RH refining, the composition of the molten steel is as follows: Cr 0.0045%, Ni 0.0036%, Mn 0.0054%, and the rest is Fe and unavoidable impurities;

[0052] S6, continuous casting: continuously casting the molten steel prepared according to the above steps into a continuous casting billet, thereby completing the preparation of pure iron material for lithium iron phosphate battery.

[0053] After actual testing, the contents of chromium, nickel, and manganese in the pure iron material prepared by the method for preparing pure iron material for lithium iron phosphate batteries of Example 2 of the present invention are as follows: Cr 0.0045%, Ni 0.0037%, and Mn 0.0053% by mass, which fully meet the composition requirements of pure iron for lithium iron phosphate batteries of Cr≤0.006%, Ni≤0.004%, and Mn≤0.008%.

[0054] In summary, compared with the prior art, the pure iron material for lithium iron phosphate battery and the preparation method thereof of the present invention have the following advantages and beneficial effects:

[0055] 1) Through mechanism research, the factors affecting the contents of chromium, nickel and manganese in molten iron are determined, the influence of ironmaking process on residual elements in molten iron is analyzed, the quality of iron ore and its influence on the composition of molten iron are analyzed, and according to the factors affecting the composition of molten iron, the composition of blast furnace charge and ironmaking process are optimized, and the contents of chromium, nickel and manganese in iron ore and sintered ore used as raw materials for blast furnace ironmaking are controlled to be: Cr≤0.025%, Ni≤0.0035%, Mn≤0.08%. A part of the molten iron is cast into cast iron blocks to replace scrap steel as coolant for converter steelmaking, and the rest of the molten iron used as raw material for converter steelmaking is pre-treated by oxygen blowing to remove chromium and manganese, and then slag removal is carried out, so as to effectively improve the quality level of molten iron and meet the needs of pure iron smelting.

[0056] 2) Study the behavior of chromium, nickel and manganese in converter smelting and refining, analyze the changing trends and influencing factors of chromium, nickel and manganese in the above processes, thereby optimizing converter smelting, refining processes, slag removal operations, etc., to maximize the removal rate of chromium and manganese content in the converter steelmaking and refining process.

[0057] 3) With the effective implementation of the present invention, the control level of chromium, nickel and manganese content in pure iron is significantly improved, which fully meets the composition requirements of pure iron for lithium iron phosphate batteries of Cr≤0.006%, Ni≤0.004%, and Mn≤0.008%. The product has high purity, low smelting cost, and strong production operability, which is helpful to promote the development and technological progress of my country's new energy battery and new energy vehicle industries, and has good social significance and application prospects.

[0058] It should be noted that, in this article, the term "comprise" or any other variation thereof is intended to cover non-exclusive inclusion, so that an article or device including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such article or device.

[0059] It should also be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the present invention.

Claims

1. A method for preparing pure iron material for lithium iron phosphate battery, characterized in that: The following steps are involved: S1, blast furnace ironmaking: blast furnace ironmaking is carried out with iron ore and sinter as raw materials, wherein the contents of chromium, nickel and manganese in the iron ore and sinter are controlled to be: Cr≤0.025%, Ni≤0.0035%, Mn≤0.08% by mass percentage, and the composition of molten iron prepared by blast furnace ironmaking is: Cr≤0.03%, Ni≤0.0036%, Mn≤0.10% by mass percentage, and the rest is Fe and unavoidable impurities; S2, molten iron pretreatment: a part of the molten iron prepared by the step S1 is cast into cast iron blocks, which are used as cooling materials for subsequent converter steelmaking instead of scrap steel; the rest of the molten iron prepared by the step S1 is pretreated with oxygen blowing to remove chromium and manganese, and used as raw materials for subsequent converter steelmaking. In the oxygen blowing to remove chromium and manganese, 10-15 kg of lime and red mud balls are added to each ton of molten iron for slag making, wherein the FeO content of the red mud balls is controlled to be ≥80%, and the oxygen supply intensity is controlled to be 1.2-1.5 Nm 3 / (t·min), oxygen blowing time is controlled at 15 to 25 minutes, slag removal operation is carried out after oxygen blowing chromium removal and manganese removal pretreatment is completed, and the slag removal amount is greater than 80% of the total slag amount, and the composition of molten iron is as follows by mass percentage: Cr≤0.015%, Ni≤0.0035%, Mn≤0.04%, and the rest is Fe and unavoidable impurities; S3, converter steelmaking: using the cast iron block obtained in step S2 as a coolant and the molten iron pre-treated by oxygen blowing to remove chromium and manganese in step S2 as a raw material, converter steelmaking is carried out, and the weight of the cast iron block is 10-13% of the weight of the molten iron; converter slag making in converter steelmaking is carried out in two steps: the first step is to add 18-20kg / t of lime and 11-15kg / t of raw dolomite according to the weight of the molten steel in the converter furnace to make slag, and the converter is blown for 5-7 minutes before the slag is discharged, and the amount of residual slag in the furnace is controlled to not exceed 30% of the total slag; the second step, according to the weight of the molten steel in the converter, add 15-20kg / t of lime and 10-15kg / t of raw dolomite to make slag, and continue oxygen blowing smelting; the total smelting time of the converter is 35-40 minutes, and after the smelting is completed, the converter tapping slag is blocked, and the slag amount in the ladle is controlled to be no more than 1.5% of the weight of the molten steel. The composition of the converter tapping steel is as follows: Cr≤0.005%, Ni≤0.0036%, Mn≤0.006%, and the rest is Fe and unavoidable impurities; S4, slag removal: slag removal is performed on the molten steel in the converter, and the amount of residual slag in the ladle after slag removal is controlled to be no more than 20% of the original slag amount; S5, RH refining: After RH refining for 4 to 5 minutes, oxygen is blown into the molten steel to further remove residual chromium and manganese elements. The oxygen blowing amount is controlled at 1.0 to 1.2 Nm per ton of molten steel. 3 After oxygen blowing, the vacuum degree is maintained within 100Pa until the RH refining treatment is completed. After the RH refining is completed, the composition of the molten steel is as follows: Cr≤0.0045%, Ni≤0.0036%, Mn≤0.0055% by mass percentage, and the rest is Fe and unavoidable impurities; S6, continuous casting: continuously casting the molten steel prepared according to the above steps into a continuous casting billet to prepare the pure iron material for lithium iron phosphate battery.

2. The method for preparing the pure iron material for lithium iron phosphate battery according to claim 1, characterized in that: The size of the cast iron block is 100 mm×100 mm×100 mm.

3. The method for preparing the pure iron material for lithium iron phosphate battery according to claim 1, characterized in that: In the step S1, the contents of chromium, nickel and manganese in the iron ore are controlled by mass percentage as follows: Cr 0.023%, Ni 0.0030%, Mn 0.06%, the contents of chromium, nickel and manganese in the sintered ore are controlled by mass percentage as follows: Cr 0.024%, Ni 0.0033%, Mn 0.07%, and the composition of the molten iron prepared by blast furnace ironmaking is by mass percentage as follows: Cr 0.02%, Ni 0.0031%, Mn 0.07%, and the rest is Fe and unavoidable impurities; In step S2, during the oxygen blowing chromium and manganese removal pretreatment, 13 kg of lime and red mud balls are added per ton of molten iron to make slag, wherein the FeO content of the red mud balls is controlled to be 85%, and the oxygen supply intensity is controlled to be 1.2 Nm 3 / (t·min), oxygen blowing time is controlled to be 19 minutes, the slag removal amount in the slag removal operation is 89% of the total slag amount, and the composition of the molten iron by mass percentage is: Cr 0.01%, Ni 0.0030%, Mn 0.039%, and the rest is Fe and unavoidable impurities; In the step S3, the weight of the cast iron block is 11% of the weight of the molten iron; in the first step of converter slag making, 20kg / t of lime and 15kg / t of raw dolomite are added according to the weight of the molten steel in the converter to make slag, and the converter is blown for 5 minutes before the slag is poured, and the amount of residual slag in the furnace is controlled to be 21% of the total slag; in the second step of converter slag making, 18kg / t of lime and 13kg / t of raw dolomite are added according to the weight of the molten steel in the converter to make slag, and oxygen blowing smelting is continued; the total converter smelting time is 38 minutes, and after the smelting is completed, the converter is tapped to block the slag, and the amount of slag in the ladle is controlled to be 1.5% of the weight of the molten steel, and the components of the converter tapped steel are as follows by mass percentage: Cr 0.005%, Ni 0.0033%, Mn 0.0056%, and the rest are Fe and unavoidable impurities; In step S4, the amount of residual slag in the ladle after slagging is controlled to be 16% of the original slag amount; In step S5, oxygen is blown into the molten steel after RH refining for 5 minutes, and the oxygen blowing amount is controlled to be 1.2 Nm per ton of molten steel. 3 After RH refining, the composition of molten steel is as follows by mass percentage: Cr 0.0044%, Ni 0.0033%, Mn 0.0053%, and the rest is Fe and unavoidable impurities.

4. The method for preparing the pure iron material for lithium iron phosphate battery according to claim 1, characterized in that: In the step S1, the contents of chromium, nickel and manganese in the iron ore are controlled by mass percentage as follows: Cr 0.025%, Ni 0.0031% and Mn 0.075%, the contents of chromium, nickel and manganese in the sintered ore are controlled by mass percentage as follows: Cr 0.023%, Ni 0.0034% and Mn 0.078%, and the composition of the molten iron prepared by blast furnace ironmaking is by mass percentage as follows: Cr 0.025%, Ni 0.0035% and Mn 0.08%, and the rest is Fe and unavoidable impurities; In step S2, during the oxygen blowing chromium and manganese removal pretreatment, 14 kg of lime and red mud balls are added per ton of molten iron to make slag, wherein the FeO content of the red mud balls is controlled to be 83%, and the oxygen supply intensity is controlled to be 1.5 Nm 3 / (t·min), oxygen blowing time is controlled to be 16 minutes, the slag removal amount in the slag removal operation is 86% of the total slag amount, and the composition of the molten iron by mass percentage is: Cr 0.014%, Ni 0.0035%, Mn 0.038%, and the rest is Fe and unavoidable impurities; In the step S3, the weight of the cast iron block is 13% of the weight of the molten iron; in the first step of converter slag making, 19kg / t of lime and 14kg / t of raw dolomite are added according to the weight of the molten steel in the converter to make slag, and the converter is blown for 6 minutes before slag removal is performed, and the amount of residual slag in the furnace is controlled to be 25% of the total slag; in the second step of converter slag making, 16kg / t of lime and 15kg / t of raw dolomite are added according to the weight of the molten steel in the converter to make slag, and oxygen blowing smelting is continued; the total converter smelting time is 39 minutes, and after the smelting is completed, the converter is tapped to block the slag, and the amount of slag in the ladle is controlled to be 1.3% of the weight of the molten steel, and the components of the converter tapped steel are as follows by mass percentage: Cr 0.0049%, Ni 0.0035%, Mn 0.0059%, and the rest are Fe and unavoidable impurities; In step S4, the amount of residual slag in the ladle after slagging is controlled to be 19% of the original slag amount; In step S5, oxygen is blown into the molten steel after RH refining for 4 minutes, and the oxygen blowing amount is controlled to be 1.1 Nm per ton of molten steel. 3 After RH refining, the composition of molten steel is as follows by mass percentage: Cr 0.0045%, Ni 0.0036%, Mn 0.0054%, and the rest is Fe and unavoidable impurities.